Inhomogeneous Grain Research Articles

Effects of the Primary Carbide Distribution on the Evolution of the Grain Boundary Character Distribution in a Nickel-Based Alloy

Grain boundary engineering (GBE) was carried out on a nickel-based alloy (GH3535, Ni-16Mo-7Cr-4Fe), which intrinsically has many strings of primary molybdenum carbides. The strings induce inhomogeneous grain size distributions and increase the difficulties in achieving a GBE microstructure. In this work, the effects of the primary carbide distribution on the grain boundary network (GBN) evolution were investigated. A higher proportion of Σ3n grain boundaries (GBs) associated with extensive multiple twinning events was achieved in the specimen with more dispersive and finer primary carbides, which are the results of cross-rolling, i.e., cold rolling with a changed direction. In a starting microstructure with many strings of primary carbides, the dense and frequent occurrence of particle-stimulated nucleation (PSN) around the carbides induced more general high-angle GBs into the GBN, and the inhibition of GB migrations by the carbide strings suppressed the formation of large-sized highly twinned grain clusters. As a consequence, the Σ3n GBs could not be effectively enhanced.

Experimental study of the “AE quiet period” on the eve of brittle failure in hard rock

Acoustic emission (AE) signals on the eve of brittle failure in hard rock often indicate a quiet period, i.e., a significant decrease in the number of AE signals. To address the current problem of the poor understanding of the quiet period, the failure process of hard rock was simulated by tests and acquired the AE signals. The AE signal during the quiet period were analyzed. First, compared with the AE signals in other loading periods, the AE signals during the quiet period are characterized by a greater hit amplitude, a greater rise time and ring count, a sudden increase in the cumulative absolute energy, a greater amplitude of the signals in the main frequency band and so on. Second, the inhomogeneity of rock grains, stress level and loading rate all have a nonnegligible influence. The more inhomogeneous the rock grains are, the higher the stress level is, or the larger the loading rate is, the longer the duration of the quiet period is. Third, a hard rock damage evolution equation based on AE considering the effect of the quiet period is proposed, which can reasonably reflect the objective fact of accelerating damage during this period. Finally, the quiet period is due to the brittle failure of hard rock with inhomogeneous grains under high stress conditions, so identifying the quiet period is important for AE-based monitoring and warning of hard rock failure.

Processing heterogeneously structured oxide-dispersion-strengthened Fe-10Cr-6.1Al-0.3Zr-0.1Y alloy for simultaneously enhanced strength and ductility

An oxide-dispersion-strengthened (ODS) Fe-10Cr-6.1Al-0.3Zr-0.1Y alloy with a bimodal grain size distribution was developed via a simple process of internal oxidation and powder forging. The intentionally promoted heterogeneous microstructure consists of coarse-grained “core” regions enclosed by mutually connected fine-grained “shell” zones, facilitated by unevenly distributed oxide particles. The sample sintered and then forged at 1150 °C exhibited a yield strength of 598 MPa, a tensile strength of 734 MPa, and a fracture elongation of 25.1 %. Such simultaneously enhanced strength and ductility are significantly above those of cast or previous powder-consolidated counterparts. During tensile deformation, a strain gradient is built up across the inhomogeneous grains and a high density of geometrically necessary dislocations was observed near the interfaces of matrix/oxide particles, both contributing to heterogeneous deformation-induced strengthening. This elevates the work hardening rate and consequently the tensile elongation. Quantitative analysis indicates that the dislocation build-up during forging makes the dominant contribution to the high yield strength of Ox-1150. The present study offers a new route to the preparation of heterogeneously structured ODS Fe-Cr-Al alloys and provides guidance for optimizing the mechanical properties of such alloys in terms of strength-ductility synergy.

