Effect of crystallization on the macro and micro residual stress of enamel coating

In this paper, we investigate microstructural and mechanical properties of enamel coating after different heat treatment periods. The results show that the refractory BaAl₂Si₂O₈, CaAl₂Si₂O₈ and MgCr₂O₄ crystals precipitate from parent enamel, and crystallization volume fraction reaches saturation at 40 % after heat treatment 32 h. Moreover, from the experimental and theoretical analysis of residual stress, the macro and micro compressive residual stresses increase with increasing the crystallized volume fraction. And, the continuous macro compressive residual stress and small-scale microstructure inhomogeneities could significantly lead to the shear stress concentration near the enamel coating surface, which results in the typical fish-scaling failure of enamel. Meanwhile, we also find that a slit method with geometric phase analysis (GPA) under focused ion beam scanning electron microscopy (FIB/SEM) system could more reliably characterize residual stress of enamel coating because of phase transformation than traditional X-ray diffraction (XRD) method.