Papers by Author: Da Zhi Yang

Abstract: NiTi alloys are widely used for bone implants due to their good mechanical properties. However, they can suffer certain disadvantages, such as leaching of toxic nickel ions and poor osteoinductive properties. A porous (Ca, P)-doped TiO2 /dense Ti double coatings on NiTi alloy with porous (Ca, P)-doped TiO2 coating as the top layer and a dense Ti coating as the interlayer should possess a very good combination of bioactivity and chemical stability. In this paper, the double coatings were formed by applying a duplex process of arc ion plating (AIP) and micro-arc oxidation (MAO). X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) have been used to investigate the microstructure and morphology of the coatings.

Abstract: Instent restenosis (ISR) has been a key factor that restricts the further use of intraoronary stents. And the mechanical interaction between the stent and the artery has been indicated as one of the significant causes for the activation of stent-related restenosis. However, there is very little quantitative information about the interaction of stent with artery. In order to improve the general understanding of coronary stenting, finite element method (FEM) has been used to model the revascularization of a stenosed artery through the insertion of a balloon-expandable stent. Given a stent design, the deformed shape of the stent and possible areas of the artery injury were presented. The fact that the distal end of stent penetrated into the artery wall may help to explain the phenomena that much restenosis occurs at the ends of stents. The recoil ratios of the stent model, the plaque-artery model and the stent-plaque-artery model were 2%, 26.7% and11.3%, respectively. They were well consistent with the experimental data. In conclusion, this work would be helpful for the general understanding of intraoronary stent implantation and stent design optimization.

Abstract: By using the discrete variational method and constructing cluster model, the effect of a few Hf、Zr addition on martensite transformation temperature of TiNi alloy was investigated in electronic level. It is found that the bond order of the strongest bond in the clusters is promoted by introducing the Hf、Zr atoms and the magnitude of bond order is ascendant with increasing number of Hf、Zr atoms in the cluster. At the same time, contour plots of valence charge density on the parent (110) plane show the variety on bond. The change of martensite transformation temperature of TiNi alloy with Hf、Zr concentrations can be reflected by the value of the density of states at the Fermi level for the (110) crystal plane.

Abstract: The Ti50Ni25Cu25 particle/Al composite was fabricated with 30 vol.% Ti50Ni25Cu25 particles by hot pressing and followed by extruding methods. The internal friction (IF) measurements of the composite were carried out on an inverted torsion pendulum. Ti50Ni25Cu25 particles embedded in Al matrix improve the damping capacity of the composite. The internal friction behavior of Ti50Ni25Cu25 particles is consistent to that of the Ti50Ni25Cu25 bulk material. The mismatch of thermal expansion coefficients between Ti50Ni25Cu25 and Al contributes to the damping capacity of the composite. A high damping capacity of the composite could be obtained at low vibration frequency and large vibration amplitude.