Effects of addition of refractory carbides on characteristics of cobalt in cemented carbides

Effects of addition of refractory carbides on characteristics of cobalt in cemented carbides

punch were p r e h e a t e d to 350 -t- 20°C and the preforms were protected against oxidation during sintering by a ceramic coating. It was shown t h...

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punch were p r e h e a t e d to 350 -t- 20°C and the preforms were protected against oxidation during sintering by a ceramic coating. It was shown t h a t there is a power law relating forged density to the ratio of horizontal and vertical restraints in the die. Microscopic examination showed flow of p o r e s and grains, recrystallization a n d s h e a r i n g of p o r e s a n d c o n f i r m e d t h e density measurements. The P alloy showed superior forgability compared with the pure re.

Ceramic compaction A NEW INJECTION MOULDING CONCEPT FOR PRODUCTION OF CUTTING TOOL INSERTS L. Wolberg, G. Moser (Dorst America Inc, Bethlehem, USA). A new concept in compaction of cutting tool inserts, using hard metals, cermet or ceramic powders was presented. The system uses 'ghost shift' for rapid tool and material changes. The process of moulding, tool cleaning, h a n d l i n g and d e b u r r i n g of compacts was completely a u t o m a t e d and was explained. A t t e n t i o n was given to quality control. The future p r o s p e c t s of the system were discussed with regard to technical and economic aspects. STUDY OF COMPACTIBILITY OF METALLIZED CERAMIC POWDERS AND CERAMIC/METAL POWDER MIXTURES S. Li et al (University of Twente, Twente, Netherlands). A compaction equation for Al203 powder coated with TiB in an Ni matrix was derived from e x p e r i m e n t s on the compaction of the p o w d e r s . The e q u a t i o n c o n t a i n s t h r e e constants including a compaction modulus which increased with the ceramic c o n t e n t of the mixture and reduces with reduction in particle size. An Ni(P) coating and the A1203 reduces compaction resistance and a TiN coating increases compaction modulus. The two o t h e r empirical constants were also investigated. MODEL FOR CYCLIC COMPACTION OF CERAMIC POWDER K. Kim et al (Postech, Korea). The e f f o r t s o f b i a s p r e s s u r e a n d f r e q u e n c y on d e n s i f i c a t i o n of c e r a m i c powders were investigated u n d e r cyclic compaction conditions. Cyclic compaction was shown to be more effective t h a t single stroke static pressing. A correlation was d e d u c e d between densification a n d the cycle-dependent p r e s s u r e / v o l u m e fraction r e l a t i o n for c e r a m i c p o w d e r s . The r e l a t i o n s h i p p r o p o s e d by C o o p e r a n d Eaton and e x p e r i m e n t a l d a t a were used. Good agreement between theoretical and

experimental reported.

