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Half a century of hardmetals
H a l f a c e n t u r y of hardmetals Developments such as CVD and PVD coatings, sinter-HIP and the increasing popularity of indexable inserts have revolutionized the hardmetal i n d u s t r y a n d its p r o d u c t s . The l a s t 5 0 y e a r s h a v e a l s o s e e n s i g n i f i c a n t a d v a n c e s in t h e r a w m a t e r i a l s u s e d in h a r d m e t a l s . Kenneth J.A. Brookes of International Carbide Data reviews some of the developments which have influenced the course of e v e n t s in t h e h a r d m e t a l s i n d u s t r y o v e r t h e p a s t five decades.
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hilst n o w e n o r m o u s l y larger and of far g r e a t e r e c o n o m i c i m p o r t a n c e , th e h a r d m e t a l i n d u s t r y seems at first to have u n d e r g o n e no f u n d a m e n t a l t e c h n i c a l c h a n g e d u r i n g t h e last 50 years. S i n t e r e d or c e m e n t e d carbides b ased on t u n g s t e n c a r b id e and cobalt b i n d e r still m a k e up th e bulk of p r o d u c t i o n and are m a d e in r o u g h l y t h e s a m e way. Alloy c o m p o s i t i o n s and p r o d u c t s are in m a n y r e s p e c t s similar to t h o s e m a d e m o r e t h a n h a l f a lifetime ago, a n d m a n y of t h e quality c o n t r o l m e t h o d s have scarcely altered. But t h e r e have i n d e e d been p r o f o u n d changes. T h o u g h it's n o t easy to d e t e r m i n e t h e m a n u f a c t u r i n g d a t e of a good q u al i t y w e a r r e s i s t a n t carbide c o m p o n e n t w i t h i n t h i r t y or forty years, only a small and fastd e c r e a s i n g p r o p o r t i o n of today's c u t t i n g tools fall into t h a t category. D e v e l o p m e n t s such as c h e m i c a l v a p o u r d e p o s i t i o n (CVD) a n d p h y s i c a l v a p o u r d e p o s i t i o n (PVD) coating, h o t isostatic p r e s s i n g an d sinterHIP, a t t r i t o r milling, s p r a y drying a n d pelletizing, c a r b o n i t r i d e c e r m e t s an d indexable insert design have truly r e v o l u t i o n i z e d t h e i n d u s t r y a n d its p r o d u ct s.
H o w it s t a r t e d It's i m p o s s i b l e to discuss t h e d e v e l o p m e n t s of th e last 50 years w i t h o u t at least a brief look at earlier history. H a r d m e t a l m a n u f a c ture is a relatively y o u ng i n d u s t r y w h o s e life-span goes back only to t h e 1920s. It b e g a n in G e r m a n y , in O s r a m ' s B e r l i n r e s e a r c h laboratories, with Karl Schr5ter's i n v e n ti o n of s i n t e r e d t u n g s t e n carbide with a l i q u i d - p h a s e cobalt binder. Initially int e n d e d as a d ie m a t e r i a l for d r a w i n g t u n g s t e n f i l a m e n t wire for i n c a n d e s c e n t lamps, its p o t e n t i a l for c u t t i n g tools was
22
MPR December 1995
recognized a l m o s t immediately. The vast and influential Krupp o r g a n i z a t i o n marketed the new m a t e r i a l as 'Widia' (from %vie d i a m a n t ' -- like a d i a m o n d ) and licensed o t h e r c o m p a n i e s a r o u n d t h e world for its m a n u f a c t u r e . T h r o u g h o u t t h e 1930s, partly in an effort to find a way a r o u n d Krupp and O s r a m p a t e n t s , p a r t l y b e c a u s e of t h e i m p e n d i n g w ar and t h e strategic n a t u r e of t u n g s t e n deposits, and partly because of t he sh eer e x c i t e m e n t of t ech n o l o g i cal achievement, great efforts were m a d e to displace or s u p p l e m e n t t u n g s t e n c a r b i d e as h a r d c o m p o n e n t a n d c o b a l t as b i n d e r (see table). Surprisingly, t h e original composition has survived into t h e 1990s as an i n d u s t r y standard, t h o u g h m o s t of t h e later alloy d e v e l o p m e n t s were born in t h e years leading up to t h e 1939-45 war. Sintered h a r d m e t a l s m a d e an i m m e n s e c o n t r i b u t i o n to t h e G e r m a n war effort when, b ecau se of a dire s h o r t a g e of t u n g s t e n in G er m an y and G e r m a n - o c c u p i e d Europe, t he refractory m e t a l h ad to be used at m a x i m u m possible efficiency. Because it was f o u n d t h a t a k i l o g r a m of t u n g s t e n in t u n g s t e n c a r b i d e could cu t m u c h m o r e m e t a l far m o r e quickly t h a n a kilogram of t u n g s t e n in high sp eed steel (HSS), it was d ecr eed t h a t cernented carbides ( ' h a r t m e tall') should be used to r ep l ace tool steel cu t t i n g tools w h e r e v e r possible. Simultaneously, t h e G e r m a n a r m e d forces discovered the p o t e n t i a l of sintered carbides as a r m o u r - p i e r c i n g shell cores and d e m a n d e d m o s t of t h e available t u n g s t e n for this purpose. However, so i m p o r t a n t was t he new c u t t i n g - t o o l m a t e r i a l , t h a t on this occasion industry defeated the military an d m a n y shell cores w e r e r e p r o c e s s e d into tool tips. In o r d e r to keep its t e c h n o l o g y h i d d e n as far as possible, during t h e w ar only t he K r u p p o r g a n i z a t i o n a n d its a s s o c i a t e s m a n u f a c t u r e d t h e full r a n g e of W i d i a co m p o si t i o n s, factories in occupied countries being r e s t r i c t e d to a single grade and a very l i m i t ed n u m b e r of s t a n d a r d products. In t h e Allied and n e u t r a l countries, similar d e v e l o p m e n t s were taking place, t h o u g h w i t h o u t t h e d e s p e r a t e i n t en si t y and pioneering b a c k g r o u n d of Krupp Widia. Many of today's m o s t i m p o r t a n t m a n u f a c t u r e r s saw t h e i r b i r t h or rapid e x p a n s i o n d u r i n g t h e w a r years.
0026-0657/95/$7.00 ,~ 1995, Elsevier Science Ltd.
All of which leads to the most prol()un(I a n d far reaching event in the inune(lia[(' post-war years of the h a r d m e t a l in(tust~5, c o r r e s p o n d i n g with the early years of Metal P o w d e r Report. This was the p u b l i c a t i o n by Allied interrogation and investigation t e a m s of a l m o s t every d e t a i l of Krupp Widia c a r b i d e c o m p o s i t i o n s , p r o d u c t i o n techniques, control m e t h o d s a n d research projects. The largest of these reports was p u b l i s h e d by the British Intelligence Objecti~ves S u b c o m m i t t e e a n d was used as a r e m a r k a b l y i n e x p e n s i v e 'textbook' (costing a b o u t £1) by carbide m a n u f a c t u r e r s worldwide for at least the n e x t decade. Much of t h i s i n f o r m a t i o n w o u l d n e v e r h a v e become available, even to licensees, u n d e r ~ ormal circumstances. Nevertheless, in the early post-war years, G e r m a n i n d u s t r y h a d a s u b s t a n t i a l advant a g e over m a n u f a c t u r i n g i n d u s t r i e s in Britain, the USA a n d elsewhere, in t h a t it
w~l~ ('~('miall5 ~('~r('(! l(, ~",~.rhide tooling, higher ~l)('~'(I ma('him,r/, :~(I e n h a n c e d l)v()du('!i~i!y, ~vh(,r(,a~ !h(, .\/li~,(t' factories were ~[ill std)slammll.~ lo(.l~(,(t into the tiSS era.
