A design of experiments approach was used to characterize process-microstructure relationships in the twin wire arc process using zinc feed stock. Specifically, the effect of arc current, primary atomizing gas pressure, secondary atomizing gas pressure, and standoff distance on deposition efficiency, spray pattern shape, atomization behavior, coating porosity, and coating surface roughness were investigated. All work was conducted using a Praxair 8835 torch spraying 02Z zinc feed stock. It was found that primary and secondary atomizing gas pressure significantly affected spray pattern shape, atomization behavior, coating porosity and coating surface roughness. Arc current significantly affected spray pattern shape. Standoff distance significantly affected deposition efficiency, spray pattern shape, and surface roughness. Discussion will focus on using the relationships identified through this experiment to tune the wire arc process.

Concentrating solar power (CSP) systems represent a zero emission method for conversion of sunlight to electricity. CSP systems use an array of mirrors to concentrate sunlight on the surface of a heat exchanger and heat a working fluid. These heat exchanger surfaces must have high absorptivity and low emissivity in the solar spectrum. In addition, they must be capable of extended operation at temperatures in excess of 600°C. Initial development of solar selective coatings using the air plasma spray process will be discussed. Eight different coating materials were deposited onto 304L stainless steel substrates. Solar absorptance and emittance were measured from each coating in three conditions: as-deposited, after heat treatment at 600°C for six hours, and after polishing to a 1 µm finish. A figure of merit based upon solar power tower (SPT) operation was calculated from these data and compared to the industry standard solar selective coating for SPT receivers, Pyromark Series 2500 high temperature paint. This comparison shows that Ni-5Al, 80WC-20Co, and CeO plasma-sprayed coatings all have potential as solar selective surfaces for SPT receivers.

In this investigation, very low pressure plasma spraying (VLPPS) was used to produce yttria-stabilized zirconia (YSZ) coatings through both liquid and vapor deposition. Coatings created by liquid deposition were found to have a microstructure consisting of dense splats, while vapor-deposited layers exhibited a columnar structure similar to coatings produced by e-beam PVD. Columnar microstructure formation was dependent on substrate temperature and vapor flux continuity. Clear evidence of competitive crystal growth was observed in well-defined columnar coatings. Microstructures consisting of layers of splats and columns were also observed.

A Sulzer-Metco 6P Powder Flame Spray Torch spraying an alumina-titania ceramic powder RX60 6-axis robotic was characterized using an Accura G3(Tecnar Automation; Quebec, Canada) and a DPV-2000 (Tecnar Automation; Quebec, Canada). The two sensors were mounted side-by-side and a robot was used position the torch in relation to each sensor. Process gas flows were set using laminar flow element mass flow controllers. Accura and DPV measurements of particle temperature (Tp) and particle velocity (Vp) were made in succession at each operating condition without changing torch operating conditions. Data for a single designed experiment was collected with both sensors allowing for comparison of the two sensors across the operating space of a typical powder flame spray process.