TaC Addition Research Articles

WC-20%Co合金およびこれにTaCを添加した合金の性質

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.

Some Properties of WC-TaC-Co and WC-Tic-Co Alloys affected by Low Temperature Annealing

Cemented carbides containing 15 vol.% of Co and 10 wt.% of TaC or TiC in total carbides were vacuum-sintered and two kind of specimens having different carbon content respectively in each alloy were obtained. Some properties of these alloys affected by low temperature annealing at 700°C and 800°C were mainly studied in comparison with those of straight WC-Co alloys to get an information on the influences of TaC or TiC in the cemented carbides. Brief conclusions of this experiment were as follows: (1) Transverse-rupture strength and magnetic saturation of the alloys containing TaC or TiC increase with increasing of carbon content of the alloys, in the phase range corresponding to two phase range of straight alloys, but on the contrary, hardness, specific resistivity and lattice constant of the binder phase decrease. (2) After annealing, rupture strength, specific resistivity, magnetic saturation and lattice constant of the binder decrease and the change of these properties is in general remarkable in low carbon alloys than in high carbon. (3) The phenomena above mentioned are in good agreement with those of WC-Co straight alloys. So the change of properties by annealing is considered also due to the fact that the W atoms highly dissolved in the binder phase of low carbon alloys precipitate during the course of the anealing, as already reported on the WC-Co alloys. (4) The rate of the precipitation, however, will decrease by the addition of TaC or TiC to the WC-Co alloys.

少量のTaCを添加したWC-TaC-10%Co合金の性質について

WC-TaC-10%Co alloys containing 0.5, 1.0, 3.0%TaC (added in the form of a mixed carbide) and having various carbon contents were vacuum-sintered at 1375°C for 2 hr. The particle size of the WC powder used was controlled to obtain an approximately same grain size of carbides in the sintered alloys. Some properties of the as-sintered alloys and the effect of low-temperature annealing (at 800°C up to 50 hr) on them were studied as a function of the TaC and carbon contents, using the experimental method as used in previous investigations(1)∼(4).The main results are as follows: (1) The relations(1)∼(4) recently obtained by the authors on sintered WC-Co straight alloys, namely, that the properties of two phase alloys are remarkably influenced by their carbon contents and also by low temperature annealing when the carbon contents are lower, are substantially maintained in the alloys containing TaC. (2) The composition of binder phase, width and position in the two phase range (a γ+TaC+WC three phase range) of the WC-TaC-10%Co alloys do not change by the addition of TaC. (3) The alloys containing TaC are higher in hardness than the straight alloys, but the strength scarcely decreases. (4) The aging rate at a low temperature is retarded in the alloys containing TaC.