Abstract
Splats of hydroxylapatite (HA) and alumina were obtained via plasma spraying using systematically varied combinations of plasma velocity and temperature, which were achieved by altering the primary plasma gas flow rate and plasma gas composition. Particle size was also varied in the case of alumina. Splat spreading was quantified via computer- aided image analysis as a function of processing variations. A comparison of the predicted splat dimensions from a model developed by Madejski with experimental observations of HA and alumina splats was performed. The model tended to underestimate the HA splat sizes, suggesting that evaporation of smaller particles occurred under the chosen experimental conditions, and to overestimate the observed alumina splat dimensions. Based on this latter result and on the surface appearance of the substrates, incomplete melting appeared to take place in all but the smaller alumina particles. Analysis of the spreading data as a function of the processing variations indicated that the particle size as well as the plasma temperature and velocity influenced the extent of particle melting. Based on these data and other considerations, a physical model was developed that described the degree of particle melting in terms of material and processing parameters. The physical model correctly predicted the relative splat spreading behavior of HA and alumina, assuming that spreading was directly linked to the extent of particle melting.
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Abbreviations
- A n :
-
Nozzle cross-sectional area (m2)
- d :
-
Particle size (m)
- E k,Es,Ev :
-
Kinetic, surface, and viscous energies (J)
- H :
-
Plasma gas enthalpy (J/mole)
- δH m :
-
Latent heat of fusion (J/mole)
- k :
-
Thermal conductivity (Js-1m-1 K-1)
- M g :
-
Plasma gas mass flow rate (kg/hr)
- MW:
-
Molecular weight (g/mole)
- Re :
-
Dimensionless Reynolds number
- t :
-
Time(s)
- T :
-
Temperature (K)
- V :
-
Plasma gas velocity (m/s)
- W :
-
Electrical power input (J/s)
- Wloss :
-
Rate of heat loss to the torch cooling water the torch cooling water (J/s)
- We :
-
Dimensionless Weber number
- ξ:
-
Dimensionless splat radius
- ρ:
-
Density (g/cm3)
- ρg :
-
Average plasma gas density (g/cm3)<╖>
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Yankee, S.J., Pletka, B.J. Effect of plasma spray processing variations on particle melting and splat spreading of hydroxylapatite and alumina. JTST 2, 271–281 (1993). https://doi.org/10.1007/BF02650476
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DOI: https://doi.org/10.1007/BF02650476