Fig.1 displays the results of pin on disk wear test for Fe-based metallic glass coating layers manufactured via the thermal sprayprocesses. First, with respect to the results obtained from 49.00N wear load, the average coefficient of frictions values are plasma:0.224; HVOF:0.304 and VPS:0.351. The coefficient of friction was found to be the lowest for the plasma material, and the highest for the VPS coating layers. The coefficient of friction of the plasma material was found to be almost constant with increasing wear distance. However, in the HVOF and VPS materials, the coefficient of friction was grad-ually increased and then decreased with increase in the wear distance. It is well known that the coefficient of friction decreases in abrasive materials mainly due to contact area increase and solid lubrication effect.
Fig.1. Pin on disk wear results of thermal sprayed Fe based metallic glass coating layers;(a) friction coefficients,(b) wear volumes of substrate and coating layers.
The wear volumes of the substrate under different load conditions could be obtained as 31.36 N:2.602 mm3,49.00 N:5.962 mm3 and 68.6N:8.244 mm3, showing a regular characteristic that wear volume gradually rises with increase in load. The wear volume of plasma material was 31.36 N:0.476 mm3,49.00 N:0.676 mm3 and 69.60 N: 0.708 mm3. The plasma material was found to have 5.46 (31.36N)~11.64(68.60 N) times better wear resistance than the substrate. The wear volume of HVOF material was 31.36 N:0.045 mm3,49.00 N:0.048 mm3 and 68.60 N:0.124 mm3, demonstrating that wear resistance was 57.82(31.36N)~66.48(68.60 N) times better than the substrate and 10.48(31.36 N)～5.70(68.6 N) times more superior than the plasma material. The VPS material had wear volume by load as strong as 31.36 N:0.019 mm3,39.20 N:0.020 mm3 and 49.00 N:0.022 mm3, demonstrating that the material had the most excellent wear resistance property. The wear resistance of the VPS material was max.271(49.00N) times more excellent than the substrate,30.72 times(49.00 N) than the plasma material, and 2.18 times(49.00 N) than the HVOF.
In order to identify the wear mechanism of the thermally sprayed Fe-based metallic glass coating layers, the worn-out surface (49.00N) was observed macroscopically and the results are shown in Fig.2.The plasma material showed very rough surface in the wear track and the generation of adhesive wear. In addition, after abrasion, it was observed to have black phase areas in localized areas, which was not seen in the initial microstructure. The worn-out surfaces of HVOF andVPS materials had both abrasive wear and adhesive wear behaviors. Additionally, black phase area existed as island types on the worn-out surface. This black phase area, in particular, was created more coarsely in the VPS coating layers than in other materials.
Fig.2. Macroscopic worn-out surface images of thermal sprayed Fe based metallic glass coating layers at 49.00 N wear condition;(a) Plasma,(b) HVOF,(c) VPS.
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