Expanding the toughness field of hardmetals

Expanding the toughness field of hardmetals The applications of high speed steels and conventional hardm e t a l s a r e well k n o w n . But w h e n HSS is u s e d in s o m e applications, it has insufficient abrasion resistance for a good p e r f o r m a n c e even when toughn e s s is h i g h e n o u g h f o r a s u c c e s s f u l a p p l i c a t i o n . This fact motivated Bonastre of Caldes de Montbui, Spain, to carry out an R&D project with the aim of producing a n e w group of alloys covering the field b e t w e e n the high toughness conventional h a r d m e t a l s and the high speed steel, say M. Albajar and F. Fernandez. ~

A

r

P o w d e r characterization

FIGURE 1: TMD's field of application.

r

ABP~SION RESISTANCE

[]

DIAMOND C U B I C N I T R I D E (BCN)

[] i

I

i cE'

Ics AN° c RMETs

TMD

TOUGHNESS

POWDERS

new group of TMD alloys is presented (from the Spanish words Tenaces de Metal Duro). They are WC based alloys with a metallic m a t r i x containing Co-Ni-Fe and a d d i t i o n s of elements from transition metals of V and VI groups, they are obtained by a liquid phase sintering powder metallurgy (PM) process. The corrosion resistance shown by high speed steel (HSS) in acids is not very good. Therefore a n o t h e r objective with the TMD alloys has been to produce a material more resistant to corrosive environments t h a n HSS. This objective has been widely att a i n e d . Also, m e c h a n i c a l , p h y s i c a l a n d chemical p r o p e r t i e s achieved with TMD alloys confirm t h a t the empty field between h a r d m e t a l s and HSS has been filled. Tools and machine p a r t s currently made in steel, which fail as a result of corrosion, abrasion or fatigue, can now be made with the TMD alloys.

MORPHOLOGY

SIZE DISPERSION

CHARACTERISTICS

(~m) ~max

O. 70 ~m

Co

Vermicular

Medium

¢min O. 20 Dm F O R M PE = 0 . 4 6 7 1

Ni

Spherical with )olyhedrical form aggregates

Medium

¢m&x 4.O0 Dm Cmin 1.42 ~m F O R M PE = 0.7851

Fe

Spherical

Large

Cm&x 3 . 7 0 ~am ¢min O. 16 ~m F O R M PE = 0 . 7 7 3 3

WC

Faceted polyhedrical

Large

Cm&x 7 . 0 0 ~lm ¢min i. 40 ~m F O R M PE = 0. 6745

Cr3C 2

Rounded angles

Medium

L 2.10 L 0.80 1 1.60 1 0.15 F O R M PE = 0 . 6 1 9 6

Mo2C

Angular particles

Large

L 2.90 L 0.53 1 1.40 1 0.13 F O R M PE = 0 . 6 1 7 6

18 MPR December 1991

0026-0657/91/$3.50 ©, Elsevier Science Publishers Ltd

A morphological and m o r p h o m e t r i c a l study of the starting powders has been done (Table 1). A knowledge of the nature, composition, m o r p h o l o g y a n d size of t h e d i f f e r e n t starting powders is important, not only to fix the sintering conditions of the different alloys but also for the correct e x p l a n a t i o n of the structure and p r o p e r t i e s achieved with them. By means of scanning electron micros c o p y (SEM) t h e m o r p h o l o g y of t h e different powders was identified. The studied p a r a m e t e r s were the perimeter (P), area (A), minimum d i a m e t e r (Dmin), m a x i m u m d i a m e t e r (Dmax) and a form factor defined as FORM PE = 4~ A / P 2. The size and dispersion of the different powders, both carbides and metallic binder, are quite acceptable. This ensures a good initial property correlation. The p o w d e r p u r i t y ( T a b l e 2) w a s determined by means of X-ray microanalysis (EDS). Impurity analysis was determi-

TABLE 1: Morphological and morphometrical study of the powders.

n a t e d by m e a n s of e m i s s i o n s p e c t r o s c o p y (Table 2). The n a t u r e of t h e p h a s e s was d e t e r m i n a t e d by m e a n s of X-ray diffraction (Table 2). Analysis only h a s a q u a l i t a t i v e a n d qualificative value. This s t u d y shows t h e high p u r i t y of t h e s t a r t i n g p o w d e r s used.

