Multistage Transformation Research Articles

In situ SEM studies of the transformation sequence of multistage martensitic transformations in aged Ti-50.8 at.% Ni alloys

The transformation behaviour of the multistage martensitic transformation in aged Ti-50.8 at.% Ni alloys was investigated by differential scanning calorimetry (DSC) and in situ scanning electron microscopy (SEM). The specimens aged from 673 to 748 K for 3.6 ks under an unregulated heat treatment atmosphere exhibited the double-stage transformation during cooling. The quadruple-stage transformation was observed in the specimens aged at 773 and 798 K, and the triple-stage transformation appeared in the specimen aged at 823 K under an unregulated heat treatment atmosphere. The distribution and size of Ti3Ni4 precipitates were heterogeneous in these specimens. The single-stage transformation in the specimen aged at 848 K was similar to that of the solution-treated specimen. In the forward quadruple-stage transformation, the R-phase transformation occurred in the intermediate region and around the grain boundary. The first martensitic transformation, which corresponded to the M1 peak in the DSC cooling curve, took place in the intermediate region of grains via the R phase. The second transformation, which corresponded to the M2 peak, occurred around the grain boundary via the R phase. The final transformation, which corresponded to the M3 peak, arose directly from the B2 parent phase at the grain centre. The transformation sequence and areas described above were quantitatively verified by comparing the SEM observations with the DSC measurements. The transformation sequence of the triple-stage transformation was also discussed.

Age-induced multi-stage transformation in a Ni-rich NiTiHf alloy

Abnormal multi-stage transformations have already been studied in binary Ni-rich NiTi alloys. In this research, this kind of transformation was investigated in a low supersaturated Ni-rich ternary NiTiHf high-temperature shape memory alloy by aging at intermediate temperatures for various durations. Meticulous examinations of the results of differential scanning calorimetry tests demonstrated the heterogeneous precipitation of (Ti,Hf)3Ni4 particles and the three-stage transformation (one-stage R and two-stage B19′) in the aged alloy. Aging provided a significant rise in transformation temperatures (TTs) until they reached their equilibrium states, corresponding to the equilibrium Ni content at each aging temperature. Equilibrium TTs were higher when aging was performed at a lower temperature. The remarkable increase in TTs was compared with those in aged Ni-rich NiTi alloys, and discussed based on the variation in valence electron concentration. A model was also proposed for the microstructural evolution during aging. Furthermore, aging provided enhanced hardness and strain recovery for the alloy. In particular, aging at a lower temperature resulted in a considerable improvement in hardness and shape recovery, which was discussed based on the microstructural changes in the aged alloy. Equilibrium Ni content at each aging temperature proved to be a crucial parameter in controlling the alloy properties, even in heterogeneous precipitations.

Structure and Properties of NiTi Shape Memory Alloys after Severe Plastic Deformation

The results presented here concern two NiTi alloys (near-equiatomic NiTi and Ni-rich alloy) subjected to plastic deformation by compression combined with reversion oscillating torsion. The maximal strain obtained was εc = 6.20. Finally the alloys were annealed at the temperature range 300 – 500°C for 1 hour. The structure of the as-prepared alloys was studied with the use of temperature X-ray diffraction and TEM observations. Also the DSC and bend and free recovery ASTM tests were carried out. It was found that the structure consists of a mixture of highly deformed B2 parent phase and B19’ martensite. The TEM studies revealed some amorphous areas in the most strained region of the samples. Annealing at lower temperatures caused formation of nanocrystalline structure that grew to the microcrystalline and finally well-defined polygonized structure in annealed at 500°C specimens. Multi-stage transformation was observed in the annealed at lower temperatures samples.

