钇,铈对低铪镍基K444返回合金组织与力学性能的影响

研究了Y,Ce对含铪(Hf)镍基铸造高温合金K444返回料(添加50%返回料)合金的力学性能和组织的影响.研究结果表明:适量Y,Ce(Y<0.03%,Ce<0.015%(质量分数))添加到返回料合金后,一方面,Y,Ce具有去除N,O等有害杂质的作用,使O含量由15×10~(-6)降低到8×10~(-6),N含量由35×10~(-6)降低到18×10~(-6),从而使返回料合金得到净化.另一方面,Y,Ce细化了枝晶组织,减少了共晶和大块状碳化物数量,并且强化了晶界.和未加Y,Ce的返回料合金相比.添加Y,Ce使返回料合金室温拉伸强度提高约100 MPa,塑性提高近一倍;使900℃的高温瞬时拉伸性能波动较为平稳,塑性提高近一倍.添加Y,Ce还可以提高返回合金900℃/274 MPa条件下的持久性能,达到新料水平;可以明显延长K444返回合金900℃/274 MPa条件下的蠕变第二阶段,提高蠕变寿命.

Effect of Yttrium and Cerium on Microstructure and Mechanical Properties of Revert Nickel-Base Superalloy K444 With Low Hafnium Content

The effects of Y and Ce doping on the mi-crostructure and mechanical properties of a revert Hf contained nickel base superalloy K444 (with 50% re-vert alloy) were investigated. The results showed that an appropriate addition of Y and Ce (Y < 0. 03%, Ce <0. 015%) in the revert alloy could reduce the harmful impurity O from 15×10~(-6) to 8×10~(-6) and N from 35×10~(-6) to 18×10~(-6), and consequently purify the revert alloy. On the other hand, Y and Ce led to fine dendrites, decreased eutectics and block car-bides, and strengthened grain boundary. Compared with the revert alloy without Y and Ce, the Y and Ce doped alloy possessed 100 MPa higher tensile strength and double tensile ductility at room temperature.While at 900℃ the variation of tensile ductility of the Y and Ce doped revert alloy was slighter, and the ten-sile ductility doubled that of the revert alloy without Y and Ce. With Y and Ce doping, the stress-rupture life of the revert alloy at 900℃/274 MPa was prolonged and approached to that of virgin alloy. In addition, the secondary stage during creep at 900℃/274 MPa was prolonged and thus the creep rupture was im-proved.