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To control the ferrite and martensite microstructure in dual-phase steels, the phase transformation from ferrite (α) to austenite (γ) on heating is essential. For a comprehensive understanding of the γ formation in the early stage of the α → γ phase transformation, the orientation relationships and the boundaries between α and γ grains were investigated using a 3D electron backscatter diffraction analysis. It was found that, when the orientations of the α and γ grains hold the K–S relationship or the N–W relationship, the orientation of the boundary does not correspond to the exact close-packed planes {011}α or {111}γ, but deviates within the vicinity of these crystal planes based on a variety of misorientations of up to 40 deg. Most of the boundary planes with the K–S relationship are parallel to the crystal planes between {011}α and {111}α of the α grain, and {111}γ and {012}γ of the γ grain. Focusing on the crystallographic feature of the boundary planes in austenite phase, the mechanism of the α → γ transformation is discussed.

Niinomi M., Akahori T., Nakai M., et al. Quantitative and qualitative relationship between microstructural factors and fatigue lives under load- And strain-controlled conditions of Ti-5Al-2Sn-2Zr-4Cr-4Mo (Ti-17) fabricated using a 1500-ton forging simulator. Materials Transactions 60, 1740 (2019); https://doi.org/10.2320/matertrans.ME201904., The fatigue lives of forged Ti-17 using a 1500-ton forging simulator subjected to different solution treatments and a common aging treatment were evaluated under both load- and strain-controlled conditions: high and low cycle fatigue lives, respectively. Then, the tensile properties and microstructures were also examined. Finally, the relationships among fatigue lives and the microstructural factors and tensile properties were examined. The microstructure after solution treatment at 1203 K, which is more than the β transus temperature, and aging treatment exhibits equiaxed prior β grains composed of fine acicular ¡. On the other hand, the microstructures after solution treatment at temperatures of 1063, 1123, and 1143 K, which are less than the β transus temperature, and aging treatment exhibit elongated prior β grains composed of two different microstructural feature regions, which are acicular α and fine spheroidal α phase regions. The 0.2% proof stress, σ₀.₂, and tensile strength, σB, increase with increasing solution treatment temperature up to 1143 K within the (α + β) region, but decrease with further increasing solution treatment temperature to 1203 K within the β region. The elongation (EL) and reduction of area (RA) decrease with increasing solution treatment temperature, and it becomes nearly 0% corresponding to a solution treatment temperature of 1203 K. The high cycle fatigue limit increases with increasing solution treatment temperature up to 1143 K, corresponding to the (α + β) region. However, it decreases with further increase in the solution treatment temperature to 1203 K in the β region. The fatigue ratio in high cycle fatigue life region is increasing with decreasing solution treatment temperature, namely increasing the volume fraction of the primary α phase, and it relates well qualitatively with the volume fraction of the primary α phase when the solution treatment temperature is less than the β transus temperature. The low cycle fatigue life increases with decreasing solution treatment temperature, namely increasing the volume fraction of the primary α phase. The low cycle fatigue life relates well quantitatively with the tensile true strain at breaking of the specimen and the volume fraction of the primary α phase for each total strain range of low cycle fatigue testing.

Different amounts of Cr were added to a metastable β-type Ti–22Nb (at.%) alloy to obtain desirable mechanical properties, including a low Young’s modulus, high strength, and good plasticity. The mechanical properties and microstructural changes were investigated. Cr has a high ability to stabilize the β phase, as well as suppress both α″ martensite and ω phase transformations during quenching and the stress-induced α″ martensite transformation during tension. Solid solution strengthening is scarcely achieved by Cr addition. The changes in mechanical properties can be attributed to the different β stabilities. The Ti–22Nb–(0,1)Cr alloys have metastable β phases and exhibit double yielding phenomena, indicating a stress-induced α″ martensite transformation. The Ti–22Nb–(2,3)Cr alloys with stable β phases exhibit distinct work hardening caused by a {332}β β twinning, which also occurs in the Ti–22Nb–(0,1)Cr alloys, but not in the Ti–22Nb–4Cr alloy. Low Young’s moduli of approximately 60 GPa are obtained for the Ti–22Nb–(1,2)Cr alloys. The Ti–22Nb–2Cr alloy exhibits desirable properties for biomedical applications, including an ultimate tensile strength of approximately 600 MPa and elongation of approximately 20%.

