We report a heat treatment technique that enabled the hardness of polycrystalline cubic/wurtzite boron nitride composite to reach that of polycrystalline diamond. The process consists of surface heating the composite using a continuous wave laser followed by tandem waterjet quenching of the laser beam path to cause stress-induced phase transitions. Visual examination indicated a change in optical transparency through a color change from black to white. Raman spectroscopy revealed the partial transformation of wBN to cBN and formation of amorphous boron. Vicker's microhardness test showed a dramatic increase in the nominal hardness from 40 to 75GPa.

Lasers are widely used for macro- and micromachining applications in numerous industries such as automotive, electronics, and medical manufacturing. However, there are many challenges encountered in the utilization of lasers for nanomachining. The most critical requirement is that the diffraction limit of laser light must be overcome. With recent developments in laser technology in terms of short-wavelength and ultrashort pulse width, there is a wealth of opportunities to beat the diffraction limit for nanomachining of structures, devices, and materials. In this review paper, first the state-of-the-art lasers are examined from the perspective of the requirements of nanomachining. Second, a set of both serial and parallel types of laser-based, “top-down” nanomachining methods is described. Third, preliminary results obtained in our laboratory of the most recent, novel approach involving surface plasmon polaritons for the potential of massively parallel nanomachining are presented. Finally, the potential of lasers for cost-effective nanomanufacturing is assessed.

Excimer laser annealing (ELA) is well known to cause the transformation of amorphous to crystalline structures in semiconductor materials such as silicon and germanium. However, there exists a disagreement on whether this phase transition involves the formation of a liquid phase or takes place exclusively in the solid-state. In this work, ELA of amorphous 65A1-23 Cu-12Fe quasi-crystalline (QC) coatings was performed to elucidate the mechanism of the phase transition. Magnetron sputtering was used to deposit 10 to 12 mu m in thick amorphous QC coatings on steel, aluminum and titanium substrates followed by ELA to convert them into crystalline phases. X-ray diffraction data of ELA samples was used to determine the threshold energy fluence for phase trans formation. A two-dimensional, finite-element thermal model was applied to estimate the temperature distributions and melt depth as a function of energy fluence. The effect of ELA on the surface roughness was measured and also used to identify the phase change. Results suggest that ELA caused melting, of about a 3 mu m layer of the coating at the threshold fluence and more at higherenergy fluences. The surface roughness (arithmetic average) was increased from an average of 0.06 mu m in as magnetron-sputtered to 0.4 mu m in laser-crystallized coatings. It is concluded that the presence of thin molten layer is a necessary and sufficient condition for the phase transition to occur and that the formation of a molten layer roughens the laser-modified surface, a chief drawback of ELA.

We report an atomistic simulation study of laser-induced graphitization on the diamond (111) surface. Our simulation results show that the diamond to graphite transition occurs along different pathways depending on the length of the laser pulse being used. Under nanosecond or longer laser pulses, graphitization propagates vertically into bulk layers, leading to the formation of diamond-graphite interfaces after the laser treatment. By contrast, with femtosecond (0.2--0.5 ps) laser pulses, graphitization of the surface occurs layer by layer, resulting in a clean diamond surface after the ablation. This atomistic picture provides an explanation of recent experimental observations.

The effects of annealing and diode laser scribing were investigated on amorphous iron-base alloy ribbons to further reduce their core losses. A maximum core loss reduction of 6% was achieved in the as-cast samples and 32% in the annealed ones. The decrease in core loss is attributed to the reduction in residual stresses and domain refinement.

The electrical power industries are experiencing a considerable energy loss in transformers and motors because of inefficiencies caused by core loss. The objective of our research is to investigate any effect of laser scribing on the reduction of the core loss in the low cost, non-oriented steels used in numerous utility applications. A 15 W diode laser transmitted through fiber optics was used to scribe 0.35 mm thick, non-oriented 3 wt% Si steel. The magnetic properties including the core loss and permeability were evaluated both before and after laser scribing. A maximum core loss reduction of 0.08 W kg−1 at a magnetic induction of 1 T and a 21% increase in relative permeability were obtained at the optimum laser parameters. These results are comparable to those of laser scribed, expensive grain-oriented steels. The core losses were further reduced using a treatment procedure consisting of laser scribing, chemical etching, and stress relief annealing performed in sequence. The laser scribing method is simpler, energy efficient, and can be implemented in the production line.

