Γ2 Phase Research Articles

Strengthening Cu-containing high entropy alloys through ultrasonic solidification constructed heterostructures

The solidification process of FeCoNiCu1.5Al0.2 high-entropy alloy (HEA) with two FCC phases was modulated by three-dimensional (3D) ultrasounds with 20 kHz frequency and 22 μm amplitude. The statically solidified alloy was composed of a primary γ1 phase growing into coarse dendrites and a Cu-rich γ2 phase dispersed in interdendritic spacings. Once 3D ultrasounds were applied, the primary γ1 phase was refined into small equiaxed grains and the secondary γ2 phase was distributed around their grain boundaries. Based on the estimation of local sound pressure and undercooling, as well as acoustic spectra examination, it is concluded that transient cavitation was the dominant reason for the formation of tiny equiaxed γ1 phase by remarkably increasing local nucleation rate, which also promoted the generation of connected γ2 phase together with acoustic streaming effect. The yield strength, ultimate strength and total elongation for ultrasonically solidified alloy sample were simultaneously enhanced by 73 %, 54 % and 13 %, which were up to 605 MPa, 845 MPa and 35 % respectively. According to LUR tests and dislocation characterization, both hetero-deformation induced (HDI) strengthening and grain refinement strengthening contributed to the increase of yield strength, while the former mainly enhanced ultimate strength and ductility synergistically. This indicates that 3D ultrasonic solidification provides an effective approach to overcoming the strength-ductility trade-off for Cu-containing HEAs.

Effect of ultrasonic solidification on the microstructure, mechanical and corrosion properties of FeCoCrNiCuAl0.4 high entropy alloy

One-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) ultrasound with 20 kHz frequency were successfully applied into the solidification process of FeCoCrNiCuAl0.4 high entropy alloy (HEA) to investigate their effects on microstructural evolution and application performance improvement. During static solidification, the primary γ1 phase developed into coarse dendrites with strip-like γ2 phase that diffusely distributed in the interdendritic regions. With the increase of ultrasound dimension, a novel heterostructure characterized by γ2 phase growing continuously among the fine equiaxed γ1 grains appeared. Transient cavitation, which intensified by the rise of ultrasound dimension, was analyzed to be the dominant factor in refining γ1 phase by significantly enhancing its nucleation rate, while the increased acoustic flow promoted the uniform distribution of easily segregated Cr and Cu elements by accelerating solute diffusion. These jointly contributed to the formation of such refined network heterostructure. Owing to the grain refinement strengthening and hetero-deformation induced (HDI) strengthening, the yield strength and ultimate strength of 3D ultrasonically solidified alloy were respectively enhanced by 29 % and 47 % without notable sacrifice of ductility. Meanwhile, the self-corrosion current density of the alloy was also reduced with the improvement of corrosion resistance, which mainly arose from the more balanced corrosion potential brought about by the uniform solute distribution and continuous network heterostructure.

The growth kinetics of intermetallic compounds by the fast diffusion path at the interface of Co and molten Zn

This study investigates the growth and microstructure formation of intermetallic compounds at the solid/liquid interface of a Co/Zn diffusion couple prepared using an isothermal bonding method and annealed isothermally at 703 K, 723 K, and 743 K for up to 48 h. The experimental observations and analysis revealed the formation of three Zn-rich intermetallic compounds: γ (Co5Zn21), γ1 (CoZn7), and γ2 (CoZn13). The γ2 phase, having the highest Zn content, formed the thickest layer, while the γ and γ1 phases exhibited slower growth. The total thickness of these layers increased proportionally to the annealing time, following a power function. The growth of intermetallic compounds was predominantly controlled by interdiffusion, with the γ2 phase forming island-like structures that merged over time, creating fast diffusion paths of liquid Zn. The annealing temperature had a minimal impact on the growth rate, with slightly faster growth observed at lower temperatures due to finer needle-like interfaces within the molten Zn, which created more efficient diffusion paths. These findings underscore the importance of understanding the kinetics and mechanisms of intermetallic compound formation for optimizing material properties and processing conditions in industrial applications.

