Production and properties of functionally gradient films varying from amorphous Al(Ti, N) to hexagonal Al(Ti)N phase

Abstract

The application of sputtering in a mixed gas of argon (Ar) and nitrogen (N2) to Al80Ti20 resulted in the formation of compositionally and structurally gradient film consisting of amorphous Al(Ti, N) and hexagonal Al(Ti)N phases. By continuously changing the partial pressure (PN) of N2 from 0.02 to 0.1 Pa in a total Ar+N2 pressure of 1 Pa, the resulting phase is an amorphous Al(Ti, N) in the PN range below 0.06 Pa and changes to an Al(Ti)N through coexistent amorphous plus Al(Ti)N phases in the higher PN range. The average sputtered rate of the film was 0.9 μm/ks and the N2 concentration along the film thickness increases to 63 at% with an increase in PN to 0.1 Pa. As PN increases, the wave vector at the peak position of the amorphous halo in the X-ray diffraction patterns decreases continuously and crystallization temperature increases from 662 to 728 K. The Knoop hardness and the electrical resistivity measured along the film thickness increase from 325 to 2310 and from 2.4×10-7 Ωm to an infinite value, respectively, with an increase in N2 content in the amorphous phase and the subsequent phase transition to Al(Ti)N. The load leading to a failure in the film is 0.44 N which is about twice as large as that (0.24 N) for the Al(Ti)N phase. Thus, the sputtered amorphous-hexagonal phase film is concluded to have functionally gradient characteristics resulting from the compositional and structural gradients.