Massive Phase Transformation Research Articles

Effects of hatch spacing on densification, microstructural and mechanical properties of β-solidifying γ-TiAl alloy fabricated by laser powder bed fusion

β-solidifying γ‑titanium aluminide (γ-TiAl) alloys, which typically contain β-phase stabilizers such as Nb and Cr, hold great promise for the aerospace industry and can potentially be processed through additive manufacturing to realize performance unachievable using conventional methods. However, the effects of laser powder bed fusion (L-PBF) parameters on the characteristics of the thus obtained samples remain underexplored. To address this gap, we herein examined the effects of hatch spacing on the densification, microstructural, and mechanical properties of L-PBF-fabricated Ti-44Al-6Nb-1.2Cr (at.%) alloy samples, revealing that the strong influence on thermal history induced the variation in densification and formation of two microstructure types. 0.01 mm hatch spacing resulted in repetitive slow cooling and sufficiently remelting, thus suppressing crack formation, promoting high densification, and inducing a complex phase transformation involving the formation of a basket-weave-structured α2 phase and the 〈001〉 alignment of the β phase along the build direction. 0.06 mm hatch spacing resulted in rapid cooling and insufficient heat accumulation, favoring the massive phase transformation, a jagged morphology α2 phase with a randomly distributed crystallographic texture. Hardness was mainly correlated with phase constitution and volume fraction, whereas compressive properties were jointly determined by additional effects of multiple factors such as grain size and crystallographic texture. This work provides the fundamental insights required to suppress defect formation in β-solidifying γ-TiAl alloys and tailor their microstructure for mechanical property enhancement.

The Effect of Heat Treatment on the Microstructure and Mechanical Properties of Powder Metallurgy Ti-48Al Alloy

Heat treatment is the critical step in achieving a refined microstructure and enhanced mechanical properties of TiAl-based alloys. This study investigated the influence of heat treatment temperature, cooling method, and heat treatment time on the microstructure and mechanical properties of an extruded powder metallurgy Ti-48Al alloy, and achieved the control of fully lamellar fine microstructures and the enhancement of performance through a simple heat treatment, rather than the traditional approach of homogenization followed by heat treatment. The results indicate that the heat treatment temperature determines the type of microstructure, while the cooling rate dictates the lamellar width. As the heat treatment temperature was increased from the two-phase region to the α single-phase region, the microstructure transitioned from duplex to near lamellar, and the alloy strength initially increased and then decreased, influenced by both the lamellar colony ratio and grain size. A rapid cooling rate (water quenching) induces a non-diffusive massive phase transformation, whereas a slow cooling rate (air cooling) gradually forms α2/γ lamellar colonies. Therefore, a suitable heat treatment regime for the powder metallurgy Ti-48Al alloy was determined to be 1340 °C/5 min/air cooling. The microstructure of the alloy was near lamellar, consisting of lamellar colonies approximately 50 μm and a small number of γ equiaxed grains of about 10 μm. Subsequently, the alloy exhibited a room temperature tensile strength of 784 MPa and a yield strength of 763 MPa, representing improvements of 17.0% and 38.7% over the extruded alloy, respectively. This research provides a reference for establishing a heat treatment process for powder metallurgy TiAl alloys.

Extensive phase transformation in an equiatomic CrCoNi medium entropy alloy under extreme uniaxial tension

The dynamic tension behavior of an equiatomic CrCoNi medium entropy alloy (MEA) has been studied at both room temperature (RT, 298 K) and liquid nitrogen temperature (LNT, 77 K). Microstructural observations show that extensive phase transformations were activated in this alloy under dynamic tension at LNT instead of the activation of the deformation twins under high strain rate only or quasi-static loading at LNT. The appearance of massive nanoscale phase transformation bands along multiple slip directions even created a network structure of HCP lamellae in the FCC grains. This leads to defect accumulation at the intersection regions and results in the formation of new HCP variants, inverse phase transformations to FCC structure and even amorphous domains. Such transformation induced plasticity (TRIP) effects including the mutual interactions of crossover phase transformation bands on the plasticity and tension fracture of the MEA under extreme loading conditions were further discussed. These findings provide a deeper understanding of the deformation mechanisms in the equiatomic MEA under extreme loads.

