Yttria enhanced CuCr composites fabricated by laser powder bed fusion: Microstructure, properties and strengthening mechanisms

Abstract

Complex and harsh service environments impose higher demands on comprehensive performance of high-strength and high-conductivity Cu-Cr series alloys. This work introduces Y₂O₃ nanoparticles into CuCr alloy by the laser powder bed fusion (LPBF) process, aiming to further enhance its mechanical properties while preserving its electrical conductivity. The spherical Cu-0.7Cr-2Y₂O₃ composite powders with excellent flowability are prepared using the spray drying and pre-sintering methods. Different laser powers and scanning speeds are utilized to optimize the LPBF forming processes. The CuCr-Y₂O₃ composites with a high relative density of 99.4% are successfully fabricated at a laser power of 250 W and a scanning speed of 400 mm/s. The effect of aging treatments on the evolution of the microstructure and properties of as-printed CuCr-Y₂O₃ composites is systematically analyzed. In the LPBF samples, Y₂O₃ particles with an average size of 46.7 nm are homogeneously dispersed in the copper matrix, and few Cr nano-precipitates are observed. Following aging treatment, the morphology and size of Y₂O₃ particles remain consistent, while a greater density of Cr phases, with an average size of 7.3 nm, precipitate and exhibit a coherent interface relationship with the matrix. Aging treatment conducted at 460°C for 1.5 h results in a peak tensile strength of 691.6 MPa, elongation of 21.5%, electrical conductivity reaching 79.6% IACS, microhardness values of 152.7 HV at room temperature and 112.2 HV at 500°C. Moreover, the conductivity mechanisms and strengthening mechanisms are discussed. The full aging of solid solution Cr elements and minimal negative effects of Y₂O₃ particles on electron scattering, contribute to the excellent electrical conductivity. The superior mechanical properties at both room and elevated temperatures are primarily attributed to the synergistic strengthening effect provided by the shearing mechanism of fine Cr precipitates and the Orowan mechanism of Y₂O₃ particles and lager Cr precipitates.