On the other hand, there was an obvious trend of increasing microhardness of all coatings with sputtering time elongation, being the highest for 3-hour sputtering time, decreasing with sputtering time reduction, which might be explained by a widely accepted physical phenomenon, and sputtering time has a directly proportional relation with the coating thickness, supported by our findings elsewhere [ 23 ]; therefore, the improvement of surface microhardness of all coatings with sputtering time prolongation was seen in the present study, which coincided with Zhang et al.
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