Effect of Annealing on the Transformation Behavior and Mechanical Properties of Two Nanostructured Ti-50.8at.%Ni Thin Wires Produced by Different Methods

A Ti-50.8at.%Ni wire produced using a co-drawing method and a commercial Ti-50.8at.%Ni wire were annealed between 450°C and 700°C. Grains with diameter less than 100nm were revealed by TEM for both wires before annealing treatment. However, the microstructural heterogeneity of the co-drawn wire is more obvious than that of the commercial wire. The transformation behavior and mechanical properties of both wires were found to be sensitive to the annealing temperature. Multi-stage martensitic transformation was observed in the co-drawn wire, compared with the one-stage A↔M transformation in the commercial wire after annealing at 600°C for 30min. Moreover, the ultimate tensile stress and plateau stress of the commercial wire were found to be higher than that of the co-drawn wire under the same annealing conditions. The differences of total elongation, plateau strain and pseudoelastic recoverable strain between the commercial wire and the co-drawn wire were also observed. The differences of the transformation behavior and mechanical properties between the commercial wire and the co-drawn wire are attributed to the microstructural difference between these two wires.

Effect of Thermal Cycling on Multistage Martensitic Transformation in Aged Ti–50.8 at% Ni Alloy

The effect of thermal cycling on multistage martensitic transformation (MMT) in aged Ti­50.8at% Ni alloy was investigated. The specimens were solution-treated at 1273K for 3.6ks and then aged at 773K for 3.6ks in vacuum without atmosphere regulation. Upon cooling, the aged specimens clearly showed quadruple-stage transformation denoted as B2 ¼ R ¼ M1 ¼ M2 ¼ M3. The peak temperatures of exothermic reactions R*, M1*, and M2* (corresponding to the R-phase, M1 and M2 transformations, respectively) in the differential scanning calorimetry (DSC) cooling curve were rather stable up to 100 thermal cycles, since there were fine Ti3Ni4 precipitates with high distribution density in the intermediate and grain boundary regions. These precipitates prevented the formation of dislocations during thermal cycling. On the other hand, the peak temperature of exothermic reaction M3* (corresponding to the M3 transformation) drastically decreased with increasing the number of thermal cycles since there were large Ti3Ni4 precipitates with low distribution density. Many dislocations were observed in the central regions of grains after 100 thermal cycles. [doi:10.2320/matertrans.M2013309]

Research on the MPPT Stability of the Single-Stage and Single-Phase Photovoltaic Grid-Connected System

At present the multi-stage transformation topology are more used in photovoltaic (PV) grid-connected system, although the control of this structure is relatively simple but the conversion efficiency is difficult to improve due to increase in transformation series. The single stage topology has a simple topology with high reliability and efficiency because of low power consumption, but control algorithm is more complex because of its power convert main circuit without DC-DC. This paper describes a method for maximum power point tracking (MPPT) in the single-stage and single-phase PV grid-connected system. In the paper, the nonlinear output characteristics of the PV including I-V & P-V are obtained in changed solar insulations or temperature based on MATLAB, and the MPPT algorithm which is based on the particle swarm optimization (PSO) method is also described. The simulation model of the single-stage and single-phase PV grid-connected system is built , and simulation results show the MPPT algorithm has excellent dynamic and static performances ,which verifies the PSO method is effective for MPPT in the single-stage and single-phase PV grid-connected system.

Determining transformation temperatures of equiatomic TiNi shape memory alloy by dynamic mechanical analysis test

Abstract Strain variation induced by martensitic transformation of Ti 50 Ni 50 shape memory alloy (SMA) is investigated by dynamic mechanical analysis (DMA) test. The extent of the positive and negative strain variation is mainly associated with the softening and hardening rate of storage modulus E 0 , respectively. The occurrence of the strain variation is related to DMA instrument design since the stress accommodation cannot keep up with the drastic change of the E 0 softening/hardening rate during transformation. Strain variation is very sensitive and can rapidly respond to the E 0 change, thus martensitic transformation temperatures of SMAs associated with a multi-stage transformation can be determined precisely from the onset/finish of the strain variation.