Massive transformation in dual-laser powder bed fusion of Ti6Al4V alloys

In the present investigation, we fabricated additively manufactured Ti6Al4V parts using dual laser-powder bed fusion (DL-PBF) and identified the occurrence of a massive transformation. A detailed and systematic study of the massive transformation in the DL-PBF process by changing the energy and time offset of the lag laser beam and its effect on the microstructural and mechanical properties was undertaken. A mixture of martensite and massive phases was observed within the prior β grains in DL-PBF, and the dimensions of these massive grains increased with an increase in the lag laser beam energy, while acicular α′ martensite was present in the single Laser-PBF. The massive phase showed a featureless patch-shaped region, which consisted of thin laths, and they were associated with the prior β grain boundaries. The irregular patch-shaped regions showed inferior Vickers hardness when compared with acicular α′ martensite, and the ultimate tensile strength was lower in the DL-PBF than in the single Laser-PBF. The columnar prior-β grain was present in all the samples (both in the single- and dual-beam laser) and the dimensions of the grains varied with increasing the lag laser beam energy. These present results showed that the DL-PBF process significantly influenced the microstructural and mechanical properties of the Ti6Al4V materials, and provided a deep insight into massive phase transformation in AM titanium alloys and its effect on the mechanical properties.

Effects of posttreatment on the metal-ceramic bond properties of selective-laser-melted Co-Cr dental alloy—Part 2: Heat treatment after porcelain firing

Statement of problemThe selective laser melting (SLM) technique has been a promising method of fabricating Co-Cr metal-ceramic restorations; however, the lower metal-ceramic bond properties of SLM Co-Cr restorations have become a major issue in clinical use. PurposeThe purpose of this in vitro study was to propose and verify a method of improving the metal-ceramic bond properties of SLM Co-Cr alloy with heat treatment after porcelain firing (PH). Material and methodsForty-eight (25×3×0.5 mm) Co-Cr specimens, divided into 6 groups (Control group [CG]; 550 °C; 650 °C; 750 °C; 850 °C; 950 °C) according to PH temperatures, were prepared by using SLM techniques. The 3-point bend tests were performed to evaluate the metal-ceramic bond strengths; subsequently, the fracture feature was assessed by using a digital camera and scanning electron microscope (SEM) coupled with an energy-dispersive X-ray spectroscopy (EDS) detector, to determine the area fraction of adherence porcelain (AFAP). The interface morphologies and element distribution were determined with SEM/EDS detectors. Phase identification and quantification were examined with an X-ray diffractometer (XRD). A 1-way ANOVA and the Tukey honestly significant difference tests were used to analyze bond strengths and AFAP values (α=.05). ResultsThe bond strengths were 35.33 ±1.25 MPa for the CG group, 34.53 ±3.20 MPa for the 550 °C group, 38.20 ±2.60 MPa for the 650 °C group, 42.85 ±2.31 MPa for the 750 °C group, 33.28 ±3.85 MPa for the 850 °C group, and 29.09 ±2.86 MPa for the 950 °C group. Significant differences were not observed among the CG, 550 °C, and 850 °C groups (P>.05) but were found among the other groups (P<.05). Fracture and AFAP results displayed a mixed fracture mode of adhesive and cohesive fracture. The thicknesses of native oxide films across the 6 groups were relatively close as the temperature increased, but the thickness of the diffusion layer increased as well. Excessive oxidation and massive phase transformation caused holes and microcracks to appear in the 850 °C and 950 °C groups, reducing bond strengths. XRD analysis evidenced that the phase transformation of γ→ε occurred at the interface during PH treating. ConclusionsPH treatment significantly affected the metal-ceramic bond properties of SLM Co-Cr porcelain specimens. The 750 °C-PH-treated specimens displayed higher mean bond strengths and improved fracture characteristics among the 6 groups.

Investigation of a Ni-38Mo binary alloy fabrication by mechanical alloying and spark plasma sintering

The present work investigated a Ni-38Mo binary alloy with a specific interest in Ni solid solution and Ni-Mo intermetallic phases. To this end, a homogeneous Ni-Mo alloy powder obtained via mechanical alloying was consolidated by spark plasma sintering (SPS). The main constitutive phases post-SPS were a Ni(Mo) solid solution and the δ-NiMo intermetallic phase. Subsequent heat treatment at 1200 °C caused an increase in microhardness to 985 HV, while an additional aging process at lower temperatures caused a softening effect associated with the presence of β-Ni4Mo. Microstructural observation suggested that heat treatment at 1200 °C was responsible for the promotion of δ-NiMo in favor of mechanical properties and the stability of such intermetallic phase, which prevented massive phase transformation in subsequent heating. Thus, the present work may lay the groundwork for a multipurpose Ni-Mo alloy having attractive structural and functional properties.

