Mechanical properties and microstructures of three dimensionally printed stainless steel powder compacts under hot isostatic pressing

MasterThe mechanical properties and microstructural characteristics (grain sizes, dislocation densities) of SUS316L powder compacts which is additively manufactured with the metal three dimensional printer were compared by changing the parameters of post-hot isostatic pressing. In order to study the influences of the applied temperatures and pressures during hot isostatic processing, four cycles of hot isostatic pressing were considered. Moreover, the effects of materials of containers (or capsules) for hot isostatic pressing on the mechanical properties and microstructures were investigated. In this thesis, three kinds of conditions such as glass, austenite stainless steel 304, and capsule free were considered. And the powder compacts were fabricated in the conventional powder metallurgy (P/M) route as counterparts to the post-hot isostatic pressed samples. The additively manufactured specimens were built in two different directions in the purpose of investigating the cause of anisotropic mechanical properties. Microstructures of additively manufactured samples were observed with optical microscope and electron backscatter diffraction (EBSD). Dislocation density which is known as the factor to affect mechanical properties and hardness was measured through the XRD profile analysis. Unlike the conventional XRD profile analysis method, in this thesis, both the new quadratic and linear form of the modified Warren-Averbach equation were introduced. The measured mechanical properties were analyzed with considering the changes of microstructures and microstructural characteristics (grain sizes, and dislocation densities) of additively manufactured materials processed by hot isostatic pressing. The experimental results indicate that the mechanical properties and microstructural characteristics were changed mainly by temperatures. Meanwhile, holding time of post-hot isostatic pressing also changed the microstructures and microstructural characteristics. The anisotropy of mechanical properties of the samples built in two different building direction became isotropic in higher temperature and longer holding time