深冷循环对SiC/Al复合材料宏微观残余应力的影响

Impact of Cryogenic Cycling on the Macro and Microscopic Residual Stress in SiC/Al Composites

铝基碳化硅(SiC/Al)复合材料因其高比模量、高比强度和良好尺寸稳定性等特点广泛应用于精密光学领域。SiC/Al复合材料热处理过程中产生的宏/微观残余应力是影响其尺寸稳定性的关键因素。为了阐明残余应力的降低方法和效果,提高精密光学零件的尺寸稳定性,本工作使用中子衍射和有限元模拟,分析了深冷循环处理对于体积分数为35%的SiC/6092Al复合材料在退火状态下宏微观残余应力的影响,研究了深冷循环次数、样品尺寸、增强相颗粒尺寸和深冷循环温度差等影响因素。结果表明,深冷循环能引起基体塑性应变,从而显著降低退火态SiC/Al复合材料的相应力,并且随着深冷循环次数的增加,单次循环相应力降低效果减弱。深冷循环导致的塑性应变集中在颗粒周围的基体,主要影响颗粒和周围基体的相应力大小,与样品尺寸无明显关联,并且深冷循环不增加退火态样品的宏观残余应力。复合材料多次深冷循环后的相应力降低量与SiC颗粒尺寸无关,并且,多次深冷循环对相应力的降低效果与深冷循环温度差关系较小,100~-196℃和200~-196℃进行多次深冷循环对相应力的改变十分接近。

Aluminum-based silicon carbide(SiC/Al)composites are widely used in the field of precision optics by virtue of their high specific modulus,high specific strength,and excellent dimensional stability.The dimensional stability of these composites is primarily influenced by macroscopic and microscopic residual stresses induced during the heat treatment process.This study employed neutron diffraction and finite element method(FEM)to investigate the impact of cryogenic cycle treatment on both macroscopic and microscopic residual stresses within the 35%SiC/6092Al composite material in the annealed state.The results of this study will clarify the methods and effects of reducing the residual stress and improving the dimensional stability of precision optical parts.The study focused on the influencing factors such as the number of cryogenic cycles,sample size,reinforcement particle size and temperature difference of cryogenic cycles.The results show that the deep cryogenic cycles can remarkably reduce the internal stress of SiC/Al composites in the annealed state;as the number of cryogenic cycles increases,the internal stress reduction effect of a single cycle weakens.The cryogenic cycles primarily induce plastic strain in the matrix around particles,thereby influencing the internal stress between the particles and the surrounding matrix.No significant relationship is found between cryogenic cycles and external dimensions.Moreover,the cryogenic cycle barely increases the macroscopic stress of the annealed sample.For composites with equal volume fraction of SiC particles,the reduction in the internal stress after multiple cryogenic cycles is the same regardless of the SiC size.Moreover,the effect of multiple cryogenic cycles on the reduction in internal stress slightly affected the cryogenic cycle temperature difference.Cryogenic cycles at temperatures ranges of 100~-196℃and 200~-196℃exhibit almost identical alterations in internal stress.