Phase Stability and Mechanical Properties of the Monoclinic, Monoclinic-Prime and Tetragonal REMO4 (M = Ta, Nb) from First-Principles Calculations

YTaO4 and the relevant modification are considered to be a promising new thermal barrier coating. In this article, phase stability and mechanical properties of the monoclinic (M), monoclinic-prime (M′), and tetragonal (T) REMO4 (M = Ta, Nb) are systematically investigated from first-principles calculations method based on density functional theory (DFT). Our calculations show that M′-RETaO4 is the thermodynamically stable phase at low temperatures, but the stable phase is a monoclinic structure for RENbO4. Moreover, the calculated relative energies between M (or M′) and T phases are inversely proportional to the ionic radius of rare earth elements. It means that the phase transformation temperature of M′→T or M→T could decrease along with the increasing ionic radius of RE3+, which is consistent with the experimental results. Besides, our calculations exhibit that adding Nb into the M′-RETaO4 phase could induce phase transformation temperature of M′→M. Elastic coefficient is attained by means of the strain-energy method. According to the Voigt–Reuss–Hill approximation method, bulk modulus, shear modulus, Young’s modulus, and Poisson’s ratio of T, M, and M’ phases are obtained. The B/G criterion proposed by Pugh theory exhibits that T, M, and M’ phases are all ductile. The hardness of REMO4 (M = Ta, Nb) phases are predicted based on semi-empirical equations, which is consistent with the experimental data. Finally, the anisotropic mechanical properties of the REMO4 materials have been analyzed. The emerging understanding provides theoretical guidance for the related materials development.

Development of Liquid Diene Rubber Based Highly Deformable Interactive Fiber-Elastomer Composites

The preparation of intelligent structures for multiple smart applications such as soft-robotics, artificial limbs, etc., is a rapidly evolving research topic. In the present work, the preparation of a functional fabric, and its integration into a soft elastomeric matrix to develop an adaptive fiber-elastomer composite structure, is presented. Functional fabric, with the implementation of the shape memory effect, was combined with liquid polybutadiene rubber by means of a low-temperature vulcanization process. A detailed investigation on the crosslinking behavior of liquid polybutadiene rubber was performed to develop a rubber formulation that is capable of crosslinking liquid rubber at 75 °C, a temperature that is much lower than the phase transformation temperature of SMA wires (90–110 °C). By utilizing the unique low-temperature crosslinking protocol for liquid polybutadiene rubber, soft intelligent structures containing functional fabric were developed. The adaptive structures were successfully activated by Joule heating. The deformation behavior of the smart structures was experimentally demonstrated by reaching a 120 mm bending distance at an activation voltage of 8 V without an additional load, whereas 90 mm, 70 mm, 65 mm, 57 mm bending distances were achieved with attached weights of 5 g, 10 g, 20 g, 30 g, respectively.

Structure and properties of near-a titanium products obtained by direct laser deposition and heat treatment

Advanced techniques of obtaining products require careful selection of materials for various industries. Titanium alloys are widely used in the aerospace, shipbuilding and mechanical engineering industries. The development of near-a titanium alloys should be considered a significant achievement in the field of metallurgy and heat treatment (HT) of titanium alloys. This article presents a study carried out with the aim of optimizing heat treatment modes for high-temperature titanium alloys obtained by direct laser deposition (DLD). Heat treatment was carried out in the temperature range (700-1000°C), covering three typical temperature ranges, i.e. the temperature range for the partial decomposition of martensite, the temperature range for the complete decomposition of martensite, and the phase transformation temperature were subsequently selected as the heat treatment temperatures. Based on metallographic analysis, the influence of heat treatment modes on the structure, as well as the tensile properties at room temperature, of TA15 titanium DLD-samples.

Effect of Temperature on Phase Transformation of NiTi-based Shape Memory Alloy

For NiTi-based alloys, the phase transition temperature directly affects and limits their application fields. In order to apply the NiTi-based shape memory alloy in the wider field, it is necessary to control the phase transformation temperature. Studies have shown that the content of Ni element in the NiTi-based alloy and the precipitates of the alloy, such as NiTi2, Ni3Ti2 and Ni4Ti3, will affect the phase transition temperature of the alloy. At the same time, adding a third or even a fourth element to the NiTi binary alloy can also effectively regulate the phase transition temperature of NiTi-based alloy. We then pay attention to the problems confronting the current state of the NiTi-based shape memory alloy. We have confidence that the NiTi-based shape memory alloy have a bright future in the development and innovation of excellent properties.

