Role of crystallization on the thermomechanical behavior of enamels used for automotive application

Abstract

The in-situ microstructure evolution of a standard black enamel and the stress evolution during thermal treatments are investigated through the deposition of the enamel on a model, inert Si substrate. The sintering of the glass frit by viscous flow results in the formation of pores. The crystallization of the glass frit constituting the enamel has been observed to affect the rheological properties of the enamel, increasing its relative viscosity, and leading to an increase in the stress regeneration temperature during cooling. It was observed that an increase in elastic stress in the enamel during cooling, due to a thermal expansion mismatch between the enamel and the substrate, resulted in the initiation and propagation of cracks when tensile stress reached 170 MPa. It was found that viscous flow at high temperatures during subsequent thermal cycles promotes self-healing of previously formed cracks.