Influence of Inhomogeneous Anisotropic Copper Grains in TSV on the Thermo-Mechanical Behaviors in the Annealing Process

Influence of Inhomogeneous Anisotropic Copper Grains in TSV on the Thermo-Mechanical Behaviors in the Annealing Process

Enhanced dielectric, magnetic and magnetoelectric properties in 0.5BaFe12O19 - xBaTiO3 - (0.5-x)CoFe2O4 composites

(0.5)BaFe12O19 - xBaTiO3 - (0.5-x)CoFe2O4; (x = 0.1, 0.2, 0.3 & 0.4) composite system was developed through conventional solid-state technique. XRD with Rietveld refinement confirmed pure tri-phasic composites with no impurity. The microstructure of samples has inhomogeneous grain packing with average size of grains ∼0.5 μm and typically decreased with BaTiO3 increment. The dielectric constant showed low-frequency dispersion and increased with BaTiO3 increment, hence maximum at 400 °C for composite x = 0.4 (∼2.8 × 103 at 1 kHz). Composites are ferrimagnetic in nature along with presence of firm exchange coupling among BaFe12O19/CoFe2O4 ferrite phases. The samples are multiferroic owing to typically high magnetoelectric coupling coefficient which increased with BaTiO3 increment, thus composite x = 0.4 attains highest value of 4.56 mV/cm.Oe on application of ac magnetic field (Hac = 45 Oe). The results indicate that the composites are suitable for magnetic field sensors and memory storage devices.

Combining crystal plasticity and phase field model for predicting texture evolution and the influence of nuclei clustering on recrystallization path kinetics in Ti-alloys

A three-dimensional computational framework has been developed combining a crystal plasticity (CP) and a phase-field (PF) approach that can efficiently simulate static recrystallization (SRX) and grain growth during the hot-forming in Ti-alloys. In the framework, the CP slip system parameters have been accurately calibrated by solving an inverse optimization problem from available experimental tension and compression stress–strain data through CP simulations performed via an orientation distribution function (ODF)-based computational model. Using the CP model, the evolution of inhomogeneous local deformation, deformed texture, and grain dislocation density have been simulated in the plastically deformed polycrystalline Ti-alloys. The PF model then predicts microstructure evolution and kinetics of SRX from CP-informed dislocation density during the annealing phase. Experimental information on microstructural heterogeneity in terms of the initial arrangement of nuclei distribution has been used to guide the development of the framework that can provide deeper insights into unique morphological evolution for various types of grain impingement as well as experimental validation of SRX kinetics. Finally, when the proposed model has been quantitatively validated through experimentally measured texture evolution and SRX path kinetics, excellent agreement is achieved. The current study highlights a systematic modeling framework that is capable of predicting crystallographic texture, microstructural evolution, and kinetics in the course of SRX for a clear understanding of the relationship between the mechanical properties, various microstructural descriptors, and thermo-mechanical process in the regime of material design.

The Sintering Aids Maintain Giant Strain in Lead‐Free NBT–ST Piezoceramics Sintered at 975 °C

The 0.74Na1/2Bi1/2TiO3–0.26SrTiO3 codoped with Li2CO3 and B2O3 is studied to develop the low‐temperature sintered lead‐free piezoceramic for multilayer applications. The studied piezoceramics are synthesized by a conventional solid‐state reaction method. Their crystal structures, microstructures, ferroelectrics, and strain properties are analyzed. Interestingly, the addition of Li2CO3 and B2O3 reduces the sintering temperature of the 0.74Na1/2Bi1/2TiO3–0.26SrTiO3 sample from 1175 to 975 °C. All samples show a pseudocubic perovskite structure with a dense microstructure and an inhomogeneous grain size distribution. The electric‐field‐induced polarization loops of the samples are saturated at 4 kV mm−1. More importantly, the 0.74Na1/2Bi1/2TiO3–0.26SrTiO3 + 1 wt%Li2CO3 + 1 wt%B2O3 sample sintered at 975 °C shows a Smax/Emax value of 510 pm/V under an applied electric field of 2 kV mm−1, which is promising for multilayer lead‐free piezoelectric actuator applications.

PREDICTION OF MICROSTRUCTURE EVOLUTION OF 316LN AUSTENITIC STAINLESS STEEL USING CELLULAR AUTOMATA AND A NOVEL EVALUATION METHOD FOR GRAIN SIZE INHOMOGENEITY

Inhomogeneous grain size is a significant structural defect in large forgings. This study employed cellular automata to simulate the dynamic recrystallization (DRX) of 316LN steel and analyzed the grain distribution during DRX. The accuracy of the CA method was verified by comparing its results with the results of a thermal simulation test on Gleeble 1500D. Subsequently, a novel method for evaluating grain size inhomogeneity was proposed. The grain size inhomogeneity coefficient Gu was introduced to determine the evolution of grain size inhomogeneity during DRX. This coefficient accurately and objectively reflects grain inhomogeneity. The impact of the initial and recrystallized grain size on the inhomogeneity during DRX was also analyzed.

