Martensitic Transformation Research Articles

On Self-Positioning and Self-Fixation of Parts Made of Alloys with Shape Memory Effect under Component Assembling

Introduction Violation of mutual positioning and fixation of parts worsens the operation of the equipment. Traditional approaches to solving the problem under consideration have been sufficiently studied: interchangeability of parts and the use of special equipment. Both methods involve a significant number of additional elements and assembly operations. Fixation is often provided by means of force fitting and welding. Disadvantages of these methods include assembly, residual and other stresses, engineering constraints, etc. To solve these problems, alloys with thermoelastic phase transformations are used, which provide shape memory effects (SME) to manifest themselves. This article describes, for the first time, self-positioning and self-fixation using the example of parts specially made from an alloy with SME. Materials and Methods. The pin element under pressing mandrels the blind hole of the cup and enters the seat. The alloy with SME was Ti-55.7wt%Ni. The temperature of the onset of its austenitic transformation was As = 95°C ± 5°C. The elemental composition was determined by a Shimadzu EDX-8000 X-ray fluorescence spectrometer, the phase composition — by a Shimadzu XRD-7000 diffractometer. The temperature was specified through differential scanning calorimetry. The range was 20–300°C, the heating rate was 5 deg/min. A Guide T120 thermal imager and a RangeVision DIY 3D scanner with structured illumination were used. After pressing the pin into the cup at different angles, the alignment and deviations between the axes of the cup and the pin were examined. Then, the cup was heated to 110–120°C, cooled, and control measurements were taken.Results. Values of the deflection angle after pressing were 0.2–11°. With a rigid structure and an installation angle of 0°, the pin deflected in the mounting hole by 0.2–0.5°. The axes shifted and did not intersect. The pin was not always completely pressed in. This indicated uneven deformation of the metal and different stress values around the hole. Such a unit would soon fail. The pin took the required position after heating the cup to 110–120°C (this temperature was higher than at the end of the reverse martensitic transformation). The angular deviation of the axes was noted to be 0.03–0.1°. The maximum misalignment (0.04 mm) corresponded to high positioning accuracy. Heating during the reverse martensitic transformation created internal stresses that returned the initial geometry of the cup. They also formed the forces that positioned and fixed the pin in the hole. That is, it is the parts that provide positioning and fixation (this is selfpositioning and self-fixation).Discussion and Conclusion. For self-positioning and self-fixation of parts due to the shape memory effect, it is necessary to avoid sharp transition lines between the surfaces of parts during design, select rounded corners or fillets, and get a clean surface without burrs. Self-fixation and self-positioning reduce defects and inaccuracies during assembly. The use of certain alloys increases the profitability of equipment production.

Decomposition features and mechanical properties of aging Ti49Ni51 alloy with shape memory effects subjected to heat treatment

The features of the microstructure of the Ti–51 at.%Ni shape memory alloy have been studied after aging at various temperatures. In combination with studies using optical and electron microscopy and X-ray analysis, mechanical properties were tested for tensile strength at room temperature. It has been established that the aged alloy is distinguished by a high level of mechanical properties (tensile strength up to 1200 MPa with a relative elongation of up to 35 %) due to highly dispersed homogeneous decomposition and the effect of simultaneous hardening and increased plasticity as a result of deformation-induced martensitic transformation.

Multimodal assessment of mechanically induced transformation and damage in TRIP steels using X-ray nanotomography and pencil-beam diffraction tomography

A comprehensive multimodal measurement environment integrating X-ray computed tomography (CT) and special X-ray diffraction (XRD) using a collimated beam has been developed and was applied for the first time to investigate martensitic transformation and damage behaviour in transformation-induced plasticity (TRIP) steels. The transformation and damage behaviour of numerous γ grains were analysed individually to understand the behaviours and to identify the factors controlling these processes.A transition was observed from a stress-assisted transformation in the early loading phase, controlled by mechanical driving forces, to a strain-induced transformation controlled by dislocation density. A characteristic reversal in the transformation rate was observed whereby γ grains with a crystallographic orientation that initially undergo rapid transformation due to high mechanical driving force underwent a sudden deceleration of transformation. Conversely, γ grains with an orientation that initially underwent gradual transformation rapidly completed transformation. The preceding hard phase inhibited the transformation of neighbouring γ grains through the triple effects of reducing stress triaxiality, relaxing stresses and constraining plastic deformation.The growth of pre-existing voids was modest, and material damage was dominated by voids that were newly formed during deformation from α′ grains. The initiation and progress of damage were influenced by the combined effects of the γ grain morphology and their interaction with surrounding α′ grains. The complexity of the local morphology governed the martensitic transformation and damage behaviour, and geometrical parameters were identified as highly sensitive indicators for describing this phenomenon. Finally, industrial measures to design damage-resistant TRIP steels based on these research findings are discussed.