The size effect on the mechanical behaviors of single crystalline Fe-31.2Pd (at.%) micropillars with four different pillar diameters (approximately 2 μm, 1 μm, 500 nm and 400 nm) were studied by compressing in the [001] direction. Both the Young's modulus and yield stress increase with the decrease of pillar diameter. The main defects in the plastically deformed pillars are the {111} deformation twins, which could be covered by high density of dislocations after further plastic deformation in a 400 nm pillar. A repeatable elastic-like strain ~4% was observed for more than 40,000 cycles.

We have investigated the influence of twin boundary properties on the damping behavior of single crystalline Fe-31.2Pd (at%) alloy, which exhibits a weak first-order martensitic transformation. Different static tensile stress was applied by dynamic mechanical analyzer to adjust the twin boundary density and hydrogen was doped to modify the twin boundary mobility. A high damping capacity (tan δ > 0.1) in a wide temperature range from about 140 K to 230 K was observed under a low static stress of about 0.3 MPa. Hydrogen doping further increased the maximum value of the damping capacity by introducing a relaxation tan δ peak. The damping capacity decreased with increasing static stress probably due to the decrease in twin boundary density.

Depending on Pd content, disordered Fe-Pd alloys take various crystal structures: body-centered cubic (BCC), body-centered tetragonal (BCT), face-centered tetragonal (FCT) and face-centered cubic (FCC) structures. We have measured specific heat of Fe-Pd alloys to understand the lattice stability and electronic state of the alloys. At the phase boundary between FCT and FCC phases, electronic specific heat coefficient shows a local maximum and the Debye temperature shows a local minimum. A local maximum of electronic specific heat coefficient also appears in the BCC region with Pd content of near 10 at.%.

Elastocaloric effects in shape memory alloys are usually caused by latent heat associated with the stress-induced martensitic transformation. We report here that the rubber-like behavior of the R-phase in nanocrystalline Ti-50.8Ni (at.%) wires, realized by an aging heat treatment under tensile stress, also contributes a significant elastocaloric effect. The efficiency of the elastocaloric effect caused by the rubber-like behavior is higher than that caused by the stress-induced B2 ↔ B19′ transformations because of the small energy dissipation. The usage of the rubber-like behavior is a method to extend the temperature window of the elastocaloric effect in shape memory alloys.

The microstructures, tensile properties, and fatigue lives of the forged Ti-17 using a 1500-ton forging simulator subjected to different solution treatments and a common aging treatment under both load- and strain-controlled conditions to evaluate high cycle fatigue and low cycle fatigue lives, respectively were examined. Then, the tensile properties, microstructures, and relationships between fatigue lives and the microstructural factors were discussed. The fatigue limit under load-controlled conditions increases with increasing solution treatment temperature up to 1143 K, which is in the (α + β) region. However, it decreases with further increase in the solution treatment temperature to 1203 K in the b region. The fatigue ratio at fatigue limit is increasing with decreasing solution treatment temperature, namely increasing the volume fraction of the primary α phase, and it relates well qualitatively with the volume fraction of the primary α phase when the solution treatment temperature is less than the b transus temperature. The fatigue life under strain-controlled conditions to evaluate the low cycle fatigue life increases with decreasing solution treatment temperature, namely increasing the volume fraction of the primary α phase. The fatigue life under strain-controlled conditions to evaluate the low cycle fatigue life relates well quantitatively with the tensile true strain at breaking of the specimen and the volume fraction of the primary α phase for each total strain range.

