Reducing Porosity in LPBF TI-6AL-4V by Parameter Optimization and Low Temperature Hot Isostatic Pressing Cycle

Powder bed based additive manufacturing has advantages in its ability to make specialized parts with complex geometries. Unfortunately, components made through such processes of suffer from manufacturing defects including porosity. To study pore formation and removal, specimens of Ti-6Al-4V were built at varied levels of laser power, travel speed, hatch spacing, and layer thickness to obtain a variety of initial defect populations. The specimens were then subjected to a hot isostatic pressure (HIP) at 850 °C and 200 MPa to evaluate the low temperature high pressure (LTHP) cycle’s ability to remove pores. Image analysis was used to estimate the relative density of specimens in both the as-built and the post-HIP condition. A visible trend between GED (global energy density) and porosity was identified for a layer thickness of 20 μm, but not when the layer thickness was 40 μm. HIP removed most pores but was less effective at removing faceted pores. Qualitative analysis revealed a moderate change in microstructure. Vicker’s microhardness measurements showed that hardness decreased after HIP. There was a relationship between hardness and GED in the as-built condition, but the post-HIP hardness was nearly uniform

3D PRINTING OF 316L STAINLESS STEEL AND ITS EFFECT ON MICROSTRUCTURE AND MECHANICAL PROPERTIES

Laser powder bed fusion or 3D printing is a potential candidate for net shape forming and manufacturing complex shapes. Understanding of how various parameters affect build quality is necessary. Specimens were made from 316L stainless steel at 0°, 30°, 60°, and 90° angles measured from the build plate. Three tensile and four fatigue specimens at each angle were produced. Fracture morphology investigation was performed to determine the fracture mode of specimens at each build angle. Microstructural analysis was performed on one of each orientation. The average grain size of the samples was marginally influenced by the build angle orientation. Tensile yield strength was the highest for 0° and decreased in the order of 60°, 30°, and 90° angles; all had higher yield strength than wrought. Unlike with the tensile results, the 60° had the highest fatigue strength followed by the 0°, then the 30°, and the 90° build angle had the lowest fatigue strength. Tensile specimens all failed predominantly by ductile fracture, with a few locations of brittle fracture suspected to be caused by delamination. Fatigue fracture always initiated at void space. Keywords

Residual Stress Mapping of GRCop-84 Fabricated by SLM

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