B2 Phase Research Articles

Effects of cooling rate on borides morphology and structure in cast β-solidifying γ-TiAl alloy

Borides have been found to play a significant role in determining the mechanical properties of cast TiAl alloys. In order to investigate the influence of cooling rate on the morphology and structure of borides, SEM and HRTEM techniques were utilized to analyze borides in Ti-43Al-4Nb-1Mo-0.5B (at. %) cast plates with varying thicknesses. A higher cooling rate was observed to result in the formation of elongated, curvy borides with high aspect ratios, increased planar faults, and complex structures consisting of a combination of B2 phase and various boride phases. Conversely, a slower cooling rate yielded shorter bar-shaped borides with fewer planar faults. This variation in boride morphology can be attributed to the differing thicknesses of the solute-rich layer, where the eutectic reaction occurs, at the solidification front during fast and slow cooling processes. Bf-TiB with a habit plane of (010) was identified as the dominant phase at all cooling rates. Borides in the [100] and [001] directions demonstrated a faster growth rate compared to those in the [010] direction. Additionally, HRTEM results indicated the presence of TiB2 while Ti3B4 was absent. This can be explained by the limited phase region of Ti3B4 in both the binary Ti-B and ternary Ti-Al-B phase diagrams, which is the smallest among all phases. These findings enhance the understanding of how cooling rate influences the morphology and structure of borides in TiAl alloys, thus providing insights for optimizing alloy design and manufacturing processes.

Effect of Heat Treatment on the Microstructure and Mechanical Properties of the Al0.6CoCrFeNi High-Entropy Alloy.

The effect of heat treatment on the microstructure and tensile properties of an as-cast Al0.6CoCrFeNi high-entropy alloy (HEA) was investigated in this paper. The results show that the as-cast Al0.6CoCrFeNi HEA presents a typical FCC dendrite morphology with the interdendritic region consisting of BCC/B2 structure and heat treatment can strongly affect the microstructure and mechanical properties of HEA. Microstructure analysis revealed the precipitation of a nano-sized L12 phase in the FCC dendrite and the formation of the FCC and σ phases in the interdendritic region after annealing at 700 °C. The coarse B2 phase was directly precipitated from the FCC dendrite in the 900 °C-annealed sample, with the coexistence of the B2, FCC, and σ phases in the interdendritic region. Then, the interdendritic region converted to a B2 and FCC dual-phase structure caused by the re-decomposition of the σ phase after annealing at 1100 °C. The tensile test results show that the 700 °C-annealed HEA presents the most significant strengthening effect, with increments of corresponding yield strength being about 107%, which can be attributed to the numerous nano-sized L12 precipitates in the FCC dendrite. The mechanical properties of 1100 °C-annealed alloy revert to a level close to that of the as-cast alloy, which can be attributed to the coarsening mechanism of B2 precipitates and the formation of a soft FCC phase in the interdendritic region. The observed variation in mechanical properties during heat treatment follows the traditional trade-off relationship between strength and plasticity.

Effects of solution temperatures on microstructures and mechanical properties of B4C/7A04Al composites: A comparison study with 7A04Al alloys

