Formation of titanium and aluminum films by supersonic free-jet PVD method

This paper presents the development of supersonic free jet PVD as a new coating method for structural material to overcome technical problems contained in other coating methods. This PVD method consists of evaporation in gas atmosphere and deposition in vacuum, i.e., ultra-fine particles are formed, carried and deposited to form film in a space of connected chambers, where ultra-fine particles formed by the evaporation of material in an evaporation chamber with helium gas atmosphere are carried to a substrate with gas flow generated by the pressure difference between the evaporation chamber and a vacuumed deposition chamber and deposited with high velocity to form film. This study aims to form the metallic films of titanium and aluminum with the method and to elucidate the effects of control parameters for the development of the method. The velocity of ultra-fine particles should be an important parameter for the film formation. In order to increase carrier gas velocity to increase particle velocity, we designed a nozzle on the assumption of one-dimensional isentropic flow to attain the gas velocity of Mach 3.6 at the outlet of the nozzle. The results obtained are as follows: (1) Reduction of coarse particles by suppressing the stagnancy and secondary agglomeration of particles is necessary for producing metallic films of titanium and aluminum. (2) Growth rate of film increases in proportion to electric power to evaporate source metal. (3) To heat a nozzle is effective for the formation of film without voids. (4) No cracks were formed by indenting the diamond indenter of micro Vickers hardness tester at the interface between substrate and coated film with the force of 4.9 N, which indicates strong adhesion between them.