Current researches lack investigations into the effects of high temperature and biaxial coupled loading conditions on microdefects. This paper primarily focuses on the nucleation and early propagation behavior of microcracks near micron-sized artificial microdefects in the alpha-phase Ti-2Al-2.5Zr alloy under in-plane biaxial fatigue loading, utilizing the coupling method of quasi-in-situ test, X-ray three-dimensional (3D) computed tomography (CT) and crystal plasticity (CP) simulation. The anisotropy exhibits under various biaxial loading paths is also investigated. It is found that, at room temperature (RT), the Ti-2Al-2.5Zr alloy exhibits the limited dislocation slip activity, which restricts the grains' capacity of accommodating deformation. The microcrack nucleation is susceptible to microdefect at RT. At 350 degrees C, the Ti-2Al-2.5Zr alloy presents high-level slip activity, which retards the micro-crack nucleation near the microdefect at the early stage of the biaxial fatigue test. However, as dislocation slip accumulates, microcracks rapidly propagate because grains experience hardening and the ability to coordinate deformation diminishes. Crystal plasticity finite element model (CPFEM) simulation results indicate that the number of stress concentration areas near the microdefects is much higher in biaxial tension than that in uniaxial tension. Therefore, the crack sensitivity of the grains surrounding the microdefects is greater in biaxial fatigue tests. Besides, microdefects significantly reduce the constraint effect compared to that in homogeneous Ti-2Al-2.5Zr alloy structure during biaxial tension. Such heterogeneity can lead to the crack nucleation develop more rapidly than uniaxial tension once it occurs. The reconstruction and analysis of micron-level microdefect regions have been achieved through the combination of CPFEM and high-precision characterization techniques.

Lead-bismuth eutectic (LBE) is a promising coolant for advanced nuclear systems, but its corrosion compatibility with structural steels remains a critical challenge. This work reports an unusual corrosion behavior of 15-15Ti austenitic stainless steel in oxygen-controlled (5 x10-7 wt%) LBE at 550 degrees C. Through a combined microscale and nanoscale characterization approach (SEM, EDS, EBSD, TEM), two distinct oxidation morphologies are identified. The first is a conventional triplex structure with an outer magnetite layer, an inner Fe-Cr spinel, and a Nirich internal oxidation zone (IOZ). The second is an unusual structure, characterized by an outer magnetite layer, an epitaxially-grown Mn-Cr spinel layer sandwiched between two nanoscale Cr2O3 layers, atop a ferritization zone. The Mn-Cr spinel forms via a solid-state transformation from an initial Fe-Cr spinel, driven by Mn diffusion, which densifies the oxide and significantly retards its growth. However, this Mn-Cr spinel layer is susceptible to LBE penetration, leading to complex LBE decomposition and Cr23C6 precipitation within the ferrite layer. The ferritization process is shown to initiate via solid-state diffusion, forming a continuous layer, and progresses via a dissolution-reprecipitation mechanism, resulting in a fragmented morphology. This study provides novel insights into the critical role of minor alloying elements, particularly Mn, in steering corrosion pathways, offering essential guidance for designing corrosion-resistant steels for LBE service.

Biaxial tensile tests of Ti-2Al-2.5Zr titanium alloy were conducted at room temperature (RT) and 350 degrees C to systematically investigate the slip transfer effect between neighboring grains. The slip transfer behavior was analyzed based on the Global Schmid factor (GSF) and the geometric compatibility factor (m '). The results show that under RT biaxial deformation, slip system activation follows Schmid's law, leading to stochastic slip transfer characteristics governed by the slip systems activated in adjacent grains. At 350 degrees C, extensive dislocation slip accumulates near the grain boundaries of individual grains and "forces" neighboring grains to activate slip systems with high m ' values near the boundaries to accommodate the deformation, even when these slip systems exhibit low GSF values. Crystal plasticity finite element models (CPFEM) were constructed based on the real microstructure, with boundary conditions derived from scanning electron microscopy-digital image correlation (SEM-DIC) measurements to simulate biaxial deformation at RT and 350 degrees C. The simulation results demonstrate that stress concentration at the intersections of multiple grain boundaries is significantly higher than that at individual grain boundaries, which results in the accumulation of dislocation slip and severe concentration of deformation under biaxial tensile tests at 350 degrees C. The research findings of this paper are presented intuitively through SEM-DIC, and supported by the CPFEM simulation results.

