Yongzhong Zhan

β-type Ti-10Mo-1.25Si-xZr biomaterials for applications in hard tissue replacements

In order to develop new β-type Ti-based biochemical materials, a series of Ti-10Mo-1.25Si-xZr (x=4-13) alloys were designed and prepared using vacuum arc melting method. Phase analysis and microstructural observation showed that all the as cast samples consisted of equiaxed β-Ti phase. With the increase of Zr content, the structure of grain boundary changed from semi-continuous network to denser granular, and the microstructure was refined. The solid solution effect of the β-phase stabilization elements (i.e. Mo, Zr and Si) predominantly determined the mechanical properties. These β-type Ti-10Mo-1.25Si-xZr biomaterials exhibited a good combination of high compressive strength, high yield stress, good plasticity, as well as rather low Youngs modulus (in the range of 23.086 GPa-32.623 GPa), which may offer potential advantages in the applications in hard tissue replacements (HTRs).

Ab initio investigation of structural, electronic, mechanical, and thermodynamic properties of AlSc2 intermetallic compound under pressure

The dependences of the structural, electronic, mechanical, and thermodynamic properties of AlSc2 compound on pressure were investigated for the first time by means of the first-principles method based on the density functional theory with generalized gradient approximation and local density approximation. It was found that the pressure has significant effects on the equilibrium volume, mechanical properties, electronic properties and the heat capacity. Our calculated structural data are in good agreement with the previous experimental and theoretical data results. The calculated elastic constants indicate that the AlSc2 compound is mechanically stable in the pressure range of 0–50 GPa. The Zener ratio A and linear compressibility coefficients kc/ka are used to estimate anisotropic elasticity. The isotropic bulk modulus B, shear modulus G, Young’s modulus E, and Poisson’s ratio ν of polycrystalline AlSc2 compound were determined using the Voigt-Reuss-Hill averaging scheme. The B/G, Poisson’s ratio and micr...

Microstructural investigation on antifriction characteristics of self-lubricating copper hybrid composite

Abstract Owing to good antifriction properties and high wear resistance, copper hybrid composites reinforced with hard ceramic particles and solid lubricant components are regarded as promising materials for applications in sliding electrical contacts. The present work investigates the antifriction mechanism of a (SiC+Gr)/Cu composite from a microstructural viewpoint, so as to assist the development and application of this material. A graphite rich tribolayer formed on the worn surface was responsible for good tribological properties of the composites. Testing results showed that nanoparticles of graphite were involved in a mechanically mixing process by adhering to both the other wear debris and the two contacting surfaces, thereby developing a solid lubricant tribolayer. The nanographite to nanographite contacting mode, formed between the composite and the counterface, significantly improved wear resistance and friction stability. The forming and failure process of the graphite rich tribolayer was studied. A mechanism has been developed based on the experimental results.

Phase diagram of Er-Sn-Te system for diluted magnetic semiconductor developments

Abstract Phase diagrams of the RE (rare earth)-IV-VI systems are very important for the design of rare earth doped diluted magnetic semiconductors (DMSs), but related information is very limited. In this work, the phase equilibria of the Er-Sn-Te system in whole compositional range at room temperature were investigated mainly by means of X-ray powder diffraction (XRD) and differential thermal analysis (DTA). The existences of 9 binary compounds, i.e., SnTe, ErTe 3 , Er 2 Te 3 , ErTe, Er 5 Sn 3 , Er 11 Sn 10 , ErSn 2 , Er 3 Sn 7 and Er 2 Sn 5 were confirmed. The phase diagram consisted of 12 single-phase regions, 21 binary phase regions and 10 ternary phase regions. The maximum solid solubility of Er in SnTe was determined to be about 7.5 at.%, none of the other phases in this system revealed a remarkable homogeneity range at room temperature. No ternary compound was found in this work.

Microstructure optimization and mechanical properties of lightweight Al–Mg2Si in-situ composite

Abstract This research investigated the effects of Er addition (0–1 wt.%), cooling rate and hot extrusion on the microstructure, hardness and tensile properties of Al-15 wt.% Mg2Si in-situ composite. The results show that addition of Er with high concentrations changes primary Mg2Si particles from irregularly shaped to polygonal shaped and also transforms needle-shaped Al5FeSi compounds into a short rod morphology. Microstructural studies revealed that water-cooling is more beneficial to acquire polygon shaped primary Mg2Si and fish-bone Al3Er. Through hot extrusion, the networks of eutectic Mg2Si phase and fish-bone Al3Er compound are broken. In addition, the results of tensile testing show that both Er addition and water-cooling improve the ultimate tensile strength and elongation. The optimum tensile behavior was achieved by adding 0.6 wt.% Er to the water-cooled Al–Mg2Si composite after hot extrusion.