Products In Che d('(a(l(' t'()llo~xm~ 1!~$7~, m i n i n g bits look r()ughl5 hall' (d all ~im(,r(,d carbides produ(:(~d, cul t m~ 1,)o1~ ;d).ui 25 ',; a n d wear pacts an(] mi~('ellalw()us a p p l i ( a t i o n s the remain(]('t. Most ('tilling i()()ls were of brazed con~trt~c~i(m at~(I \irt uaily the only clamped IUe[ al('tltt i]lg ilt~(q! ~ ,~('re o f ceramics or ()f ('(,train (:arbid(, grades which suffered li-om extr(.,m(~ t)rilthmess or lack of weft.ability' for brazing alloys. H a r d m e t a l was rated as an exl)ensiv(', if not exotic, material a n ( ] (JYdy a veLs' br;~ve m a n would have suggested throwing away a tip with a slightly worn cuH:ing edge, r a t h e r t h a n regrinding a n d r e t u r n i n g it Io service.
T A B L E 1" S e l e c t e d d a t e s in s i n t e r e d h a r d m e t a l s 1923-25 1929-31 1930-31 1931 1938 1944 1948-70 1949 1950 1952-66 1956 1957 1959 1965-70 1965-75 1965-78 1968-69 1968-69 1968-70 1968-73 169-70 1969-71 1972-75 1974-77 1973-78 1976-79 1979 1980 1981 1981 1983-92 1992-95 1993-95 1994
WC-Co WC-TiC-Co TiC-Mo2C-Ni, Cr, Mo WC-TaC(VC, NbC) - Co TaC-Ni TiC-TaC-Co WC-Cr3C2-Co TiC-VC-Ni, Fe TiC-NbC-Ni, Co Sub-micron WC-Co TiC-VC-NbC-Mo2C-Ni TiC(Mo2C, TaC)-Ni, Co-Cr TiC-heat-treatable steels and alloys WC-TiC-Ta (Nb) C-Cr3C2-Co TiC-TiB2 WC-TiC-HfC-Co TiC-Mo2C-Ni, Mo Hot isostatic pressing TiC, TiN, Ti(C,N), HfC, HfN and AI203 CVD coatings on WC-base hardmetal WC-TiC-Ta (Nb) C-HfC-Co WC-TiC-Nb (Ta) C-HfC-Co (Ti, Mo)C-Ni, Mo TiC-AI203 TiC-TiN-Ni Thermochemical surface hardening TiC-TaN-Ni PCD on WC-base Hardmetal Multi-carbide, carbonitride/nitride and multiple carbide/carbonitride/nitride/ oxide coatings Comples carbides with Ru additions TiC-TaC-Mo2C-Ni alloy Ti(C, N)-precipitation-hardened superalloy Many thin coatings with AION (aluminium oxynitride) layers W/Ti/Mo-base carbide/carbonitride cermet with complex co/Ni-base binder Sinter-HIP Plasma CVD diamond coating Coating complex carbonitrides Fine-grain WC/Co agglomerates in tougher WC/Co matrix
*All dates in this table are approximations. MPR December 1995 23
FIGURE 1: Sumltomo's 'bumpy', 'spiky', 'bubbly' and 'wavy' hardmetal ineerts with centre.hole fixing.
• 1 MPR December 1995
As labour costs rose, initially in the US, but later in Europe and other developed countries, it became cheaper to replace a precision clamped insert rather than regrind a brazed tool. Not only the regrinding cost but also the cost of downtime and resetting the machine tool were i m p o r t a n t factors. Insert life could be extended by adding more cutting edges or corners to one or both sides of an insert up to six on a triangle or eight on a square -so that they gradually became known as 'indexable' r a t h e r t h a n the s o m e w h a t derogatory 'throwaway'. Early indexable inserts were simple shapes, flat on both sides and with provision for add-on clamped chipbreakers. Compressive strength was an important property of the tool material because to use both sides of such simple, parallel-faced inserts, negative rake was necessary to provide side clearance. This considerably increased the cutting forces, necessitating stronger and more powerful machines. There soon developed a thriving refurbishing industry, with specialist companies purchasing worn inserts at scrap or bargain prices, regrinding them to smaller sizes, then selling at a discount with guaranteed as-new performance. Such was their success in the early 1960s that some manufacturers' production rates, swollen by the magnitude of indexable insert acceptance, levelled off and even began to fall. The hardmetal industry was 'saved', and most of the specialist regrinding companies doomed, partly by the increasing use of moulded-in chipbreakers (Figure I), hard to duplicate in regrinding, but especially by the advent of chemical vapour deposition (CVD) coating. CVD of titanium carbide was invented in the early 1960s at the Laboratoire Suisse de l~cherches Horlogique as a wear resistant finish for steel watch-cases, much cheaper
than the solid carbide scratchproof cases still made for the luxury end of the watch trade. CVD simultaneously extended the life of steel-cutting inserts and made it virtually impossible for reground but uncoated inserts to give similar performance. Improvements in cutting speeds and operational lives were dramatic, extending the use of indexable inserts into new areas. The attractive goldo coloured titanium nitride soon followed. Physical vapour deposition (PVD) was also developed in a number of countries, an alternative line-of-sight process with corresponding advantages and disadvantages. Coated hardmetal now makes up more than 80% of all metalcutting insert sales which in turn take more than 50% of worldwide hardmetal production. Carbide tooling design has made remarkable strides since the advent of massproduced indexable inserts. Gaining greatly from computer-based CAD programs, both inserts and toolholders have become far more complex, with a variety of clamping systems to e n s u r e a c c u r a t e seating and precise cutting-edge location without resetting. Most popular are those with centrehole screw fixing or, pioneered by Iscar, the simplest possible fixing, in which a precision insert is held in a slot in the toolholder by friction and cutting forces alone. In the important mining and oil industries carbide, rather than steel, is now the conventional rock-drilling material, but here again there was a revolution. After it had been shown that repeated hammerblows rather than a cutting action breaks rocks, the older design cross-bits were very largely replaced by blunter button-bits, expressly designed to smash rocks by impact alone. There are other now conventional applications for versatile cemented carbide that in 1946 were unheard of or in early infancy. Thus a large part of the population, young and adult alike, now carry around minute spherical pieces of sintered carbide and press upon them frequently i n the course of each day, for high-precision carbide balls are used in countless millions for even the cheapest of ball-point pens. Equally, most houses contain at least one of the ubiquitous carbide-tipped m a s o n r y drills, at one time reserved as the expensive and jealously guarded tools of professional craftsmen. Indeed, it would be tedious to parade in detail the many new applications of hardmetal, and the areas, from endmflls to rolling mills, in which it is now the preferred material. Though it can be extremely cost-effective, designers are generally taught to regard it as expensive for any use beyond cutting or forming tools, only to be employed when all else has failed.
FIGURE 2: Extrusion of hardmetals has advanced considerably in recent decades. Konrad Friedrich's extrusion press produces carbide rod with precisely controlled multiple-spiral coolant holes. (Photo: K.J.A. Brookes.)