In this study, the effect of B-type S-hydrides (with near-basal habit planes) on the low-cycle fatigue (LCF) behavior of Ti-2Al-2.5Zr alloy was studied through in-situ SEM fatigue testing. Tensile tests, in-situ observation of fatigue testing and post-fatigue microstructure examination demonstrated that the B-type S-hydrides not only exerted a hindering effect on slip but were also capable of undergoing plastic deformation in conjunction with the matrix, without fracturing. The slip behavior of dislocations across the phase interface was discussed. An increase in hydrogen content (or B-type S-hydrides) led to an extension of the LCF life of Ti-2Al-2.5Zr alloy. This was primarily achieved by prolonging the crack initiation life, whereas it had a relatively minor effect on the crack propagation life. The enhancement of crack initiation life could be attributed to the retardation of cyclic plastic strain accumulation and strain incompatibility, both being outcomes of the hindering effect of hydrides on slip. During the crack propagation stage, there was no change in the crack propagation mode (transgranular mode) with increasing hydrogen content. Additionally, no cases of rapid crack propagation along the S-hydrides were detected. These could be attributed to the plastic deformation capacity exhibited by the B-type S-hydrides, and their perpendicular orientations relative to the crack propagation direction. Therefore, the B-type S-hydrides exhibited a minor impact on the crack propagation life. It is believed that this study provides an insight into the influence of the B-type S-hydrides on the LCF behavior of Ti-2Al-2.5Zr alloy.

To elucidate the mechanistic link between dislocation reactions and texture evolution in refractory BCC alloys, this study investigates a Mo-Re alloy under axial compression at 650 degrees C. Multi-scale characterization reveals that kink band formation acts as a critical accommodation mechanism governing texture evolution. Crucially, the observation of kinking signifies strong plastic anisotropy, driven by the enhanced activation of single {112} slip systems (promoted by Re addition and temperature). While the coordinated activity of {110} and {112} families generates sessile networks that contribute to hardening, preferential pile-ups of edge dislocations on {112} planes create the lattice instability necessary for kinking. This instability is accommodated by cooperative block rotations (kinking). In this process, active dislocations are consumed to generate kink boundaries. Consequently, kinking drives the rapid transformation of single-slip-dominant < 101 > //AD grains toward the stable <111 > //AD texture, whereas multi-slip <001 > //AD grains reorient only partially. Concurrently, continuous deformation bands bridge crystallographic gaps between rigid blocks and the matrix to maintain compatibility. The synergistic interplay between abrupt kink bands and continuous deformation bands effectively accommodates strain during moderate deformation. However, at high strains, the prevalence of the hard-oriented < 111 > //AD texture imposes geometric hardening, effectively suppressing further kinking and slip, which leads to the loss of strain accommodation. These findings clarify how kink-mediated plasticity governs texture evolution, thereby enhancing the ductility and damage tolerance of refractory alloys.

1.Introduction Molybdenum(Mo)is a refractory metal characterized by a high melting point(2896 K),high thermal conductivity(138 W m-1 K-1),excellent mechanical properties at elevated tempera-tures,and good resistance to wear and corrosion[1-3].Conse-quently,Mo and its alloys have attracted significant interest in high-temperature applications,such as in the aviation and nuclear power industries[4].However,the intrinsic brittleness of Mo at room temperature complicates its manufacturing through tradi-tional methods,limiting its application in these fields[4].The ad-dition of rhenium(Re)has been shown to improve the ductility of Mo alloys at room temperature,thereby enhancing their machin-ability and workability[5].Despite this,the high melting point of Mo-Re alloys continues to present considerable fabrication chal-lenges[6].Typically,Mo-based alloys are processed through pow-der metallurgy,and necessitate subsequent processes(such as ma-chining[7],forging[8],welding[9,10],etc.)to obtain the final parts.Conventional fabrication methods for Mo-based alloys face challenges such as inconsistent weld quality,low efficiency,and difficulty forming complex geometries,as well as reduced tool life due to their high hardness[11].Moreover,these processes struggle to produce lightweight,intricate components[11].Therefore,inno-vative approaches are needed to efficiently manufacture complex Mo and Mo-alloy parts.