A laser beam offers the benefits of high precision, contamination-free, high speed, and low bulk temperature for machining of chemically vapour deposited (CVD) diamond thin films that in turn enable ultrafine finishing of diamond coated cutting tool inserts and drills, and for finishing and drilling of diamond coated multichip module applications. In this work, laser hole drilling and polishing of CVD diamond (free-standing diamond and coated tool inserts) and HOPG (highly oriented pyrolytic graphite) using a 248 nm wavelength, 23 ns pulsed excimer laser were conducted. The threshold energy fluence required for ablation of diamond and graphite was nearly the same but the material removal rate rapidly increases with the energy fluence for the graphite compared to diamond. At an energy fluence of 10 J cm-2, the depth removed per pulse was 0.05 μm and 0.30 μm for diamond and graphite respectively. Raman microprobe analysis indicates that the laser machining induced the transformation of diamond to disordered forms of carbon in CVD diamond and some transformation of graphite to diamond in HOPG. The experimental data indicates that the transformation of diamond to graphite requires an energy input of 1.44 × 107 J per mole. For a given set of laser parameters, the depth per pulse was substantially higher for diamond coated tool inserts compared to the free-standing diamond. The surface roughness of CVD diamond was reduced by 0.25 μm per pulse at an energy fluence of 16 J cm-2

Laser scribing of 3% silicon steel laminations was carried out using three different lasers: a KrF excimer laser, a pulsed Nd:YAG laser and a continuous wave CO2 laser. The processing parameters included the energy fluence at the surface of the workpiece, pulse repetition rate and pulse separation distance (for the pulsed lasers), scan separation distance and scan direction. The samples were tested for hysteresis loss, permeability, coercivity, remanence and saturation induction before and after laser treatment. An overall improvement in the core loss was observed in the laser-scribed samples. The best improvement in core loss was obtained in excimer laser scribing on the rolling direction and CO2 laser scribing in the transverse direction. Three mechanisms were proposed to explain the improvement in energy efficiency characteristics of the silicon-steel samples: magnetic domain refinement, stress relaxation and inhibition of domain-wall movement. Domain refinement, namely the formation of subdomains, results from the shocks induced by the beam. Laser scribing also relieves the stresses that are induced in the material during manufacture. The scribe lines increase the surface resistivity of the material, resulting in reduced eddy current loss. Tensile stresses are created between the laser scribe lines that elongate the domains and serve to refine the domain-wall spacing thus inhibiting the wall movement and reducing core losses.

A laser chemical vapour deposition process for growing fluorinated diamond thin films on two bearing materials, SiC and 440 C stainless steel, is described. The type of laser, carbon feedstock, laser-precursor gas interactions, and deposition conditions have been established. Raman spectroscopy analysis revealed that the films deposited on SiC consisted of a mixture of diamond and graphite, while the films on 440 C steel were composed of diamond, diamond-like carbon and graphite. The feasibility of diamond formation using laser light-gas interactions is explained.

A thermochemical heat transfer model in oxygen-assisted laser cutting of carbon steel has been developed in terms of the laser mode pattern, the power density, combustion reaction, kerf width and cutting speed. This model emphasizes the chemical combustion effect as well as the laser mode pattern, which are usually neglected by most existing laser cutting models. Good agreement was obtained between theoretical and experimental results, indicating that approximately 55–70% of the cutting energy is supplied by the combustion reaction of the steel with oxygen, which is consistent with experimental data obtained by other investigators.

