ALUMINUM OXIDE COATINGS PRODUCED WITH THE
HIGH VELOCITY OXY-FUEL PROCESS
J. Gutleber, S. DePalo, W. Smith, H. Herman
and D. Crawmer*
*Praxair Surface Technologies, Appleton, WI
High Velocity Oxy-Fuel (HVOF) spraying is an emerging
process for producing dense protective coatings for tribological applications.
Traditionally, ceramic materials are thermal spray processed using plasma
technology where the density of the coating is limited by the velocity
of the particles in the plume. An alternative is to use HVOF to spray the
ceramic material to produce high quality dense coatings. CTSR, in conjunction
with Praxair Thermal Spray Systems, is carrying out studies on determining
the relationship among processing parameters, in flight particle behavior
and resultant microstructures of alumina (-22/+5 m
m) coatings produced using HVOF. Fig. 1 shows the Praxair HV-2000 torch,
which when used in an extended combustion chamber configuration, has the
capability to spray alumina.
Figure 1. HVOF Torch
Using the Laserstrobe Control Vision system, the
particle velocity was 680 ± 50 m/s with
hydrogen as the fuel gas.
Figure 2. HVOF Alumina splat
Figure 3. Optical Micrograph of HVOF sprayed Alumina coating
Fig. 2 shows a solidified alumina splat
produced by HVOF onto a polished substrate.
The density of these coatings can
be observed in the cross-section micrograph given in
Figure 3. Coating hardness was 1105 ±
63, DPH300. The primary phase in the coating was g
-Al2O3, Figure 4.
Figure 4. XRD Pattern
for HVOF sprayed Alumina coating
The results indicate that HVOF
can be used to produce dense alumina coatings. Electrical and tribological
properties of these coatings are under investigation.
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12/30/98 VG