Correlations between spraying conditions and microstructure for alumina coatings produced by HVOF and VPS
- Univ. of Cambridge (United Kingdom)
- TWI, Cambridge (United Kingdom)
Coatings have been produced on steel substrates by thermal spraying of alumina, using the High Velocity Oxy-Fuel (HVOF) and Vacuum Plasma Spraying (VPS) techniques. Only fine powder ({approximately} 10 {micro}m) could be sprayed by HVOF, but VPS was carried out both with this powder and two coarser ones. Particle impact velocities were measured using a mechanical technique based on twin rotating cylinders. These were shown to be in the range 100--300 m s{sup {minus}1} for VPS, depending primarily on the chamber pressure. The limited data obtained to date indicate that velocities during HVOF are appreciably higher. The phase constitutions of the coatings were studied using three different techniques. The coatings were in all cases found to consist largely of {gamma}-alumina. The {alpha}-alumina content, attributable to the presence of unmolten particles, varied between about 10% and 30%. Porosity contents, determined using high precision densitometry, were in the range 2--8%. For the VPS coatings, higher impact velocities, lower {alpha} phase contents and lower porosity levels were found for the intermediate size ({approximately} 15 {micro}m) particles, the latter two being similar to those for the HVOF coatings. The erosion resistance of these two coatings were also found to be similar.
- OSTI ID:
- 160454
- Report Number(s):
- CONF-940684--; ISBN 0-87170-509-5
- Country of Publication:
- United States
- Language:
- English
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