Effect of gradient microstructure on wear behavior of carbon steel

Ultrasonic impact treatment (UIT) fabricated a gradient microstructure surface layer on carbon steel. The microstructural features were characterized by scanning electron microscopy, electron backscatter diffraction, and x-ray diffraction; the microhardness and wear behavior of the gradient microstructure surface were also studied. Results showed that an approximately 250 ?m thick gradient microstructure was clearly observed, with low-angle grain boundaries and strong ?111? texture. The microhardness exhibited a gradient change of a depth of 269 HV in the top surface layer to 160 HV in the matrix. The wear mechanism changed from abrasive to fatigue wear when the sliding speed increased from 10 mm s(?1) to 30 mm s(?1). Under sliding speeds of 10 mm s(?1) and 20 mm s(?1), better wear resistance was attributable to the formation of oxides on the gradient microstructure surface. However, under the high speed of 30 mm s(?1), the gradient layer exhibited a high friction coefficient and wear rate.