Enhanced nano-level mechanical responses on additively manufactured Cu-Cr-Zr copper alloy containing Cu₂O nano precipitates

Copper alloys has excellent electrical conductivity and thermal stability. These properties may also relay on the manufacturing process which helps to enhance their mechanical strength. In this research, nano-mechanical properties of Laser Powder Bed Fusion (LPBF) Cu-Cr-Zr copper alloy was investigated to reveal the influence of Cu₂O nano precipitates. The fabricated copper parts were inspected for their grain orientations and irregularities using Optical Microscopy (OM) and Field Emission Scanning Electron Microscopy (FESEM) with Energy Dispersive X-ray analysis (EDX). The printed copper alloy possesses polycrystalline grain structure with columnar and equiaxed grains along the build directions. The formed Cu₂O nano precipitates were confirmed by the X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM) and their grain orientations were assessed through Electron Backscatter Diffraction (EBSD) analysis. The homogenous distribution of precipitates formation was confirmed by the nano-hardness mapping and reduced elastic modulus mapping in which the indentation was performed in the specific area of 20 µm x 20 µm. The maximum nano-hardness of 1.05 GPa and maximum reduced elastic modulus of 137.6 GPa was obtained. Using the topographic wear tracks, the worn-out depth of 267.9 nm and 352.4 nm was witnessed in the nano-scratch and nano-wear test. Strain rate sensitivity of the copper alloy parts were also examined based on 3 different strain rates (3.3 ×10⁻⁵, 1.6 ×10⁻⁵ and 2.6 ×10⁻⁴ s⁻¹) and the results displays the negative strain rate behaviour of the printed copper alloy parts. The maximum Ultimate Tensile Strength (UTS) of about 340 ± 6 MPa was observed in the strain rate of 3.3 × 10⁻⁵ s⁻¹ and also the fracture morphology substantiated the ductile behaviour of the printed copper alloy parts by the occurrence of dimples and necking.