To prepare particle-reinforced aluminum matrix composites with ultra-high strength, high-strength 7xxx Al alloys are commonly employed as matrices. Heat treatment plays a crucial role in enhancing the mechanical properties of the alloys and their composites, but the influence of solution temperatures on composites based on 7xxxAl alloys remains unexplored. In this study, the effects of solution temperatures on the microstructures and mechanical properties of B4C/7A04Al composites fabricated via powder metallurgy (PM) technology were investigated, as well as those of 7A04Al alloys for comparison. Before solution treatments, the prominent second phases in the composite were MgZn2 phases, while those in the 7A04Al alloy consisted of MgZn2 and Al2CuMg phases. At lower solution temperature (420 °C), MgZn2 phases dissolved completely, whereas Al2CuMg phases persisted. Al2CuMg phases dissolved at 450 °C, and thus the 7A04Al alloy obtained the optimum strength and elongation. Further elevating the solution temperature caused abnormal grain growth (AGG) in the 7A04Al alloy, leading to a deterioration of strength and plasticity. In contrast, at various solution temperatures, the composite exhibited stability in grain size, which could be attributed to the pinning effects of B4C particles and Mg(Al)B2 phases, the reaction products between the boron impurity and the Al matrix. However, at higher solution temperatures (510 °C and 600 °C), the segregation of Mg and O around B4C particles was aggravated, and thus the elongation of the composite deteriorated. Interestingly, the strength remained relatively unaffected due to the strengthening effects of Mg(Al)B2 phases. The results indicate that the composite exhibited a broad range of solution temperature with comparable strength and elongation across a temperature range of 420 °C–470 °C. But for the 7A04Al alloy, the optimal solution temperature is 450 °C.

Unraveling hot deformation behavior and microstructure evolution, flow stress prediction of powder metallurgy BCC/B2 Al1.8CrCuFeNi2 HEA

In this work, hot compress tests were conducted at the strain rate range of 1–0.001 s−1 and the temperature range of 900–1050 °C to unravel the hot deformation behavior of a powder metallurgy (PM) Al1.8CrCuFeNi2 high entropy alloy with BCC/B2 structure. Arrhenius model and radial basis function artificial neural network (RBF-ANN) machine learning (ML) method were used to model flow stress. RBF-ANN ML method possesses superior predictability. Elongated grains almost change to equiaxed grains under the low strain rate of 0.001 s−1 due to the activity of continuous dynamic recrystallization (CDRX). There are no significant changes in the distribution, size and content of fine B2 and BCC eutectic phases during deformation. Stress index ranges form 2.2–2.6 at various strains. Dislocation viscous gliding and grain-boundary sliding (GBS) are predominant deformation modes. The contribution of GBS to deformation is more significant at low strain rate. For dislocation slip, multiple slip systems are activated,{123̅}<111> slip system has higher Schmid factor. Hot processing ability is improved at high temperature and low strain rate. Absorbing of dislocation at grain boundaries and the dominance of GBS deformation mode under high temperature and low strain rate condition can avoid instability.

In-situ investigation of tensile anisotropy mechanism in an advanced Ti2AlNb-based alloy associated with CRSS ratio and damage model

Combined with in-situ tensile test and electron backscatter diffraction technology, the critical resolved shear stress (CRSS) ratio of O phase and the damage model of grain boundaries were proposed to reveal the tensile anisotropy mechanism of Ti–22Al–25Nb alloy isothermally forged in B2 phase region. In-situ observation suggests that the single slip mode of lamellar O phase is the major deformation behavior, and its preferential slip dominates the yield of the material. Based on the types, number, Schmid factor (SF) and orientation of slip activation, the CRSS ratio of basal <a>, prism <a>, first-order and second-order pyramidal <c+a> slips for O phase is estimated to be 1.19: 1: 1.37: 1.39. Meanwhile, basal and prism <a> slips mainly appear the radial and axial directions (RD and AD) samples with [012] and [100] texture, while the [001], [010] and [212] texture of OD (45° to RD) sample shows an increase in pyramidal <c+a> slips. Thus, the slip activation of O phase depends on the grain orientation and CRSS, resulting in significant strength anisotropy. Furthermore, the microcracks and secondary cracks at grain boundaries are significantly affected by the slip accumulation of lamellar O phase at the O/O and O/B2 interfaces. Considering the stress state of the grain boundary, a damage model about crack nucleation and propagation is proposed to explain the ductility anisotropy. From this, the RD sample has a higher crack nucleation and propagation resistance than the AD and OD samples due to the flattened morphology of B2 grains.

