Martensitic Phase Research Articles

Modeling of localized phase transformation in pseudoelastic shape memory alloys accounting for martensite reorientation

A reliable prediction of the pseudoelastic behavior necessitates the involvement of martensite reorientation in the model. This is important not only under non-proportional loading but in general when the phase transformation proceeds in a localized manner, which results in complex local deformation paths. In this work, an advanced model of pseudoelasticity is developed within the incremental energy minimization framework. A novel enhancement of the model over its original version lies in the formulation of a suitable rate-independent dissipation potential that incorporates the dissipation due to martensitic phase transformation and also due to martensite reorientation, thus yielding an accurate description of the inelastic transformation strain. The finite-element implementation of the model relies on the augmented Lagrangian treatment of the non-smooth incremental energy problem. Thanks to the micromorphic regularization, the related complexities are efficiently handled at the local level, leading to a robust finite-element model. Numerical studies highlight the predictive capabilities of the model. The characteristic mechanical behavior of NiTi tube under non-proportional tension–torsion and the intricate transformation evolution under pure bending are effectively captured by the model. Additionally, a detailed analysis is carried out to elucidate the important role of martensite reorientation in promoting the striations of the phase transformation front.

Elucidation of annealing effects on austenite–martensite and magnetic phase transitions in Mn2Ni1.6Sn0.4 ribbons synthesized from bulk alloys prepared by RF induction melting

We investigate the consequences of annealing on the structure, microstructure, magnetic, and electrical transport of Mn2Ni1.6Sn0.4 ribbons. The 40–60 μm thick ribbons were formed by melt spinning of the bulk ingot synthesized by RF induction melting. Ribbons were annealed at 600 °C for 12 hrs and the other at 800 °C for 2 hrs in vacuum. All ribbons crystallize into a cubic symmetry (space group F4¯3m). The orthorhombic phase appears as the secondary one. In ribbons annealed at 600 °C, the crystallite size decreases from ∼ 47 nm to ∼ 29 nm, and annealing at 800 °C doubles the crystallite size to ∼ 96 nm. The least amount of microstrains (17x10−4) in the as-synthesized ribbon is consistent with the occurrence of the superlattice peaks (111) and (200). Lower intensities of the superlattice peaks in 600 °C and 800 °C ribbons are consistent with higher microstrains (25x10−4 and 24x10−4). Hence, a higher degree of Ni-Mn ordering improves magnetic properties in annealed samples. The as-synthesized ribbon has an austenite-phase Curie temperature of TCA∼303K, which enhances to TCA∼320K and TCA∼310K after annealing at 600 °C and 800 °C. The ribbon annealed at 600 °C has the highest saturation moment. All the ribbons show the exchange-bias (EB) effect, and the most pronounced effect is seen in the 800 °C annealed ribbon. Microstructure uniformization and relative strengths of the Ni-Mn and Mn-Mn interactions improve the magnetics. Near TC, MT=M0TC-Tβ is satisfied (β = 0.31, 0.36, and 0.37, for as-synthesized, 600 °C and 800 °C annealed ribbons). The low-temperature spontaneous magnetization obeys the Bloch law MT=M01-AT32, with a deviation in 600 °C annealed ribbon due to spin freezing. The ρ-T has been fitted in the different temperature ranges using the various combinations in ρT=ρ0+AphT+BsdTα. At T < 85 K, the resistivity of the as-synthesized ribbon follows ρT=ρ0+BsdTα, with α≈1.47, while for the 600 °C annealed ribbon, α≈1.49. The exponent α∼1.5 supports the existence of the spin glass state in the lower temperature region of as-synthesized and 600 °C annealed ribbons. In the high-temperature range, the linear ρ-T behavior is described by ρT=ρ0+AphT and consistent with the electron–phonon scattering.

