新型高温合金21Cr-32Fe-41Ni高温长期时效组织演变研究

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。

Microstructure Evolution of A New Superalloy 21Cr-32Fe-41Ni After Long-term Aging at High Temperature

Fe-Ni based alloys are used in high temperature 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 microscopy ( SEM ), transmission electron microscopy ( TEM ), electron probe microanalysis ( EPMA ) and chemical phase analysis. The results show that the precipitates in the alloy after long-term aging were mainly γ′, σ, α-Cr, MC phases. The weight percentage and size of the dispersed spherical γ′ in the matrix increased rapidly within 500 h aging. With the increase of aging time from 500 h to 2000 h, the weight percentage and size increase rate of γ′ gradually decreased. During the long-term aging process, the σ phases were distributed along the grain boundaries in block or strip shape, and within grains in needle or strip shape. The distribution of α-Cr phases in the grains was the same as that of σ phases. With the increase of aging time, the number of σ and α-Cr phases increased and they gradually coarsened. The σ phases with discontinuous distribution along the grain were gradually connected, and there was a tendency to develop into a network distribution. With the increase of aging time to 2000 h, the strengths of the alloy increased first and then decreased. They reached the peak after aging for 500 h. The hardness kept increasing.