Pulsed laser deposition of titanium oxide coatings at room temperature—structural, mechanical and tribological properties

Abstract

Titanium oxide (TiO x ) coatings exhibit extraordinary optical, electrical and tribological properties, but very less is known about coatings deposited at room temperature. In the present work this gap was closed by employing the room temperature pulsed laser deposition (PLD) technique. In order to simulate different deposition conditions, the substrate (AISI M2, molybdenum) surfaces were situated parallel (‘on-axis’ geometry) and perpendicular (‘off-axis’) to the pure titanium targets ablated by the Nd:YAG lasers with a wavelength of 1064 nm. The combination of a four-beam PLD evaporator with a suitable movement of the substrates resulted in a high-rate film growth on large surfaces. The coating structure investigated by X-ray diffraction consists of a mixture of monoclinic β-TiO 2 and amorphous TiO x phase. The ratio of the amount of the phases, the hardness and the elastic constants strongly depend on the O 2 gas pressure and the target–substrate arrangement applied for deposition. Owing to the very high adhesion and their very smooth surfaces, the TiO x coatings exhibit friction coefficients of approximately 0.55 and wear rates of lower than 10 −15 m 3 N −1 m −1, turning out that titanium oxide coatings deposited by means of PLD are very promising candidates for wear protection applications.