il MIcRo il POWDER ~ALYSIS ~ - - ~ EDS I M~

rl ~

H R

i I

Process

A PM process, t h a t is a l r e a d y u s e d for h a r d m e t a l p a r t s m a n u f a c t u r e d in o u r factory, h a s been followed ( F i g u r e 2). F o r t h e p r e p a r a t i o n of t h e different alloys s t u d i e d c o m m e r c i a l l y a v a i l a b l e powd e r s were used, with t h e e x c e p t i o n of WC w h i c h w a s m a n u f a c t u r e d i n - h o u s e from d o m e s t i c scheelite ore. This is a c h e m i c a l p r o c e s s consisting of a c h e m i c a l a t t a c k a n d successive filtrations, evaporations and bufferings to p r o d u c e a m m o n i u m p a r a t u n g s t a t e (AVF); which after calcination, H2 r e d u c t i o n a n d c o n t r o l l e d c a r b u r a t i o n , gives t h e t u n g s t e n c a r b i d e used. The different powders, s u i t a b l y mixed, milled, l u b r i c a t e d a n d g r a n u l a t e d , were p r e s s e d to give a green part. Hot i s o s t a t i c p r e s s i n g (HIP) in o u r own facility followed by green machining, w h e n required, a n d a liquid p h a s e s i n t e r i n g in proper furnaces; produced the finished p a r t s r e a d y for testing. S t a r t i n g from t h e s e r a w m a t e r i a l s several c o m p o s i t i o n s were p r e p a r e d (Table 3), w i t h different w e i g h t p e r c e n t of b i n d e r phase, to p r o d u c e t h e alloys: TMD 60; TMD 50; TMD 40; and TMD 30.

II D

II ~ P.ASES IIT~CESI

II MD

Ni

Ni

Ni

Ca,A1 Mg, Fe Si,Cr Cu

FCC

Fe

Fe

Fe

Mn,Ca

Mg

B, Ni

BCC

WC

W

W

Pb

Cu

Na

H

Zn

O

Mn, B

0

Cr3C2 Cr,Al,Cl

Cr

Mo2C

Mo

Mo

Fe,Ni Si Ca,Al

Pb,Fe Mg Ca,Co

Na

Si, B

Fe

MF=very strong. F=strong. R=medium. D=weak. MD=very weak. FCC=face cubic centered. BCC=body cubic centered. H=hexagonal. O=ortorrombic

TABLE 2: Powder analysis.

STARTING

POWDERS

I

Y

I POSER's CONtROl, ] ? I

MILLING

[~

VAPORATION

/

[

GRANULATION

I

ALLOY CONTROL

[

[

PRESS

I

[

PRESINTERING

]

[INTE EDIATE OONROL J 1 [

sINT'.ING I

Structural characterization

The s t r u c t u r a l c h a r a c t e r i z a t i o n was d o n e using o p t i c a l a n d s c a n n i n g e l e c t r o n microscopy techniques. By m e a n s of m i c r o a n a l y sis EDS c o u p l e d to SEM a n d X-ray i m a g e s of s t r u c t u r a l zones a n d t h e c o n c e n t r a t i o n of line profile elements, t h e d i s t r i b u t i o n of t h e different e l e m e n t s in t h e p r e s e n t p h a s e s can be d e t e r m i n e d . The m e t a l l o g r a p h i c s t r u c t u r e of p o l i s h e d s a m p l e s can be revealed using r e a c t a n t s such as: M u r a k a m i ' s solution, for e x p o s i n g t u n g s t e n carbides; a n d Nital 2% r e a g e n t or a q u e o u s solution of FeC13, for e x p o s i n g t h e metallic phase. Illumination techniques such as N o m a r s k i ' s interference can also be used. In all samples, diffusion b e t w e e n carbides a n d t h e m e t a l l i c p h a s e d e v e l o p e d d u r i n g t h e s i n t e r i n g p r o c e s s e s , was observed: -- t h e r e are only two p h a s e s present: WC ap h a s e , a n d fl p h a s e of a Co-Ni-Fe solid

EMISSION SPECTROSCOP~

Jr

[ FINISHING MACHINING

I

SINTER-HIP

]

HIP

FIGURE 2: Production routes.

