Bioactivity of fluorapatite/alumina composite coatings deposited on Ti6Al4V substrates by laser cladding

Abstract

Hydroxyapatite (HA) is one of the most commonly used coating materials for metal implants. However, following high-temperature deposition, HA easily decomposes into an unstable phase or forms an amorphous phase, and hence, the long-term stability of the implant is reduced. Accordingly, the present study investigates the use of fluorapatite (FA) fortified with 20 wt% alumina (a-Al 2 O 3 ) as an alternative biomedical coating material. The coatings are deposited on Ti6Al4V substrates using a Nd:YAG laser cladding process performed with laser powers and travel speeds of 400 W/200 mm/min, 800 W/400 mm/min and 1200 W/600 mm/min, respectively. The results show that for all of the specimens, a strong metallurgical bond is formed at the interface between the coating layer and the transition layer due to melting and diffusion. The XRD analysis results reveal that the cladding layers in all of the specimens consist mainly of FA, b-TCP, CaF 2 , Ti and h-Al 2 O 3 phases. In addition, the cladding layers of the specimens prepared using laser powers of 400 and 800 W also contain CaTiO 3 and CaAl 2 O 4 , while that of the specimen clad using a power of 1200 W contains TTCP and CaO. Following immersion in simulated body fluid for 14 days, all of the specimens precipitate dense bone-like apatite and exhibit excellent bioactivity. However, among all of the specimens, the specimen that is prepared with a laser power of 800 W shows the best biological activity due to the presence of residual FA, apatite-generating CaTiO 3 and a rough cladding layer surface.

Biomedical materials and techniques to improve the tribological, mechanical and biomedical properties of orthopedic implants – A review article

“…C. S. Chien et al studied Flourapatite as substitute of HA. The presented FA showed better stability and same bioactivity as HA [10]. Hongjian Zhou et al revealed that nanoscale HA proved better biocompatibility, enhanced mechanical properties, and osseointegration properties [75].…”

“…These bioactive materials faced limitations in medical applications especially load-bearing implants because they are brittle and weak [9]. These materials have very low fracture toughness (usually < 1 MPa.m 1/2 ) compared to cortical bones (2-10 MPa.m 1/2 ) [10]. In the other applications which no load or small loads are induced, the bioactive materials proved excellent treatment results, as an example the middle ear bones replacement [11].…”

“…After that, it became of great interest to be used in bone implants [7]. Ti is considered non-toxic, even at high doses, to the human body [6], [10], [31].…”

Comparison of Mechanical and Barrier Properties of Al2O3/TiO2/ZrO2 Layers in Oxide–Hydroxyapatite Sandwich Composite Coatings Deposited by Sol–Gel Method on Ti6Al7Nb Alloy

“…The simultaneous achievement of appropriate bioactive and mechanical properties of hydroxyapatite on a metal substrate can be achieved by applying a composite coating using an HAp and oxide mixture. Numerous studies [25][26][27][28][29] have investigated the variation of the microstructural, compositional, morphological, or surface properties of such coatings and their influence on the bioactivity, mechanical, and bonding strength. There is also another approach, consisting of the production of layered composite coatings, where the oxide layer, e.g., TiO 2 [30][31][32], ZrO 2 [32][33][34], Al 2 O 3 [26,31], and SiO 2 [30], is applied directly to the substrate and the HAp layer is deposited on top of it.…”

An analytical model to predict and minimize the residual stress of laser cladding process

“…In this process, a laser heat source is used to deposit a thin layer, mostly at micro-scale, of a desired material on a substrate material [2]. One of the challenges of this process is the formation of tensile residual stresses in the thermally treated area [3][4][5].…”