High temperature sintering and MIM lead PM trends at world congress

PM TECHNOLOGY TRENDS

1992 POWDER RGY

High t e m p e r a t u r e sintering JUNE21.~6,S~AN~FF~A~NCISCO and M IM lead PM trends at World Congress M

ore t h a n 450 technical p a p e r s f~om 30 countries a r o u n d t h e world were s u b m i t t e d to t h e Metal Powder I n d u s t r i e s F e d e r a t i o n for p r e s e n t a t i o n at t h e 1992 Powder Metallurgy World Congress. These have been whittled down s o m e w h a t b u t will still m a k e u p 90 technical sessions, a powder injection moulding symposium and poster presentations. Alongside this p r o g r a m m e a n u m b e r of special sessions for e x a m p l e on powder m e t a l l u r g y (PM) c o m p o s i t e s , m e c h a n i c a l alloying a n d t h e a u t o m o t i v e / P M i n d u s t r y relat i o n s h i p , will be held. Metal Powder Report p r e v i e w s of some of the more interesting new developments w h i c h will be discussed in San Francisco.

Powder

production

In p o w d e r a t o m i z i n g v a c u u m melting often h a s to used to melt difficult alloys because of t h e p r o b l e m of oxidation. A practical inerting process would allow o p e r a t o r s of air m e l t i n g f u r n a c e s to e x t e n d t h e i r range of alloys, reducing powder costs and improving quality, says J o h n Dunkley of Davy McKee (session 42). Trials of U n i o n C a r b i d e ' s L a m i n a r B a r r i e r P r o c e s s (LBI) w e r e carried o u t on a 30 kg melter to see w h a t i m p a c t t h e technique h a d on alloy fluidity, oxygen pickup a n d m e l t losses of reactive elements. A variety of special applications, such as packed b e d h e a t exchangers, require a source of uniform spherical alloys particles from 0.15-1.0 m m in diameter, says M.G. Osborne rof t h e Ames Laboratory (session 48). To satisfy this need t h e t e a m developed a centrifugal atomization process whereby a low speed r o t a t i n g q u e n c h b a t h was used to q u e n c h droplets atomized by a large rapidly spinning disk. It was found t h a t

18 MPR May 1992

s p h e r i c a l p a r t i c l e s of s i l v e r with d i a m e t e r s 0_45-0.65 m m could be p r o d u c e d in a n air environment_ H. Kohmoto of Mitsubishi M a t e r i a l s Corp ( s e s s i o n 60) describes Plasma-Melt-Gas-Atomization, a process developed to produce ultra-clean intermetallic powders. The m e a n d i a m e t e r of t h e p o w d e r s p r o d u c e d is 100 p m a n d oxygen c o n t e n t is 700 ppm. PMGA powder of Nb22 at% AI h a s a m i c r o s t r u c t u r e identical to t h a t of melt s p u n ribbon, which leads Mitsubishi to conclude t h a t t h e process h a s a fairly high solidification rate. The Osprey s p r a y forming process is a p o p u l a r subject for p r e s e n t a t i o n s . J.W. Sears will give details of a p r o g r a m m e at B i r m i n g h a m University (session 56) to s p r a y f o r m t i t a n i u m alloys i n t o s h e e t a n d t u b e s . While a t e a m from M a n n e s m a n n Demag a n d PEAK Werkstofftechnik (session 6 2 ) will give a synopsis of t h e commissioning of, a n d first results from, a s p r a y d e p o s i t i o n p l a n t to p r o d u c e a l u m i n i u m in billets 300 mm in diameter and 1000 m m long. The p l a n t h a s been designed for high production rates a n d a high process yield. Vacuum p l a s m a spraying is t h e subject of a p r e s e n t a t i o n by C~- Power of Rockwell Intern a t i o n a l et al (session 68). The t e c h n i q u e is being developed for use in n e a r - n e t fabrication of aerospace hardware. It is rep o r t e d t h a t NARloy-Z, a high conductivity copper alloys used to line t h e c o m b u s t i o n c h a m b e r of t h e Space Shuttle engines a n d I n c o n e l 718, w h e n processed by VPS, show m a t e r i a l s properties b e t t e r t h a n those of critical grade cast material.

