Microstructure and properties of Ti-6Al-4V fabricated by low-power pulsed laser directed energy deposition

作     者：Hua Tan Mengle Guo Adam T. Clare Xin Lin Jing Chen Weidong Huang 

作者机构：State Key Laboratory of Solidification ProcessingNorthwestern Polytechnical UniversityXi'an710072China Key Laboratory of Metal High Petformance Additive Manufacturing and Innovative DesignMIIT ChinaNorthwestern Polytechnical UniversityXi'an 710072China Institute for Advanced ManufacturingFaculty of EngineeringUniversity Of NottinghamNG7 2RDUK Department of MechanicalMaterials and Manufacturing EngineeringFaculty of Science and EngineeringUniversity o f Nottingham China199 Taikang East RoadUniversity ParkNingbo315100China 

出 版 物：《Journal of Materials Science & Technology》 (材料科学技术（英文版）)

年 卷 期：2019年第35卷第9期

页      面：2027-2037页

核心收录：

学科分类：08[工学] 0805[工学-材料科学与工程（可授工学、理学学位）] 

基　　金：supported by the National Key Research and Development Program of China (No. 2018YFB1106302) the National Natural Science Foundation of China (Grant No. 51475380) the Aeronautical Science Foundation of China (Grant No. 2016ZE53) 

主　　题：Directed energy deposition Ti-6Al-4V Microstructure Thermal cycle history Mechanical properties 

摘      要：Thin-wall structures of Ti-6A1-4V were fabricated by low-power pulsed laser directed energy deposition. During deposition, consistent with prior reports, columnar grains were observed which grew from the bottom toward the top of melt pool tail. This resulted in a microstructure mainly composed of long and thin prior epitaxial β columnar grains (average width ^200μm). A periodic pattern in epitaxial growth of grains was observed, which was shown to depend upon laser traverse direction. Utilizing this, a novel means was proposed to determine accurately the fusion boundary of each deposited layer by inspection of the periodic wave patterns. As a result it was applied to investigate the influence of thermal cycling on microstructure evolution. Results showed that acicular martensite,α phase, and a small amount of Widmanstatten, a laths, gradually converted to elongated acicular a and a large fraction of Widmanstatten a laths under layer-wise thermal cycling. Tensile tests showed that the yield strength, ultimate tensile strength and elongation of Ti-6Al-4V thin wall in the build direction were 9.1 %, 17.3% and 42% higher respectively than those typically observed in forged solids of the same alloy. It also showed the yield strength and ultimate tensile strength of the transverse tensile samples both were 13.3% higher than those from the build direction due to the strengthening effect of a large number of vertical β grain boundaries, but the elongation was 69.7% lower than that of the build direction due to the uneven grain deformation of β grains.