WC-10%Ni超硬合金の性質と結合相組成との関係

Relations between basic properties of sintered WC-Co base alloys at the room temperature and the composition of the binder phase, that is, the carbon content of the alloys, have been investigated. It was found that the properties were strongly affected by the binder phase composition, although any harmful phase was not formed in-the structures of alloys. On the other hand, researches on the subject for sintered WC-Ni.alloys have never been carried out and it is still vague whether Co is superior to Ni or not as the binder metal of cemented carbides.<BR>Therefore, studies on the properties of the WC-10%Ni alloy in relation to the composition of the binder phase were carried out. The results were compared with those already known for WC-10%Co alloy, to get an accurate knowledge on the superiority of Co or Ni as the binder metal. Specimens were vacuum-sintered at mostly 1450°C for lhr. The carbon content of alloys was closely controlled. Results obtained are summarized as follows.<BR>(1) Sintering temperature of WC-10%Ni alloy was higher by about 70°C than that of 10%Co alloy. This shows that the temperatures at which the liquid phase is formed, are in this case higher by about 70°C than corresponding temperatures of WC-10%Co two phase alloys. (2) The two phase range in WC-10%Ni alloy extended from about 5.77 to 6.06%C in WC and the width of the range corresponded to about 0.3%C (the values in WC-10%Co alloy are about 6.04-6.22%C and 0.15-0.18%C, respectively). Based on the former result, it is clear that the free carbon phase is formed more easily in Ni-binding alloy than the other. (3) The amount of W dissolved in the binder phase varied abruptly from about 10% to 31% according to the carbon content of the two phase alloys (the value in Co-binding alloy is in the range from 2-3% to 9.10%). (4) Properties such as density, hardness, transverse-rupture strength, magnetic saturation and resistance to acidic solution, etc. showed regular changes in the phase range. These changes were explained by the composition changes in the binder phase. The maximam strength of the alloy was obtained at about the highest carbon side of the range ; however, the value was inferior to that of the Co-binding alloy. The reason may be that the content of the W dissolved in the binder phase in Ni-binding alloy is much higher than that of the other. The alloy having carbon content of less than 5.95% was found to be non-magnetic. (5) Aging phenomena taken place during annealing at temperatures as low as 800°C were not observed in the Ni-binding alloy. (6) The rapid grain growth of WC was observed in the high carbon alloys. (7) From these results, Co was confirmed to be by far superior to Ni as the binder metal of cemented carbides, except for a few cases.