Correlation between grain size and dynamic response of NiTi alloy during intense shock-induced multi-spallation

This work committed to performing non-equilibrium molecular dynamics simulations to explore the influence of grain size on multi-spall performance of nanocrystalline nickel-titanium (NiTi) alloy. By comparing the calculated Hugoniot relationship with present experimental results, the Finnis-Sinclair (FS) type potential used in this work was verified to be suited for reproducing the shock behavior of NiTi alloy at high strain rate. During shock wave evolution, a single plastic wave was clearly observed in the sample with grain size of 5 nm, while there was a more pronounced elastic-plastic double wave structure at larger grain size. According to the free surface velocity history, the predicted spall strength exhibited a decreasing tendency and subsequently increased when the grain size decreased from 50 to 5 nm, indicative of a critical grain size (10 nm). Correspondingly, there were multiple spall planes appearing in the sample, the grain size of which was not smaller than the critical one. Contrarily, a single spall plane was observed at 5 nm. By counting the void distribution statistic, we found that as the grain size increased, the void-nucleation behavior changed from the intergranular to intergranular/transgranular coexisting pattern. In consequence, more nucleation sites were provided to promote an increase in the number of voids. Interestingly, for intergranular, there were much more voids involved in spallation at smaller grain size, which was attributed to grain boundary effect. The results demonstrated that void evolutions rarely occurred at the grain boundaries parallel to the loading direction. Moreover, when the grain size was larger than 5 nm, the B19 phases were found to be produced around those potential void-nucleation sites. After void nucleation, these B19 phases decreased till disappearance, accompanied by the proliferation of a large number of [100] dislocations. Such dislocations accumulated in the region without voids could block the void growth in this region, which was expected to be the reason for the formation of multiple spall planes. On the contrary, the absence of dislocations at 5 nm was inclined to the fact that the space for dislocation emission and aggregation was preoccupied by nucleated voids.

Tailoring microstructure and tensile properties of low-cost AlCrFeNi-based high-entropy alloys via Co and/or Ti addition

Al-Cr-Fe-Ni high-entropy alloys (HEAs) have low cost but suffer from intrinsic brittleness, leading existing research to concentrate on compressive properties. This study explores alloying strategies to improve tensile properties for these HEAs. Minor elements including 5 at.% Co, 5 at.% Co + 3 at.% Ti, and 5 at.% Co + 5 at.% Ti are added to investigate their impact on microstructure, tensile properties, and solidification behavior for Fe30Ni35Cr21.25Al13.75 HEA. The addition of both Co and Ti has a synergistic effect on the alloys; however, it does not alter the types of phases present, as the face-centered cubic (FCC), body-centered cubic (BCC), and B2 phases are maintained. Specifically, the increase of Ti content promotes the transformation of the primary phase from FCC to BCC and causes the BCC phase to undergo spinodal decomposition. The addition of Co alone decreases the strength, whereas the synergistic combination of Co and Ti enhances the yield strength (from ∼571 MPa to ∼625 MPa) and ultimate tensile strength (from ∼1112 MPa to ∼1288 MPa). Nonetheless, the total elongation is only reduced by 1.5% with this combination. Specially, introducing 5% Ti into the alloy instantly renders it brittle. These results provide valuable insights into improving the mechanical properties and understanding the solidification behavior of low-cost Al-Cr-Fe-Ni HEAs through synergistic alloying.

Study of the effects of laser power and scanning speed on the microstructural morphologies and physical properties of L-PBF produced Ni52.39Ti47.61

This study examined the effect of variations in the laser power and scan speed for 52.39 at.%Ni-47.61 at.%Ti samples produced via laser powder bed fusion (L-PBF). The laser power was varied between 150W and 180 W, the scanning speeds were varied between 500 mm/s and 1000 mm/s, and other process parameters were kept constant. The resulting microstructures and physical properties of the produced samples were evaluated. In particular, the phase type and phase transformation characteristics, composition, Vickers microhardness, and microstructures were examined. It was observed that variation in the mean microhardness and relative density were not significant at a constant scan speed of 1000 mm/s, regardless of the laser power value. Samples processed at a laser power of 180W (with all other parameters kept constant) exhibited a bimodal micro- and nano structures. It was found that the samples with bimodal microstructure had a higher lattice strain, extent of B2 phase, and higher phase transformation temperatures.

