Evolution of L12 Ordered Precipitates in Cu-Fe-Si Alloy System and Its Influence on Potential Strength-Conductivity Properties

We report a copper-based alloy strengthened by L1(2) ordered precipitates and exhibiting a strength of 370 MPa and thermal conductivity of 290 (W/m.K) at 400 degrees C. The alloy is based on a Cu-Fe-Si system with the optimum composition of Cu-2.5at%Fe-2.5at%Si and processed by the suction casting of the melt. The strengthening precipitates are crystallographically L1(2) ordered. The precipitates were evolved during post-solidification cooling and are coherent with continuous fcc copper matrix. Ordered precipitates show a cube-on-cube orientation relationship with the matrix. This feature promotes low interfacial energy and are useful for retaining high temperature strength. The composition of the precipitates was determined through 3D-APT studies and found to be similar to Fe68Cu9Si24 (at.%). The coherent nature of the order-disorder interface and the low solid solubility of iron in the copper matrix impart resistance to coarsening at high temperatures. The high strength at room temperature (similar to 690 MPa) is attributed to the coherency strain around the uniformly dispersed precipitates. However, order hardening plays a significant role at higher temperatures as coherency strain decreases with temperature, evidenced by the loss of strain contrast in TEM images. The combination of the significant stability of the microstructure and high-temperature strength makes this alloy attractive for high heat flux application at elevated temperatures domain.