Synergetic enhancement of ultimate strength and damping properties by pore structure in novel porous Cu-Al-Mn shape memory alloy

To meet the higher device vibration reduction requirements, novel porous Cu71Al18Mn11 shape memory alloys (SMAs) with controllable porosity were prepared using Cu, Al, and Mn elemental powders as raw materials. To further enhance the strength and damping performance of SMAs, a low-temperature reactive synthesis combined with spark plasma sintering (LTRS+SPS) process was used. In this paper, the effects of LTRS+SPS process on pore structure and texture, compressive strength, and damping properties of porous Cu71Al18Mn11 alloy were studied. The outcomes indicated that LTRS+SPS process can effectively improve both compressive strength and damping properties. The associated closed pore structure caused by this process and the second phase γ2 phase formed by element diffusion result in a variety in compressive strength from 324.6 MPa to 617.9 MPa, which were 3.9 times that of the comparable porosity alloy with alloy powder as raw material by vacuum sintering. Meanwhile, the damping value changed from 0.27 to 0.10, which was 4.5 times that of the homogeneous dense alloy. The increase in damping property is caused by the increase of motionable interfaces in the matrix for the introduction of pores, which leads to the increase of energy dissipation. Besides. the interaction between the second phase γ2 and dislocation contributes to the improvement of damping, as well as the compressive strength. These findings in this paper provide new insights and references for the structural design and microstructure design of high-performance Cu-based alloys.

A novel Ni-alloyed Cu-Al-Ga-Fe shape memory alloy with excellent shape recovery performance

In this study, a novel Ni-alloyed Cu-Al-Ga-Fe single crystal alloys were reported for the first time. The microstructure, martensitic transformation, shape memory effect, and superelasticity of Cu-12.5Al-4Ga-3Fe-xNi (x = 2, 3, 5) and Cu-13.5Al-4Ga-3Fe-xNi (x = 3, 4, 5) were investigated. The results show that Cu-12.5Al-4Ga-3Fe-xNi (x = 2, 3, 5) single crystals consist of the parent phase, 18 R martensite, and β(FeAl) nano-precipitates. As the increase in Al content, Cu-13.5Al-4Ga-3Fe-xNi (x = 3, 4, 5) single crystals consist of the parent phase, γ1(Cu9Al4) phase, and β(FeAl) nano-precipitates. The martensitic transition finishing temperatures (Mf) of 12.5Al alloys are all higher than room temperature, while the reversible martensitic transition finishing temperatures (Af) of 13.5Al alloys are all lower than room temperature. Cu-12.5Al-4Ga-3Fe-3Ni single crystal shows the highest SME of 7.6 % with 100% strain recovery. Similarly, the Cu-13.5Al-4Ga-3Fe-3Ni single crystal demonstrated the highest superelasticity of 11 %. Additionally, the Cu-13.5Al-4Ga-3Fe-3Ni single crystal maintained 100 % strain recovery even after 4500 cycles of compression deformation at 6 %, although the critical stress of stress-induced martensite decreased with each cycle. These findings suggest that the Cu-Al-Ga-based shape memory single crystal alloys obtained in this study have promising applications in driving response devices.

Optimizing lithium-silver alloy phases for enhanced energy density and electrochemical performance

Lithium (Li) metal batteries though with high energy density are still facing issues like Li dendrite growth, dead Li formation, and thick solid electrolyte interphase (SEI) formation, hindering their long-term stability. Recently, Li-Ag alloys have been reported to potentially address these challenges possibly due to their superior conductivity, lithiophilicity, and mechanical stability. In the pursuit of high-energy-density batteries, Li-Ag alloys typically employ a high Li content phase (γ1). In this study, we applied density functional theory (DFT) calculations to compare the thermodynamic stability, Li adsorption, and Li diffusion of Ag-rich Li-Ag alloy within the γ1 phase (AR-γ1), Ag-poor Li-Ag alloy within the γ1 phase (AP-γ1), and pure Li. AR-γ1 showed better thermodynamic stability and improved Li adsorption and diffusion properties compared to AP-γ1 and pure Li. Electrochemical tests further confirmed the advantages of AR-γ1 in terms of electrode kinetics and cell stability compared to AP-γ1 and pure Li. Our study offers guidance for the selection of the most suitable Li-Ag alloys that can be utilized in high-energy-density lithium batteries.