The industry M P R has w i t n e s s e d a g r e a t ~uml~*r ~1 c ha nge s to t h e c o m m e r c i a l o r g a m / . ~ i , m ,~1 the h a r d m e t a l s industry. Many o1 (h,)f(. ~l~:t~ were listed in t h e early days hElx¢~ di.~q)~ p e a r e d , a n d o t h e r s h a v e amalga,~m~,,d, c h a n g e d t h e i r n a m e or been ¢ a k ~ ()\(,r. The once n e a r i m p r e g n a b l e German/l]:~gsl~ip Krupp Widia is n o w t h e Widia divisioH ()f I IS c o m p a n y C i n c i n n a t i Milacron -- not ev(~n in the h a r d m e t a l s i n d u s t r y j u s t thre(~ years ago, b u t now also i n c o r p o r a t i n g m::tj(~r I lS m a n u f a c t u r e r s Valenite a n d Walmet. both the o l d e s t in t h e business and a major v, oridwide o p erat o r. S w e d i s h - h e a d q u a r t e r e d Sandvik Coroma nt , an i m p o r t a n t 'also-ran' h a l f a centt~ry ago, is n o w by far t h e largest carbide p r o d u c e r in t h e world. Since t h e collapse oi t h e 'Iron Curtain', Sandvik has also acquired, or gained s u b s t a n t i a l control of.. a r~umber of i m p o r t a n t h a r d m e t a l p r o d u c e r s i~ e a s t e r n Europe, n o t a b l y t h o s e in Moscow ( w h i c h S a n d v i k h e l p e d to b u i l d ) a n d ~;atowice, P o l a n d ( at o n e t i m e a Seco licensee). Seco's own e m p i r e n o w takes in Carboloy, t h e o n e - t i m e US General Electric s~bsidiary and 50 years ago p r o b a b l y t h e largest p r o d u c e r in t h e world. K e n n a m e t a L n o w t h e global n u m b e r two, is also a ma ssive operator, especially since its takeover of t h e G e r m a n Hertel organization. Moving in t h e o p p o s i t e direction, at t h e t a w m a t e r i a l en d of t h e p r o d u c t i o n cycle p e r h a p s t h e largest US p r o d u c e r of hardm e t a l i n t e r m e d i a t e s , GTE Sylvania, has been a c q u i r e d by t h e G e r m a n compan:~ Osram (where it all b e g a n ) to b e c o m e O sra m Sylvania. Surprisingly, Ceram~tal, b a s e d in tin~ L u x e m b o u r g , is n o w a m a j o r h a r d m e t a l producer, t h a n k s to a string of acquisitions. as is t h e US-based H a r b o r Group, which takes in RTW, Carbidie, A t r a x a n d numer()us o t h e r o n e - t i m e i n d e p e n d e n t s . Nevertheless, for every h a r d m e t a l prod u c e r t h a t is absorbed, m e r g e d or simply closed, a n o t h e r s e e m s to s t a r t up somewhere. W h e t h e r to fill niche markets, to m e e t local n eed s in d e v e l o p i n g c o u n t r i e s or to supply i n - h o u s e special p r o d u c t s , t h e r e s e e m t o be e n d l e s s o p p o r t u n i t i e s f o r e x p a n s i o n in or into this vital industry.
Powders A key d e v e l o p m e n t in h a r d m e t a l s is t h e decreasing n u m b e r of i n d e p e n d e n t but m u c h l a r g e r p o w d e r s u p p l i e r s at t h e e x p e n s e of i n - h o u s e p r o d u c t i o n . Forty to fifty years ago, any self-respecting c a r b id e s i n t e r e r would, a l m o s t as a m a t t e r of course, carburize its own powders. Today, very few such c o m p a n i e s remain. Mainly b e c a u s e oI c o m m e r c i a l p r e s s u r e s b u t also b e c a u s e of c h a n g e s in o p e r a t i o n , m o s t h a r d m e t a l
~il'~r~,l~*v~. [),ll'('}l;l,~(' l'~'~l(I)r('~/r})lll'ized pow(t(*r~ lr()m ('×!r,'m~% btrg( ~ i~dustry wide flq)l)li~*l~ ~N(h ;l~ i [ ( ' Starck or Osram
r~'~(~ll i~Lg i t(~m ('('(m()mi~,s of scah,, i m p r o v e d ('(Ht,'-;ifl('t/(+) t'l'(~lt/ l;tt'g(+l• t)atch(+s, r e d u c e d r(+(luirt+m(,ttt li,l iH hotlse t e c b n o l o g y an d (]m~litb (.()lltr()lf, 5+w(,[• highly skilled work('r~ +m(I t~<) idh, -~+ri)u]izing capacity w h e n btt~itt<~s~ if ~la('k. Th(+ main d i s a d v a n t a g e s Eli'(:! t}l(* "('()ltllll()l/ d~nominat<)r sy n d r o m e' wh(~r(d)~ ~'(,mpanie.~ working fl'om t h e s a m e raw mat~,ri~tis teml to p r o d u c e similar final products, a~d tb(, loss -- a l m o s t t h e d e a t h -- of it~(hl.~lrh'-wide knowledge of i m p o r t a n t manufa(~lm'mg processes. S i n t e r e r s w i t h part:icuiar experi(mce of p o w d e r t e c h n o l o g y are r e l u c t a n t to see t h e i r h a r d - w o n knowhow m a d e available to all and t h e r e f o r e cease to m a k e fl]ll use of it; themselves. As a result, base carbid(~ c o m p o s i t i o n s in general use in 1995 are ~e~'tainly no better, and in some cases less advanced, t h a n t h e best of t h o s e available s o m e 50 years earlier. The mim)rity of h a r d m e t a l sinterers still o p e r a t i n g i n - h o u s e c a r b u r i z i n g facilities i n c l u d e s o m e w h o specialize in m i n i n g tools and can o p e r a t e e c o n o m i c c o n t i n u o u s p l a n t s for coarse t u n g s t e n carbide powder; some, like Korea Tungsten, whose m a i n p r o d u c t s are h a r d m e t a l i n t e r m e d i a t e s ; and t h e still i m p o r t a n t s e c t o r -- i n c l u d i n g g i a n t s like K e n n a m e t a l b u t also s o m e small-scale b u t e x p e r t p r o d u c e r s -- w h o have been in t h e i n d u s t r y a long t i m e and see no c o m p e l l i n g reason to discard t h e know--how t h a t gives a p e r f o r m a n c e edge over c o m p e t i t o r s . T h o u g h d i s a p p o i n t i n g in some areas, significant advances have been m a d e in p o w d e r processing an d average p r o d u c t i o n qualil~ has i n d e e d benefited. A m o n g t h e i m p r o v e m e n t s are a m o r e general use of ' m i c r o g r a i n ' carbides, w h i ch c o m b i n e toughness w i t h e x c e l l e n t h a r d n e s s an d w e a r r e s i s t a n c e and are p a r t i c u l a r l y suitable for solid car b i d e tooling. T h o u g h t by s o m e to have been d e v e l o p e d in t h e 1960s, t h ese grades were certainly being produced, w i t h o u t t h e m i c r o g r a i n a p p e l l a t i o n and in s o m e secrecy, by a few c o m p a n i e s in t h e w a r t i m e a n d ear l y p o s t - w a r y e a r s a n d p e r h a p s even earlier.
