Structure and mechanical properties of co-deposited TiAl thin films

Abstract

Titanium–aluminium compounds are very attractive materials for aerospace and high performance engine applications owing to their low density, high temperature strength and high specific strength. Specific compositions may also be suitable as solar absorber surfaces. Consequently, a detailed investigation of the titanium-aluminium binary alloy coating system is being carried out. Coatings have been deposited from pure titanium and aluminium cathodes, via the closed field unbalanced magnetron sputtering technique. Two different magnetron co-sputtering techniques were used: co-deposition, giving a gradient in coating composition across the surface of the substrates; and multi-layer deposition, giving fine multi-layers of different thickness. A range of compositions from 0 to 100% titanium was deposited. The coatings were studied in the as-deposited condition and after successive annealing treatments in order to obtain stable intermetallic phases. Changes in structure and phase composition were studied by SEM and XRD analysis after each annealing process. Mechanical analysis was also conducted, consisting of hardness and friction and wear testing. This paper concentrates mainly on the multi-layer deposited films and the results obtained to date are presented here.