Research On High Cycle Fatigue Properties Of SiC_p/2A14Al Composites

Particle reinforced metal matrix composites have excellent comprehensive properties.They can overcome the limited potential of traditional metal materials and are powerful alternatives for them in the aerospace field.Aerospace materials have strict requirements on high cycle fatigue properties.Therefore,further research on the high cycle fatigue properties of particle reinforced metal matrix composites is particularly critical for their future application in the aerospace field.In this paper,SiC_p/2A14Al composites prepared by stirring casting and subjected to extrusion processing and T6 heat treatment are used as the research object.The main target is to analyze the effect of the volume fraction of reinforcement particles on tensile properties,microstructure,fatigue curve,conditioned fatigue limit,fatigue crack initiation and fatigue crack growth of the materials,and the effect of surface treatment technology on improving the fatigue life of the materials is also analyzed.The conclusions are listed as follows:1、As the volume fraction of reinforcement particles increases,the yield strength,tensile strength,and elastic modulus of SiC_p/2A14Al composites increase,while the elongation decreases.The composites have a good microstructure.There are no large-scale casting defects in the composites and the reinforcement particles are evenly distributed.The stress level acting on SiC_p/2A14Al composites has a good linear relationship with the logarithm of their fatigue life,and there is no horizontal part in the fatigue curve,which is the same as the aluminum alloy.The conditional fatigue limit of SiC_p/2A14Al composites estimated by the two methods is similar,reflecting the accuracy of the linear fitting equation.As the effect of the volume fraction of reinforcement particles on the conditional fatigue limit of the composites is consistent with the yield strength and tensile strength,an empirical formula for describing the relationship between the conditional fatigue limit and tensile strength of the composites is derived based on the research results of the aluminum alloys.2、The fatigue sources of SiC_p/2A14Al composites with different volume fraction of reinforcement particles are mainly casting defects,"matrix enrichment"and alloy phase fracture.Among them,the proportion of casting defects is the lowest,and the proportion of alloy phase fracture is the highest.The proportion of"matrix enrichment"will gradually decrease as the volume fraction of reinforcement particles increases.In the threshold region,the addition of reinforcement particles does not enhance the fatigue crack closure effect and has no effect on the threshold of fatigue crack growth.In the Paris region,the failure of reinforcement particles,the debonding of the reinforcement particles to the metal matrix,and the cracking of the weak metal matrix adjacent to the reinforcement particles are the main failure mechanisms.Since the final size of the reinforcement particles is small,the proportion of the debonding of the reinforcement particles to the metal matrix is higher.In addition,the failure mechanism of 20%SiC_p/2A14Al composites indicates that too high volume fraction of reinforcement particles is harmful to the high cycle fatigue performance of the material.3、When only the high temperature shot peening process is used as the surface treatment of SiC_p/2A14Al composites,the weakening factors for the high cycle fatigue performance will dominate.The mechanical grinding and polishing process can remove the pits left by the high temperature shot peening process and reduce the surface roughness of the material.The maximum compressive stress and overall layer depth of the residual compressive stress field introduced by high-temperature shot peening are high,which can eliminate the weakening effect of mechanical grinding and polishing process on the shot peening effect.The effective combination of them can significantly improve the surface state of the composites,thereby increasing their fatigue life.High temperature shot peening can also cause more severe surface work hardening,but this effect is not a major strengthening factor for the high cycle fatigue performance of the composites.