Complementary In Situ Characterization of Superelasticity in Fe–Mn–Al–Ni–Ti Shape Memory Alloys by Acoustic Emission, Digital Image Correlation and Infrared Thermography

AbstractCoupled in situ investigations were conducted on a Fe–Mn–Al–Ni–Ti single crystal deformed in compression and two Fe–Mn–Al–Ni–Ti oligo-crystals deformed in tension. Acoustic emission measurements were employed to monitor the degradation of superelasticity and the stabilization of martensite due to dislocation processes. These observations were corroborated by the application of digital image correlation and infrared thermography measurements. A poor strain reversibility and a premature plastification of the parent phase were observed in case of the single crystal due to an unfavourable crystal orientation. A contradictory transformation behaviour of the two oligo-crystals was observed, with one specimen showing a promising strain reversibility and characterisitic signs of degradation, and the other specimen exhibiting a limited strain reversibility due to an unusual confinement of the martensitic phase transformation to an unfavourably oriented grain. In the former case, an increase in the dislocation density within five cycles was detected through a shift of the acoustic signals’ median frequencies. In the latter case, a strong coupling between martensite nucleation and dislocation generation led to a pronounced martensite stabilization after one loading cycle. For all specimens, temporal sequence effects related to the coupling of martensite nucleation and dislocation generation were detected by means of acoustic emission.

Physical mechanisms for dependence of temperature-induced phase transition and shape memory effect on grain size in nanocrystalline NiTi shape memory alloys

Physical mechanisms for dependence of temperature-induced phase transition and shape memory effect (SME) on grain size (GS) of nanocrystalline NiTi shape memory alloys (SMAs) were revealed by combining experiment and molecular dynamics simulation. Influences of GS on phase transition temperature and stress level during tension loading below martensite transition finish temperature Mf are interpreted by core-shell theory that energy of shell (grain boundary (GB)) is higher than that of core (grain interior), so shell becomes an obstacle to deformation of the core and the obstacle increases with reducing GS because the fraction of GB increases with decreasing GS. Due to the constraint of shell, martensite transition during cooling is so incomplete that stress-induced martensite occurs in nanocrystalline NiTi SMAs deformed below Mf. After unloading, some stress-induced martensite phases are retained due to the lack of driving force for reverse martensite transition at low temperature. This is why SME occurs in the alloy with GS below 10 nm when no temperature-induced phase transition happens. Under the same tension strain, inelastic strain after unloading increases with increasing GS. The increase of GS causes the increase of SME strain, and the residual strain after heating the deformed nanocrystalline NiTi SMAs stems from the plastic deformation of martensite and austenite in grain interior during tension.

Effect of cladding speed on the microstructure and hardness of high-hardness B-bearing Cr17Ni2 coating

The B-bearing iron-based coating produced by laser cladding exhibits super-high hardness. However, the strengthening mechanism of B-bearing Cr17Ni2 coating and non-equilibrium phase transformation during the cooling stage require further investigation. The study focused on the B-bearing Cr17Ni2 coatings produced by laser cladding at four speeds ranging from 10 mm/s to 200 mm/s. The results show that the thickness of the single layer in the coatings gradually decrease as the increase of scanning speed. The secondary dendrite arms spacing and grain size also decrease with increasing scanning speed. The microstructure of the coating consists of a martensitic phase and a eutectic phase consisting of Cr2B compounds and austenite. Combined with G\\R diagram and finite element analysis, the microstructure refining mechanism of the coating has been concluded. The effect of fine grain strengthening, solid solution strengthening, precipitation strengthening, and dislocation strengthening on hardness is investigated. It has been observed that the coating hardness increases with increasing scanning speed. This change in the hardness of the coatings is mainly because of the grain and precipitate refining.

Manufacturing of new dual phase steel with a combination of macro-laminated and micro-laminated morphology

ABSTRACT In this study, a new dual phase steel with a combination of macro-laminated and micro-laminated morphology was fabricated for the first time. Friction stir welding, heat treatment, and cold rolling were employed to produce the new laminated DP steel. The microstructure of produced DP steels consisted of elongated ferrite and martensite phases in the St52 layers. The microhardness profiles and stress–strain curves of produced laminated DP steels showed that the best mechanical properties corresponded to the traverse speed of 70 mm/min due to less hardness gradient. The failure morphology indicated good interfacial bonding that prevented delamination during the tensile deformation.