A deep insight of re-entrant martensitic transformation mechanism in Co2Cr(Ga,Si) shape memory alloys

Co2Cr(Ga,Si) shape memory alloys have a wide application temperature range due to the unique re-entrant martensite phase transformation (RMT) behavior. Nevertheless, the microscopic mechanism of RMT remains elusive and unsystematic. The heart of this investigation lies the comprehensive exploration of phase stability, phase transformation path, and martensite slip direction during RMT from martensite (D022-PM) to austenite (L21-FM). In this work, we systematically investigate the re-entrant martensitic transformation of Co2Cr(Ga,Si) SMAs using first-principles methods for the first time. Firstly, the density of states (DOS) calculation indicates that the stability of L21-FM is higher than D022-PM. The charge density calculation further indicates that the bonding strength between Co atoms and Cr (Si) atoms in the L21-FM phase is the highest. In addition, Fermi surface calculation further reveals that phase instability is due to the Fermi surface nesting caused by electron-phonon coupling. Moreover, the minimum energy path was calculated by the G-SSNEB method for the first time, which indicates the RMT can occur. Finally, the calculation of the elastic constants indicates that RMT is caused by the crystal plane slip of the D022-PM phase along the <110> direction. Our calculations provide the electronic-level and thermodynamic mechanism for RMT of Co2Cr(Ga,Si) alloy and shed some light on the revelation of the phase transformation mechanism.

Composition dependence of phase transformation and shape memory effect of Ti-Zr-Pd-Pt high temperature shape memory alloys

Ti-Zr-Pd-Pt alloys have been considered as potential candidates for high-temperature shape memory alloys (HT-SMAs). In this study, nine alloys were prepared to investigate the effect of multi-component alloying on the phase transformation and shape memory effect. The structural phase diagram of martensite in Ti–Zr–Pd–Pt quaternary alloys was firstly systematically investigated to provide insights and predictions for further research. The phase transformation is divided into three groups: typical martensitic transformation (MT) area, supercooling-controlled phase transformation area and diffusion-assisted phase transformation area. The martensite structure changes from B19 to B33 with the addition of Zr over 25 %. The contribution of Pt contents to raising the martensitic transformation temperature (MTT) became less pronounced with increasing Zr contents. As for shape recovery, over 87 % shape recovery was obtained even under 300 MPa in Ti-10Zr-Pd-Pt alloys, among which Ti-10Zr-15Pt-35Pd presents the highest recovery ratio of over 97 %.

Interpretable machine learning for simultaneous designing martensitic transformation temperature and thermal hysteresis of high-entropy shape memory alloys

As an excellent functional material, high-entropy shape memory alloy (HESMAs) exhibits tremendous application potential in various fields such as actuators and energy exploration due to its advantages of high strength, high hardness, and corrosion resistance. The key factors determining the application potential of HESMAs are martensitic transformation temperature and thermal hysteresis. However, the design of HESMAs is a great challenge due to the large component search space. Here, we firstly propose a workflow aiming to achieve dual objectives: predicting the martensitic transformation peak temperature (Mp) and thermal hysteresis (Thy) to achieve a rapid design for HESMAs. The key features are obtained by correlation screening and Borutashap feature screening. The Mp and Thy models are training by eXtreme Gradient Boosting Regression algorithm(XGBR) combined with Bayesian Optimization algorith. Finally, XGBR model demonstrates superior performance in predicting both Mp (Rtrain2= 0.993, Rtest2= 0.902) and Thy (Rtrain2= 0.998, Rtest2= 0.928). By applying these models, we are able to identify potential candidates for targeted HESMAs in vast search spaces, specifically, low Mp and wide Thy HESMAs,room Mp and narrow Thy HESMAs, and high Mp HESMA. In addition, we utilize the Shapley additive interpretation method to explain the model's behavior, establishing a more transparent relationship between features and Mp and Thy individually. This proposed strategy is providing valuable guidance for the subsequent targeted design of HESMAs.