Obtaining superior damping property of a Cu–Al–Mn shape memory alloy through ultra-high temperature aging

Ultra-high temperature aging was conducted on the Cu-11.9Al-2.5Mn (wt.%) shape memory alloy (SMA) with the aim of damping improvement. The martensite laths were refined, and the controllable precipitation of γ2 phase was realized. As the aging temperature decreased or the aging time prolonged, the amount of γ2 particles increased. The damping of the Cu–Al–Mn SMA measured in this study belongs to non-linear damping, and the damping plateau in the martensite state mainly arises from the sliding of the martensite/martensite interfaces and the stacking faults in martensitic variants. The increased density of the martensite/martensite interfaces caused by grain refinement, the de-pinning of dislocations, and the annihilation of quenched-in vacancies after aging contributed to the increase of damping, whereas the increased density of stacking faults and the pining of γ2 particles on various interfaces leaded to the decrease of damping. The specimen aged at 590 °C for 5 min has the highest damping plateau. Its damping capacity at room temperature is 3.5 times that of the quenched specimen. The effect of aging on the tensile properties was also studied, and based on in-depth microstructural observation, correlated mechanisms were discussed.

Influence of micro-addition of lanthanum on grain characteristics, mechanical properties, and corrosion behavior of CuAlNiMnLa shape memory alloy

The study investigated the grain size criteria, mechanical characteristics, and corrosion behavior of Cu-14Al-4.5Ni-0.7Mn shape memory alloy (SMA) with the micro-addition of 0.06 wt% Lanthanum (La). Using standard melting and casting procedures, the alloy compositions were melted at 1300 ℃ in an arc furnace with an argon atmosphere. The cast compositions without thermal treatment were machined and tested for physical properties including density and percentage porosity, corrosion behavior, and mechanical properties like hardness, ultimate tensile strength, yield strength, fracture strain, percentage elongation, specific strength, and fracture toughness. The average grain size, profile plot, and grain size distribution were all determined using ImageJ software. The microstructural observations revealed the presence of α-phase, β-phase, and intermetallic phases, including the coarse α+γ2 phase, which contributed to the improved characteristics. The inclusion of lanthanum resulted in a drop in the average grain size of the parent alloy from 9.25 μm to 6.08 μm, indicating a clear correlation between property improvement and microstructure refinement. The composition's tensile strength and yield strength increased with the La micro-addition by 22.14% and 20.31% respectively while the hardness value increased by 17.3%. The fracture strain of the modified composition increased by 20% compared to the unmodified composition while the percentage elongation increased by 7.7% and a 22.5% increase in fracture toughness was achieved. The modified CuAlNiMn SMA also showed a significant improvement in corrosion resistance to NaCl solutions which was so evident at 144 hours of the study for 0.5 M of NaCl solution and at 96 hours for 1.0 M of NaCl solution. The results showed that CuAlNiMn SMA with micro-addition of La had better physical, corrosion, and mechanical characteristics than unmodified CuAlNiMn alloys

Nickel-aluminum bronze (NAB) alloy design under two-steps casting and submerged friction stir processing