MPR December 1995 25
Over50 Years a leading worldwide producer of premium-quality intermediate carbide and nitride powders for the hardmetal industry • macrocrystalline tungsten carbide • macrocrystalline titanium carbide • macrocrystalline niobium carbide
• titanium nitride and carbonitride • tantalum carbide • tungsten titanium carbide
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1651 Kingsway Avenue Port Coquitlam, B.C. Canada V3C 1S3 phone 604/941-9611 facsimile 604/941-3525
KENNAMETAL"
No i m p o r t a n t c h a n g e s are al)t)arent since t h a t era in grain-refining additives. w i t h e x p e n s i v e t a n t a l u m cart)ide still popular but the cheaper and arguably more effective c h r o m i u m carbide illcreas ingly preferred. An i m p o r t a n t d e p a r t u r e was ~h~, family of n i c k e l - m o l y b d e n u m - b o n d e d t i ! a t r i u m carbide h a r d m e t a l s developed by l t u m e n i k a n d Moskowitz a r o u n d 1960 at Ford's D e a r b o r n research laboratories, but with origins clearly traceable to the early 1930s. F o r e r u n n e r of today's t i t a n i u m - b a s e d carbonitrides, their manufacture depended greatly on c o n s i s t e n t raw m a t e r i a l s a n d ~ a c u u m sintering. M t h o u g h great claims were made, t h e i r efficient use was limited n m i n l y to high surface speeds a n d relatively small feeds. O t h e r i n t e r e s t i n g d e v e l o p m e n t s (see table) include Inco Europe's almost accidental i n t r o d u c t i o n of precious metal r u t h e n i u m as a t o u g h e n i n g agent in complex allo)' ('emented carbides, licensed to Stellram and Marshall Hardmetals; Mitsubishi's dispersion-hardened superalloy binders; the class of 'intermediate' m a c h i n a b l e materials bestknown as 'Ferro-Tic' and typically t i t a n i u m carbide in a heat-treatable steel matrix; and u n u s u a l c u t t i n g - t o o l m a t e r i a l s based on cubic boron nitride b u t with substantia] a m o u n t s of metallic binders. The l a s t t e n y e a r s h a v e s e e n t h e i n c r e a s i n g use of h a r d m e t a l s b a s e d on ~itanium carbonitride, extremely complex in both c o m p o s i t i o n a n d m i c r o s t r u c t u r e a n d generally k n o w n as 'cermets' (though ,~cientifically the t e r m refers to a n y combin a t i o n of CERamic a n d b i n d e r METal, and in J a p a n it m e a n s any h a r d m e t a l based on t i t a n i u m r a t h e r t h a n t u n g s t e n ) . These rnaterials are increasingly v a l u a b l e for the most critical s t e e l - m a c h i n i n g situations, al tfigh speeds a n d often s u b s t a n t i a l feeds. ![nterestingly, one of the latest d e v e l o p m e n t s ~:s the a p p l i c a t i o n of p e r f o r m a n c e - e n h a n cing, single- or multi-layer, CVD a n d / o r PVD coatings to c a r b o n i t r i d e inserts. A c o n t i n u i n g d e v e l o p m e n t over the years has b e e n t h e p r o d u c t i o n of e v e r - f i n e r powders. Other t h i n g s being equal, virtually every h a r d m e t a l p r o p e r t y -- hardness, modulus, wear resistance, compressive strength a n d so on -- is e n h a n c e d as the :average grain size of the h a r d c o m p o n e n t (carbide) becomes s m a l l e r a n d the grainsize d i s t r i b u t i o n t i g h t e r . Equally, even though it is liquid at the s i n t e r i n g temperature, d i s s e m i n a t i o n of the m a t r i x m e t a l is improved with finer raw material. F i f b~ years ago, powder of 1 to 1.2 ~tm was regarded as 'fine' a n d below 1 t~m (in those days officially a ' m i c r o n ' ) as 'submicron', to the few c o m p a n i e s able to produce it. Today it is possible to produce.
()n a \el.~' small scale, t)ow(lers of.just a few n a n ( ) m e l r e s a v e r a g e size. Nomen('lature still lags b e h i n d science, how(~er, ;is a Iesu[T of w h i c h we have such illalbeit
defined
carbide
pro-
d u c t s as ' m i c r o g r a i n ' , ' n a n o g r a i n ' , 'superfine', 'extra-fine" a n d a variety of others, with everc h a n g i n g definitions: for example, 0.4 btm can be 'sub-mu', extra-fine, ultra-fine or even 'nanosize', according to the manufacturer. One u n d o u b t e d imp r o v e m e n t is in o u r ability to m e a s u r e a n d categorize accurately grain size distribution, r a t h e r t h a n simply average g r a i n size. Laser t e c h n i q u e s w i t h c o m p u t e r r e a d o u t are n o w commonplace, t h o u g h the very finest powders still p r e s e n t difficulties in this regard. Equally, commercial col)all quality has improved out of all recognition. Fifty years ago, virtually the only way t() o b t a i n high quality cobalt powder processed from oxalate was to make it yourself. Nowadays it is a s t a n d a r d raw material a n d few h a r d m e t a l m a n u f a c t u r e r s would c o n t e m plate any alternative. A n e a t idea developed recently in the United States is of compacts consisting of f i n e - g r a i n l o w - c o b a l t a g g l o m e r a t e s emb e d d e d in a m u c h t o u g h e r m a t r i x of higher-cobalt, m e d i u m grain-size carbide. The p a t e n t e d p r o d u c t combines the wear resistance of the fine particles with the
FIGURE 3: The almost universal move to large, batch-type, vacuum sintering furnaces means that large carbide rings, such as this one at Hartmetall, can now be pressed in quantity and sintered or sinter-HIPed with little difficulty. (Photo: K.J.A. Brookes.)
FIGURE 4: SEM photo of Sandvik grade GC415, with successive coating layers of TiC, AI203 and TiN.
MPR December 1995 27
high speed steel in particular, has made it
ahnost s~lonymous with performance enhancing coating, as evidenced by such trade
FIGURE5: Treys of goldcoloured cutting inserts, after removal from the coating reactor. (Photo:
K.J.A. Brookes.)
strength and shock resistance of the matrix. One can see many possibilities for this kind of product in the future.
Coatings The most important single development in the hardmetal industry in the last fifty years has been the application of thin, wearresistant coatings by chemical and, latterly, physical deposition techniques. The nearest equivalent of the 1950s was 'Wimet Laminate', an otherwise conventional hardmetal with a sintered-on, relatively thick surface layer rich in titanium carbide, to combine a tough centre with enhanced crater resistance at the surface. It was never very successful, however, not only because of delamination caused by thermal stresses but also due to the development of highly alloyed 'solid-solution' hardmetals which combined both high strength and crater resistance without laminar discontinuities and gave much improved performance. The early CVD coating of titanium carbide mentioned earlier was soon supplemented or supplanted by titanium nitride and carbonitride, then in due time by alumina, aluminium oxynitride, hafnium
compounds and multiple layers with two, three (Figure 4) and eventually up to thirteen distinct coatings. In parallel with CVD, a variety of physical vapour deposition (PVI)) coating techniques were also developed, mainly for steel where they had the advantage that, being lower temperature methods, they had little or no effect on heat treated steel microstructures. CVD, by contrast, is operated in a furnace and has never been very successful for steel. PVD, however, very new ten years ago, is now just as much a s t a n d a r d t e c h n i q u e for h a r d m e t a l s as CVD, and especially popular for tool steels. The attractive gold coloured appearance of titanium nitride (Figure 5), for a lengthy period the only available PVD coating on
28 MPR December 1995
names as 'Goldmaster' and 'Goldcoat'. As a result, many producers routinely add a CVD or PVD TiN topcoat, even when there is no real technical or scientific reason, citing such pseudo-scientific properties as 'lubricity' to the ill-informed user. All-over CVD coating causes slight rounding of the cutting edge, whereas 'line of sight' PVD techniques more easily retain a sharp edge. Nevertheless, because of the way in which cut metal flows around the insert's cutting edge, a very sharp edge is seldom desirable, as witness the popularty of 'edge honing' before service. More recent developments in coating combine the attributes of both CVD and PVD either successively or simultaneously (plasma CVD). The latest technique, however, is CVD of hardmetal with pure diamond or a 'diamond-like' amorphous coating. Producing the coating itself has been found to be surprisingly easy, requiring none of the s u p e r - h i g h p r e s s u r e s or t e m p e r a t u r e s hitherto t h o u g h t to be necessary. The problem is retaining the coating on the hardmetal, so far solved -- not necessarily definitively -- by a very few companies who closely guard their secret know-how. Applications are limited, though. Diamond, solid or coating, cannot cut ferrous materials such as steel and cast iron without rapid chemical breakdown. Initial uses include the machining of abrasive non-ferrous alloys such as silicon-aluminium, and nonmetallics like glass and carbon composites. A far larger potential user, however, is the electronics industry, which has a vast requirement for free standing, high conductivity, wear resistant, electrically insulating substrates for microchips.
