Selected Topics on Material Strength and Thermally Activated Deformation Processes

Abstract

Thermally activated deformation processes are discussed with reference to the studies done by the present author and his coworkers. First, dislocation motion in one-and two-dimensional periodic stress fields is analyzed to understand the deformation mechanisms of bcc metals and spinodally decomposed alloys. The role of the thermally activated kink-pair formation on the temperature and strain-rate dependence of strength is also discussed. Secondly, diffusion-controlled processes pertinent to high-temperature deformation are discussed by applying a unified and fundamental rate equation derived previously. Thirdly, mechanisms for the temperature and strain-rate dependence of polycrystals and ultrafinegrained and nanocrystalline materials are introduced. A proposed model taking into account the thermally activated dislocation depinning at grain boundaries is discussed.

Thermal Shock Life Prediction of the SiC Wide Bandgap Power Module Semiconductor Package Considering Creep Behavior of the Ag Sintered Interconnect and Viscoelastic Properties of the Epoxy Molding Compound

“…The homologous temperature is determined by the melting point of the material, and there is a literature that time-dependent plasticity such as the creep dominates at temperatures above 50% of the melting temperature. , However, the room temperature is only 34% of homologous temperature of silver (note that the melting point of the silver is 961 °C, 1234 K), and the effect of creep is supposed to be relatively small, contrarily to the experimental result (Figure d). Several papers explain that sintered Ag shows a significant creep behavior at room temperature due to its coble creep mechanism. , Coble creep is a type of diffusion creep (i.e., dislocation creep, Nabarro–Herring creep, Coble creep, etc. ), in which the atoms diffuse outside the grain boundary. , In Coble creep, the creep rate varies inversely with the cube of the grain size, the smaller the grain size, the greater the effect of coble creep as shown in eq , ε̇ = ADGb kT ( δ b ) ( σ G ) true( b d true) 3 where A is the dimensionless coefficient, which is dependent on the geometry of grains, D is the diffusion coefficient at grain boundary, G is the shear modulus, b is the Burgers vector, k is the Boltzmann constant, T is the absolute temperature, δ represents the effective grain boundary thickness, σ is the applied stress, and d is the grain size of the materials.…”

“…Several papers explain that sintered Ag shows a significant creep behavior at room temperature due to its coble creep mechanism. 50,51 Coble creep is a type of diffusion creep (i.e., dislocation creep, Nabarro−Herring creep, Coble creep, etc. ), in which the atoms diffuse outside the grain boundary.…”

Atomic Scale Simulations of Relationship between Macroscopic Mechanical Properties and Microscopic Defect Evolution in Ultrafine-grained Metals

“…3, the critical stress for the defect nucleation from GB should show grain size dependence. Kato and Wang proposed a thermally activated dislocation process [28][29][30] , where deformation of UFG metals was determined by the depinning and bow-out process of dislocations at GB. According to this model, although our simulation was performed at 0 K, grain size dependence in Fig.…”