Increase Of Transformation Temperature Research Articles

Effect of Diameter Expansion Ratio on Recovery Properties of TiNiFe Alloy Pipe Coupling

The reverse transformation temperature, recovery strain and pull-out force of TiNiFe alloy pipe couplings under different diameter expansion ratios (7%, 9%, 11%, 13%, 15%) were studied. The results show that the martensite reorientation occurs and the elastic strain energy released decreases with the increase of the expansion ratio, which leads to the increase of martensite reverse transformation temperature as’ and Af’. The recovery strain increases and the recovery rate decreases with the increase of expansion ratio. The expansion ratio of pipe couplings has a great influence on the pull-out force, which is related to the fit clearance and the diameter of the connected rod. When the fit clearance is the same, the larger the expansion ratio is, the greater the pull-out force is, and when the diameter of the connected rod is the same, the pull-out force decreases with the increase of the expansion ratio.

Effect of Hot Rolling on the Thermomechanical properties of a Superelastic Cu-Al-Be-Cr Alloy

Abstract Shape memory alloys are generally produced by casting processes and are subsequently homogenized. However, to obtain semifinished products on an industrial scale, the ingots from the casting process must be hot worked. In particular, final bar and sheet products can be obtained by hot rolling process. During intense hot work, surface oxidation of the material and microstructural changes may cause modifications to its original thermomechanical properties. In this sense, the present work aimed to study the correlation of the superelastic behavior in a Cu-Al-Be-Cr alloy before and after subjecting it to the hot rolling thermomechanical process. Abnormal grain growth was observed for a hot rolled sample with 30% reduction in initial alloy thickness. This abnormal growth in relation to non-rolled alloy caused an increase in phase transformation temperatures, a reduction in residual strain, a reduction in induction stress and an increase in alloy superelasticity.

The effects of shape-setting on transformation temperatures of pseudoelastic shape memory alloy springs

Abstract Since shape memory alloy (SMA) wires can hardly ever be reliably employed under compressive loadings, SMA springs are developed as axial actuators with the ability of withstanding both tension and compression. In this paper, shape memory alloy helical springs are produced by shape-setting two types of wires: one with shape memory effect (SME) and the other with pseudoelasticity (PE) at the ambient temperature. Phase transformation temperatures of the produced springs are measured by differential scanning calorimetry (DSC), and the influences of effective parameters including cold work, heat treatment temperature and duration, and cooling rate are investigated on transformation temperatures of the products. The results show that phase transition temperatures of the fabricated springs can be tuned by performing cold work and by adjusting temperature and duration of the conducted heat treatment as well as the subsequent cooling rate. It is found that transformation temperatures of the springs fabricated using the SME wire increase as the heat treatment temperature increases. However, for samples manufactured using PE wire, transformation temperatures first increase and then decrease with the increase in the heat treatment temperature. An increase in the cooling rate leads to a decrease in the austenite final temperature (Af), and an increase in the extent of cold work leads to the increase in transformation temperatures especially Af.

Effect of Ga2O3 on the structure and properties of TeO2–GeO2 glass doped with Pr3+

A novel glass from the TeO2–GeO2–Ga2O3 system was developed. We studied two series of glass with GeO2/TeO2 molar ratio varied from 0.14 to 0.5 doped with Pr3+. The objective of this paper is to analyze an effect of 16.7 mol% of Ga2O3 admixture on the thermal stability, structure of the glass and the thermoluminescence (TL) properties such as glow curves shape. We showed that Ga2O3 stabilizes the glass, increasing transformation temperature and reducing ΔH significantly. The conversion of [TeO4] to [TeO3] units is observed with an increase of GeO2/TeO2 ratio. The Ga3+ ions play a role of the modifier and facilitate connection between structural units of two glass-formers, preventing phase separation. However, GeO2 increases the band gap of the telluride glass. The admixture of 0.3 mol% Pr6O11 enhances the thermoluminescence of the glass but in different way for series with and without Ga2O3.

