Evaluation of Corrosion Fatigue Behaviour of Laser-welded NiTi Alloys using Bending Rotation Fatigue Test in Simulated Body Fluid

Shape memory NiTi alloys have been used extensively for medical device applications such as orthopedic, dental, vascular and cardiovascular devices on account of their unique shape memory effect (SME) and super-elasticity (SE). Laser welding is found to be the most suitable method used to fabricate NiTi-based medical components. However, the performance of laser-welded NiTi alloys under corrosive environments is not fully understood and a specific focus on understanding the corrosion fatigue behaviour is not evident in the literature. This study reveals a comparison of corrosion fatigue behaviour of laser-welded and bare NiTi alloys using bending rotation fatigue (BRF) test which was integrated with a specifically designed corrosion cell. The testing environment was Hanks’ solution (simulated body fluid) at 37.5oC. Electrochemical impedance spectroscopic (EIS) measurement was carried out to monitor the change of corrosion resistance at different periods during the BRF test. Experiments indicate that the laser-welded NiTi alloy would be more susceptible to the corrosion fatigue attack than the bare NiTi alloy. This finding can serve as a benchmark for the product designers and engineers to determine the factor of safety of NiTi medical devices fabricated using laser welding.

Influence of strain and polycrystalline ordering on magnetic properties of high moment rare earth metals and alloys

Despite being the most suitable candidates for solenoid pole pieces in state-of-the-art superconductor- based electromagnets, the intrinsic magnetic properties of heavy rare earth metals and their alloys have gained comparatively little attention. With the potential of integration in micro- and nanoscale devices, thin films of Gd, Dy, Tb, DyGd and DyTb were plasma-sputtered and investigated for their in-plane magnetic properties, with an emphasis on magnetisation vs. temperature profiles. Based on crystal structure analysis of the polycrystalline rare earth films, which consist of a low magnetic moment FCC layer at the seed interface topped with a higher moment HCP layer, an experimental protocol is introduced which allows the direct magnetic analysis of the individual layers. In line with the general trend of heavy lanthanides, the saturation magnetisation was found to drop with increasing unit cell size. In-situ annealed rare earth films exceeded the saturation magnetisation of a high-moment Fe65Co35 reference film in the cryogenic temperature regime, proving their potential for pole piece applications; however as-deposited rare earth films were found completely unsuitable. In agreement with theoretical predictions, sufficiently strained crystal phases of Tb and Dy did not exhibit an incommensurate magnetic order, unlike their single-crystal counterparts which have a helical phase. DyGd and DyTb alloys followed the trends of the elemental rare earth metals in terms of crystal structure and magnetic properties. Inter-rare-earth alloys hence present a desirable blend of saturation magnetisation and operating temperature.

CHARACTERIZATION OF THE AU SURFACE-STRUCTURE OF AL-L-AU LIGHT-EMITTING TUNNEL-JUNCTIONS

Visible light is emitted from the Au-air interface of Al-I-Au thin-film tunnel junctions (deposited over a thin layer of CaF2 on glass) as a result of the decay of surface plasmon polaritons (SPPs). We show the surface topography of such a Au film and relate its large-scale features to the outcoupling of fast SPP's to photons. The absence of short-scale roughness features is explained by thier disappearance through surface diffusion. To confirm this a controlled sequence of 5-nm, 20-ms scanning tunneling microscope (STM) W tip crashes has been used to produce indentations 3 nm deep with a lateral dimension of 5-7 nm on a Au crystal in air at room temperature. Four sequences of indentations were drawn in the form of a square box. Right from the start, feature decay is observed and over a period of 2 h a succession of images shows that the structure disappears into the background as a result of surface diffusion. The surface diffusion constant is estimated to be 10(-18) cm2 s-1. The lack of light output via slow mode SPPs is an inevitable consequence of surface annealing.

