钴基合金Co-Al-W-Ta-Nb的显微组织与高低温力学性能

Microstructure and Mechanical Properties of Co-Al-W-Ta-Nb Alloys at Room- and High-Temperatures

摘要:

以新型Co基合金Co-9Al-9W-2Ta为基础，分别用4at%、6at%和9at%的Nb元素替代等量的W(分别称4Nb、6Nb、9Nb合金，无Nb添加的称为0Nb合金)，研究Nb含量对合金显微组织和高低温力学性能的影响。结果表明：铸态组织由Co基固溶体γ相和γ+Co3Nb共晶组成（Nb可部分被W和/或Ta取代），随Nb含量提高，共晶组织体积分数增大。1200 ℃/8 h固溶+800 ℃/100 h时效处理后，γ中析出尺寸为数百纳米并与之共格的γ’-Co3(Al，W)相或Co3Nb相，显微组织由γ/γ’组织(0Nb)逐步向γ/γ’/Co3Nb组织(4Nb和6Nb合金)和γ/Co3Nb组织转变(9Nb合金)。合金在600 ℃开始出现反常屈服，反常屈服强度峰值对应温度大约在700 ℃

Abstract:

The microstructural evolution and room/high-temperature mechanical properties were investigated for a Co-9Al-9W-2Ta alloy with 4at%, 6at% and 9at% Nb additions to replace the same content of W (referred as to 4Nb, 6Nb and 9Nb alloy hereafter, 0Nb for the alloy without Nb addition, and the content of W+Nb=9 at% for all alloys) prepared by arc-melting. Results show that the as-cast alloys exhibit a microstructure composed of Co-base solid solution γ phase (γ-CoSS) and eutectic of γ+ intermetallic compound Co3Nb. While after 1200 °C, 8 h solution and 800 °C, 100 h aging, the cubic γ’ phase with a size of 200~300 nm precipitates homogeneously and coherently on the γ matrix for the 0Nb~6Nb alloys. Besides, cellular and/or needle-like Co3Nb phases are found in the 4Nb~9Nb alloy. The 6Nb alloy shows the highest yield strength in the temperature range of 600~700 °C, while the 4Nb alloy has the highest strength at 800 °C. Alloys exhibit yield stress anomalies at temperatures above 600 °C, and the temperature corresponding to the anomaly stress peak is about 700 °C