Cr对Nb-16Si-22Ti-2Al-2Hf合金显微组织与高低温力学性能的影响

 以Nb-16Si-22Ti-2Al-2Hf成分为基础，分别添加了2%和17%(原子分数,后同)的Cr元素替代Nb(分别称2Cr和17Cr合金),研究了Cr含量对Nb-16Si-22Ti-2Al-2Hf合金相组成、显微组织形貌、室温断裂韧性和高温强度的影响,分析了高低温失效机制。结果表明,铸态和1 375 ℃×100 h热处理后2Cr合金由Nbss和Nb₅Si₃两相组成;当Cr含量为17%时,出现了具有C15结构的Laves Cr₂Nb相,合金由Nbss、Nb₅Si₃和Cr₂Nb三相组成,热处理后在Nb₅Si₃中还析出了球状Cr₂Nb相。随着Cr含量由2%提高到17%,热处理合金的室温断裂韧性K_Q由14.32 MPa·m^1/2下降到10.30 MPa·m^1/2。合金强度与Cr含量的关系受温度影响,随Cr含量提高,室温和1 150 ℃时合金的硬度或强度增高,而1 250 ℃和1 350 ℃时合金强度降低。如1 150 ℃时2Cr和17Cr合金的屈服强度σ_0.2分别为349 MPa和387 MPa;1 350 ℃时分别为306 MPa和74 MPa。

Effect of Cr Additions on Microstructures and Mechanical Properties of an Nb-16Si-22Ti-2Al-2Hf Alloy at Room and High Temperatures

Based on the composition of Nb-16Si-22Ti-2Al-2Hf, 2 at% and 17 at% Cr (referred to as 2Cr and 17Cr alloys) are respectively added to replace Nb. Effects of Cr additions on phase constitution, microstructure, room temperature fracture toughness and high temperature strength are investigated, and failure mechanisms at room and high temperatures are analyzed. It is found that the microstructure of the as-cast and heat-treated (annealed at 1 375 ℃ for 100 h) 2Cr alloy is composed of Nbss and β-Nb₅Si₃, while that of the 17Cr alloy consists of the Nbss, β-Nb₅Si₃ and Laves Cr₂Nb with a C15 structure, and the spherical C15-Cr₂Nb precipitates are found in the β-Nb₅Si₃ of the heat-treated 17Cr alloy. As the Cr content increases from 2 at% to 17 at%, room temperature fracture toughness K_Q of the annealed alloy decreases from 14.32 MPa·m^1/2 to 10.30 MPa·m^1/2. Strength, as a function of the Cr content, is dependent on temperature. At room temperature and 1 150 ℃, the hardness or strength increases with the Cr content, whereas at 1 250 ℃ and 1 350 ℃, the strength decreases. For example, the 0.2% yield strengths σ_0.2 of the 2Cr and 17Cr alloys are 349 MPa and 387 MPa at 1 150 ℃, but 306 MPa and 74 MPa at 1 350 ℃, respectively.