激光熔化沉积成形TiAl合金组织及力学性能研究

Microstructure and Mechanical Properties of TiAl Alloy Prepared by Laser Melting Deposition

利用增加预热措施的激光熔化沉积(LMD)方法制备出高度为30cm、致密无裂纹的Ti-48Al-2Cr-2Nb合金(以下简称TiAl合金),对其内部缺陷、显微组织、相组成和力学性能进行了研究。微纳CT(computed tomography)测试结果显示,预热后制备的TiAl合金致密度为99.996%,气孔数量明显少于未预热制备的TiAl合金;利用光学显微镜及扫描电子显微镜发现其显微组织为片层组织、亚稳的魏氏组织和羽毛状组织;通过能谱仪设备仅观察到Cr、Nb元素存在轻微偏析;对试样进行电子背散射衍射实验,试样主要相组成为γ相,含有少量的α_(2)相及B2相;预热后制备的TiAl合金的平均局部取向差(KAM)值略高于未预热制备的合金;此外,对致密无裂纹的合金的硬度和拉伸性能进行了测试,合金的显微硬度为350HV0.5,室温抗拉强度为497MPa,延伸率为0.49%,其拉伸性能高于传统铸造的TiAl合金。因此,增加预热措施对LMD成形高致密度且无裂纹的TiAl合金具有重要的指导意义。

A dense and crack free Ti48Al2Cr2Nb alloy(TiAl alloy)with a height of 30 cm is prepared using laser melting deposition(LMD)method with preheating process,and the internal defects,microstructure,phase composition and mechanical properties of the alloy are studied.The micro/nano CT(computed tomography)testing results show that the density of the TiAl alloy formed after preheating is 99.996%and the number of pores is significantly less than that of the TiAl alloy formed without preheating.The microstructure of the sample is lamellar structure,metastable Weinstein structure,and feathery structure observed by optical microscopy and scanning electron microscopy.Only slight segregation of Cr and Nb elements is observed through energy spectrometer equipment.Electron back scatter diffraction experiment is conducted on the sample,and the main phase composition of the sample isγphase,containing a small amount ofα_(2) and B2 phase.The average kernel average misorientation(KAM)value of TiAl alloy formed after preheating is slightly higher than that of the alloy formed without preheating.In addition the hardness and tensile properties of the dense and crack free alloy are tested,the alloy has a microhardness of 350 HV0.5,a tensile strength of 497 MPa,and an elongation of 0.49%.Its tensile properties are higher than those of traditional casting TiAl alloy.Therefore,the preheating process has important guiding significance for the LMD formation of highdensity and crack free TiAl alloys.