Compaction technology R. Tadepalli a n d Terry McCabe from Metalworking Technology (session 10) c o n c e n t r a t e on a

d e s i g n a p p r o a c h for p r e f o r m prediction. An e x p e r t system was developed to contain beauristic r u l e s w h i c h p r o v i d e a m e a n s for predicting t h e preform s h a p e a n d a finite e l e m e n t analysis is p e r f o r m e d on t h e predicted preform shape to simulate the consolidation process. Tadepalli a n d McCabe say t h a t t h e work exemplifies t h e r a t i o n a l process design m e t h o d for m a n u f a c t u r i n g p r o c e s s e s with specific application to PM. Press powder flow compaction (PPFC) was used by S. T a k a h a s h i , N i h o n University, (session 31), to form powder to a deep wall cup shape. The powder c o n t a i n e d some liquid paraffin b i n d e r w h i c h p e r m i t t e d an increase in green density by allowing powder to flow from t h e cup b o t t o m to t h e cup wall d u r i n g c o m p a c t i o n . However, this difference is little e n o u g h so t h a t high density can still be obtained. The shrinkage of t h e s i n t e r e d c o m p a c t is v i r t u a l l y uniform and the debinding process is considerably easier t h a n t h a t n e e d e d for m e t a l injection m o u l d i n g (MIM). A new compacting concept for t h e p r o d u c t i o n of cutting inserts from hardmetals, ceramics or cermets is to be presented by Dorst (session 39). The s y s t e m c o n t a i n s c o m p o n e n t s developed specially for 'ghost shift' o p e r a t i o n for r a p i d change of tool a n d material, as well as for flexible c o m p l e t e a u t o m a t i o n of pressing, tool cleaning, c o m p a c t a n d s i n t e r tray handling, a n d d e b u r r i n g of c o m p a c t s . T h e s e will be exp l a i n e d in detail. D o r s t will also p r e s e n t t h e first results obtained u n d e r realistic conditions a n d discuss future prospects of such systems. Various a l t e r n a t e compacting t e c h n i q u e s are also being presented_ The wet powder pouring process can be considered as a relatively straightforward, a n d energy saving p o w d e r s h a p i n g technology, say A. Ru-

1992 POWDER

JUNE 21-261 SAN FRANCISCO

20 MPR May 1992

PM

TECHNOLOGY

tier et al f~om t h e Forschungsz e n t r u m Julich. The p r o c e s s facilitates a room t e m p e r a t u r e fluid carrier-binder-powder m i x t u r e . A typical d e b i n d i n g and sintering cycle, carried out in t h e s a m e furnace, can be c o m p l e t e d in less t h a n t e n hours, say the developers. The final p a r t s have good surface quality and a s o u n d internal structure. A m e t h o d for consolidating AI-Fe-X alloys which eliminates lateral flow is being p r e s e n t e d by Sumitomo Electric Industries (session 43). The matrix alloy is modified to p r o m o t e solid state sintering and to eliminate the ductile surface oxide layer. This, says K. Kondoh, is a m a j o r advance towards realizing near net s h a p e powder forging of the alloys. Mechanical properties of the new alloys are equivalent to or b e t t e r t h a n similar alloys c o n s o l i d a t e d by c o n v e n t i o n a l powder extrusions. The process is simple and less t h e r m a l l y activating; therefore rapidly solidified microstructures are preserved which results in excellent mechanical properties. A new system for the compaction of helical gears will be p r e s e n t e d by G. Moser of Dorst et al ( s e s s i o n 44). R e s u l t s obtained in the first long term tests with respect to p r o d u c t p r o p e r t i e s and quality of helical gears p r o d u c e d by the system will be given. M. Goncalves of IPI' (session 49) has developed an alternative p r o c e s s i n g route for t h e p r o d u c t i o n fully c o n s o l i d a t e d high s t r e n g t h PM a l u m i n i u m alloys. In this a p p r o a c h the hot extrusion of air atomized powder contained larger t h a n usual p a r t i c l e s is c a r r i e d out. No degassing in cans is necessary. Results s h o w t h a t conventional high s t r e n g t h alloys 2XXX and 7XXX can be p r o d u c e d w i t h room t e m p e r a t u r e tensile properties at l e a s t e q u i v a l e n t to ingot metallurgy alloys can be successfully produced. The resalts emphasize the possibility of obtaining PM A1 alloys in which t h e expensive and inconvenient s t e p s of gas atomization and degassing can be avoided, says Goncalves. Still looking at e x t r u s i o n t e c h n i q u e s t h e U n i v e r s i t y of Mining and Metallurgy (session 49) claims to have developed a m e t h o d for forming high density PM p r o d u c t s without the need

TRENDS

for sintering. A device is used which permits simultaneous cyclic extrusion and upsetting. The structure and p r o p e r t i e s of aluminium and c o p p e r b a s e d p r o d u c t s are similar to those for t h e same materials formed plastically from cast feedstock.

