Effect of substrate oxidation on spreading of plasma-sprayed nickel on stainless steel

Abstract

Plasma-sprayed, molten nickel particles (∼ 60 μm diameter) were photographed during impact on oxidized 304L stainless steel surfaces that were maintained at either room temperature or at 350°C. Steel coupons were oxidized by heating them at different temperatures. A fast chargecoupled device (CCD) camera captured time-integrated images of the spreading splat. A two-color pyrometer collected thermal radiation from particles and recorded the evolution of their temperature after impact. Molten nickel particles impacting on oxidized steel at room temperature fragmented significantly, while heating the surfaces produced splats with disk-like morphologies. Impact on steel that was highly oxidized induced the formation of finger-like splash projections at the splat periphery. Thermal contact resistance between splats and non-heated oxidized steel was calculated from splat cooling rates and found to decrease as the degree of oxidation increased. On heated, oxidized steel thermal contact resistance was much lower and did not change significantly with the degree of oxidation. It was concluded that thermal contact resistance was largely influenced by adsorbates on the steel surface that evaporated when the surface was heated or oxidized.

Splat Formation Mechanism in Thermal Spraying

“…As the slope of the splat temperature history curve, dT/dt, was defined to be the cooling rate of the splat, the splat cooling rates on heated substrates were remarkable higher than those substrates with room temperature, and increases with substrate heating temperature. Similar result has been proposed while some kinds of micrometer-sized particles were thermally sprayed onto flat substrate surfaces (32)- (34) , which proposed that the investigation on the thermal history of the millimeter-sized free falling droplet is meaningful for understanding the individual thermal sprayed particle. Moreover, the measurement of temperature histories at droplet-substrate interface of Cu splats deposited onto AISI304 substrate kept at various ambient pressures in deposition chamber are shown in Fig.…”

“…As reported up to now, effect of dominating process factors on the flattening behavior of an individual splat onto flat substrate surface has been systematically investigated through theoretical (4), (5) , numerical (6)- (8) and experimental methods (9)- (11) in the last few decades.…”

Formation of Solid Splats During Thermal Spray Deposition

“…When metal surfaces are preheated over the transition temperature ( Ref 4,5,10,13,25,26,30,37,38,40,43,52,56,[60][61][62][63][64][65][66] or treated with laser energy densities high enough to modify the oxide layer (Ref 17,20,58), the surface is changed. In addition to desorbtion of adsorbates, the oxide layer composition, thickness and roughness is modified.…”

Effects of Surface Chemistry on Splat Formation During Plasma Spraying

“…The underlying cause of the change in splat morphology is not clearly understood. It has been attributed to desorption of gases ( Ref 7,8,11,12), oxidation of the surface ( Ref 3,9), and changes in surface roughness (Ref 1, 3). Jiang (Ref 11) showed that the contact area between splat and substrate is increased and the adhesion is improved on substrates where the adsorbed gas has been removed or reduced.…”