Some aspects of future laser technology are given for modification of metal surfaces. This attempt includes new laser sources optical elements for beam guiding and forming, sensor elements for higher process reliability and modified processes.

Enhanced beam coupling of a Ferranti 400W CO2 laser beam has been observed on Cu and Al surfaces via interaction with a plasma generated by a Lumonics Excimer laser. This paper presents the results of such experiments.

Laser beam cladding has been refined such that clad characteristics are precisely determined through routine process control. This paper first reviews the state of the art of laser cladding optical equipment, as well as the fundamental process/clad relationships that have been developed for high power processing. Major categories of industrial laser cladding are then described with examples chosen to highlight particular process attributes.

Application of alloy coatings with superior oxidation resistance at elevated temperatures (1200°C) on superalloy components is of interest at present. There is a general consensus that the addition of rare earths such as hafnium (Hf) to these alloys has a pronounced effect on their performance. An in situ laser cladding technique was used to produce Ni-Al-Cr-Hf alloys on a nickel alloy substrate. Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), and Scanning Transmission Electron Microscope (STEM) attached with Energy Dispersive X-ray (EDX) analyzers were employed for microstructural evolution studies of alloys produced during the laser cladding process. The microstructure of these alloys mainly consists of dendrites of Y' of the Ni3Al type with about 11-14 wt% Hf and an interdendritic eutectic phase. Electron microscopy in the dendritic zones reveals ordered domains whose morphology depends on laser cladding process parameters. Variation in these parameters produced only subtle changes in the composition and cell spacing of the dendritic phase. The eutectic constituent consists of a Hf-rich phase and a Hf-lean phase in an alternating lamellar structure. Convergent beam diffraction and x-ray spectroscopy techniques were used to characterize the constituents. A possible phase transformation sequence has been suggested. Differential Thermal Analysis (DTA) work indicates that the Y' dissolution temperature for the claddings is at least as high as the substrate material (Rene 80). Single cycle oxidation tests of eight hours at 1200°C in slowly flowing air reveal that the claddings have a lower weight gain rate than the substrate itself. Microchemistry and microstructure of the oxidized samples are examined using SEM attached with EDX and Auger Electron Spectroscopic (AES) techniques. The improvement in the oxidation resistance is believed to be at least partially due to the mechanical pegging between alumina coated hafnia protrusions and the unoxidized metal matrix.

By the laser melt/particle injection process, an in situ composite surface layer of particulate material in a matrix made up of the parent metal is formed. The particles are usually metal carbides which makes the injected surface layer hard and wear resistant. In this paper, the processing technique and the microstructures obtained are described. In addition, the hardness and wear characteristics of the modified surface are discussed.

Commercial acceptance of laser coating technology suffered for many years due to questions about its economic viability. During this period, however, many companies, universities, and government research groups were busy developing the technology to overcome these questions. Today, laser coating technology is having a major impact as a high quality, economical method of hardfacing for wear and corrosion resistance in several key industries. This has occurred because of advances in five key areas: 1. High power laser design 2. Method of alloy deposition, and associated hardware 3. In-process feed back control system hardware/software development 4. Alloy systems 5. Marketing/sales sophistication High power lasers have improved in mode stability, power conversion efficiency, and optical flexibility (reflective vs. transmissive materials). This has enabled the process engineer to increase deposition efficiency, and maintain flexibility on the use of optics specifically designed for a user application. Improvements in the method of alloy deposition have led to developments such as the DPF system with specialized nozzles developed for specific user applications. Another effective technique includes the use of pre-fabricated cast alloy chips that are welded to the component surface on the specific area requiring protection. The development of feedback control systems that integrate process control software with hard tooling, the laser, and the alloy delivery system are greatly improving process reliability and product quality. Because of this, "in-process" quality control is becoming a viable alternative to traditional methods of quality control. Metallurgical evaluations of some of the most widely used hardfacing alloys and base materials have been investigated by numerous researchers. Analysis has confirmed that laser applied coatings are of high metallurgical quality, extremely low in dilution, and distort less due to low heat input. The technology can also be used to apply. wear/corrosion resistant alloys heretofore considered unweldable. These technological advances, coupled with application experience have proven that laser coating technology is not only a viable alternative to conventional hardface and/or spray coatings; but in many cases significantly reduces the overall manufacturing costs of a coated product. Early marketing efforts focused on direct "coating process to coating process" comparisons with competing technologies.

