In the laser treatment of a workpiece (9), e.g. for surface hardening, melting, alloying, cladding, welding or cutting, the adverse effect of reflectivity of the surface, when a pure, monochromatic laser (6) is used, is remedied by the simultaneous application of a relatively shorter wavelength beam (1). The two beams (1)(5) may be combined by a beam coupler (4) or may reach the workpiece (9) by separate optical paths (not shown). The shorter wavelength beam (1) improves the coupling efficiency of the higher- powered laser beam (5).

Laser Material Processing

Zinc dialkyldithiophosphate additives are used to control wear and inhibit oxidation in almost all engine oils as well as many other types of lubricant. They limit wear primarily by forming a thick, protective, phosphate glass-based tribofilm on rubbing surfaces. This film formation can occur at low temperatures and is relatively indifferent to the chemical nature of the substrate. There has been considerable debate as to what drives ZDDP tribofilm formation, why it occurs only on surfaces that experience sliding and whether film formation is controlled primarily by temperature, pressure, triboemission or some other factor. This paper describes a novel approach to the problem by studying the formation of ZDDP films in full film EHD conditions from two lubricants having very different EHD friction properties. This shows that ZDDP film formation does not require solid–solid rubbing contact but is driven simply by applied shear stress, in accord with a stress-promoted thermal activation model. The shear stress present in a high-pressure contact can reduce the thermal activation energy for ZDDP by at least half, greatly increasing the reaction rate. This mechanism explains the origins of many practically important features of ZDDP films; their topography, their thickness and the conditions under which they form. The insights that this study provides should prove valuable both in optimising ZDDP structure and in modelling ZDDP antiwear behaviour. The findings also highlight the importance of mechanochemistry to the behaviour of lubricant additives in general.

/pdf/on-the-mechanism-of-zddp-antiwear-film-formation-bn0vvu0rhb.pdf

On the Mechanism of ZDDP Antiwear Film Formation

http://home.eps.hw.ac.uk/~ryf1/JMPT-99-231.pdf

Some considerations on the mitigation of fretting damage by the application of surface-modification technologies

Third body effects on friction and wear during fretting of steel contacts

Sputtered MoS 2 thin films provide lubrication and wear improvements for vacuum and space applications. When exposed to humid environments, however, the MoS 2 films are prone to rapid deterioration by oxidation. In this study, we synthesized a composite coating, which consists of titanium metal and solid lubricating MoS 2 layers by the unbalanced magnetron sputtering process. Experimental results indicate that the Ti interlayers among the MoS 2 –Ti composite films effectively enhance the density and stability of the film structure. Transmission electron microscopy, X-ray diffractometry, and Raman analyses reveal the amorphous nature of the MoS 2 –Ti coating, which contains only a short-range order within the Ti interlayers. Ball-on-disc tribotests of the MoS 2 –Ti composite films show a higher friction coefficient, increased wear life and microhardness, and reduced wear debris as Ti interlayers increased in thickness. In addition to its densification and strengthening effect, the Ti interlayer also reacts preferentially with oxygen to form TiO 2 and thus effectively suppresses adverse oxidation of MoS 2 . Thus, in humid environments, the MoS 2 –Ti composite film is highly promising as a solid lubricant, as evidenced by its prolonged wear life and resistance to oxidation.

Microstructural and tribological characterization of MoS2-Ti composite solid lubricating films

Tribological properties of silicon nitride ceramics coated with molybdenum films under boundary lubrication

Slip amplitude effects and microstructural characteristics of surface layers in fretting wear of carbon steel

Fretting wear behaviour of 2Cr13 stainless steel before and after laser treatment

The ion implantation of N + B (3.1 × 10 17 N ions cm -2 at 90 keV followed by 3.2 × 10 17 B ions cm -2 at 90 keV) into GCrl15 bearing steel was carried out. The phase structure and the distribution and binding energy of elements in the implanted layer were investigated using X-ray diffraction, Auger electron spectroscopy and X-ray photoelectron spectroscopy. The dry sliding friction and wear behaviour of the implanted layer and GCr15 bearing steel substrate was also examined in detail using a friction and wear machine. It is found that a surface layer with a lower friction coefficient and a higher wear resistance than the substrate was obtained by implanting N + B into GCr15 bearing steel. Because of dispersion strengthening of the hexagonal BN phase and e-Fe 2 N-Fe 3 N phase and solid solution strengthening of B atoms, the surface hardness of the implanted layer is increased. As a result of the increased hardness and the existence of a graphite-like carbon film on the surface of the implanted layer, the antiadhesive and antiabrasive properties of the implanted layer were considerably enhanced. the friction coefficient was reduced from 0.60 to 0.20 and the wear resistance was also greatly improved.

Zhang Xushou

Papers

Tribological properties of silicon nitride ceramics coated with molybdenum films under boundary lubrication

Slip amplitude effects and microstructural characteristics of surface layers in fretting wear of carbon steel

Fretting wear behaviour of 2Cr13 stainless steel before and after laser treatment

Effects of N + B ion implantation on the tribological behaviour of GCr15 bearing steel

The enhancement of wear life and moisture resistance of sputtered MoS2 films by metal ion implantation