Numerical Simulation And Experimental Investigation On Thermal-mechanical Behavior During Selective Laser Melting Of TiNi Shape Memory Alloy

As one of the typical technologies of Additive Manufacturing(AM), Selective Laser Melting(SLM) has been paid more attention and widely applied in the industrial manufacturing and daily life.During the process of SLM, the selected powder bed areas have experienced the circulation of rapid heating/cooling, which results in the generation of the thermal stress and strain inevitably. The presence of residual stress and strain shows a serious effect on the materials processing and degrades the dimensional accuracy as well as the properties. Thus, it is important to study the thermal and stress field formed during the process of SLM in order to advance the manufacturing techniques and improve the properties of the fabricated part.In this thesis, the dynamic simulation of the thermal-mechanical behevior during the SLM process of Ti-Ni two component powder was performed using the ANSYS software. Considering of the temperature-dependent material properties and the phase change during SLM process, the Gaussian heat source model was established to act on the powder bed continuously. The effect of the laser parameters(laser power and scanning velocity) on the characteristics of the molten pool and the thermal behaviors was investigated. It showed that the temperature of the powder bed elevated with the increase of the laser power and the decrease of the scan velocity. The sizes of the molten pool varied non-linearly with the variety of the laser parameters. As the laser power of 200 W and scan velocity of 100 mm/s were applied, the depth(63 ?m) and width(81 ?m) of the molten pool were appropriate.Based on the simulation results of the temperature field, the stress field during SLM process of the Ti-Ni two component powder was conducted using an indirect thermal-mechanical coupling method combined with the transform of element material properties. As the appropriate parameters were confirmed, the stress variations in different positions of the fabricated part were analyzed. It showed that the thermal stress varied constantly as the movement of the laser source. The compress stress was obtained near the molten pool while the tensile stress was found in the fabricated component. As the process of SLM was finished, the larger residual stress was found at edge of the part. The residual stress increased non-linearly as the laser power and scan velocity increased equally.As the simulation results were obtained, the corresponding SLM experiment was conducted to fabricate the TiNi alloy samples. The microstructures of the SLM-fabricated samples using different parameters were observed. Residual stresses in the samples were measured using micro-indentationmethod. Comparisons of the experimental data and simulation results showed that the simulation results were in accordance with the measurement. The numerical simulation can successfully predict the influence of laser parameters on the residual stress of SLM-fabricated component.