Variations in the composition and origin of hydrocarbon gases from inclusions in minerals of the Khibiny and Lovozero plutons, Kola Peninsula, Russia

Relationships between methane and its homologues mainly contained in fluid microinclusions have been studied in 332 monomineralic fractions from the Khibiny and Lovozero alkaline plutons. Hydrocarbon gases (HCG) were extracted for subsequent chromatographic analysis using the bulk method of sample comminution. The molecular weight distribution (MWD) of gaseous alkanes in the same and associated minerals is different depending on geological setting of the samples. The molecular mass of HCG increases (i) with decrease in temperature and capture of fluid inclusions in the course of transformation of primary magmatic minerals and the formation of late minerals as products of intensified postmagmatic processes; (ii) in the direction from khibinite at the margin and foyaite in the core of the Khibiny pluton to the central ring structure; and (iii) from the bottom to top of the differentiated complex in the Lovozero pluton. The results obtained coupled with other geochemical data suggest multistage generation and transformation of hydrocarbons from the magmatic to the final low-temperature hydrothermal stage. The MWD of hydrocarbon components in gases occluded by minerals can serve as an indicator of conditions characteristic of rock and ore formation, as well as of the consecutive formation and transformation of associated minerals revealing ambiguous and controversial relationships.

The role of bioreductive activation of antitumour anthracycline drugs in cytotoxic activity against sensitive and multidrug resistant leukaemia HL60 cells

Clinical usefulness of anthracyclines belonging to bioreductive antitumour drugs is limited by the occurrence of multidrug resistance (MDR). The aim of this study was to examine the role of structural factors of antitumour anthracycline drugs in the ability to undergo bioreductive activation by NADPH cytochrome P450 reductase (CPR) and determine the impact of this activation on increasing the activity especially in regard to MDR tumour cells. It was evidenced that at high NADPH concentration (500μM) anthracyclines having non-modified quinone structure: doxorubicin (DOX), daunorubicin (DR) and idarubicin (IDA) were susceptible upon CPR catalysis to undergo a multi-stage chemical transformation concerning their chromophore part. Additionally, it was evidenced that the modification of the sugar moiety of DOX did not disturb the susceptibility of the obtained derivative (4′-O-tetrahydropyranyl-doxorubicin, pirarubicin, PIRA) to undergo CPR reductive activation. It was also evidenced that the derivatives having modified quinone groupment (5-iminodaunorubicin, 5-Im-DR) were not able to undergo reductive activation by CPR. The high impact of CPR-dependent reductive activation of anthracycline drugs on increasing the activity in regard to sensitive leukaemia HL60 cell line and its MDR sublines overexpressing P-glycoprotein (HL60/VINC) and MRP1 (HL60/DOX) was evidenced. Furthermore, significant changes in binding manner of activated compounds to naked DNA and cellular nucleus in comparison to their non-activated forms were also observed. It could prevent the export of formed adducts out of the cell by MDR proteins and may explain significant increases in intracellular accumulation of these compounds in HL60/VINC and HL60/DOX cells.

Nonmonotonic two-way shape memory in titanium nickelide

Abstract A recent trend for application of shape memory alloys is concerned with the development of micro- and nano-scale devices where increasingly more precise effects caused by reversible martensitic transformations are taken into consideration or used. As a result, effects finer than one-way shape memory become of greater interest and relevance for practical use. Among them the reversible effects can be mentioned that represent non-monotonic strain behavior during a monotonic change of temperature. Procedures of initiation of reversible effects are rather complex for realisation. The key conditions are the possibility of formation of two-way shape memory of two types – martensitic and austenitic, or the availability of multi-stage martensitic transformation for the alloy. Also, the martensitic and austenitic two-way shape memory effects should be realised either in different temperature intervals or at different parts of the specimen. The authors propose a relatively simpler way of obtaining the reversible two-way shape memory by straining of the specimen in austenitic state. It is also shown that apart from the reversible two-way shape memory effect the other two of austenitic or martensitic type can be realised independently of each other. It is established that the reversible two-way shape memory deteriorates with the number of cycles. The two-way shape memory of austenitic type is less steady with thermocycling than the two-way shape memory of martensitic type, which leads to the disappearance of deformation reverse during cooling.

FIB/SEM Applied to Quantitative 3D Analysis of Precipitates in Ni-Ti

Ni4Ti3 precipitates with a heterogeneous distribution growing in a polycrystalline Ni50.8Ti49.2 alloy have been investigated in a Dual-Beam FIB/SEM system. The volume ratio, mean volume, central plane diameter, thickness, aspect ratio and sphericity of the precipitates in the grain interior as well as near to the grain boundary were measured or calculated. The morphology of the precipitates was classified according to the Zingg scheme. The multistage martensitic transformation occurring in these kinds of samples is interpreted in view of the data of this heterogeneous microstructure of matrix and precipitates.