Damage mechanisms analyses in DP steels using SEM images, FEM, and nonlocal peridynamics methods

An investigation is performed to study the damage mechanisms of dual phase steels using experimental analysis, local finite element simulation, and nonlocal peridynamics (PDs) method. The uniaxial tensile tests and preparation of metallography and SEM images have been used to peruse the pattern of deformation and voids in different phases. Understanding of the relationship between real microstructure and damage mechanisms can often not be obtained from microstructural investigation using experiments only. Here, a novel numerical approach is presented to investigate damage mechanisms in multiphase materials at micro scale level using both local and nonlocal numerical analyses and microstructural images from a scanning electron microscope (SEM). The nonlocal PDs method is capable to overcome many challenges associated with convergence problems in other numerical methods and to detail-oriented study of damage initiation and propagation autonomously. In this study, images of real microstructure are used as RVEs and imported to the FEM software and PD-developed code. Moreover, the effects of different constitutive models for the interface of ferrite and martensite phases on the bond breakage and damage patterns have been also investigated.

The mechanism for the superior isotropic mechanical properties attained in a cross rolling TiNb alloy

In the present study, the Ti–41Nb (wt.%) alloy featuring a microstructure composed of β and α″ phases have been prepared through the application of the Cross Rolling (CSR) technique to achieve a near-isotropic superior mechanical behavior. The experimental findings revealed that the CSR sample exhibits a uniform β matrix, randomly dispersed α″ martensite and a high density of dislocations and grain boundaries. Subsequent experiments unveiled that the CSR sample displays an almost isotropic mechanical response across three typical directions, Rolling Direction (RD), a 45° deviation from RD, and Transverse Direction (TD), evidenced by comparable stress-strain curve profiles and ultimate tensile strength (UTS) values. Due to the randomly distributed textures and high density of dislocations and grain boundaries, the stress-induced martensitic (SIM) transformation exhibits a similar characteristic in three typical directions, that is, the SIM transformation took place homogeneously and continuously. Consequently, the CSR sample can achieve a near-isotropic and outstanding mechanical performance due to the similar characteristics of martensitic phase transformation and the strengthening effect brought by the high density of dislocations and grain boundaries.

Tailoring Weldability for Microstructures in Laser-Welded Near-α Titanium Alloy: Insights on Mechanical Properties

With the development of lightweight aerospace structures, the use of the high-quality and efficient laser welding of near-α titanium alloys has received widespread attention and favor thanks to its superior comprehensive performance. The welding experiment of 3 mm thick TA15 titanium alloy was carried out by YAG laser welding, and the material weldability, microstructure, microhardness, and mechanical properties of welded joints were systematically studied. The results indicated that laser welding of TA15 titanium alloy can produce well-formed welded joints without defects such as cracks and porosity. The welded metal used was a typical basket-weave microstructure composed of a large number of α′ martensitic phases and a small number of high-temperature residual β phases, and the heat-affected zone was a staggered arrangement of undissolved α phase and needle-like α′ martensite. The microhardness of the welded joint showed a hump distribution, and the hardness of WM fluctuated between 410 and 450 HV since the martensitic transformation occurred during the solidification of the weld under thermal cycling, and the β phase changed to the needle-like α′ phase. The tensile test indicated that the fracture position was located in the base metal area, and the fracture morphology showed the equiaxial dimple morphology of different sizes in a ductile fracture mode. The welded metal had the lowest impact performance (average value of 5.3 J) because the weld area was predominantly coarse α′ martensite. This experiment conducted systematic, in-depth, and extensive research on welding processes, hardness, tensile, impact, and fracture mechanisms. Based on the special product applications in the aerospace field, it was more targeted and conducive to promoting the application of the welding process in this material.

Interplay between the reversibility of the inverse magnetocaloric effect and kinetic arrest in Ni-Co-Mn-Sn Heusler alloys

The nature of martensitic phase transitions and its modification as a function of composition and application of magnetic field have been studied in detail for Ni40Co10Mn40Sn10-xGax (x=0, 0.3, 0.4 and 0.5). The phase transition temperature (TM) increases with increasing x. The kinetic arrest (KA) of the austenitic phase has been observed for x=0 and 0.3, which disappeared for x>0.3. The KA results in a decrease in the change of magnetization (ΔM) across TM. However, the isothermal entropy change ΔS varies almost linearly with [dTM/d(μ0H)]−1 (field-induced shift in TM) irrespective of the composition variation and thermal cycling. This behavior indicates that the variation of dTM/d(μ0H) is the dominant factor determining the magnitude of the ΔS rather than ΔM. Consequently, the effect of KA on ∆M has a negligible influence on ΔS in the studied Heusler alloys. The reduced field-sensitivity in TM associated with the temperature-induced decrease of magnetization in the ferromagnetic austenitic phase leads to a decrease of the thermal hysteresis and an increase of ΔS. As a result, a large reversible (|ΔSrev|=21 J/kg K for Δμ0H=5 T) has been observed for x=0.5, which exceeds previously reported values for Sn-based Heusler alloys.