Li Q., Ma D., Li J., et al. Low young's modulus Ti-Nb-O with high strength and good plasticity. Materials Transactions 59, 858 (2018); https://doi.org/10.2320/matertrans.M2018021., Oxygen was added to Ti-38Nb (mass%) alloys to improve their mechanical properties. Ti-38Nb-xO (x = 0.13, 0.24, 0.46, mass%) alloys were prepared by arc melting, and subsequently subjected to homogenization, hot rolling, and solution treatment. It was found that adding oxygen suppresses the martensite transformation and exhibits strong solution strengthening effect. Single β phase is obtained in Ti-38Nb-0.24O, whereas Ti-38Nb-0.13O is composed of both α′′ and β phases. Both alloys exhibit double yielding phenomena during tension, indicating a stress-induced martensitic transformation. Ti-38Nb-0.46O exhibits a non-linear deformation, a low Young's modulus of 62 GPa, high tensile strength up to 780 MPa, and elongation around 23%, which are promising characteristics for biomedical applications.

In this paper, we discuss the development of Fe-Co-Cr-Mn-Ni-C high-entropy alloys (HEAs), which can be cast in air atmosphere (hereafter called HE cast iron alloys). FexCoCrMnNiCy HE cast iron alloys were designed by the addition of carbon to realize the reduction atomosphere during melting and casting, with subsequent thermodynamic calculations for the decrease in the liquidus temperature focusing on the liquidus of carbides and the face-centered cubic (FCC) phase. The ingots were cast with conventional high-frequency melting methods in silica-based crucibles under Ar flow and air atmosphere, respectively. The formation of the FCC phase was observed in the ingots of FexCoCrMnNi (x = 1, 2, and 3) HEAs. Composites of the FCC phase and Cr-rich carbides were obtained in the ingots of FexCoCrMnNiCy HE cast iron alloys with compositions of FeCoCrMnNiC0.2, Fe2CoCrMnNiC0.4, and Fe3CoCrMnNiC0.8. The constituent phases and solidification microstructures of the FexCoCrMnNiCy HE cast iron alloy ingots were not dependent on the processing atmosphere (Ar flow versus air atmosphere). Keywords: High entropy alloys, Metals and alloys, Cast iron, Microstructure, Solidification, Thermodynamics, HEAs

We have investigated the influence of thermal cycles on martensitic transformation of a Co2Cr(Ga,Si) ferromagnetic Heusler alloy. The as-quenched specimen exhibits successive L21(L)–D022–L21(H) martensitic transformation in the cooling process, which is known as reentrant martensitic transformation. However, heating to 800 K (527 °C) for reverse D022–L21 transformation with a rate of 10 K/min (10 °C/min) stabilizes the parent phase, meaning that the martensitic transformation is suppressed by the thermal cycles. We found precipitate after thermal cycles, and it will be the reason for the stabilization of parent phase.

We have detected an inverse elastocaloric effect in a Ti-51Ni (at%) alloy which contains aligned coherent particles of Ti3Ni4 formed by aging under tensile stress. In this alloy, the temperature of the specimen decreases when stress is applied due to a stress-induced reverse martensitic transformation (from the R-phase to the B2-phase) The temperature decrease caused by this effect is about 1.1 K at 300 K. The internal stress field around the Ti3Ni4 precipitate is responsible for this effect. A further increase in the tensile stress causes a temperature rise due to a conventional elastocaloric effect.

We have determined the easy axis of magnetization of Fe3C (cementite) using a powder specimen prepared by an electrolytic extraction method. The easy axis is determined to be the c-axis (the shortest axis) of the orthorhombic structure with the space group Pnma. The result is different from the one previously reported by neutron diffraction (b-axis). The magnetic energy difference between the easy axis and the average of other two axes is approximately 400 kJ/m3 at 5 K.

