Spray nozzle assembly for gas dynamic cold spray and method of coating a substrate with a high temperature coating
The invention relates to an improved design for a spray gun and application system for cold gas dynamic spraying of a metal, alloy, polymer, or mechanical mixtures thereof. The gun includes a rear housing comprising a powder inlet and a gas inlet, a front housing removably affixed to the rear housing and comprising an mixing cavity therein for mixing of the powder and gas and an exit therefrom, a nozzle holder having a bore disposed therethrough and removably affixed to the front housing, and a polymeric nozzle positioned within the nozzle holder, an interior taper of the nozzle holder bore complementing an exterior taper of the nozzle. The nozzle having an initially converging, subsequently diverging centrally disposed bore therein adapted to receive the mixed powder and gas from the mixing chamber and the nozzle holder including a cooling jacket which is thermally coupled to the nozzle adjacent the nozzle inlet and mechanically coupled downstream of the nozzle inlet.
1. A method for gas dynamic cold spraying a substrate with a high temperature coating comprising the steps of
(a) providing a substrate
(b) providing a powder which has a melting temperature of more than about of 700° C. which powder is to be applied to the substrate;
(c) providing an apparatus having a housing with an inlet for a gas and a mixing cavity disposed within the housing for mixing the powder and the gas in communication with the inlets, the cavity having an exit therefrom;
(d) providing a nozzle assembly including a nozzle holder having a nozzle collar which includes a bore centrally disposed therethrough, and said nozzle assembly further including a cooling jacket including a cooling media, and a non-metallic nozzle having an exterior surface, a central longitudinal axis and a centrally disposed bore therethrough,
(i) said nozzle bore having an internal passage defining a converging section extending partway therethrough from, an inlet of the nozzle bore and a diverging section extending toward an outlet end of the nozzle bore,
(ii) the nozzle bore inlet in communication with said mixing cavity exit,
(iii) the nozzle collar forming a thermal mechanical interface with the exterior surface of the nozzle, where the interface is spaced apart from the converging section of the internal passage along the central longitudinal axis of the nozzle to allow the cooling media to be in thermal contact with the exterior surface of the nozzle corresponding to the converging section of the nozzle, and
(e) applying said powder to said substrate from the mixing cavity through the nozzle of the nozzle assembly.
2. A method for gas dynamic spraying as set forth in claim 1 wherein the powder is a superalloy.
3. A method for gas dynamic spraying as set forth in claim 2 wherein the powder is one or more alloys of nickel chromium aluminum yttrium, cobalt chromium aluminum yttrium, iron chromium aluminum yttrium.
4. A method for gas dynamic spraying as set forth in claim 1 wherein the powder is a high temperature alloy.
5. A method for gas dynamic spraying as set forth in claim 1 wherein the powder comprises one or more of titanium, tantalum, and niobium.