Low-Pressure Vacuum Plasma Spraying LPPS, VPS

Low-pressure plasma spraying (LPPS), a.k.a vacuum plasma spraying (VPS) is the injection within an evacuated spray chamber of metal or ceramic powder 

Optimised LPPS parameters were plasma power of 30 kW, argon gas flow rate of 30 slpm, hydrogen flow rate of 4 simp, powder feed rate of 12 g min-1, chamber pressure of 60 mbar and stand-off distance of 220 mm. Immediately adjacent to the interface substrate-coating an approximately 0.1 pm thick interdiffusion zone developed in the Ti6Al4V substrate with elevated Ca, P and O contents followed by a thin layer of ACP and then by a layer of oxyhydroxyapatite (Ca/P 1.67) as ascertained by Raman spectroscopy (absence of the stretching vibration of OH- 

XRD investigation showed that some thermal decomposition occurred during LPPS in coatings of type Cl as revealed by the presence of traces of TCP and even CaO. Coatings of type C2 contained a reduced amount of TCP but no CaO. Postspray annealing at 900 °C for 10 h removed all traces of decomposition phases as well as ACP that is known to crystallise under these conditions by transforming to HAp (Filiaggi, Coombs and Pilliar, 1991). 

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