Research On Micro-comperssive Size Effect Mechansim Of GH4169 Nickel-based Superalloy

Plastic micro-forming is widely used to process metal micro-parts because of its high processing efficiency,high precision and low production cost.Nickel-based superalloy,as the main materials used in aerospace turbine discs and other parts,have broad application prospects.The miniaturization of aerospace products is developing rapidly,but with the reduction of the characteristic size of products in twodimensional direction to sub-millimeter level,the theory of macro-forming process of materials can not be fully applied to micro-forming,and the phenomenon of size effect appears in materials.It is important to study the size effect in plastic microforming for the development of micro-forming.In this paper,the GH4169 nickel-based superalloy in solid solution state and aging state with ? phase were obtained by different heat treatment systems.Microcompression experiments were carried out on micro-cylinders.The effects of grain size,ratio of sample size to grain size,content and morphology of delta phase on flow stress and inhomogeneous deformation during plastic deformation were analyzed,and polycrystalline materials under different conditions were constructed.A theoretical model of flow stress size effect of polycrystalline materials in different states is constructed,and the mechanism of size effect of materials in different states is revealed.Finally,based on the finite element simulation of crystal plasticity theory,the grain evolution during micro-compression is visualized,and the mechanism of inhomogeneous deformation is revealed.The results of micro-compression experiments of solid solution GH4169 alloy show that the flow stress decreases with the increase of grain size.When the ratio of sample size to grain size is less than 9.7,the flow stress does not decrease but increases.The strain hardening behavior during micro-compression can be divided into three stages.The proportion of three strain zones varies with the increase of grain size and a theoretical model of the size effect of flow stress on mesoscopic scale is constructed.With the increase of aging heat treatment time,the content of ? phase increases,the morphology changes from granular to acicular,and the distribution changes from grain boundary to grain boundary and within grain.The results of micro-compression experiments of GH4169 alloy with ? phase which was be aged show that the flow stress increases with the increase of ? phase content at the same grain size.Considering the influence of grain size and content of delta phase on flow stress,a theoretical model of flow stress size effect for mesoscopic materials containing delta phase was established.After deformation,the specimen is divided into three deformation zones according to the strain distribution,and the flow law is the same as that during macro unidirectional compression.The existence of ? phase reduces the grain deformation.The inhomogeneous deformation of the sample occurs,and the surface roughness of the sample increases with the decrease of the ratio of sample size to grain size.With the increase of the content of the ? phase,the surface roughness of the sample decreases.The micro-compression deformation of GH4169 alloy was simulated by crystal plastic finite element method.The strain incompatibility between grains increased,and the strain distribution and grain deformation were not uniform,which was in agreement with the experimental results.