W-CoCrNi合金的烧结致密化及其组织与性能

Sintering densification,microstructure and properties of W-CoCrNi alloy

本文采用粉末冶金技术制备以CoCrNi中熵合金为黏结相的W-CoCrNi高密度钨合金,研究黏结相含量和烧结温度(1300~1500℃)对合金显微组织和力学性能的影响。结果表明:烧结态合金组织由W相、CoCrNi相、Co_(7)W_(6)相和亚微米富Cr颗粒组成。随着烧结温度的升高,合金致密度随之升高。合金在1500℃以下烧结时,致密化机制主要为固相烧结机制,固相烧结驱动力主要来自于表面能的降低和Co_(7)W_(6)新相的形成。当烧结温度达1500℃时,合金致密化机制主要为液相烧结机制,致密化过程包含W向CoCrNi熔体中的溶解和扩散、Co_(7)W_(6)相析出和钨颗粒球化三个阶段。1500℃烧结温度下制备的75W-CoCrNi和95W-CoCrNi合金的压缩屈服强度分别为1060 MPa和1602 MPa,75W-CoCrNi合金在压缩应变超过50%时仍未断裂。随着CoCrNi黏结相含量的增加,合金致密度随之升高,压缩变形能力增加,但压缩屈服强度降低。

In this paper,high-density tungsten alloys with CoCrNi medium entropy alloy as bonding phase were prepared by powder metallurgy technology.The effects of bonding phase content and sintering temperature(1300−1500℃)on the microstructures and mechanical properties of the alloy were investigated.The results show that the sintered alloy are mainly composed of W phase,CoCrNi solid solution phase,Co_(7)W_(6) phase and Cr-rich submicron particles.The relative density of the alloy decreases with the increase of sintering temperature.The densification mechanism of the alloy sintered below 1500℃is mainly solid-phase sintering mechanism,and the driving force of solid-phase sintering is mainly from the reduction of surface free energy and the formation of Co_(7)W_(6) phase.When the sintering temperature reaches 1500℃,the densification mechanism is mainly liquid-phase sintering mechanism,and the densification process includes three stages:dissolution and diffusion of W to CoCrNi melt,Co_(7)W_(6) phase precipitation and spheroidization of tungsten particles.The compressive yield strengths of 75W-CoCrNi and 95W-CoCrNi sintered at 1500℃are 1060 MPa and 1602 MPa,respectively,and the fracture of 75W-CoCrNi alloy does not occur when the compressive strain exceeds 50%.With the increase of CoCrNi binder phase content,the density of the alloy increases,the compressive deformation ability increases,whereas the compressive yield strength decreases.