超硬合金の結合相中に生じるε相の組織観察

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The structure and the thermal stability of ε phase formed by the strain-induced transformation of binder phase near the ground surface-layer in WC-Co cemented carbide, have been investigated mainly by optical microscopy. For microscopic studies, two-phase WC-20%Co alloy specimens with high and low carbon contents and with coarse WC grains (-50μ) were sintered in vacuum at 1400°C for 1 hr. For X-ray studies, two-phase WC-45%Co alloy specimens with fine WC grains (-1.6μ) were sintered at low temperature around 1250°C to minimize the grain size of binder phase. Results obtained were as follows: (1) The depth of layer of the ε phase formed by grinding was naturally affected with cobalt contents, carbon contents and mean grain size of WC in the alloy. (2) The ε phase was formed in a plate shape along slip bands in binder phase, suggesting that the habit plane of ε phase is (111)γ. (3) The rapid growth of the phase due to annealing was observed at relatively high temperatures up. to about 400°C and 600°C in high carbon and low carbon alloys, respectively. The increased amount of the ε phase seemed to be affected by the amount of ε phase pre-existed and the grain size of binder phase. The above results were considered to have a close relation with mechanical properties of cemented carbide at these temperatures. (4) The precipitate of Co3W appearing by annealing low carbon alloy at high temperatures was usually observed along the ε phase pre-existed.
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超硬合金の結合相中に生じるε相の組織観察

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