Pei-Qiang Wu

Electrochemical noise measurements on stainless steel during corrosion-wear in sliding contacts

Abstract In this study, electrochemical noise measurements performed during corrosion–wear sliding tests with the working electrode coupled to a microelectrode, are presented. A microelectrode was used to record during fretting experiments current variations resulting from a modification of the working electrode induced by sliding. The tribocorrosion system investigated consists of an AISI 304 stainless steel plate sliding in a reciprocating mode against a corundum ball, both immersed in electrolytes of different pH. A detailed discussion of the in situ electrochemical noise measurements demonstrates that they are useful to identify and/or to unravel materials modification processes taking place during corrosion–wear sliding tests on passivating materials.

Tribological behavior of plasma Mo–N surface modified Ti–6Al–4V alloy

Abstract A Mo–N surface modified layer on Ti–6Al–4V alloy was obtained using a plasma surface alloying technique. A comparison of the tribological behavior of untreated and plasma Mo–N modified Ti–6Al–4V alloy has been made in this study. Results show that the Mo–N modified layer with a single Mo2N phase significantly improves the tribological behavior of the treated Ti–6Al–4V alloy under oscillation sliding wear in ambient air. The Mo–N surface modified layer not only reduces the coefficient of friction, but also decreases the wear of Ti–6Al–4V alloy and prevents the first bodies from sticking at the contacting points.

Hybrid processes — a versatile technique to match process requirements and coating needs

Abstract The properties of thin hard coatings and consequently their functionality are influenced by microstructural characteristics such as phase composition and grain size distribution. Recent studies indicate that microlaminated hybrid coatings offer an opportunity to establish unique and controllable microstructural characteristics. A variety of interlayers has been used in hybrid coatings for various purposes: (1) to enhance the adherence between coatings and substrates, (2) to prevent crack initiation, (3) to give good shock resistance, (4) to tailor the thermal expansion characteristics, which leads to good interfacial strength, (5) to prevent diffusion of substrate species into coatings or vice versa during annealing, (6) to enhance corrosion protection of coating and substrate, and (7) to enhance sliding wear resistance or lower sliding friction. In order to obtain the above mentioned properties, various surface modification techniques such as (1) electrodeposition, (2) thermal treatment, (3) ion plating, (4) ion implantation, and (5) sputtering can be used to prepare hybrid coatings. This review includes a discussion on surface modification techniques and properties of different hybrid coatings.

Comparison of fretting wear of uncoated and PVD TiN coated high-speed steel under different testing conditions

Katholieke Univ Leuven, Dept Met & Mat Engn, B-3001 Louvain, Belgium. WTCM, B-3590 Diepenbeek, Belgium. Limburgs Univ Ctr, IMO, B-3590 Diepenbeek, Belgium.Wu, PQ, Katholieke Univ Leuven, Dept Met & Mat Engn, de Croylaan 2, B-3001 Louvain, Belgium.

Comparison of wear and corrosion wear of TiN coatings under uni- and bidirectional sliding

Katholieke Univ Leuven, Dept Met & Mat Engn, B-3001 Louvain, Belgium. Limburgs Univ Ctr, Inst Mat Res, Div Mat Phys, B-3590 Diepenbeek, Belgium.Wu, PQ, Katholieke Univ Leuven, Dept Met & Mat Engn, De Croylaan 2, B-3001 Louvain, Belgium.

The fretting behaviour of PVD TiN coatings in aqueous solutions

The friction and wear of physical vapour deposition TiN coatings and steel vibrating against corundum in distilled water, seawater, and sodium phosphate solutions have been investigated. The coefficient of friction measured on the TiN-coated surface remained at a level of around 0.2 whereas the uncoated steel substrate exhibited a significantly higher friction. The TiN coating appeared to degrade by oxidational wear. The progress of the wear damage was largely influenced by the transfer layer of titanium oxides formed on the corundum counterbody. The narrow transfer layer formed in distilled water caused a premature perforation of the TiN coating due to the reduction of the real contact area. The results showed that this unfavourable wear behaviour can be avoided by adding sodium phosphate to distilled water resulting in an accelerated removal of the transfer layer.

Comparison of fretting wear of Cr-rich CrN and TiN coatings in air of different relative humidities

Abstract The CrN and TiN coatings deposited on tool steel substrates by ion beam assisted deposition (IBAD) and triode ion-plating techniques, respectively, were investigated. The fretting wear of these coatings has been determined in air of different relative humidities (RHs). The results show that the coefficient of friction of the CrN coatings versus corundum at 50 and 85% RH is about 0.3, slightly higher than that of the TiN coatings. However, the TiN coatings exhibit a high coefficient of friction of about 0.8 at RH

Lubricating reaction products on TiN coatings during sliding wear in phosphoric acid

Abstract The debris structure influences the tribological behaviour of TiN coatings sliding against corundum. During sliding wear in environmental air, self-lubricating debris can be generated depending on the conditions. The (micro)structure of the debris varies with the relative humidity, temperature, mechanical attrition and temperature. In this paper, the wear rate and the friction of TiN coatings are compared with uncoated tool steel substrates sliding against corundum in: humid air, demineralised water, and phosphoric acid (0.02 M H 3 PO 4 ). Differences in the tribological behaviour are explained in terms of the interaction with the environment. In phosphoric acid, TiN coatings sliding against corundum show very low friction forces and wear rates due to the formation of a lubricating gel.

Ion Conduction Model Applied to Repassivation Kinetics of Tribo-Activated Surfaces

Repassivation kinetics of wear scars on AISI 304 stainless steel immersed in sodium chloride and sodium phosphate solutions are studied by electrochemical noise and potentiostatic techniques. The classical high-field ion conduction model is used to quantify the repassivation kinetics of tribo-activated stainless steel surfaces under potentiostatic conditions. A modified ion conduction model is proposed to quantify the repassivation kinetics at open-circuit potential. This model provides a unique approach to investigate potential and current transients with charge density in freshly generated wear scars, and to derive the parameters of the repassivation kinetics of wear scars.