Transmission Electron Backscatter Diffraction Research Articles

Epitaxial Metal Electrodeposition Controlled by Graphene Layer Thickness.

Control over material structure and morphology during electrodeposition is necessary for material synthesis and energy applications. One approach to guide crystallite formation is to take advantage of epitaxy on a current collector to facilitate crystallographic control. Single-layer graphene on metal foils can promote "remote epitaxy" during Cu and Zn electrodeposition, resulting in growth of metal that is crystallographically aligned to the substrate beneath graphene. However, the substrate-graphene-deposit interactions that allow for epitaxial electrodeposition are not well understood. Here, we investigate how different graphene layer thicknesses (monolayer, bilayer, trilayer, and graphite) influence the electrodeposition of Zn and Cu. Scanning transmission electron microscopy and electron backscatter diffraction are leveraged to understand metal morphology and structure, demonstrating that remote epitaxy occurs on mono- and bilayer graphene but not trilayer or thicker. Density functional theory (DFT) simulations reveal the spatial electronic interactions through thin graphene that promote remote epitaxy. This work advances our understanding of electrochemical remote epitaxy and provides strategies for improving control over electrodeposition.

Effects of twin-boundary precipitates on twin stability and yield strength of a Mg-Nd-Ag-Zr alloy

The effects of precipitates at {10 1‾ 2} twin boundaries on twin stability and yield strength of a Mg-Nd-Ag-Zr alloy are investigated by transmission electron microscopy and electron back-scattered diffraction. Twin-boundary precipitates are observed in the pre-deformed alloys after subsequent ageing treatments over a temperature range of 200–450 °C. Such twin-boundary precipitates significantly enhance the thermal stability of {10 1‾ 2} twins, which remain relatively stable even at 480 °C. The stress stability of {10 1‾ 2} twins is also improved due to the pinning effect of the twin-boundary precipitates, leading to a strengthening effect on the alloy. More twin boundaries can be introduced via pre-deformation at a much higher strain rate of 1000 s−1, and such dynamic pre-compression with subsequent ageing treatments is more effective in improving the yield strength due to the formation of more stable {10 1‾ 2} twin boundaries.

Microstructural and isotopic analysis of shocked monazite from the Hiawatha impact structure: development of porosity and its utility in dating impact craters

U–Pb geochronology of shocked monazite can be used to date hypervelocity impact events. Impact-induced recrystallisation and formation of mechanical twins in monazite have been shown to result in radiogenic Pb loss and thus constrain impact ages. However, little is known about the effect of porosity on the U–Pb system in shocked monazite. Here we investigate monazite in two impact melt rocks from the Hiawatha impact structure, Greenland by means of nano- and micrometre-scale techniques. Microstructural characterisation by scanning electron and transmission electron microscopy imaging and electron backscatter diffraction reveals shock recrystallisation, microtwins and the development of widespread micrometre- to nanometre-scale porosity. For the first time in shocked monazite, nanophases identified as cubic Pb, Pb3O4, and cerussite (PbCO3) were observed. We also find evidence for interaction with impact melt and fluids, with the formation of micrometre-scale melt-bearing channels, and the precipitation of the Pb-rich nanophases by dissolution–precipitation reactions involving pre-existing Pb-rich high-density clusters. To shed light on the response of monazite to shock metamorphism, high-spatial-resolution U–Pb dating by secondary ion mass spectrometry was completed. Recrystallised grains show the most advanced Pb loss, and together with porous grains yield concordia intercept ages within uncertainty of the previously established zircon U–Pb impact age attributed to the Hiawatha impact structure. Although porous grains alone yielded a less precise age, they are demonstrably useful in constraining impact ages. Observed relatively old apparent ages can be explained by significant retention of radiogenic lead in the form of widespread Pb nanophases. Lastly, we demonstrate that porous monazite is a valuable microtexture to search for when attempting to date poorly constrained impact structures, especially when shocked zircon or recrystallised monazite grains are not present.