A novel technique based on laser-induced chemical reduction of metal salts has been developed to produce surface coatings on metal-matrix composites (MMCs). The substrate is predeposited with a paste, containing concentrated salts of the elements to be coated along with a thickening agent, and then subjected to high power laser radiation. The rise in surface temperature during laser irradiation led to the decomposition of salts to their native metals. The combination of metal and metalloid elements in the reaction zone forms an amorphous layer due to the specific chemical ratio and rapid cooling rate. The thickness of the coatings obtained were of the order of 50–100 μm. The coatings exhibited amorphous and microcrystalline structures, possessed hardness in the range of 300–1700 Hv (substrate hardness 80–90 Hv), had superior sliding wear resistance and excellent corrosion resistance. The advantages of this process include the formation of complex coatings on MMCs by a simple, versatile technique which does not require any vacuum or inert atmosphere.

A laser physico-chemical vapour deposition (LPCVD) technique was developed based on the interaction of an ultraviolet laser beam with a boron nitride target and borazine gas to synthesize cubic boron nitride (CBN) thin films on silicon substrates. The process involved a hybrid of pulsed laser ablation (PLA) of a solid HBN target and chemical vapour deposition (CVD) using borazine as a feed stock. The films were characterized with scanning electron microscopy, X-ray diffraction and infrared spectroscopy. Results indicate that the thin films consisted of almost single-crystalline CBN structures and that the film quality in terms of adherence, particulate density and smoothness was excellent. The purity and crystal structure of target material, laser beam wavelength and energy fluence were the key variables that controlled the film characteristics. In contrast to LPCVD, the conventional PLA method did not generate CBN films.

A dual-beam technique involving two CO2 gas lasers with a power capacity of 1.5 kW each, was used to cut steel and superalloy. A comparison with single-beam CO2 laser cutting showed that dual beams were capable of enhancing the cutting thickness and speed without deteriorating the quality of cut. Heat-conduction models, assuming the laser beams as line sources, were used to estimate the cutting thickness and speed as a function of distance between the two laser beams. Experimental data, coupled with theoretical modelling, have provided a new concept, namely stretching the width of the laser beam in the direction of cutting to cut thicker section solids at moderate speeds.

In laser cutting, the largest single application of lasers in manufacturing, the assist gas plays an important role in affecting the cutting performance. The assist gas is usually oxygen or an inert gas. In this work a mixture of acetylene and oxygen was employed to create combustion reactions during CO2 laser cutting that enabled an improvement in the cutting speed, and cut quality of a difficult-to-machine superalloy. A comparison with laser cutting of a plain carbon steel under identical conditions was also made to determine the usefulness of combustion energy. Results indicate that both cutting speed and quality are enhanced by the reduction in the viscosity of slag formed during cutting (which assisted in ejection of the slag through the bottom of the kerf) due to the heat released by the acetylene burning inside the kerf. Correlations of experimental data with a theoretical model provided the influence of combustion power and gas-flow power on the cutting phenomena.

Ductile nickel aluminide, Ni3Al+B, is an intermetallic alloy with high strength and ductility making it a promising structural material for both elevated temperature and cryogenic temperature applications. In order to be able to use this alloy over a spectrum of temperature-critical applications, it must be capable of being joined or welded. The weldability of a cast nickel aluminide alloy containing boron was studied using laser welding. Welding was carried out at laser beam traverse speeds ranging from 42.33–254 mms−1 in the bead-on-plate and butt-joint configurations. Two types of surface preparation, namely chemical cleaning and mechanical polishing, were used prior to laser welding. The quality of the laser welds was evaluated through mechanical tests (hardness and tensile), X-ray diffraction and microscopical observations. High-magnification examination of the welds revealed fine columnar structures in the weld zone. The hardness of the weld zone was substantially higher than that of the base metal. Microscopic examination also revealed the welds to contain shrinkage cracks. For a constant set of laser parameters, the chemically etched surfaces provided deeper penetration than the mechanically polished surface. The performance of the laser-welded joint is rationalized.