Atomic insights into shock-induced alloying reaction of premixed Ni/Al nanolaminates.

In material processing and handling processes, premixed interlayer often replace the ideal Ni/Al interface, which would become a new origin of alloying reaction. This work investigates shock-induced reaction mechanism and kinetics of premixed Ni/Al nanolaminates with molecular dynamics simulations and theoretical analysis. The reaction is found to be driven by the crystallization evolution in premixed interlayer and the diffusion of premixed atoms. Among them, multi-stage reaction patterns are strongly manifested by the crystallization evolution characteristics. Specifically, "crystallization-dissolution-secondary growth" and "crystallization-dissolution" of B2 phase respectively correspond to the solid-state and solid-liquid reaction cases, where crystallizations are fitted well by Johnson-Mehl-Avrami kinetics model. Interestingly, the different growth mechanisms of B2 grain are revealed, namely nuclei coalescence and atomic diffusion. Moreover, the analysis of microscopic diffusion theory indicates a certain non-random diffusion nature for solid-state reaction initiation, but near-purely random diffusion for solid-liquid reaction initiation. The diffused Al atoms possess a limited diffusion coefficient and enhanced diffusion correlation, resulting in extremely slow mixing rate in Ni layer. In addition, the influence law of Ni concentration in premixed interlayer on reactivity parameters can be quantitatively described by a quadratic function.

Microstructure evolution and phase transformation mechanism of Ti–46Al–8Nb–2.5V alloy based on phase transformation geometric models

The microstructure of conventionally solidified and rapidly solidified Ti–46Al–8Nb-2.5V alloys was analyzed with phase transformation geometric models, revealing the phase transformation mechanisms. The β→α→γ phase transformation processes follow Burgers and Blackburn orientation relationships (ORs), respectively, from which the calculated transformation between the β/β0 and γ phases follow K–S OR. Whlie, the direct β/β0→γ phase transformation can be directly observed in the microstructure, which follows a variety of ORs, mainly following the K–S OR but also following the N–W or Bain ORs, most of which deviate from the strict ORs. In cases where N–W and Bain ORs are followed, there is a large dislocation spacing between the habit planes of the β/β0 and γ phases, resulting in low static energy at the interface and narrow elongated morphology of precipitated phases. Conversely, when following K–S OR for β/β0 → γ phase transformation, interfacial migration energy is relatively lower and grain precipitated phases is larger. The rapidly solidified microstructure of Ti–46Al–8Nb-2.5V alloy consists of the massive α2 phase, massive γ phase, and basket-weave β0 phase closely resembling those found in β-type titanium alloys. After annealing at service temperature, the rapidly solidified alloy forms a microstructure highly similar to that of conventionally solidified TiAl alloy. Various metastable phases, such as the Ti2Al, L12 and Ti1.4Al phases, precipitate in the blocky γ phase, which provides a theoretical basis for studying the phase transformations of TiAl alloys in service.

Effect of cooling rate during solidification on structure and mechanical properties of Cu45Zr48Al7 glass-forming alloy

The CuZr-based bulk metallic glass matrix composites have attracted great attention in recent years owing to their unique mechanical properties compared to bulk glassy samples. The vital effect of B2 CuZr phase on mechanical properties was previously confirmed in CuZr-based alloys with equiatomic concentrations of copper and zirconium. In this paper, the structures and mechanical properties of the Cu45Zr48Al7 alloy, which has hypereutectoid composition with respect to stoichiometric B2 CuZr phase, were studied. This alloy exhibits high glass-forming ability, but low tendency to form the B2 CuZr phase during solidification. However, we demonstrated that depending on the cooling rate during solidification, governed by sample diameter, either bulk metallic glass or bulk metallic glass matrix composite can be produced. In order to allow partial crystallization of the B2 phase during solidification with the volume fraction allowing to observe the strain hardening effect, the minimum cooling rate should be lower than 40 K/s. The composite consisting of a glassy outer layer and a crystalline core composed of the B2 phase exhibits fracture strength of the same level as the bulk glassy sample (above 1800 MPa) obvious work-hardening with a plastic deformation of about 6%.