Cold deformation behavior and microstructure evolution of biomedical Cu-containing L605 alloy

The effect of copper (Cu) addition on the microstructure evolution and deformation mechanism of L605 (Co-20Cr-15 W-10Ni) alloy during cold deformation was investigated by using transmission electron microscopy (TEM), X-Ray diffraction (XRD) and electron backscatter diffraction (EBSD) analysis. The results indicated that the addition of Cu slightly decreased the yield strength and ultimate tensile strength, while it significantly increased the elongation. EBSD results revealed that hexagonal close-packed (HCP) martensite was generated during cold deformation and increased with increasing cold deformation level. The deformation microstructure of both alloys at different cold deformation levels shows that the stacking faulting was the primary deformation mechanism at early stage of cold deformation, in contrast, dislocation planar-slip and face-centered cubic (FCC) to HCP martensitic transformation were prevailed at both medium and late cold deformation level. Cu addition significantly suppressed the dislocation and stacking fault multiplication at early deformation stage and delayed the martensitic transformation at medium and late deformation stage, which could be ascribed to the relatively high stacking faulting energy by Cu addition, resulting in the low strain hardening behavior in the entire deformation process. These cumulative results and analyses could provide a solid foundation for the further development of this novel type of biomedical Cu-containing cobalt-based alloy.

Stress relaxation mechanism and life evaluation of titanium alloy springs under long-term thermo-mechanical coupling conditions

The primary failure mode for helical compression springs under prolonged static thermo-mechanical coupling conditions is stress relaxation rather than fatigue failure. Unfortunately, for the investigation of spring failure modes, previous research has mainly focused on fatigue failure, while lacking exploration of the evolution of its microscopic mechanisms underlying stress relaxation and the resultant changes in mechanical properties. To elucidate the microstructure evolution mechanism of dual-phase titanium alloy springs exposed to long-term thermo-mechanical coupling conditions and to evaluate their life and reliability, a series of stress relaxation tests on Ti-6Al-4V titanium alloy springs were carried out. The degradation of mechanical properties in Ti-6Al–4V springs under various temperatures and compressive deformations was analyzed. Additionally, microscopic mechanisms were further examined using transmission electron microscopy (TEM) and electron backscattering diffraction techniques (EBSD). Based on these investigations, a stress-life model for Ti-6Al-4V springs was established through maximum likelihood estimation (MLE) and the Power-Exponential equation, followed by an evaluation of its reliability and life. The findings of this paper can provide engineering application guidance into the safe and reliable operation of dual-phase titanium alloy springs under thermo-mechanical coupling conditions.

Evolution mechanism of interfacial microstructure and regulation of mechanical properties of laser-arc hybrid weld-brazing aluminum/steel joints under different post-welding heat-treatment temperatures

Control of the interfacial microstructures and mechanical properties of aluminum/steel joints after welding is crucial to prolonging the service lives of such structures. In this study, the influence of post-welding heat treatment (PWHT) on aluminum/steel laser-arc weld-brazing joints was investigated, with particular focus on the evolution mechanisms of the interfacial microstructures and regulation of the mechanical properties. Transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) results confirmed the presence of the monoclinic Fe4Al13 and hexagonal Al8Fe2Si phases at the aluminum/steel interface. Upon increasing the heat-treatment temperature, micro-characteristics of the intermetallic compound (IMC) passed through three different stages (weak elemental diffusion–reaction–drastic change) depending on the temperature employed; these stages differed from the PWHT phenomenon observed for the aluminum/steel solid-state welded joints. EBSD analyses revealed decreases in the grain size and textural strength of the IMC layer following PWHT at 180 °C/1 h, while the Fe4Al13 phase gradually transformed into Al8Fe2Si phase during PWHT at 520 °C/1 h, ultimately leading to an increase in the grain size and a higher textural strength. Additionally, PWHT effectively eliminated the residual tensile stress in aluminum/steel joints and improved the softening of the heat-affected zone (HAZ). Upon PWHT at 180 °C/1 h, the synergistic effects of the elimination of residual stress, an enhanced softening in the HAZ, and changes in the IMC layer, led to improved joint properties. Furthermore, the maximum tensile strengths of the joints with and without reinforcement increased to 221.9 MPa (from 209.8 MPa) and 165.3 MPa (from 148.1 MPa), respectively.

Mechanical properties and microstructural evolution of 5052 aluminumalloys by multi-pass stretching and induced electro-pulsing treatment

A compound-forming method that combines multi-pass stretching and induced electro-pulsing treatment (IEPT) is proposed. The effects of induced current on the microstructure and mechanical properties of material were investigated using transmission electron microscopy and electron backscatter diffraction measurements. The samples stretched by 5% each time showed 145% increase in elongation after 4 stretching and IEPT cycles. The IEPT caused “stress drop” in pre-deformed sheets, while the plasticity increased. Meanwhile, the dislocation density decreased, the deformation structure changed to the substructure, and the grain size increased slightly. The material anisotropy was reduced and a new 《111》//TD texture appeared after IEPT. The combination of electrical effect and Joule heating enhanced dislocation mobility and vacancy movement. The temperature distribution, with a maximum temperature reaching 144.7 °C, was simulated using ANSYS software. The theoretical calculation results were consistent with experimental data.

