Corrosion behaviour of NiTi endodontic instruments

Abstract

The present study investigates the influence of the sterilisation treatment conducted at 50°C in 5% sodium hypochlorite solution (NaClO) on the corrosion behaviour of endodontic instruments made of NiTi (GT Rotary and K3) and stainless steel (K file) by measuring potentiodynamic polarisation curves in the same environment at 37°C. For comparison, the electrochemical characterisation was also carried out on endodontic instruments that were not sterilised. The characterisation of the sample surface after the electrochemical tests were carried out by means of scanning electron microscopy coupled with X-ray energy dispersive spectroscopy. There was no significant influence of the sterilisation treatment on the corrosion behaviour of K file and GT Rotary endodontic instruments. However, a negative influence of the sterilisation treatment on the corrosion resistance of K3 endodontic instruments was observed, and the effect appears to be more dramatic for longer sterlisation treatment periods.     

Microstructural characteristics of directionally solidified Ni–43Ti–7Al alloys

Abstract

Ni–43Ti–7Al (at-%) alloy was directionally solidified at different withdrawal rates (2, 20 and 100 μm s^?1) and a constant temperature of 1550°C by liquid metal cooling method. Results show that as the withdrawal rate decreases from 100 to 2 μm s^?1, the cellular arm spacing increases from 39·5 to 126 μm, the size of Ti₂Ni and the stability of the liquid/solid interface also increase, while the volume fraction of Ti₂Ni decreases from 3·1 to 0·9%. Moreover, microstructural analysis reveals that a NiTi+Ti₂Ni anomalous eutectic structure is formed in intercellular regions of directionally solidified samples withdrawn at 20 and 100 μm s^?1. However, in the sample withdrawn at 2 μm s^?1, Ti₂Ni phases represent strip and liquid droplet morphologies in the intercellular region. Finally, the possible explanation to the change of microstructure is discussed.     

NiTi 形状记忆合金环向预应力混凝土结构强化现象的研究

采用 NYL-80 型压力试验机进行抗压试验,用YJ-26型静态电阻应变仪测量各级荷载下对应的横竖向应变,同时观察和记录试件的破坏现象,研究了NiTi形状记忆合金环向预应力混凝土结构的强化现象.结果表明SMA环向预应力混凝土柱与同等条件的普通混凝土柱相比,其极限荷载和抗裂性能都有较大的提高.     

Structural, electrical and mechanical properties of magnetron sputtered NiTi/PZT/TiOx thin film heterostructures

Shape memory alloy (NiTi) thin films coupled to ferroelectric lead zirconate titanate (PZT) produce an intelligent material capable of performing both sensing and actuating functions. In the present study, we report on the in-situ growth of NiTi/PZT/TiO_x heterostructure on Pt/Ti/SiO₂/Si substrates using magnetron sputtering technique. Deposition processing, microstructure, surface morphology, electrical properties and mechanical properties of these heterostructures were systematically investigated. The top NiTi films exhibit austenitic B2 structure with preferred (110) orientation. The varying thickness of NiTi films had a significant influence on properties of NiTi/PZT/TiO_x heterostructure. The bottom TiO_x layer was observed to favor the growth of perovskite PZT films with (100) orientation. Nanoindentation tests of these heterostructures were performed at room temperature. The mechanical hardness of the top NiTi layer of lower thickness was found to be highly influenced by underneath PZT layer. The heterostructure exhibited an interesting martensite to austenite phase transformation and polarization-electric field hysteresis behavior with remanent polarization (P_r) and the coercive field (E_r) of 17.1 μC/cm² and 69.6 kV/cm, respectively. These heterostructures having a layer of SMA material coupled to a ferroelectric material with underneath TiO_x layer are of immense technological importance for MEMS devices.     

纳米SiC颗粒增强NiTi形状记忆复合材料制备及其力学性能和阻尼行为

采用粉末冶金梯级烧结法成功制备出轻质、高强且具有一定孔隙率的纳米SiC颗粒增强NiTi合金基形状记忆复合材料(SiC/NiTi).研究发现,所制备的SiC/NiTi复合材料具有稳定的线性超弹性;SiC颗粒的引入使SiC/NiTi复合材料具有较高的压缩强度和等效压缩强度,且强度随SiC含量的增加而提高.研究还表明,SiC...     

