Microstructure and properties of Ti-6Al-4V fabricated by low-power pulsed laser directed energy deposition
来源期刊：JOURNAL OF MATERIALS SCIENCE TECHNOLOG2019年第9期
论文作者：Hua Tan Mengle Guo Adam T.Clare Xin Lin Jing Chen Weidong Huang
文章页码：2027 - 2037
摘 要：Thin-wall structures of Ti-6 Al-4 V 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,α laths,gradually converted to elongated acicular α and a large fraction of Widmanstatten α laths under layer-wise thermal cycling.Tensile tests showed that the yield strength,ultimate tensile strength and elongation ofTi-6 Al-4 V thin wall in the build direction were 9.1%,17.3% and42% 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.
Hua Tan1,2，Mengle Guo1，Adam T.Clare3,4，Xin Lin1,2，Jing Chen1,2，Weidong Huang1
1. State Key Laboratory of Solidification Processing, Northwestern Polytechnical University2. Key Laboratory of Metal High Performance Additive Manufacturing and Innovative Design, MIIT China, Northwestern Polytechnical University3. Institute for Advanced Manufacturing, Faculty of Engineering, University Of Nottingham4. Department of Mechanical, Materials and Manufacturing Engineering, Faculty of Science and Engineering, University of Nottingham China
摘 要：Thin-wall structures of Ti-6 Al-4 V 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,α laths,gradually converted to elongated acicular α and a large fraction of Widmanstatten α laths under layer-wise thermal cycling.Tensile tests showed that the yield strength,ultimate tensile strength and elongation ofTi-6 Al-4 V thin wall in the build direction were 9.1%,17.3% and42% 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.
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