Transforming Fe-Cu alloys with unprecedented BCC Cu precipitates toward dual mechanical functionalities

• Below Fe phase transition temperature, PM-HIP pressure contracted the lattice, enabling coarse BCC Cu precipitate growth. • At 973 K, full coherency between BCC Cu and BCC Fe led to brittle behavior and the highest tensile strength. • The 973 K specimen showed higher thermal conductivity due to full coherency, unlike 1173/1273 K with FCC Cu and interface effects. An Fe-10Cu alloy was fabricated without internal defects using a powder metallurgy-hot isostatic pressing (PM-HIP) method under high pressure conditions to determine the changes in its microstructure and physical properties according to the sintering temperature. In general, Cu precipitates in Fe-Cu alloys have been observed in an FCC structure, and studies on BCC Cu precipitates smaller than 6 nm have only been theoretically reported. However, for the first time, we found that Cu precipitates with a BCC structure larger than 50 nm may occur in an Fe-Cu alloy. An Fe-Cu alloy containing BCC Cu precipitates in a fully coherent relationship with the α-Fe matrix was observed to have completely different brittle fracture mode, along with higher tensile strength and thermal conductivity compared to an Fe-Cu alloys containing FCC Cu precipitates.