RAW

M A T E R I A L S

WT %

TUNGSTEN

CARBIDE

_> 65.0

CHROMIUM

CARBIDE

_<

3.0%

_<

5.0%

IRON

<

5.0%

COBALT

<_ 25.0

NICKEL

_< 2 5 . 0 %

mOLYBDENUM

CARBIDE

%

%

TABLE 3: Composition.

solution; p h a s e h a s a s i m p l e h e x a g o n a l struct u r e with s t o i c h i o m e t r i c s t r u c t u r e h l (W) in all alloys; -- t h e h i g h e s t c o n c e n t r a t i o n of W occurs in the centre of a-phase carbides and --a

MPR December 1991 19

ALLOYS HARDMETAL TEST DENSITY (g/cm 3 )

T

G 5V

G 4V

13.1

13.5

M

D

TMD 60 TMD 50 TMD 40 TMD 30 12.7

12.8

28

30

640

710

830

1020

2480 2650 I 2560 COMPRESSIVE STRENGTH (MPa ) 3195 I 3350 I 2700

2640

2630

2630

3210

3405

3635

32

27

20

COERCIVE FIELD JOe)

68

80 I

13.3

13.8

41 I

55

HARDNESS ( Hv30 )

870

980

T.R.S. (MPa )

KIC ~ ,~ (MNm-O/z)

24

J

YOUNG 'S MODULUS (GPa )

19 I

40

4 5 3 4 8 5 4 1 6 4 2 6 4 7 1 5 2 9

H

ABRASION RESISTANCE I (rev/IO mm3) 15.2 HSS M 2 =

18.1119.4119.8

20.9124.3

820 Hv30.

g r a d u a l l y d e c r e a s e s n e a r e r to t h e c a r b i d e surface; -- s o m e of W is f o u n d inside t h e m e t a l l i c phase; -- Cr a n d Mo b e c o m e p a r t of t h e m e t a l l i c p h a s e from t h e original carbides; - - N i , Co a n d Fe diffuse into t h e c<-phase a n d a c o n c e n t r a t i o n of t h e m is f o u n d in t h e c a r b i d e surface; a n d --the structural characterization shows t h a t in all t h e alloys, b e c a u s e of t h e composition and the manufacturing process, t h e m a t r i x p h a s e h a s a face c e n t r e d cubic structure. This gives t h e alloy c o n s i d e r a b l y i m p r o v e d p r o p e r t i e s c o m p a r e d to t h e c o n v e n t i o n a l h a r d m e t a l in w h i c h a m i x e d h e x a g o n a l s t r u c t u r e is found. This is b e c a u s e t h e fcc s t r u c t u r e , w h i c h h a s f o u r sliding c o m p a c t p l a n e s , h a s t h e a b i l i t y to u n d e r g o p l a s t i c s t r a i n a n d so a h i g h e r toughness.

TABLE 4: Achieved values for the different parameters. CORROSION I

HNO3 I%

rIMEI~RD-I T,D IRss ,21 IMETAL I

I

I

(h> I,g/d,,I,g/d,,Img/d,,I 888 1176 1397 1642 2518 2817 3115 3327 3088 5079 4083 5568

I

841 1224 1522 1720 2068 2235 2380 2467

8 I0 21 24 27 30 45 48

I TMD IHSS M2

IHE?AL I

3 6 g 21 27 33 49 56

7296 12537 17075 29420 35416 41450 45393 53470

10.0 10.7 12.8 16.9 18.6 18.5 19.3 22.4

I

1.4 1.4 2.4 3.1 3.1 3.1 3.8 4.9

TIMIIHARD- TMD HSS M2

0,8 1.1 3.8 4.5 4,5 4.5 6.1 6.1

iHSSM2:

4 7 i0

120 210 264

53 131 205

90 220 357

23 27 30 33 47

445 495 548 581 729

582 635 711 734 846

954 1118 1266 1381 1958

50 53

763 804

56 69

139 412 578 642 711 762 943 993 1075

I

I

56 299 747 798 854 901 1044 1085 1152

597 i724 5822 6584 7444 8107 11181 11980 13359

CITRIC ACID 5% TIMEIHARD- TMD RSS M2 ]METAL

lib> I,g/d,' =g/d,'l=g/d,' I

618 3534 6859 30718 37253 42269 47139 78929 85937

4 9 23 27 31 34 46 50 56

LACTIC ACID 5%

JTIMI]HARD-]METAL TMD

iMETAL (h) Img/dm2 mg/dm 2 mg/dm z

I TMD I,ss M2

IMETAL I

(h) Img/dm2 mg/dm ~ mg/dm2 4 8 i0 23 27 31 33 46 50 54 56 69

871 2089 908 2232

847 945 2389 1009 1069 3013

77 35 201 80 242 110 426 582 485 631 563 684 574 722 760 848 814 884 866 922 884 935 1034 1040

81 332 521 1584 1883 2198 2371 3520 3820 4103 4318 5412

............................

i ..............

I ..............

v ..............

r ..............

I ..............

~ ..............