curves

for

A1203

was

Hardmetals ALUMINIUM CONTAMINATION OF C E M E N T E D CARBIDES DURING SINTERING K.A. Thorsen (Technical University of Denmark, Copenhagen, Denmark). The effects of Al, which c o n t a m i n a t e d c e m e n t e d carbides, during sintering was i n v e s t i g a t e d . The c o n t a m i n a t i o n w a s attributed to A1 reduced from the A1203 sand used in the trays in H a t m o s p h e r e sintering furnaces. The A1 alloys with the liquid Co p h a s e in the hard metals and is s u b s e q u e n t l y oxidized to A1203 on the surface of the carbides and thus interferes w i t h b r a z i n g . S i m p l e r e m o v a l of t h e surfaces AlzO3 is inadequate since fresh oxide forms from the A1 still dissolved in the Co phase. Salt b a t h t r e a t m e n t was reported to leave a surface free from oxide. The use of ZrO 2 instead of A12Oa was suggested. E F F E C T S OF ADDITION OF REFRACTORY CARBIDES ON CHARACTERISTICS OF COBALT IN C E M E N T E D CARBIDES. L. Yao, C. Yang ( Z h u z h o u C e m e n t e d C a r b i d e R e s e a r c h Inst, Z h u z h o u City, China). An i n v e s t i g a t i o n of t h e e f f e c t s of additional carbides, TaC, NbC and Cr3C2, on the characteristics of Co in WC-Co was described. Wettability t e s t s of Co on WC, using the sessile drop method, were carried out. The structure and composition of the WC w e t t e d z o n e w e r e e x a m i n e d a n d mechanical properties and structures of the Co-Cr3C 2 alloys were measured. The r e s u l t s w e r e d i s c u s s e d in t e r m s o f t h e r m o d y n a m i c s . It was concluded t h a t Cr3C2 reduced the wetting of WC by Co and t h a t Cr3C2 s t r e n g t h e n s the Co phase. FLUIDIZED BED SYNTHESIS OF NANOPHASE T U N G S T E N CARBIDECOBALT COMPOSITE POWDERS B.I~ Kim et al (Korea Inst of Machinery and Metals, Korea). A m e t h o d for processing WC-Co powders with nanoscale structures was described. The three stage process involves preparation of a s t a r t i n g s o l u t i o n , p r e c i p i t a t i o n a n d s p r a y d r y i n g of a precurser powder and thermochemical conversion into the required n a n o p h a s e WC-Co composite powder. The a d o p t i o n of fluidized bed technology for the final step enables increased yield of powder to be o b t a i n e d . The b a s i s of t h e fluid b e d technology for the production of n a n o p h a s e WC-Co powders was discussed.

MAKING OF FINE AND S U P E R F I N E T U N G S T E N CARBIDE POWDER Z. Tao (Zhuzhou Cemented Carbide Works, Zhuzhou City, China). An investigation of the factors which control the particle size of WC powders was described. The physical properties of the starting W powder and carburizing conditions were studied. A relationship between W powder size and grain size was established. In order to produce WC powder less t h a n 0.5 p.m it was found necessary to use W powder below 0.3 p.m. It was noted t h a t the particles t e n d e d to agglomerate during carburizing. E F F E C T OF P R E S S U R E SINTERING AND POST-TREATMENT ON THE STRENGTH OF C E M E N T E D CARBIDES B. North et al (Kennametal Inc, Latrobe, USA). The literature concerning the use of HIP or pressure sintering to reduce residual porosity in c e m e n t e d carbides was reviewed with respect to composition, microstructure and s u b s e q u e n t processing. The effects of over pressure sintering and surface t r e a t m e n t s were considered. Over-pressure sintering, only, resulted in e n h a n c e m e n t of strength when physical vapour deposited coatings were applied. Unground and chemical vapour deposited materials failed because of surface defects.

Particulate materials STRUCTURE OF CERMETS MADE BY HOT P R E S S U R E IMPULSE M E T H O D S L.N. Permyakov et al (Research Inst of SIA 'Lutch', Russia). A comparison of impulse consolidated and HIP cermets was made. The cermets were Zr oxides or carbides with Zr or Cr as the matrix and spherical powders were used. The process were r e p o r t e d to result in similar structures. Twinning was noted and a fine grained matrix. The HIP material showed a greater degree of grain growth. CHARACTERISTICS OF HIGH COMPRESSIBLILTY ATOMIZED IRON POWDERS H. Sakuma et al (Kobe Steel, Hyogo, J a p a n ) . It was shown by e x p e r i m e n t t h a t by reducing the impurity c o n t e n t of atomized steel powder and by control of particle size d i s t r i b u t i o n t h e c o m p r e s s i b i l i t y of t h e p o w d e r could be increased. The green density was r e p o r t e d to reach 7.08 g/cm 3 by p r e s s i n g a t 4 9 0 MPa, t h e h i g h c o m p r e s s i b i l i t y p o w d e r was c o m p a r e d with conventional powder with respect to compressibility, ejection force, occurrence of cracks and magnetic properties.

MPR December 1992 53