Quasi-linear superelasticity and associated elastocaloric effect in boron-doped polycrystalline Ni-Mn-Ti alloys

Ni-Mn-Ti shape memory alloys show great potential in solid-state elastocaloric cooling owing to very prominent elastocaloric effect along with first-order stress-induced martensitic transformation. However, large stress hysteresis inherent to martensitic transformation greatly restricts the energy efficiency and cyclic stability of elastocaloric response. Here, we demonstrate the effective manipulation of stress hysteresis as well as the resulting elastocaloric effect through doping boron to Ni-Mn-Ti alloys. With the incremental boron content in (Ni50Mn31Ti19)100–xBx (x = 0, 0.2, 0.5, 1, 1.5) alloys, a plateau-type superelastic behavior with large stress hysteresis gradually evolves into a quasi-linear one with slim hysteresis, giving rise to significant improvement in the energy conversion efficiency of elastocaloric response. In a (Ni50Mn31Ti19)99B1 alloy, the coefficient of performance of material (COPmat) can be as high as 24 ∼ 33. Moreover, under a compressive strain of 4%, large cooling |ΔTad| values higher than 6.5 K in the (Ni50Mn31Ti19)99B1 alloy are maintained for over 8000 superelastic cycles, showing an enhancement of one order of magnitude in the cyclability with respect to that of boron-free Ni50Mn31Ti19 alloy. We attribute the enhanced elasocaloric response to the significantly improved mechanical properties but reduced stress hysteresis endowed by relatively high content of boron doping.

Pyramidal dislocation driven martensitic nucleation: A step toward consilience of deformation scenario in fcc materials (II)

Dislocation glides and their interactions with other defects are central to our understanding of deformation mechanism enhancing plasticity and damage tolerance. Martensitic transformation (MT) is a fascinating phenomenon overcoming strength-elongation trade-off and thus tailoring structure-property architecture. However, dislocation plasticity of Fe-based hexagonal close-packed (hcp) martensite is still challenging due to its metastability, further complicated by controversies surrounding pyramidal dislocation even in pure hcp metals. To resolve the uncertainties, we address the pyramidal-dislocation-driven plasticity in Fe-based hcp martensite by employing in-situ transmission electron microscopy (TEM) and high-resolution (HR) annular bright field (ABF) imaging together with dislocation-contrast analyses. We show that the activation and dissociation of pyramidal dislocation govern the initial stage of plastic deformation, while subsequent cross-slip by the cooperative motion of dissociated pyramidal dislocations plays a key role in nucleation of new hcp martensite. By incorporating current dislocation model into previous models coupled with stacking-fault-energy concept, we propose a synthesized deformation scenario that offers a comprehensive perspective on plasticity and transformability.

Особенности тонкой структуры Ni-Al покрытий, полученных методом HV-APS

Introduction. Development of Ni-Al intermetallic compounds is one of the priority directions of modern machine building. Due to such characteristics as high heat resistance, high temperature strength, and low density, nickel aluminides are used as functional coatings in the aerospace industry. The main methods of Ni-Al coating surfacing are High-Velocity Oxygen-Fuel and High-Velocity Air-Fuel spraying (HVOF and HVAF), atmospheric plasma spraying (APS) and its modification such as High-Velocity Atmospheric Plasma spraying (HV-APS) which provides non-equilibrium cooling conditions. Since there are eight different intermetallic compounds, as well as martensite transformation, Ni-Al coatings is quite interesting to study. The work purpose is to study the features of the martensitic structure in HV-APS coatings, and also to establish the effect of heating temperature on its decomposition. Materials and methods. Ni-Al coatings were surfaced onto a low-carbon steel substrate using the HV-APS method. Studies of the fine structure of the coatings were carried out using transmission electron microscopy (TEM). In addition, the influence heating temperature on structural transformations of the coatings was analyzed. Results and discussion. Two types of particles are formed in HV-APS coatings: with a dendritic and granular structure. The most part of HV-APS coatings consists of particles with a two-phase grain structure (NiхAl1-х and γ'-Ni3Al grains). Only NiхAl1-x grains undergo martensitic transformation at cooling. Martensite in large grains (sizes greater than 500 nm) has a lamellar structure, while small grains are completely transformed into one martensite plate. In addition, the coatings contain grains in which martensite plates (NiхAl1-х) and β-phases alternated. It is shown the behavior of martensitic plates at colliding with each other, as well as with the γ′-Ni3Al grain. Heating up to 400 °C contribute the begins of martensite decomposition in individual grains with the release of a secondary phase; after heating up to 600 °C all martensite dissolves.

