Increase Of Transformation Temperature Research Articles

Volatilization of boron from E-glass melts

Boron is known to volatilize from borate and borosilicate melts at high temperatures. The rate of boron loss from E-glass melts, as measured using the B–O overtone band in the infrared spectrum of this glass, has been measured at several temperatures and partial pressures of water vapor. The rate of volatilization increases dramatically with increasing partial pressure of water vapor in the atmosphere surrounding the melt at constant temperature and with increasing melting temperature at constant partial pressure of water vapor. The boron concentration decrease is accompanied with an increase in hydroxyl concentration. The net effect of changes in boron and hydroxyl concentration is an increase in glass density, refractive index, and glass transformation temperature.

Martensitic Transformation in Ni–Mn–Ga Alloy Under High Magnetic Fields

An effect of magnetic field on the martensitic transformation (MT) temperature in ferromagnetic shape memory Ni 49.4 Mn 27.7 Ga 22.9 single crystal with the MT temperature 285 K is studied by measuring and theoretical treatment of the magnetization versus temperature dependencies in a wide range of the high magnetic fields higher than saturating one. In this way, a linear approximation of the field dependence of MT temperature was proved for the high-field range. The linear increase of transformation temperature is characterized by the slope of 3.5 x 10 -2 K/kOe. This value is essentially larger than the value 2 x 10 -2 K/kOe reported by Gonzales-Comas et al. [Phys. Rev. B 60 (1999) 7085-7090] for the Ni 49.5 Mn 25.4 Ga 25.1 alloy with a low MT temperature. This difference is in an agreement with the predictions of the Landau theory.

Transformation plasticity at different phase transformations of bearing steel

Simulation of heat treatment processes presupposes that material data exist for the description of the phase transformation. During the heat treatment transformation and thermally caused stresses develop, which affect the behaviour of the phase transformation. The subject of this paper is the interaction between phase transformation and internal stress. The investigations show the influence of constant tensile loading on transformation strains occurring during the isothermal pearlitic and bainitic transformation and also the martensitic transformation of the bearing steel 100Cr6. The transformation plasticity parameter K increases during pearlitic transformation, with increasing transformation temperature linear, but decreasing for bainitic transformation with increasing temperature. Umwandlungsplastizität eines Wälzlagerstahls bei unterschiedlichen Phasenumwandlungen Die FE-Simulation von Wärmebehandlungsvorgängen erfordert Stoffwerte zur Beschreibung der Phasenumwandlung. Während der Wärmebehandlung treten thermisch und umwandlungsbedingte Spannungen auf, die das Umwandlungsverhalten beeinflussen. Der Einfluss derartiger Spannungen auf die Umwandlung waren Gegenstand der hier vorgestellten Arbeit. Die durchgeführten Untersuchungen zeigen den Einfluss einer während der Umwandlung angelegten konstanten Spannung auf die Umwandlungsplastizität. Der Parameter K, der das Ausmaß der Umwandlungsplastizität beschreibt, nimmt während der perlitischen Umwandlung mit steigender Temperatur zu, bei bainitischer Umwandlung dagegen ab.

Effect of Si on the thermo-mechanical deformation and spheroidization of medium carbon steels

Medium carbon steels (0.45 %C) having various Si content (0.2–1.5%) were thermo-mechanically processed in a controlled hot deformation simulator, a Thermecmaster-Z, and subsequent heat-treatment was performed for spheroidization. The effects of Si on the thermo-mechanical deformation and the spheroidization behavior were investigated. The results showed an increase in transformation temperatures, A3 and A1, with increasing Si content. Also, both grain size and fraction of the ferrite after the thermo-mechanical deformation increased with increasing Si content. Furthermore, the spheroidization of the thermo-mechanically processed medium carbon steels was improved by the addition of Si. The non-stop hot deformation-spheroidization process, which eliminates extra cooling-reheating processing steps, was found to be highly effective for Si-added medium carbon steels.

Characterization of High-Speed Microactuator Utilizing Shape Memory Alloy Thin Films

Dynamic actuation properties of two types of high-speed microactuators utilizing Ti-Ni-based thin films were investigated. One type is a microactuator utilizing a Ti-Ni-Pd thin film which has high transformation temperatures. Cooling rate of a microactuator increases with increasing temperature difference between transformation and atmosphere temperatures, thus the increase in transformation temperature is effective to increase the actuation response. The other type is a microactuator using R-phase transformation of a Ti-Ni thin film which has a narrow transformation temperature hysteresis. The narrow transformation temperature hysteresis of the R-phase transformation is effective to increase the actuation response. Both types of actuators are promising for high response applications. The working frequency of the microactuators reached 100Hz in the two types of microactuators utilizing the martensitic transformation of the Ti-Ni-Pd thin film and the R-phase transformation of the Ti-Ni thin film.

