Cavitation and grain growth during superplastic forming

Purpose: The purpose of the paper is to study the cavitation and grain growth during superplastic forming. Design/methodology/approach: Superplastic alloys exhibit the extremely large elongation to failure by their high strain rate sensitivity. Cavities have widely been observed during superplastic deformation of metals and alloys and lead to the degradation of material properties such as tensile, creep, fatigue and stress-corrosion behavior. In this work, a finite element method is developed, which considers the grain growth and the effect of material damage. Findings: The effects of material parameters and deformation damage on the superplastic deformation process are numerically analyzed, and the means to control cavitation growth is discussed. The microstructural mechanism of grain growth during superplastic deformation is also studied. A new model considering the grain growth is proposed and applied to conventional superplastic materials The relationships between the strain, the strain rate, the test temperature, the initial grain size and the grain growth respectively in superplastic materials are discussed. Practical implications: The effect of variation of strain rate sensitivity (m value) on the strain limit of the superplastic deformation is investigated, and the theoretically calculated values are compared with the experimental results. Originality/value: A new microstructure model based on the microstructural mechanism of superplastic deformation has been proposed. This model has been successfully applied to analyze conventional superplastic materials.