Hydrogen-induced delayed fracture behavior of notched 316L austenitic stainless steel: Role of grain refinement

Generally, grain refinement is considered to strengthen and mitigate the hydrogen embrittlement resistance of material. However, the effect of grain refinement on hydrogen-induced delayed fracture is rarely reported, especially concerning the extensive existence of geometric inhomogeneity such as notches. In this work, the effect of grain size on hydrogen-induced delayed cracking of notched 316L stainless steel under in-situ hydrogen charging is investigated. It is found that the brittle zone of delayed fracture of notched specimens is much larger than that in slow strain rate tensile of smooth specimens. This is due to the alternation of hydrogen diffusion and crack propagation during delayed fracture. After grain refinement, the time of delayed fracture increases significantly for the notched specimens, even the fracture does not happen, owing to the increase of austenitic stability. It is unusual that, regardless of grain size, α’ martensite is not detected at the crack tip, because the accumulated hydrogen at crack tip reduces plastic strains and suppresses martensite transformation.

Insights into effects of Fe doping on phase stability, martensitic transformation, and magnetic properties in Ni-Mn-Ti-Fe all-d-metal Heusler alloys

In this work, the effects of Fe doping on phase stability, martensitic transformation, and magnetic properties of Ni50Mn37.5-xTi12.5Fex (x = 3.125, 6.25, 9.375) all-d-metal Heusler alloys were systematically investigated by first-principles calculations. The results indicate a tendency for doped Fe atoms to aggregate within the Ni50Mn37.5-xTi12.5Fex alloys. As Fe concentration increases, a gradual reduction in both lattice constants and phase stability of austenite and martensite is observed. In the absence or presence of minimal Fe doping, both austenite and martensite exhibit antiferromagnetic behavior. However, at x = 9.375, a transition to a ferromagnetic state is observed in the austenite phase. This transition is attributed to the activation of the ferromagnetic coupling effect in the austenite phase induced by Fe doping in the Ni-Mn-Ti alloy. In contrast, the martensite phase maintains its antiferromagnetic characteristics throughout the doping range. A comprehensive analysis of the electronic structure elucidates the underlying physical mechanisms responsible for the martensitic transformation and magnetic property changes.

Breaking the strength-ductility trade-off in austenitic stainless steel at cryogenic temperatures: Mechanistic insights

At cryogenic temperatures, 316L austenitic stainless steel (ASS) exhibits remarkable strength while retaining high ductility, defying the conventional stress-strain trade-off. Despite extensive studies documenting the cryo-tensile properties of ASSs, the underlying mechanisms behind this phenomenon remain largely unexplored. This study systematically re-examines the tensile properties of 316L stainless steel and the associated mechanisms across a range of low temperatures (293 K, 223 K, 123 K, and 77 K). The reasons for the superior stress-strain balance (∼80 % GPa) are discussed using results from electron backscatter diffraction (EBSD) microstructure characteristics. The results undoubtedly suggest that the transformation mechanisms, specifically the shift from deformation twinning to martensitic transformation (γ → ε → α′), play a crucial role in enhancing elongation at cryogenic temperatures. At these temperatures, the Gibbs free energy difference between ε-martensite and γ-austenite approaches zero, resulting in slow martensite growth. The stress-strain curves at low temperatures satisfy the Considère criterion, indicating delayed necking under these conditions. This behavior is ascribed to the presence of various hierarchical microstructures, including ε, α′, γ-twins, ε-twins and their intersections, which act as sources of work hardening. This study provides new insights into deformation behavior of ASSs under cryogenic conditions.

Improving ductility and strength of high-entropy alloy [formula omitted] via multi-directional forging and annealing

A dual-phase high-entropy alloy Fe50Mn30Co10Cr10 is treated via multi-directional forging (MDF) and subsequent annealing at 600°C–1000°C. Different microstructures with totally different grain sizes and phase ratios are obtained. The MDF increases yield strength and ultimate tensile strength at the expense of ductility. Via annealing the MDF-processed alloy at 1000°C, the full recrystallized sample yields a excellent combination of high strength and good ductility due to the grain boundary strengthening, transformation-induced plasticity and twinning-induced plasticity. The yield strength, ultimate tensile strength and elongation at failure are 16.2%, 14.2% and 35.3% than those of the as-cast sample. The postmortem characterizations of this annealed sample show strong 〈111〉 texture in the austenite phase along the loading direction and intense martensite transformation with the gradually disappearance of the annealing twins.