Ti-2Al-2.5Zr titanium alloy is used to manufacture heat exchange equipment for nuclear reactors, and it inevitably faces the issue of degradation caused by hydrogen absorption during long-term service. In this study, we investigated the evolution of the phase, microstructure, orientation relationships (ORs), and habit planes of hydrides in Ti-2Al-2.5Zr with hydrogen content, using X-ray diffraction (XRD), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The results indicated that exclusively delta-hydrides were formed in Ti-2Al-2.5Zr across all the hydrogen content (119 ppm similar to 1550 ppm).These delta-hydrides displayed two distinct types of ORs with alpha-titanium, i.e., {0001}(alpha) // {001}(delta), <1210>(alpha) // <110>(delta) (OR1) with prismatic habit plane of {1010}(alpha) // {110}(delta), and {0001}(alpha) // {1}(delta,) <1110>(alpha) // <1210>(delta) (OR2) with near-basal habit planes of {0001}(alpha) // {111}(delta) and {101}, m approximate to 5-7. In Ti-2Al-2.5Zr alloys with a hydrogen content not exceeding 500 ppm, hydrides were predominantly OR2 in nature. By comparing with the previously reported results for pure Ti, the addition of Zr and Al was confirmed to favor the formation of OR2 hydrides and bring the habit plane of OR2 hydrides closer to the {0001} basal plane. The first-principles calculations revealed that the addition of Zr and Al reduced the unstable-stacking fault energy gamma US and stacking fault energy gamma SF for basal plane, therefore leading to OR2 hydrides prefer to precipitate in Ti-2Al-2.5Zr. As the hydrogen increased to 1550 ppm, the size and density of OR1 hydrides increased markedly, leading to the formation of long interconnected chains of hydrides through the auto-catalytic nucleation mechanism of transgranular growth of hydrides. The orientation of the long chains was related to the texture of alloy and the ORs and habit planes of hydrides.

The fatigue cracking mechanism of Ti-2Al-2.5Zr alloy was investigated under different stress amplitudes. The evolution of fatigue damage was analyzed using quasi in-situ tests. The dependence of transgranular and intergranular crack nucleation on microstructure features was discussed in detail. The mechanisms of slip-induced and twinning-detwinning (T-D) induced crack nucleation were elucidated, respectively. It was found that, at the stress amplitude of 442 MPa, the slip damage, in the form of intrusions/extrusions, dominated crack nucleation. Transgranular cracks primarily nucleate along the prismatic planes of the variants with highest Schmid Factor of prismatic slip (SFpris.); intergranular cracks are mainly induced at grain boundaries (GBs) by slip impacting/shearing GB behaviors and at GB triple junctions due to strain incompatibility. As the stress amplitude increased to 475 MPa, the dominant crack mode transitioned from slip-dominant cracks to T-D induced cracks and intergranular cracks due to the competition between the T-D and slip behavior. Twin boundaries (TBs), GBs, slip planes adjacent to the activated T-D regions, and the twin pairs/chains in adjacent grains were identified as preferred sites for crack nucleation.

The dislocation slip of welded joints and its interactions with phase interfaces during deformation are critical to the mechanical performance of welded alpha Ti-4Al-2V alloy. Due to the influence of thermal cycling, the welded joint can be divided into five distinct zones based on microstructure. The mechanical properties of the welded Ti4Al-2V alloy are influenced by both the microstructural evolution during deformation and the mechanical properties of these zones. In this study, DIC tensile testing, In-situ EBSD characterization, TEM/STEM analysis of each zone, and thermodynamic calculations were used to explore the stress distribution and dislocation behavior in the different zones during deformation. This work revealed that severe necking occurred in the WZ (weld zone) region during deformation, making it the initiation site for macroscopic fracture. In the WZ region, dislocations were identified as the primary deformation mechanism, which follows the Schimid Law. And the yield strength of this region was found to be approximately equal to that of the macroscopic sample. Acicular alpha ' martensite, residual beta, secondary alpha and stacking fault were observed in the welded joint regions, which might contribute to the strength and ductility of the welded joint of Ti-4Al-2V alloy. Besides, a deformation mechanism for different regions in the welded joint was proposed in this study, based on experimental results and theoretical calculations.