Synthesis and characterization of sol-gel hydroxyapatite coatings deposited on porous NiTi alloys

A hydroxyapatite (HA) coating was deposited onto a porous NiTi alloy via dip-coating using a sol-gel procedure with triethyl phosphite and calcium nitrate as phosphorus and calcium precursors, respectively. Adjusting the concentration and viscosity of the sol as well as changing the spin-coating rotational velocity or dip-coating times, enabled uniform coatings with controllable thickness at the sub-micron scale to be successfully deposited on the external surface and within the pores of the porous NiTi alloy. Cross-sectional SEM analysis and EDS characterization of the HA films show that the coating on the inner surface of the pores is thicker than that on the outer surface. The results of an immersion test in a Tris solution show that the HA coating possesses excellent stability, and the rates of Ni ion release through the HA coatings on the porous NiTi alloys of different porosity ratios in a simulated body fluid decrease markedly compared with the uncoated alloys. There is also a remarkable increase in the apatite forming ability of the HA coated porous NiTi alloy in a calcium containing solution.     

Deposition and characterization of cold sprayed nanocrystalline NiTi

Binary 50Ni-50Ti mixture was prepared by mechanical alloying from elemental powders. After 48 h of milling, the nanocrystalline B2-NiTi powder was produced. Then, this as-milled powder was deposited by cold spraying in order to produce a target which can be used to create thin films by magnetron sputtering technique. The objective is to improve the electrical characterizations of the NiTi/SiO₂/Si M.O.S structures. The morphology evolution of the powder particles, the phase identification and the alloying evolution process as function of milling time were studied using scanning electron microscopy, X-ray diffraction and transmission electron microscopy. In addition, the target was also characterized using X-ray diffraction, Scanning electron microscopy, and microhardness measurements. The milling of powders leads to the formation of disordered nanocrystalline B2-NiTi with a crystallite size of about 12 nm and a microstrain of level 2.10%, after 48 h of milling. The microstructure, the composition and grain size of the milled powders for 24 h and 48 h characterized by TEM are heterogeneous. The as-deposited intermetallic NiTi can be retained in the coating with a lattice parameter of 0.3 nm, crystallite size of 14 nm, microstrain and high microhardness of 2% and 694 Hv_0.25, respectively.     

退火工艺对NiTi形状记忆合金恢复力的影响

通过力学性能测试、显微组织观察和预应变后约束下的恢复力测试等手段,研究了退火工艺对Ni50.2Ti49.8合金恢复力的影响.结果表明,预应变为12%时,恢复力达到最大;退火温度升高,恢复力下降.合金的屈服强度是影响恢复力的重要因素,屈服强度越高,在马氏体逆相变过程的相界面迁移能力越强,恢复力就越大.     

Nanoindentation of NiTi shape memory thin films at elevated temperatures

The shape memory effect and nanoindentation response of various phases of sputtered NiTi shape memory thin films were investigated as a function of temperature. The phase transformation temperatures of NiTi films were observed to be sensitive to a compositional shift. The mechanical properties of NiTi thin films also presented a significant response to phase transformations. At the same load, the maximum indentation depth for austenite is smaller than for martensite, indicating that martensite is softer than austenite. A martensite thin film was converted to austenite via in situ heating nanoindentation and displayed the mechanical properties similar to the austenite film at room temperature. These results underscore the validity of elevated temperature nanoindentation methods as a means of interrogating the mechanical properties of materials that undergo thermally-induced phase transformations. The details of the load–displacement curves are also described.     

Friction-Induced Hardening Behaviors and Tribological Properties of 60NiTi Alloy Lubricated by Lithium Grease Containing Nano-BN and MoS2

Abstract

Hardened 60NiTi alloy, which possesses a unique set of desirable properties, has been considered as an attractive candidate for the bearing materials used in space mechanisms. However, the typical hardening process (quenching from high temperatures with a high cooling rate) may result in quench cracking, especially in casting parts. With this in mind, the feasibility of friction-induced surface hardening of 60NiTi under the lubrication of lithium-based greases containing nanoparticles was explored in our research. In addition, the tribological properties of 60NiTi alloy lubricated with lithium-based greases containing different proportions of nanoparticles were investigated. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy-dispersive spectroscopy (EDS) were used to characterize the surface of worn 60NiTi. An obvious friction-induced hardening effect on the 60NiTi alloy disc surface was identified, which was due to the formation of a hard metastable Ti₃Ni₄ phase and B2TiNi phase during the friction process. The lubrication effects of all of the modified grease were superior to those of the base grease, and the antiwear properties were closely related to the types of single nano-additives and the proportion of composite nano-additives.