Phase transition and internal friction behaviors in Mn-doped Co-V-Ga shape memory alloys

Shape memory alloys with a high abundance of mobile interfaces exhibit remarkable internal friction (IF) behaviors, which can be utilized for the reduction of noise and vibration. In this study, we systematically investigate the martensitic transformation and internal friction behaviors in the Mn-doped Co53V35–xGa12Mnx (x = 0 - 10) polycrystalline alloys. Our findings indicate that using Mn to replace V results in decreased transformation temperatures but increased thermal hysteresis. The addition of Mn enhances magnetic exchange interaction, leading to a gradual enhancement in magnetization difference across martensitic transformation, thereby compromising the transformation entropy change and arresting the martensitic transformation. At a frequency of 0.4 Hz, the intensity of transformation IF peak is enhanced from 0.124 to 0.178 with increasing the Mn content from 0 to 4.5 %, as a result of deteriorated geometrical compatibility between austenite and martensite due to the addition of Mn. Furthermore, hydrogenation treatments substantially improve both the peak intensity and frequency dependence of peak position for the relaxation-type IF, demonstrating the great contribution from hydrogen-twin boundary interaction.

A strategy for simultaneously enhancing the strength and ductility of metastable β titanium alloys: Coupling heterogeneous structure and TRIP effects

The applicability of metastable β titanium alloys is frequently constrained by their relatively low yield strength. This study has successfully designed a metastable β titanium alloy with heterogeneous microstructures (HS) comprising both deformed and recrystallized grains, achieved through simple cold rolling followed by short-term annealing. Compared to traditionally coarse-grained (CG) specimen that is entirely crystallized and equiaxed, the HS specimen exhibit not only a postponed initiation of double yielding but also superior yield strength (enhanced by 27.8 %) and ductility (enhanced by 7 %). The delayed double yielding and enhanced strength in the HS specimen are ascribed to the restriction of dislocation motion by α" martensite and the heterogeneous deformation induced (HDI) strengthening mechanisms. The ductility of the HS specimen exceeds that of the CG specimen, owing to the combined effect of HDI hardening and the transformation-induced plasticity (TRIP) effects. The more pronounced TRIP effect in the HS specimens results from the synergistic effect of the elevated HDI stress and the applied external stress, which promotes the occurrence of stress-induced martensitic phase transformation. This study offers a novel strategy for the development of high-performance metastable β titanium alloys.

Quantitative analysis of the micromechanical behavior and work hardening in Fe-0.1C–10Mn steel via in-situ high-energy X-ray diffraction

In the current work, the micromechanical behavior and work hardening behavior of Fe-0.1C–10Mn (in wt.%) steel deformed at 100, 63, 25 and −50 °C were investigated via in-situ high-energy X-ray diffraction (HE-XRD) technique. As the deformation temperature decreased, the yield strength (YS) and ultimate tensile strength (UTS) increased, while the total elongation (TE) reached a maximum value at 25 °C. The transformation kinetics of retained austenite (RA) was fitted by the Olson and Cohen (OC) model. The phase stress and flow stress contributed by the constituent phases were obtained based on the lattice strain and the volume fraction of the corresponding phase. The work hardening rate was decomposed into four contributors related to the TRIP effect and load partitioning, ie., the austenite phase stress, load partitioning between austenite and martensite, martensitic formation rate and load partitioning between ferrite and austenite. The influence of each contributor on the work hardening behavior was quantitatively evaluated and stacked, the stacked results agreed reasonably well with the experimental work hardening rate obtained from the true stress-strain curve. Finally, the volume fraction of austenite to martensite transformation promoted by the Lüders band (LB) and the stacking fault energy (SFE) of RA were found to be highly temperature-dependent. A linear relationship was revealed between the volume fraction of austenite to martensite transformation during the LB propagation and the SFE of RA. These findings offer insights into the TRIP effect and the LB propagation in medium-Mn steels.

