Formation Mechanism Of Stacking Faults In SiC_nw/Al Composites And It's Interaction With Dislocations

The addition of reinforcement to aluminum matrix can greatly improve its strength,but inevitably leads to plastic deterioration.As a result,aluminum matrix composites own high strength and plasticity simultaneously have always been one of the hot topics.Recent studies have found that the introduction of some surface defects,such as Stacking Faults or micro-twins,can change the deformation behavior of aluminum to a certain extent,and enhance the strength and plasticity at the same time.However,currently,the introduction of Stacking Faults or twin crystals in aluminum mostly occurs in nanocrystals or nano-film,and it has not been reported in large bulk materials.Base on our research group's many years of experience on Al matrix composite materials research,this article put forward a technical route: with the help of SiC nanowires,three-dimensional nano-spaces were constructed,then filled with Al liquid to form Al matrix composite material,the mismatch of Si C nanowires and Al matrix in thermal expansion coefficient will generates residual thermal stress,which can induce the formation of Stacking Faults or twin.In the prepared composites,we found the existence of a large number of dislocations and micro twins,meanwhile,the composites showed excellent mechanical properties.this result provides a new idea for composites reinforcement and introducing Stacking Faults or twins into Al.In this paper,30 vol.%SiC_nw/Al composites were prepared by pressure impregnation method,stress homogenization and three-directions constraint deformation treatment were carried out to obtain more excellent mechanical property.In this paper,the distribution of residual stress in the matrix of composite materials was simulated based on ANSYS finite element simulation platform.Found these: The narrower the nanowire distance mean the greater the residual stress;with the increase of distance from the interface,the stress decreases gradually;stress concentration is more likely to occur at the tip.Some phenomena were observed in experiments: only in SiC_nw/Al composites with high volume fraction Stacking Faults could be observed;The farther it is from the interface,the narrower the width of the Stacking Faults is;"Bamboo-like" nanowires were more likely to induce Stacking Faults.These phenomena were in perfect agreement with simulation results,thus confirming that Stacking Faults in aluminum matrix was induced by residual stress.Through the research on composites microstructure and interface stress state,this article revealed the formation mechanism of Stacking Faults in composite matrix under such a technical route.With the help of molecular dynamics simulation,the relationship between residual stress level in the Al,the Generalized Stacking Faults Energy?GSFE?and expand behavior of full dislocations were built.Besides,the process of Stacking Faults formation was reproduced.The results of microstructure research showed that the tensile stress wich perpendicular to the packed plane could reduce the stable Stacking Faults energy??SF?of Al to some extent,and enlarge the difference between stable Stacking Faults energy and unstable Stacking Faults energy??USF?,thus creating conditions for the occurrence and stable existence of Stacking Faults.It was found that the width of the Stacking Faults in the matrix increased with the decrease of the nanowire spacing and the distance from the interface,which was consistent with the variation trend of the residual thermal stress.In the study on mechanical properties and strengthening mechanism of composites,the interaction between Stacking Faults and dislocations,and the motion characteristics of Stacking Faults are studied by molecular dynamics,the mechanism of Stacking Faults reinforcement is summarized.The reinforcement of Al matrix by Stacking Fault is mainly achieved by hindering the movement of the dislocations and forcing the dislocations to change their original slip direction.The "absorption" effect of Stacking Faults to the dislocations also largely avoids the dislocations plug and stress concentration,thus improved the ability to proceed plastic deformation.In addition,the Stacking Faults formed by dislocations expansion also changed the motion characteristics of dislocation itself,making it more difficult to occur cross-slip.Taking these factors into consideration,the existence of Stacking Faults can indeed realize the synchronous enhancement of plasticity and strength of aluminum matrix.In this paper,a large number of Stacking Faults with width >10nm were introduced into large-size block Al through a simple process.We found that the residual stress or lattice strain can change the full dislocations expansion behavior in the crystal by affecting the Generalized Stacking Faults Energy of aluminum,the consistency of experimental and theoretical simulation well reveals the influence of stress on the Generalized Stacking Faults Energy?GSFE?.