This research aimed to investigate the impact of friction stir processing (FSP) as a modifying technique on the microstructure and mechanical properties of Cu–10Al, Cu–10Al–5Ni, and Cu–10Al–5Ni–5Fe nickel-aluminum bronze (NAB) alloys under two different conditions of ambient and underwater submerged conditions concerning the as-cast state of these materials. Adding nickel as an alloying element to the Cu–10Al composition resulted in the formation of NiAl intermetallic compound and a 3 % increase in the volume percentage of secondary phases. Furthermore, incorporating iron into the Cu–10Al–5Ni composition prevented the formation of detrimental γ2 phase and instead created κ intermetallic compounds within the structure, leading to an overall increase of approximately 14 % in the volume percentage of secondary phases compared to the Cu–10Al composition. The initial coarse, rough, and heterogeneous structure of the cast samples was transformed into a fine, equiaxed, and homogeneous structure through the friction stirring modification conducted in both air and underwater environments for all alloy compositions, primarily due to action of dynamic recrystallization (DRX). Notably, a finer structure was achieved when the FSP was performed underwater in the submerged state. Regarding developments in mechanical properties, FSP treatment performed in air demonstrated an average enhancement of 15 % in strength and hardness across all three compounds. In contrast, the flexibility of Cu–10Al, Cu–10Al–5Ni, and Cu–10Al–5Ni–5Fe alloys in terms of elongation to failure was reduced by 70 %, 80 %, and 20 %, respectively, in comparison to the cast samples. Conversely, the underwater submerged FSP led to a notable increase of 55 % in both strength and hardness for all three compounds. However, the ductility of the alloys was reduced by 80 % compared to the cast states.

Effects of carbon nanotube addition on the microstructures, martensitic transformation, and internal friction of Cu–Al–Ni shape-memory alloys

In this study, we analyze the influences of carbon nanotube (CNT) addition on the martensite transformation and internal friction of Cu–Al–Ni shape-memory alloys (SMAs). X-ray diffraction and differential scanning calorimetry results demonstrate that Cu–13.5Al–4Ni–xCNT (x = 0, 0.2, 0.4, 0.6, and 0.8 wt%) SMA/CNT composites exhibit a β1(DO3)⇄β1′(18R)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\upbeta }_{1}({\\mathrm{DO}}_{3})\\rightleftarrows {\\upbeta }_{1}^{\\mathrm{^{\\prime}}}(18\\mathrm{R})$$\\end{document} martensitic transformation. The martensitic transformation temperatures and transformation enthalpies of the martensitic transformation peaks for the Cu–13.5Al–4Ni–xCNT (x = 0–0.8 wt%) composites gradually decrease with the increase in the amount of CNT addition. Compared to the Cu–13.5Al–4Ni SMA, the Cu–13.5Al–4Ni–xCNT (x = 0.2–0.8 wt%) SMA/CNT composites exhibit significant improvements in the amount of dissipation of energy (storage modulus (E′))\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${E}^{\\prime}))$$\\end{document} and mechanical strength. However, the tan δ of the internal friction peak gradually decreases with the increase in the CNT content above 0.6 wt%. The reduction in tan δ is attributed to the decrease in the magnitude of the austenite-to-martensite transformation and precipitation of γ2 (Cu9Al4) phase particles, which impede the interface motion in between the parent/martensitic phase and martensitic phase.

Multiple magnetic transitions induced by Mn-doping in orthochromite HoCrO3

It has been established that both hybridization with magnetic rare earth cation and crystal field originating from structural anisotropy can affect the spin orientation of magnetic transition metal perovskite. In this work, we have systematically studied the crystal structure, magnetization, and magnetic structure of Mn-doped rare earth orthochromites HoCr1−xMnxO3 (x = 0–0.85) by means of X-ray diffraction, magnetometry, and neutron powder diffraction. With increasing Jahn–Teller active Mn3+-substitution for Cr3+, the crystallographic distortion is gradually enhanced and causes a systematic evolution of magnetism. With doping, the Cr(Mn) ordering temperature is gradually suppressed, and multiple magnetic configurations Γ2, Γ1, and Γ4 phases appear consecutively. The rich transition phenomena are ascribed to a competition between increased structural anisotropy and weakened Ho-Cr(Mn) hybridization with doping. In a low doping regime with x = 0.1–0.5, Γ2 phase is predominant in low temperature, and a magnetization reversal is observed, reflecting the opposite sign of Cr-Mn DMI coefficient with respect to the Cr-Cr and Mn-Mn interaction. In the high doping range with x = 0.6–0.8, the long-range order of Cr(Mn) sublattice is gradually suppressed while a short-range order becomes dominant. For x = 0.85, a magnetic structure resembling o-HoMnO3 is observed.