BaSn0.96-XZr0.04MXO3 (M = Mn, Fe or Co, x = 0, 0.02) for spin-based devices: Ferromagnetic properties

In this study, Zr and/or Mn, Fe or Co ions were used to induce a robust room temperature ferromagnetic nature in perovskite BaSnO3 for high performance information applications. Dilute magnetic semiconductor compositions with formula of BaSn0.96-XZr0.04MXO3 (M = Mn, Fe, Co, x = 0, 0.02) have been synthesized at 1150 °C. For all compositions, mono-phase of cubic BaSnO3 structure with very small impurities of SnO2 were recorded based on X-ray diffraction analysis. The relation between ionic size of dopants and crystal dimension of BaSnO3 suggests the of Sn4+-site by Zr4+, Mn2+, Fe2+ or Co2+ ions. Extended absorption tails to visible light region were found for BaSn0.94Zr0.04Mn0.02O3 and BaSn0.94Zr0.04Co0.02O3 samples, owing to strong defect band transition absorption. Due to the addition of Zr and/or Mn, Fe or Co ions high refine of BaSnO3 morphology from inhomogeneous large grains to well distribute small one were seen. The XPS results of BaSn0.96Zr0.04O3 and BaSn0.94Zr0.04Co0.02O3 samples confirm that Ba, Sn, O and Zr are in the oxidation states of +II, +IV, −II and +IV/+III, respectively. Magnetically, incorporation of 4 wt% Zr4+ ions (empty 4d-orbital) induced a full-saturated spin ferromagnetic order with saturation magnetization of 1.16 emu/g, retentivity of 0.11 emu/g and coercivity of 147 Oe. Also, codoping by Zr/Co ions stimulates a full-saturated spin ferromagnetic order with saturation magnetization of 1.36 emu/g, retentivity of 0.17 emu/g and coercivity of 149 Oe. The empty 4d-Zr4+ ions have high ability in reversing the diamagnetic nature of BaSnO3 to ferromagnetic one through interaction with oxygen vacancies. The outer 4d-shell of Zr and 3d-orbital of Co with the oxygen vacancies induce the strong magnetic exchange interaction. Through looking into the previous studies on the magnetic properties of BaSnO3, the recorded saturation magnetization of 4 wt% Zr and 4 wt% Zr + 2 wt% Co ions are remarkable values.

Crystal Structure and Microwave Dielectric Property of xMgO-SiO2 (x = 1~2) System for 5G Applications

Mg2SiO4 and MgSiO3 ceramics with superior microwave dielectric properties are considered to be promising candidates for 5G applications. However, a slight deviation from the stoichiometric Mg/Si ratio will significantly influence their microwave dielectric properties, which will hinder their practical applications. In this work, the xMgO-SiO2 (x = 1~2) ceramics were synthesized by a solid-state reaction method. The influence of the Mg/Si ratio x on the crystalline phase, microstructure, and microwave dielectric properties was investigated through X-ray diffraction (XRD), a scanning electron microscope (SEM), and the resonant cavity method. The XRD patterns revealed the coexistence of Mg2SiO4 and MgSiO3 within the x range of 1~2, which was further demonstrated by the energy-dispersive X-ray spectra. The SEM images show a typical polycrystalline morphology of ceramics with an inhomogeneous grain size distribution. It is found that the microwave dielectric properties fluctuate at both sides of the x range while those remain relatively stable with minor changes at the intermediate components, indicating an obvious low composition dependence helpful for practical applications. Further, a demonstrator of a microstrip patch antenna for 5G applications using the 1.5MgO-SiO2 ceramic was designed and fabricated, and a return loss of −16.2 dB was demonstrated, which demonstrated the potential applications.

