Coatings have been produced by entraining relatively large diameter metal powders in a supersonic airflow. For the first time, most of the particles in the powders have diameters >50 μm. Substantial plastic deformation is involved in the conversion of the particle's kinetic energy into heat and strain energy in this kinetic spray process. As suggested by simple estimates and confirmed by coating grain structures, the particles are not melted or thermally softened in this coating process. These coatings have a relatively low oxide content, low thermal stress, high adhesion, low porosity and hardness somewhat higher than those of corresponding bulk materials. Threshold or critical velocities for coating formation are discussed. Critical velocities for the relatively large particles were observed to be substantially less than have been reported earlier for smaller diameter (<50 μm) particles. Coating particle rotation and deformation due to particle impact resulted in a corresponding decrease in porosity. Bond formation, particle deformation and grain deformation were found to be highly anisotropic, depending on the direction of the incident particle velocity. At higher incident velocities, increasing metallic bond formation between particles was observed. This is consistent with a metallic form for stress/strain curves obtained via tensile tests on Al coatings removed from the substrate. The coating elastic modulus was found to be less than half that of bulk Al. Measured ultimate tensile strengths and yield points of Al coatings were comparable to those of bulk Al. This may be due to work hardening resulting from the plastic deformation necessary for coating formation. These tensile test results are consistent with coating cohesive strengths as measured by stud pull tests. Higher powder feed rates produced coatings with higher failure loads in three point bending, higher coating cohesion and lower coating strength anisotropy, presumably due to a peening effect. Four velocity-dependent stages of coating formation are proposed based on observations reported here. Coating properties arise from a competition between these stages. Parallels with models of dynamic (explosive) powder compaction are made. This is the first comprehensive model for kinetic spray coating formation.

Coatings have been produced by entraining metal powders in an air flow which is accelerated by a de Laval type of nozzle. The particles are not melted or thermally softened prior to impingement onto the substrate. The coating process depends primarily on the kinetic energy of the incident powders. The coatings have low oxide content and low thermal stress, and can exhibit relatively low porosity and high adhesion. The mechanism by which the coatings are formed is not well understood, and it is the goal of this work to provide some insights into this mechanism. We have produced a new high-velocity spray apparatus which allows the spray parameters to be controlled and monitored for the first time. This, together with our simulations of air and particle velocities and temperatures, has provided new information on the coating process. Al, Cu, and Fe powders were sprayed onto Al, brass, Cu, and steel substrates. A threshold behavior was observed for coating deposition as a function of nozzle inlet air temperature, with a roughly linear behavior above the threshold. Results are obtained as a function of nozzle inlet air pressure and temperature, powder feed rate, and nozzle–substrate stand-off distance. The effect of the choice of substrate metal was relatively weak in our experiments. Results seem consistent with necessary inelastic processes such as plastic deformation and/or partial melting of the powder particles upon collision with the substrate. More research is needed to define the relative importance of these phenomena or of other possible mechanisms.

A one-dimensional, transient model is developed for solving the system of coupled, nonlinear, partial differential equations governing the fields in our experimental investigations of laser-induced heating and subsequent thermal ignition in an open, premixed ethylene-oxidizer system. The model includes complex chemistry and transport processes, and features a realistic and experimentally consistent laser/absorption submodel for the ignition source. The model is used to explain the character of the temperature-time history prior to ignition, above and beyond traditional heat transfer theories, and shows that perturbations in the laser's output characteristics can explain the range of delay times observed experimentally. Furthermore, the laser/absorption/ignition model is used to explain the experimentally observed phenomenon of ignition occurring beyond the focus of the laser. Ignition chemistry is shown to be dominated by the same reactions, in terms of rates of progress and rate coefficient sensitivity analysis, in spatially dependent ignition events as in purely kinetic studies, with sensitivity of ignition delay virtually the same. Lastly, a theory is developed and used to quantify the effect that species diffusion has on retarding ignition in a spatially dependent system. This retarding effect may contribute more or less than kinetic processes to the ignition delay period. This retarding effect is shown to be not only due to suppressed radical concentrations, but also to diffusion of fuel back towards the ignition source.

MAGNECODE uses laser surface heating to pattern permanent magnets for position sensor applications. Thermal and magnetic models provide good predictions of the geometry of the laser heated regions and the resulting spatial variations in the magnetic field. Important design factors are discussed and a comparison with other magnetic sensor technologies is given.

The thermal energy transferred to noncombusting gases by a spark at pressures from 1 to 7 atmospheres was measured using a pressure-rise calorimeter. The energy transfer efficiency (from electrical to thermal energy) was determined for conventional coil ignition systems, a plasma jet ignitor, and an ultra-short pulse (USP) ignitor

The concentration of radicals such as OH, O, and H above a flame are determined in part by three body recombination reactions. These radicals are responsible for CO oxidation and also NO production via the Zeldovich mechanism. The chemistry of the recombination region was modeled on a computer using a mechanism with nine species and nineteen reactions. A sensitivity analysis of the model was carried out to determine the effects of errors in rate constants, diffusion coefficients, and initial concentrations on the model predictions. Similar results were obtained using both the FAST (Fourier Amplitude Sensitivity Test) algorithm developed by Cukier and coworkers and a simpler brute force method. The sensitivity was large for only a few parameters. In particular, for fuel lean flames, the OH decay rate is mainly sensitive to the rate constant for H+O2+M→HO2+M. The hydroxyl concentration profiles above atmospheric, premixed, laminar methane-air flames were measured using laser absorption spectroscopy. Measurements were made for both fuel lean and stoichiometric flames. Predictions from the computer model were in reasonable agreement with the experimental profiles. The rate constant for the H+O2+H2O→HO2+H2O reaction which gives the best fit between the experiment and the model is 8±3×10−32 cm6/molecule2 at 1500 K. This is larger than that derived from earlier flame measurements, but is in reasonable agreement with shock tube results and the theoretical predictions of R. J. Blint. The model shows that the hydrogen-oxygen system stays in partial equilibrium throughout, most of the recombination zone. However, CO and CO2 do not stay in partial equilibrium.

We have directly measured the repopulation rate for an individual rotational level in the electronic ground state of a homonuclear molecule. A pulsed dye laser was used to depopulate (v″, J″) level of Na2 by pumping a transition of the form (v′, J′) ← (v″, J″) in the B1Πu‐X1Σ+g blue–green band system. The (v″, J″) state was repopulated by collisions with other sodium species and with an argon buffer gas. The transmission of a second, delayed, pulsed dye laser was monitored, serving as a probe of the (v″, J″) state’s population at various delay times. The argon pressure was varied and the procedure repeated. The Na2–argon collision cross section may also be determined by this method.