[en] The authors have developed a new technique for deposition on low temperature substrates driven by laser induced dielectric breakdown of gas phase precursors. Metal films of Ni, Fe, and refractory metal alloys show excellent grain refinement and metastable phase incorporation due to rapid quenching from the gas phase. The technique, including the role of gas phas nucleation and growth in the formation of the films, is described. The authors have deposited metal films of Ni, Fe, and Mo by decomposition of the respective carbonyls and of W and Mo by hydrogen reduction of the respective hexafluorides. The focused beam of a pulsed carbon dioxide laser operating on the 10.6 micrometer line creates a region of high electric field sufficient to break down a gas mixture consisting of metal precursors and a buffer gas. The resulting laser plasma is highly excited with temperatures measured spectroscopically in excess of 50,000 K. This initial temperature insures that all precursor gases are fully decomposed. This plasma cools very rapidly to temperatures at which chemistry can begin to occur. The reaction zone thus created is centered at a distance of 5 mm from the substrate which is at room temperature. Deposition on the unheated substrated results with very fine grain structures. Because high vacuum is not required, the chamber can be recycled with a clean substrate in a few minutes, resulting in a high throughput of the films. The authors have described a new laser driven method for chemical vapor deposition which is compatible with temperature sensitive substrates and which results in fine grained polycrystalline films, often of metastable phases. The deposition process has been shown to involve gas phase nucleation and growth followed by surface sintering

[en] A new technique for the deposition of nickel metal films by gas-phase pyrolysis of nickel tetracarbonyl gas is described. A pulsed CO₂ laser is used to form a reaction zone adjacent to a cold substrate, resulting in a rapidly quenched film. The technique relies on dielectric breakdown of a mixture of source and carrier gases and therefore lends itself to a variety of source gases and chemistries. Adherence data and compositional and structural analyses are presented

[en] The authors report on thin films produced by laser breakdown chemical vapor deposition from nickel and iron carbonyls and by implanting Ni foils with varying levels of characterized by transmission electron microscopy. Decomposition of Ni(CO)₄ produced polycrystalline films of fcc Ni and metastable ordered hexagonal Ni₃C. This metastable phase is identical to that produced by gas carburization, rapid solidification of Ni-C melts, and ion implantation of C into Ni at low concentration. Increasing the H₂ content in the gas mixture during laser deposition reduces the grain size of the films significantly with grain sizes smaller than 10 nanometers produced. Laser decomposition of Fe(CO)₅ produces films with islands of fcc gamma-Fe and finely dispersed metastable Fe₂O₃ and Fe₃O₄ were found in these samples. Implants of C into pure Ni foils at 77 degrees K and at a concentration of 35 at.% produced amorphous layers. Implants at the same dose at room temperature did not produce amorphous layers

[en] The authors have examined the effect of surface processing in air, using excimer laser light at 248 nm wavelength, on the oxygen content, microstructure, and surface hardness of Ti-6Al-4V. Processing with a single pulse results in the transformation of the α + β material to α' martensite. Multiple pulse processing results in rapid incorporation of oxygen in the material. Oxygen initially dissolves in the material in the liquid phase. As the concentration exceeds the solid solubility limit during solidification, TiO particles precipitate. In contrast to equilibrium oxidation processes in Ti, only TiO is observed as an oxidation product; further processing results in increased oxygen incorporation and an increased volume fraction of TiO but no other oxides of Ti. The TiO particle size is a function of the oxygen concentration and the number of pulses, with some grain growth occurring after many pulses. The effects of solution hardening by dissolved oxygen and precipitation hardening by the TiO are identifiable as functions of oxygen concentration and mean free path between particles, respectively. A maximum surface hardness almost twice that of electropolished Ti-6Al-4V is observed

[en] Surface modification can improve materials for structural, tribological, and corrosion applications. Excimer laser light has been shown to provide a rapid means of modifying surfaces through heat treating, surface zone refining, and mixing. Laser pulses at modest power levels can easily melt the surfaces of many materials. Mixing within the molten layer or with the gas ambient may occur, if thermodynamically allowed, followed by rapid solidification. The high temperatures allow the system to overcome kinetic barriers found in some ion mixing experiments. Alternatively, surface zone refinement may result from repeated melting-solidification cycles. Ultraviolet laser light couples energy efficiently to the surface of metallic and ceramic materials. The nature of the modification that follows depends on the properties of the surface and substrate materials. Alloying from both gas and predeposited layer sources has been observed in metals, semiconductors, and ceramics. Surface enrichment of Cr by zone refinement of stainless steel has also been seen. Rapid solidification after melting often results in the formation of nonequilibrium phases, including amorphous materials. Improved surface properties, including tribology and corrosion resistance, are observed in these materials. 65 refs., 9 figs

[en] The migration of ion implanted ¹³C in tempered martensitic steel (nominal composition) 1.05 wt. % C, 0.2 wt. % Si, and 0.3 wt. % Mn) during excimer laser melting was examined utilizing the resonance of the ¹³C(p,γ)¹⁴N reaction at E_p = 1747.6 keV. Depth concentration profiles after five and ten laser pulses of 1 J/cm² revealed a deviation from random walk diffusion in a homogeneous media. This was modelled by using partitionless solidification and solubility controlled flow of carbon in the iron-carbon melt. A diffusion length of 2 square root of Dτ = 34 ± 2 nm during the period τ of the melted phase was deduced. Ion implanted surfaces were initially crystalline but significant crystalline to amorphous transformation occurred following laser treatment

[en] This paper investigates the hardness and tribological properties of Cu/TiB₂ multilayer structures deposited on substrates of tempered martensitic steel. Films of Cu and TiB₂ were also deposited as hardness standards. The wear properties of the films were found to be poor, because of lack of adhesion. However, the films do appear to have good fracture toughness. The hardness of the multilayer was 18% greater than that predicted by the law of mixtures applied to the reference standards and, when corrected for variations in substrate hardness, very nearly equal to that of the TiB₂ film. Irradiation by 400 keV Ne-ions to doses of 1.0, 6.0, and 12 x 10¹⁵ ion/cm² results in a slight hardening of the multilayer. The structure was found to have excellent stability against radiation damage

No abstract available

[en] The authors have used excimer laser surface processing to melt and mix single Ti layers into the surface of polycrystalline SiC substrates. The mixing of Ti into the surface is very rapid and efficient. Examination of Rutherford backscattering (RBS) data for different mixing conditions shows the formation of a preferred composition at the Ti-substrate interface which propagates from the interface with further mixing. Reconstruction of the RBS spectrum indicates that the composition of the layer is Ti₄₅C₃₇Si₁₈. X-ray diffraction demonstrates the formation of Ti silicides and carbides in the surface region. Profiling of C in both mixed and uncoated samples by 6 MeV He⁺ scattering demonstrates that laser processing of the SiC does not cause major changes in the stoichiometry of the substrate material

[en] The authors developed a new technique for deposition on low temperature substrates driven by gs laser induced dielectric breakdown of gas phase precursors. Metal films of Ni, Fe, and refractory metal alloys show excellent grain refinement ( < 10 nm) and metastable phase incorporation due to rapid quenching from the gas phase. The technique, including the role of gas phase nucleation and growth in the formation of the films, the microstructures obtained, and some of the properties of the films are described