The crystal b a l l What shall we see in the future? Finer powders for sure, and hardmetals with improved properties, both for cutting tools and the myriad of other applications. For cutting tools, even more complex carbonitride compositions, and more competition from both ceramics and superhard materials as they take up the challenge. We can also • expect to see more hardmetals combining hard, wear-resisting agglomerated particles in a matrix of differing composition and properties. And the pot of gold at the end of this particular rainbow?. In the writer's opinion, it may well be coatings of cubic boron nitride, a superhard material capable (in solid polycrystalline form) of out-performing conventional hardmetals in the machining of ferrous metals. •
':~. !!
hilst n o w e n o r m o u s l y larger and of far g r e a t e r e c o n o m i c i m p o r t a n c e , th e h a r d m e t a l i n d u s t r y seems at first to have u n d e r g o n e no f u n d a m e n t a l t e c h n i c a l c h a n g e d u r i n g t h e last 50 years. S i n t e r e d or c e m e n t e d carbides b ased on t u n g s t e n c a r b id e and cobalt b i n d e r still m a k e up th e bulk of p r o d u c t i o n and are m a d e in r o u g h l y t h e s a m e way. Alloy c o m p o s i t i o n s and p r o d u c t s are in m a n y r e s p e c t s similar to t h o s e m a d e m o r e t h a n h a l f a lifetime ago, a n d m a n y of t h e quality c o n t r o l m e t h o d s have scarcely altered. But t h e r e have i n d e e d been p r o f o u n d changes. T h o u g h it's n o t easy to d e t e r m i n e t h e m a n u f a c t u r i n g d a t e of a good q u al i t y w e a r r e s i s t a n t carbide c o m p o n e n t w i t h i n t h i r t y or forty years, only a small and fastd e c r e a s i n g p r o p o r t i o n of today's c u t t i n g tools fall into t h a t category. D e v e l o p m e n t s such as c h e m i c a l v a p o u r d e p o s i t i o n (CVD) a n d p h y s i c a l v a p o u r d e p o s i t i o n (PVD) coating, h o t isostatic p r e s s i n g an d sinterHIP, a t t r i t o r milling, s p r a y drying a n d pelletizing, c a r b o n i t r i d e c e r m e t s an d indexable insert design have truly r e v o l u t i o n i z e d t h e i n d u s t r y a n d its p r o d u ct s.
H o w it s t a r t e d It's i m p o s s i b l e to discuss t h e d e v e l o p m e n t s of th e last 50 years w i t h o u t at least a brief look at earlier history. H a r d m e t a l m a n u f a c ture is a relatively y o u ng i n d u s t r y w h o s e life-span goes back only to t h e 1920s. It b e g a n in G e r m a n y , in O s r a m ' s B e r l i n r e s e a r c h laboratories, with Karl Schr5ter's i n v e n ti o n of s i n t e r e d t u n g s t e n carbide with a l i q u i d - p h a s e cobalt binder. Initially int e n d e d as a d ie m a t e r i a l for d r a w i n g t u n g s t e n f i l a m e n t wire for i n c a n d e s c e n t lamps, its p o t e n t i a l for c u t t i n g tools was
22
MPR December 1995
recognized a l m o s t immediately. The vast and influential Krupp o r g a n i z a t i o n marketed the new m a t e r i a l as 'Widia' (from %vie d i a m a n t ' -- like a d i a m o n d ) and licensed o t h e r c o m p a n i e s a r o u n d t h e world for its m a n u f a c t u r e . T h r o u g h o u t t h e 1930s, partly in an effort to find a way a r o u n d Krupp and O s r a m p a t e n t s , p a r t l y b e c a u s e of t h e i m p e n d i n g w ar and t h e strategic n a t u r e of t u n g s t e n deposits, and partly because of t he sh eer e x c i t e m e n t of t ech n o l o g i cal achievement, great efforts were m a d e to displace or s u p p l e m e n t t u n g s t e n c a r b i d e as h a r d c o m p o n e n t a n d c o b a l t as b i n d e r (see table). Surprisingly, t h e original composition has survived into t h e 1990s as an i n d u s t r y standard, t h o u g h m o s t of t h e later alloy d e v e l o p m e n t s were born in t h e years leading up to t h e 1939-45 war. Sintered h a r d m e t a l s m a d e an i m m e n s e c o n t r i b u t i o n to t h e G e r m a n war effort when, b ecau se of a dire s h o r t a g e of t u n g s t e n in G er m an y and G e r m a n - o c c u p i e d Europe, t he refractory m e t a l h ad to be used at m a x i m u m possible efficiency. Because it was f o u n d t h a t a k i l o g r a m of t u n g s t e n in t u n g s t e n c a r b i d e could cu t m u c h m o r e m e t a l far m o r e quickly t h a n a kilogram of t u n g s t e n in high sp eed steel (HSS), it was d ecr eed t h a t cernented carbides ( ' h a r t m e tall') should be used to r ep l ace tool steel cu t t i n g tools w h e r e v e r possible. Simultaneously, t h e G e r m a n a r m e d forces discovered the p o t e n t i a l of sintered carbides as a r m o u r - p i e r c i n g shell cores and d e m a n d e d m o s t of t h e available t u n g s t e n for this purpose. However, so i m p o r t a n t was t he new c u t t i n g - t o o l m a t e r i a l , t h a t on this occasion industry defeated the military an d m a n y shell cores w e r e r e p r o c e s s e d into tool tips. In o r d e r to keep its t e c h n o l o g y h i d d e n as far as possible, during t h e w ar only t he K r u p p o r g a n i z a t i o n a n d its a s s o c i a t e s m a n u f a c t u r e d t h e full r a n g e of W i d i a co m p o si t i o n s, factories in occupied countries being r e s t r i c t e d to a single grade and a very l i m i t ed n u m b e r of s t a n d a r d products. In t h e Allied and n e u t r a l countries, similar d e v e l o p m e n t s were taking place, t h o u g h w i t h o u t t h e d e s p e r a t e i n t en si t y and pioneering b a c k g r o u n d of Krupp Widia. Many of today's m o s t i m p o r t a n t m a n u f a c t u r e r s saw t h e i r b i r t h or rapid e x p a n s i o n d u r i n g t h e w a r years.
0026-0657/95/$7.00 ,~ 1995, Elsevier Science Ltd.
All of which leads to the most prol()un(I a n d far reaching event in the inune(lia[(' post-war years of the h a r d m e t a l in(tust~5, c o r r e s p o n d i n g with the early years of Metal P o w d e r Report. This was the p u b l i c a t i o n by Allied interrogation and investigation t e a m s of a l m o s t every d e t a i l of Krupp Widia c a r b i d e c o m p o s i t i o n s , p r o d u c t i o n techniques, control m e t h o d s a n d research projects. The largest of these reports was p u b l i s h e d by the British Intelligence Objecti~ves S u b c o m m i t t e e a n d was used as a r e m a r k a b l y i n e x p e n s i v e 'textbook' (costing a b o u t £1) by carbide m a n u f a c t u r e r s worldwide for at least the n e x t decade. Much of t h i s i n f o r m a t i o n w o u l d n e v e r h a v e become available, even to licensees, u n d e r ~ ormal circumstances. Nevertheless, in the early post-war years, G e r m a n i n d u s t r y h a d a s u b s t a n t i a l advant a g e over m a n u f a c t u r i n g i n d u s t r i e s in Britain, the USA a n d elsewhere, in t h a t it
w~l~ ('~('miall5 ~('~r('(! l(, ~",~.rhide tooling, higher ~l)('~'(I ma('him,r/, :~(I e n h a n c e d l)v()du('!i~i!y, ~vh(,r(,a~ !h(, .\/li~,(t' factories were ~[ill std)slammll.~ lo(.l~(,(t into the tiSS era.
Products In Che d('(a(l(' t'()llo~xm~ 1!~$7~, m i n i n g bits look r()ughl5 hall' (d all ~im(,r(,d carbides produ(:(~d, cul t m~ 1,)o1~ ;d).ui 25 ',; a n d wear pacts an(] mi~('ellalw()us a p p l i ( a t i o n s the remain(]('t. Most ('tilling i()()ls were of brazed con~trt~c~i(m at~(I \irt uaily the only clamped IUe[ al('tltt i]lg ilt~(q! ~ ,~('re o f ceramics or ()f ('(,train (:arbid(, grades which suffered li-om extr(.,m(~ t)rilthmess or lack of weft.ability' for brazing alloys. H a r d m e t a l was rated as an exl)ensiv(', if not exotic, material a n ( ] (JYdy a veLs' br;~ve m a n would have suggested throwing away a tip with a slightly worn cuH:ing edge, r a t h e r t h a n regrinding a n d r e t u r n i n g it Io service.
