分层厚度对选区激光熔化成形Ti-5Al-2.5Sn合金组织与性能的影响规律

Influence of Layer Thickness on Microstructure and Mechanical Properties of Selective Laser Melted Ti-5Al-2.5Sn Alloy

研究了分层厚度对选区激光熔化(SLM)技术成形Ti-5Al-2.5Sn(TA7)钛合金试样致密度、显微组织和力学性能的影响规律。结果表明:在激光功率和扫描间距一定的条件下,当分层厚度≤40 mm时,致密度随激光体能量密度的下降不断提高;当分层厚度>40 mm时,致密度则随激光体能量密度的下降先升高后降低。随分层厚度的增大和扫描速率的降低,SLM成形过程中的冷却速率逐步下降,当冷却速率低于6.8×10~7K/s时,显微组织由针状马氏体α′逐渐向岛状α_m转变。通过优化工艺参数,在所有分层厚度(20~60 mm)下均能成形致密的TA7试样,其显微硬度、屈服强度和断裂强度超越铸件和锻件;且当分层厚度≤40 mm时,韧塑性超越铸件,达到锻件水平。成功探索出能够兼顾TA7样品成形效率、冶金质量及力学性能的优选分层厚度及SLM工艺参数组合。

As an additive manufacturing technology, selective laser melting（SLM） process can solve the manufacturing difficulty of Ti-5 Al-2.5 Sn（TA7） easily. But the low building efficiency of SLM retards its wide applications in aviation, petrochemical and other fields. In order to solve the above problem, the influence of layer thickness on relative density, microstructure and mechanical properties of SLMed TA7 samples were studied in this work. The results show that when the laser power and hatching space are constant, the relative density gradually increases with the decrease of the laser volume energy density under the layer thicknesses less than or equal to 40 mm, whereas first increases and then declines with the decrease of the laser volume energy density under the layer thicknesses larger than 40 mm. At the same time, with the increase of layer thickness and the decrease of scanning velocity, the cooling rate gradually decreases during the SLM processing, when the cooling rate is lower than 6.8×10~7 K/s, the microstructure will gradually transform from acicular martensite α＇ to massive α_m. Through the optimization of SLM parameters, the dense TA7 bulk specimens with higher microhardnesses, yield strengths and ultimate strengths in comparison to the as-cast and deformed TA7 alloys can be obtained under all layer thicknesses（20~60 mm）. While when the layer thicknesses are not larger than 40 mm, the ductility of the SLMed TA7 is also superior to that of the as-cast TA7 and comparable to that of the deformed TA7. Finally, the optimal layer thickness and combination of SLM process parameters are successfully determined to balance the building efficiency, metallurgical quality and mechanical properties of the TA7 alloy parts.