Investigating the Residual Stress Distribution in Selective Laser Melting Produced Ti-6Al-4V using Neutron Diffraction

The Selective Laser Melting (SLM) process makes rapid manufacture of both prototype and structural components possible for a variety of metals. However, high residual stresses are inherent to the building process and can pose a number of problems; including part distortion, cracking and a reduction in the components' mechanical strength and fatigue life. Exact stress distributions through the part volume are often not known as the methods commonly used to measure residual stresses are surface or near surface stresses. As such, the influence of build parameters, residual stresses on resultant SLM-produced part integrity is not understood. Neutron diffraction allows for the measurement of residual stress through the volume of a part using measured lattice strains, thereby providing a tool to gain insight into the SLM process and the formation of residual stresses. In this work, neutron diffraction was used to determine the distribution of residual stress in a set of rectangular SLM-produced Ti-6Al-4V samples. Results show that an increase in layer thickness reduces the stress gradients in the part. There is also evidence that changing the exposure strategy can prevent stresses from developing along a preferential axis, making a more homogeneous stress field.