关键词: 激光选区熔化, TiAl合金, 裂纹, 形成机理, 基板预热

Abstract: Crack is the most common and destructive defect in TiAl alloys processed by selective laser melting (SLM). The Ti-47Al-2Cr-2Nb alloy specimens are fabricated by SLM, detected by X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray EDS Analysis and residual stress detection, the cracking mechanism and Inhabiting is designed. The experimental results showed that:The crack is considered as cold cracks in samples, which has typical characteristics of the transgranular fracture. Due to the rapid heating and cooling during the SLM, the residual stress inside the formed part is higher than the tensile strength of the material, resulting in the formation of cracks. The cracks originate from the existence of defects such as powder sticking and notch on the side edge of the samples. In addition, the samples contain a large amount of α2 brittle phase and pores, which is also beneficial to the generation and expansion of cracks. As the temperature of substrate preheating is gradually increased to 300℃, on the one hand, the temperature gradient is reduced, the thermal expansion and contraction of the material is weakened, and the residual stress inside the sample is reduced from (267.2±13.4) MPa to (172.6±8.6) MPa. On the other hand, β phase is more stable because of preheating, and the content of α2 brittle phase is reduced. Finally, the number and size of cracks in the sample are obviously controlled, and the relative density of the sample is also increased from 87.64% to 93.84%.

Key words: selective laser melting, TiAl alloys, cracks, formation mechanism, substrate preheating