Various techniques of laser glazing are presented. Rules are given for the choise of systems which are suitable for producing amorphous surface layers. Methods of demonstrating the existence of a truly amorphous layer are discussed. Two examples are given: I) electron beam glazing of Ni-Nb coated single crystals 2) laser beam glazing of Fe-B coated Fe-Cr-C cold working steel.

An investigation is reported of the laser surface melting of four alloy steels with carbon contents ranging up to 1 wt%. Studies were made of the profiles, microstructures and hardnesses of zones produced using a laser power of 1.7 kW and a range of traverse speeds and beam diameters. The observed zone profiles were correlated with calculations from a three-dimensional, moving source, heat transfer model. In the high carbon steels, the shallow laser melted zones contained substantial amounts of retained austenite.

Phase transformations in laser-processed Fe-0.2%C-Cr surface alloys with 5%, 10%, 20%, and 30%Cr were studied by light and electron microscopy.Alloys containing 5% and 10%Cr were found to be fully martensitic with a dislocated lath type substructure. Thin films of retained austenite and a homogeneous dispersion of fine carbides were observed at the lath boundaries and prior austenite grain boundaries. The alloy with a 20%Cr content showed a unique microstructure of twinnedaustenite needles in a dislocated ferrite matrix while the alloy containing 30%Cr exhibited a dislocated ferrite structure with M23C6 carbides.

An investigation is done on partial surface hardening and alloying on cast iron by means of a high power laser beam. Samples of cast iron have been covered with alloying material i.e. Ti, Cr, Si, V and Nb respectively. The samples were irradiated with a 2.5 kW laser beam. A partial melting of the surface occured and the alloys were dissolved. The carbide structure in the resolidified part was governed by the alloy addition. The carbide structure was metallographicly analysed. The effect of different parameters as beam diameter, scanning rate, power and alloy content have been investigated and the crack frequency has been evaluated.

The addition of molybdenum to nickel base superalloys which contain a γ′ volume fraction of ≦ 0.35 allows them to be consolidated from powder by laser processing at solidification rates of ∼1040C/s. The as-solidified microstructure of these alloys is dendritic, and consists of a fine dispersion ∼20nm cuboidal γ′ in a supersaturated FCC γ matrix. When annealed at 500–700°C, additional age hardening occurs via the precipitation of ≤l0nm, Dla-structure Ni4Mo, DO22 - structure Ni3Mo and/or Pt2 Mo-structure Ni2Mo. This combined strengthening by very fine γ′ and NixMo dispersions in laser-processed material makes alloys of this type attractive for potential turbine disk applications. However, the 6–15 at % molybdenum required to prevent cracking during laser consolidation renders many of these alloys prone to a previously unreported, embrittling cellular phase transformation, γ + γ′ + NixMo→ γ′ + orthorhombic Ni3Mo, at temperatures of ≦900°C.

Commercial aluminum bronze (Cu-Al-Fe) alloys have been laser quenched with both continuous and pulsed CO2 laser sources. Metastable near surface regions of approximately 10 μm thickness have been produced. The quenched surfaces have been characterized by optical microscopy, SEM, EDX, AES and glancing angle XRD. The behavior of both laser quenched and “as received” conventional surfaces have been tested in both cavitation erosion and corrosion environments. In some cases significant differences are observed and can be rationalized from the microstructural changes accompanying the self quenching.

Electron beam glazed surfaces on a circular bar are of sufficiently good quality either for direct use or after light mechanical grinding. The technique may be applied for reconstituting plasma deposited layers thereby eliminating porosity and obtaining a highly homogeneous refined microstructure. By this treatment it was found that the microhardness of a plasma deposited layer of chromium carbide in molybdenum binder increased from 525 V.H.N. to 750 V.H.N.

Shaped continuous-wave laser beams have been used to alloy molybdenum coatings into Fe-C substrates. The Mo overlay was first deposited by the plasma spray process in an inert gas environment. Slowly scanned laser radiation then melted a layer 2 to 5 times the thickness of the original Coating causing the two metallic species to mix. Melt proceeded from the coating/substrate interface, the Mo melt temperatures being significantly higher than that of the base material. Fusion zone microstructures for individual melt passes appeared to be homogeneous, and molybdenum composition was found to be relatively uniform. With overlapping melt passes, the microstructures became more complex with heat effects apparent in the overlap regions.

Rapid solidification processing (RSP) has been carried out on an Fe/Cr/Mn/Mo/C alloy using both electron-beam melting and piston-and-anvil techniques. Preliminary TEM results show RSP produces a refined duplex microstructure of ferrite and martensite, with a typical ferrite grain size of 0.50–3.0 microns. This RSP microstructure is significantly different from that observed in the conventionally austenitized and quenched alloys—a lath martensitic microstructure with thin films of retained interlath austenite. The morphological change produced by RSP is accompanied by an increase in hardness from 48Rc to 61Rc (^ 480 to 720 VHN). It is intended to use electron-beam specimens to examine the potential beneficial effect of RSP upon sliding wear resistance and, by careful TEM studies, it will be possible to characterize the microstructure and its role in the hardness and wear behavior of the RSP alloy.

The details of morphological instability occurring during rapid solidification have been studied in In+, Ga+, Sb+, Bi+, Ge+, Fe+ and Cr+ implanted silicon specimens after pulsed laser annealing. The average cell sizes were determined at the onset of instability and in the region of well-developed instability using x-section and plan-view electron microscopy. The total and substitutional solute concentration profiles were determined using Rutherford backscattering and channeling techniques. The formation of cells and the critical solute concentrations associated with instability were studied as a function of velocity of solidification, which was varied by controlling the substrate temperature or the laser parameters. The results on the cell formation and the critical solute concentrations were compared with the predictions of the perturbation theory which took into account the dependence of distribution coefficients on the velocity of solidification. A good agreement between the calculations and the experimental results was obtained. We also examined theoretically the effect of reduction in surface tension due to segregation of impurities on cell sizes and critical solute concentrations associated with instability.