T ..............

t ..............

i

60000

.............. i .............. i.............. i.............. ! .............. i .............. i .............. ]......... I{ .............. i 5 0 0 0 0 ............... i .............. i .............. i .............. i .............. i .............. i .............. i .......... i .............. i .............. , 4 0 0 0 0 ........................................... i.............. i .............. t ........ . ......... . .......... .t ............................ 30000

............... i .............. i.............. i.........ni ........ II..i .........|J .........|i ........................ |i i .............. i

20000

r ..............

! .....................................

i

0 1

I

F

Ill

3

, .........

L

I

, .........

~i

6

HAROMETAL

20 MPR December 1991

it|]], T ..................

B

...............

10000

The p r o p e r t i e s of t h e n e w TMD alloys have b e e n c o m p a r e d in r e f e r e n c e w i t h t w o hardmetal alloy with a matrix phase w e i g h t p e r c e n t v a l u e close to t h a t of TMD. They were also c o m p a r e d w i t h a M2 t y p e high s p e e d steel. In all cases t e s t s were d o n e under international standards. Table 4 shows t h a t t h e TMD p r o p e r t i e s a r e a n i m p r o v e m e n t on t h o s e of h a r d m e t a l . In p a r t i c u l a r , t o u g h n e s s , Km a n d a b r a s i o n resistance. The mechanical properties achieved i n d i c a t e t h a t t h e TMD alloys will fill t h e g a p b e t w e e n e x i s t i n g high s p e e d steels a n d high t o u g h n e s s h a r d m e t a l s . This w a s t h e m a i n objective of t h e d e v e l o p m e n t .

Corrosion resistance study TABLE 5: Weight loss by unit of surface in the different environs used.

70000

Physical and mechanical properties

(h) Img/d='l=g/~l=g/d=~

I("1 I=g/d"l'g/d='l'g/d"

R2S04 I%

79 22. 306 63 407 176 536 336 589 562 613 594 631 616 768 704 816 755 860 795 964 887 1481 1246 1581 2045 1704 2151

I

HCI 5%

TI,EIM~o

I

I

i 4 7 20 23 26 30 33 36 39 43 57 60 64

J

NaOH 5%

ITI,EI,~D

I

TEST

RESISTANCE

I

I

: ..........

,i

B

~. .........

" li

10 i

TMD

, .........

j ,1

21 24 TIME (h)

I

I .........

~ ..........

i

i

! .........

, ..........

,i

!

27

30

T ..............

r ..............

,_. '. '

~ .............................

45

HSS M2

OO26-O657/91/$3.50 ©, ElsevierScience Publishers Ltd

I

S a m p l e s (40 x 25 x 5 m m ) o f TMD, h a r d m e t a l a n d M2 HSS were e x p o s e d to several acid a n d b a s i c e n v i r o n m e n t s : nitric a c i d 1%; h y d r o c h l o r i c a c i d 5%; s o d i u m h y d r o x i d e 5%; s u l p h u r i c a c i d 5%; a n d lactic a c i d 5%; w i t h t h e a i m of c o m p a r i n g t h e i r c o r r o s i o n r e s i s t a n c e in t h e s e e n v i r o n m e n t s . In all cases a h i g h e r c o r r o s i o n r e s i s t a n c e for TMD in r e l a t i o n to M2 HSS w a s noted, a n d a s i m i l a r b e h a v i o u r to t h a t of h a r d m e t a l (Table 5 a n d Figures 3 to 7).

46

FIGURE 3: Corrosion resistance (HN03 1%).

Field of application of TMD alloys Both the p a r t i c u l a r p h y s i c a l a n d m e c h a n i cal p r o p e r t i e s a n d t h e c h e m i c a l s t a b i l i t y of TMDs m a k e t h e m s u i t a b l e for use in h a r d service conditions, d i s c o n t i n u o u s s t r e s s e s a n d i m p a c t loads. This o p e n s a wide range of a p p l i c a t i o n s with s u r p r i s i n g r e s u l t s in special cases of m e t a l drawing, m a c h i n e s t r u c t u r a l p a r t s , tools a n d p a r t s e x p o s e d to s t r o n g wear, mining, a n d m e t a l l i c a n d nonm e t a l l i c m a t e r i a l s machining. TMD alloys have been specifically devel o p e d for a p p l i c a t i o n s which require: -- high m e c h a n i c a l strength; -- i m p r o v e d t o u g h n e s s c o m p a r e d to h a r d metals; -- good a b r a s i o n resistance; -- e x c e l l e n t t h e r m a l s t r e s s resistance; a n d -- good c o r r o s i o n resistance. F o r i n s t a n c e in t h e m a n u f a c t u r e of: --cutting, h e a d i n g , swaging, e x t r u s i o n , d r a w i n g a n d o t h e r dies; -- special profile dies for drawing, s t r e t c h ing a n d sizing; -- cold a n d h o t rolling rollers; -- m i n i n g a n d p u b l i c w o r k s tools; a n d --other applications where the combination of good m e c h a n i c a l p r o p e r t i e s m a k e t h e m d e s i r a b l e for t o o l s o r m a c h i n e parts.