An anlysis is made of applications of surface treatments by means of high power lasers on automobile components performed by Istituto R.T.M. in Vico Canavese, Italy. The Institute has worked with high power lasers for the last ten years and has taken an active part in promoting laser technologies in the automobile industry in Italy and abroad, also supplying automated optomechanical components.

Laser material processing is a technolgy with well controllable parameters. However, in order to control the parameters it is necessary to measure them. The basic parameters to be measured are usually the input power, the discharge current, the output power. But for a reliable operation the laser beam intensity distribution in the unfocussed part should be observed and the intensity in the focal area should be optimized. Additionally, the interaction between the laser and the material is depending on some material properties. So, the interaction can change, although all laser beam parameters are stable. In order to avoid this, a monitoring of the interaction is necessary. Examples for the before mentioned controls and diagnostics are given in the report.

Surface treatments with high power laser beams require in most of the applications special forms of the intensity distribution. Usually the intensity distribution should be constant ("flat") in one or two directions, i.e. a "line" or a "rectangular" distribution. This can be achieved by means of a light pipe beam integrator, rotating mirrors, segmented mirrors or other mirror based concepts. The most common of this tools are reported and their advantages are discussed.

Binding of proteins to polystyrene plates used in enzyme linked immunosorbent assays (Elisa tests) has been improved by three different methods using UV radiation from an excimer laser. The methods studied were: i) a high fluence method, where material was ablated from the surface using focussed radiation, ii) a low fluence method, where de-focussed radiation was used to form new chemical species photochemically without material removal, and iii) a coating process, where the UV radiation was used to cure a surface coating on the plates which contained functional groups which would provide good sites for bonding. All three processes have been studied over a broad range of experimental parameters, and conditions leading to improved binding of protein have been determined for each process.

Many automotive parts, such as hoods and decklids, are made by adhesively bonding sheet molding compound (SMC) sub-assemblies. The presence of contaminants such as mold releases, together with variable chemical composition, characterizes the SMC surface. Thus some form of surface preparation is required to ensure reproducible adhesive bonding. This paper describes how a reproducible bonding surface can be obtained by ablation of the variable outer layer with an infrared laser. The effect of laser beam power density and fluence on surface properties, ablation depth, and adhesion is discussed. As laser beam delivery systems can be readily automated, this procedure has substantial potential for use in an automated SMC manufacturing system.

It has been found that excimer laser radiation, at intensities of 108-109 W cm-2 irradiating metal targets in air, can result in both surface roughening and oxidation. The increased absorptivity E(A,T), as a result of the surface modification, has been measured directly. Using a calorimetric technique, the measured absorptivity at 10.6μm, indicates that the coupling of CO2 laser radiation can be greatly enhanced with a pre-treating series of overlapping excimer pulses.

The surfaces of the polyimide Kapton obtained by irradiation with 308 nm pulsed ultraviolet radiation from a XeCI excimer laser in air were studied. DRIFT (Diffuse Reflectance Infrared Fourier Transform) analysis of the processed material indicated an increase in surface area as a result of ablative etching. This was verified through the use of SEM (Scanniig Electron Microscopy) scans of the treated polyimide film. At high fluences (7.8 J/cm ) and high numbers of pulses on the same target area, the infrared spectrum of the sample showed the appearance of broadband absorption between 2000 - 4000 cm-1. This was attributed to the formation of carbonaceous residue on the surface of the film.

Excimer laser radiation with a high energy density was used for structured removal of ceramics. Patterns down to 20 μm over an extended area were generated by mask projection. For the oxides (Al203, ZrO2) a specific removal rate of 0.01 μm/(J/cm2) per pulse was determined above a threshold of 3 J/cm2, and no saturation behavior at higher energy density was observed. Non-oxidic ceramics (SiC, Si3N4, ALN, BN) show saturation at a rate close to 20 J/cm2. The short pulse ensures minimal mechanical and chemical change of the surface layer under irradiation.