Fe-0.4C合金の強磁場中等温フェライト変態における組織配向

Structural elongation and alignment in an Fe-0.4C alloy isothermally transformed in high magnetic fields has been studied by quantitative microscopy analysis. It has been already reported by the authors that an elongated and aligned structure is obtained during continuous cooling as far as some conditions are satisfied. It is shown in this paper that an elongated and aligned two-phase structure is formed in high magnetic fields by isothermal ferrite transformation both below and above Curie temperature. To clarify if the elongated structure is formed in the nucleation stage or growth stage, transformation behavior in magnetic fields has been investigated and it was found that equiaxed ferrite grains nucleate randomly at austenite grain boundaries and they become elongated by preferred growth along the direction of applied magnetic field. Effects of isothermal transformation temperature on the degree of elongation has been studied. Below Curie temperature, the degree of elongation increases with increasing transformation temperature, whereas it decreases above Curie temperature. Small chemical driving force for ferrite precipitation and large magnetization of ferrite in high magnetic fields favor the formation of elongated structure.

펄라이트 함유강에서 연성에 영향을 미치는 미세조직 인자

The effect of transformation temperature on microstructural features and their effects on ductility in 0.55%C steels were investigated, compared with in 0.82%C eutectoid steel. The samples were austenitized at 100<TEX>$0^{\circ}C$</TEX> for 30min. followed by quenching in a salt bath in the temperature range of 500 ~ <TEX>$620^{\circ}C$</TEX>. It was found that reduction of area(RA) increased with increasing transformation temperature and then, decreased after reaching its maximum value in steels containing pro-eutectoid ferrite less than 6%. The thickness of lamellar cementite was found to be the main factor controlling RA. Additionally, the presence of cementite thickness for the maximum ductility in all the tested steels was observed as about 0.015<TEX>${\mu}{\textrm}{m}$</TEX> for tested steels.

Martensitic transformation and magnetic properties of Heusler alloy Ni–Fe–Ga ribbon

The martensitic transformation and magnetic properties of ferromagnetic shape memory alloy Ni 50+ x Fe 25− x Ga 25 ( x = − 1 , 0, 1, 2, 3, 4) ribbons have been systematically studied. It has been found that with the increase of Ni concentration, the martensitic transformation temperature increases, but the Curie temperature decreases. Both the two-step thermally induced structural transformation and the one-step transition have been observed in NiFeGa alloys with different compositions. It is found that the two-step transition became the one-step transition after the ribbon being heat treated at 873 K or higher. X-ray diffraction patterns show that only L 2 1 → B 2 transition occurs in the samples treated at 873 K, while the γ phase will form in the samples treated at higher temperature. Transmission electron microscopy (TEM) studies show that the alloys with martensitic transformation temperature above the room temperature are non-modulated martensite with the large domain size, being different from the stoichiometric Ni 2FeGa alloy that is a modulated martensite with small domain size. The influences of Fe substitution for Ni in Ni 2FeGa on the saturation magnetization and exchange interaction are also discussed.

Kinetics of the discontinuous precipitation of a liquid phase in Cu–In alloys

The morphology and growth kinetics of the discontinuous precipitation of liquid and depleted solid phases from a supersaturated solid solution has been studied. The transformation was carried out in the two-phase (liquid + solid a) field in the temperature range 996-1050 K in two Cu-In alloys containing 8.9 and 9.5 at.% In. A lamellar structure consisting of alternate lamellae of a and liquid phases has been observed to grow from the grain boundaries of the supersaturated a solid solution. The nucleation of the liquid droplets occurred at the grain boundary and a thin layer of liquid formed between the droplets. The liquid film started migrating resulting in the development of a lamellar structure. In both alloys the growth rate increased with increasing temperature of transformation but the interlamellar spacing decreased with increasing transformation temperature. The growth kinetics was analyzed using the models of Cahn and Petermann and Hornbogen and from a mass balance using Fick's first law. From the diffusivity and activation energy values it can be concluded that the growth of the cellular structure occurs by solute transport through the liquid film.

Structural Elongation and Alignment in an Fe-0.4C Alloy by Isothermal Ferrite Transformation in High Magnetic Fields

Structural elongation and alignment in an Fe-0.4C alloy transformed in high magnetic fields has been studied by quantitative microscopy analysis. An elongated and aligned two-phase structure is formed in high magnetic fields by isothermal ferrite transformation both below and above Curie temperature. Equiaxed ferrite grains nucleate randomly at austenite grain boundaries and they become elongated by preferred growth along the direction of applied magnetic field. Below Curie temperature, the degree of elongation increases with increasing transformation temperature, whereas it decreases above Curie temperature. Small chemical driving force for ferrite precipitation and large magnetization of ferrite in high magnetic fields favor the formation of elongated structure.

