The study focuses on microstructural evolution in a WC-Co powder mixture during Selective Laser Melting (SLM) and hot isostatic pressing (HIP) processing. This powder mixture contained a 13 ± 0.6% weight fraction of Co binder and WC particles of mean size of 3.0 ± 1.9 μ$\mathrm{m}$. SLM of the mixture produced samples of various densities, depending on the volumetric energy density (VED) applied. High VED levels led to densities of up to 88%. The aspects affected by changes in VED included the pore density as well as the resulting types of phases and the size of WC phase particles. At high VED, the material began to develop cracks due to embrittlement. This had multiple causes: coarsening of $\alpha$-phase (WC), evaporation of $\beta$-phase (Co binder), and precipitation of $\eta$-phase. At low VED levels, pores formed, typically of nonsymmetric shapes, with sizes larger than 500 μ$\mathrm{m}$. Subsequent HIP processing led to an increased density, up to 96% of solid material. Contributions to this increased density were provided by structure transformations, namely, coarsening of $\alpha$-phase by up to 1300% when compared to the powder grain size, and formation of $\eta$-phase. The results provided a basis for steering further research to explore to a greater depth the SLM and HIP processing of selected WC-Co powder mixtures with as yet unused ranges of process parameters.

The main objective of this article is to familiarize readers with the first outputs from PhD research by David Bricín, especially with the metallographic analysis, which was carried out on the first series of printed samples. The PhD thesis deals with the processing of powder mixtures based on WC-Co using selective laser melting (SLM) and other technologies. This article specifically deals with the use of SLM for the processing of a WC-Co powder mix. The grains of this powder mixture are not granular, but separate grains of carbides and binders. This powder blend was processed on a 3D SLM printer using various printing parameters. Variable parameters included laser power and scanning speed. Other print parameters were kept constant. The properties of the powder mixture and the printed samples were evaluated by metallographic analysis using light and scanning electron microscopy. These analyses were further supplemented by X-ray diffraction phase analysis, chemical analysis by EDX, and analysis of mechanical properties by compression strength testing. The evaluation of the analyses determined how the printing parameters and the type of powder used affect the development and distribution of the structure in the printed samples and how the mechanical properties of the print are then affected. For example, it has been found that increasing the scanning speed results in a more pronounced mixing between the carbide grains and the binder, which then has a positive influence on the mechanical properties of the print. In addition, the experiments found the energy at which the porosity in the printed samples was significantly reduced, and the direction in which further experiments are to take.

Detail záznamu - Assessment of usability of WC-Co powder mixtures for SLM - Detail záznamu - Vědecká knihovna UJEP