Erosion of Surfaces at Elevated Temperature

The standard picture of erosion from a chemically inert surface exposed to energetic particles can be divided into two categories. The first, physical sputtering, is independent of surface temperature and proportional to the incident particle flux such that the physical sputtering rate, Rps = Yps Jin (where Yps is the temperature independent physical sputtering yield and J n is the incident particle flux). The second is the sublimation/evaporation rate, JQ, which does not depend on the flux of incident particles and strongly increases with increasing surface temperature. 

The erosion rate is, therefore, expected to remain constant, with increasing temperature, until the sublimation/evaporation rate becomes comparable to the physical sputtering rate. As the surface temperature increases further, the increase expected from sublimation should dominate the erosion. This conventional picture, however, is contradicted by experimental data where the erosion yield is found to be temperature dependent and a strong increase in the erosion rate is observed at temperatures less than those expected from thermodynamic sublimation (see Fig. 14.8). 

Nelson [29] first observed this dramatic increase in the loss rate of material from metal surfaces at elevated temperature while subjected to ion beam bombardment. The increase in the loss rate began at a lower temperature than could be explained by the vapor pressure of the material, yet the enhanced loss term had the same characteristic dependence on temperature as that exhibited by surface evaporation. Subsequent measurements on a variety of materials, including W [30] and C [31,32] exhibited similar behavior. 

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