Effects of Topography and Modified Layer by Plasma-Shot Treatment on High-Speed Steel

In this study, plasma shot (PS) treatment was applied to high-speed steel (HSS) surfaces using a titanium carbide electrode to confirm the effect of discharge current (I_p) on the formation of a single dimple and analyze a modified layer. The roughness of modified surfaces increased when I_p increased, and energy-dispersive X-ray spectrometry showed an increase in titanium atom density when I_p and electrode consumption volume (V_e) increased. A friction test confirmed that the modified surface’s friction was reduced by discharge dimples under low-load conditions. Vickers hardness test confirmed that the hardness of the modified surface was ~ 300–600 HV higher than that of an untreated HSS surface. Moreover, it increased with an increase in I_p. However, application of PS treatment to the edge of surfaces on the workpiece caused shape deterioration. The deterioration size of the edge of the modified layer increased when I_p increased. To solve this issue, we propose a novel method named position-adjusted PS (PA-PS) treatment. PA-PS treatment is used to adjust the end of the electrode in the order of tens of micrometers from the edge of the workpiece to avoid the deterioration of the edge form. Under I_p = 21 A, PA-PS formed a modified layer without deteriorating the edge shape of the workpiece, thus confirming the PS characteristics applied to HSS surfaces. Moreover, PA-PS treatment solved the shape deterioration of the edge on modified surfaces via PS treatment.