DZ125合金表面碳化铬／Ni_3Al堆焊涂层显微组织

MICROSTRUCTURE OF PILE-UP WELDING CHROMIUM CARBIDE/Ni_3Al COMPOSITE CLADDING ON DZ125 ALLOY

采用药芯焊丝法制得Ni-Al-Cr_3C_2复合焊丝,将该焊丝堆焊于DZ125合金表面.在氩弧物理热的作用下,Ni与Al化合成Ni_3Al并释放大量反应热;Cr_3C_2发生分解,并在随后凝固过程中重新析出细小的富Cr的M_3C_2和M_7C_3相.受冷却速率的影响,靠近母材区域的碳化物尺寸小于外层区域.母材合金元素进入焊接熔池中,发生一系列碳化和氧化反应,生成的化合物按自由能高低随温度降低顺序析出,导致在焊接熔合区形成大量富Hf,Ta,Ti和W的MC复合碳化物和少量氧化物,距焊层表面越近,数量越少直至消失.

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.