In situ synthesized low modulus biomedical Zr-4Cu-xNb alloys.

In order to develop new biomaterials for hard tissue replacements, the Zr-4Cu-xNb (x=0, 0.3, 0.6 and 0.9) biomedical alloys with required properties were designed and prepared using vacuum arc melting method for the first time. Phase analysis and microstructure observation showed that all the as-cast Zr-4Cu-xNb samples consisted of α-Zr and Zr3Cu. In addition, the lamellar eutectoid is found near the grain boundary. These alloys exhibited moderate compressive strength (1150-1300 MPa), yield stress (750-1000 MPa), favorable plastic strain (19%-27%), high elastic energy (11 MJ/m(3)-16 MJ/m(3)) and low Youngs modulus (25GPa-31GPa). This good combination of mechanical properties indicates them potential biomedical materials for biological hard tissue replacements.

Phase equilibria of the Al-Cr-Pr ternary system at 773 K

Abstract The phase equilibria of the Al-Cr-Pr ternary system at 773 K have been experimentally determined based on results of X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray analysis. 2 ternary compounds, Al20Cr2Pr and Al8Cr4Pr, as well as 11 binary compounds, i. e. Al7Cr, Al4Cr, α-Al9Cr4, α-Al8Cr5, AlCr2, α-Al11Pr3, Al3Pr, Al2Pr, α-AlPr, AlPr2 and β-AlPr3 were confirmed. No compound was found in the Pr-Cr binary system. The isothermal section of the Al-Cr-Pr ternary system at 773 K consists of 15 three-phase regions, 30 two-phase regions and 16 single-phase regions. Homogeneity ranges of intermetallic compounds at 773 K have been determined.

Electronic structures and magnetism of diluted magnetic semiconductors Sn1−xGdxTe: A density functional theory study

The structural, energy stability, and magnetic properties of the diluted magnetic semiconductors Sn1−xGdxTe (x = 3.125 at. %, 6.25 at. %, and 12.5 at. %) were investigated based on density functional theory. The calculated lattice parameters of the Sn1−xGdxTe compounds at zero pressure and zero temperature are in very good agreement with the existing experimental data. The energy stability of different configurations was also investigated, and the results show that Gd atoms prefer to occupy the nearest neighbor positions to the next nearest. It is hopeful to obtain ferromagnetic actual samples with Gd concentration around 6.25 at. %. It also confirms that there is presence of a small ferromagnetic interaction, competitive with the main antiferromagnetic interaction. However, this ferromagnetic interaction is too weak to show global magnetic moment.

Effects of Fe and Nb content on microstructure and mechanical characteristics of biomedical Ti based alloys

Abstract The microstructures and resulting mechanical properties of Ti–xNb–6Zr–7·5Sn–yFe (x=24, 30, 35 and y=1, 2, 2·5 wt-%) alloys were investigated for biomedical application. The microstructures were examined by means of optical microscopy, SEM and X-ray diffraction, and Vickers hardness, compressive elastic modulus and the yield strength have been measured. X-ray diffraction analysis showed that the alloys consist of β+α or β+α+α″ phases. The volume fraction of each phase changes with the variation of Fe and Nb contents according to consulting the relation between the contents of β stabilising elements and phase composition of Ti alloys after quenching from β phase region. The different microstructures result in various mechanical properties of the alloys. Ti–24Nb–6Zr–7·5Sn–2Fe has the higher strength/modulus ratio, i.e. the lower elastic modulus and the higher yield strength; hence, it is more suitable than the other alloys for biomedical applications.

Phase equilibria in the Y-Ti-Si system at 773 K

Abstract Physico-chemical analysis techniques, including X-ray powder diffraction, scanning electron microscopy, optical microscopy and differential thermal analysis were employed in constructing the isothermal section of the Y – Ti – Si system at 773 K. The isothermal section consists of 12 single phase regions, 21 binary phase regions and 10 ternary phase regions. No ternary compound is found in the work. None of the phases in this system reveals a remarkable homogeneity range at 773 K.