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JTST HIGHL IGHTS

ADVANCED MATERIALS & PROCESSES •

AUGUST 2014

plasma spray (SPPS) created layered porosity, called inter-pass

boundaries, in yttria-stabilized zirconia (YSZ) TBCs. IPBs have

been shown to be effective in reducing thermal conductivity. Op-

timization of the IPB microstructure by SPPS produces YSZ TBCs

with a thermal conductivity of 0.6 W/mK, approximately a 50%

reduction compared to standard air plasma spray (APS) coatings.

Preliminary tests show SPPS YSZ with IPBs exhibit equal or

greater furnace thermal cycles

and erosion resistance compared

to regular SPPS and commer-

cially made APS YSZ TBCs.

“Deposition

Behavior of

Semi-Molten Spray

Particles During

Flame Spraying of

Porous Metal Alloy”

Jian-Tao Yao, Jun-Qiang

Ren, Hui-Bin Huo,

Guan-Jun Yang, Cheng-Xin

Li, and Chang-Jiu Li

To understand semi-molten

spray particle deposition behav-

ior, porous 316L stainless steel

deposits were fabricated by

flame spray with semi-molten

particles with different melting

degrees and spray angles. The

effects of spray angle relative to

deposition efficiency and deposit porosity were investigated. The

morphology of individual splats deposited on flat surfaces at dif-

ferent angles was examined. Results show that spray angle signif-

icantly influences deposit porosity, pore structure, and deposition

efficiency. The slipping of solid cores in semi-molten spray parti-

cles was clearly observed when semi-molten particles impact the

polished substrate with an inclined angle. A random model simu-

lated the particle deposition process and, after considering the ef-

fects of both solid particle slipping upon impact and particle

melting degree, simulated porosity calculations agreed well with

the experimental observation.

“Numerical Analysis of Multicomponent

Suspension Droplets in High-Velocity Flame

Spray Process”

Ebrahim Gozali, Mahrukh Mahrukh, Sai Gu,

and Spyros Kamnis

The liquid feedstock or suspension as a different mixture of

liquid fuel ethanol and water is numerically studied in the high-

velocity suspension flame spray (HVSFS) process, and results

for homogenous liquid feedstock of ethanol and water are com-

pared. The mixture’s effects on droplet aerodynamic breakup,

evaporation, combustion, and gas dynamics of the HVSFS

process are thoroughly investigated. The exact location where

particle heating is initiated (above the carrier liquid boiling point)

can be controlled by increasing water content in the mixture. In

this way, particle inflight time in the high-temperature gas re-

gions can be adjusted to avoid adverse effects from surface

chemical transformations. The mixture is modeled as a multi-

component droplet, and a convection/diffusion model, which

takes into account the convective flow of evaporating material

from the droplet surface, is used to simulate the suspension evap-

oration. The model consists of several sub-models that include

premixed combustion of propane-oxygen, non-premixed ethanol-

oxygen combustion, modeling of multicomponent droplet

breakup and evaporation, as well as heat and mass transfer be-

tween the liquid droplets and gas phase.

Evaporation rate of droplets carrying four different percentages of

ethanol-water in solvent along the centerline.

ASM Handbook,

Volume 5A: Thermal Spray Technology

Volume 5A

is a replacement for the

Handbook of Thermal Spray Tech-

nology,

edited by J.R. Davis (2004). It provides an introduction to

modern thermal spray processes including plasma spray, high ve-

locity oxy-fuel, and detonation gun deposition, as well as a descrip-

tion of coating properties and their wear, corrosion, and thermal

barrier characteristics. Principles, types of coatings, applications,

performance, and testing/analysis also are covered.

Visit

asminternational.org

to learn more.

Schematic illustration of a semi-molten

particle impact condition: (a) at an

off-normal spray angle on a flat

substrate, (b) at a normal spray angle

on a previous particle. V: impact

velocity; V

: normal velocity;

: tangential velocity.