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采用真空非自耗电弧熔炼法制备了含C量不同的Nb-20Ti-16Al合金,C元素含量为0%,1%和10%(原子分数),而后在1100℃下进行不同时间的热处理。通过X射线衍射分析(XRD),扫描电子显微镜(SEM)和电子探针(EPMA)观察合金的组织。合金的高温压缩强度在材料热力加工模拟试验机Gleeble-3800上进行,应变速率为1×10~(-2)s~(-1),测试温度为1100℃。室温断裂韧性在显微维氏硬度计上通过压痕法进行。实验结果表明,铸态合金在1100℃热处理过程中,Nb-20Ti-16Al合金中过饱和Nb_(ss)(铌基固溶体)发生了分解,即发生了Nb_(ss)→Nb_(ss)+Nb_3Al反应;而添加了C元素的合金中,在Nb_3Al析出的同时,碳化物发生了分解,反应可表示为Nb_(ss)+(Nb,Ti)C→Nb_(ss)+Nb_3Al。随着保温时间的延长,Nb_3Al的尺寸和体积分数增加,而Nb_(ss)的体积分数减小。C元素的添加能够使Nb_(ss)和Nb_3Al的晶格常数减小,表明C原子主要以置换原子的形式固溶于Nb_(ss)和Nb_3Al中。随着C元素的增加,热处理后的合金Nb_(ss)体积分数减小,高温压缩强度增加,而室温断裂韧性下降。
Nb-20Ti-16Al alloys with different contents of C were prepared by vacuum non-consumable arc melting method. The content of element C was 0%, 1% and 10% (atomic fraction), and then heat treated at 1100 ℃ for different time . The alloy structure was observed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron probe (EPMA). The high-temperature compressive strength of the alloy was tested on a Gleeble-3800 thermomechanical simulator with a strain rate of 1 × 10 -2 s -1 and a test temperature of 1100 ° C. Room temperature fracture toughness is measured on a micro Vickers hardness tester by the indentation method. The experimental results show that the supersaturated Nb_ (ss) (niobium-based solid solution) in Nb-20Ti-16Al alloy decomposes during the heat treatment of the as-cast alloy at 1100 ℃, ie Nb_ (ss) → Nb_ (ss) In the alloy with C element addition, the carbides decompose during the precipitation of Nb 3 Al and the reaction can be expressed as Nb_ (ss) + (Nb, Ti) C → Nb_ (ss) + Nb_3Al. With the extension of holding time, the size and volume fraction of Nb_3Al increased while the volume fraction of Nb_ (ss) decreased. The addition of C element can reduce the lattice constants of Nb_ (ss) and Nb_3Al, indicating that the C atom mainly dissolves in Nb_ (ss) and Nb_3Al as a substitutional atom. With the increase of C element, the Nb_ (ss) volume fraction of heat treated alloy decreases, the compressive strength at high temperature increases, and the fracture toughness at room temperature decreases.