Ti-2Al-2.5Zr is widely used in piping and structural support applications, however, the rolling forming process results in anisotropic deformation during service. This behavior has implications for the manufacturing processes and structural safety assessments in engineering applications. In this study, the plastic anisotropic deformation behavior of a rolled Ti-2Al-2.5Zr plate was investigated using uniaxial tensile tests along the transverse, normal, and 45° directions. Acoustic emission, electron backscatter diffraction, and scanning electron microscopy methods were used to investigate dislocation slip and twinning mechanisms. The results indicated that different microscopic deformation mechanisms caused the significant macroscopic anisotropy of Ti-2Al-2.5Zr. The primary mechanisms involved were prismatic slip, pyramidal slip, and {10-12} extension twinning. The stress direction determined the influence of each of these mechanisms during the yielding and plastic deformation phases. Application of the visco-plastic self-consistent model established the relationship between the macroscopic mechanical responses and microscopic deformation mechanisms. It was revealed that Ti-2Al-2.5Zr achieved its optimum strength when the initial texture aligned most of the grain c-axis at angles ranging from 30° to 50° relative to the deformation direction. This finding provides a direction for the texture design of Ti-2Al-2.5Zr in engineering materials.

As a structural metal used in advanced mechanical equipment, the alpha-phase titanium alloy Ti-2Al-2.5Zr exhibits complex plastic flow during forming, necessitating an understanding of the microscopic deformation mechanism under complex stress states. This study utilized in-situ neutron diffraction experiments combined with crystal plasticity theory to investigate the lattice deformation behavior of different {hk,l} grain families in Ti-2Al-2.5Zr rolled plates under tensile, combined tensile-shear, and shear stress states. The results indicated that the in-plane plastic deformation of rolled plates was predominantly governed by prismatic slip. The stress state significantly impacted the lattice deformation behavior of different {hk,l} grain families. Specifically, tensile-stress components favored the initiation of double prismatic slip, whereas shear-stress components promoted the activation of single prismatic slip. Lattice rotation induced by prismatic slip followed a specific pattern and had stable orientation corresponding to the applied stress state. Once the lattice rotated to the stable orientation for prismatic slip, it could no longer continue to rotate via prismatic slip. The inability of the lattice to rotate introduced additional hardening, making the activation of prismatic slip more difficult. These findings provide new insights for optimizing the forming processes and advancing the crystal plasticity theory.

The service life of heat-resistant materials is crucial for safe operation in the nuclear industry. Usually, it is necessary to coat the surface of the materials with a heat-resistant coating. In this paper, XPS, EDS, XRD, SEM, and TEM characterization techniques were used to study the corrosion behavior of continuous high-power magnetron sputtered (C-HPMS) AlOx coatings with different oxygen contents exposed to lead-bismuth eutectic (LBE) at 350 degrees C-650 degrees C for 2000 h was investigated. Stable oxide gamma-Al2O3 and Al2PbO4 were formed at 350 degrees C-550 degrees C, which will increase the hardness and Young's modulus of the coating, and the dense layer Al2PbO4 and AlOx layer inhibited the outward diffusion of iron and the inward diffusion of O. At 650 degrees C, the internal Fe will be oxidized to Fe3O4, resulting in corrosion resistance failure. Therefore, the AlOx coating at the oxygen injection rate of 120 sccm (O/Al = 1.5) is best, which can resist corrosion at T < 550 degrees C. Finally, the corrosion mechanism of the AlOx coating in liquid LBE is discussed, providing a research idea for developing high-performance anti-corrosion coatings.

