Mechanism in scratching of calcium fluoride with magneto-plasticity

Abstract

Magnetic field-tuned dislocation plasticity (i.e., magneto-plasticity) has attracted growing attention for assistance to limit the damage evolution of brittle ceramics in the material removal process. However, the mechanism controlling material removal of brittle ceramics with magneto-plasticity remains far from clear. Therefore, combined stress field modeling and molecular dynamics (MD) simulations were performed for scratching of a ceramic material, calcium fluoride (CaF2), to investigate the magneto-plasticity mechanism during the material removal process of brittle ceramics. The stress field calculation with magneto-plasticity was first conducted, which suggests a general reduction in scratching stress on the subsurface under the magnetic field effect. It is also found that the degree of reduction in scratching stress is significantly influenced by the magnetic field intensity and direction as well as strain rate. The reduced scratching stress is responsible for the suppressed formation and evolution of cracks and defects in scratching. Subsequently, MD simulations in scratching of CaF2 show that the application of a magnetic field can facilitate dislocation nucleation, enlarge the range of dislocation propagation, and regularize the dislocation distribution, indicating the advancement in elastic-plastic transition and dislocation mobility. From the views of energy criterion and crystal plasticity, a magnetic field can decrease the required work and resolved shear stress for dislocation slip, which results in a lower scratching stress level. The combined theoretical method of this study broadens the comprehension of magneto-plasticity on deformation mechanism in the material removal process of ceramics and offers theoretical direction for the application of magnetic field assistance in ceramic processing.