Simulating the evolution of non-metallic inclusions during the forging process

Radial forging of metallic materials requires both high temperatures and large plastic deformation. During this process, non-metallic inclusions (NMIs) can debond from the metallic matrix and break apart, resulting in a linear array of smaller inclusions, known as stringers. The evolution of NMIs into stringers can result in matrix load shedding, localized plasticity, and stress concentrations near the matrix-NMI interface. Due to these factors, stringers can be detrimental to the fatigue life of the final forged component, especially when present near a free surface. By performing a finite element model of the forging process with cohesive zones to simulate material debonding, we contribute to the understanding of processing induced deformation and damage sequences on the onset of stringer formation for both Type 1 and Type 2 alumina NMIs in a Ni-200 matrix. Through a parametric study, the interactions of forging temperature, strain rate, strain per pass, and interfacial decohesion on the NMI damage evolution metrics are studied, specifically NMI particle separation, rotation, and cavity formation. For Type 2 alumina NMIs, embedded in a Ni-200 matrix, the simulations indicate that at temperatures below 800 °C, particle separation dominates the NMI damage sequences, whereas at temperatures between 900 °C - 1000 °C, below an interfacial bond strength of 178 MPa, cavity formation is the dominate damage evolution mechanism, resulting in matrix load shedding and stress concentrations around the NMI.