Magnetic properties and structural phase transformations of NiMnGa alloys

The magnetic properties and structural phase transformations of Heusler alloys Ni/sub 2+x/Mn/sub 1-x/Ga and Ni/sub 2-x/Mn/sub 1+x/2/Ga/sub 1+x/2/ were investigated. It was found that the martensitic transformation temperature increases and the Curie temperature decreases with decreasing Mn concentration in the Ni/sub 2+x/Mn/sub 1-x/Ga system, but the magnetic properties decrease faster than those do in the Ni/sub 2-x/Mn/sub 1+x/2/Ga/sub 1+x/2/ system. This suggests that the influence of the conduction electron concentration and the distance between Mn atoms on the Curie temperature is stronger than the magnetic dilution effect. The martensitic transformation temperature shows a peak value at x=0.06 in the Ni/sub 2-x/Mn/sub 1+x/2/Ga/sub 1+x/2/ system. A large stress-free magnetic-field-induced strain (MFIS) of 1.8% has been obtained at room temperature in a single crystal sample with the composition of the first system.

Effect of aging on martensitic transformation in γ-MnCu alloy

Abstract Effect of isothermal aging was investigated on fcc–fct martensitic transformation behavior of Mn–14at.%Cu alloy. It was revealed that by aging at temperatures ranging from 630 to 690 K, the transformation temperature increases markedly and the residual resistivity decreases in parallel. DSC peak profiles have also been modified significantly by aging. A good linear correlation has been found between the changes in the information temperature and those in the resistivity. It is also shown that the observed transformation temperature increase, resistivity decrease and their linear correlation can be well explained by the rule of mixture assuming the heterogeneous microstructure, which forms as a result of spinodal decomposition as reported in previous studies.

Retarded C54 transformation and suppressed agglomeration by precipitates in TiSi2 films

We report the effects of excess Si phase on the C54 transformation and the thermal stability of TiSi2 thin films as a function of Si/Ti (x) ratio. The resistivity and x-ray diffraction data of TiSix(x=2.1–2.4) films showed a retardation of C54–TiSi2 transformation with incremental molar ratio x; the TiSix (x=2.1–2.3) films were completely transformed to C54-TiSi2 with rapid thermal annealing (RTA) of 750 °C, while the TiSix (x=2.4) films were transmuted to C54–TiSi2 over the RTA of 800 °C. Transmission electron microscopy study revealed that the growth of Si precipitates in the Si-rich TiSix films competes with the grain growth during the transformation of C49 to C54 TiSi2 phase, resulting in the increase of C54 transformation temperature. An excellent sheet resistance (Rs) and its standard deviation in concert with a reliable gate oxide integrity were attained from the Si-rich TiSi2/polycrystalline-Si (poly-Si) structure up to the solid state annealing of 850 °C for 60 min. These attributes are due to the reduced solid state reaction at TiSi2/Si interface and the suppressed TiSi2 agglomeration by Si precipitates. The average Rs of the 0.12-μm-wide TiSi2(800 Å)/poly-Si gate lines is lower than 4.5 Ω/□, demonstrating a robust gate electrode structure for gigabit scale device application.

Creep Behavior of NiTi Shape Memory Alloys and the Effect of Pre-Creep on the Martensitic Phase Transformation

The paper reports creep data of a Ni-rich NiTi-alloy at stresses and temperatures in the range of 500 °C and 150 MPa. The apparent activation energy for creep and the creep stress exponent were found to be 421 kJ/mole and 5. Tempering and pre-creep result in a 20°C increase of phase transformation temperatures (PTTs). The effect of an additional plastic deformation (as compared to a stress free aging treatment) is that PTT-peaks broaden and overlap on cooling and broaden on heating. This can only be rationalized on the basis of a difference in microstructures between the tempered and pre-crept materials.

Correlation between fcc–fct transformation behavior and spinodal decomposition in γ-MnCu alloys

Abstract The effect of γ phase aging was investigated on fcc–fct martensitic transformation behavior for Mn–14∼30 at.% Cu alloys. The martensitic transformation in these alloys is ‘quasi martensitic’ as characterized by a small hysteresis and a continuous change in lattice parameters below the transformation temperature. It was shown that by aging at temperatures ranging from 630 to 690 K, the transformation temperature increased markedly and the residual resistivity decreased in parallel. Differential scanning calorimetry (DSC) peak profiles were also modified significantly by aging and the heat of transformation increased. A good linear correlation has been found between the changes in the transformation temperature and those in the resistivity. It is also shown that the observed increase in transformation temperature, decrease in resistivity and their linear correlation can be well explained by the rule of mixture assuming a heterogeneous microstructure, which formed as a result of the spinodal decomposition.