Laser powder bed fusion of full martensite Cu-Al-Mn-Ti alloy with good superelasticity and shape memory effect

A copper-based shape memory alloy Cu-11.85Al-3.2Mn-0.1Ti with desirable superelasticity and shape memory effect was printed by laser powder bed fusion (LPBF), which demonstrated the feasibility of engineering applications through the deformation and recovery of complex corrugated structural components. The microstructure of LPBF-printed Cu-11.85Al-3.2Mn-0.1Ti was composed of full β1' martensite with a high density of stacking faults and twin crystals. The abnormal phase constitution of full martensite in the printed Cu-11.85Al-3.2Mn-0.1Ti is correlated to substrate preheating and thermal cycling during LPBF. The start and finish transformation temperatures of martensite (Ms and Mf) and austenite (As and Af) were 172.5 °C, 144.4 °C, 180.2 °C and 209.2 °C, respectively. The printed samples exhibited compressive strength of 1319 MPa with a compressive fracture strain of 16.1%. The printed alloy displayed remarkable superelasticity and shape memory effect. The superelastic recovery rate reached a maximum value of 87% at 6% pre-strain, corresponding to a superelastic recovery strain of 5.22%. The mechanism of superelasticity is attributed to the rubber-like deformation behavior. Moreover, the pre-strained samples demonstrated a desirable shape memory effect under the temperature stimulation, where the shape memory recovery rate of up to 100% at a pre-strain of 6%, corresponding to a shape memory recovery strain of 0.78%. The reasons for the favorable shape memory effect were: (i) the thermoelastic inversion of martensitic transformation and (ii) the precipitation of γ2(Cu9Al4) phase along the grain boundaries. As a result, these findings suggest that the LPBF technique can produce Cu-Al-Mn-Ti parts with superelasticity and good shape memory properties, which provided valuable references for printed copper-based shape memory alloys with full martensitic structures.

Giant near-elastic deformation in novel porous Cu-Al-Mn shape memory alloys

Based on the concept of microstructure control and multiphase doping, a novel strong-textured porous (STP) Cu-Al-Mn (CAM) shape memory alloy was fabricated through multi-stage sintering process. Porosity ranging from 31.1 to 11.4 % and the largest near-elastic deformation approached 8.0% were achieved in the STP Cu71Al18Mn11 alloy. Through in-depth characterization, it is confirmed that STP-CAM has less γ2 phase compared to porous ordinary polycrystalline alloy, and exhibits strong 〈001〉 and 〈101〉 -oriented texture along the direction of sintering pressure, as well as low angle grain boundaries, which contributes to the large near-elastic deformation observed in this novel porous SMAs.

Microstructure and properties of galvannealed coatings at different galvannealed time

Microstructure and properties of galvannealed coatings at different galvannealed time was studied by electron probe micro-analyzer (EPMA), X-ray diffractometer (XRD) and V-bend test. The study showed that δ and Γ1 phase was formed at galvannealed 15 s, and δ, Γ1 and Γ phases were formed at galvannealed 20 s and 25 s. The cracking area of coatings was propagated along Γ1/steel or Γ/steel interface and intersected with the serious cracks, which caused the coatings to be dropped. With the extension of galvannealed time, the areas of cracks and fracture at Γ/steel interface were reached 50% at galvannealed 25 s, and interfacial adhesion of Γ/steel was decreased due to the increase in thickness of Γ phase.

Micro-electrochemical insights into pit initiation site on aged UNS S32750 super duplex stainless steel

An aging treatment of UNS S32750 super duplex stainless steel at 1173 K for 1.0 ks produced σ and secondary austenite (γ2) phases in the α and γ phase boundary regions. Small amount of Mn-Cr oxide and MnS complex inclusions were present in the steel. No pitting was observed during the potentiodynamic polarization of a small area (200 × 200 µm) without inclusions in 1 M MgCl2 at 348 K. Because the electrode area included α, γ, σ, and γ2 phases, these phases and their boundaries alone could not act as initiation sites for pitting. The electrode area size was gradually reduced from 3 × 3 mm to 1 × 1 mm, and pitting corrosion was observed to occur at the Mn-Cr oxide and MnS complex inclusions in a region that appeared to be the γ2 phase near the σ phase.

