Ceramic coating is a very popular technology for improving the properties of structural materials. A titanium nitride (TiN) coating is a typical example and has been widely applied to cutting tools, electronic devices and many other fields utilizing its superior physical properties. This paper sought to produce a graded TiN coating on a Ti substrate by combining Supersonic Free-Jet PVD (SFJ-PVD) with a reactive plasma-metal reaction technique. The authors have developed SFJ-PVD as a new coating method in which a coating film is formed by depositing nanoparticles with very high velocity onto a substrate. SFJ-PVD can provide a high deposition rate and thick film coating. Gradually changing the nitrogen flow rate during deposition produces a graded TiN coating, in which composition changes gradually from pure Ti to TiN. A monolithic TiN coating is also produced with SFJ-PVD. XRD analysis of the graded TiN detected peaks for Ti, Ti 2 N and TiN, while only a TiN peak is observed in the monolithic TiN coating. EPMA analysis of a graded coating reveals a gradual compositional change from pure Ti to TiN. Few pores or cracks are observed in a graded TiN or in a monolithic TiN formed under the optimized conditions of SFJ-PVD.

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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. (Received February 19, 2001; Accepted May, 15, 2001) Keywords: ultra fine particle, gas evaporation, physical vapor deposition, supersonic free jet, aluminum, titanium

The authors previously developed Supersonic Free-Jet PVD (SFJ-PVD) as a new coating method in which a coating film is formed by depositing nanoparticles at very high velocity onto a substrate. This SFJ-PVD provides a rapid deposition rate and produces a mixture of different kinds of nanoparticles formed in different evaporation chambers on the substrate. This paper describes the preparation of graded Al/ AlTi, Ti-Al, and Ti-Al-N coating films with SFJ-PVD. Ti-50 at%Al film and graded Al/AlTi film are produced by depositing Al and Ti nanoparticles formed in different evaporation chambers with the controlled evaporation rates of Al and Ti. Ti-Al-N film is produced by depositing nanoparticles formed in the evaporation chamber with a controlled partial pressure of N 2 in an atmosphere of He. Mixing Ti and Al nanoparticles by depositing them onto a substrate produces in-situ syntheses of -TiAl and 2 -Ti 3 Al intermetallic compounds on the substrate regardless of the substrate temperature in these experimental conditions. A smooth, compact, and defect-free structure is formed both at the interface between the substrate and the coating films and inside the coating films. XRD analysis reveals the crystal structure of the Ti-Al-N film to be TiN, Ti