Yuqin Zhang

The stability and elastic properties of NaCl-type MN (M = Ti, V, Zr, Nb, and Ta) compounds investigated by first principles

The first principles calculations based on density functional theory (DFT) are adopted to investigate the stability, elastic constants, Debye temperature, and hardness of MN (Mxa0=xa0Ti, V, Zr, Nb, Ta). The NaCl-type cubic structures of MN (Mxa0=xa0Ti, V, Zr, Nb, and Ta) compounds are optimized, and the lattice parameters are in good agreement with the experimental values. The calculated values of cohesive energy and formation enthalpy indicated that they are stable structures. The mechanical properties are presented by our calculation, which are elastic constants, bulk modulus, shear modulus, Young’s modulus, and Poisson’s ratio. The Debye temperature of MN (Mxa0=xa0Ti, V, Zr, Nb, Ta) are obtained and the results show that the value of TaN is the lowest of them. The hardness of MN (Mxa0=xa0Ti, V, Zr, Nb, and Ta) compounds is 23.2, 25.0, 14.0, 16.0, 16.5xa0GPa, respectively.

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, xxa0=xa05, 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 1500xa0MPa) 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.

Mechanical and corrosion properties of Ti-35Nb-7Zr- x HA composites fabricated by spark plasma sintering

Abstract To improve the bioactivity of Ti-Nb-Zr alloy, Ti-35Nb-7Zr- x HA (hydroxyapatite, x =5, 10, 15 and 20, mass fraction, %) composites were fabricated by spark plasma sintering. The effects of the HA content on microstructure, mechanical and corrosion properties of the composites were investigated utilizing X-ray diffraction (XRD), scanning electron microscope (SEM), mechanical tests and electrochemical tests. Results show that all sintered composites are mainly composed of β-Ti matrix, α-Ti and metal–ceramic phases (CaO, CaTiO 3 , CaZrO 3 , Ti x P y , etc). Besides, some residual hydroxyapatites emerge in the composites (15% and 20% HA). The compressive strengths of the composites are over 1400 MPa and the elastic moduli of composites ((5%–15%) HA) present appropriate values (46–52 GPa) close to that of human bones. The composite with 15% HA exhibits low corrosion current density and passive current density in Hanks solution by electrochemical test, indicating good corrosion properties. Therefore, Ti-35Nb-7Zr-15HA composite might be an alternative material for orthopedic implant applications.