Lithium-containing aluminium alloys are of considerable current interest in the aerospace and aircraft industries because lithium additions to aluminium improve the modulus and decrease the density compared to conventional aluminium alloys. Many such alloys are under develøpment for aircraft applications, which usually involves mechanical fastening. While aluminium-lithium alloys are fusion weldable with gas metal arc, gas tungsten arc and electron beam processes, they suffer from problems of weld porosity, heat-tearing cracking, poor penetration and low joint efficiency. In this paper, the weldability of aluminium-lithium alloys is briefly reviewed. The weldability of commercial aluminium-lithium alloy 2090 in the peak-aged condition was studied using laser welding. The quality of the welds was evaluated through mechanical tests (hardness and tensile tests) and microscopical observations. Mechanical property data and microscopical observations of the welds on prior surface-prepared (milled) material revealed a low degree of the weld surface degradation and an absence of porosity. This coupled with the attractive joint efficiencies suggest the superiority of the laser welding to conventional arc welding of this alloy. The performance of laser-welded butt joints is rationalized.

Al-Li alloys are of considerable interest in aerospace industries because the addition of Li improves the stiffness and reduces the density of aluminum. Mechanical fastening methods are currently used to join these alloys. Although such alloys are fusion weldable using MIG and TIG methods, the major problems included hot tearing, porosity, low penetration and poor joint efficiency. In this study, a 2 kW continuous wave CO2 gas transport laser was used to weld 1.6 mm thick plates of a commercially available Al-Li alloy 2090. A comparison was made with conventional arc and electron beam welding processes. Results indicated tht the joint efficiency of laser welds was greater than arc welds and comparable to that of electron beam welds. Unlike arc welds, there was no evidence of hot tearing in the laser welds. Initial surface preparation had a significant effect on the porosity and tensile strength.Al-Li alloys are of considerable interest in aerospace industries because the addition of Li improves the stiffness and reduces the density of aluminum. Mechanical fastening methods are currently used to join these alloys. Although such alloys are fusion weldable using MIG and TIG methods, the major problems included hot tearing, porosity, low penetration and poor joint efficiency. In this study, a 2 kW continuous wave CO2 gas transport laser was used to weld 1.6 mm thick plates of a commercially available Al-Li alloy 2090. A comparison was made with conventional arc and electron beam welding processes. Results indicated tht the joint efficiency of laser welds was greater than arc welds and comparable to that of electron beam welds. Unlike arc welds, there was no evidence of hot tearing in the laser welds. Initial surface preparation had a significant effect on the porosity and tensile strength.

A 1.2-kW, continuous wave, CO2-gas laser was used to transformation harden or melt the surface of gray and ductile cast irons. Effects of surface-hardened layers on solid particle erosion showed that the erosion rate decreased with an increase in surface hardness and case depth. The order of matrix microstructures that increased the erosion rate were ledeburite, tempered martensite, and pearlite. These results were opposite to those observed in bulk-hardened alloys. Erosion mechanisms of brittle, gray iron included micromachining in the untreated condition and grain boundary cracking in the laser-treated condition. In contrast, erosion modes of ductile iron were plastic flow followed by cracking in the untreated condition and platelet formation and fatigue in the laser-treated conditions. The beneficial effects of surface hardening on erosion were examined and discussed.

The influence of laser surface transformation hardening on the sliding wear characteristics and mechanisms of ASTM class-40 gray and 80-55-06 ductile cast irons was investigated. A 1.2 kw, continuous wave, CO2 gas laser was employed to scan the beam successively across the surfaces of cast irons to generate hardened and tempered layers with various case depths. A pin-on-disk wear test system was then used to study the wear behavior as functions of case depth, microstructure, hardness, and surface roughness. As expected, a dramatic improvement in resistance to scuffing and sliding wear was obtained. However, the most significant result was the occurrence of negligible oxidational wear for a load range that increased with an increase in case depth. Resistance to mild and severe wear, mild-to-severe wear transition load, and frictional heating were increased with an increase in case depth. Analysis of worn surfaces and wear debris revealed that negligible oxidational wear in laser-hardened irons is due to two mechanisms: oxidation and adhesion of oxide to the substrate. In contrast, the mild oxidational wear of untreated irons occurs through the formation of loose oxide debris. The mechanisms of severe wear were plastic deformation, delamination, and adhesion; the rate process was controlled by adhesion for laser hardened irons and delamination for untreated irons.