Advances in engineered surfaces for functional performance

Light amplification by stimulated emission of radiation (laser) is a coherent and monochromatic beam of electromagnetic radiation that can propagate in a straight line with negligible divergence and occur in a wide range of wave-length, energy/power and beam-modes/configurations. As a result, lasers find wide applications in the mundane to the most sophisticated devices, in commercial to purely scientific purposes, and in life-saving as well as life-threatening causes. In the present contribution, we provide an overview of the application of lasers for material processing. The processes covered are broadly divided into four major categories; namely, laser-assisted forming, joining, machining and surface engineering. Apart from briefly introducing the fundamentals of these operations, we present an updated review of the relevant literature to highlight the recent advances and open questions. We begin our discussion with the general applications of lasers, fundamentals of laser-matter interaction and classification of laser material processing. A major part of the discussion focuses on laser surface engineering that has attracted a good deal of attention from the scientific community for its technological significance and scientific challenges. In this regard, a special mention is made about laser surface vitrification or amorphization that remains a very attractive but unaccomplished proposition.

Laser processing of materials

Hydrodynamic lubrication of textured steel surfaces under reciprocating sliding conditions

The first part of this article presents a review of the main process parameters controlling pressure generation in a confined mode The effect of laser intensity, target material, laser pulse duration, and laser wavelength are, therefore, discussed An optimized process can then be defined The second part of this article deals with the surface modifications induced by laser-shock processing The generation of residual compressive stresses is then highlighted Finally, in the third part, the interest of laser-shock processing is discussed for several typical applications A conclusion will present the future trends of this technique

Physics and applications of laser-shock processing

Underwater and water-assisted laser processing: Part 1—general features, steam cleaning and shock processing

The role of porosity in the dry sliding wear of a sintered ferrous alloy

Laser beams provide a highly concentrated energy source that can easily be transmitted and manipulated using fibre optics and other optical cOlnponents such as mirrors. Advantages of laser treatment of componentsinclude: lowdistortion of treated parts; the ability to treat specific areas accurately; flexibility compared with, for example, electron beams; and the ability to conduct treatlnent in air or in inert or reactive gases. Apart fr01n cutting and welding, the first application in the Inaterials field was for heat treatment and involved laser surface hardening in the solid state, based on the heating of a thin sUlface layer that was self quenched by the bulk of the cOlnponent. Numerous further treatments have since been developed that involve melting of the surface layer, with or without addition of material, and more recently purely mechanical processes based on the laser shock phenomenon have emerged. The main laser processes that have already been commercialised or are expected shortlyto b...

Surface modification using high power lasers: influence of surface characteristics on properties of laser processed materials

A potentially promising application of laser shock processing is in the superficial densification of porous materials. The present work studies the effect of laser shock processing on the dry sliding wear behaviour of powder metallurgical (P/M) Distaloy AE specimens of four different porosity levels in the range 9–22 vol.%. The wear mode for laser-shocked specimens compared with that of the corresponding unshocked specimens was investigated using a pin-on-disc apparatus and a 99% pure sintered alumina counterbody. Densification was characterized using quantitative image analysis since shock treatment resulted in a porosity gradient in the processed depth. The basic mechanisms involved in the wear of the specimens were shown to be oxidation, abrasion and plastic deformation leading to metallic particle detachment. Laser shock densification increased the wear resistance of the specimens with initial porosity lower than 10 vol.%. In contrast, the wear resistance of the specimens with high initial porosity (16.8 and 21.1 vol.%) and large initial pore size (greater than 20 μm) was shown to decrease after laser shock, since the beneficial mechanism of debris entrapping by the pores and pore filling could not take place.

B. Dubrujeaud

Papers

The role of porosity in the dry sliding wear of a sintered ferrous alloy

Surface modification using high power lasers: influence of surface characteristics on properties of laser processed materials

Dry sliding wear behaviour of a P/M ferrous alloy superficially densified by laser shock processing