Shape-Memory Effect and the Topology of Minimal Surfaces

Martensitic transformations, viewed as continuous mappings between triply periodic minimal surfaces (TPMSs), as suggested by Hyde and Andersson (Z. Kristallogr. 1986, 174, 225–236), are extended to include paths between the initial and final phases. Reversible transformations, which correspond to shape-memory materials, occur only if lattice points remain at flat points on a TPMS throughout a continuous transformation. For the shape-memory material NiTi, the density functional calculations by Hatcher et al. [Phys. Rev. B2009, 80, 144203] yield irreversible and reversible paths with and without energy barriers, respectively, in agreement with our theory. Although there are TPMSs for face-centered and body-centered cubic crystals for iron, the deformation between them is not reversible, in agreement with the non-vanishing energy barriers obtained from the density functional calculations of Zhang et al. (RSC Advances2021, 11, 3043–3048).

Simulation methods for local microstructure evolution-cooling and time–temperature transformation behavior in heat treatment of tool steels

This paper presents the development of a simulative workflow capable of predicting microstructural evolution during heat treatment processes. It represents a meaningful advance in this field by extending existing simulation models previously published by the authors. In this previous work, the software solutions MatCalc®, MATLAB®, and Abaqus FEA® were coupled to calculate several local microstructural properties: the carbide content, the type, the distribution, and the chemical composition of the matrix. In addition, the model could determine the proportions of microstructural components such as martensite and retained austenite within the matrix. The hardening treatment was simplified by assuming a fast quenching, leading to complete martensitic phase transformation. However, this assumption may not be valid for larger components, leaving room for optimization. Therefore, the simulation model in this publication has been successfully extended to include local solution-state dependent time–temperature transformation behavior. In addition, an automated microstructure simulation of the entire component is now possible. As an application example, two tool geometries of different sizes were simulated with an identical furnace heat treatment. The same furnace temperature (T = 1050 °C) and the same holding time (t = 60 min) were simulated with a slow air cooling (Tair = 25 °C). The austenitizing temperature and holding time were chosen to dissolve a sufficient amount of carbides during austenitization, and the slow cooling rates were chosen to form diffusion controlled phases such as bainite or pearlite. To validate the simulation model, the simulated time–temperature sequences were reproduced experimentally in a quenching dilatometer. The resulting real microstructures were compared with the simulated ones.

Effect of prior cold rolling on the dry wear performance of GCr15 bearing steel with multiphase microsturcture

In this work, the effect of cold rolling on the wear performance of GCr15 bearing steel with multiphase microstructure has been investigated. The microstructural observation shows that prior cold rolling facilitates to the dissolution of carbides during austenitization. With the increase of cold rolling reduction, the residual austenite content is increased after multiphase heat treatment. The wear results indicate that friction coefficient as well as wear rate distinctly decreases with the increase of rolling reduction. It is also found that the transformation of martensite from residual austenite induced by wear stress increases the surface compressive stress and hardness for the rolled specimens, thereby leading to the enhancement of dry wear resistance.

Martensitic transformations and magnetic properties of Ni50−xMn37Sn13Fex(x = 0.5, 1, 1.5) melt-spun ribbons

AbstractThe present study investigates the influence of iron (Fe) doping on the martensitic transformation and magnetic properties of Ni50−xMn37Sn13Fex(x = 0.5, 1, 1.5) magnetic shape memory alloys in ribbon form. The ribbons were prepared using arc-melting followed by melt-spinning processes and were characterized using X-ray diffraction, scanning electron microscopy, differential scanning calorimetry, and vibrating sample magnetometry. Our findings demonstrate that the addition of Fe shifts the martensitic transformation to lower temperatures and increases the Curie point of the austenitic phase, $$T_{c}^{\text A}$$ T c A , leading to an enhanced magnetism in the austenitic phase. Moreover, a significant increase in the magnetization jump $$(\Delta M)$$ ( Δ M ) is observed, from $$ 3.3\;{\text{emu\ g}}^{-1} $$ 3.3 emu\ g - 1 for $$x=1$$ x = 1 to $$17 \, {\text{emu\ g}}^{-1} $$ 17 emu\ g - 1 for $$x=1.5$$ x = 1.5 under a $$50 \, \text {Oe}$$ 50 Oe applied magnetic field. The structural transformations are also found to be sensitive to the external applied magnetic field. The isothermal magnetization curves exhibit the exchange bias effect, which confirms the coexistence of antiferromagnetic and ferromagnetic coupling in the samples. Furthermore, the exchange bias effect increases with the Fe content.