A multistage differential transformation method for approximate solution of Hantavirus infection model

The goal of this study is presented a reliable algorithm based on the standard differential transformation method (DTM), which is called the multi-stage differential transformation method (MsDTM) for solving Hantavirus infection model. The results obtanied by using MsDTM are compared to those obtained by using the Runge–Kutta method (R–K-method). The proposed technique is a hopeful tool to solving for a long time intervals in this kind of systems.

Thermally Induced Transformations of Amorphous Carbon Nanostructures Fabricated by Electron Beam Induced Deposition

We studied the thermally induced phase transformations of electron-beam-induced deposited (EBID) amorphous carbon nanostructures by correlating the changes in its morphology with internal microstructure by using combined atomic force microscopy (AFM) and high resolution confocal Raman microscopy. These carbon deposits can be used to create heterogeneous junctions in electronic devices commonly known as carbon-metal interconnects. We compared two basic shapes of EBID deposits: dots/pillars with widths from 50 to 600 nm and heights from 50 to 500 nm and lines with variable heights from 10 to 150 nm but having a constant length of 6 μm. We observed that during thermal annealing, the nanoscale amorphous deposits go through multistage transformation including dehydration and stress-relaxation around 150 °C, dehydrogenation within 150-300 °C, followed by graphitization (>350 °C) and formation of nanocrystalline, highly densified graphitic deposits around 450 °C. The later stage of transformation occurs well below commonly observed graphitization for bulk carbon (600-800 °C). It was observed that the shape of the deposits contribute significantly to the phase transformations. We suggested that this difference is controlled by different contributions from interfacial footprints area. Moreover, the rate of graphitization was different for deposits of different shapes with the lines showing a much stronger dependence of its structure on the density than the dots.

Quantitative three-dimensional analysis of Ni4Ti3 precipitate morphology and distribution in polycrystalline Ni–Ti

The three-dimensional size, morphology and distribution of Ni4Ti3 precipitates in a Ni50.8Ti49.2 polycrystalline shape memory alloy with a heterogeneous microstructure have been investigated using a focused ion beam/scanning electron microscopy slice-and-view procedure. The mean volume, central plane diameter, thickness, aspect ratio and sphericity of the precipitates in the grain interior as well as near to the grain boundary were measured and/or calculated. The morphology of the precipitates was quantified by determining the equivalent ellipsoids with the same moments of inertia and classified according to the Zingg scheme. Also, the pair distribution functions describing the three-dimensional distributions were obtained from the coordinates of the precipitate mass centres. Based on this new data it is suggested that the existence of the heterogeneous microstructure could be due to a very small concentration gradient in the grains of the homogenized material and that the resulting multistage martensitic transformation originates in strain effects related to the size of the precipitates and scale differences of the available B2 matrix in between the precipitates.

Solid-phase synthesis for beginners: Choice of tools and techniques for implementation of multistage transformations

Several mini-libraries were prepared by solid-phase synthesis: C,N-substituted glycines (1) and 2,5-diaminobenzoic acids (2) using Wang resin as well as diarylthioureas (3) and diaryl-guanidines (4) using Rink resin. Comparative analysis of the instruments and technique for these reactions was provided by applying glass vials with filters (BillBoard kit) to prepare the class (1), the tea-bag technique for the class (2), and plastic rods (Lanterns) for the classes (3) and (4). All reactions (supplied with detailed protocols) were optimized for use as a tool of practical student education.

