Characterizations on Mechanical Properties and In Vitro Bioactivity of Biomedical Ti–Nb–Zr–CPP Composites Fabricated by Spark Plasma Sintering

To alleviate the bio-inert of Ti alloys as hard tissue implants, Ti–35Nb–7Zr–xCPP (calcium pyrophosphate, x = 5, 10, 15, 20 wt%) composites were prepared by mechanical alloying (MA) and following spark plasma sintering (SPS). Mechanical behaviours and in vitro bioactivity of these composites were investigated systematically. Results showed that the composites consisted of β-Ti matrix, α-Ti, and metal–ceramic phases such as CaO, CaTiO3, CaZrO3, and TixPy. With increasing CPP content, the composites had higher strength (over 1500 MPa) and higher elastic modulus, but suffered almost zero plastic deformation together with lower relative density. When the CPP contents were 5 and 10 wt%, the compressive elastic moduli were 44 and 48 GPa, respectively, which were close to those of natural bones. However, the compressive elastic modulus of the composites increased significantly when CPP contents exceed 10 wt%, thus deteriorating the mechanical compatibility of the composites owing to more α-Ti and metal–ceramic phases. Besides, the surface of Ti–35Nb–7Zr–10CPP composite was deposited as a homogeneous apatite layer during soaking in simulated body fluid (SBF). It indicates a good bioactivity between the implant materials and living bones.