Phase transformation mechanisms, microstructural characteristics and mechanical performances of an additively manufactured Ti-6Al-4V alloy under dual-stage heat treatment

Understanding phase transformation behaviors and microstructural evolutions during optimized post-heat treatments is essential for tuning the mechanical performances of additively manufactured titanium alloys. In this work, distinctive dual-stage heat treatments were proposed for improving the microstructure and properties of the laser powder bed fusion processed Ti-6Al-4V alloy. The effects of the heat treatments on phase transformation behaviors, microstructural characteristics, mechanical and tribological properties of the alloy were investigated systematically. The dual-stage heat treatments combined with salt bath quenching proved to be an effective approach for obtaining fine lamellar α/β microstructures through the introduction of martensitic and massive phase transformations, as well as achieving optimized strength and ductility. The grain boundary populations of the alloy were strongly influenced by the phase transformation behaviors. Moreover, high-density dislocations were introduced during the dual-stage heat treatments, and the <a> type dislocations were dominant. The nonadditive strengthening mixture rule between obstacles and dislocations was substantiated in this alloy. Different wear mechanisms were found in the dual-stage heat-treated alloys depending on their microstructural characteristics. Furthermore, the underlying mechanisms of phase transformation, strengthening and toughening are also discussed.

Effects of oxygen addition on the microstructure, phase transformations, and oxidation resistance of TiAl alloys

This study investigated the effects of oxygen addition on the microstructure, phase transformations, and oxidation resistance of TiAl alloys at 1023 K. The addition of oxygen stabilized the α (α2) phase at the expense of the γ phase and reduced the oxidation mass gains of the TiAl alloys by more than 20%. Oxide scales composed of external scattered Ti-rich oxide particles/Al-rich/Ti-rich mixed Ti/Al oxides, and internal affected zones with Al-rich precipitates were observed in all oxidized samples. The results showed that the microstructure and phase transformations of the alloys were altered by adding 1 at% oxygen. The addition of O accelerated the α → α2 chemical ordering reaction and partly suppressed the α → γ massive phase transformation. The oxidation resistance of the TiAl alloys in air at 1023 K was not significantly affected by the addition of oxygen.

Intercalation‐assisted massive phase transformation: The key to SHS synthesis?

AbstractSelf‐propagating high‐temperature synthesis (SHS) is the term used for a spontaneous, irreversible combustion of initial reagents when ignited. There is limited knowledge of the mechanistics of this versatile materials synthesis process for Chevrel phase compounds (CPCs), which limits its applicability. In this report, the successful and rapid processing of three classes of sulfide CPCs via SHS is demonstrated, and a mechanism is provided to explain rapid transformation rates and nanostructured products that are fully transformed. Cu4Mo6S8, Ni2Mo6S8, and Fe2Mo6S8 compounds were synthesized, and thermochemical measurements revealed that an overall reaction temperature did not surpass the melting points of the reactants. The nature of the specific SHS process is argued here to involve an intercalation‐assisted massive phase transformation facilitated by the use of an MoS2 precursor.

Quasi-in-situ investigation on microstructure degradation of a fully lamellar TiAl alloy during creep

Microstructure degradation of a fully lamellar TNM alloy during creep has been investigated by using the quasi-in-situ creep tests, which were conducted at 750 °C under 250 MPa, for (1–5.4) % creep strain. The results indicated that the fully lamellar structure exhibited gradual microstructure degradation during creep. At the primary creep region, dynamic recrystallization of the γ phase occurred at the colony boundary and a massive proportion phase transformation occurred, these caused microstructure instability and a relatively large primary strain. Within the steady-state creep region, the steady creep strain rate was 8.89E-8 s−1. The fine (α2+γ) clusters with more interface provided obstacles for the dislocation movement because of α2 parallel decomposition. Moreover, the interfacial β0 phase precipitation was suppressed the α2 → γ transformation and remained the integrity and continuity of the lamellae structure, which was attributed to the steady-state creep resistance. At the tertiary creep region, many cavities nucleated at the colony boundary or γg/β0 phase boundaries due to the local stress concentration. The dynamic recrystallized of the γg area was extended and damaged the integrity of the fully lamellar structure. Moreover, the partial dissolution of α2 lamellae caused discontinuous lamellae and reduced the creep resistance. It concluded that microstructure stability has a strong influence on creep resistance.

