Pores Structure Change Induced by Heat Treatment in Cold-Sprayed Ti6Al4V Coating

In this study, the evolution of pores structure in cold-sprayed Ti6Al4V coating (TC4) was analyzed before and after 600-1100 degrees C heat treatment. It was found that almost no change happened to pores under the heat treatment temperature below 600 degrees C. When the heat treatment temperature was increased to 700 degrees C, the coating recrystallized, and pores turned to spheroid and healed because of the "bridging" effect. Some of the pores coarsened after 800 degrees C and 900 degrees C heat treatment. This kind of phenomenon grew severer when the heat treatment temperature increased to 1000 degrees C and 1100 degrees C. On the whole, with the increment of temperature, for the coating prepared at relatively low temperature, apparent porosity measured by image analysis method tended to go down first and then up, but it decreased all the time for the coating prepared at relatively high temperature. The reason for this phenomenon was contributed to the bonding state of particles in the coating. Only when there were fewer weakly bonded interfaces, the detachment between the particle interfaces which may be caused by release of residual stress did not occur, and there was no pores expansion and internal connectivity, so the porosity continuously decreased.