Some Properties of WC-20%Co and WC-5%TaC-20%Co Alloys

Abstract

The purpose of this report is to examine some properties of WC-20%Co and WC-5%TaC-20%Co alloys as a function of the carbon content, and to compare their properties with WC-(TaC)-10%Co alloys already reported^(1)∼(9).
Two series of alloys, viz., WC-20%Co and WC-5%TaC-20%Co with various carbon contents in the two or three-phase (γ+carbides) range, were prepared by vacuum-sintering at 1375°C for 1 hr. The grain size of carbides in all the alloys was controlled to be approximately the same through some treatments before sintering.
The main results are as follows:
(1) A maximum value of the transverse-rupture strength is obtained at the low carbon alloys in the two or three-phase range. However, in the case of 10% alloys, the maximum value is at the high carbon alloys. (2) The addition of TaC up to 5% does not decrease the transverse-rupture strength, but the 3%TaC addition to 10%Co alloys decreases its value. (3) The width of the two or three-phase range is approximately two times as wide as that of 10%Co alloys. (4) The TaC addition increases the hardness but decreases the density. (5) The γ-phase contains almost no TaC. (6) The aging phenomena accompanied by the Co₃W type precipitation is also ascertained in these alloys, but there is the difference that the hardness and the coercive force of these alloys increase after aging.