Anak Khantachawana

Texture of Ti–Ni rolled thin plates and sputter-deposited thin films

Abstract Ti–Ni alloy thin plates and thin films were made by the rolling method and r.f. sputter-deposition technique, respectively. In order to apply these Ti–Ni shape memory alloy thin plates and thin films for microactuators, it is very important to know the crystallographic texture and clarify the planar anisotropy in shape memory strain. The texture was investigated by X-ray diffraction and crystallite orientation distribution functions (ODF) were measured. The rolled thin plates revealed a specific deformation or recrystallization texture depending on annealing temperature, while the thin films showed a uniform crystallite orientation distribution or a typical [110] fiber texture depending on sputtering condition. The transformation strain depended on direction on the specimen plane of the rolled thin plates, while it was almost the same irrespective of direction in the sputter-deposited thin films.

The Comparison of Biocompatibility Properties between Ti Alloys and Fluorinated Diamond-Like Carbon Films

Titanium and titanium alloys have found several applications in the biomedical field due to their unique biocompatibility. However, there are problems associated with these materials in applications in which there is direct contact with blood, for instance, thrombogenesis and protein adsorption. Surface modification is one of the effective methods used to improve the performance of Ti and Ti alloys in these circumstances. In this study, fluorinated diamond-like carbon (F-DLC) films are chosen to take into account the biocompatible properties compared with Ti alloys. F-DLC films were prepared on NiTi substrates by a plasma-based ion implantation (PBII) technique using acetylene (C2H2) and tetrafluoromethane (CF4) as plasma sources. The structure of the films was characterized by Raman spectroscopy. The contact angle and surface energy were also measured. Protein adsorption was performed by treating the films with bovine serum albumin and fibrinogen. The electrochemical corrosion behavior was investigated in Hanks’ solution by means of a potentiodynamic polarization technique. Cytotoxicity tests were performed using MTT assay and dyed fluorescence. The results indicate that F-DLC films present their hydrophobic surfaces due to a high contact angle and low surface energy. These films can support the higher albumin-to-fibrinogen ratio as compared to Ti alloys. They tend to suppress the platelet adhesion. Furthermore, F-DLC films exhibit better corrosion resistance and less cytotoxicity on their surfaces. It can be concluded that F-DLC films can improve the biocompatibility properties of Ti alloys.

Effect of heat-treatment on the texture and anisotropy of transformation strain in Ti-Ni-Fe rolled thin plates

Abstract Rolling and annealing processes were applied to make Ti–50.5Ni–0.4Fe (at.%) thin plates. Such processes create a specific texture in the plates, and the texture causes an anisotropy of transformation strain to appear. The purpose of this study is to investigate the effect of annealing on the texture and anisotropy of the transformation strain in Ti–50.5Ni–0.4Fe (at.%) plates with a cold-rolling reduction of 37.5% and a thickness of 100 μm. They were annealed at 673, 873 and 1273 K, respectively, for 3.6 ks. A crystallite orientation distribution function (ODF) was measured by using diffraction from {110}, {211} and {200} planes. Inverse pole figures were drawn on the basis of the ODF. Using the crystallite axis density in the inverse pole figures, the transformation strain was calculated as a function of the angle from the rolling direction (RD) in the rolling plane. In the rolling plane, the transformation strain was almost constant in a range of the angles from 0 to 30°, and decreased with a further increase of the angle. The anisotropy of the transformation strain in the rolling plane became strongest in a specimen annealed at 873 K.

Property Improvement of TiNi by Cu Addition for Orthodontics Applications

This study aims to investigate mechanical properties and transformation behavior of TiNiCu shape memory alloys to obtain optimal conditions for utilizing as orthodontic wires. TiNi binary alloys with Ni-content 50.6 at.%, TiNiCu alloys with Cu-content ranging from 5 to 10 at.% were prepared. The alloys were melted by electrical arc-melting method and then homogenized at 800°C for 3600 s. The alloys were subsequently sliced into thin plates (1.5 mm) by EDM wire cutting machine. To evaluate mechanical properties, the specimens were cold-rolled with 10, 20 and 30%, followed by heat treatment at 400°C and 600°C for 3600 s, respectively. A Differential Scanning Calorimeter (DSC) was used to detect transformation temperatures. Mechanical properties were evaluated by micro hardness and three-point bending tests. The results showed that transformation temperatures were strongly increased with increasing Ni-content. Moreover, the decrease in transformation temperature after increasing level of cold-rolling reduction ratio suggests that internal stress can depress transformation. However, internal stress seemed to support the introduction of superelasticity for each specimen. In addition, specimens heat treated at 400°C have, more appropriate properties as orthodontic wires than those heat-treated at 600°C due to the remaining effect of cold-working. These results can be take into consideration for optimizing alloy composition and mechanical properties of TiNiCu shape memory alloys for orthodontics wires purposes.

A particle swarm optimization approach for optimal design of PID controller for position control using Shape Memory Alloys

This paper presents the optimal design of PID controller based on a particle swarm optimization (PSO) approach for position control using spring shape memory alloys (SMA) actuator. The mathematical model of experimental system had been approximate near the operating point for the PSO algorithm to adjust PID parameters for the minimum integrated absolute error (IAE) condition. The results show the adjustment of PID parameters converting into the optimal point and the good control response base on the optimal values by the PSO technique.

