Splat solidification

To rationalize the isothermal assumption, Dykhuizen 39() discussed two related physical phenomena. First, heat may be drawn out of the substrate from an area that is much larger than that covered by asplat. Thus, the 1 -D assumption in the Stefan problem becomes invalid, and a solution of multidimensional heat conduction may make the interface between a splat and substrate closer to isothermal. Second, the contact resistance at the interface is deemed to be the largest thermal resistance retarding heat removal from the splat. If this resistance does not vary much with substrate material, splat solidification should be independent of substrate thermal properties. Either of the phenomena would result in a heat-transfer rate that is less dependent on the substrate properties, but not as high as that calculated by Madej ski based on the... 

Hofmeister et al. 4l() employed two high-speed thermal imaging systems to record spatial and temporal temperature distributions at the splat-substrate interface, and to observe droplet spreading during impact and solidification on a quartz plate. They observed... 

Further extensions of Madej ski s mod ell4011 may include (a) turbulence effect, (b) Rayleigh instability or Taylor instability and droplet breakup, (c) vibrational energy, and (d) influence of solidification on flow)514 Some issues related to the deformation and solidification of droplets on a flat substrate in splat quenching have been addressed in Refs. 380 and 514. To date, analytical models addressing droplet impingement on a semi-solid surface have not been found in available literature. 

Dhiman and Chandra [20] developed an analytical model to predict the substrate temperature at which splashing would occur by using a one-dimensional model for solidification of a molten metal droplet in contact with a semi-infinite substrate. They assumed that splashing occurred if the thickness of the solid layer reached that of the splat by the time the droplet had finished spreading. The thermal contact resistance between the droplet and surface was found to play a critical role in... 

At high magnification, the microroughness of the plasma-sprayed surface is more random than that produced by any chemical process. The pores are quite deep, and many knob-like protrusions can be seen. These protrusions result from the splat cooling and rapid solidification of the Ti-6A1-4V droplets as they strike the substrate. At lower magnifications, some macroscopic inclusions are evident. 

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