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iTSSe
TSS
A D V A N C E D M A T E R I A L S & P R O C E S S E S | N O V E M B E R / D E C E M B E R 2 0 1 6
4 6
iTSSe
TSS
JTST
HIGHLIGHTS
14
alloy coatings tested in previous research. On the other hand,
corrosion resistance of the coating material (tested by electro-
chemical polarization in 0.1 M HCl solution) is quite low. Even
in the absence of interconnected porosity, this results in ex-
tensive, selective damage to the Fe-base matrix. This coating
material is therefore unadvisable for highly corrosive environ-
ments (Fig. 2).
EFFECT OF SOLID SHIELD ON COATING
PROPERTIES IN ATMOSPHERIC
PLASMA SPRAY PROCESS
Ting Liu, Lili Zheng, and Hui Zhang
This paper investigates the impact of shrouded shield
structure on plasma spray processes and optimal shield
structure selection. Plasma flame characteristics’ response to
solid shield structures is studied first, and experimental inves-
tigations are then performed for both atmospheric (APS) and
shrouded (SPS) plasma spray processes. Useof a conical shield
with a divergence angle of 5.5° and 90-mm length is effective
to form a low-oxygen (<2%) and high-temperature (>3000 K)
region in the plasma flame, which covers the main area where
particles pass by. The average particle temperature is higher
in SPS than APS with the given conditions, and such behavior
is intensified as solid shield length increases. Using SPS, more
disk-shaped splats are obtained and the oxygen concentration
in the coating is significantly reduced. The degree of oxidation
in the coatings is further reduced as the length of the solid
shield increases from 50 to 90 mm. Applying the solid shield
leads to high flame temperature and low oxidation; howev-
er, substrate overheating and velocity reduction may occur.
For the cases studied, optimal shield length is around 90 mm
(Fig. 3).
COLONIZATION OF BACTERIA ON
THE SURFACES OF COLD SPRAYED
COPPER COATING ALTERS THEIR
ELECTROCHEMICAL BEHAVIORS
Xinkun Suo, Peng Xia, Yi Liu, Leila Abdoli, Xiaotao Luo,
Guanjun Yang, and Hua Li
Copper coatings were fabricated on stainless steel plates
by cold spray. Attachment and colonization of
Bacillus sp.
on
the surfaces of cold spray copper coatings in artificial seawa-
ter were characterized and their effects on anti-corrosion per-
formance of coatings were examined. Attached bacteria were
fixed and observed using field emission scanning electron
microscopy (FESEM). Electrochemical behaviors including
potentiodynamic polarization and electrochemical imped-
ance spectroscopy with and without bacterial attachment
were evaluated using the commercial electrochemical analy-
sis station, Modulab. Results show that
Bacillus sp.
prefers to
settle on low-lying spots of coating surfaces in an early stage,
followed by recruitment and attachment of extracellular poly-
mers (EPS) secreted through metabolism of
Bacillus sp.
The
bacteria survives on coating surfaces with the protection of
EPS. The attachment model is proposed to illustrate bacteria
behaviors on the surface of copper coatings. Electrochemical
data shows that current density within the
Bacillus sp.
envi-
ronment decreases compared to that without. Charge-trans-
fer resistance increases markedly in bacteria-containing ASW,
suggesting that corrosion resistance increases and corrosion
rate decreases. The influence mechanism of bacteria settle-
ment on corrosion resistance of cold spray copper coatings is
discussed (Fig. 4).
Fig. 3 —
Optical micrograph of splat morphology: APS process.
Fig. 4 —
Surface morphology of copper powder.