Sintering Ceramic belt sintering furnaces can provide properties equivalent to o t h e r high t e m p e r a t u r e sintering m e t h o d s at a lower cost to the manufacturer, says Howard Sanderow of Managem e n t & Engineering Technologies (session 16). He carried out a study with B. Cole of Sinterite Products to d e t e r m i n e the effect of sintering t e m p e r a t u r e on the physical and mechanical properties of low alloys steels, stainless steels and soft magnetic alloys. Liquid Air Corp ( s e s s i o n 18) says t h a t it can now guarantee a carbon level of _ 0.05%C thanks to an efficient control system using synthetic gases. This system is able to regulate the carbon exchange in several furnaces by analysing t h e a t m o s p h e r e in d i f f e r e n t zones of each furnace. A novel processing idea for the integrated sintering/coating of powder articles with chrom i u m a n d its c o m p o u n d s comes from L-~ Barkov of t h e State Technical University ( s e s s i o n 65). The p r e s s e d powder article is c o a t e d in a m e t a l - o x i d e m i x t u r e a n d s i n t e r e d . The pores and defects are closed as a result of diffusion from the CrFe solid solution a n d a surface layer up to 0.5 m m thick is f o r m e d . The m e t h o d allows corrosion-resistant powder articles to be produced. In the same session C.C. Ge from t h e University of Science & Technology in Beijing describes WMVE a new process for making M2 PM HSS bars from w a t e r atomized powders with a high oxygen content. The initials for the process come from magnetic separation, vacuum loose sintering a n d h o t e x t r u s i o n . The technique is cost-effective and competitive with melting processes in lowering investment, simplifying the production route, says the team. In addition significant savings in energy and materials can be made. The dimensional change of

c o m p a c t s during in sintering is a problem. A. Griffo of Pennsylvania State University (session 63) studied w h a t h a p p e n s at each stage of sintering Fe-Cu-C c o m p a c t s and has developed a m e a n s of o b t a i n i n g a zero dimensional change in t h e compacts, by using selected sintering parameters. The d e v e l o p m e n t m e a n s t h a t compacts can be p r e s s e d to the final net shape, says Griffo.

Ferrous materials Powders which give high s t r e n g t h in the as-sintered condition are economically advantageous, however to develop new m a t e r i a l s w i t h h i g h e r tensile s t r e n g t h it is necessary to also s t r e n g t h e n the soft p h a s e s in the microstructure which result f~om the plain iron powder. C.M. Lindbergh from Hoganas (session 5) describes a new diffusion b o n d e d p o w d e r which after a single pressing and sintering shows a dimensional change close to zero and reaches tensile strength levels of 900 MPa. Using a composite type alloying m e t h o d Kawasaki Steel Corp (session 51) says t h a t it has been able to be p r o d u c e a low alloy steel w i t h a green density 0.1 g / c m a higher t h a n conventional prealloyed powder. Tensile s t r e n g t h is also increased considerably. The wear resistance is equivalent to conventional alloys. S. LeBeau (session 32) says t h a t Phoenix Metal Powers is commercializing a new ferrous powder production process based on mechanical grinding of recycled SAC carbon steel. Early p r o d u c t i o n lots have been used to p r o d u c e a u t o m o t i v e c o m p o n e n t s via p r e s s and sinter technology.

Non-ferrous materials The presence of the hard, brittle, tin rich delta p h a s e in 90/10 bronze materials is unacceptable to end users because of its adverse effect on shaft wear, high noise levels, etc. K. Das at Makin Metal Powders (session 71) h a s d e v e l o p e d a w a t e r atomized prealloyed bronze p o w e r w h i c h is c a p a b l e o f

PM

p r o d u c i n g a ful.ly d e v e l o p e d microstructure which is free of delta p h a s e when sintered at t e m p e r a t u r e s well below those currently used in bearing production. Although prealloyed it is said to have good g r e e n s t r e n g t h and up to 30% improvement in running life and shaft wear characteristics. Camshaft belt pulleys made from s i n t e r e d a l u m i n i u m are attracting i n t e r e s t because of their low weight. However, conventional PM A1 alloys have too low a wear resistance for the a p p l i c a t i o n . H. D a n n i g e r of Vienna Technical University (session 71) has developed a w e a r r e s i s t a n t A1 b a s e d on s t a n d a r d A1-Cu-Mg-Si Pm alloys by admixing different types of hard particles. C a m s h a f t belt pulleys m a d e fxom the material have shown satisfactory dimensional tolerances and excellent wear resistance in an environm e n t containing abrasive dust. S t a i n l e s s steel alloys designed for PM processing which offer improved corrosion resistance over conventional alloys will be p r e s e n t e d by A m e t e k (session 7).

