Papers by Author: Lian Cheng Zhao

Abstract: The martensitic transformation behavior and shape memory effect (SME) have been investigated in a Ni-rich Ti29.6Ni50.4Hf20 high temperature shape memory alloy (SMA) in the present study. After aging, the transformation temperatures of Ti29.6Ni50.4Hf20 alloy increase obviously due to the precipitation of (Ti,Hf)3Ni4 particles. And the transformation sequence changes from one-step to two-step. When the experimental alloy is aged at different temperatures for 2h, the transformation temperatures increase rapidly with increasing the aging temperature and then change slightly with further increasing the aging temperature. Most of the martensite variants preferentially oriented in the aged Ti29.6Ni50.4Hf20 alloy. The aged Ti29.6Ni50.4Hf20 alloy shows the better thermal stability of transformation temperatures than the solution-treated one because the precipitates depress the introduction of defects during thermal cycling. In addition, the proper aged Ti29.6Ni50.4Hf20 alloy also shows the larger SME than the solution-treated one since the precipitates strengthen the matrix strongly.

Abstract: In: Eu: Fe: LiNbO3 crystals were firstly grown from a congruent melt according to the Czochralski method, with the various ratios of Li/Nb =0.885, 0.946, 1.051. The new crystal composition and defect structure were analyzed by the UV-Vis spectroscopy. In the two-wave coupling experiments, writing and erasure time, maximum diffraction efficiency, photorefractive sensitivity and dynamic range were measured and calculated. The dependence of the photorefractive properties on the defect structure of In: Eu: Fe: LiNbO3 Crystals were discussed.

Abstract: An oxide film containing Ca and P was obtained in an electrolyte containing calcium glycerphosphate (Ca-GP) and calcium acetate (CA) by microarc oxidation. The surfaces of the oxide films were porous and rough, and the Ca/P ratio in the oxide film was 1.71 when the oxide film was formed in the electrolyte containing 0.06 M Ca-GP and 0.25 M CA at current density 50 A/m2 and final voltage 350 V. The oxide film with Ca/P ration 1.71 was treated hydrothermally at 190°C for 10 hours in an autoclave. It was found that hydroxyapatite crystals were precipitated on the oxide film after hydrothermal treatment. The oxide films were investigated by means of electron probe micro analyzer, X-ray diffraction, scanning electron microcopy before and after hydrothermal treatment.

Abstract: In present paper, the mechanical properties and fracturegraphs of Mn-rich polycrystalline alloys are investigated by compression tests and scanning electron microscope (SEM) observations. It is shown that the fracture strength and the rupture strain decrease with the increase of Mn content. It is suggested that the substitution of Mn for Ga reduces the ductility of Ni-Mn-Ga alloys. SEM observations of fracture surface show us typical intergranular crack. There are many little holes and micro-cracks on the grain boundary, which weakens the bond strength of grain boundary causing the intercrystalline cracking.

Abstract: The torsion property and rotary fatigue fracture behavior of SmartÒ K file and R reamer made of nickel titanium alloy have been studied by means of Shimadzu Autograph DDS-10T universal tester and man-made cyclic system with curved copper tubes as simulated root canal. The instrument surface and the cyclic fatigue fracture surface have been investigated by optical microscope and scanning electron microscope. Comparing with ANSI/ADA specification no.28, maximum torsion values of both SmartÒ K and R endodontic instruments are satisfied in practice. Tensile stresses on the outer surface of the endodontic instruments play a dominant role in fracture initiation during cyclic fatigue fracture. The cyclic number corresponding to cyclic fatigue fracture decreases with the increase of the instrument size number/ curvature. SmartÒ K- and R endodontic instruments exhibit good ductility characteristics, therefore superior resistance to fracture.

Abstract: The biocompatibility of the NiTi alloy self-expanding stent, its dilating effect on the vascular wall, and the apoptosis of smooth muscle cells (SMCs) were studied by implantation of stent into the rabbit’s abdominal aorta for different period. All the animals lived throughout the study. There was no detectable migration or dissection of the stent, and there were no acute closures or sub-acute thromboses in the vessels. The rates of patency were 100% both at the beginning when the stent was implanted and at the end when the animal was sacrificed. It may be concluded that the vascular intima covers the whole stent at the 8-week point. The atherosclerotic process existed in the vascular intima in contact with the stent surface, while the proliferation and apoptosis of SMCs occured simultaneously. After stent implantation, the apoptosis happened in both intima and media, which indicated that the stent might not only stimulate the intima but also compress the media, leading to proliferation and apoptosis. This might contribute to vessel remodeling after stenting.

Abstract: The feasibility of using an alternating magnetic field from induction heating furnace to heat the NiTi stent and the influence of hyperthermic on smooth muscle cells (SMCs) have been studied in the present work. The electromagnetic field is capable of significantly heating NiTi stents and the heating temperature can be adjusted by changing the voltage and heating time of the furnace and the position of NiTi stents. The shape and living status of SMCs were influenced by the heat treatment procedures. There were three stages of SMCs reaction to heat: (1) when the temperature below 44°C, the living status was not changed; (2) between 44°C to 50°C, the cells shrinked and were less dyed with trypan blue, which indicated that they were still alive; (3) when the temperature was above the 50°C, all the cells died. It was found that from 44°C to 50°C, the SMCs died in apoptosis, which might allow us to heat the implanted stent to prevent restenosis.

Abstract: The microstructure, optical absorption properties and luminescence function of GaN thin films grown on the sapphire substrate with the buffer layer of GaN by metal-organic chemical vapor deposition (MOCVD) have been studied by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), infrared transmission spectrum, ultraviolet-visible absorption spectrum and photoluminescence. XRD results show that the crystal structure of GaN is hexagonal wurtzite structure. The thin films have preferred orientation in c axis with very high quality. TEM images of the cross-sectional specimen show that the thickness of every layer in the superlattice are uniform with the average period of 13.3 nm, but there are high-density dislocations in the superlattices region. From related optical experimental data, it is found that optical absorption edge is at about 370 nm. The theory calculation indicates that the five samples are direct transition semiconductor and band-gaps are about 3.4 eV. The refractive indexes of the samples increase with photon energy enhancing and decrease with the wavelength increasing. The results show that the extinction coefficients reach the lowest point at 370 nm. Photoluminescence test results show that superlattice has preferable luminescence property. In addition, the yellow luminescence is found in all samples.

Abstract: Poly(L-lactide) (PLLA) was synthesized by the ring-opening polymerization of L-lactide and the shape memory behavior was studied using DSC and bending test experiments. The results indicate that the specimen shows the shape memory effect (SME), the small crystalline phase of PLLA and the mobility of amorphous phase may be responsible for the SME. The shape recovery of samples decreases and approaches to steady with the testing number increases.

Abstract: Ti-50.6 at.% Ni shape memory alloy was coated with tantalum using multi arc ion-plating technique with the aim to increase its radiopacity and biocompatibility. The surface characteristics were investigated by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The results of XPS survey spectra show that a thin oxide film are formed inside tantalum coating as a result of natural passivation of Ta in atmosphere. The hemocompatibility was evaluated in vitro by clotting time and platelet adhesion measurement. The results of our study showed that the clotting time of tantalum was higher than that of the TiNi alloys and no sign of accumulation and only slight pseudopodium was observed on the tantalum coatings, suggesting that the tantalum coatings can improve the biocompatibility of TiNi alloy.