Analysis of the Effect of Hydrostatic Pressure on the Nonvariant Eutectic Transformation in Al–Si, Al–Cu, and Al–Cu–Si Systems

Differential barothermal analysis (DBA) is used to analyze the effect of hydrostatic pressure of 100 MPa on characteristic temperatures of a number of eutectic alloys (wt %), such as Al–10Si, Al–12Si, Al‒22Cu, Al–33Cu, and Al–7Cu–7Si. According to DBA data, the increase in pressure resulted in an increase in the temperatures of phase transformation; in practice, the most important of them is the nonvariant eutectic transformation temperature that determines the solidus of alloys. It was found that, for the binary systems, the temperatures of the nonvariant eutectic transformation L → (Al) + Si and L → (Al) + Al2Cu increase by 6 and 11°С (from 577 to 583°С and from 548 to 559°С, respectively); for the ternary system, the temperature of transformation L → (Al) +Al2Cu + Si increases by 6°С (from 520 to 526°С). Theoretical analysis, performed using thermodynamic models and Thermo-Calc software, shows that the increase in the eutectic transformation temperature with increasing pressure is directly dependent on the relative decrease in the molar volume of system upon associated eutectic transformation. In this case, the excess dissolution of silicon in (Al) under high pressure can lead to an additional decrease in the molar volume of the system, whereas the increase in the copper solubility is thermodynamically unfavorable.

Effects of composition on transformation temperatures and microstructure of Ni-Ti-Hf shape memory alloys

Abstract High transformation temperature shape-memory alloys (HTSMA) usually present a martensitic transformation temperature (Ms) starting at 100 oC. That is the case of high nickel Ni-Ti-Hf alloys. This article presents experimental results obtained from arc melting of Ni50Ti50-XHfX .at% (X = 8, 11, 14, 17 and 20 .at%) alloys. This process homogenized every composition with similar relative crystallinity. Results confirm that transformation temperatures (TT) increase with increasing the amount of Hf. A martensitic matrix is formed by two metastable phases: R and B19'. From all the alloys studied, the B19' phase presented the highest percent fraction. Gradually adding Hf3 .at% promoted a slow increase of crystalline fraction of R phase and a slow reduction of phase (Ti, Hf)2 Ni, located at grain boundaries. Coherent/semi-coherent interface between (Ti, Hf)2 Ni phase and the matrix may intensify the driving force for the formation of R phase, present on X-ray diffractograms.

Effect of zirconium on the properties of polycrystalline Cu-Al-Be shape memory alloy

This paper presents an investigation of the effect of zirconium on the properties of polycrystalline Cu-Al-Be shape memory alloy. Mechanical and shape memory properties have been evaluated by varying the compositions of Zr to Cu88.13-Al11.42-Be0.45 alloy ranging from 0.05 to 0.4 wt% with step 0.1 wt%. The results unveil reduction in the grain size of 89.18% with the improved tensile strength of 667 ± 30 MPa and ductility of 23.95 ± 0.86% and excellent shape recovery ratio of 100% with the addition of Zr up to 0.3 wt%. Increase in transformation temperatures is observed with the addition of Zr.

Influence of Zirconium Percentage on Microhardness and Corrosion Resistance of Ti50 Ni50-xZrx Shape Memory Alloys

To obtain high temperature shape memory alloys of the lower cost Ni-Ti-X system, elements such as Hf and Zr are introduced to modify the thermal and mechanical properties of these alloys. This work studied the production and characterization of Ti50 Ni50-x Zrx alloys (x = 0, 5, 10 at.%) with the aim of improving their thermal, mechanical and corrosion resistance properties. In the resulting alloys, transformation of phase B2 into phase B19' occurred in a single stage. The addition of zirconium led to an increase of transformation temperatures, as well as the appearance of second phase particles in the grain boundaries of the matrix. The increase in zirconium percentage favored the increase of corrosion resistance from 520.23KΩ to 1007.30KΩ and of microhardness from 346HV to 543HV for the N0 and N10 alloys, respectively.

