Analysis of stress state and crack initiation time around hard-brittle particles in nickel-based alloys by interface model

Abstract

The finite element method was used to simulate the stress distribution around hard-brittle particles with different particle-matrix interface states in nickel-based alloy with different sample thicknesses under 760 ℃/357 MPa and 980 ℃/250 MPa. The cohesive interface model was used to simulate different particle-matrix interface states. The effects of particle-matrix interface states, geometric characteristics of particles, particle positions in the sample, matrix orientation, and other factors on stress distribution were summarized. Through a thorough analysis of the stress distribution surrounding the particles, the crack initiation time was calculated. The results showed that the maximum stress around the particles was greater when the interface was in completely de-bonded CD state (no binding force between particles and the matrix) compared to the completely bonded CB state (completely coherent between particle and matrix). Furthermore, when the interface was CD, the larger the aspect ratio of the particles, and the closer they were to the surface of the sample, the greater the maximum stress around the particles. When the interface stiffness was reduced (due to mismatch or damage), the stress distribution did not change significantly under high interface stiffness conditions. However, when the interface stiffness decreased to a certain extent, the maximum stress value rapidly increased. In addition, the stress concentration factor began to change when the ratio of sample thickness to particle size (ξ) was less than 5. When the interfacial bonding was weak (with low interface stiffness), the crack initiation time around particles with large aspect ratio decreased significantly with the decrease of interface stiffness. Compared with the condition of 760℃/357 MPa (the same ratio of load to yield strength at 980℃), the crack initiation time around the particle was shorter at 980℃/250 MPa, and the influence of particle geometric features was smaller.