The Bainite Reaction Kinetics in Austempered Ductile Iron

Bainitic reaction kinetics in ductile iron contained according to Ukrainian standard (weight %) 3.60-3.80 carbon, 2.60-2.80 Si, ∼ 0.12 Mn, ∼ 0.60 Cu and additionally alloyed by Mo (0.15-0.20) has been studied. It was found that the overall transformation kinetics becomes slower as transformation temperature increase. This is because more intensive redistribution of carbon into austenite at higher temperatures. Two austenites wlith different carbon content have been fixed and kinetics of their lattices parameters has been studied.

Effects of Thermal Ageing in β-Phase in Cu-Al-Ni Single Crystals

The effect of isothermal ageing of β-Cu-Al-Ni alloys at low temperatures (473K and 573K) on the martensitic transformation has been studied using differential scanning calorimetry and transmission electron microscopy. Three single crystals with different Al content (13.5, 13.6 and 13.8 wt%) and the same Ni concentration (4%) were used. Before ageing, the samples were annealed at 1070K and quenched to room temperature. The transformation temperatures remained nearly constant during the initial stages of ageing and started to increase noticeably after a given ageing time, which is shorter in the samples with higher Al content. For the alloy with highest Al content, the Ms decreased slightly at the beginning of ageing at 473K. The transformation to two coexisting martensitic structures, β' (18R) and γ' (2H) has been observed. The proportion of each one changes with the composition and ageing, the γ' phase being promoted for increasing ageing times and temperatures. A good correlation exists between the initial ageing stage, in which there is no evolution of transformation temperatures, with the coexistence of the two martensites. The formation of the two kinds of martensites is related to the short range reordering processes taking place during ageing, specially of as quenched next nearest neighbours disordered Cu-Al pairs. The results would indicate that the disordered Cu-Al pairs stabilize the β' martensite and when these pairs recover the correct positions, the γ' becomes the stable martensite. The high increase of transformation temperatures with ageing at 573K is related to two different precipitation processes observed.

Martensitic Transformation Behavior of a Shape Memory Ti&amp;ndash;40.5Ni&amp;ndash;10Cu Alloy Affected by the C11&lt;I&gt;&lt;SUB&gt;b&lt;/SUB&gt;&lt;/I&gt;-type Precipitates

Effect of aging at 873 K on the two-step B2→B19→B19' transformation of a shape memory Ti-40.5Ni-10Cu alloy was studied. It was found that the start temperature of the B2→ B19 transformation and that of the Bl9→B19' transformation increase with increasing aging time. The start temperatures of the reverse transformations also increase. The temperature range of the two-step transformation decreases with increasing aging time. The aged Ti-40.5Ni-10Cu alloy is composed of the matrix with B2-type structure (a C =0.3029 nm) and precipitates with Cll b -type structure (a t =0.3132 nm, c t =0. 7991 nm). The precipitates are partly coherent with the matrix and are plate-like in shape having a orientation relationship [100] C //[100] t and [001] C //[001] t , and a habit plane {001) C' The increase of transformation temperature is caused by the precipitation through aging. The precipitation increases the Ti content of the matrix, and the precipitates act as a nucleation sites of B19 martensite due to strain field around them preferable for the B19 martensite.

Cyclic Deformation of TiNi Shape Memory Alloy.

An experiment with cyclic loading and unloading and an experiment with heating and cooling under the constant stress of TiNi shape memory alloys were carried out. The starting condition and the completing one of the martensitic transformation and the reverse transformation, the cyclic behavior of recovery strain and the conditions for application of recovery deformation were discussed. The results are summarized as follows. During the thermomechanical cycles, the yield stresses of the martensitic transformation and the reverse one decrease, but the transformation temperatures increase. The starting condition and the completing one of both transformations under the cyclic deformation are described by the behavior of the transformation lines in the stresstemperature plane. During the thermal cycles under constant stress, the recovery strain may appear or diminish depending on the relation among the initial strain, the heating temperature and the cooling temperature, thus showing complex cyclic deformation behavior. The cyclic recovery strain is represented by the relation among the heating temperature, the cooling temperature, the transformation lines and the transformation strain. It is important for the shape memory alloy elements to determine the conditions for application based on the cyclic characteristics of the transformation stress, the transformation strain and the transformation temperature.

Deformation behaviour of TiNi shape memory alloy subjected to variable stress and temperature

Experiments with cyclic loading-unloading and experiments with heatingcooling under constant stress of TiNi shape memory alloys were carried out. This paper shows that, during the thermomechanical cycles, the transformation stresses of the martensitic transformation and the reverse transformation decrease, but the transformation temperatures increase. The cyclic recovery strain is represented by a relation between the heating temperature, the cooling temperature, the transformation lines in the stress-temperature plane and the transformation strain.