Very low pressure plasma spraying (VLPPS) is an emerging process allowing manufacturing oxide and metallic coatings by condensation of vapors generated by feedstock powder vaporization. This process operates at unusually low pressures, typically between 100 and 1000 Pa. This paper aims at presenting recent developments for manufacturing Ti,Al,N coatings via a reactive mode. At first, nitrogen was used as the primary plasma forming gas to enrich spraying surrounding with nitriding species. Plasma jet mass enthalpy and substrate surface temperature were varied to evidence nitride phase formation during spraying. Then, a secondary nitrogen injection was implemented and located close to the surface to be covered in view of creating a continuous nitrogen supply to promote the nitriding mechanisms on the surface. SEM, XRD, GDOES and NHT were implemented to characterize coatings structure. This study highlights the nitrides formation versus spray operating conditions. The microstructural and mechanical features as well as the chemical composition are presented.

Very low pressure plasma spraying (VLPPS) has been used to manufacture thin, dense, finely-structured ceramic coatings for various applications. This paper presents the results of work in which VLPPS is used to deposit metal. Aluminum was chosen as a demonstrative material, due to its moderate vaporization enthalpy (38.23 KJ·cm -3 ), with the objectives of better understanding the behavior of a solid precursor injected into the plasma jet, leading to the formation of vapors, and controlling the factors affecting coating structure. Nearly dense aluminum coatings were successfully deposited by VLPPS at 100 Pa with an intermediate power (45 kW) plasma torch. Optical emission spectroscopy (OES) was used to observe the behavior of the metal powder injected into the plasma jet, and simplified CFD modeling provided a better understanding of thermophysical mechanisms. The effect of powder size distribution, substrate temperature, and spray distance were studied. Coatings were characterized by SEM observations and Vickers microhardness measurements.