A stress test method of polycrystal 95%Al₂O₃ based on Vickers indentation-induced cracks

Introduction: Polycrystalline alumina is a critical material in the containment of nuclear reactors, and its stress must be evaluated. Objective: The current Vickers fracture residual stress test methods are mainly used for amorphous materials. To realize the preliminary application in engineering practice, exploring suitable stress test methods for polycrystalline alumina and testing the micro-zone stress of 95%Al₂O₃ in 4J33/95%Al₂O₃brazed joints is necessary. Methods: The specimens were loaded with different stress states by pre-stressing tooling, and the stress distribution in the test area was clarified through finite element analysis. Then, Vickers indentation experiments were carried out to count the indentation radius a, the crack length l, and the direction of crack propagation θ. Results: With the crack size not exceeding the grain size and the effects of microstructure (intergranular pores, intragranular pores, and grain boundaries) and crystal orientation on the crack projection length reduced, a model was developed for calculating the relationship between the crack projection length and the pre-stress of polycrystalline alumina at low load indentation in Palmqvist, with a maximum absolute deviation of 23.3 MPa and a maximum relative error of 49.7 %. The microzone stresses on the ceramic side of 4J33/95 % Al₂O₃brazed joints were characterized. Conclusion: The stress detection method based on Vickers indentation cracks proposed in this study provides a new idea for evaluating residual stresses in polycrystalline alumina; however, the universality of this method in polycrystalline alumina with different grain sizes and its applicability in other polycrystalline brittle materials can still be further explored.