G.P. Toker, S.E. Saghaian, H.E. Karaca, N.S. Moghaddam, M. Nematollahi, M. Elahinia
University of Kentucky,
Keywords: selective laser melting, shape memory alloys, NiTiHf
Summary:Selective laser melting (SLM) is a subgroup of Additive Manufacturing (AM) and an attractive fabrication method which allows creating complex shape, dense and porous parts for desired applications. Fabrication parameters such as laser power, scanning speed, and energy density play a significant role on the mechanical and metallographic characteristic on the SLM fabricated parts and properties can be controlled with process parameters. Up to now, numerous studies have been conducted on shape memory alloys, dense or porous SLM parts have been fabricated particularly NiTi alloy which is well-known among the shape memory alloy. Since NiTi alloy cannot perform above the 100 oC, they are not proper for high temperatures applications. Ternary alloying elements can be added to improve both transformation temperatures (TTs) and mechanical properties. Hf is the most common alloying element to increase the TTs due to its lower cost and higher influences. NiTiHf alloys can be operated at high temperature and also high strength required applications. This current study is a new approach of the NiTiHf SLM fabricated parts. Various combination of process parameters has been employed to fabricate the NiTiHf SLM parts; crack, and porous level has been investigated to determine the optimum process parameters. It was found that low energy density resulted in higher porosity level and low strength, decreased as energy density increased. Additionally, transformation temperatures were revealed based on the process parameters and TTs are found to be higher than 150 oC. Thermo-mechanical tests are also performed to observe the effect of fabrication parameters on the shape memory behavior of NiTiHf SLM parts.