Effect of Pressing Amount in High-Temperature Assisted Ultrasonic Deep Rolling on Microstructure and Properties of Cermet Coatings

Abstract

In order to further improve the coating microstructure and properties，a new surface micro-crystallization technique，high temperature assisted ultrasonic deep rolling (HT+UDR)， was used to treat the cermet coating， which could soften the cermet coating by high temperature treatment， thus reducing the strength and hardness of the coating，and large plastic deformation would occur on the coating surface during ultrasonic deep rolling. In this paper， SEM， EDS， hardness test and XRD were used to investigate the effect of different pressing amounts (0.20 mm，0.25 mm，0.30 mm) in high temperature assisted ultrasonic deep rolling on the microstructure，structure and properties of ceramic coating on 45 steel substrate. Results showed that after HT+UDR+0.25 mm treatment， the longitudinal cracks in the coating were closed or transformed into transverse cracks under the action of plastic flow， and the porosity was small. After work hardening and grain refinement， the surface hardness was further increased to 650.2 HV. The residual tensile stress on the coating surface was changed into residual compressive stress，with the maximum value of -337.9 Mpa. However， cracks appeared on the surface layer of the coating after HT+UDR+0.30 mm treatment， and the dynamic recrystallization behavior of the surface was intensified. The decrease of dislocation density led to the release of residual stress， which was 8.67%lower than that of HT+UDR+0.25 mm treatment.

Keywords

• high-temperature assisted|ultrasonic deep rolling|pressing amount|cermet coating