Additively manufactured CuCrZr alloy: Microstructure, mechanical properties and machinability

Abstract

Manufacturing CuCrZr alloy parts with high strength and high surface quality by selective laser melting (SLM) is a challenging task. This study investigates the microstructure, mechanical properties and machinability of SLM processed and heat-treated CuCrZr alloy through tensile test, compression test and ultra-precision machining. The microstructure analysis shows that the grain morphology and orientation are highly related to the laser track and building direction. Grain epitaxial growth is found on both horizontal (XY) and vertical (XZ) planes, which bends at the boundary of the molten track/pool. After heat treatment, molten track boundaries disappear and the slender and bent grains on the XY plane are replaced by polygonal square grains, but the large epitaxial grains on the XZ plane still remained. X-ray diffraction results indicate that the as-built sample contains α-Cu, Cr and CuxZry phases and building direction has an influence on the crystallographic orientation distribution. As-built (AB) CuCrZr alloy shows a comparable yield strength (218.0 MPa) with solution + ageing-treated (SAT) (231.3 MPa), which is much higher than that of the solution-treated (ST) counterpart (131.0 MPa). Although the ultimate tensile strength of the AB sample is lower than that of the SAT sample, its elongation at break (46.5%) is much higher than the latter (19.1%). The compressive strength of the AB sample is slightly lower than the SAT sample but higher than the ST sample. At low cutting speed, the ST sample shows a higher cutting force. High cutting speed will lead to the increase of cutting force of the AB and SAT samples but has a much lower effect on the ST sample. The XZ plane of the AB sample shows better machined surface quality. SAT sample has the highest material recovery during cutting and its chip will change from spiral to arc shape with the increase of cutting speed.