We have constructed a time-temperature-transformation (TTT) diagram for the martensitic transformation in a Ti-51.3Ni (at%) alloy. The transformation proceeds when the specimen is held at fixed temperatures between 110 K and 140 K, but not at other temperatures. The time required for the formation of 0.1% of the martensite phase is plotted as a TTT diagram. It exhibits a C-curve with a nose temperature near 130 K. Application of a thermal activation model to the TTT diagram suggests that the size of a nucleus of the martensite phase is about (2.2 nm)3.

The elastocaloric effect under tensile stress along the [001] direction has been investigated in an Fe-31.2Pd (at.%) alloy, which exhibits a weak first-order martensitic transformation at 230 K from a face-centered cubic structure to a face-centered tetragonal (c/a

Ti-51Ni (at%) alloys including coherent precipitates of Ti3Ni4 exhibits thermally-induced B2-R transformation. If the Ti3Ni4 is formed under tensile stress, it orientates preferentially so that its habit plane becomes perpendicular to the tensile axis. In such specimens, stress-induced reverse R-B2 transformation is reported to occur. In the present study, the stress-induced reverse R-B2 transformation behavior was studied by infrared camera and in situ X-ray analysis. The infrared camera observation revealed that the temperature of the specimen decreases homogeneously by the application of tensile stress within the resolution of the camera. The in situ X-ray analysis revealed that stress-induced reverse R-B2 transformation and rearrangement of variants of the R-phase occurs simultaneously in the specimen.

The solid-state amorphization (SSA) behavior of the intermetallic compound Ti50Ni44Fe6 was investigated using high-voltage electron microscopy. In situ transmission electron microscopy clarified a particular SSA process consisting of the appearance of diffuse scattering during the initial stage of SSA and the subsequent disappearance of the diffuse scattering during irradiation. Irradiation-induced commensurate–incommensurate (C–IC) and IC–B2 transformations occurred before SSA. Both the martensitic transformation (MT) and SSA behaviors were significantly affected by the replacement of Ni by Fe in Ti50Ni50−xFex.

A disordered Fe-31.2Pd (at.%) alloy exhibits a weak first-order martensitic transformation (MT) from a face-centered cubic structure to a face-centered tetragonal structure. We employed a Dynamic Mechanical Analysis (DMA) to understand the transformation behavior. As the temperature decreases, the storage modulus E ′ decreases in the parent phase and increases in the martensite phase. The loss tangent (tan δ ) shows a slight increase when approaching M s (=225 K), suggesting the formation of movable interfaces even above M s . The value of tan δ is nearly proportional to (1 − c/a ) 2 below M s , meaning that highly mobile twinned interfaces are essential for internal friction below M s . The so-called transitory term of tan δ is negligibly small for the MT of this alloy.

We have examined the transformation strain, Δe, in the [0 0 1] direction of an Fe-31.2Pd (at.%) shape memory alloy under compressive stress applied in the same direction. When the stress is absent, the alloy exhibits a cubic to tetragonal martensitic transformation at 230 K with |Δe| of 1.4%. As the stress increases, the transformation temperature increases linearly and |Δe| decreases linearly and vanishes at 40 MPa (280 K). This point is the critical point of this transformation at which the first-order nature disappears, and the critical exponent β is evaluated to be 0.47 ± 0.04.

In typical shape memory alloys, significant elastocaloric effects appear in association with stress-induced martensitic transformations. However, we report here that in an Fe-31.2Pd (at.%) alloy, a significant elastocaloric effect appears due to lattice softening, which causes a weak first-order martensitic transformation at T0 (∼230 K). We found that in a wide temperature range of between 175 K ( T0), the alloy exhibits an adiabatic temperature decrease of more than 1.5 K when a compressive stress of 200 MPa applied in the [0 0 1] direction is removed. The refrigeration capacity calculated in this temperature range is 5 MJ/m3.