Evolution of microstructure and properties of AA 7072/7075/7072 composite sheets during various finish rolling temperature

In this present study, AA 7072/7075/7072 composite sheets with different finish rolling temperatures (210–350 °C) were prepared by the muti-pass hot finish rolling process. Effects of final rolling temperature on microstructure and properties of AA 7072/7075/7072 composite sheets were investigated after aging (AA 7075-T6 composite) via optical microscopy (OM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and transmission electron microscope (TEM). It was found that bendability of AA 7075-T6 composite alloy is highly dependent on finish rolling temperature. The results show that when increasing the finish rolling temperature, the tensile properties of 7075 hot rolled (7075-F) decreases, while tensile properties of 7075 annealed (7075-O) composites sheets increase. With excessive finish rolling temperature (280 °C and above), grain is not uniform along the thickness direction and texture was dominated by Goss texture. Bending test results show that break occurred for AA7075-T6 composite sheet when the finish rolling temperature was 280 °C and above. Texture and inhomogeneous coarse grain propagate formation of crack and degenerate bendability of the alloy.

Microstructural Inhomogeneity and Mechanical Properties of Ti–6.4Al–3.3Mo–1.6Zr–0.2Si Alloy Fabricated by Laser Metal Deposition

Laser metal deposition (LMD) additive manufacturing has gained growing interest in the aerospace industry. Herein, a Ti–6.4Al–3.3Mo–1.6Zr–0.2Si (TC11) titanium alloy is produced by LMD. The inhomogeneity of multiscale grain morphology and mechanical properties are systematically investigated. The results indicate that the melting pool (MP) morphology can be divided into three areas: melting pool center (MPC), melting pool boundary (MPB), and heat‐affected zone (HAZ), respectively. The widths of α laths in MPB are larger than that in HAZ and MPC, which result in a lower microhardness in MPB than that in MPC. Besides, the columnar grains are generally distributed along the deposition direction. The average widths of the α laths in the top and bottom MPC regions are about 0.58 and 0.67 μm, respectively. Correspondingly, the ultimate tensile strength and fracture elongation of the top and bottom samples are 1,053.5 MPa, 16.7%, and 1,011.5 MPa, 20.7%, respectively, which suggest the inhomogeneity of mechanical properties. The initiation fracture sites of both the top and bottom samples are presumed to be the α lath inside the MPB according to stress distribution analysis. The formation mechanisms of inhomogeneous grain structures and their influences on mechanical performance are also discussed.

Evaluation of residual stress reproducibility and orientation dependent fatigue crack growth in powder bed fusion stainless steel

The complex thermal gradients of additive manufacturing (AM) result in residual stress and distinctive grain morphologies that influence mechanical performance and contribute to concern regarding the fatigue properties of AM parts. In this study, residual stress, microstructure, and fatigue crack growth rate (FCGR) results were compared in AM Type 304L stainless steel produced by laser powder bed fusion (PBF) on different systems using similar process parameters. Residual stress measured in the build direction was remarkably consistent in all PBF builds. Backscatter electron large area images revealed similar grain morphologies in the different builds, all of which exhibited elongated grains in the build direction and inhomogeneous grain size and shape. Fatigue crack growth investigated both parallel and perpendicular to the build direction revealed higher measured crack growth rates in the near-threshold regime in both orientations of the PBF material compared to wrought material. The difference in near-threshold fatigue crack growth rates is attributed primarily to the influence of processing-induced residual stress quantified by the residual stress intensity factor. These values revealed consistent FCGR effects in each orientation across specimens extracted from different builds and were then used to reveal a convergence of the corrected FCGR data of all PBF and wrought specimens.

Heterogenous structure and formation mechanism of white and brown etching layers in bainitic rail steel

The failures of conventional pearlitic rail steels are strongly affected by the formation of hard and brittle white and brown etching layers (WEL and BEL, respectively) on the rail raceway during service. Bainitic rail steels with an excellent strength–toughness balance are promising candidates for next generation rail steels. It is generally difficult to generate hard and brittle WEL/BEL in bainitic rails because of the low carbon content. This study reports, for the first time, the formation of a unique multilayer heterostructured WEL/BEL in a field-tested bainitic rail. The heterogenous structures of WEL/BEL were characterized using transmission electron microcopy, focused ion beam, energy-dispersive X-ray spectroscopy, electron energy loss spectroscopy, electron probe microanalysis, atom probe tomography, and nano-indentation techniques. Results demonstrate that WEL is mainly composed of fine-grained martensite or ferrite and retained austenite, whereas BEL is a composite structure containing nanocrystalline martensite or ferrite, retained austenite, cementite, and oxide or O-rich particles. The oxide or O-rich particles are primarily formed within BEL through local oxidation, resulting in secondary partitioning of the alloying elements between the oxidation product and its surrounding matrix. BEL is hard but brittle due to the formation of brittle twinned martensite, cementite, and oxide particles, whereas the adjacent WEL is relatively soft and ductile. Based on these findings, the heterostructured WEL/BEL formation mechanism is preliminarily discussed in terms of inhomogeneous grain refinement, localized oxidation, chemical alterations (including both chemical segregation in the initial microstructure and secondary partitioning of the alloying elements during local oxidation), and phase transformation.