The interesting phenomenon of facet cracking of Ti-2Al-2.5Zr alloy exposed to high-cycle fatigue (HCF) loading at the high temperature of 350 degrees C was reported for the first time. Moreover, the HCF tests at room temperature were also conducted for comparison. The crack nucleation mechanisms with essential differences at both room and elevated temperatures were comparatively studied based on the elaborate characterizations, though the facet cracking was observed in both cases. At room temperature, the facets are parallel to the slip plane with the maximum Schmid factor and tend to crack along the direction of maximum shear stress. In contrast, the facets do not show any preferential crystallographic plane at 350 degrees C and tend to grow in the direction perpendicular to the maximum principal stress, particularly in the grains oriented for multiple slip systems. The difference in terms of the crack initiation was ascribed to different slip behavior of dislocations based on a comprehensive TEM characterization and analysis. The single slip-dominated planar dislocation arrays are activated at room temperature, while the activated multiple slip systems, leading to the formation of three-dimensional dislocation configuration of veins, which is closely related with the dynamic strain aging and dislocation interactions.

In this study, crack-free and highly dense Mo-Re alloys were successfully fabricated using the laser powder bed fusion (L-PBF) additive manufacturing process. The fabricated alloys exhibited excellent mechanical properties at room temperature. During the L-PBF process, oxides ranging from micron to nanometer sizes were observed within the alloy matrix. These oxides were uniformly distributed and showed no grain boundary segregation. After deformation, the interaction between these oxides and dislocations was confirmed via the transmission electron microscopy investigations. The interaction between oxides and dislocations might play a significant role in enhancing the ductility of the alloy.

Molybdenum alloys are promising materials for high-temperature gas-cooled reactor fuel cladding due to their excellent performance at elevated temperatures, favorable mechanical properties, corrosion resistance, and low neutron absorption cross-section. However, their high melting point and inherent hardness require annealing to improve processability. This study investigates the effects of vacuum annealing on the microstructure and texture evolution of rotary swaged Mo-Re alloys. The as-swaged alloy exhibits a fibrous structure with elongated grains along the axial direction (AD). Annealing at 1200 degrees C results in a bimodal microstructure, with both deformed and recrystallized grains, indicating a partially recrystallized (PRX) state. Furthermore, annealing at 1300 degrees C leads to a completely recrystallized (CRX) microstructure. The recrystallization mechanism is primarily driven by sub- grains coalescence. The texture of the rotary swaged Mo-Re alloy is dominated by a strong (101 )//AD fiber texture, accompanied by a weaker (001 )//AD texture. After recrystallization, the intensity of the <101>//AD texture decreases, while the <001>//AD texture becomes more prominent. These texture changes suggest that the <001>//AD texture promotes recrystallization, whereas the <101>//AD texture hinders it. The evolution of the recrystallization texture is attributed to the preferential growth of <001>//AD grains and stress-driven grain rotation. These findings provide valuable insights for optimizing the heat treatment process of rotary swaged Mo-Re alloys.

Corrosion transition during uniform corrosion of zirconium alloys receives much attention since it is the major degradation procedure. However, predicting the time and oxide thickness at transition has been hindered by the lack of knowledge about transition kinetics and how it responds to varied temperatures. Current study investigated the temperature-sensitivity of corrosion kinetics, transition behavior and microstructures of various zirconium alloys corroded in superheated steam ranging from 390 °C/10.3 MPa to 455 °C/10.3 MPa by autoclave experiment and microscopy analyses. Transition time was found to follow Arrhenius-type relationship with temperature for the first time. Both the transition oxide thickness and metastable oxide thickness increased with temperature, which was theoretically deduced and experimentally confirmed. In Zr-4 oxides, a transition thickness varying from 3.3 μm at 390 °C to 4.2 μm at 455 °C was observed. Microstructure results presented rather large HCP-ZrO particles (200∼400 nm) at O/M interface and they were even larger at the protruded positions. An intense sub-stoichiometric atmosphere was identified at O/M interface, promoting the growth of metastable oxides. The activation energy of transition kinetics was 86∼114 kJ/mol, which is close to diffusion activation energy of oxygen in tetragonal zirconia. A new model based on parabolic-law empirical relationship was thus proposed to predict transition kinetics. Predictions regarding the time to oxidation breakaway at 900–1000 °C were reported, and the results were in good agreement with the experimental data.