Fe 3 Pt with a degree of order of S = 0.75 shows a second-order-like martensitic transformation from a cubic structure to a tetragonal one at approximately 90 K. We found by neutron diffraction that this alloy exhibits a large elastic strain of more than 6% by the application of compressive stress in the [001] direction. A large elastic anisotropy caused by lattice softening in elastic constant C’ , which occurs on approaching the transformation temperature, was found to be responsible for the large elastic strain of Fe 3 Pt.

We have investigated local structures around Ni and Fe atoms by X-ray fluorescence holography (XFH) method in incommensurate (IC) phase of Ti-42Ni-8Fe(at.%) alloy and obtained the results as the followings; (i) The atomic distances between Ni atom and Fe atom and those 2nd nearest neighbor atoms are 0.27 nm and 0.29 nm, respectively. (ii) The atomic image intensities of 1st nearest neighbor atoms around Fe atoms are much weaker than those around Ni atoms. These results indicate that nanometer-sized heterogeneous strain exists and it is the cause of nanometer-sized domain in IC phase.

In this Rapid Communication we report a phenomenon in a disordered interacting electron system. The measurements of structural, magnetic, and transport properties of $\mathrm{FeA}{\mathrm{l}}_{2\ensuremath{-}x}\mathrm{G}{\mathrm{a}}_{x}$ ($0\ensuremath{\le}x\ensuremath{\le}0.5$) show that antiferromagnetic transition in these intermetallic compounds occurs concomitantly with a disorder-induced weak localization of electrons; the temperatures ${T}_{N}$ and ${T}_{m}$, at which antiferromagnetic transition and the weak localization respectively occur, closely track each other as the Ga concentration is varied. The antiferromagnetic transition is confirmed from the magnetic and specific heat measurements, and the occurrence of weak localization is confirmed from the temperature variation of resistivity and magnetoresistance measurements. With increasing Ga concentration, substitutional disorder in the system increases, and the consequent disorder-enhanced magnetic exchange interaction and disorder-induced fluctuations simultaneously drive antiferromagnetic transition and weak localization, respectively, to higher temperatures.

Diffuse satellites appearing in electron diffraction pattern of shape memory Ti–(50 − x )Pd– x Fe (14, 16, 18, 19 and 20, in at.%) alloys have been investigated. The satellites appear in each alloy below T min , where its electrical resistivity shows a local minimum. The positions of satellites are g B2 + 〈 ζ ζ ¯ 0〉 * , where g B2 is a reciprocal lattice vector of the B2-phase. The value of ζ is smaller than 1/5 at T min for all the alloys; it increases with decreasing temperature and decreases with increasing iron content. The value of ζ at T min agrees with the length of the nesting vector previously calculated by the present authors. This result implies that Fermi surface nesting is the origin of diffuse satellites in Ti–(50 − x )Pd– x Fe alloys.

The Cu precipitation 780 MPa grade steel has higher resistance to cold cracking than the conventional steels. To study this, we have investigated the hydrogen evolution characteristics of the Cu steel heat-affected zone (HAZ) by the thermal desorption spectroscopy method and compared with those of conventional 780 MPa steel HAZ. The thermal cycle tests were conducted to obtain the HAZ microstructures, and the peak temperatures were selected from 500 to 1400 °C at intervals of 100 °C. Hydrogen was then charged, and the hydrogen evolution curves were measured at a heating rate of 100 °C/h. The results show that the amounts of hydrogen released from the specimens whose peak temperatures of the thermal cycle tests were 1000 °C or higher are lower, while the results of the conventional steels have the opposite tendency. We numerically calculated the hydrogen evolution curves to determine physical constants, and using these constants, we also calculated the hydrogen concentration profiles of the y-groove weld cracking test and found that the hydrogen concentration of the Cu steel HAZ near the fusion line tends to become lower than those of the conventional steel HAZ. This phenomenon is considered one of the reasons for the higher cold cracking resistance of the Cu steel.

