Increasing Wear Resistance of Titanium Alloys by Anode Plasma Electrolytic Saturation with Interstitial Elements
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JMEPEG (2017) 26:2404–2410 DOI: 10.1007/s11665-017-2655-1
Increasing Wear Resistance of Titanium Alloys by Anode Plasma Electrolytic Saturation with Interstitial Elements P.N. Belkin, S.A. Kusmanov, I.G. Dyakov, S.A. Silkin, and A.A. Smirnov (Submitted October 20, 2016; in revised form March 6, 2017; published online April 10, 2017) In our previous studies, we have shown that anode plasma electrolytic saturation of titanium alloys with nitrogen and carbon can improve their tribological properties. Obtained structure containing oxide layer and solid solution of diffused element in titanium promotes the enhancement of running-in ability and the decrease in the wear rate in some special cases. In this paper, further investigations are reported regarding the tribological properties of alpha- and beta-titanium alloys in wear test against hardened steel (50 HRC) disk using pin-on-disk geometry and balls of Al2O3 (6.25 mm in diameter) or bearing steel (9.6 mm in diameter) with ball-on-plate one and normal load from 5 to 209 N. Reproducible results were obtained under testing samples treated by means of the plasma electrolytic nitriding (PEN) with the mechanical removal of the oxide layer. Friction coefficient of nitrided samples is 0.5-0.9 which is somewhat higher than that for untreated one (0.48-0.75) during dry sliding against Al2O3 ball. An increase in the sliding speed results in the polishing of nitrided samples and reduction of their wear rate by 60 times. This result is obtained for 5 min at 850 °C using PEN in electrolyte containing 5 wt.% ammonia and 10 wt.% ammonium chloride followed by quenching in solution. Optical microscope was employed to assist in the evaluation of the wear behavior. Sizes of wear tracks were measured by profilometer TR200. Keywords
carburizing, friction coefficient, nitriding, plasma electrolysis, titanium alloys, wear rate
1. Introduction PES of metals and alloys with interstitial elements arouses much interest because of its advantages (Ref 1, 2). Workpieces do not require preconditioning. Continuous motion of the medium in vapor-gaseous envelope (VGE) provides rapid supply of saturating components to workpieces and removal of reaction products. Owing to small VGE thickness, high workpiece heating rates (up to 100 °/s) can be reached owing to small VGE thickness which avoids grain growth and associated deterioration of materialÕs properties. In addition, small VGE thickness contributes to rapid stabilization of processing conditions as the equilibrium concentration of adsorbed carbon is reached within several seconds (Ref 3). As a result, processing time is reduced to several minutes. It is established that wear resistance of steel or cast iron can be enhanced using PEN (Ref 4), carburizing (PEC) for lowallow steel AISI H13 (Ref 5), nitrocarburizing (PEN/C) for low-carbon steel (Ref 6) or borocarburizing (PEB/C) (Ref 7). The PEN/C of AISI 304 stainless steel with diamond-like carbon coating is noteworthy (Ref 8). The processes of PEN, PEC, and PEB of titanium alloys are also shown to in
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