Heterogeneous bimodal microstructure and its formation mechanism of Mg-Gd-Y-Zn-Zr alloy during isothermal compression

Heterogeneous bimodal microstructure and its formation mechanism of Mg-Gd-Y-Zn-Zr alloy during isothermal compression at 450 °C and 0.001 s−1 was investigated in detail. Based on microstructure analysis, Mg-Gd-Y-Zn-Zr alloys with bimodal grain size distribution and bimodal texture distribution were obtained by uniaxial isothermal compression. There were more heavily bimodal levels in grain size and texture at true strain greater than 0.8. There was a significant inhomogeneous plastic deformation between and within the grains in Mg-Gd-Y-Zn-Zr alloy during the deformation, which is attributed to the difference the grain orientation and a large number of intergranular block-shaped LPSO phases. Further studies revealed that particle-stimulated nucleation (PSN) caused by a large intergranular LPSO phases and continuous dynamic recrystallization (CDRX) developed layer by layer toward the grain interior were the main grain refinement mechanisms. This PSN and CDRX mechanism contributed to the fine grains in bimodal grain size distribution and the random texture in bimodal texture distribution. However, the original coarse grains with basal orientation were preserved during deformation due to smaller plastic deformation and energy storage. Meanwhile, grain boundary segregation and intragranular lamellar LPSO precipitate promoted CDRX by retarding DDRX. In addition, the grain boundary pinning effect dominated by grain boundary segregation and intragranular lamellar LPSO precipitate hindered the coarsening of fine DRXed grains, which was the ultimate guarantee for the formation of bimodal microstructure. Ultimately, inhomogeneous plastic deformation, DRX, and grain boundary pinning effect were demonstrated as the necessary conditions for the formation of heterogeneous bimodal microstructure during thermal deformation of Mg-Gd-Y-Zn-Zr alloy.

Electrochemical dissolution behavior of phosphorus and boron doped Inconel 718 alloy in NaNO3 solution

As a promising material for the blisk of high-pressure compressors in aeroengines, modified Inconel 718 (IN718) alloy with phosphorus and boron additions is a new derivative of IN718 with higher temperature capabilities. Herein, electrochemical tests and electrochemical machining (ECM) experiments of the modified IN718 alloy in NaNO3 solution were conducted to investigate the electrochemical dissolution behavior. Microstructure and microtexture analysis revealed that modified IN718 fabricated by forging mainly comprises γ phase, carbide, and δ phase, and its grain size distribution is uneven. Furthermore, the anodic behavior of the modified IN718 alloy in NaNO3 solution was investigated by the polarization curve and electrochemical impedance spectroscopy. The results show that an uneven passivation film forms on the surface of modified IN718 due to the inhomogeneous grain size, which reduces the corrosion resistance. Then, ECM experiments at different corrosion times (1 s, 3 s,5 s, 7 s) and current densities (50 A/cm2, 100 A/cm2, 130 A/cm2, 160 A/cm2) were conducted. The results show that the δ phase existed like a needle-plate and the machined surface quality was poor. The corrosion resistance of the fine grains and δ phase was better than that of the coarse grains, which is the main factor influencing the surface quality. Finally, dissolution models were proposed to characterize the dissolution behavior of modified IN718 in NaNO3 solution.

In-situ surface study of the mechanism of high temperature deformation in an Al-Cu-Li alloy

The 2195 Al-Cu-Li alloy is able to obtain an elongation of 203% by high temperature stretching. The microstructure evolution and deformation mechanism of non-recrystallized Al-Cu-Li alloy after high temperature stretching were studied. The results show that the inhomogeneous grain structure is the main factor affecting the elongation. High resolution surface studies with focus ion beam show that intragranular dislocation slip provides up to 57% of the total strain and grain boundary sliding plays an accommodating role.