T A B L E 1" S e l e c t e d d a t e s in s i n t e r e d h a r d m e t a l s 1923-25 1929-31 1930-31 1931 1938 1944 1948-70 1949 1950 1952-66 1956 1957 1959 1965-70 1965-75 1965-78 1968-69 1968-69 1968-70 1968-73 169-70 1969-71 1972-75 1974-77 1973-78 1976-79 1979 1980 1981 1981 1983-92 1992-95 1993-95 1994
WC-Co WC-TiC-Co TiC-Mo2C-Ni, Cr, Mo WC-TaC(VC, NbC) - Co TaC-Ni TiC-TaC-Co WC-Cr3C2-Co TiC-VC-Ni, Fe TiC-NbC-Ni, Co Sub-micron WC-Co TiC-VC-NbC-Mo2C-Ni TiC(Mo2C, TaC)-Ni, Co-Cr TiC-heat-treatable steels and alloys WC-TiC-Ta (Nb) C-Cr3C2-Co TiC-TiB2 WC-TiC-HfC-Co TiC-Mo2C-Ni, Mo Hot isostatic pressing TiC, TiN, Ti(C,N), HfC, HfN and AI203 CVD coatings on WC-base hardmetal WC-TiC-Ta (Nb) C-HfC-Co WC-TiC-Nb (Ta) C-HfC-Co (Ti, Mo)C-Ni, Mo TiC-AI203 TiC-TiN-Ni Thermochemical surface hardening TiC-TaN-Ni PCD on WC-base Hardmetal Multi-carbide, carbonitride/nitride and multiple carbide/carbonitride/nitride/ oxide coatings Comples carbides with Ru additions TiC-TaC-Mo2C-Ni alloy Ti(C, N)-precipitation-hardened superalloy Many thin coatings with AION (aluminium oxynitride) layers W/Ti/Mo-base carbide/carbonitride cermet with complex co/Ni-base binder Sinter-HIP Plasma CVD diamond coating Coating complex carbonitrides Fine-grain WC/Co agglomerates in tougher WC/Co matrix
*All dates in this table are approximations. MPR December 1995 23
FIGURE 1: Sumltomo's 'bumpy', 'spiky', 'bubbly' and 'wavy' hardmetal ineerts with centre.hole fixing.
• 1 MPR December 1995
As labour costs rose, initially in the US, but later in Europe and other developed countries, it became cheaper to replace a precision clamped insert rather than regrind a brazed tool. Not only the regrinding cost but also the cost of downtime and resetting the machine tool were i m p o r t a n t factors. Insert life could be extended by adding more cutting edges or corners to one or both sides of an insert up to six on a triangle or eight on a square -so that they gradually became known as 'indexable' r a t h e r t h a n the s o m e w h a t derogatory 'throwaway'. Early indexable inserts were simple shapes, flat on both sides and with provision for add-on clamped chipbreakers. Compressive strength was an important property of the tool material because to use both sides of such simple, parallel-faced inserts, negative rake was necessary to provide side clearance. This considerably increased the cutting forces, necessitating stronger and more powerful machines. There soon developed a thriving refurbishing industry, with specialist companies purchasing worn inserts at scrap or bargain prices, regrinding them to smaller sizes, then selling at a discount with guaranteed as-new performance. Such was their success in the early 1960s that some manufacturers' production rates, swollen by the magnitude of indexable insert acceptance, levelled off and even began to fall. The hardmetal industry was 'saved', and most of the specialist regrinding companies doomed, partly by the increasing use of moulded-in chipbreakers (Figure I), hard to duplicate in regrinding, but especially by the advent of chemical vapour deposition (CVD) coating. CVD of titanium carbide was invented in the early 1960s at the Laboratoire Suisse de l~cherches Horlogique as a wear resistant finish for steel watch-cases, much cheaper
than the solid carbide scratchproof cases still made for the luxury end of the watch trade. CVD simultaneously extended the life of steel-cutting inserts and made it virtually impossible for reground but uncoated inserts to give similar performance. Improvements in cutting speeds and operational lives were dramatic, extending the use of indexable inserts into new areas. The attractive goldo coloured titanium nitride soon followed. Physical vapour deposition (PVD) was also developed in a number of countries, an alternative line-of-sight process with corresponding advantages and disadvantages. Coated hardmetal now makes up more than 80% of all metalcutting insert sales which in turn take more than 50% of worldwide hardmetal production. Carbide tooling design has made remarkable strides since the advent of massproduced indexable inserts. Gaining greatly from computer-based CAD programs, both inserts and toolholders have become far more complex, with a variety of clamping systems to e n s u r e a c c u r a t e seating and precise cutting-edge location without resetting. Most popular are those with centrehole screw fixing or, pioneered by Iscar, the simplest possible fixing, in which a precision insert is held in a slot in the toolholder by friction and cutting forces alone. In the important mining and oil industries carbide, rather than steel, is now the conventional rock-drilling material, but here again there was a revolution. After it had been shown that repeated hammerblows rather than a cutting action breaks rocks, the older design cross-bits were very largely replaced by blunter button-bits, expressly designed to smash rocks by impact alone. There are other now conventional applications for versatile cemented carbide that in 1946 were unheard of or in early infancy. Thus a large part of the population, young and adult alike, now carry around minute spherical pieces of sintered carbide and press upon them frequently i n the course of each day, for high-precision carbide balls are used in countless millions for even the cheapest of ball-point pens. Equally, most houses contain at least one of the ubiquitous carbide-tipped m a s o n r y drills, at one time reserved as the expensive and jealously guarded tools of professional craftsmen. Indeed, it would be tedious to parade in detail the many new applications of hardmetal, and the areas, from endmflls to rolling mills, in which it is now the preferred material. Though it can be extremely cost-effective, designers are generally taught to regard it as expensive for any use beyond cutting or forming tools, only to be employed when all else has failed.
FIGURE 2: Extrusion of hardmetals has advanced considerably in recent decades. Konrad Friedrich's extrusion press produces carbide rod with precisely controlled multiple-spiral coolant holes. (Photo: K.J.A. Brookes.)
