Investigation On Micro Characters Of Selective Laser Melting And Hot Isostatic Pressing Post-treatment

Selective laser melting (SLM) is a novel rapid prototyping technology which has many advantages in shortening developing circle and fabricating metal parts with high quality and complicated shape directly. Researchers at home and abroad have studied its mechanism, but SLM parts have many problem resulting in poor property, which restricts their application.Taking Ni-based high-temperature alloy GH4169 and AISI316L stainless steel as the materials, preparation work, SLM parameters and hot isostatic pressing(HIP) post-treatment were investigated to improve the properties of SLM part by studying surface topography, fine texture, micro-hardness and relative density of parts.The results show that: (1) Selecting proper powder, base plate and protecting gas and pre-treating them properly can promote the property of SLM parts. (2) The higher laser power, the bigger of scanning track width; the thicker of layer, the more likely balling phenomenon appears, and the lower of the final part relative density; the more oxygen contented in the atmosphere, the more obvious balling phenomenon; when the scanning lap ratio is between 40%~60%, the balling phenomenon is less and surface accuracy is good. (3) After HIP the vacuum cracks in SLM parts heal completely, the volume of the anomalous holes inside the parts reduces, and the holes become spherical or near spherical. SLM parts with the small processing thickness, will be well bonded, and have high relative density, the crystal grains of which are big after HIP. But to the SLM parts with the big thickness, the bad cementation between each layers and closed holes inside which are post-processed by HIP, the crystal grains are tiny and distribute along the SLM processing layer. The relative density of HIP parts rise after HIP, especially for most of those holes are close holes; if most of the holes are through holes, highly pressed gas will go into the holes, then the relative density cannot be raised a lot; samples after HIP are still anisotropic in mechanical properties, and the micro-hardness is not related to the distance to sample surface.The achievement of this study can give advice to promote the property of SLM part before, in, and after SLM.