Massive transformation in FeNi nanopowders with nanotwin-assisted nitridation

L10-ordered FeNi alloy (tetrataenite), a promising candidate for rare-earth-free and low-cost permanent magnet applications, is attracting increasing attention from academic and industrial communities. Highly ordered single-phase L10-FeNi is difficult to synthesis efficiently because of its low chemical order–disorder transition temperature (200–320 °C). A non-equilibrium synthetic route utilizing a nitrogen topotactic reaction has been considered a valid approach, although the phase transformation mechanism is currently unknown. Herein, we investigated the basis of this reaction, namely the formation mechanism of the tetragonal FeNiN precursor phase during the nitridation of FeNi nanopowders. Detailed microstructure analysis revealed that the FeNiN precursor phase could preferentially nucleate at the nanotwinned region during nitridation and subsequently grow following a massive transformation, with high-index irrational orientation relationships and ledgewise growth motion detected at the migrating phase interface. This is the first report of a massive phase transformation detected in an Fe–Ni–N system and provides new insights into the phase transformation during the nitriding process. This work is expected to promote the synthetic optimization of fully ordered FeNi alloys for various magnetic applications.

Microstructure evolution and tensile property of TiAl alloy using continuous direct energy deposition technique

Attributing to the fast solidification and thermal cycling during additive manufacturing process, massive phase transformation could take place thus leading to the formation of unpredictable microstructures with large variation in mechanical properties. In this paper, a continuous direct energy deposition technique (CDED) is adopted to prepare TiAl alloy seceding from the thermal cycling, and the evolution of microstructure, microhardness and tensile properties of alloy are investigated. Results indicate that the microstructure of alloy composes of columnar grains with very fine (α2 +γ) lamellae, and no heat-affect band is observed. A heat transfer model is established to assist in explaining the solid-phase transformation and microstructure formation mechanism of TiAl alloy. Furthermore, a special duplex γ microstructure (DP γ) forms which composes of massive γ phase surrounded by feathery-like γ phase. By dissecting crystallographic orientation from EBSD results, the formation mechanism of DP γ is clarified as the result of sequential solid-state phase transition in (α + γ) phase region, in which the feathery-like microstructure forms firstly followed by the massive γ phases nucleating at the inter-phase boundaries of feathery-like γ. Tensile property of as-deposited alloy reveals of 535 MPa with 1% elongation, and the highest hardness of around 320HV is detected at the top region of alloy with the finest interlamellar spacing.

Tuning of structure, grain orientation and mechanical properties in reactively sputtered (Al,Mo,Ta,V,W)N

(Al,Mo,Ta,V,W)-N0.79, -N0.33, and -N0.88O0.12 coatings were sputtered in N2-rich, N2-lean, and N2+O2 containing atmospheres. The face-centered cubic structured coatings feature as-deposited hardness values of 32.3, 39.7, and 34.5 GPa, respectively. The (Al,Mo,Ta,V,W) N0.79 and (Al,Mo,Ta,V,W)N0.33 consist of highly oriented columns, plus some very large grains in the latter coating. During vacuum annealing at 800 °C for 30 h, the (Al,Mo,Ta,V,W)N0.79 loses N down to 25 at.%, while the (Al,Mo,Ta,V,W)N0.33 remains stable. Their alignment in chemical composition also caused an approach of their hardness values with 35.2 and 38.1 GPa, respectively. The (Al,Mo,Ta,V,W)N0.88O0.12 exhibits partly tilted and randomly oriented smaller columnar grains than the nitrides, and the hardness drops from 34.5 to only 14.1GPa when vacuum annealed due to massive phase-transformations toward individual oxides and the connected crack formation.

