后处理工艺对激光选区熔化成形Hastelloy-X合金显微组织和低周疲劳性能的影响

Effect of Post Treatment Process on Microstructure and Low Cycle Fatigue Properties of Selective Laser Melting Formed Hastelloy-X Alloy

采用激光选区熔化(SLM)技术制备Hastelloy-X合金,研究了不同的后处理工艺(1 175℃×2 h固溶处理、1 175℃/150 MPa×1 h或1 175℃/150 MPa×2 h热等静压处理)对合金显微组织和低周疲劳性能的影响。结果表明:SLM成形合金具备典型的熔池边界形貌和由细小树枝晶构成的柱状晶组织,同时存在微裂纹、气孔、孔洞等冶金缺陷;固溶处理消除了合金熔池边界,且晶粒由柱状晶向等轴晶转变,热等静压处理则能进一步闭合合金中的裂纹和气孔,同时沿晶界析出不连续的细小MC型碳化物;相比于固溶态合金,热等静压态合金具有更好的低周疲劳性能,其中2 h热等静压时间下得到的合金低周疲劳寿命略高;固溶处理态合金的疲劳裂纹以穿晶形式扩展,而热等静压态合金以穿晶+沿晶混合模式扩展。

Hastelloy-X alloy was fabricated by selective laser melting(SLM) process, and the effects of different post treatment processes(solution treatment of 1 175 ℃×2 h, hot isostatic pressing of 1 175 ℃/150 MPa×1 h or 1 175 ℃/150 MPa×2 h) on the microstructure and low cycle fatigue properties of the alloy were studied. The results show that the SLM formed alloy had a typical molten pool boundary morphology and a columnar crystal structure composed of fine dendrites, and there were metallurgical defects such as microcracks, pores and holes. Solution treatment eliminated the boundary of the alloy molten pool, and the grains transformed from columnar to equiaxed. Hot isostatic pressing could further close the cracks and pores in the alloy, and small discontinuous MC carbides precipitated along the grain boundaries. Compared with solution treated alloy, hot isostatic pressed alloy had better low cycle fatigue properties, and the low cycle fatigue life of the alloy obtained under 2 h hot isostatic pressing time was slightly higher. Fatigue cracks propagated in a transgranular manner for solution treated alloy, while propagated in a mixed transgranular+intergranular mode for hot isostatic pressed alloy.