The crystallization process, microstructure, martensitic transformation and mechanical properties of Ti-Ni-Zr alloy ribbons

In the present study, the Ti-Ni-Zr alloy ribbons with the various Zr contents were fabricated at the optimum process conditions. The crystallization process and the effect of the following annealing treatments on the microstructural evolution, martensitic transformation behavior, mechanical properties and shape memory effect of the annealed Ti-Ni-Zr alloy ribbons were investigated systematically. The results revealed that the phase constituents were dependent on the Zr contents, and can be tailored by the annealing treatment. The λ1 precipitate existed in all annealed Ti-Ni-Zr alloy ribbons and NiZr phase appeared only in the annealed Ti-Ni-Zr alloy ribbons with the Zr content more than 25 at.%. With the annealing temperatures increasing, the martensitic transformation temperature increase. And the Ti-Ni-Zr alloy ribbons with the higher Zr content showed the relatively lower transformation temperatures owing to the presence of the NiZr precipitate. The nano-scale λ1 precipitate and NiZr phase can enhance the matrix strength and improve the mechanical properties, while the appearance of the lots of the NiZr phase would deteriorate the shape memory effect. Among, the annealed Ti-Ni-Zr alloy ribbon showed the excellent combination of the higher transformation temperatures, superior mechanical and strain recovery characteristics. In summary, the evolution of the microstructure containing the martensitic/austenitic state, type/size of the precipitate, and distribution state of the precipitate resulted in the changing of the martensitic transformation, mechanical properties and shape memory effect.

Ultra-high temperature multi-component shape memory alloys

This paper presents martensitic transformation characteristics of selected multi-component (Ni,Pd)50(Ti,Hf,Zr)50 alloys, with an emphasis on superelasticity and thermal actuation behavior. We report, for the first time, austenite finish temperatures beyond 700 °C in NiTi-based high temperature shape memory alloys without the presence of platinum and gold. The increase in transformation temperatures, and transformation stress and recovered strains at elevated temperatures are attributed to the high configurational entropy of the studied alloys. Based on the current findings, we introduce multi-component ultra-high temperature shape memory alloys, which are expected to pioneer a completely new field of study and applications for shape memory alloys.

Shape memory behavior of Ni40.3Ti39.7Hf15Pd5 and Ni40.3Ti44.7Hf10Pd5 alloys

The microstructure and shape memory properties of Ni40.3Ti39.7Hf15Pd5 and Ni40.3Ti44.7Hf10Pd5 alloys were investigated. It was revealed that transformation temperatures of these alloys can be tailored by thermal treatments and composition alteration. Heat treated Ni40.3Ti39.7Hf15Pd5 can show shape memory effect at above 100 °C. Both alloys showed shape memory effect, however, superelasticity was not observed due to the large thermal hysteresis and high rate of increase in transformation temperatures with stress. Both alloys have higher strength but considerably lower transformation strain than NiTi. Microstructure features also were investigated for grains, distribution and composition of secondary phase. It was revealed that secondary phases lead to decrease the recoverable strains of the NiTiHfPd alloys. As-received Ni40.3Ti44.7Hf10Pd5 and Ni40.3Ti39.7Hf15Pd5 have recoverable strains of 1.12% and 0.43% under 700 MPa, respectively.

Martensite aging in 〈001〉 oriented Co49Ni21Ga30 single crystals in tension

Co–Ni–Ga high-temperature shape memory alloys (HT-SMAs) are well-known candidate materials for damping applications at elevated temperatures. Recent studies showed that upon heat treatment in stress-induced martensite under compressive loads transformation temperatures can be increased significantly, qualifying Co–Ni–Ga for HT-actuation. The increase in transformation temperatures is related to a change in chemical order recently validated via neutron diffraction experiments. Since SMAs show distinct tension–compression asymmetry in terms of theoretical transformation strains and bearable stresses, understanding the impact of martensite aging in tension is crucial for future applications. The current results indicate that martensite aging in tension provides for a further improvement in functional properties.

Effect of Ti and B on the Wartensitic Transformations and Microstructures in Polycrystalline Cu-12(wt. %) Al-4(wt. %) Ni High Temperature Shape Memory Alloys

Addition of grain refiners/alloying elements is one of the most effective methods to reduce the grain size in the alloys, thereby, enhancing the mechanical and other properties of the alloy. Titanium and boron are added to polycrystalline Cu-12Al-4Ni (wt. %) high temperature shape memory alloy in the present study which were synthesized using induction melting furnace in air atmosphere. The alloys were betatized for one hour at temperature of 920°C and then were quenched in iced water. Further, they were characterized using the techniques of optical microscopy, X ray diffractometry, differential scanning calorimetry and hardness testing. Boron added alloys show thick plates of β1 ’ martensite with increase in transformation temperature as compared to base alloy whereas titanium added alloys show mixture of fine and thick plates of β1 ’ as well as γ1 ’ martensite with decrease in the transformation temperature as compared to the base alloy. Precipitation of second phase takes place in both titanium and boron alloying to CuAl-Ni base alloys.