Multiphase Alloy Nuclear Waste Forms Developed for Pyrochemical U-10Mo Scrap Recovery Waste Streams

The US High Performance Research Reactor (USHPRR) Conversion program is developing an Al-clad Zr-bonded U-10Mo nuclear fuel foil to enable the conversion of research reactors to high-assay low-enriched uranium (HALEU) alloy fuel. Fabrication scrap from the fuel manufacturing will be electrorefined to recover the HALEU, which will generate waste streams consisting of Zr, Mo, and residual U retained in the stainless steel anode basket used in the electrorefiner. Four alloys were formulated with different relative amounts of Zr, Mo, and 316L-SS to represent the expected range of waste compositions. Laboratory-scale ingots were made and metallurgically characterized to assess differences in the microstructures and distributions of the surrogate waste metals. Different amounts of the same dominant phases with similar compositions were formed in most materials: a γ-austenite based matrix, two ZrFe2 intermetallic phases that could host residual uranium, an FeCrMo sigma (σ) intermetallic phase, a chi (χ) phase, and a secondary austenite (γ2) phase. Electrochemical tests were conducted to compare the corrosion behaviors in acidic and alkaline brine solutions for a range of simulated environmental redox conditions. Corrosion of the Mo-rich γ and γ2 solid solutions and the σ and χ intermetallic phases occurred. The multiphase alloy waste form formulated with the lowest molybdenum and highest zirconium contents showed the highest corrosion resistance and has sufficient amounts of ZrFe2 to immobilize trace amounts of residual uranium in the waste stream. The alloy formulation strategy and testing approach will be presented with key results.Work conducted at Argonne National Laboratory is operated for the U.S. Department of Energy, Office of Science under contact DE-AC02-06CH11357.

Comparison of microstructure and shape memory properties between two Cu-Al-Mn alloys produced by additive manufacturing technology

In this work, two Cu-Al-Mn alloys, including Cu-12.5Al-3Mn alloy and Cu-12.5Al-3Mn-1Fe alloy, considering the powder core wire with a structure resistant to element burning as additive manufacturing materials, were prepared by arc melt deposition process. The microstructures were studied utilizing OM, SEM, and XRD. The shape recovery rates under different pre-strains and the recovery behavior under intense thermal stimulation were analyzed by bending tests. Results showed that after adding Fe, the microstructure of the Cu-12.5Al-3Mn alloy transformed from hyper-eutectoid structure to eutectoid structure, inhibiting the precipitation of the brittle γ2 phase. Cu-12.5Al-3Mn-1Fe alloy possessed narrower martensitic laths, a more satisfactory martensitic substructure, and better martensitic orientation consistency than Cu-12.5Al-3Mn alloy due to the formation of a new κ phase after quenching. The shape recovery rate of the Cu-12.5Al-3Mn-1Fe alloy was maintained at 100% at a pre-strain of 4% to 8%, and then it started to decrease when the pre-strain reached 10%. The analysis result showed that Cu-12.5Al-3Mn-1Fe alloy, produced by additive manufacturing, has excellent shape memory properties, which not only result from the changes in the microstructure but are also attributed to the protective effect of the anti-damage structure of the powder core wire on the alloy elements.

Mechanical Behavior and Structural Characterization of a Cu-Al-Ni-Based Shape-Memory Alloy Subjected to Isothermal Uniaxial Megaplastic Compression.

