Microstructure heterogeneity, mechanical properties and thermal conductivity of pure copper fabricated by metal material extrusion additive manufacturing process

초록

Pure copper was prepared by using metal material extrusion additive manufacturing (M-MEX) technology, and its microstructure, room temperature mechanical properties, deformation behavior, and thermal conductivity were investigated. The apparent relative density was 94 %, with an Archimedes density of 97.82 %, and low planar porosity (<0.5 %) in the solid-fill regions. The microstructure consisted of equiaxed grains with Sigma 3 annealing twins, reducing grain size by similar to 40 %, and showed heterogeneity with high-angle grain boundaries and elongated micro voids due to the extrusion strategy. Room temperature tensile results showed that the tensile strength of M-MEX specimens was around 200 MPa and the elongation was around 57 %, which was superior to the binder jetting additive manufactured copper, and the strength and elongation were similar to that of copper manufactured by powder bed fusion technologies. Some different deformation behaviors were identified depending on the relationship between extrusion pattern and tensile loading direction due to microstructural heterogeneity. Thermal conductivity was 329.45 Wm(-1)K(-1) (BD) and 333.17 Wm(-1)K(-1) (WD), outperforming coppers produced by laser-powder bed fusion (L-PBF) and binder jetting (BJ) processes. While minor anisotropy in thermal conductivity was noted due to pore orientation, M-MEX copper demonstrated near-isotropic properties overall. In addition to the above results, digital image correlation technique, and electron backscattered diffraction analysis were performed. Based on these, the heterogeneous microstructure and defect formation mechanism of M-MEX built copper and its deformation mechanism and thermal conductivity behavior were also discussed.

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