Wear on tool steel AISI M2, D6 and 52100 coated with Al2O3 by the MOCVD process

Present work investigates the wear resistance of tool steels and 52100 steel coated with Al2O3 by MOCVD process. The wear tests by sliding and abrasion were performed in a pin-on-disk and ball-on-disk apparatus whose pin and ball substrates were steels fabricated from AISI M2, D6 and 52100. The MOCVD coating processes were carried out in a research laboratory apparatus at 200 °C under N2 + O2 atmosphere. The counterface disks were ABNT 1008 steel sheet used in the brazilian fridge industry. The wear resistances of the coated tool steels were evaluated trough the pin-on-disk test, using a sliding velocity 0.6 m/s, normal loads of 20 and 30 N, total sliding distance of 2400 m and controlled conditions of temperature and humidity. The pin and ball material substrate were quenched and tempered, and the disks were tested as received. From the plotted graphs of lost volume versus sliding distance, it was observed that occurred a greater wear rate of AISI D6 pins without coating, this is possibly due to more severe adhesion and delamination mechanisms. The AISI M2 and D6 pin coated with Al2O3 showed similar wear resistance and higher resistance than the uncoated D6 pin. However, the tested sphere of AISI 52100 showed different behaviour under 20 N normal load. For both sphere coated with Al2O3 and uncoated the wear rate were similar. From microscopy observations, in order to have accurate measures of ball wear rate, it is proposed a new method to measure wear resistance of ball and pin in the pin-on-disk tests: wear can be measured by the wear track width or area left on the ball tip. The graphs of track width versus sliding distance are shown and the curves for tested material and coating are compared. Pin and ball lower lost volume rate and wear track width with sliding distance is related to greater surface hardness after heat treatment and the coating process. Nitrided M2 and D6 tool steels coated with Al2O3 showed superior wear resistance characteristics for cold working tooling. The spheres of AISI 52100 coated with Al2O3 presented poor wear resistance due to surface defects.