Xiaobo Sheng

Surface treatment of NiTi shape memory alloy by modified advanced oxidation process

A modified advanced oxidation process(AOP) utilizing a UV/electrochemically-generated peroxide system was used to fabricate titania films on chemically polished NiTi shape memory alloy(SMA). The microstructure and biomedical properties of the film were characterized by scanning electron microscopy(SEM), X-ray photoelectron spectroscopy(XPS), inductively-coupled plasma mass spectrometry(ICPMS), hemolysis analysis, and blood platelet adhesion test. It is found that the modified AOP has a high processing effectiveness and can result in the formation of a dense titania film with a Ni-free zone near its top surface. In comparison, Ni can still be detected on the outer NiTi surface by the conventional AOP using the UV/H2O2 system. The depth profiles of O, Ni, Ti show that the film possesses a smooth graded interface structure next to the NiTi substrate and this structure enhances the mechanical stability of titania film. The titania film can dramatically reduce toxic Ni ion release and also improve the

EFFECT OF AL CONTENT ON MICROSTRUCTURE AND PROPERTIES OF AN INTERMETALLIC Ni-Ti (Al) COMPOUND/Ni GRADED COATING DEPOSITED ON COPPER SUBSTRATE

Copper and its alloys with high electrical and thermal conductivity are a group of widely used engineering materials in numerous applications. In order to improve the tribological properties of copper substrate, an electroplating nickel layer was firstly deposited on copper substrate, subsequently these electroplated specimens were treated by slurry pack cementation process at 900°C for 12 h using a slurry mixture composed of TiO2 as titanizing source, pure Al powder as aluminzing source and also a reducer for titanizing, an activator of NH4Cl and albumen (egg white) as cohesive agent. The effect of Al content on the microstructure and the properties of the coating has been studied. The results showed that an intermetallic Ni-Ti (Al) compound/Ni graded layer was formed on copper substrate after slurry pack cementation process. With the rise of Al content in slurry mixture, the microhardness of the graded coating increased and the friction coefficient decreased from 0.35 to 0.18, at the same time, the slurry pack process gradually transited from the titanizing process to an aluminizing one. Correspondingly the main phases of the coating were changed from Ni-Ti intermetallic compounds into Ni-Al ones.

Structure and magnetic properties of RFe9Mn3 compounds with R = Y, Tb, Dy, Ho and Er

Following the discovery of Nd2Fe14B compound [1] which has been treated as the third generation of the rare earth permanent magnets, the Sm2Fe17 carbides and nitrides [2] with the rhombohedral Th2Zn17-type structure, and Nd(Fe,Ti)12 nitrides [3] with the ThMn12type structure have been found possessing excellent intrinsic permanent magnetic properties. So the iron rich rare earth-transition metal compounds (RnTm) become new potential candidates for permanent magnet applications, and the study of these compounds is attracted intensively world wide. To understand the influence of these interstitial atoms it is necessary to first understand better the interactions that are present in the parent compounds. In this letter, the magnetic properties like the Curie temperature and the saturation magnetization in RFe9Mn3 (R = Y, Tb, Dy, Ho and Er) compounds have been investigated. The mean-field constants of DyFe9Mn3 and HoFe9Mn3 compounds have also been calculated. The Mn element has been chosen because it can show some very interesting magnetic behaviors such as large magnetic moment in some compounds. All the RFe9Mn3 samples with R = Y, Tb, Dy, Ho and Er were prepared by argon arc melting from starting materials of at least 99.5% purity. The alloys were melted five times to ensure homogeneity. After arc melting, the polycrystalline specimens were sealed into evacuated quartz tubes and annealed at 1073 K for 50 h and then quenched into water. The phase composition, the structure and the lattice parameters for the RFe9Mn3 compounds with R = Y, Tb, Dy, Ho and Er were determined by means of the X-ray diffraction (XRD) patterns of free powder samples. Fig. 1 shows the X-ray diffraction patterns of RFe9Mn3compounds with R = Y, Tb, Dy, Ho and Er. The lattice constants a, c and the unit-cell volume V are shown in Table I. It can be seen that all of the investigated compounds are single phase and crystallized in ThMn12-type structure. The lattice constants a, c and the unit cell volume V decrease with increasing atomic number from Tb to Er, reflecting the lanthanide contraction. The specific magnetization was measured on free powder with an extracting-sample magnetometer at 5 K