Micro-crystallographically revealing the plasticity-evolved behaviors of thick Ti–6Al–4V laser-arc hybrid welded joint

Revealing the plasticity-evolved behaviors is of great significance for developing high-reliability thick Ti–6Al–4V welded joint for deep-sea exploration equipment. This research effort entailed a collaborative utilization of transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) techniques to reveal the evolution behaviors of microstructure, weld texture, and grain boundaries for thick Ti–6Al–4V laser-arc hybrid welded joint with thickness of up to 40 mm. The discerned outcomes of this study underscored that the mixture strategy of large-sized lath martensite, densely entangled dislocations, and dislocations pile up at grain boundaries in distinct welding layers significantly enlarged the inhomogeneous plasticity of thick Ti–6Al–4V welded joint. Besides, the intensified cylindrical-texture within the weld leads to a substantial augmentation in the occurrence of Schmidt Factor concentrations above 0.3, indicative of a larger fraction of grains assuming a soft-orientation. Furthermore, the investigation unveiled an increase in the proportion of low angle grain boundaries demonstrably augmented the distribution density of geometrically necessary dislocations (GNDs) within the welds, which in conjunction with the enhanced cylindrical texture substantially elevated the grains deformability, consequently reinforcing the plasticity of welded joint. This work has provided insights into the evolution behavior of thick Ti–6Al–4V welded joint for greatly improving the plastic properties of welded structure, and substantially enhancing the service safety for deep-sea exploration equipment.

Effect of CaO Content and Annealing Treatment on the Room-Temperature Mechanical Properties of AZ61 and AZ61-CaO Alloys

In the present study, the effect of annealing treatment on the room-temperature mechanical performance of AZ61, AZ61-0.5CaO and AZ61-1CaO was thoroughly investigated. The as-rolled samples were annealed at 400 °C for 1 h followed by furnace cooling. Microstructural characterization was carried out using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron back-scattered diffraction (EBSD). Moreover, room-temperature uniaxial tensile tests were carried out on the non-annealed and annealed samples along the rolling direction at the strain rate of 10−3 s−1. Microstructural analysis showed the presence of profuse {101¯2} twinning in non-annealed samples and the twinning fraction was increased by the addition of CaO content. SEM showed the formation of precipitates in the AZ61-CaO alloys and TEM confirmed the precipitates to be (Mg, Al)2Ca. The room-temperature tensile tests showed that the mechanical properties of AZ61 were slightly reduced by the addition of CaO, which was attributed to the higher local stress concentration due to the twin–twin interactions. Furthermore, the annealing treatment led to significant enhancement in the YS and UTS of AZ61-1CaO, which is related to the precipitation hardening induced by the intermetallic precipitates.

The effects of high temperature thermal treatments on β-Ga2O3 films grown on c-sapphire by low-pressure CVD

As a simple and effective method for improving the crystalline quality of epitaxial Ga2O3 film, post-thermal treatment has been identified as a competitive process involving crystal reconstruction accompanied by defect formation. In this study, β-Ga2O3 films grown on a c-sapphire substrate using low-pressure chemical vapor deposition were subjected to thermal treatment at 1000 °C in air for various duration to investigate the effects of treatment time on the films. The full width at half maximum (FWHM) of x-ray rocking curves initially decreased from 1.62° to 0.98° with increasing treatment time up to 5 h, indicating improved crystallinity. This improvement is likely a result of the reduced angle between Ga2O3 grains and the reconstructed Ga2O3 lattice, oriented towards the (−201) plane due to the thermal treatment, as observed in the transmission electron microscope and electron back-scattering diffraction results. However, under 7 h of treatment, the crystallinity of Ga2O3 degraded, as evidenced by an increased FWHM, as well as by x-ray photoelectron spectroscopy, photoluminescence, and time-of-flight secondary ion mass spectrometry results. This degradation can be attributed to the presence of massive oxygen vacancies and the substitutional incorporation of nitrogen into oxygen sites (NO), resulting in defects.