Effect of shotpeening on sliding wear and tensile behavior of titanium implant alloys

Titanium has good biocompatibility and so its alloys are used as implant materials, but they suffer from having poor wear resistance. This research aims to improve the wear resistance and the tensile strength of titanium alloys potentially for implant applications. Titanium alloys Ti–6Al–4V and Ti–6Al–7Nb were subjected to shotpeening process to study the wear and tensile behavior. An improvement in the wear resistance has been achieved due to surface hardening of these alloys by the process of shotpeening. Surface microhardness of shotpeened Ti–6Al–4V and Ti–6Al–7Nb alloys has increased by 113 and 58 HV(0.5), respectively. After shotpeening, ultimate tensile strength of Ti–6Al–4V increased from 1000 MPa to 1150 MPa, higher than improvement obtained for heat treated titanium specimens. The results confirm that shotpeening pre-treatment improved tensile and sliding wear behavior of Ti–6Al–4V and Ti–6Al–7Nb alloys. In addition, shotpeening increased surface roughness.

Microstructure, properties and application of YAl2 intermetallic compound as particle reinforcements

An yttrium aluminum (YAl2) intermetallic compound ingot was prepared in an induction furnace under vacuum. The microstructure of YAl2 ingot was characterized by optical microscopy, scanning electron microscopy, and X-ray diffraction. The load bearing response of YAl2 intermetallic was investigated and compared with SiC ceramic by indentation combined with optical microscopy and scanning electron microscopy. Additionally, the tensile properties of the Mg–Li matrix composites reinforced with ultrafine YAl2 particles fabricated by planet ball milling were tested. The results show that the intermetallic compound ingot in this experiment is composed of a main face-centered-cubic structure YAl2 phase, a small amount of YAl phase, and minor Y and Al-rich phases. YAl2 intermetallic compound has excellent stability and shows better capability in crack resistance than SiC ceramic. The YAl2 intermetallic compound has better deformation compatibility with the Mg–14Li–3Al matrix than SiC reinforcement with the matrix, which leads to the superior resistance to crack for YAl2p/Mg–14Li–3Al composite compared to SiCp/Mg–14Li–3Al composite.

Radiative rates for E1, E2, M1, and M2 transitions among the 3s23p5, 3s3p6, and 3s23p43d configurations of Cl-like W LVIII

We report calculations of energy levels, radiative decay rates, and lifetimes for transitions among the 3s²3p⁵, 3s3p⁶, and 3s²3p⁴3d configurations of Cl-like W LVIII. The general-purpose relativistic atomic structure package (GRASP) has been adopted for our calculations. Comparisons are made with the most recent results of Mohan et al. (Can. J. Phys. 92, 177 (2014). doi:10.1139/cjp-2013-0348) and discrepancies in lifetimes are noted, up to four orders of magnitude in some instances. Our energy levels are estimated to be accurate to better than 0.5%, whereas results for radiative rates and lifetimes should be accurate to better than 20%.

Modeling of titanium alloys by using artificial neural networks

Titanium alloy exhibits an excellent combination of bio-compatibility, corrosion resistance, strength and toughness. The microstructure of an alloy influences the properties. The microstructures depend mainly on alloying elements, method of production, mechanical, and thermal treatments. The relationships between these variables and final properties of the alloy are complex, non-linear in nature, which is the biggest hurdle in developing proper correlations between them by conventional methods. So, we developed artificial neural networks (ANN) models for solving these complex phenomena in titanium alloys.

In the present work, ANN models were used for the analysis and prediction of the correlation between the process parameters, the alloying elements, microstructural features, beta transus temperature and mechanical properties in titanium alloys. Sensitivity analysis of trained neural network models were studied which resulted a better understanding of relationships between inputs and outputs. The model predictions and the analysis are well in agreement with the experimental results. The simulation results show that the average output-prediction error by models are less than 5% of the prediction range in more than 95% of the cases, which is quite acceptable for all metallurgical purposes.