Thermal shock resistance of cobalt bonded tungsten-tantalum-titanium mixed carbides

Thermal shock resistance of cobalt bonded tungsten-tantalum-titanium mixed carbides

h o m o g e n e o u s s t r u c t u r e was 5%;. (3). p r o p e r t i e s of t h e m a t e r i a l , KIC and transverse rupture strength (TRS) were in...

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h o m o g e n e o u s s t r u c t u r e was 5%;. (3). p r o p e r t i e s of t h e m a t e r i a l , KIC and transverse rupture strength (TRS) were increased by use of HIP; (4). An alloy c o n t a i n i n g Ti(C,N)-20%Cr3C2-0.2%BaC0.5%Ni was found to have 0.1% porosity, a TRS of 650 MPa and IQc of 3.8 MPa.m 1/2. It is suggested that the improved properties can be a t t r i b u t e d to a fine h o m o g e n e o u s structure. SINTERING OF CHROMIUM CARBIDE BASED MATERIALS BY HOT ISOSTATIC PRESSING (HIP) H. Hiraishi et al, J. Japan Soc. Powder and PowderMetaUurgy, Vol 38, No 2, 1991, 135144, (In Japanese) The sintering, by HIP, of c h r o m i u m carbide materials with Cr.C atomic ratios in the range 0.54 to 0.83 has been studied. It was found that densification is influenced by t h e %C for t h e p r o p e r t i e s a n d applications considered, particularly wear resistance at elevated temperatures. The o p t i m u m C c o n t e n t was found to be 14.3wt%. Presintering prior to HIP reduced the density which could be attained from 95 to 89%. Fracture toughness was measured at 4.2 MPa.m 1/2 and crack propagation velocity was 9x103 m/sec. ROLE OF MOLYBDENUM CARBIDE AND TITANIUM NITRIDE IN THE SINTERING OF MATERIALS CONTAINING TITANIUM AND CHROMIUM CARBIDES T. Hachisuka, J. Japan Soc. Powder and Powder Metallurgy, Vol 38, No 2, 1991, 145152, (In Japanese). The effects of additions of TiN and Mo2C on the sintering of cutting tool materials containing TiC- 15%TiN-8%CrsC2-7%Mo2C were investigated. Sintering was up to 1600°C for 2 hours in a mildly carburizing atmosphere at 10 -1 Torr. The alloys sintered by a liquid phase mechanism and full d e n s i f i e a t i o n was a t t a i n e d at 135°C. E x a m i n a t i o n of the sintered materials showed that a solid solution between TIN and Mo2C was formed. Impurities, Fe, Co and Ni, were dissolved into the low Cr carbides at 1350 and 1400°C. STRUCTURE CHANGES PRODUCED BY DEFORMATION OF TITANIUM CARBIDE BASED CERMETS M. Ueki et al, J. Japan Soc, Powder and Powder Metallurgy, Vol 38, No 2, 1991, 161167, (In Japanese). Differences in the structures of WC and TiC c e m e n t e d c a r b i d e s , at h a r d n e s s indentation sites after heat treatment, are reported. A duplex structure in the matrix was found in TiC base alloys which was absent from the WC materials. It was suggested that there was a strain induced transformation in the zone surrounding the hardness indentations.

68 MPR September 1991

SLIDING WEAR CHARACTERISTICS OF IRON CEMENTED BORIDE MATERIALS AGAINST COPPER T. Watanabe et al, J. Japan Soc. Powder and Powder Metallurgy, Vol 38, No 2, 1991, 175-181, (In Japanese) Friction and wear characteristics of MoFe-B cermets, against Cu, were investigated under lubricated and unlubricated conditions. Comparison was made with cemented carbides and tool steels. Under lubricated conditions at low sliding speeds, the results were similar for the three materials studied and depended mainly on the surface roughness. At higher sliding speeds friction for the tool steel increased but for the cemented carbide and boride decreased. Under mild wear conditions, w i t h o u t lubricant, the cermets had a slightly higher friction than the tool steel, and under severe wear the boride cermet had a lower rate than the tool steel or the cemented carbide.

PLASTIC FLOW WEAR MECHANISMS IN STEEL MATRIX CEMENTED CARBIDE AT HIGH TEMPERATURES ¥. Xinghe and M. Shaobo, (Hefei Polytechnic Univ, China), PM Technology, Vol 9, No 1, 1991, 15-20, (In Chinese). The structure and high temperature p l a s t i c f l o w w e a r of s t e e l b o n d e d cemented carbides have been investigated. It was shown that the mechanisms of plastic flow wear are by separation of hard particles from the matrix and abrasion.

THERMAL SHOCK RESISTANCE OF COBALT BONDED TUNGSTENTANTALUM-TITANIUIM MIXED CARBIDES L. Huahui et al, (Shanghai Research Inst for Materials, China), PM Technology, Vol 9, No 1, 1991, 28-33, (In Chinese). Mixed Ti-W-Ta carbides bonded with Co were subjected to rapid thermal cycling. The bend strength decreased with the number of cycles and evidence of plastic deformation was detected in the Co matrix of specimens with a high strength. Cleavage fracture was observed for specimens with low residual strength after thermal cycling.

austenitic age h a r d e n i n g steel. It was found possible to braze the alloy into cutters and satisfactory service lives are reported.

Metal injection moulding METAL INJECTION MOULDING (MIM) OF HIGH PERFORMANCE MATERIALS M. Dropmann et al, (Forschungszentrum Jfilich, Jfilich, Germany, Metall., Vol 45, No 5, 1991, 444-448, (In German). The paper draws attention to the use of MIM in the production of small, complex c o m p o n e n t s a n d t h e i m p o r t a n c e of minimizing contamination, by O and C f r o m t h e p r o c e s s i n g , if t h e s p e c i a l properties of, e.g. Ni base superalloys, are to be attained. To this end, raw materials and all processing steps require optimization. Powder particle size and size distribution, binder formulation and removal characteristics and suitable rheological p r o p e r t i e s of t h e p o w d e r / binder mixture with minimum binder c o n t e n t r e q u i r e close a t t e n t i o n . With proper optimization and control it was shown to be possible to economically produceparts with smooth surfaces and high density by MIM and HIP in a range of alloys using metal powders up to 150 ~m in size.

Porous materials GAS FILTRATION WITH POROUS MEDIA PARTIALLY SATURATED WITH WETTING LIQUID Y.N. Kryuchkov, Poroshkovaya MetaUurgiya, No 2, 1991, 50-55, (In Russian). The effect of wetting a porous medium on the permeation of gases during filtering has been analysed. A 'winding coefficient' is defined and used to describe the transfer of gas through the filter. This coefficient is increased as the extent of blocking of the pores by a liquid is increased. According to liquid content the coefficient increases from unity to infinity.

Refractory metals JI



W. Haikuan and X. Junzheng, (Beijing Research Inst for Powder Metallurgy, China), PM Technology, Vol 9, No 1, 1991, 2327, (In Chinese). The development of a steel bonded carbide cutting tool material for use in coal cutting machines is described. The p o w d e r u s e d for t h e m a t r i x was an

Y.F. L o m n i t s k ~ a and Y.B. Kuzma, Poroshkovaya MetaUurgiya, No 2, 1991, 82-86, (In Russian). Phase equilibria in Zr-W-P, Zr-Mo-P and Zr-Re-P were established by use of X-ray analysis. The existence of new phases is reported.