| Abstract: | A Ni-Al-Cr3C2 welding wire produced by metal-powder-core technique was pile-up welded on the surface of DZ125 alloy. During welding, the physical heat of arc and Ni-Al exothermic reaction made Ni react with Al to form Ni3Al as matrix, and the precipitated Cr3C2 dissolve again to form fine Cr-rich M3C2 and M7C3 phases distributed in matrix during solidification. The size of chromium carbide particles near the coating/substrate interface is smaller than that near the surface of welding layer due to the difference of cooling rates. In addition, alloying elements in DZ125 alloy diffused into welding melting pool, and then were carbonized or oxidized. The formed carbides and oxides are mainly influenced by the concentration of the alloying elements and the free energies of formation of these compounds. As a result, many carbides and oxides are rich in Ta, Hf, Ti and W. With reaching coating surface, these compounds decrease in amount and even disappeare. |
