Friction and wear behavior of laser cladding Ni/hBN self-lubricating composite coating

Ni/hBN coating was successfully prepared on 1Cr18Ni9Ti stainless steel substrate by means of laser cladding. The microhardness profile of the composite coating along the depth direction was measured, while its cross-sectional microstructures and phase compositions were analyzed by means of scanning electron microscopy and X-ray diffraction. Moreover, the friction and wear behavior of the composite coatings sliding against Si3N4 from ambient to 800 degrees C was evaluated using a ball-on-disc friction and wear tester, and the worn surface morphologies of the composite coatings and counterpart ceramic balls were observed using a scanning electron microscope. At the same time, the worn surfaces of the ceramic balls were also analyzed using a 3D non-contact surface mapping profiler as well. It was found that the laser cladding Ni/hBN coating on the stainless steel substrate had high microhardness and good friction-reducing and antiwear abilities at elevated temperatures up to 800 degrees C. The composite coating registered slightly increased friction coefficient and wear rate as the temperature rose from ambient to 100 degrees C then the friction coefficient and wear rate decreased with increasing temperature up to 800 degrees C (with the slight increase in the wear rate at 700 degrees C and 800 degrees C to be an exception). The laser cladding Ni/hBN coating was dominated by mixed adhesion and abrasive wear as it slid against the ceramic ball below 300 degrees C. With further increase in the test temperature up to 400 degrees C and above, it was characterized by mild adhesion wear and plastic deformation. Since the laser cladding Ni/hBN coating registered an increased wear rate at temperatures of 600 degrees C and above, it was not suggested to be used for wear prevention and protection of the stainless steel at elevated temperature above 800 degrees C. (C) 2007 Elsevier B.V. All rights reserved.