College of Engineering
Materials Engineering Department
BS in Materials Engineering
Ryan T. Smith
One of the major drawbacks of selective laser melting (SLM) as a form additive manufacturing is that it produces parts with severe residual stress that leads to poor mechanical performance due to the thermal cycling of the printing process. In this project, two different heat treatments (high temperature annealing and low temperature annealing) are applied to 316L stainless steel subsized tensile bars fabricated by SLM process to minimize the amount of residual stress in the samples. Residual stress is indirectly measured by X-ray diffraction (XRD), as well as microscopic analysis, hardness testing, and tensile testing are applied to characterize the samples. Unfortunately, the residual stress could not statistically be determined because of large measurement errors even though error corrections were applied. However, the HRB hardness values are determined to be 91.8 HRB for as-built samples, 80.7 HRB for after high temperature annealed samples, and 95.5 HRB for after low temperature annealed samples. The high temperature heat treatment followed by annealing showed a reduction in hardness values, as expected. The low temperature heat treatment appeared to show an increase in hardness. Optical microscopy and scanning electron microscopy (SEM) showed that small dendritic structures, which are ubiquitously seen throughout as-built samples, are gone in the high temperature annealed samples.