Modification of high-temperature oxidation of titanium diboride films by implantation with tantalum and titanium ions

Titanium diboride is an attractive material for protective coatings because of its high hardness, high electrical and thermal conductivities. However, many of its high-temperature applications are limited because of its poor oxidation behaviour beyond 700 degrees C. This paper presents a novel approach consisting of doping with implantation of higher valency atoms, to improve its oxidation resistance up to 900 degrees C. TiB2 films (nominal thickness 0.5 mu m) were deposited on polished substrates of stainless steel and alumina using a RF sputtering deposition system. Alumina was chosen as an inert substrate that is more "RBS friendly". Ions of Ta (as a higher valence dopant species) or Ti (to study self ion damage effects) were implanted using a MEVVA ion implanter at an extraction voltage of 65 kV corresponding to an average energy of 190 keV for Ta and 140 keV for Ti ions. Ion doses of 1 x 10(15) to 1 x 10(17) ions cm(-2) (corresponding to dopant concentrations of about 0.1-10 at.%) were implanted at nominal RT. After implantation, some samples were vacuum-annealed (30 min at 900 degrees C, at 1 x 10(-5) Torr) to crystallise the films and/or reduce the ion damage. Oxidation of the implanted samples was conducted at 800 and 900 degrees C for 1-4 h in air. Analysis was performed by using RES, SIMS, XRD and SEM techniques. The results show: (1) as-deposited films undergo rapid corrosion and spalling on oxidation; (2) as-implanted films show little improvement and undergo rapid corrosion and spalling on oxidation; (3) when implanted films are first vacuum-annealed and then oxidised, they show an improvement in corrosion resistance and do not undergo any spalling. Ta is thus an effective dopant for improving the oxidation resistance of TiB2 films. (C) 1998 Elsevier Science S.A.