Microstructure and phase composition of hard alloys produced from nanocrystalline powder mixture WC-6wt.%Co with C, Al and ZrC additives

A large specific surface area of WC nanopowder determines its high chemical activity and makes it very sensitive to various impurities, among which oxygen is most harmful unavoidable. During heating, interacts with carbon being removed in the form CO/CO 2 , finally leads appearance embrittling η-phases hard alloy, abnormal growth grains, formation a porous microstructure. To prevent heavy decarburization during vacuum sintering alloy from nanocrystalline powder mixture WC-6wt.%Co, this work we compared three methods: addition extra compensate for loss as result decarburization; Al bind impurity into O 3 before WC; ZrC ZrO . Nanocrystalline mixtures based on WC-6 wt.%Co without additions C, Al, were prepared microcrystalline powders WC, Co, ZrC, black by high-energy milling, then they compacted cylindrical mold uniaxial pressing at pressure ~460 MPa sintered graphite crucibles 15 min 1380 °C ~10 -2 Pa. The heating rate temperature was 10 °C/min. initial powders, therefrom, alloys certified using X -ray diffraction, analysis, scanning electron microscopy, BET adsorption method, helium pycnometry, Vickers method. studies performed showed that average particle size all does not exceed 100 nm, content them varies 3.3 4.3 wt.% depending additives. It established only part contained chemisorbed state takes sintering. additive completely oxidized milling transforms aggravates results multiphase relatively microstructure alloy. On contrary, additives managed less it. shown presence inclusions impede intensive grains sintering, but rather promotes Carbon deficit slightly suppresses grain leading an increase density microhardness, oxide reduces values these properties.