熔体超温处理对GH742返回料凝固组织和力学性能的影响

Influence of melt superteating treatment on solidification microstructure and mechanical properties of Ni-based superalloy GH742

摘要:

采用熔体超温处理方法考察了熔体超温处理温度对GH742返回料凝固组织和力学性能的影响规律。结果表明：当熔体超温处理温度低于1550℃时，随熔体超温处理温度的升高，晶粒和枝晶组织显著细化，枝晶偏析和合金中N、O、S元素含量降低，然而，进一步升高至1600℃，晶粒和枝晶组织粗化、枝晶偏析增大、合金中N、O含量升高。熔体超温处理显著影响枝晶干γ′相特征，却对MC型碳化物影响较小。MC型碳化物形貌为棒状或块状，且随熔体超温处理温度升高无明显变化，但尺寸和面积分数均略微减小。枝晶干γ′相形态则随熔体超温处理升高由近球形向近立方状转变，尺寸呈现先增后减趋势。合适的熔体超温处理可显著提高返回料的室温拉伸强度，但对塑性无明显影响，其原因被归因于凝固组织的变化。

Abstract:

The melt superheating treatment is carried out for reverted GH742 superalloy. Under the same solidification conditions, the microstructure evolution and its influence on mechanical properties is systematically investigated by changing the melt superheating temperature. The results show that the grain and dendrite are refined, and the dendrite segregation and the contents of N, O and S are decreased with the melt superheating temperature increasing from 1450 ?C to 1550 ?C. However, the grain and dendrite becomes coarse, dendrite segregation becomes serious and the contents of N, O increase after the melt superheating treatment at 1600 ?C. The morphology of MC carbide is rod-shaped or blocky. The melt superheating treatment has no significant influence on the morphology of MC carbide, but slightly decrease its size and area fraction. With increasing melt superteating treatment temperature, γ′ morphology changes from near-sphere to cube, but γ′ size first reduces with the increase of melt superheating temperature between 1450 ?C and 1550 ?C, but increases when the superheating temperature is higher than 1550 ?C. Corresponding to this, the tensile strength at room temperature is significantly improved after melt superheating treatment at 1550 ℃, but the ductile has no obvious change.