Microstructure and mechanical properties of AA5052 after electromagnetic hydraulic forming

Hydroforming (HF) is a traditional sheet metal forming method with high forming efficiency and reliability. However, under HF, the material at room temperature is easy to crack due to the low strain rate. Electromagnetic hydraulic forming (EMHF) is a high-speed forming process, which can significantly improve the forming limit of materials. Nevertheless, there is a lack of research on the performance and microstructure of parts deformed under EMHF. In this paper, AA5052 sheets are formed into flat bottom parts under the HF and EMHF processes. The tensile properties and hardness of the deformed parts are tested. The yield strength and tensile strength of the EMHF samples were higher by 7.5% and 9.0%, respectively, compared to those of the HF samples. Transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) showed that the EMHF samples had higher internal dislocation density, smaller grain size, higher proportion of small-angle grain boundaries, and higher texture intensity compared to those of the HF samples. This corresponds to the higher strength and hardness observations. Finite element models of the EMHF and HF configurations were developed. The deformation velocity of the EMHF sample exceeded 200 m/s and the strain rate exceeded 600 s−1, while the maximum local liquid pressure reached 211 MPa. The comparison of the thickness distribution obtained by simulation and experimentally indicated that the simulation results were in good agreement with the experimental ones. Moreover, the reasons for the improvement of strength and hardness are discussed, and the strength evolution mechanism is elaborated.

Ascertaining the microstructural evolution and strengthening mechanisms of the gradient nanostructured pure titanium fabricated by ultrasonic surface rolling process

This work utilized the ultrasonic surface rolling process (USRP) to construct a gradient nanostructured (GNS) layer in pure titanium. The microstructural characterization at different depths was conducted using a transmission electron microscope (TEM) and electron backscatter diffraction (EBSD) to elucidate the grain refinement mechanisms. Results showed that the {10−12} extension twins (ETs) and {11−22} compression twins (CTs) and their intersections accommodate the strain at the early deformation stage. As the strain increased, the dense dislocation walls (DDWs) and dislocation cells (DCs) gradually evolved into laminated structures with low-angle grain boundaries (LAGBs). Compared to conventional severe plastic deformation (SPD) technology, the LAGB-dominated grain refinement mechanism delays the onset of the transformation process from LAGBs to high-angle grain boundaries (HAGBs). With the coaction of discontinuous dynamic recrystallization (dDRX) and amorphization, the grains are extremely refined to 11.7 nm. Tensile test results suggested that a considerable strength-ductility synergy is achieved. The enhanced strength was attributed to grain size, dislocation, and synergetic strengthening mechanisms, accounting for 55.5 %, 20.7 %, and 23.8 %, respectively. This work deepens the current understanding of the formation mechanism of the GNS layer in pure titanium processed by USRP and the relationship between microstructure and mechanical properties.

Hot Deformation Behavior of Hastelloy C276 Alloy: Microstructural Variation and Constitutive Models.

Isothermal deformation experiments of the Hastelloy C276 alloy were executed using the Gleeble-3500 hot simulator at a temperature range of 1000-1150 °C and a strain rate range of 0.01-10 s-1. Microstructural evolution mechanisms were analyzed via transmission electron microscope (TEM) and electron backscatter diffraction (EBSD). Results reveal that the influences of hot compression parameters on the microstructure variation features and flow behaviors of the Hastelloy C276 alloy were significant. The intense strain hardening (SH) effects caused by the accumulation of substructures were promoted when the strain rates were increased, and true stresses exhibited a notable increasing tendency. However, the apparent DRV effects caused by the annihilation of substructures and the increasingly dynamic recrystallization (DRX) behaviors occurred at high compressed temperature, inducing the reduction in true stresses. In addition, a physical-based (PB) constitutive model and a long short-term memory (LSTM) model optimized using the particle swarm optimization (PSO) algorithm were established to predict the flow behavior of Hastelloy C276 alloy. The smaller average absolute relative error and greater relation coefficient suggest that the LSTM model possesses a higher forecasting accuracy than the PB model.