The industry M P R has w i t n e s s e d a g r e a t ~uml~*r ~1 c ha nge s to t h e c o m m e r c i a l o r g a m / . ~ i , m ,~1 the h a r d m e t a l s industry. Many o1 (h,)f(. ~l~:t~ were listed in t h e early days hElx¢~ di.~q)~ p e a r e d , a n d o t h e r s h a v e amalga,~m~,,d, c h a n g e d t h e i r n a m e or been ¢ a k ~ ()\(,r. The once n e a r i m p r e g n a b l e German/l]:~gsl~ip Krupp Widia is n o w t h e Widia divisioH ()f I IS c o m p a n y C i n c i n n a t i Milacron -- not ev(~n in the h a r d m e t a l s i n d u s t r y j u s t thre(~ years ago, b u t now also i n c o r p o r a t i n g m::tj(~r I lS m a n u f a c t u r e r s Valenite a n d Walmet. both the o l d e s t in t h e business and a major v, oridwide o p erat o r. S w e d i s h - h e a d q u a r t e r e d Sandvik Coroma nt , an i m p o r t a n t 'also-ran' h a l f a centt~ry ago, is n o w by far t h e largest carbide p r o d u c e r in t h e world. Since t h e collapse oi t h e 'Iron Curtain', Sandvik has also acquired, or gained s u b s t a n t i a l control of.. a r~umber of i m p o r t a n t h a r d m e t a l p r o d u c e r s i~ e a s t e r n Europe, n o t a b l y t h o s e in Moscow ( w h i c h S a n d v i k h e l p e d to b u i l d ) a n d ~;atowice, P o l a n d ( at o n e t i m e a Seco licensee). Seco's own e m p i r e n o w takes in Carboloy, t h e o n e - t i m e US General Electric s~bsidiary and 50 years ago p r o b a b l y t h e largest p r o d u c e r in t h e world. K e n n a m e t a L n o w t h e global n u m b e r two, is also a ma ssive operator, especially since its takeover of t h e G e r m a n Hertel organization. Moving in t h e o p p o s i t e direction, at t h e t a w m a t e r i a l en d of t h e p r o d u c t i o n cycle p e r h a p s t h e largest US p r o d u c e r of hardm e t a l i n t e r m e d i a t e s , GTE Sylvania, has been a c q u i r e d by t h e G e r m a n compan:~ Osram (where it all b e g a n ) to b e c o m e O sra m Sylvania. Surprisingly, Ceram~tal, b a s e d in tin~ L u x e m b o u r g , is n o w a m a j o r h a r d m e t a l producer, t h a n k s to a string of acquisitions. as is t h e US-based H a r b o r Group, which takes in RTW, Carbidie, A t r a x a n d numer()us o t h e r o n e - t i m e i n d e p e n d e n t s . Nevertheless, for every h a r d m e t a l prod u c e r t h a t is absorbed, m e r g e d or simply closed, a n o t h e r s e e m s to s t a r t up somewhere. W h e t h e r to fill niche markets, to m e e t local n eed s in d e v e l o p i n g c o u n t r i e s or to supply i n - h o u s e special p r o d u c t s , t h e r e s e e m t o be e n d l e s s o p p o r t u n i t i e s f o r e x p a n s i o n in or into this vital industry.
Powders A key d e v e l o p m e n t in h a r d m e t a l s is t h e decreasing n u m b e r of i n d e p e n d e n t but m u c h l a r g e r p o w d e r s u p p l i e r s at t h e e x p e n s e of i n - h o u s e p r o d u c t i o n . Forty to fifty years ago, any self-respecting c a r b id e s i n t e r e r would, a l m o s t as a m a t t e r of course, carburize its own powders. Today, very few such c o m p a n i e s remain. Mainly b e c a u s e oI c o m m e r c i a l p r e s s u r e s b u t also b e c a u s e of c h a n g e s in o p e r a t i o n , m o s t h a r d m e t a l
~il'~r~,l~*v~. [),ll'('}l;l,~(' l'~'~l(I)r('~/r})lll'ized pow(t(*r~ lr()m ('×!r,'m~% btrg( ~ i~dustry wide flq)l)li~*l~ ~N(h ;l~ i [ ( ' Starck or Osram
r~'~(~ll i~Lg i t(~m ('('(m()mi~,s of scah,, i m p r o v e d ('(Ht,'-;ifl('t/(+) t'l'(~lt/ l;tt'g(+l• t)atch(+s, r e d u c e d r(+(luirt+m(,ttt li,l iH hotlse t e c b n o l o g y an d (]m~litb (.()lltr()lf, 5+w(,[• highly skilled work('r~ +m(I t~<) idh, -~+ri)u]izing capacity w h e n btt~itt<~s~ if ~la('k. Th(+ main d i s a d v a n t a g e s Eli'(:! t}l(* "('()ltllll()l/ d~nominat<)r sy n d r o m e' wh(~r(d)~ ~'(,mpanie.~ working fl'om t h e s a m e raw mat~,ri~tis teml to p r o d u c e similar final products, a~d tb(, loss -- a l m o s t t h e d e a t h -- of it~(hl.~lrh'-wide knowledge of i m p o r t a n t manufa(~lm'mg processes. S i n t e r e r s w i t h part:icuiar experi(mce of p o w d e r t e c h n o l o g y are r e l u c t a n t to see t h e i r h a r d - w o n knowhow m a d e available to all and t h e r e f o r e cease to m a k e fl]ll use of it; themselves. As a result, base carbid(~ c o m p o s i t i o n s in general use in 1995 are ~e~'tainly no better, and in some cases less advanced, t h a n t h e best of t h o s e available s o m e 50 years earlier. The mim)rity of h a r d m e t a l sinterers still o p e r a t i n g i n - h o u s e c a r b u r i z i n g facilities i n c l u d e s o m e w h o specialize in m i n i n g tools and can o p e r a t e e c o n o m i c c o n t i n u o u s p l a n t s for coarse t u n g s t e n carbide powder; some, like Korea Tungsten, whose m a i n p r o d u c t s are h a r d m e t a l i n t e r m e d i a t e s ; and t h e still i m p o r t a n t s e c t o r -- i n c l u d i n g g i a n t s like K e n n a m e t a l b u t also s o m e small-scale b u t e x p e r t p r o d u c e r s -- w h o have been in t h e i n d u s t r y a long t i m e and see no c o m p e l l i n g reason to discard t h e know--how t h a t gives a p e r f o r m a n c e edge over c o m p e t i t o r s . T h o u g h d i s a p p o i n t i n g in some areas, significant advances have been m a d e in p o w d e r processing an d average p r o d u c t i o n qualil~ has i n d e e d benefited. A m o n g t h e i m p r o v e m e n t s are a m o r e general use of ' m i c r o g r a i n ' carbides, w h i ch c o m b i n e toughness w i t h e x c e l l e n t h a r d n e s s an d w e a r r e s i s t a n c e and are p a r t i c u l a r l y suitable for solid car b i d e tooling. T h o u g h t by s o m e to have been d e v e l o p e d in t h e 1960s, t h ese grades were certainly being produced, w i t h o u t t h e m i c r o g r a i n a p p e l l a t i o n and in s o m e secrecy, by a few c o m p a n i e s in t h e w a r t i m e a n d ear l y p o s t - w a r y e a r s a n d p e r h a p s even earlier.
