Cold spray apparatus using a self-cleaning aerospike nozzle

A spray gun for accelerating a working fluid comprising a carrier gas having solid particles entrained therein to a supersonic velocity for depositing said particles on a substrate, said spray gun comprising an aerospike nozzle including a duct and an aerospike with a first portion disposed in said duct to form a working fluid flow path between an inner surface of said duct and an outer surface of said aerospike and a second portion tapering from an outlet of said duct to a downstream end, wherein:

• said inner surface of said duct wall and said outer surface of said first portion of said aerospike are configured to accelerate fluid introduced to a working fluid flow path inlet at a Mach number M<1, to M=1 at a throat region between said fluid flow path inlet and a working fluid flow path outlet, and to a supersonic velocity M>1 at said working fluid flow path outlet, said second portion of said aerospike being configured to maintain said working fluid at a supersonic velocity from said working fluid flow path outlet to a nozzle exit at said downstream end of said second portion of said aerospike;
• said spray gun further comprises a main flow path for a main fraction of said carrier gas, a bypass flow path for a bleed fraction of said carrier gas, and a particle feeder for introducing particles into said fluid flow path at a particle feed location upstream of said throat region to form said working fluid;
• and
• said bypass flow path includes bleed openings for introducing said bleed fraction to said main flow path upstream of said particle feed location for creating a buffer layer of carrier gas on the surface of said aerospike in said working fluid flow path.