Significantly Improving the High-Temperature Tensile Properties of Al17Cr10Fe36Ni36Mo1 Alloys by Microalloying Hf.

Dual-phase high-entropy alloys with excellent room temperature and high-temperature properties have been widely studied as potential high-temperature structural materials. However, interface weakening causes its high-temperature performance to decline at higher temperatures, severely limiting further development. In this study, a series of Al17Cr10Fe36Ni36Mo1Hfx (x = 0, 0.03, 0.15, 0.3, 0.5, and 0.8 at%) alloys were prepared to study the effect of Hf content on the microstructure and mechanical properties of the matrix alloy. The results indicate that with the addition of the Hf, the Hf-rich phase began to precipitate at the interface and inside the B2 phase in the matrix alloy. In contrast, the morphology of both the FCC and B2 phases had no noticeable change. With the increase in Hf content, the high-temperature strength and ductility of the alloy first increased and then decreased, while the room temperature performance remained almost unchanged. Benefiting from the hindrance of the Hf-rich phase to grain boundary sliding and dislocation movement during high-temperature deformation, the tensile strength, yield strength, and plasticity of the matrix alloy increased from 474 MPa, 535 MPa, and 8.7% to 816 MPa, 923 MPa, and 42.0% for the Al17Cr10Fe36Ni36Mo1Hf0.5 alloys, respectively. This work provides a new path for designing a high-entropy alloy with excellent high-temperature mechanical properties.

Synergetic strengthening through ultrafine-grained anisotropic microstructure and nanoscale heterogeneity in CoCuFeMnNi high entropy alloy wires

This study investigated the post-drawn annealed CoCuFeMnNi high-entropy wires with distinct dual phase structure and B2 nanoprecipitates. The exceptional hardness observed of the post-drawn annealed CoCuFeMnNi wires can be attributed to the synergetic effect of the ultrafine-grained (UFG) structure and nanoscale precipitation/heterogeneity in the post-drawn annealed CoCuFeMnNi wires.

Improved corrosion resistance of laser melting deposited CoCrFeNi-series high-entropy alloys by Al addition

The microstructural evolution, pitting performance, and passive-film properties of AlxCoCrFeNi high-entropy alloys (HEAs) fabricated via laser melting deposition (LMD) were investigated using material characterization techniques and electrochemical measurements. The substrates of the LMD HEAs transform from a face-centred cubic (FCC) to a body-centred cubic (BCC) structure with increasing Al addition. The BCC-structured B2 and A2 phases precipitate in the HEA substrate when the Al content reaches 10 mol.%. Ternary-phase HEA with Al addition of 10 mol.% exhibits the best corrosion resistance, which is attributed to favourable modifications in the Cr2O3 content and passive-film thickness.

Improvement in compressive creep resistance of Ti-43.5Al–4Nb–1Mo-0.1B alloy via micro-alloying with C and Si

In the present work, the effects of the addition of C and Si on the compressive creep behavior of Ti-43.5Al–4Nb–1Mo-0.1B (TNM) alloy at 850 °C and 900 °C under 260 MPa were investigated. The results show that micro-alloying with C and Si can significantly strengthen the compressive creep resistance of TNM alloy. During compressive creep, obvious dynamic recrystallization occurs in TNM alloy, including major discontinuous dynamic recrystallization and minor continuous dynamic recrystallization. The development of dynamic recrystallization greatly softens the alloy, which leads to large creep deformation. Meanwhile, with the increase of creep strain, the bearing area increases and the actual stress decreases, which eventually results in the secondary creep behavior. In addition, the content of α2 phase increases during compressive creep, which can be attributed to two phase transformations. After adding C and Si, the B2 phase content is decreased and the lamellar colony size is increased, which contributes to the improvement of creep resistance. In addition, fine and dispersed Ti3AlC and Ti5Si3 particles precipitate in α2 lamellae during compressive creep, and maintain definite orientation relationships with α2 and γ phases. This will delay the decomposition of α2 lamellae and greatly improve the lamellar stability. Then, the excellent lamellar stability will inhibit the development of dynamic recrystallization, thus effectively reducing the creep rate.

