Wear behaviour of ceramic biocomposites based on hydroxiapatite nanopowders

The biomaterials most widely used for hard tissue implants (in orthopaedics, dental implants, and skull bones) are Ti-based biomaterials and Ti coated with hydroxiapatite (HAP). Because metallic biomaterials have some disadvantages as reported previously (mainly due to the difference between the mechanical characteristics of the human bone and the metallic implant), biocomposites have become an interesting solution to improve the hard tissue implants for the human body. This article presents the experimental results concerning the processing of HAP/Ti biocomposites by powder metallurgy technology. The initial powder mixture consists of HAP powder particles (< 200 nm) reinforced with 100 mu m titanium particles in the ratio 3:1 (wt%). Two different sintering routes are used: spark plasma sintering (SPS) at (1000-1100)degrees C for 10 or 20 min and two-step sintering (TSS) with the first step at 900 degrees C/1 min, followed by the second step at 800 degrees C for 300, 600, 900 or 1200 min. The ball-on-disc dry wear tests are developed using, as a moving counterpiece, DIN 100Cr6 tool steel balls (6 mm diameter; Ra < 3.2 mu m; HRc 60-64; density > 7.6 g/cm(3)). The tribological behaviour of the processed biocomposites is appreciated on the basis of the coefficient of friction and wear rate, corroborated with the wear track depth. The final remarks of this article underline the potential use of SPS technology to obtain HAP/Ti biocomposites with comparable wear properties as similar materials processed by more complex technologies. Also, TSS allows processing HAP/Ti materials comparable with the SPS-ed ones from the point of view of the wear behaviour, except for the dwell time of the second step, which is critical for the wear behaviour.