Modeling of martensitic phase transformation accounting for inertia effects

As a diffusionless phase transformation, martensite evolves at the speed close to sound, with its kinetics and morphology dominated by the mechanical energy. However, the mechanism of martensitic phase transformation with the consideration of inertia is rarely investigated. This paper presents a multiphase-field model, where the transformation strain in martensite performs as the mechanical wave source, and in return the kinetic energy contributes to the driving force for phase transformation. As a result, the mechanical fields, i.e., the stress and the velocity, are derived according to the increment of the transformation strain. The propagation direction of the mechanical wave is corrected by considering the growth of the martensitic nucleus. With the 1D and 2D analysis, as well as the comparison against 2D static case, the mechanism of martensitic phase transformation is investigated, and the advantage of mechanical model accounting for inertia effects is illustrated.

Microstructure, martensitic transformation kinetics, and magnetic properties of (Ni50Mn40In10)100−xCox melt-spun ribbons

AbstractThe effect of Co-doping on the structure, microstructure, martensitic phase transformation kinetics, and magnetic properties of the melt-spun (Ni50Mn40In10)1−xCox (x = 1, 2, and 3) Heusler ribbons, named hereafter Co1 (x = 1), Co2 (x = 2), and Co3 (x = 3), was assessed using X-ray diffraction, scanning electron microscope, energy-dispersive spectroscopy, X-ray fluorescence, differential scanning calorimetry, and vibrating sample magnetometer. The XRD results reveal the formation of a 14M martensite structure alongside the face-centered-cubic (fcc) γ phase. The crystallite size ranges between 50 and 98 nm for the 14M martensite and from 9 to 16 nm for the γ phase. The mass fraction of the γ phase lies between 36.4 and 44.2%. Co-doping affects the lattice parameters and the characteristic temperatures (martensite start, martensite finish, austenite start, and austenite finish). The calculated activation energy values for the non-isothermal martensitic transformation kinetics are 257 kJ mol−1 and 135.6 kJ mol−1 for the Co1 and Co2, respectively. The produced ribbons show a paramagnetic behavior. The variation in the coercivity can be related to the crystallite size and mass fraction of the γ phase. The produced ribbons exhibit an exchange bias at room temperature that decreases with increasing the Co content.

Different phase transformation behaviors of B2-CuZr crystalline phase and their associated mechanical properties by molecular dynamics using different potentials

Metastable CuZr-based alloys have attracted much attention due to their high glass-forming ability and shape memory effect. Many experiments have underscored the pivotal role of the B2-CuZr phase as an effective inclusion to improve both the strength and ductility of metallic glass matrix composites. The improved ductility can be attributed to the dilatation induced by martensitic transformation, while the strengthening effect is owed to the higher strength and hardness of the martensite phase compared to the austenite phase. Well-designed atomistic simulations can predict the mechanical behavior of materials before experiments and offer sufficient information on the atomic scale. The selection of an appropriate interatomic potential is a primary concern in any atomistic simulation and needs to be carefully considered to ensure reliable results. The uniaxial tensile behavior of B2-CuZr crystalline phase is investigated by molecular dynamics simulations using five typical potentials, namely the potentials developed by Mendelev-2007, Mendelev-2009, Mendelev-2016, Mendelev-2019 and Cheng-2009. The phase transformation behavior during tension, Young’s modulus, and yield strength of the simulated samples exhibit variations when different potentials are employed. Notably, only by employing Mendelev-2019 and Cheng-2009 potentials, the strength and Young’s modulus of the transformed phase are higher than the untransformed austenite phase, corresponding well with experimental results. This work emphasizes the impact of different interatomic potentials on phase transformation behaviors within a specific simulation context.