Coherency strains of H-phase precipitates and their influence on functional properties of nickel-titanium-hafnium shape memory alloys

A Ni50.3Ti41.7Hf8 alloy was studied after two-step aging treatments consisting of 300°C for 12h followed by 550°C for different times. An anomalous change in transformation temperatures was observed as the second aging time was increased from 7.5 to 13.5h. Initially with increased aging time (0.5–7.5h) at 550°C, coherency strain fields about H-phase precipitates increased. The corresponding backstress favored martensite formation, hence an increase in transformation temperatures. However, a point was eventually reached where misfit dislocations relaxed those strain fields and the effect was reduced, resulting in a decrease in transformation temperatures.

Characteristics of Transformation and Low-temperature Deformation of Ti-51.1Ni Shape Memory Alloy

Abstract Effects of annealing temperature on the phase transformation and the low temperature deformation characteristics in the deformed Ti-51.1Ni (at%) shape memory alloy (SMA) were investigated by differential scanning calorimetry (DSC), optical microscope (OM) and tensile test. The results show that the transformation types of Ti-51.1Ni alloy are changing from A→R/M→R→A to A→R→M/M→R→A to A→R→M/M→A (A-parent phase B2, R-R phase, M-martensite phase) upon cooling/heating along with increasing annealing temperature. The R transformation temperatures and martensite temperature hysteresis decrease, while the M transformation temperature increases and the R temperature hysteresis nearly keeps at about 6.5 °C. When deformation happen at 10 °C, the 400∼550 °C annealed Ti-51.1Ni SMA exhibits as the shape memory effect (SME) + superelasticity (SE), the 600∼700 °C annealed SMA shows SE, and the characteristics of alloy change from SME + SE to SE. In addition, the annealing recrystallization temperature of Ti-51.1Ni SMA is 590 °C, and the 590∼650 °C annealed alloy could obtain excellent capability of plastic deformation and 50.83 % values of fracture strain, so the forming processing temperature could be in the range of 590∼650 °C. When the Ti-51.1Ni alloy are used for energy consumption of damper and damping device, the suitable annealing temperature could be higher than 550 °C, and for making superelastic device, the suitable annealing temperature could be below 400 °C or above 600 °C.

PROPERTIES OF Ni-Ti-X SHAPE MEMORY ALLOYS PRODUCED BY ARC RE-MELTING

This paper deals with Ni-Ti46 and Ni-Ti-X wt. % alloys prepared by arc re-melting under argon protective atmosphere. The melting was repeated three times to obtain a homogenous chemical composition of samples. Niobium, vanadium and silicon were chosen as alloying elements and they were added into the alloy in an amount of 5 wt. %. Microstructure, phase composition, hardness and transformation behaviour were investigated parameters. Properties of cast alloys are compared with alloys of the same chemical composition prepared by powder metallurgy method – self-propagating high-temperature synthesis (SHS). Arc re-melting produced a more homogeneous microstructure with a lower content of the Ti2Ni phase than powder metallurgy methods in case of Ni-Ti-X alloys. Quite a high amount of the secondary phase (a mixture of the Ni2Ti, NiTi and Ti2Ni phases) was created in the microstructure of Ni-Ti46 wt. % alloy. The addition of silicon caused an increase of transformation temperatures and hardness.