E

6

II

~

HARDMETAL

Z7 TIME

i

~0

Z/

(h)

TMO

HSS

nB

M2

FIGURE 4: Corrosion resistance (NaOH 5%).

1 4 0 0 0 T

...............

! ................

! ................

, ................

: ................

r ...............

~. ...............

: ................

~ ................

I

ooot ............................................................... i................i...............i ........................., ..........t ~oooo~ ............... ,................ i ................ i ................ i ................ i ............... i ......... i. ..........,,, ......... n

~ooo

............... i................ i ................ i .......... i ........... i .......... i .......... i............ i ........... i

4ooo .............. i................ i............ i........... "........... }..........!..........!............ !........... ! ............... ................ ............ i........... ........... i.......... ',...................... .......... ! 0

4

8

23

II

HARDMETAL

27

31 34 46 TIME (h) TMD i HSS M2

i

56

50

FIGURE 5: Corrosion resistance (HN03 5%).

9°°°° I .........T ......... T ......... T .......... !.......... !.......... !.......... !.......... !,!

.......... !.......... !.......... !.......... !..........

Acknowledgement .........

700001

,~ .........

I

$ .........

$ ..........

]

!

i ....................

I

i ..........

!

~. .......

I

]

i ......

i ..........

I

]

] ..........

I

] ..........

!

i ..........

]

i ..........

I

i

I

600001 '......... i.......... [......... i.......... [........................................... i................... i ...... i..... i.......]

This article is t h e r e s u l t of w o r k d o n e in a r e s e a r c h a n d d e v e l o p m e n t (R&D) p r o j e c t with s u p p o r t of t h e 'CDTI ( c e n t r o p a r el D e s a r r o l o Technologico I n d u s t r i a l ) ' a n d t h e 'Ministerio de I n d u s t r i a y Energia', in t h e New M a t e r i a l s N a t i o n a l P r o g r a m m e . We w o u l d like to t h a n k t h e r e s e a r c h group of t h e ' D e p a r t a m e n t o de Ing. Q u i m i c a y Metalurgia, U n i v e r s i d a d de B a r c e l o n a ' w h i c h p e r f o r m e d m o s t of t h e physical, m e c h a n i c a l a n d c h e m i c a l tests.

SO000~, ......~....... -~......~...... i ......... !.......... i........ •i .......i...... i ........ !......]

E

,oooo4

I

',.....!.......{

........., ........., ........., ..........,..........,...,,.-..,., ....... ,....... ...........,.....................,..........,..........

m

i

i

2oooo{.........; .........~.........; ......i i~...... J.......Ili.......;.......i.......i..........i..........i..........i..........i..........{ 10000f ......... i ........ ~ ......... ~ ' " ' i ' i " " !

_i

oI

. . . . . [] ...... I ' } . . . . . . . i ....... i .......... i .......... i ........ i ....... i ....... i

.i.. m! B!~!~IJ!_ 4 7 20 2~ 26

30 TIME

i

HARDMETAL

!

,~

t_ ! _ ' , _ ! _ ! _ . ! i 36 ~9 4s 57 60 64

(h)

TMD

ll

H$S M2

FIGURE 6: Corrosion resistance (HCI 5%).

References (1). I. Sanchiz ' E s t r u c t u r a y P r o p i e d a d e s de Nuevas A l e a c i o n e s Tenaces d e Metal Duro', Tesis de L i c e n c i a t u r a ( F a c u l t a d d e Quimic a - U n i v e r s i d a d de Barcelona. F e b r e r o 1991. (2). J.M. G u i l e m a n y et al, ' I n f o r m e de c a r a c t e r r e s e r v a d o U n i v e r s i t a t de Barcelon a - B o n a s t r e S.A. ( 1 9 9 0 ) ' (3). M. A l b a j a r et al, ' A l e a c i o n e s TMD a m p l i a n el c a m p o de t e n a c i d a d del Metal Duro', M e m o r i a s de al III Reuni5n N a c i o n a l de Ciencia de Materiales. 333-335, Sevilla 1990. ISBN SE-1721-1990.

E

-

4 I

7

10

HARDMETAL

23 II

27 TMD

30

33

TIME(h)

47 II

50

53

56

69

HSS M2

FIGURE 7: Corrosion resistance (lactic acid 5%).

MPR

December

1991

21