Characterization of AlSi10Mg-CP-Ti Metal/Metal Composite Materials Produced by Electro-Sinter-Forging

Metal–metal composites represent a particular class of materials showing innovative mechanical and electrical properties. Conventionally, such materials are produced by severely plastically deforming two ductile phases via rolling or extruding, swaging, and wire drawing. This study presents the feasibility of producing metal–metal composites via a capacitive discharge-assisted sintering process named electro-sinter-forging. Two different metal–metal composites with CP-Ti/AlSi10Mg ratios (20/80 and 80/20 vol.%) are evaluated, and the effects of the starting compositions on the microstructural and compositional properties of the materials are presented. Bi-phasic metal–metal composites constituted by isolated α-Ti and AlSi10Mg domains with a microhardness of 113 ± 13 HV0.025 for the Ti20-AlSi and 244 ± 35 HV0.025 for the Ti80-AlSi are produced. The effect of the applied current is crucial to obtain high theoretical density, but too high currents may result in Ti dissolution in the Ti80-AlSi composite. Massive phase transformations due to the formation of AlTiSi-based intermetallic compounds are observed through thermal analysis and confirmed by morphological and compositional observation. Finally, a possible explanation for the mechanisms regulating densification is proposed accounting for current and pressure synergistic effects.

Additive manufacturing of high-strength commercially pure titanium through lanthanum oxide addition

Preventing the formation of columnar grains and refining the microstructure in an effective way have been great challenges in additive manufacturing of titanium and its alloys. In this paper, the effect of La2O3 addition on the microstructure and mechanical properties of commercially pure titanium (CP-Ti) fabricated through selective laser melting (SLM) was comprehensively studied. Experimental results revealed that the microstructure of CP-Ti were composed of massive phase and fine parallel laths, whereas a homogenous microstructure with acicular colonies was obtained in CP-Ti + La2O3. Due to the increase of nucleation sites in SLM-fabricated CP-Ti + La2O3, the massive phase transformation was suppressed, and the average grain size was refined to 1.47 μm. The spherical La2O3 particles with the size of less than 50 nm were uniformly distributed within the αˊ matrix, containing high-density dislocations and twins. After grain refinement, the yield strength and ultimate tensile strength were enhanced up to 858 MPa and 940 MPa, respectively, with the elongation of 8.6%. The enhancement of mechanical properties was mainly attributed to the combined effects of grain refinement strengthening, dislocation strengthening and La2O3 dispersion strengthening.

Massive Phase Transformation as a New Prospective on Microstructural Design in a Titanium Alloy - A Review

Microstructural design is generally applied to improve the mechanical property of titanium alloy by introducing different phase transformations and thermomechanical treatments. Aside from the martensitic and diffusion transformation, the occurrence of massive transformation occurs in Ti alloy. Massive transformation is categorized as civilian phase transformation, which resulted in the change of crystal structure of an alloy with a given composition without changing the chemical composition of its initial phase. It happened when the body centered-cubic β phase changed into hexagonal closed-pack α phase without decomposing into α+β. Massive transformation involves a diffusion and growth mechanism in a short-range and generally occurs during the introduction of high cooling rates to restrict the full diffusion mechanism. Owing to the nature of a rapid cooling rate as a requirement for massive transformation, the massive phase is normally found together with the product of martensitic transformation. On the other hand, the product of massive transformation is observed as a blocky grain with a featureless characteristic using optical microscopy and. Phase identification using electron backscattered diffraction shows that the region of αm shows only the presence of the α phase. It was reported for containing a high dislocation density similar to martensitic transformation. Specifically, in Ti alloy, the higher magnification using scanning electron microscopy shows fine sub-lamellar morphology, which observed as a combination product morphology between martensitic and diffusion transformation. It resulted in the mechanical property of the massive phase is between those two morphologies. Hence, it brings a new perspective on designing the microstructure of Ti alloy, which can be used to improve the mechanical property of Ti alloy.

Cyclic plasticity of an interstitial high-entropy alloy: experiments, crystal plasticity modeling, and simulations

The development of high-entropy alloys (HEAs) comprising multiple principal components is an innovative design strategy for metallic materials from the perspective of thermodynamic entropy. However, despite their potential candidacy for engineering applications, the lack of research on the cyclic loading responses as well as constitutive modeling of the HEAs is a major constraint. Therefore, the present work focuses on the cyclic plasticity of a typical carbon-doped interstitial HEA (iHEA) with nominal composition Fe49.5Mn30Co10Cr10C0.5 (at.%). The results of stress-controlled cyclic tests with nonzero mean stress showed that the iHEA exhibits significant cyclic hardening and stress level–dependent ratcheting. Owing to its improved cyclic hardening, the saturated ratcheting strain rate of the iHEA is lower than that of conventional steels such as the 316L stainless steel. Furthermore, microscopic characterizations revealed that the cyclic deformations caused massive martensitic phase transformation and hierarchical structures in the iHEA. The experimental results were used to develop a physical mechanism-based crystal plasticity constitutive model that is capable of describing the cyclic plasticity of the iHEA, which was implemented into a finite element framework. The simulation results showed that the loading stress significantly affected the microstructural evolutions, leading to a stress level–dependent cyclic plasticity. Thus, this investigation provides a fundamental basis for fatigue tests and service life prediction/optimization of the iHEA in the future, which can promote its engineering applications.

