Laser powder bed fusion of copper matrix iron particle reinforced nanocomposite with high strength and high conductivity

Liquid-liquid phase separation, and the resulted solute segregation, during conventional solidification have been a long-term challenge to produce copper (Cu)-iron (Fe) immiscible composites with high strength and high conductivity. The present work reports an effective solution to this issue through laser powder bed fusion (L-PBF) in-situ alloying of Cu-8 wt.% Fe. Microstructure observation showed that the fast cooling within micron-scale melt pools fully eliminated the Fe segregation and therefore the L-PBF fabricated nanocomposite achieved the homogeneous microstructure, which featured equiaxed fine grains around 1 µm in size. Ageing of the nanocomposite at 600°C for 1 h enabled precipitation of two types of nanoparticles. One is coarser Fe nanoprecipitates with body-centered cubic (BCC) structure and diameter of 100-300 nm, mainly distributing along grain boundaries. The other is smaller Fe nanoprecipitates with face-centered cubic (FCC) structure and diameter of 10-35 nm, being observed within the grains and having coherent interfaces with the Cu matrix. As a result, the aged Cu-Fe nanocomposite achieved tensile strength of 462.9±6.6 MPa with 30.4%±1.7% elongation to failure and 74.5% IACS (International Annealed Copper Standard) electrical conductivity. The formation mechanisms of the nanoprecipitates and the strengthening mechanisms of the nanocomposite are discussed.