Microstructure and Mechanical Properties of Ti6Al4V Alloy by Laser Integrated Additive Manufacturing with Alternately Thermal/Mechanical Effects
LU Haifei, LV Jiming, LUO Kaiyu, LU Jinzhong()
School of Mechanical Engineering, Jiangsu University, Zhenjiang 212013, China
Cite this article:
LU Haifei, LV Jiming, LUO Kaiyu, LU Jinzhong. Microstructure and Mechanical Properties of Ti6Al4V Alloy by Laser Integrated Additive Manufacturing with Alternately Thermal/Mechanical Effects. Acta Metall Sin, 2023, 59(1): 125-135.
To meet the requirements of the long fatigue life and high reliability of the key components of the aeroengine as well as solve the challenges of “structure control” and “performance control” based on the fact that plastic deformation can effectively eliminate internal stress and close metallurgical defects generated by the thermal effect, a laser integrated additive manufacturing technology with alternately thermal/mechanical effects is developed. In this study, Ti6Al4V alloy was chosen as the research object. The distributions of residual stress and metallurgical defects and the microstructural evolution of the formed components were systematically studied. The effects of surface laser shock peening (LSP) and interlayer LSP without coating (LSPwC) treatments on mechanical properties were investigated using a tensile test. The results showed that after LSP, tensile residual stress was transformed into compressive residual stress. Additionally, laser shock waves could effectively improve the metallurgical defects in selective laser melting (SLM)-formed components. Moreover, high-density dislocation structures and numerous twins in two directions were produced in coarse α' martensite by laser shock waves, which jointly promoted the grain refinement of α' martensite. The ultimate tensile strength and elongation of Ti6Al4V fabricated by the laser integrated additive manufacturing technology with alternately thermal/mechanical effects reached 1543 MPa and 15.53%, which are 46.5% and 91.5% higher than those of the SLM-formed components, respectively, yielding a good combination of strength and ductility.
Fund: National Natural Science Foundation of China(52175409);National Natural Science Foundation of China(52175323);Jiangsu Provincial Science and Technology Projects in China(BE2021072);Jiangsu Provincial Science and Technology Projects in China(BE2022069-4)
About author: LU Jinzhong, professor, Tel: (0511)88797198, E-mail: jzlu@ujs.edu.cn
Fig.1 Schematics of selective laser melting (SLM) (a), laser shock peening (LSP) (b), the preparation of SLM and SLM-LSP specimens (c), and dimensions of tensile specimen (unit: mm) (d) (CAD—computer-aided design, LSPwC—laser shock peening without coating)
Fig.2 In-depth residual stress distributions of SLM and SLM-LSP specimens
Fig.3 Cross-setional OM images of SLM (a) and SLM-LSP (b) specimens (The dotted lines represent the interfaces between the third layer and second layer)
Fig.4 TEM images in the surface layer of SLM specimen (a) acicular α' martensite (b) magnified image of square region in Fig.4a and the corresponding SAED pattern (inset) (c) mechanical twins (d) dislocation lines
Fig.5 TEM images in the surface layer of SLM-LSP specimen (a) refined α' martensites (b) a large number of parallel mechanical twins and high density dislocation structures (c) magnified image of region Ⅰ in Fig.5b (d) SAED pattern of region Ⅰ in Fig.5b showing {101} twin (T—twin, M—martensite) (e) magnified image of region Ⅱ in Fig.5b (f) SAED pattern of region Ⅱ in Fig.5b showing {102} twin
Fig.6 TEM analyses of dislocations in the surface layer of SLM-LSP specimen (a, b) HRTEM image (a) and corresponding SEAD pattern (b) (c) inverse fast Fourier-transform (IFFT) image of square region in Fig.6a (d) atom arrangement on the () plane (e) atom arrangement on the () plane (f) atom arrangement on the (0001) plane
Fig.7 3D reconstruction graphs revealing 3D pore characteristics (a, c) and statistical results of the size and number of defects (b, d) for SLM specimen (a, b) and SLM-LSP specimen (c, d)
Fig.8 Engneering stress-strain curves of the tensile SLM and SLM-LSP specimens
Fig.9 SEM fracture morphologies of SLM (a, a1, a2) and SLM-LSP (b, b1, b2) specimens (B.D.—building direction)
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