Study on the wear resistance and mechanism of AlCrCuFe2NiTix high-entropy surfacing alloys

The revolutionary design concept of high-entropy alloys has brought new opportunities and challenges to the development of advanced metal materials. In this work, the design idea of a high-entropy alloy is combined with the characteristics of flux cored wire, and AlCrCuFe2NiTix high-entropy flux cored wires were prepared. AlCrCuFe2NiTix high-entropy surfacing alloys were prepared using gas metal arc welding technology. The wear properties of AlCrCuFe2NiTix high-entropy surfacing alloys were analysed using an MFT-4000 reciprocating friction and wear tester. The phase composition and microstructure of AlCrCuFe2NiTix high-entropy surfacing alloys were analysed using XRD, SEM, EBSD, and TEM, and the strengthening mechanism and wear mechanism of the alloy were discussed. The results show that AlCrCuFe2NiTix high-entropy surfacing alloys are composed of the BCC/B2 + FCC phase. With increasing Ti content, the Laves phase begins to precipitate and exists stably. The microstructure of the alloy presents a typical dendritic structure, and the DR region is rich in Fe, Cr, Al and Ni. The BCC and B2 phases are coherently distributed in the dendrites with a spinodal decomposition network structure. The ID region is rich in Cu and Ti, and the Cu-rich FCC phase is segregated in the form of nanoparticles in the ID region, while the lamellar Laves phase precipitates in the ID region. With increasing Ti content, the microhardness of AlCrCuFe2NiTix high-entropy surfacing alloys shows an increasing trend, while their wear loss, friction coefficient, specific wear rate and other indicators show a trend of first decreasing and then increasing. The maximum microhardness is 597 HV, and the minimum specific wear rate is 9.1606 × 10−8 mm3/N mm. This is mainly because the precipitation of the B2 coherent phase and Laves phase hinders the movement of dislocations, resulting in an improvement in the strength and microhardness of the alloy. However, excessive Ti addition causes the Laves phase to increase sharply and segregate in the ID region, which is extremely prone to stress concentration during dislocation movement, thus inducing crack initiation. The fractured Laves phase exacerbates the grain-abrasion of the alloy and reduces its wear resistance.

Boron microalloying for high-temperature eutectic high-entropy alloys

The eutectic high-entropy alloys have shown promising mechanical behaviors while their softening at elevated temperatures is still a challenge. Generally, the boundaries are the weak parts to be strengthened with increased temperatures in eutectic high-entropy alloys. Here, we found that the minor addition of boron in Ni30Co30Cr10Fe10Al18W2 eutectic high-entropy alloy can significantly strengthen the FCC grain boundaries and the FCC/B2 phase boundaries at elevated temperatures. A remarkable tensile yield strength over 581 MPa with elongation of 71 % at 800 °C is achieved with minor boron addition, corresponding to a 45 % increase in yield strength and 129 % improvement in ductility compared with the boron-free counterpart. Accompanied by the boron-strengthened phase boundary, sustainable dynamic recovery occurs in the FCC and B2 phases during high-temperature tensile testing, ensuring excellent ductility. Moreover, the benchmark test indicates that the strengthening effect of boron and borides on the boundaries contributes up to 166 MPa to the yield strength of eutectic high-entropy alloy at 800 °C. These findings shed light on the development of high-temperature eutectic high-entropy alloys with a microalloying strategy.