Interface microstructure evolution and bonding mechanism of low-temperature diffusion bonding of hydrogenated Zr-4 alloy

Zr-4 alloy is widely used as fuel cladding in the nuclear industry. And welding is one of the most significant procedures during the manufacturing of fuel assembly. Bonding at high temperature risks safe operation of nuclear reactors because high temperature deteriorates the properties of Zr-4 alloy. Herein, Zr-4 alloy was hydrogenated to a hydrogen content of 0.2 wt.% before diffusion bonding. Direct diffusion bonding of hydrogenated Zr-4 alloy was performed at various bonding temperatures. The microstructural evolution of the bonding interface and the interface bonding mechanism were systematically investigated. The bonding temperature of the hydrogenated Zr-4 alloy was reduced by 150 °C compared with the corresponding nonhydrogenated alloy. Furthermore, the shear strength of the joints was as high as 257 MPa (4.6 × higher than corresponding joints comprised of the nonhydrogenated alloy) at a bonding temperature of 700 °C. Transmission electron microscopy and electron backscatter diffraction indicate that plastic deformation of the joints increased because of a phase transition of the hydrides (to the β-Zr phase) during bonding, leading to high-density dislocations that accumulated at the bonding interface. The migration of the interface grain boundary was facilitated by high-density dislocations of sufficiently high energy. The bonding interface was no longer evident, enabled by dynamic recrystallization induced by migration of the interface grain boundary. Furthermore, the fracture mode of the joints was initially brittle but became ductile/brittle mixed mode with increasing temperature.

In Situ SEM, TEM, EBSD Characterization of Nucleation and Early Growth of Pure Fe/Pure Al Intermetallic Compounds.

The nucleation and growth processes of pure Fe/pure Al intermetallic compounds (IMCs) during heat treatment at 380 °C and 520 °C were observed through in situ scanning electron microscopy (SEM). The size of the IMCs were statistically analyzed using image analysis software. The types and distribution of IMCs were characterized using transmission electron microscopy (TEM) and electron backscattering diffraction (EBSD). The results showed that: at 380 °C, the primary phase of the Fe/Al composite intermetallic compounds was Fe4Al13, formed on the Fe side and habituated with Fe. The IMC was completely transformed from the initial Fe4Al13 to the most stable Fe2Al5, and the Fe2Al5 was the habitus with Fe during the process of holding at 380 °C for 15 min to 60 min. At 380 °C, the initial growth rate of the IMC was controlled by reaction, and the growth rate of the thickness and horizontal dimensions was basically the same as 0.02-0.17 μm/min. When the IMC layer thickness reached 4.5 μm, the growth rate of the thickness changed from reaction control to diffusion control and decreased to 0.007 μm/min. After heat treatment at 520 °C (≤20 min), the growth of IMC was still controlled by the reaction, the horizontal growth rate was 0.53 μm/min, the thickness growth rate was 0.23 μm/min, and the main phase of the IMC was the Fe2Al5 phase at 520 °C/20 min.

Retained austenite grain size as a strength-plasticity relationship indicator in Al-alloyed medium-Mn steel processed by intercritical annealing

Although most studies focus on the impact of the fraction of retained austenite (RA) on the relationship between strength and plasticity, this research explores the influence of the mechanical stability of RA, which is primarily affected by its grain size. To investigate this, samples of 5% Mn steel with varying fractions of RA, as well as different sizes and concentrations of carbon (C) and manganese (Mn), were produced by adjusting the soaking time during intercritical annealing (IA) between 1 and 300 min at a temperature of 680 °C. The mechanical properties of the samples were evaluated using static tensile tests. Detailed microstructural analyses were conducted before and after deformation through hardness tests, X-ray diffraction measurements (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) images, TEM-EDS microanalysis, and electron backscatter diffraction (EBSD) phase and orientation maps. Additionally, thermodynamic calculations were used to supplement the experimental findings. The results suggest that both chemical enrichment and grain size reduction have comparable effects on stabilizing the RA. The wide variation of RA grain sizes from 0.02 to 0.15 μm3 promotes a gradual and continuous martensitic transformation under strain throughout the entire strain range, leading to a uniform elongation exceeding 19% in the steel analyzed. However, the presence of an appropriate average size of RA (from ∼0.07 to ∼0.11 μm3) is crucial because grains smaller than ∼0.02 μm3 impede martensitic transformation, while coarse grains characterized by a volume greater than ∼0.13 μm3 result in significant transformation in an early stage of deformation.

Influence of homogenization treatment on microstructure and recrystallization behavior of 2195 Al–Li alloy

The microstructural evolution during homogenization treatment and the recrystallization behavior caused by Al3Zr precipitate in 2195 alloy were investigated via scanning electron microscopy, X-ray diffraction, transmission electron microscopy and electron backscatter diffraction. The severe dendrite segregation in the as-cast alloy was removed during homogenization, but the process was limited by the slower dissolution of Al–Cu phases. Moreover, the Al3Zr dispersoids precipitated in the sample homogenized by ramp heating rate of 30 °C/h (H30) were finer and denser compared to the samples subjected to other homogenization treatments (single-step, double-step, and ramp heating rate of 60 °C/h). The movement of dislocations and (sub)grain boundaries was resisted by the stronger Zener drag of finer and denser Al3Zr dispersoids. Thus, a higher recrystallization resistance during the hot compression and subsequent solution treatment was achieved for H30 sample. This work can provide theoretical guidance for optimizing the heat treatment parameters of the as-cast 2195 Al alloy.