Developing methods of constrained groove pressing technique: A review

Among various severe plastic deformation (SPD) techniques, constrained groove pressing (CGP) has arisen as a famous technique for fabricating ultrafine-grained sheet metals and alloys in recent times. The severe strain is applied to improve the mechanical performance and properties. However, inhomogeneous grain refinement, lower formability, surface unevenness, and microcracks are the common limitations of conventional CGP-processed samples. Therefore, this review inspects the latest progress through modifications of the CGP process and compares the process efficacy with the conventional process. Advanced CGP processing techniques, such as modification of die design, annealing of the processed sample, cross CGP, ring CGP, hybrid SPD, covered sheet casing CGP, and rubber pad CGP, are emerging techniques to up-scale the procedure and improve the grain refinement and thereby produce superior mechanical properties. In this review paper, the historic research of conventional CGP and its effect on grain refinement and mechanical properties is initially briefed and then recent progress through different advanced techniques is highlighted, especially in alloys. Albeit significant progress has been observed in CGP, the future scope and successful usage of CGP-processed samples in actual practice are discussed in the last stage.

Analytical modelling of heat accumulation in laser based additive manufacturing processes of metals

The flexibility of additive manufacturing processes results from the principle of subsequently adding small amounts of material in individual layers or beads on top of each other. The periodic input of energy required to melt the material can lead to an accumulation of heat, which increases the temperature of the part and changes the local temperature distribution in the melt pool. This heat accumulation results in local shape deviations of the part and can lead to inhomogeneous solidification conditions coinciding with inhomogeneous grain structures and potentially inhomogeneous mechanical properties or build failures. To produce high quality parts with homogeneous properties and to reduce unproductive dwell times, a comprehensive knowledge of the heat accumulation phenomena is required. The present work considers an explicit analytical description of the heat accumulation effect, which allows for a mathematical analysis of the influence of all contributing process parameters on the temperature increase of the part. The analytical equations were derived from simplified heat conduction equations and validated by comparison with temperature measurements from literature. The calculated temperature increase shows a good agreement with measurements observed during additive manufacturing of different materials and alloys in case of cladding or building volumes with direct energy deposition (DED) and laser powder bed fusion (LPBF). Finally, the obtained analytical solution is used to derive optimization strategies aiming to reduce heat accumulation while simultaneously increasing productivity. • Analytical equations for the prediction of the temperature increase. • Analytical description of the heat accumulation in cladding and volume building with DED and LPBF • Validation for titanium-, inconel-, steel-, and aluminum-alloys • Identification of conditions that lead to a convergence of heat accumulation • Mathematical identification of the key factors, which influence heat accumulation. • Derivation of optimization strategies to increase productivity

Plasticity enhancement mechanism: Effect of the annealing temperature on strain-induced segmented martensitic transformations and Portevin–Le Chatelier bands in 7Mn steel after deep cryogenic treatment

This study investigated the microstructural evolution and strain localization of warm deformed Fe-0.15C-7Mn steel after deep cryogenic treatment (DCT) and intercritical annealing (IA) at 600, 630, and 660 °C. After DCT and IA, the steel contained nanoscale austenite grains with inhomogeneous thermal stability and grain size. Lüders bands appeared in all the samples, whereas the Portevin–Le Chatelier (PLC) effect only occurred in the samples annealed at 630 and 660 °C. The occurrence and initiation position of the PLC bands depended on the IA temperature, which affected the final grain size, retained austenite (RA) stability, and interactions between the solute atoms/C-Mn pairs and mobile dislocations. This indicates that segmented martensitic transformations occurred in the samples annealed at 600 and 630 °C, and the transformation sequence γ → ε → α’ occurred in the samples annealed at 630 and 660 °C. The segmented martensitic transformation depended on the IA temperature, which directly affected the amplitude of fluctuations in the Mn concentration in the RA grains and resulted in the heterogeneous thermal stability of the RA. The excellent uniaxial tensile properties of the samples were ascribed to the transformation of RA with heterogeneous thermal stability to segmented martensite during deformation. The segmented martensite acted as a protective shell that shielded the encapsulated austenite in the core. • Microstructural evolution and strain localization of a medium Mn steel were studied. • The annealing temperature affects the PLC bands and microstructural evolution. • Relationship between heterogeneous stability of RA and martensitic transformations. • Mechanisms underlying the observed physical properties were investigated. • Segmented martensite transformation behavior occurs and plays a protective role in the encapsulated austenite.