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Abstract:
This work presents a combined experimental and numerical investigation of local overheating in NiAl during spark plasma sintering (SPS). Experimental studies were conducted on samples sintered under different temperature and pressure conditions to capture both the early and final stages of densification. Both perpendicular and parallel loading directions were analysed for microstructural evidence of local melting. Experimental research comprised post-process analysis using SEM and EBSD, while supplementary XRD analysis was used to assess phase stability and crystallographic characteristics. Microstructural analysis focused on regions most susceptible to overheating (contact areas, small particles trapped between larger ones). Sintered samples showed progressive densification, neck growth and grain coarsening with increasing temperature. EBSD maps of sintered compacts reveal distinct orientations across contacts, with no evidence of epitaxial or equiaxed grain growth. Experimentally, no evidence of melting due to local overheating was detected. The experimental observations were complemented by particle-scale thermo-electric FEM simulations. Geometries of equal-sized particles, arranged in a straight line and in a zig-zag chain, connected by the necks with increased resistance, were considered to analyse the temperature rise in the necks. Geometry consisting of a small particle between two large particles was analysed to assess temperature nonuniformity in heterogeneous microstructures. The results show temperature increase in contacts or in small particles; however, the resulting temperature differences are less than 1 C in all cases studied. Numerical results support the experimental findings that NiAl is not prone to local overheating in SPS under the studied conditions.