Effect of Direct Electric Resistance Heat Treatment on Mechanical Properties of NiTi Orthodontic Arch Wires

Two types of rectangular orthodontic archwires; NiTiTM and 40oCuNiTi, were heat treated by Direct Electric Resistance Heat Treatment (DERHT) using different electric currents for 4 s. Their mechanical properties were then evaluated by micro hardness and three-point bending tests. After applying 4.5-5.5 A current, the hardness of NiTiTM increased with the increased current, whereas the change in hardness of 40oCuNiTi was slight. When 6 A current was applied, the hardness of the midspan of both wires significantly decreased. From the three-point bending test, unloading forces of NiTiTM increased after treating with 5.5 A current, while those of 40oCuNiTi decreased. However, both specimens lost their superelasticity when applied with 6 A current. In conclusion, after DERHT, various changes in mechanical properties can be noted in the different types of nickel titanium archwire.

Effect of Ni-Content on Shape Memory Behavior of Ti-Rich Ti-Ni Melt-Spun Ribbons

The microstructure and shape memory behavior of Ti-rich Ti-Ni melt-spun ribbons with various Ni-contents were investigated. Ti-xNi(x=40~48at%) ribbons were fabricated by the melt-spinning method at the rotation speed of 5000rpm. They were heat-treated at 1073K for 3.6ks. It was found that the Ti-40at%Ni as-spun ribbon exhibited almost complete amorphous structure, while the specimen with more Ni-content, such as 48at%Ni ribbon exhibited the coexistence of amorphous and crystalline structures. It was also found that the maximum shape recovery strain increased with increasing Ni-content. The Ti-40at%Ni ribbon was very brittle because of many Ti2Ni precipitates formed.

Effect of Zr Addition on Mechanical Properties of Ti-Nb-Zr Alloys for Biomedical Applications

Artificial bone implant is concerned to improve their substantial features such as biocompatibility and mechanical properties. Ti-Nb alloys were considered to be one of the competitive materials because of their good biocompatibility and pseudoelasticity. In a present work, the effect of Zr addition as a third element on mechanical properties and pseudoelasticity of Ti-Nb alloys with Nb-content of 22-23at% were investigated by using cycling tests. The alloy ingots were fabricated by an arc melting method. The ingots were homogenization treated at 1273 K for 3.6ks followed by cold-rolled to a reduction ratio of 90% in thickness. All specimens were heat-treated at 873 K and some of them were aging treated at temperature ranging from 573 to 673 K after heat-treatment. Pseudoelasticity and mechanical behavior were evaluated by cycling test at room temperature. The results suggested that psuedoelasticity was confirmed in specimens without aging treatment irrespective of alloy compositions. Maximum recovery strain recovery increases with increasing Zr content. From all information acquired, it can be concluded that Ti-22Nb-(3-4)Zr(at.%) and Ti-23Nb-(2-3)Zr(at.%) alloys are the most optimum for artificial bone.

Effect of laser diode light irradiation on growth capability of human hair follicle dermal papilla cells

Low level laser therapy is widely used to relieve pain and inflammation, and to restore cellular functions. The photons of light are absorbed by mitochondria in cells, leading to an increase in the production of adenosine triphosphate (ATP), nitric oxide release, blood flow, and reactive oxygen species (ROS). This study proposed the use of a laser diode array at 808 nm to stimulate the proliferation and to activate the functions of dermal papilla cells, which were an important part of the hair growth cycle. These cells were isolated from human hair follicles and were exposed to 808 nm light at various doses from 0.5, 1, 2.5, 4, and 6 J/cm2. The rate of cell proliferation and the gene expression profile of dermal papilla cells were investigated and compared with the control in which the cells did not received any light treatment. The growth curves of the dermal papilla cells were used to determine the specific growth rates. Higher specific growth rates were observed in the cells exposed to laser at doses higher than 0.5 J/cm2. The effect of the laser light treatment on several gene markers, specifically for dermal papilla cells, was evaluated using real-time polymerase chain reaction (qPCR). Our result shows that collagen type 1 (Col1), alkaline phosphatase (Alp), and versican (Vcan) did not increase when the cells were irradiated by the laser light. Interestingly, sex determining region y-box 2 (Sox2) gene was up-regulated when 0.5 J/cm2, and 1 J/cm2 light was used, while an increase in the level of fibroblast growth factor 7 (Fgf7) gene was observed with light irradiation at 0.5 J/cm2, 1 J/cm2, 2.5 J/cm2, and 4 J/cm2. Too high irradiation dose was shown to yield no effect on the gene expression of dermal papilla cells.

The effect of light-emitting diode irradiation at different wavelengths on calcification of osteoblast-like cells in 3D culture

This study aimed to investigate the effect of four different light-emitting diode (LED) wavelengths on calcification and proliferation of osteoblast-like cells in vitro. MC3T3-E1 cells were seeded within three-dimensional collagen scaffolds and irradiated daily by LED light with peak emission wavelengths of 630-, 680-, 760- and 830-nm at constant fluency of 3.1 J/cm2 (irradiance intensity 2 mW/cm2). Cultures were measured for calcium content at day 0, 7, 14, 21, 28, 35 and 42. The significant enhancement in calcium content was observed at the early stage of culture (days 7 and 14) (p<;0.05). After that, the calcium content of irradiated groups was similar to that of the controls group. This suggests the transient effect of light irradiation on osteoblastic cell calcification. Only 680-nm irradiated samples revealed a significant enhancement of calcium content until the late stages of culture (from days 21 to 42) (p<;0.001). The cyclin D mRNA expression that was investigated 3 hours after stimulation at day3 also show that the 680-nm LED irradiation can enhance cyclin D expression more than others. For enhancing bone mineralization, LED irradiation at the 680-nm is more effective than those at 630-, 760- and 830-nm. Further studies should be investigated in order to obtain the most effective parameters of LLLI on bone regeneration in clinical setting.