Micromechanism of strength and damage trade-off in second-phase reinforced alloy by strain gradient plasticity theory

The strength and damage are mutually exclusive in most alloys. It is still a challenge to understand the role of microstructural features in affecting strength and damage tolerance simultaneously. In this study, we provide a general approach to unveil the micromechanism of strength and damage trade-off in second-phase reinforced alloy. Concretely, a microstructure-based constitutive model incorporating the strain gradient plasticity theory is developed to evaluate the overall mechanical behavior and local deformation behavior of particle-reinforced alloys by finite element simulations. The strain gradient effect exacerbates the non-uniform stress distribution, particularly enhancing the local stress level around the particle-matrix interface, thereby improving the total strain hardening of the alloys. Importantly, the strain gradient effect can significantly expand regions with local stress levels surpassing the critical stress for microcrack nucleation, ultimately leading to damage initiation and failure. This elucidates the micromechanism underpinning the trade-off between strength and damage. By revealing the competitive relationship between local stress concentration and microcrack nucleation stress, the comprehensive effects of particle size and volume fraction on the strength, strain hardening and damage tolerance are quantitatively predicted. It is recommended to adjust the particle volume fraction based on reducing the particle size to obtain the desired properties. The present work discerns the inherent origin of the strength-damage trade-off in particle-reinforced alloy and sheds light on the role of the particle size and volume fraction on the strength and damage tolerance, which can offer valuable guidance for developing high-performance particle-reinforced materials.