STUDY ON THE EVOLUTION OF GEOMETRICALLY NECESSARY DISLOCATION IN PARTICLE-REINFORCED METAL-MATRIX CO

• 作 者: Dongfeng Cao Hai Mei Lisheng Liu Xin Lai
• 机 构: StateKeyLaboratoryofMaterialsSynthesisandProcessingWuhanUniversityofTechnologySchoolofScienceWuhanUn
• 出 处: International Conference on Science and Technology of Hetero
• 发表日期: 2013年10期
• 关键词: Geometrically necessary dislocations Strain gradient Metal-matrix Size-dependenc

　　Ceramic particle-reinforced metal-matrix composites (MMCp) exhibit strong size effect due to the development of geometrically necessary dislocations (GND), when the characteristic length scale associated with non-uniform plastic deformation is on the order of microns.Such size-dependent response is commonly attributed to the density of geometrically necessary dislocations (GNDs), which represents an extra storage of dislocations required to accommodate the lattice curvature and contribute to the work hardening of the matrix material.At present, crystal plasticity theories, strain gradient theories and discrete dislocation theories can capture such size effect.But almost all of these theories are based on this assumption that GNDs have no upper limit and can increase infinitely.In reality, the GND density cannot be very large, and never exceed a maximum allowable GND density, since the strong repulsive forces between GNDs push dislocations to spread.The nano-indentation experiments have confirmed that once the indentation depth reaches the order of nanometers, the conventional accumulation way of GNDs is invalid.Huang et.al (Huang Y, Zhang F, Hwang KC, Nix WD, Pharr GM, Feng G.J Mech Phys Solids 2006;54:1668.) introduced the maximum allowable GND density max to capture the GND density by a piecewise analytic model based on the nano-indentation experiments.Based on the maximum allowable GND density, the flow stress based on Taylor hardening law can be modified as Eq.(1).