The effect of printing parameters on the properties of 17-4 PH stainless steel fabricated by material extrusion additive manufacturing

The 17-4PH stainless steel filament was characterised and utilised to study the effect of printing parameters, i.e. printing temperature, layer thickness, infill pattern and extrusion multiplier on the physical properties. The as-printed and as-sintered internal structures were analysed. The results showed that the as-printed density increases with increasing printing temperature and extrusion multiplier and decreasing layer thickness. The use of the line infill pattern also provided slightly higher as-printed density than the concentric infill pattern due to the low fraction of void between deposited paths. After sintering, the trace of these voids can be observed together with smaller-size residual pores from the spaces between powders, which is the nature of the pressureless sintering process. The microstructure of the as-sintered specimens was similar to the typical microstructure of the 17-4PH alloy fabricated by metal injection moulding process, which contains delta ferrite, martensite and Si-rich phases. In additions, the internal void generated during debinding and sintering results in unexpectedly low tensile properties and results in the difference in tensile properties between the concentric and line infill patterns.

The evolution of microstructure and micro-texture in a metastable Fe45Co35Cr10V10 medium-entropy alloy subjected to cold rolling

Microstructure and micro-texture evolution in a Fe45Co35Cr10V10 medium-entropy alloy under 10‐–88% cold rolling was investigated by electron backscattering diffraction. The variant graph method reconstructed parent γ grain orientations at 20, 30 and 40% thickness reduction to determine the operative orientation relationships (ORs) with the child ε and α′-martensite phases and to study variant selection. The parent γ phase accommodates deformation by faulting, slip, shear banding and martensitic phase transformation via the γ→ε→α′and γ→α′pathways. The ε and α′ -martensite variant selection occurs within individual parent γ grains but not in the bulk microstructure. Variant pairing in α′-martensite shifts from a preference for the same crystallographic packet group to the same Bain group with increasing thickness reduction.The development of the Brass-type micro-texture in the parent γ phase beyond 40% thickness reduction is attributed to Cuγ and Sγ orientations transforming to ε and α′-martensite, along with shear banding. The micro-texture of ε-martensite records maximum intensities for ∼011¯537¯42ε and ∼112¯61¯1¯21ε on the hkil-fibre and originating from ∼Cuγ and Sγ via the Shoji-Nishiyama OR. The α′-martensite micro-texture is characterised by the αα′, γα′ and βα′ fibres. The βα′ -fibre forms between 20% and 60% thickness reduction and rotates towards stable orientations along the αα′-fibre at higher thickness reductions. Modelling shows that orientations along the βα′ and γα′ - fibres stem from ∼Brγ and ∼Sγ and those along the αα′-fibre originate from Gγ, Brγ, Cuγ, and Sγ.

Revealing contrary contributions of the magnetic and lattice entropy to the inverse magnetocaloric effect in magnetic shape memory alloy

In this work, we studied the nature and dilemma of the inverse magnetocaloric effect using Ni50Mn36In14 magnetic shape memory alloy. In this context, the inverse magnetocaloric effects of Ni50Mn36In14 magnetic shape memory alloy polycrystalline samples were investigated as a function of annealing heat treatments by the thermo-magnetometry method. Two forms of Ni49TiMn36In14 magnetic shape memory alloy were studied: one that predominantly undergoes a magnetic phase transition and the other that exhibits both a magnetic and martensitic phase transition. The magnetic behaviors and magnetocaloric properties of these alloys were analyzed to investigate the competition between magnetic and lattice contributions to the total entropy change. Finally, the mutually contradictory role of magnetic and lattice contributions was demonstrated.

Overcoming strength-ductility trade-off in Si-containing transformation-induced plasticity high-entropy alloys via metastability engineering

Benefiting from the transformation-induced plasticity effect has been recognized as a new approach to develop high-performance Si-containing high-entropy alloys with outstanding room-temperature strength-ductility balance. However, closely controlling the kinetics of deformation-induced α΄-martensite formation is essential to further boost ductility in addition to ultrahigh strength. In the present work, this aim was fulfilled by manipulating the chemical composition of the promising FeCoCrVMnSi system with the replacement of Mn with Ni and adjusting the Si content to fine-tune the stacking fault energy and the driving force of austenite to martensite transformation. The experimental results were obtained by EBSD, TEM, XRD, and tensile testing, and the results were supported by thermodynamic calculations, work-hardening analysis, and assessment of α΄-martensite formation kinetics. Accordingly, the single-phase Fe47Co30Cr10Ni5V8-xSix system was designed. In this system, the Fe47Co30Cr10Ni5V2Si6 alloy exhibited exceptional tensile strength (∼1.1 GPa) and total elongation (72 %), outperforming the competitive dual-phase Fe46Co30Cr10Mn5V2Si7 alloy. High strength was attributed to the high solid-solution strengthening effect as well as the volume fraction of α΄-martensite, while its ductility benefited from fine-tuned kinetics of martensitic phase transformation.

