Papers by Author: Wei Dong Miao

Abstract: Ni-Ti-Nb wide hysteresis shape memory alloys of three Ni/Ti ratio components were manufactured by vacuum induction melting. The transformation temperature, mechanical properties and recovery strain were studied by using differential scanning calorimeter and material testing machine. It shows that with Ni/Ti ratio increase, the transformation temperature and mechanical properties decrease. Shape recovery strain is higher when Ni/Ti ratio is 1.068, with recovery strain range from 6.8 to 7.5. The faster the cooling rate after annealing, the higher is the transformation temperature, and the lower are the mechanical properties and recovery strain.

Abstract: Ti-6Al-7Nb titanium alloy is attractive to medical device industry for orthopedic applications, such as total hip replacement systems, fracture fixation plates, intermedullary rods and nails, spinal devices, screws, and wires. Substituting Niobium for Vanadium as the beta stabilizing element, Ti-6Al-7Nb titanium alloy shows higher biocompatability than Ti-6Al-4V titanium alloy. The present research is designed to investigate the influence of annealling temper on the mechanical properties and microstructures of Ti-6Al-7Nb titanium alloy, by optical microscopic (OM) and scanning electron microscopic (SEM), and tensile test. The results show that the microstructures after recrystalization heat treatment comprise a mount of equiaxed α grains in the matrix of equiaxed β phase with α (hcp)/ β (bcc) platelets. The microstructures with partial recrystalization α phase possess better mechanical properties which conform to the ASTM F 1295 standard and ISO 5832-11 standard. Compared with Ti-6Al-4V titanium alloy and CP titanium alloy, Ti-6Al-7Nb titanium alloy is suitable to be used as implanted biomaterial devices to replace ill-functioning or missing tissues or organs.

Abstract: Experiment investigation of mechanical, physical, and biological properties on a dental precious alloy was performed. The density of the alloy is 12.04 g/cm³, the solidus temperature is 1144.5 °C and the liquidus temperature is 1283.5 °C. The coefficient of thermal expansion of the alloy is 14.84×10^-6 /°C between 25 °C to 500 °C. The average 0.2% yield strength is greater than 400MPa, and the average percentage elongation after fracture is greater than 4%. The average bonding strength of the metal-ceramic is 41.93 MPa, much greater than the standard requirement. The biocompatibility of the alloy is excellent, there are no cytotoxicity reactivity, sensitization, irritation, mutagenicity and short-term systemic toxicity. The alloy is a superior dental alloy with excellent mechanical, physical and biological performance.

Abstract: TiNi shape memory alloys exhibiting high damping capacity are currently expected to be used as structural materials for energy dissipation or vibration control applications. In this paper, the characterization of damping behaviour of a binary TiNi SMA was performed by dynamic mechanical analyzer (DMA) instrument and differential scanning calorimetry (DSC) equipment. Damping tests measuring Tanδ, storage modulus E' and loss modulus E" of Ti49.2Ni50.8 binary shape memory alloy were investigated at different temperature, using different frequency and strain amplitude. It shows that quenching rate has a significant effect on the damping capacity of TiNi SMA by exhibiting different phase transformation behavior. Internal friction values (Q^-1) corresponding to cubic B2 parent phase to rhombohedral R phase transformation, B2-R, and R-B19' monoclinic martensite transformation are as high as 0.177 and 0.078, respectively. The occurrence of R-phase significantly softens the storage modulus and thus promotes the damping capacity of TiNi SMAs.

Abstract: A new correction instrument of pectus excavatum is introduced which is designed for a minimally invasive technique (Nuss procedure). The instrument was made of pure titanium plates, and finished by machining, surface treatment and so on. The instrument was made up of correcting bar and fixing bar. The mechanical properties of the instrument was measured with electron universal material testing machine, the safety and validity was verified by clinical doctors after being implanted into the patient. Results showed that the mechanical properties of the instrument keep constantly after implantation for two years. It is lighter than the like product, and can lighten the patent’s and the doctor’s operation bearing. It had been applied in national hospitals, and results showed that it was of better biocompatibility, and few complications were found. Clinical treatment effects were satisfactory.

Abstract: Binary NiTi shape memory alloy cast ingots with large scale size are produced by using vacuum induction melting (VIM) in lime crucible, the oxygen and carbon contents are less than 500ppm. Usually, oxygen was introduced into the melts by the dissolution of lime during melting, resulting in higher content of oxygen over 500ppm. VAR + VIM ingot metallurgy is prone to produce materials with a good chemical homogeneity. However, it is difficult for one single melting of NiTi by VIM in the lime crucible. So in the present paper, the segregation of chemical composition and the consistency of transformation temperature in NiTi alloys in as-casted condition along the cross-section area on edge and center, in homogeneization-treated condition, and in as-forged condition along the longitudinal-section area on head and tail, are measured and analyzed by differential scanning calorimetry (DSC), OM, SEM, and XRD, to indicate the chemical homogeneity in microscopic and macroscopic scale.

Abstract: Surface preparation is potentially important to the mechanical and biomedical properties of NiTi shape memory alloys. In this paper, the effect of surface preparation on fatigue life of a Ti-55.2wt%Ni alloy has been studied. Surface of the NiTi wires is prepared by five methods of chemical etching, electropolishing, oxidizing, mechanical polishing A and mechanical polishing B, and then examined by the self-developed fatigue evaluation device. Under scanning electron microscopy (SEM) the fractures of all specimens show dimple morphology. It is found that compared with the samples after chemical treatment, mechanical polishings and thermal oxidation, electropolished sample has longer fatigue life for its lower surface roughness despite a lack of face-hardened layer.