For the first time, uniaxial megaplastic compression was successfully applied to a polycrystalline shape-memory Cu-Al-Ni-based alloy. The samples before and after uniaxial megaplastic compression were examined by methods of X-ray diffraction, optical, electron transmission, and scanning microscopy. The temperature dependences of electrical resistance and the mechanical properties of the alloys under uniaxial tension were also measured. The mechanical behavior under uniaxial megaplastic compression in isothermal conditions in the range of 300–1073 K was studied using the Instron 8862 electric testing machine. The microstructure, phase composition, and martensitic transformations in the eutectoid alloy (Cu-14wt.%Al–4 wt.%Ni) were studied. The radical refinement of the grain structure of the initial hardened D03 austenite was found under controlled isothermal compression, due to dynamic recrystallization in the temperature range 673–1073 K and velocities of 0.5–5 mm/min. Compression at 873–1073 K was accompanied by simultaneous partial pro-eutectoid decomposition with the precipitation of the γ2 phase. Compression at temperatures of 673 and 773 K—that is, below the eutectoid decomposition temperature (840 K)—was accompanied by the precipitation of disperse γ2 and α phases, and ultradisperse B2’ particles. Cooling of the deformed alloy to room temperature after performing each regime of compression led to thermoelastic martensitic transformation, together with the precipitation of the β′ and γ′ phases. The formation of a fine-grained structure produced an unusual combination of strength and plasticity of the initially brittle alloy both under controlled uniaxial compression, and during subsequent tensile tests at room temperature.

Magnetization reversal, field-induced transitions and H–T phase diagram of Y1−x Ce x CrO3

We report a systematic study of the magnetic phase diagram in the H–T plane, negative magnetization (NM), exchange interactions and field-induced spin–flop transitions in the distorted perovskite Y1−x Ce x CrO3. Locked AFM and weak-FM configurations in Γ4(G z , F y , A x ) phase of YCrO3 (S = 3/2 ground state) unlocks into the Γ2 (F z , G y , C x ; ) phase of the canted AFM and FM structures with the dilute substitution of Ce (x ⩾ 0.05). The asymmetric and symmetric exchange interaction (J AS ∼ 0.11 meV and J S ∼ 0.85 meV) between the trivalent Ce and Cr enable the positive quartic-anisotropy field ( ∼ 2.85 × 102 Oe) along with the second order anisotropy field ( ∼ 5.93 × 102 Oe). Unlike the pristine YCrO3 compound, the Ce incorporated system exhibits a giant fourth-order anisotropy constant (K 4 = 1.35 × 105 erg/c.c.) due to the asymmetric exchange interaction between the trivalent Ce–Cr which further lifts the free energy of the system and causes lag in the onset of AFM ordering showing the significant thermal hysteresis (ΔT ∼ 10 K) in the field-cooled (FC)-warming measurement protocol as compared to the FC-cooling mode. The H–T phase diagram, mapped from the isothermal magnetization data and differential magnetic susceptibility data with different measurement protocols clearly distinguishes three prominent regions below the T N (∼150 K), viz (i) long-range canted AFM + weak FM phase (Γ4 (G z , F y , A x )), (ii) Γ24 mixed phase and (iii) robust Γ2 (F z , G y , C x ; , ) AFM + FM phases. Tunable spin–flopped transition (∼ 30 kOe), significant negative exchange-bias field (H EB ∼ 2.5 kOe), huge coercive field (H C ∼ 22 kOe) and large NM (ΔM ∼ 280 emu/mole) are the unique characteristic features of the current investigated system.

Terahertz spectroscopy of antiferromagnetic resonances in YFe1−xMnxO3 ≤x≤0.4 across a spin reorientation transition

We have conducted a terahertz spectroscopic study of antiferromagnetic resonances in bulk orthoferrite YFe1−xMnxO3 0≤x≤0.4. Both the quasi-ferromagnetic resonance mode and the quasi-antiferromagnetic resonance mode in the weak ferromagnetic Γ4 phase disappear near the spin reorientation temperature, TSR, for the onset of the collinear antiferromagnetic Γ1 phase (x ≥ 0.1). Below TSR, an antiferromagnetic resonance mode emerges and exhibits a large blueshift with decreasing temperature. However, below 50 K, this mode softens considerably, and this tendency becomes stronger with Mn doping. We provide a deeper understanding of such behaviors of the antiferromagnetic resonance modes in terms of the influence of the Mn3+ ions on the magnetocrystalline anisotropy. Our results show that terahertz time-domain spectroscopy is a useful, complementary tool in tracking magnetic transitions and probing the interaction between disparate magnetic subsystems in antiferromagnetic materials with multiple ionic species.