Precipitation behavior of Nb-Si-based in-situ composite manufactured by laser directed energy deposition

Understanding precipitation behaviors of laser directed energy deposition (L-DED) Nb-Si-based in-situ composite is significant to tailor the microstructure and performances. Here, FCC-Ti and α-Nb5Si3 precipitates are formed in Nb-based solid solution(Nbss) of as-built Nb-24Ti-15Si alloy, and the orientation relationships (ORs) between precipitates and Nbss have been determined with coherent interfaces among them. With Zr or (Zr+Cr) addition, only γ-Nb5Si3 precipitate is formed in the Nbss. The ORs of [12¯16]γ//[011]Nbss and (101¯0)γ//(01¯1)Nbss and semi-coherent interface is formed between γ-Nb5Si3 precipitate and Nbss in as-built Nb-24Ti-15Si-2Zr alloy, while ORs of [0001]γ//[111]Nbss and (011¯0)γ//(11¯0)Nbss are appear in as-built Nb-24Ti-15Si-2Zr-5Cr alloy with near coherent interface. The supersaturation of alloying elements in Nbss during the near-rapid solidfication of L-DED supplies the chemical driving force and the thermal cycles in L-DED process provide the thermal driving force for the formation of precipitates.