Cost-effective synthesis and thermomechanical processing of AlxCoCrFeNiCuy (x&y=0.5,1) high-entropy alloys

This study investigates the cost-effective synthesis and thermomechanical processing of AlxCoCrFeNiCuy (x&y = 0.5,1) high-entropy alloys through cold (CR) and hot rolling (HR). The alloys were synthesized using a thermochemical modelling-assisted aluminothermic non-centrifugal, self-propagating high-temperature synthesis (SHS) method, which is reported for the first time in the literature. Remelting and suction casting were conducted via vacuum arc melting upon the compositional verification through x-ray fluorescence (XRF) and energy dispersive spectroscopy (EDS) analyses. The deformabilities and hardness values of the alloys were correlated with microstructural changes that were analysed through scanning and transmission electron microscopy (SEM, TEM). Among the master alloys, FCC-A1 based Al0.5CoCrFeNiCu0.5 (Al0.5Cu0.5) and Al0.5CoCrFeNiCu (Al0.5Cu1.0) alloys exhibited highest cold deformability (145% and 170%, respectively), accompanied by significant work hardening (114% and 108% increase in hardness, respectively), primarily attributed to dislocation-dislocation interactions. It has been demonstrated for the first time that equiaxed single phase (FCC-A1) Al0.5CoCrFeNiCu0.5 high-entropy alloy can be obtained through the CR + annealing. The alloys exhibited reduced hot formability (62% and 85%, respectively) partly due to the formation of Cr-rich sigma phase instead of the Al-Ni rich B2 phase, most notable in the Al0.5Cu0.5 alloy, contrary to the CALPHAD simulations. This led to increased hardness in the alloys through precipitation hardening, achieving similar hardness values as those obtained through cold rolling (CR) with less deformation. The findings support the conclusion that the presented integrated processing strategy offers a cost-efficient means of producing Al0.5CoCrFeNiCuy alloys with enhanced mechanical and chemical properties for various engineering applications by the selection of cold and hot rolling routes.

Mirrored symbols, opposite effects: Impact of Ga and Ag additions on the martensite decomposition of the Cu81Al19 alloy

Although the presence of martensite is desirable in several applications of increasingly complex Cu-rich Cu-Al alloys, there is a lack of understanding about the effects of alloying in its stability. Martensite decomposition was investigated in as-quenched Cu81Al19, Cu79Al19Ga2, and Cu79Al19Ag2 alloys (compositions in atomic percentage) by optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, differential scanning calorimetry, and Vickers microhardness measurements. It was found that the similarity of crystalline structure between alloying element and host phase, as well as the interactions between ternary addition atoms and Al interfere with the stages of the martensite decomposition during heating. The Ga addition refined the microstructure, resulted in the precipitation of other phases, and favored the eutectoid reaction in the Cu81Al19 alloy. The Ag addition increased the tendency for martensite ordering, stabilized the β1 phase, and induced the precipitation of Ag particles from martensite on heating. Possible technological consequences arising from these results were also discussed.

Observation of itinerant ferromagnetic behaviour in equiatomic medium entropy AlNiCo alloy

A medium entropy AlNiCo alloy has been synthesized by vacuum arc melting, which shows single phase B2 structure. Atom probe tomography analysis showed that the elements are homogeneously and randomly distributed in AlNiCo alloy without any clustering tendency. A detailed analysis of temperature and field dependent magnetization data suggests an itinerant ferromagnetic ground state of AlNiCo alloy. The magneto crystalline anisotropy is evaluated to be 1.03 × 105 ergs/cm3 at 5 K. A broad maximum at low temperature in zero-field-cooled (ZFC) magnetization, as well as irreversibility of ZFC and field-cooled (FC) curves indicated a glassy behavior. This observation is supported by the memory effects observed at low temperature. The observed anomalous magnetic behavior is discussed in terms of modifications in exchange interactions. To the best of our knowledge, this is the first report on microstructure and magnetic properties of an equiatomic ternary AlNiCo alloy.