Plasma Electrolytic Polishing of Nitinol: Investigation of Functional Properties

A novel, environmentally friendly, fast, and flexible polishing process for Nitinol parts is presented in this study. Nitinol samples with both superelastic and shape memory properties at room temperature were investigated. The chemical contamination and surface roughness of superelastic Nitinol plates were examined before and after plasma electrolytic polishing. The shift in phase transformation temperature and tensile strength before and after the polishing process were analysed using Nitinol wire with shape memory properties. The obtained experimental results were compared to the data obtained on reference samples examined in the as-received condition. It was found that plasma electrolytic polishing, when the right process parameters are applied, is capable of delivering Nitinol parts with extremely high surface quality. Moreover, it was experimentally proven that plasma electrolytic polishing does not have a negative impact on functionality or mechanical properties of polished parts.

Torsional Resistance of Heat-Treated Nickel-Titanium Instruments under Different Temperature Conditions

This study compared the torsional resistance of heat-treated nickel-titanium (NiTi) instruments under different temperature conditions. Four thermomechanically treated single-use NiTi rotary instruments were selected for this study: OneShape (OS), OneCurve (OC), WaveOne Gold (WOG) and HyFlex EDM (HFE). Each instrument was further subdivided by temperature into 2 subgroups. Maximum torque and the distortion angle until fracture occurred were evaluated. Differential scanning calorimetry analysis was performed to measure the phase transformation temperature. Statistical analysis was performed using a two-way ANOVA and t-test (p < 0.05). Fractured fragments were observed using scanning electron microscopy (SEM). The two-way ANOVA showed no significant differences for different temperature conditions. At both room (RT) and body temperature (BT), OS was predominantly austenite while HFE was martensite. OC and WOG were predominantly martensite at RT and mixed phase at BT. At BT, more than half of WOG was martensite, while half of OC was austenite. SEM examination showed no topographical differences between instruments in different temperature groups. In relation to a limitation of this study, there was no difference in torsional resistance of NiTi rotary instruments between the BT and RT conditions. This implies that clinicians do not need to consider a decrease of torsional resistance of heat-treated NiTi instruments at BT.

Study on phase transformation of CMnSi steel when heat treatment

After manufacturing, if the CMnSi steel was heat treatment, it would create the multi-phase microstructure consists of highly ductility ferrite matrix, martensite, bainite and amounts of austenite. Thereby, the strength and ductility of the steel were improved. In the process of improving the quality of steel, there will be two processes: the plastic deformation process and the heat treatment process. In this paper, we present the study on the microstructure and mechanical properties of CMnSi steel which was heated. The heat treatment process of CMnSi steel is a special heat treatment process including the process of heating the steel to austenite temperature at 900 °C then keeping the heat to ensure uniformity of steel. This steel was cooled quickly from austenite temperature to phase transformation temperature which had bainite transformation equal to about 400 °C (this temperature is determined by CCT diagram). The results of microstructure analysis show that by the heat treatment process, the microstructure of steel is included three main phases: ferrite, bainite, and residual austenite. The results of mechanical tests show that after the heat treatment, the strength limit of steel is 1141 MPa, the elastic limit is 943 MPa and the elongation is 36%.

Development of Ductile Irons for High-Temperature Applications: Characterization in the As-Cast and Oxidized States

Ductile iron alloyed with molybdenum and different levels of aluminium and silicon was cast to determine the proper combination of elements to increase the temperature range of operation. Four alloys containing 1.5wt.% molybdenum and different combinations of aluminium and silicon (i.e. 3.5Si-3.0A1, 4.5Si-2.0Al and 4.5Si-3.0Al) were cast at 1350, 1400 and 1450⁰C into step blocks. The effects of alloy chemistry, pouring temperature and casting thickness in the as-cast and oxidized conditions were studied. Results from the as-cast condition show that graphite morphology (i.e., size, count and sphericity) improved with lower Si/Al ratios and intermediate pouring temperatures. Higher silicon and lower aluminium contents accompanied by intermediate pouring temperatures reduced the onset of surface and sub-surface defects. Results from the oxidized condition show that maximum oxidation resistance was achieved in alloys containing higher aluminium and silicon contents. This also increased the critical α-ferrite to γ-austenite phase transformation temperature range.

Development of Ductile Irons for High-Temperature Applications: Characterization in the As-Cast and Oxidized States

Ductile iron alloyed with molybdenum and different levels of aluminium and silicon was cast to determine the proper combination of elements to increase the temperature range of operation. Four alloys containing 1.5wt.% molybdenum and different combinations of aluminium and silicon (i.e. 3.5Si-3.0A1, 4.5Si-2.0Al and 4.5Si-3.0Al) were cast at 1350, 1400 and 1450⁰C into step blocks. The effects of alloy chemistry, pouring temperature and casting thickness in the as-cast and oxidized conditions were studied. Results from the as-cast condition show that graphite morphology (i.e., size, count and sphericity) improved with lower Si/Al ratios and intermediate pouring temperatures. Higher silicon and lower aluminium contents accompanied by intermediate pouring temperatures reduced the onset of surface and sub-surface defects. Results from the oxidized condition show that maximum oxidation resistance was achieved in alloys containing higher aluminium and silicon contents. This also increased the critical α-ferrite to γ-austenite phase transformation temperature range.