Properties of Cu-Based Shape-Memory Alloys Prepared by Selective Laser Melting

Two shape-memory alloys with the nominal compositions (in wt.%) Cu–11.85Al–3.2Ni–3Mn and Cu–11.35Al–3.2Ni–3Mn–0.5Zr were prepared by selective laser melting (SLM). The parameters were optimised to identify the process window, in which almost fully dense samples can be obtained. Their microstructures were analysed and correlated with the shape-memory behaviour as well as the mechanical properties. Suction-cast specimens were also produced for comparison. Mainly, β 1′ martensite forms in all samples, but 0.5 wt.% of Zr stabilises the Y phase (Cu2AlZr), and its morphology depends on the thermal history and cooling rate. After annealing, the Y phase is primarily found at the grain boundaries hampering grain coarsening. Due to the relative high cooling rates applied here, Zr is mostly dissolved in the martensite in the as-prepared samples and it has a grain-refining effect only up to a critical cooling rate. The Zr-containing samples have increased transformation temperatures, and the Y phase seems to be responsible for the jerky martensite-to-austenite transformation. All the samples are relatively ductile because they mostly fracture in a transgranular manner, exhibiting the typical double yielding. Selective laser melting allows the adjustment of the transformation temperatures and the mechanical properties already during processing without the need of a subsequent heat treatment.

Local Surface Phase Stability during Cyclic Oxidation Process

Surface properties are essential for many engineering material ́s design issues, such as fatigue and corrosion performances. Austenitic stainless steels used in high-temperature applications, as for instance components in biomass-fired power plants, need sufficient corrosion resistance. At temperatures above 600 °C and in water vapor environment, Cr-vaporization will create Cr-depletion, causing a local change in chemical composition. This local change in chemical composition leads to phase transformation in some austenitic stainless steels. This paper reports the surface properties regarding the local phase transformation during thermal cycling in water vapor environment. Three commercial austenitic stainless steels are investigated, AISI 304, AISI 316L and Sandvik SanicroTM 28. The thermal cycling was performed up to 650 °C in a 15 mol.% water vapor environment. AISI 304 shows local surface phase transformation related to martensitic transformation due to locally changed chemical composition and increase in the martensitic transformation temperature (Ms). However, the other two austenitic stainless steels don’t show this martensitic transformation. The phase transformation and oxidation is discussed using microstructural investigations methods such as x-ray diffraction (XRD), electron backscatter diffraction (EBSD) and energy dispersive spectroscopy (EDS).

Effects of Si on microstructure and phase transformation at elevated temperatures in ferritic white cast irons

The effects of Si on microstructure and phase transformation at elevated temperature of ferritic 31wt.%Cr-1.1wt.%C white cast irons with up to 3wt.%Si have been studied. Applications of these irons include parts requiring heat resistance at elevated temperature. The irons were produced by sand casting. The microstructure in as-cast condition and after being subjected to high temperature (700 to 1000°C) was investigated by light microscopy, X-ray diffraction, and electron microscopy. The results revealed that the as-cast microstructure consisted mainly of primary ferrite dendrites and eutectic (ferrite+M7C3). Si promotes M7C3-to-M23C6 transformation in the irons subjected to transformation at elevated temperature, but no sigma phase was found. The extent of M7C3-to-M23C6 transformation increases proportional to the increasing transformation temperature, holding time and Si content in the irons. For the iron with 1.0wt.%Si content after holding at elevated temperatures, martensite was also found, which could be attributed to carbon accretion effects in eutectic ferrite. Si was incorporated in M23C6 such that M23C6 containing Si can show darker contrast under SEM-BEI as compared to M7C3; this is the opposite to what has been observed for the cases of typical M23C6 and M23C6 containing Mo or W. The results obtained are important to understand the change in properties of ferritic, high chromium irons containing Si subjected to elevated temperature.

Effect of Cu, Mn and Sn on pearlite growth kinetics in as-cast ductile irons

In a previously published work, pearlite growth in cast irons was investigated and it was claimed that growth kinetics of pearlite in nodular cast iron does not depend on alloying elements and that only the start temperature for the transformation is modified. Since then, the authors have investigated the effect of copper at low level of manganese and the combined effect of copper and tin at intermediate manganese contents. In the first case, thermal records confirmed that copper decreases the formation temperature for both ferrite and pearlite. In the second work, an optimised content for tin, manganese and copper was found so as to improve mechanical properties while keeping fully pearlitic structures. The thermal records obtained during this latter study are here used to estimate the pearlite growth kinetics and the effect of copper and tin on it. Tin has been shown to reduce pearlite undercooling (increase of start transformation temperature) and thus to favour the formation of this constituent.