Magnetic behavior of equiatomic FeAl alloy is still not satisfactorily understood. In this work, we studied the magnetic properties of disordered FeAl alloy both experimentally and using first-principles theories and revisited the alloy system in perspective of the inhomogeneity present in the system. After obtaining magnetic exchange interactions from first-principles theories, we carried out Monte-Carlo simulations on special quasi-random structures (SQS) and compared the results with experimental measurements. We tried to understand the plethora of often differing results and explain them in terms of possible inhomogeneities in the system.

We have studied the structure change of an ordered Fe3Pt (degree of order ∼0.75) under a compressive stress applied in the [001] direction by neutron diffraction. In the absence of the stress, the alloy exhibits a weak first order martensitic transformation at 90 K from the L12-type cubic structure to the L60-type tetragonal structure. Under the compressive stress of 100 MPa, the first order nature of the thermally-induced martensitic transformation was undetectable in the temperature range of between 70 K and 270 K. The first order nature of the stress-induced martensitic transformation was also undetectable in the stress range of between 6 MPa and 300 MPa when tested at 120 K and higher temperatures. Under these conditions, the lattice parameters change continuously both in the cooling process and in the stress-applying process. Despite the disappearance of the first order nature of martensitic transformation, a significant stress-induced softening of lattice, which is regarded as a precursor phenomenon of martensitic transformation, was observed between 120 K and 265 K but not at 93 K and 295 K.We have studied the structure change of an ordered Fe3Pt (degree of order ∼0.75) under a compressive stress applied in the [001] direction by neutron diffraction. In the absence of the stress, the alloy exhibits a weak first order martensitic transformation at 90 K from the L12-type cubic structure to the L60-type tetragonal structure. Under the compressive stress of 100 MPa, the first order nature of the thermally-induced martensitic transformation was undetectable in the temperature range of between 70 K and 270 K. The first order nature of the stress-induced martensitic transformation was also undetectable in the stress range of between 6 MPa and 300 MPa when tested at 120 K and higher temperatures. Under these conditions, the lattice parameters change continuously both in the cooling process and in the stress-applying process. Despite the disappearance of the first order nature of martensitic transformation, a significant stress-induced softening of lattice, which is regarded as a precursor phenomenon...

We have investigated the martensite transformation phenomena of a Cr-Ni type weld metal, especially the effects of stress and plastic strain that exist before the martensite transformation start. Tensile specimens machined from the weld metal were firstly heated up to 800 °C to austenitize the specimens and then cooled down. During the cooling, we applied stress and plastic strain before the martensite transformation starts. The results show that the stress increases the M s temperature, while the plastic strain decreases the M s temperature. In addition, the transformation-induced plasticity was also investigated. Finite element method (FEM) analysis was conducted considering these effects, and the results show that these effects on the residual stress and the weld distortion are considerably large. The FEM analysis shows that the compressive residual stress in the weld metal is likely to be decreased by the transformation-induced plasticity. We also conducted hydrogen diffusion analysis for the case that the retained austenite exists in the weld metal by varying the M s temperature in order to consider the appropriate time period to keep a cold cracking test specimen before the crack observation.

An Fe–55Pd (at.%) alloy exhibits a disorder–order transformation from the A1-type disordered cubic phase to the L10-type ordered tetragonal phase. We have investigated the influence of the magnetocrystalline anisotropy energy on the selective formation of a variant of the ordered phase during heat treatment. We found that the strength of the magnetic field required to produce a single variant decreases from approximately 4 T to approximately 0.4 T when the ordering heat-treatment temperature is decreased from 673 to 603 K. The magnetocrystalline anisotropy energy was evaluated at these temperatures as a function of magnetic field. The nucleation ratio between different variants was evaluated through the magnetocrystalline anisotropy. It is revealed that a single variant state is obtained during the growth process when the nucleation ratio of the dominant variant exceeds approximately 1.1.