Hard materials and refractory metals A new m e t h o d for the chemical processing of WC-Co c e m e n t e d carbide with a nanoscale microstructure is p r e s e n t e d by B.K_ Kim of the Korea Institute of Machinery & Metals (session 52). T h e r m o c h e m i c a l conversion of n a n o s c a l e p r e c u r s o r powders into the WC-Co powder is carried out in a fluid bed reactor_ A wear r e s i s t a n t material that is b o t h very t o u g h a n d very h a r d is described by B. M a r t n e r a n d E. F r i e d r i c h of Dresden University of Technology ( s e s s i o n 22). A b o r o n carbide powder was i m p a c t e d into a relatively tough Fe(Cr) powder by ball milling followed by hot pressing for a s h o r t time. During abrasive wear loading the boron carbide particles become nearly completely dissolved in the surface region of the materials. Thus ensuring the formation of a hard, wear resist a n t surface layer on the tough matrix. An a d v a n c e in r e f r a c t o r y m e t a l s is d e s c r i b e d by Alloy Technology (session 58). Patti-

TECHNOLOGY

cular Ferro-TiC c e r m e t s have been designed by modifying the chemical and processing m e t h ods and are capable of providing adequate service lives as erosion resistant p a r t s in applications such as pumps, valves, nozzles for sand blasting, etc_

Composites Composite materials are becoming an increasingly i m p o r t a n t area of PM. H. Cohrt of Schunk Sintermetalwerk et al (session 41) c a r r i e d o u t a r e s e a r c h p r o g r a m m e w i t h t h e aim of developing metal m a t r i x composite (MMC) p a r t s by coaxial pressing of light metal based MMC powders. The target is to produce a light metal MMC at a price w h i c h places it w i t h i n range of c o n s u m e r goods and the automotive Industry. Some of the t e c h n i q u e s used to f a b r i c a t e m i c r o - i n f i l t r a t e d macro-laminated composites (MIMLC) were looked at by A_ Bose of the Southwest Research Institute (session 53). Potential applications include armour, wear resistant p a r t s and tough cutting tools. At the Indian Institute of Technology (session 59) P. Ram a k r i s h n a n used a PM route to fabricate continuous carbon fibre reinforced aluminium matrix composites. A c o m p o s i t e with 16 vol% carbon fibres is capable of providing a tensile s t r e n g t h of 178 MPa c o m p a r e d to 88 MPa for the unreinforced matrix. D i s c o n t i n u o u s l y reinforced aluminium materials produced b y PM a r e b e i n g developed and commercialized by Alcoa (session 28). The PM r o u t e is s a i d to p r o v i d e a excellent combination of flexibility in the m a t r i x alloy and reinforcement selection, p r o d u c t uniformity and p r o p e r t y capability for a range of industrial markets. A case study will show how t h e m a t e r i a l s can m e e t application needs with a high performance but cost effective product.

Parts and applications With the current recession in PM's major market, the automotive industry, it is w o r t h noting some of the novel applications

TRENDS

for the technology scheduled for discussion. Two p a p e r s from the University of Utrecht and Krebsoge (session 79) look at sintered chemical reactors and catalytic r e a c t o r s m a d e from s i n t e r e d metals. The applications are said to be promising; conventional r e a c t o r s can be simplified and new reactor types are possible in industry. A p a p e r on the m a n u f a c t u r e of highly porous sinter elements will also be p r e s e n t e d by Krebsoge in session 35. The economics of manufacturing PM connecting rods for V-8 engines will be e x a m i n e d by R_K_ Gupta of t h e University of Michigan-Flint (session 2). The p r o j e c t is b a s e d on t h e GM Powertrain Division, Flint engine p l a n t which is currently making t h e switch from diecast to PM connecting rods.

1992 POWDER

CONGRESS JUNE 21-26 / SAN FRANCISCO

Metal injection moulding In San F r a n c i s c o a s p e c i a l symposium devoted to powder i n j e c t i o n m o u l d i n g will r u n alongside the main programme. Some of the m o s t interesting p a p e r s look at binder systems. Megamet Industries ( p a r t B) will give details of its recently p a t e n t e d process which uses a t h e r m o s e t t i n g c o n d e n s a t i o n resin as the binder. Such materials were once believed to be unsuitable for MIM, but Megam e t has developed a technique w h i c h offers low e q u i p m e n t requirements, higher productivity and easier control. Binders are also the area covered by M.Y. Cao of Rensselaer Polytechnic (part B). The institute has developed a solid polymer solution (SPS) binder w h i c h r e m a i n s rigid d u r i n g d e b i n d i n g a n d gives p e r f e c t s h a p e r e t e n t i o n w i t h o u t any s h r i n k a g e . In G e r m a n y t h e F r a u n h o f e r I n s t a n d Henkel ( p a r t C) investigated a newly developed binder system based on special functionalized polymers and lubricants. In t e r m s of applications for MIM, S c h u n k ( p a r t L) will discuss large scale production of s t a i n l e s s steel gears. The gears are for use in an electric t o o t h b r u s h and MIM was chosen because of the c o m p l e x s h a p e s of the parts. Some 30 000 pieces are p r o d u c e d each day_

MPR M a y 1992 23