**Abstract**

The aim of this study is to determine the effect of Titania on mechanical properties and wear behavior of Alumina-10 wt.% TCP ceramics and to evaluate the performance of Titania in improving their resistance to these effects. Al2O3–10 wt.% β-TCP mingled with TiO2 to obtain a mixture which is considered as a bioactive coating that may be used in orthopedic implants. Representative bioceramic samples of such blends were prepared with different percentages of Titania and then tested using different methods and techniques. Mechanical properties, fracture toughness were evaluated using the modified Brazilian, semi-circular bending specimens. A pinon-disk tribometer was retained to study the wear behavior. Based on the obtained results, it was found that the best mechanical properties and wear resistance was displayed for Alumina-10 wt.% TCP-5 wt.% Titania composite. This composite presents a good combination of flexural strength (σ<sup>f</sup> ≈ 98 MPa), compressive strength (σ<sup>c</sup> ≈ 352 MPa), fracture toughness (KIC ≈ 13 MPa m1/2) and micro-hardness (Hv ≈ 8.4 GPa). In terms of tribological properties, the lowest wear volume and wear resistance was recorded for Al2O3–10 wt.% TCP 5 wt.% TiO2 composition.

**Keywords:** Titania, mechanical properties, wear behavior, fracture, biomaterial

#### **1. Introduction**

Biomaterial research is described through the introduction of biotechnology and advances in the comprehension of the biocompatibility of human tissues [1]. In this context, Tissue engineering applies several methods from materials engineering and life sciences in order to create artificial constructs and to achieve better and faster biological healing outcomes [2]. Bone tissue engineering researchers are interested to develop new synthetic biomaterials with similar properties to native bone [2]. Among the biomaterials, bioceramics which are widely used in medical applications and more precisely for implants in orthopedics [2].

Special attention has been given to β-tricalcium phosphate (β-Ca3(PO4) 2 ) (β-TCP) due to their bone-like chemical composition as well as excellent biological properties and its outstanding biological responses to physiological environments. The use of TCP has been limited in the human body due to its weak rupture resistance [3]. Therefore, much research has been interested in enhancing the mechanical resistance of β-TCP by the inclusion of several additives [4].

Alumina (Al2O3) have been widely studied due to their bioinert with human tissues, high wear resistance, fracture toughness and high strength [5]. The study by Sakka et al. [6] has recently been concerned with alumina/ β- tricalcium phosphate system with different percentages of β-TCP. These Al2O3/β-TCP composites have showed a good combination of tensile strength (26.69 MPa), compressive strength (173,468 MPa) and fracture toughness (8,762 MPa m1/2).

The functions of additives for alumina have been often aimed to lower the sintering temperature, customize the microstructure as well as improve the product properties. In order to improve the mechanical and tribological resistance of these composites, it is essential to introduce a reinforcing agent: metallic dispersion or ceramic oxide. In this case, among the ceramic oxide agents, the addition of Titania (TiO2) has been reported to promote the sintering. TiO2 addition not only reduces the sintering temperature of alumina, but also influences the mechanical properties [7]. Due to its excellent wear resistance, its biocompatibility, its chemical inertness and its chemical stability in aqueous environments, we have chosen titania as the agent of reinforcement to be added to the Al2O3–10 wt.% TCP composites [8, 9]. The amounts of Titania were varied from 0 wt.% to 10 wt.%. Hence, this study aims to investigate the effects of TiO2 addition to the Alumina-10 wt.% TCP composite mechanical and triboligical properties and evolution of microstructure.

Firstly, after implantation, the bone substitute suffers from several mechanical stresses notably bending and compressive stresses. Fracture, compression and bending tests are essential to ensure adequate resistance and compatibility with bone resistance and to evaluate the fracture behavior of the substitute used under tensile-shear loading [10–12].

Secondly, cracks and flaws which certainly exist in the sample reduce in a significant way the load-bearing capacity and then cause the substitute to break [13, 14]. The fracture toughness and stress intensity factor have been proposed to express the critical stress states in the vicinity of the crack tip, in the aim to analyze crack initiation and propagation [14].

Thirdly, the problem of wear due to friction in the prosthesis for the substitution of knee joints and hip has been addressed by many authors [15, 16]. This problem induces inflammatory responses in the tissues surrounding the joint which leading to a surgical Intervention. In the same vein, in artificial joints, the surfaces must be biocompatible and resisted to wear to reduce debris generation [17]. For that, the surface of the prosthesis must have sufficient mechanical and tribological stability when subjected to stresses associated with moving to avoid detachment of the surface of the implant.

In this context, our research was undertaken to discuss the influence of Titania on the densification, the mechanical and tribological behavior and microstructures of those composites as a coating for orthopedic implant. Within this context, we are interested in examining the effect of TiO2 (1 wt.%, 2.5 wt.%; 3 wt.%; 4 wt.%; 5 wt.%; 7.5 wt.% and 10 wt.%) on the Al2O3–10 wt.% TCP composites sintered at 1600°C for 60 min. To reach this purpose, after sintering, flattened Brazilian discs (FBD) were used to determine the tensile strength (σt) and the elastic modulus (E). The semicircular bending test was realized to study the σf and the mode I KIC and the mode I stress intensity factor KI was determined using the CSTBD specimen. Compression tests were conducted to determine the compressive strength (σc). Finally, the

specimens were tested in sliding experiments to measure wear volume and friction coefficient. The characteristics were examined by X-ray diffraction and scanning electron microscopy. All those parameters are used to compare various formulations and then to retain the best formulation for testing samples.
