新型Co基合金Co-9Al-(9-x)W-xMo-2Ta-0.02B的显微组织与高低温力学性能

Microstructures and Mechanical Properties of Alloys Co-9Al-(9-x)W-xMo-2Ta-0.02B at Room and High Temperatures

以新型Co基合金Co-9Al-9W-2Ta-0.02B成分为基础,分别添加了原子分数为2%、4%、6%、9%的Mo元素替代W(分别称2Mo、4Mo、6Mo、9Mo合金,W+Mo的原子分数为9%,无Mo添加的称为0Mo合金),研究了Mo元素对合金相组成、显微组织形貌、维氏硬度和高低温压缩强度的影响。结果表明铸态合金由Co的固溶体γ相和Co3(Al,Me)金属间化合物γ′相组成(其中Me为合金元素W、Mo、Ta),γ相是基体,γ′相位于γ相界。1 350℃/8h固溶+800℃/100h时效处理后0Mo、2Mo和4Mo合金的γ相中均匀析出了与之共格的立方形γ′相Co3(Al,Me),尺寸为200～300nm,原铸态的γ′相消失;6Mo和9Mo合金的组织与0Mo、2Mo和4Mo合金完全不同,γ相基体析出大量针状TCP相,原γ相晶界处的γ′相中的W和/或Ta扩散离开而变成了Co3(Al,Mo)相,但基本保持铸态特征。各合金均出现反常屈服现象,随着Mo原子分数的提高,热处理合金室温和高温强度均有所降低,且反常屈服温度向低温方向移动。

Based on the composition of Co-9Al-（9-x）W-xMo-2Ta-0. 02B, 2at%, 4at%, 6at% and 9at% Mo are added to replace W （hereafter referred to as alloys 2Mo,4Mo,6Mo and 9Mo respectively; Mo-free alloy is referred to as alloy 0Mo）. The effect of Mo additions on phase constitution, microstructure, HV hardness and room/high-temperature strength is investigated. It is found that the as-cast alloys show a microstructure composed of Co-base solid solution y phase and intermetallic Co3 （Al, Me） compound γ′ phase （where Me stands for W, Mo and Ta）. The γ phase is the matrix and the γ′phase is distributed on the grain boundaries of the y phase. After 1 350 ℃/8 h solution and 800 ℃/100 h aging, a cubic γ′ phase with a size of 200-300 nm homogeneously precipitates in the γ′ matrix for alloys 0Mo, 2Mo and 4Mo, and the as-cast γ′ phase disappears. As for alloys 6Mo and 9Mo, the microstructure is significantly changed; however, no cubic γ′ precipitates are found in the y matrix; instead there is a large number of needle-like TCP precipitates, while the as-cast γ′ phase Co3 （AI／l, Me） compound changes to Co3 （Al, Mo） compound. Abnormal yield characteristic is found for all alloys. As the Mo content increases, the room/high-temperature strength of the heat-treated alloys decreases, and the abnormal yield temperature shifts towards lower temperatures.