A Perspective of Pulsed Laser Deposition (PLD) in Surface Engineering: Alumina Coatings and Substrates

Abstract

In this article, two original studies of the alumina as porous substrate and PLD (pulsed laser deposition) thin films in view of its biomedical and tribological applications are presented. The first biomedical study aimed to evaluate the role of Al2O3 on thin deposited nanostructures. For this purpose, cerium stabilized zirconia doped hydroxyapatite thin films were deposited by PLD onto high purity, high density alumina substrates with different low porosities. For deposition, an UV KrF* (λ=248 nm, τ ~ 25 ns) excimer laser was used for the multi-pulse irradiation of the targets. The nanostructured surface morphologies of the thin films with micro droplets were evidenced by atomic force microscopy and scanning electron microscopy and the compositions with a Ca/P ratio of 1.7 by energy dispersive spectroscopy. The films were seeded with mesenchymal stem cells for in vitro tests. The cells showed good attachment and spread and covered uniformly the surface of the samples. Different functions of substrate porosities are observed in the efficiency of developing long filopodia and of obtaining the optimal intracellular organization. The second study aimed to understand the influence of micro-structural and mechanical characteristics on the tribological behaviour of stainless steel samples with PLD alumina coatings produced using an UV KrF* (λ=248 nm, τ ~ 20 ns) excimer laser and a sintered alumina target. Various microscopic observation techniques were used in order to connect the tribological response to the amorphous microstructure of the coatings. The results correspond to the determination of the mechanical characteristics by nanoindentation tests, scratch tests, and a tribological behaviour analysis of the treated steel against 100Cr6. The films were stoichiometric, partially crystallized with an amorphous matrix and their surfaces had few particulates deposited on. The obtained values of hardness and elastic modulus of the films were in good agreements with literature data.