新型高温合金21Cr-32Fe-41Ni高温长期时效组织演变研究

Microstructure Evolution of New Superalloy 21Cr-32Fe-41Ni During Long-Term Aging at High Temperature

铁镍基合金长期服役于较高温度下,因此高温下的组织稳定性是合金的重要指标之一。利用扫描电子显微镜(SEM)、透射电子显微镜(TEM)、电子探针(EPMA)、化学相分析等手段对750℃不同时效时间下新型铁镍基高温合金21Cr-32Fe-41Ni组织与性能演变规律进行研究。结果表明,长期时效后合金中析出相主要有γ′相、σ相、α-Cr相以及MC相。在时效500 h内,基体中弥散分布的球形γ′相的质量分数和尺寸快速增加。时效时间从500 h增加至2000 h,γ′相的质量分数和尺寸增加速率逐渐降低。在长期时效过程中,σ相沿晶呈块状或条状分布,并与α-Cr相同时在晶内以针状或条状析出。随时效时间增加,σ相和α-Cr相数量增加,逐渐粗化。沿晶不连续分布的σ相逐渐相连,存在向网状分布发展的趋势。随时效时间增加至2000 h,合金强度先升高后降低,在时效500 h后达到峰值,硬度保持增加趋势。

Fe-Ni based alloys serve in high temperature environment for a long time,so the microstructure stability at high temperature is one of the important indexes of the alloys.The microstructure and properties evolution of a new Fe-Ni based superalloy 21Cr-32Fe-41Ni at 750℃for different aging time were investigated by scanning electron microscope(SEM),transmission electron microscope(TEM),electron probe microanalysis(EPMA)and chemical phase analysis.The results show that the precipitates in the alloy are mainlyγ′,σ,α-Cr,and MC phases after long-term aging.The mass fraction and size of the dispersed sphericalγ′in the matrix are increased rapidly within 500 h aging.With the increase in aging time from 500 h to 2000 h,the increase rate of mass fraction and size ofγ′gradually decreases.During the long-term aging process,theσphases are distributed along the grain boundaries in block or strip shape and within grains in needle or strip shape.The distribution ofα-Cr phases in the grains is the same as that ofσphases.With the increase in aging time,the number ofσandα-Cr phases is increased and they are gradually coarsened.Theσphases with discontinuous distribution along the grain are gradually connected,and there is a tendency to develop into a network distribution.With the increase in aging time to 2000 h,the strength of the alloy increases first and then decreases,and reaches the peak after aging for 500 h.While,the hardness keeps increasing.