Thermal Post-Treatments of Powder-bed, Laser-fused Ti6Al4V and Their Effect upon Fatigue Strength
Thermal Post-Treatments of Powder-bed, Laser-fused Ti6Al4V and Their Effect upon Fatigue Strength
Wednesday, May 25, 2016: 9:30 AM
403 (Meydenbauer Center)
The microstructure of Ti6Al4V produced with powder-bed, laser-fused methods of additive manufacturing (also known as selective laser melting, SLM) has been shown to be distinctly different from the dual-phase, equiaxed structure of wrought material produced with the conventional beta solution treatment and overaging process (STOA). While the yield and ultimate strengths of SLM Ti6Al4V can exceed those of STOA-treated wrought material, the ductility of as-produced SLM material is significantly lower, with correspondingly poor fatigue strength. Although post-processing SLM Ti6Al4V with hot isostatic pressure (HIP) endows the material with increased ductility, the resulting improvement in fatigue behavior results in fatigue strengths still only about 60% of those of wrought material.
Optimal microstructures for SLM materials might be attained through judicious selection of laser/machine process parameters, but research toward that end has been limited. Moreover, typical owner/operators of commercially-built SLM machines are both discouraged by the vendors from modifying machine settings and often have neither the time nor the budget to develop optimized process parameters. We therefore sought to explore thermal post-treatments for SLM Ti6Al4V and to demonstrate their effect upon the material microstructures and the resulting mechanical properties.
Several lots of SLM Ti6Al4V were each subjected to different thermal processes, including variants of the ASTM-recommended HIP procedure, three beta-anneal, slow-cool aging (BASCA) cycles and an “extreme” thermal treatment recently presented in the literature. The mechanical behaviors of the resulting materials were explored using tensile tests and fatigue testing in fully-reversed bending. The standard HIP cycle produced the greatest ductility among these materials, while the BASCA process produced the highest quasi-static strength. Influence of the thermal post-treatments on the material microstructures and the resulting fatigue strength of SLM Ti6Al4V is presented.
Optimal microstructures for SLM materials might be attained through judicious selection of laser/machine process parameters, but research toward that end has been limited. Moreover, typical owner/operators of commercially-built SLM machines are both discouraged by the vendors from modifying machine settings and often have neither the time nor the budget to develop optimized process parameters. We therefore sought to explore thermal post-treatments for SLM Ti6Al4V and to demonstrate their effect upon the material microstructures and the resulting mechanical properties.
Several lots of SLM Ti6Al4V were each subjected to different thermal processes, including variants of the ASTM-recommended HIP procedure, three beta-anneal, slow-cool aging (BASCA) cycles and an “extreme” thermal treatment recently presented in the literature. The mechanical behaviors of the resulting materials were explored using tensile tests and fatigue testing in fully-reversed bending. The standard HIP cycle produced the greatest ductility among these materials, while the BASCA process produced the highest quasi-static strength. Influence of the thermal post-treatments on the material microstructures and the resulting fatigue strength of SLM Ti6Al4V is presented.