Micromechanical modeling of stress–strain behaviors with intermartensitic transformation in NiFeGa alloys

Magnetic shape memory alloys (MSMAs) NiFeGa are reported as good alternatives to Ni 2MnGa for their better mechanical behavior. Experimental data show its multistage transformation behavior. In spite of the recent progress in the development of material characteristics, no theoretical model has been developed to calculate the stress–strain behaviors of NiFeGa alloys. A model based on the micromechanical and the thermodynamic theory is presented for such a purpose. In the first plateau stage, the material is modeled as a three-phase composite, and a two-phase system for the second plateau stage. The end of the first plateau stage is considered as the origin of the second one. The kinetic equation is established in terms of the thermodynamic driving force derived from the reduction of Gibbs free energy of MSMA. The nonlinear and hysteretic strain response of NiFeGa is investigated under tensile load. The theoretical results are found to be in good agreement with experimental data.

Nature of the multistage transformation in shape memory alloys upon heating

The processes developing in shape memory alloys due to heating with application of load and without the latter are investigated. The accompanying multistage reverse martensitic transformation is studied by the method of differential scanning calorimetry. The causes of the multistage transformation are analyzed.

The Mechanical and Thermal Behaviors of Heat-Treated Ni-Rich NiTi Orthodontic Archwires

The near equiatomic nickel-titanium alloy is an outstanding intermetallic compound exhibiting distinctive properties associated with characteristic thermal and stress-induced martensitic transformations. The process of producing orthodontic wires has been modified to obtain the optimal shape memory behaviors. Phase transformation temperatures and load-deflection characteristics of this binary alloy are very significant variables in the performance of this alloy and can be manipulated by different thermomechanical treatments via inducing precipitation or dislocation networks in the matrix. In this study, one brand of commercial heat-activated nickel-titanium archwire (3 M Unitek) was selected and solution treated. Then, the wires annealed at 400 °C for 10, 30, and 60 min. Thermal transformation temperatures were determined using differential scanning calorimeter. It was showed that these temperatures increased with increasing the time of heat treatment and multistage transformation occurred as the result of inhomogeneities. In order to evaluate mechanical parameters of heat-treated archwires, they were placed on an arch-form fixture simulating maxillary dentition and load-deflection curves were obtained by three-point bending test at 37 °C. The results compared to as-received archwires and the best superelasticity was observed after 30 min aging.

Multi-stage transformation in annealed Ni-rich Ti 49Ni 41Cu 10 shape memory alloy

Multi-stage transformation (MST) in 500 °C annealed Ni-rich Ti 49Ni 41Cu 10 shape memory alloy (SMA) is investigated by differential scanning calorimetry (DSC), dynamic mechanical analyzer (DMA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The as solution-treated alloy undergoes B2 ↔ B19 ↔ B19′ two-stage transformations. Ti(Ni,Cu) 2 precipitates are formed in 500 °C annealed specimens. Alloy annealed at 500 °C for 6–24 h exhibits MST. This MST is confirmed by DMA tests and is composed of B2 1 ↔ B19 1 ↔ B19′ 1 and B2 2 ↔ B19 2 ↔ B19′ 2 transformations corresponding to the regions near and far from Ti(Ni,Cu) 2 precipitates, respectively. Experimental results show that the more the annealing time, the more the B2 1 ↔ B19 1 ↔ B19′ 1 transformations and finally only B2 1 ↔ B19 1 ↔ B19′ 1 transformations retain with the transformation temperatures close to those of Ti 50Ni 40Cu 10 SMA.

Multi-stage martensitic transformations induced by repeated thermal cycling of equiatomic TiNi alloy

Usually a multi-stage martensitic transformation is observed in Ni-rich TiNi alloys after heat treatment at 350–500 °C. It is due to the internal stresses created by the Ni 4Ti 3 participate. In the present work it was found that the multi-stage martensitic transformation appeared in Ti–50.0 at.% Ni alloy after thermal cycles through the temperature range of the phase transitions. Annealed sample undergoing one-stage phase transition was subjected to 32 thermal cycles in the DSC apparatus. The results had shown that three-stage forward martensitic transformation observed after 32 thermal cycle was due to the B2 → R, B2 → B19′ and R → B19′ phase transitions. It was found that the B19′ phase obtained from the B2 phase underwent the reverse transformation at higher temperatures than the B19′ phase obtained from the R phase. After annealing the cycled sample at 400 °C the transformation behavior was similar to the non-thermal cycled alloy. It was concluded that the main reason for the multi-stage phase transition induced by the thermal cycles was the phase hardening.