Molecular dynamics simulations were employed to explore the influences of the crystal orientation of tungsten (W) and the azimuthal orientation of Berkovich indenter on the mechanical response during indentation. The dislocation structures, pile-up patterns, and hardness are profoundly influenced by both the orientations. The pile-up phenomenon predominantly manifests along the perimeters of the indenter, particularly in the region where one of its facets aligns perpendicularly with a slip direction possessing a nearly horizontal inclination. The twinning and anti-twinning modes are discernible at the same time in the indented (011)-oriented W. A novel anti-twinning mechanism during indentation, involving successive gliding of 1/6(111) along the anti-twinning direction on the newly formed twin boundary and indent of 1/6(111) for the adjacent second (121) layer, was identified. Herein, we provided a comprehensive examination of the diverse formation processes observed in ring dislocations (RDs). Apart from the "lasso" mechanism, two additional processes were elucidated: twininduced formation and reaction-driven formation among three dislocations. Our findings furthermore indicate that the hardness of indented W is contingent upon a myriad of factors, encompassing the dominance of twinning or dislocation-mediated plasticity during deformation, the dominance of RD gliding or dislocation emission within the latter, and the probability of dislocations interacting to form (100) dislocations to hinder their sliding.

This study investigates the hot compression behavior of a molybdenum- Rhenium (Mo-Re) alloy, focusing on deformation mechanisms and instability. Utilizing electron backscattered diffraction (EBSD) and transmission electron microscope (TEM), we characterized the microstructure, grain orientation, and deformation behavior across temperatures (650, 750, 850, and 950 degrees C) and strain rates (0.01, 0.1, 1, and 10s-1). The study reveals that Mo-Re alloys exhibit high hot deformation resistance, necessitating optimal processing conditions for effective plastic deformation. Key findings by EBSD and TEM include the formation of dislocation networks and substructures enhancing grain plasticity. We established a constitutive equation and processing maps, providing valuable insights for industrial applications and future alloy development.

The thermomechanical fatigue (TMF) properties of Ti-2Al-2.5Zr alloy tubes with gradient nanostructured surface (GNS) layers obtained via deep rolling (DR) treatment were studied. Moreover, the isothermal low-cycle fatigue (IF) tests at the maximum temperature of TMF cycling were comparatively discussed. Furthermore, the IF and TMF tests were also performed on the as-received (AR) material without DR treatment. Results showed that the DR treatment improved the yield and tensile strength while reduced the elongation in terms of the monotonic tension properties. With regard to the fatigue properties, the fatigue life of DR samples is longer than that of AR samples, which is attributed to the formation of large number of dislocations and nanocrystalline boundaries introduced by DR treatment. The cyclic deformation behavior, such as cyclic hardening and softening was thoroughly analyzed based on the method of stress decomposition and microstructure characterization through microhardness measurement, electron backscattered diffraction (EBSD), transmission electron microscope (TEM). In addition, the dominant damage and fracture failure mechanism were revealed based on scanning electron microscope (SEM) observations. The life prediction model of DR samples based on the concept of crack growth rate is proposed.

The multi-step strain aging tests were meticulously designed in this work to reveal the physical mechanisms of static strain aging (SSA) and dynamic strain aging (DSA) behaviors in Ti-2Al-2.5Zr alloy for the first time. It was revealed that the shuffling mechanism of interstitial oxygen atoms combined with the pinning effect of locally-generated cross-slip on the movement of screw dislocations were responsible for the occurrence of strain aging. Furthermore, the effects of DSA on the low-cycle fatigue (LCF) and high-cycle fatigue (HCF) properties were elucidated in Ti-2Al-2.5Zr alloy. Results showed that the sensitivity of DSA to cyclic loading was attributed to the generation of numerous residual edge dislocation segments through local cross-slip, facilitating the formation of dislocation veins which inhibited the formation of persistent slip bands (PSBs) and led to the significantly cyclic hardening. Finally, it was emphasized that the phenomenon of DSA should be carefully considered for the structural integrity assessment of Ti-2Al-2.5Zr alloy and several suggestions were provided.