Impact response of metastable dual-phase high-entropy alloy Cr10Mn30Fe50Co10

Plate impact experiments are conducted on a metastable dual-phase high-entropy alloy (HEA) Cr10Mn30Fe50Co10 with different matrix grain sizes and phase fractions. Free surface velocity histories are obtained along with microstructure characterizations. Postmortem samples are characterized with transmission electron microscopy and electron backscatter diffraction. Multiple deformation mechanisms are observed, including dislocation slip and stacking fault in the face-center cubic (FCC) phase, dislocation slip and deformation twinning in the hexagonal close-packed (HCP) phase, and the FCC to HCP transformation. For spallation, damage is ductile in nature. Despite different microstructures, micro-voids prefer to nucleate at high-angle grain boundaries within the FCC phase, leading to similar spall strength. Upon shock loading, a dynamic plastic deformation partitioning behavior among the two phases is observed; at high shock stress, denser dislocations in the HCP phase result in increased fractions of voids around the FCC/HCP phase interface and within the HCP phase during spallation damage.

Transitions among martensitic phases during continuous deformation in metastable β Ti-10V-2Fe-3Al alloy

Martensitic transitions as a function of cold rolling strain levels, in the range of 5 – 43 %, in the solution treated condition of metastable β Ti-10V-2Fe-3Al (Ti-1023) alloy has been systematically investigated. The formation of ω and α′′, α′ martensitic phases from β phase, for the different conditions of Ti-1023 samples, has been confirmed through X-ray diffraction (XRD), transmission electron microscope (TEM) and electron backscatter diffraction (EBSD) techniques. The lattice parameters obtained from XRD confirmed that (c/a)α" and [b/(a√3)]α" ratios approached the value of ∼ 1.587 and unity, respectively, along with consistent variations in principal lattice strains and relative volume changes indicating β→α′′→α′ phase transformations, with increase in cold rolling strain levels. The presence of ω-phase for the 5 % cold rolling sample is confirmed via slow scan XRD and TEM. It is further inferred that with the cold rolling strains the ω-phase act as preferential nucleating sites promoting α′ martensite formation by suppressing the stress-induced β→α′′ martensitic transformation. Moreover, to accommodate strains, additional deformation processes such as martensite compound twinning formation and strain-induced α′′→α′ martensitic transformation are confirmed, through TEM and EBSD, respectively. With further increase in cold rolling strains to 43 %, the transformation of β→α′ and strain-induced α′′→α′ martensites are pronounced, which is consistent with the formation of equilibrium hexagonal close packed structure in titanium alloys. Finally, the present investigation suggests that orthorhombic-α′′ martensites and strain-induced α′′→α′ martensitic transformations give Ti-1023 alloy high cold deformability up to ∼ 43 %.

The evolution of microstructure and texture induced by grinding and subsequent thermal exposure of single crystal alloy

The dynamic recrystallization (DRX) behavior during grinding and static recrystallization (SRX) behavior during thermal exposure of Ni-based single crystal alloy were compared in this work. The microstructure changes after DRX and SRX were characterized by field emission scanning electron microscopy (FE-SEM) and scanning transmission electron microscopy (STEM). The grain orientation and dislocation density distribution were analyzed by transmission Kikuchi diffraction (TKD) and electron backscatter diffraction (EBSD). The results show that SRX is affected by DRX process on the ground subsurface of single crystal alloy. The nucleation sites of SRX at high temperature are derived from significant number of high-density dislocation structures generated by DRX that induced by grinding process. Compared with the equiaxed nanograins produced by DRX, micron-scale cellular and equiaxed grains are formed on the surface, and dislocation density decreases sharply after SRX. The original cube texture of single crystal superalloy changes into shear texture due to plastic deformation during grinding, and then into strong recrystallization texture at high temperature. The microstructure changes under deformation and high temperature directly affect the final properties of single crystal blades. It is of great practical significance to understand the microstructure evolution and grain orientation changes during DRX and SRX processes, so as to reveal the mechanism of single crystal transforming into polycrystal from machining process to service stage of single crystal blades.