Research on microstructure deformation mechanism of crack tip in titanium under tension along different orientations

ABSTRACTThe deformation process of titanium with an initial crack was simulated under uniaxial tension by the molecular dynamics method. The effect of [0001], and orientations on the microstructure deformation mechanisms at the crack tip was investigated using embedded atom method potentials. In the simulation, various deformation evidence were clearly observed, such as dislocation nucleation and movement, stacking faults formation, deformation twinning and phase transformation. The stress–strain curves showed that orientations had a greater influence on the plastic stage and less on the elastic stage. By applying uniaxial tension with a constant strain rate along different orientations, microstructure deformation at the crack tip was analysed. When loading along [0001] orientation, twinning was the main deformation mechanism and stacking fault occurred and expanded along slip system with the increase in strain. Applying uniaxial tension along orientation, an abnormal ‘secondary increase’ phenomenon was observed in the stress–strain curve. At the same time, dislocation loops appeared at the crack tip and they expanded, merged with the increase in strain. The massive phase transformation from HCP to BCC was observed in the model when loading along orientation, which was caused by multiple Shockley incomplete dislocations under the size limitation.

Phase transformation and enhanced coercivity in B-N-doped MnAl nanocrystalline bulk alloys prepared by high pressure torsion

High coercivity B-N-doped MnAl alloys were prepared by the traditional induction melting, high temperature homogenization, water-quenching, post-annealing, and severe plastic deformation process. The massive phase transformation of the ε→τ in the B-N-doped ε-MnAl occurs at the temperatures above 680 K and accomplishes at 760 K, both of which are slightly higher than those of the ε-MnAl without elemental doping. The Currie point of the B-N-doped τ-MnAl is measured to be 620 K, which is lower than that of the doping-free τ-MnAl. High-pressure torsion was employed to decrease the crystal size and increase the coercivity of samples. A coercivity up to 0.54 T was achieved in the B/N doped MnAl bulk sample after severe plastic deformation under 6 GPa. The aging processing on the severely deformed samples enhances the remanent magnetization significantly and decreases the coercivity slightly. Our work shows that the high-pressure torsion process is effective in developing coercivity in MnAl-based bulk magnet.

Atomic structures and migration mechanisms of interphase boundaries during body- to face-centered cubic phase transformations

Atomic structures and migration mechanisms of interphase boundaries have been of scientific interest for many years owing to their significance in the field of phase transformations. Though the interphase boundary structures can be deduced from crystallographic investigations, the detailed atomic structures and migration mechanisms of interphase boundaries during phase transformations are still poorly understood. In this study, a systematic study on atomic structures and migration mechanisms of interphase boundaries in a body-centered cubic (b.c.c.) to face-centered cubic (f.c.c.) massive transformation was carried out using the phase-field crystal model. Simulation results show that the f.c.c./b.c.c. interphase boundaries can be classified into faceted interphase boundaries and side surfaces. The faceted interphase boundaries are semi-coherent with a group of dislocations, leading to a ledge migration mechanism, while the side surfaces are incoherent and thus migrate in a continuous way. After a careful analysis of the simulated migration process of interphase boundaries at atomic scales, a detailed description of the ledge mechanism based on the motion and nucleation of interphase boundary dislocations is presented. The ledge-forming process is accompanied by the nucleation of new heterogeneous dislocations and motions of original dislocations, and thus the barrier of ledge formation comes from the hindrance of these two dislocation behaviors. Once the ledge is formed, the original dislocations continue to advance until the ledge height reaches 1/|Δg|, where Δg represents the difference in reciprocal lattice vectors between two phases. The new heterogeneous dislocation moves along the radial direction of the interphase boundary, resulting in ledge extension. The interface dislocation behaviors greatly affect the migration of the interphase boundary, leading to different migration kinetics of faceted interphase boundaries under the Kurdjumov–Sachs and the Nishiyama–Wasserman orientation relationships. This study revealed the mechanisms and kinetics of complex structure transition during a b.c.c.–f.c.c. massive phase transformation and can shed some light on the process of solid phase transformations.