微波烧结粗晶低钴YG硬质合金存在的脱碳问题及其改进

采用常规微波烧结法制备WC-Co硬质合金时,表层区域出现严重的脱碳现象,导致表层和中心区域的组织显著不同,即产生核壳结构,对合金的力学性能造成不利影响。本文作者以WC粉和Co粉为原料粉末,采用微波烧结法制备88%WC-12%Co(YG12)和94%WC-6%Co(YG6)硬质合金,在混料时添加炭黑,避免合金中脱碳相的生成。检验表明:当炭黑添加量(质量分数)接近0.2%时,YG12和YG6的抗弯强度(TRS)分别达到3 109和2 642 MPa;硬度(HRA)分别为88.7和89.8。此时,合金表面和中心区域具有一致的显微组织结构,没有发现脱碳相η(W3Co3C)。但当炭黑添加量超过0.2%时,大量析出的石墨相对合金的力学性能,尤其对硬度产生不利影响,当炭黑添加量为0.4%时,YG12和YG6的抗弯强度分别只有2 465 MPa和2 213 MPa。

Decarbonization and its improvement of coarse-grained low cobalt cemented carbide sintered by microwave irradiation

Result indicates that decarbonization phenomenon always exists when coarse grain WC-Co cemented carbide is prepared by conventional microwave irradiation,which leads to the core-shell structure owing to different microstructure between the surface and central area.The mechanical properties of the alloy are adversely affected by this special structure.In order to avoid the formation of the decarbonization phase η,i.e.W3Co3C phase,88%WC-12%Co(YG12) and 94%WC-6%Co(YG6) cemented caribde were prepared and carbon black was added when milling raw powders.The results show that the transverse rupture stress(TRS) of YG12 and YG6 can reach 3 109 MPa and 2 642 MPa,respectively;hardness rockwell A(HRA) of them can reach 88.7 and 89.8,respectively when added carbon black content is mass fraction of 0.2%,and an uniform microstructure between the surface and central area of WC-Co alloy with no η(W3Co3C) can be obtained.However,the TRS and hardness of the alloys will decrease because of a large number of graphite phase were separated out from alloy when the added carbon content is more than 0.2%.When added carbon content is 0.4%,the TRS of YG12 and YG6 are only 2 465 MPa and 2 213 MPa,respectively.