Marchese Giulio, Basile Gloria, Bassini Emilio, Aversa Alberta, Lombardi Mariangela, Ugues Daniele, Fino Paolo, Biamino Sara
Department of Applied Science and Technology, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Italy.
Materials (Basel). 2018 Jan 11;11(1):106. doi: 10.3390/ma11010106.
Hastelloy X (HX) is a Ni-based superalloy which suffers from high crack susceptibility during the laser powder bed fusion (LPBF) process. In this work, the microstructure of as-built HX samples was rigorously investigated to understand the main mechanisms leading to crack formation. The microstructural features of as-built HX samples consisted of very fine dendrite architectures with dimensions typically less than 1 µm, coupled with the formation of sub-micrometric carbides, the largest ones were mainly distributed along the interdendritic regions and grain boundaries. From the microstructural analyses, it appeared that the formation of intergranular carbides provided weaker zones, which combined with high thermal residual stresses resulted in hot cracks formation along the grain boundaries. The carbides were extracted from the austenitic matrix and characterized by combining different techniques, showing the formation of various types of Mo-rich carbides, classified as M₆C, MC and MC type. The first two types of carbides are typically found in HX alloy, whereas the last one is a metastable carbide probably generated by the very high cooling rates of the process.
哈氏合金X（HX）是一种镍基高温合金，在激光粉末床熔融（LPBF）过程中具有很高的裂纹敏感性。在这项工作中，对增材制造的HX样品的微观结构进行了深入研究，以了解导致裂纹形成的主要机制。增材制造的HX样品的微观结构特征包括尺寸通常小于1 µm的非常细小的枝晶结构，以及亚微米级碳化物的形成，其中最大的碳化物主要分布在枝晶间区域和晶界处。从微观结构分析来看，沿晶碳化物的形成产生了较弱区域，再加上高热残余应力，导致沿晶界形成热裂纹。通过结合不同技术从奥氏体基体中提取并表征了碳化物，结果表明形成了各种类型的富钼碳化物，归类为M₆C、MC和MC型。前两种类型的碳化物通常存在于HX合金中，而最后一种是一种亚稳碳化物，可能是由该过程极高的冷却速率产生的。
