The influence of acting mode of current on structure and mechanical properties of Ni-nanoTiN composite coatings

Abstract

Abstract. Ni-nanoTiN composite coatings were electrode posited on 45 steel substrate by using the ultrasonic-electrode position for nickel sulfamate bath. The effects of direct current, positive pulse current, reverse (positive and negative) pulse on surface morphology, binding force, micro hardness, friction and wear performance of Ni-nanoTiN composite coating. The results show that the micro hardness is 322.68 HV 0.1 , the critical load of binding force is 25N, bigger cracks, rough surface, coarse grains and bad wearing of coating when direct current deposition; the micro hardness is 371.74 HV 0.1 , the critical load of binding force is 40N, smaller cracks, smooth surface, relatively small grain, better friction and wear performance of coating when positive current deposition; the micro hardness is 494.18 HV 0.1 , the critical load of binding force is over 50N, non cracks, more smooth surface, tiny grains, best friction and wear performance of coating when positive and negative pulse deposition. Positive and negative pulse deposition may further refine grain, improve surface morphology, increase nanoTiN particles co-deposition and enhance mechanical properties of composite coating.