Antiferroelectric Ceramics for Energy-Efficient Capacitors by Theory-Guided Discovery.

Antiferroelectric ceramics, via the electric-field-induced antiferroelectric (AFE)-ferroelectric (FE) phase transitions, show great promise for high-energy-density capacitors. Yet, currently, only 70-80% energy release is found during a charge-discharge cycle. Here, for PbZrO3-based oxides, geometric nonlinear theory of martensitic phase transitions is applied (first used to guide supercompatible shape-memory alloys) to predict the reversibility of the AFE-FE transition by using density-functional theory to assess AFE/FE interfacial lattice-mismatch strain that assures ultralow electric hysteresis and extended fatigue lifetime. A good correlation of mismatch strain with electric hysteresis, hence, with energy efficiency of AFE capacitors is observed. Guided by theory, high-throughput material search is conducted and AFE compositions with a near-perfect charge-discharge energy efficiency (98.2%), i.e., near-zero hysteresis are discovered. And the fatigue life of the capacitor reaches 79.5 million charge-discharge cycles, a factor of 80 enhancement over AFE ceramics with large electric hysteresis.

Challenge of fabricating difficult-to-nitride materials: Formation of martensitic phase in (Fe0.8Co0.2)8N foil based on industrially suitable gas-nitriding process

Nitrogen-martensitic phase (Fe0.8Co0.2)8N was successfully synthesized by using an industrially suitable gas-nitriding process of a bulk foil. So far, the nitrogen-martensitic phase of the bulk material has not been synthesized at such a high Co content. We found that this is because the nitride was easily denitrided by elevating temperature. In this work, by exploiting a NH3 gas-nitriding process combined with quenching at a rapid cooling rate (&amp;gt;800 °C/s) in NH3 atmosphere, we found that nitrogen stayed at the surface layer of the foil. By using cross-sectional laser microscopy, the nitride region was observed as a 7-μm-thick layered shape at the surface of the 100-μm-thick foil. An x-ray diffraction technique revealed that the nitride layer was a martensitic phase that was characterized as a body-centered tetragonal structure with c/a = 1.04. These findings can be applied to nitriding and surface treatments for alloy systems in which a nitrogen solid solution is hardly formed. Our developed method is promising because the martensitic phase is expected to be formed in whole bulk by further optimizing parameters clarified in this work.

Laser-assisted manipulation of Volta potential pattern on the TC4 surface for improved hBMSCs osteogenesis

The Ti6Al4V (TC4) alloy, a prevalent biomedical material in orthopedics, still faces limitation of the insufficient osseointegration. To improve the bioactivity of TC4, introducing the electric environment onto the TC4 surface may be an effective way in the view of the necessity of endogenous electric microenvironment in bone regeneration. Herein, a Volta potential pattern was engendered on the TC4 surface via parallel laser patterning, so as to promote the osteogenic differentiation of cells. A 15 W laser successfully transformed the original α + β dual phase towards radially distributed lath-like martensite phase in the laser treated region. The atomic lattice distortion between the heterogeneous microstructures of the laser treated and untreated regions leads to a significant Volta potential fluctuation on the TC4 surface. The Volta potential pattern as well as the laser-engraved microgrooves respectively induced mutually orthogonal cell alignments. The hBMSCs osteogenic differentiation was significantly enhanced on the laser treated TC4 surfaces in comparison to the surface without the laser treatment. Moreover, a drastic Volta potential gradient on the TC4 surface (treated with 15 W power and 400 μm interval) resulted in the most pronounced osteogenic differentiation tendency compared to other groups. Modulating the electric environment on the TC4 surface by manipulating the phase transformation may provide an effective way in evoking favorable cell response of bone regeneration, thereby improving the bioactivity of TC4 implant.