MPR December 1995 25
Over50 Years a leading worldwide producer of premium-quality intermediate carbide and nitride powders for the hardmetal industry • macrocrystalline tungsten carbide • macrocrystalline titanium carbide • macrocrystalline niobium carbide
• titanium nitride and carbonitride • tantalum carbide • tungsten titanium carbide
Send today for your FREE technical data sheets! contact: Kennametal Inc. Advanced Materials Division
347 North Taylor Street Fallon, NV 89406 USA phone 702/423-5131 600/222-9327 (eastern US) 600/443-4862 (western US) facsimile 702/423-4446
Macro Division
1651 Kingsway Avenue Port Coquitlam, B.C. Canada V3C 1S3 phone 604/941-9611 facsimile 604/941-3525
KENNAMETAL"
No i m p o r t a n t c h a n g e s are al)t)arent since t h a t era in grain-refining additives. w i t h e x p e n s i v e t a n t a l u m cart)ide still popular but the cheaper and arguably more effective c h r o m i u m carbide illcreas ingly preferred. An i m p o r t a n t d e p a r t u r e was ~h~, family of n i c k e l - m o l y b d e n u m - b o n d e d t i ! a t r i u m carbide h a r d m e t a l s developed by l t u m e n i k a n d Moskowitz a r o u n d 1960 at Ford's D e a r b o r n research laboratories, but with origins clearly traceable to the early 1930s. F o r e r u n n e r of today's t i t a n i u m - b a s e d carbonitrides, their manufacture depended greatly on c o n s i s t e n t raw m a t e r i a l s a n d ~ a c u u m sintering. M t h o u g h great claims were made, t h e i r efficient use was limited n m i n l y to high surface speeds a n d relatively small feeds. O t h e r i n t e r e s t i n g d e v e l o p m e n t s (see table) include Inco Europe's almost accidental i n t r o d u c t i o n of precious metal r u t h e n i u m as a t o u g h e n i n g agent in complex allo)' ('emented carbides, licensed to Stellram and Marshall Hardmetals; Mitsubishi's dispersion-hardened superalloy binders; the class of 'intermediate' m a c h i n a b l e materials bestknown as 'Ferro-Tic' and typically t i t a n i u m carbide in a heat-treatable steel matrix; and u n u s u a l c u t t i n g - t o o l m a t e r i a l s based on cubic boron nitride b u t with substantia] a m o u n t s of metallic binders. The l a s t t e n y e a r s h a v e s e e n t h e i n c r e a s i n g use of h a r d m e t a l s b a s e d on ~itanium carbonitride, extremely complex in both c o m p o s i t i o n a n d m i c r o s t r u c t u r e a n d generally k n o w n as 'cermets' (though ,~cientifically the t e r m refers to a n y combin a t i o n of CERamic a n d b i n d e r METal, and in J a p a n it m e a n s any h a r d m e t a l based on t i t a n i u m r a t h e r t h a n t u n g s t e n ) . These rnaterials are increasingly v a l u a b l e for the most critical s t e e l - m a c h i n i n g situations, al tfigh speeds a n d often s u b s t a n t i a l feeds. ![nterestingly, one of the latest d e v e l o p m e n t s ~:s the a p p l i c a t i o n of p e r f o r m a n c e - e n h a n cing, single- or multi-layer, CVD a n d / o r PVD coatings to c a r b o n i t r i d e inserts. A c o n t i n u i n g d e v e l o p m e n t over the years has b e e n t h e p r o d u c t i o n of e v e r - f i n e r powders. Other t h i n g s being equal, virtually every h a r d m e t a l p r o p e r t y -- hardness, modulus, wear resistance, compressive strength a n d so on -- is e n h a n c e d as the :average grain size of the h a r d c o m p o n e n t (carbide) becomes s m a l l e r a n d the grainsize d i s t r i b u t i o n t i g h t e r . Equally, even though it is liquid at the s i n t e r i n g temperature, d i s s e m i n a t i o n of the m a t r i x m e t a l is improved with finer raw material. F i f b~ years ago, powder of 1 to 1.2 ~tm was regarded as 'fine' a n d below 1 t~m (in those days officially a ' m i c r o n ' ) as 'submicron', to the few c o m p a n i e s able to produce it. Today it is possible to produce.
()n a \el.~' small scale, t)ow(lers of.just a few n a n ( ) m e l r e s a v e r a g e size. Nomen('lature still lags b e h i n d science, how(~er, ;is a Iesu[T of w h i c h we have such illalbeit
defined
carbide
pro-
d u c t s as ' m i c r o g r a i n ' , ' n a n o g r a i n ' , 'superfine', 'extra-fine" a n d a variety of others, with everc h a n g i n g definitions: for example, 0.4 btm can be 'sub-mu', extra-fine, ultra-fine or even 'nanosize', according to the manufacturer. One u n d o u b t e d imp r o v e m e n t is in o u r ability to m e a s u r e a n d categorize accurately grain size distribution, r a t h e r t h a n simply average g r a i n size. Laser t e c h n i q u e s w i t h c o m p u t e r r e a d o u t are n o w commonplace, t h o u g h the very finest powders still p r e s e n t difficulties in this regard. Equally, commercial col)all quality has improved out of all recognition. Fifty years ago, virtually the only way t() o b t a i n high quality cobalt powder processed from oxalate was to make it yourself. Nowadays it is a s t a n d a r d raw material a n d few h a r d m e t a l m a n u f a c t u r e r s would c o n t e m plate any alternative. A n e a t idea developed recently in the United States is of compacts consisting of f i n e - g r a i n l o w - c o b a l t a g g l o m e r a t e s emb e d d e d in a m u c h t o u g h e r m a t r i x of higher-cobalt, m e d i u m grain-size carbide. The p a t e n t e d p r o d u c t combines the wear resistance of the fine particles with the
FIGURE 3: The almost universal move to large, batch-type, vacuum sintering furnaces means that large carbide rings, such as this one at Hartmetall, can now be pressed in quantity and sintered or sinter-HIPed with little difficulty. (Photo: K.J.A. Brookes.)
FIGURE 4: SEM photo of Sandvik grade GC415, with successive coating layers of TiC, AI203 and TiN.
MPR December 1995 27
high speed steel in particular, has made it
ahnost s~lonymous with performance enhancing coating, as evidenced by such trade
FIGURE5: Treys of goldcoloured cutting inserts, after removal from the coating reactor. (Photo:
K.J.A. Brookes.)
strength and shock resistance of the matrix. One can see many possibilities for this kind of product in the future.
Coatings The most important single development in the hardmetal industry in the last fifty years has been the application of thin, wearresistant coatings by chemical and, latterly, physical deposition techniques. The nearest equivalent of the 1950s was 'Wimet Laminate', an otherwise conventional hardmetal with a sintered-on, relatively thick surface layer rich in titanium carbide, to combine a tough centre with enhanced crater resistance at the surface. It was never very successful, however, not only because of delamination caused by thermal stresses but also due to the development of highly alloyed 'solid-solution' hardmetals which combined both high strength and crater resistance without laminar discontinuities and gave much improved performance. The early CVD coating of titanium carbide mentioned earlier was soon supplemented or supplanted by titanium nitride and carbonitride, then in due time by alumina, aluminium oxynitride, hafnium
compounds and multiple layers with two, three (Figure 4) and eventually up to thirteen distinct coatings. In parallel with CVD, a variety of physical vapour deposition (PVI)) coating techniques were also developed, mainly for steel where they had the advantage that, being lower temperature methods, they had little or no effect on heat treated steel microstructures. CVD, by contrast, is operated in a furnace and has never been very successful for steel. PVD, however, very new ten years ago, is now just as much a s t a n d a r d t e c h n i q u e for h a r d m e t a l s as CVD, and especially popular for tool steels. The attractive gold coloured appearance of titanium nitride (Figure 5), for a lengthy period the only available PVD coating on
28 MPR December 1995
names as 'Goldmaster' and 'Goldcoat'. As a result, many producers routinely add a CVD or PVD TiN topcoat, even when there is no real technical or scientific reason, citing such pseudo-scientific properties as 'lubricity' to the ill-informed user. All-over CVD coating causes slight rounding of the cutting edge, whereas 'line of sight' PVD techniques more easily retain a sharp edge. Nevertheless, because of the way in which cut metal flows around the insert's cutting edge, a very sharp edge is seldom desirable, as witness the popularty of 'edge honing' before service. More recent developments in coating combine the attributes of both CVD and PVD either successively or simultaneously (plasma CVD). The latest technique, however, is CVD of hardmetal with pure diamond or a 'diamond-like' amorphous coating. Producing the coating itself has been found to be surprisingly easy, requiring none of the s u p e r - h i g h p r e s s u r e s or t e m p e r a t u r e s hitherto t h o u g h t to be necessary. The problem is retaining the coating on the hardmetal, so far solved -- not necessarily definitively -- by a very few companies who closely guard their secret know-how. Applications are limited, though. Diamond, solid or coating, cannot cut ferrous materials such as steel and cast iron without rapid chemical breakdown. Initial uses include the machining of abrasive non-ferrous alloys such as silicon-aluminium, and nonmetallics like glass and carbon composites. A far larger potential user, however, is the electronics industry, which has a vast requirement for free standing, high conductivity, wear resistant, electrically insulating substrates for microchips.
The crystal b a l l What shall we see in the future? Finer powders for sure, and hardmetals with improved properties, both for cutting tools and the myriad of other applications. For cutting tools, even more complex carbonitride compositions, and more competition from both ceramics and superhard materials as they take up the challenge. We can also • expect to see more hardmetals combining hard, wear-resisting agglomerated particles in a matrix of differing composition and properties. And the pot of gold at the end of this particular rainbow?. In the writer's opinion, it may well be coatings of cubic boron nitride, a superhard material capable (in solid polycrystalline form) of out-performing conventional hardmetals in the machining of ferrous metals. •