Conventionally, an electroplating method, electroless plating method, sputtering deposition method, and plasma spraying method and the like have been adopted as a method for forming a film. However, a cold-spray method for forming a film using raw material powder in a solid phase has been paid attention as an alternative to the conventional methods for forming the film.
The cold-spray method is a method for forming a film including steps; putting raw material powder such as metal, alloy, intermetallic compounds, and ceramics into a supersonic gas flow heated; ejecting the raw material powder and the working gas together from a spout of a nozzle of a cold-spray gun; and crashing the raw material powder in a solid phase into a base material at high speed of 500 m/s to 1200 m/s.
The film formed by the cold-spray method is known as the film not easily oxidized nor thermally deteriorated as compared to a film formed by a conventional method. Further, the film formed by the cold-spray method is dense and excellent in adhesion, and is excellent in the film properties including electrical conductivity and thermal conductivity also.
However, the cold-spray method has drawback that raw material powder is clogged up in a nozzle in the cold-spray operation and it prevents the cold-spray method from being popular in the market. A cold-spray nozzle is usually made by using a metal material such as stainless steel, tool steel, and cemented carbide. When such a cold-spray nozzle made of metal is used in combination with a powder such as nickel powder, copper powder, aluminum powder, stainless steel powder, and “Inconel (Registered Trade Mark, the same hereinafter) alloy” powder as raw material powder, the raw material powder sticks on the inner peripheral surface of the cold-spray nozzle. Depending on the type of the raw material powder, the nozzle clogs up in a few minutes after starting of the cold-spray operation. Therefore, long time cold-spray operation has not been achieved. Such a phenomenon hinders the formation of a dense and uniform film. Same time, frequent exchange of the cold-spray nozzle may decrease the operation ratio of the cold-spray device and increase the cost for the film formation. To solve such problems, the following invention has been proposed.
Patent Document 1 discloses an object of the invention to drastically prevent both the sticking of the raw material powder to the divergent part of the nozzle and the clogging up of the cold-spray nozzle. Then, the measure disclosed is characterized in that a cold-spray nozzle that includes a convergent part and a divergent part; raw material powder is put into the convergent part from an inlet using working gas at a temperature equal to or below the melting point of the raw material powder; and eject the raw material powder from an spout of a nozzle at an outlet of the divergent part as a supersonic flow; wherein the divergent part, at least its inner peripheral surface is formed of materials including silicon nitride ceramics (N-based ceramics), zirconia ceramics (O-based ceramics), and silicon carbide ceramics (C-based ceramics), hereinafter collectively referred to as “OCN-based ceramics” is employed.
According to Examples disclosed in Patent Document 1, when copper powder is used as raw material powder and a cold-spray nozzle made of stainless steel is used, the cold-spray nozzle clogs up in approximately three to four minutes after starting of the cold-spray operation and it makes the cold-spray operation impossible. In contrast, when a cold-spray nozzle made of OCN-based ceramics was used, the phenomenon, sticking of copper powder to the inner peripheral surface of the cold-spray nozzle hardly occurs and the nozzle does not clog up even 30 minutes after starting of the cold-spray operation. Therefore, the invention disclosed in Patent Document 1 may effective to prevent the clogging up of the cold-spray nozzle.