The growth kinetics of Ni3Al were investigated in Ni//NiAl macroscopic diffusion couples annealed at 800-1000 degrees C under applied elastic compressive stress. By utilizing electron backscatter diffraction (EBSD) technology in conjunction with appropriate statistical methods, the mechanism underlying the impact of elastic stress on Ni3Al growth kinetics is elucidated. Based on the findings, the application of compressive elastic stress can enhance Ni3Al growth kinetics by increasing both atomic vibration frequency (nu) and activation entropy (Delta s). The newly formed Ni3Al phase at the Ni/NiAl interface exhibits a specific crystallographic relationship with adjacent NiAl phase, with most Ni3Al grains maintaining a Kurdjumov-Sachs (K-S) orientation relationship. Remarkably, the application of elastic compressive stress in conjunction with an increase in temperature results in a reduction of Ni3Al grains grown according to the K-S orientation relationship.

The growth behavior of Ni3Al after nucleation at the Ni/NiAl interface was investigated by using macroscopic diffusion couples at low annealing temperatures of 973-1073 K. The thickness and grain size of the Ni3Al phase at different annealing temperatures were statistically analyzed by scanning electron microscopy to evaluate the growth kinetics of the Ni3Al layer. According to the growth rate exponent, the growth of Ni3Al layer to NiAl is almost completely controlled by volume diffusion (VD) when it is above 1023 K, and by boundary diffusion (BD) when it is below 1023 K. In contrast, the growth of Ni3Al into Ni is controlled by VD almost whether at 1023 K or 1073 K. Remarkably, a continuous Al-rich Ni grain layer was formed at the Ni3Al/Ni interface by diffusioninduced recrystallization (DIR), and the experimental results for DIR region of composition and growth behavior were numerically analyzed using the thermodynamic and kinetic models, respectively. The analyses suggest that the composition of the DIR region in the Ni(Al) binary system can be determined by the thermodynamic conditions of the chemical driving force model (CDF model). Additionally, kinetic analysis using the new extended model (NE model) indicates that under current annealing conditions, interface reaction and BD control growth at the moving boundary of the DIR region. Furthermore, the temperature stability range of Ni5Al3 in the Ni//NiAl system was subjected to systematic analysis.

A dense three-layer corrosion product film was formed on aged WE43 alloy in 3.5 wt.％NaCl solution.The microstructure of the film was analyzed in detail by TEM.The three-layer corrosion product film is composed of RE2O3,MgO layer doped with RE2O3 and Mg(OH)2 layer doped with RE2O3 from the inside to the outside.A large amount of rare earth oxide particles formed both by the outward oxidation of rare earth precipitates and rare earth elements,are the main reason for the formation of the corrosion film.The RE2O3 has the preferential orientation with(211)plane and[231]direction parallel to(002)plane and[110]direction of MgO,respectively.Thus,the rare earth oxide particles can fill the gap of porous MgO layer,and improve the compactness of the film.The inner RE2O3 layer and mixed layer of MgO and RE2O3 play an important role in the formation of the film.The compact inner film can prevent the corrosion medium from reacting with the Mg matrix.

The low-cycle fatigue behavior of solutionized (T4) and aged (T6) WE43 magnesium alloys was studied at room temperature. The total strain amplitudes (Δεt/2) were 0.4%, 0.5%, 0.6%, 0.7% and 1.0%. Detailed microstructure evolution was characterized by scanning electron microscope (SEM), electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM). The results showed that plastic strain amplitude decreased with the increasing cycle number in T4 alloy, which is due to the dense persistent slip bands (PSBs) and dynamic precipitates hindering dislocation slip. In contrast, the plastic strain amplitude increases gradually in T6 alloy, which is attributed to the enhanced activation of pyramidal slip. The low-cycle fatigue life of T6 alloy with larger fatigue ductility coefficient is longer than that of T4 alloy. The Coffin-Manson model can accurately predict the fatigue life of T4 and T6 alloys compared to Jahed-Varvani (JV) energy model. For T4 alloy, the fatigue damage mechanism was dominated by basal slip. For T6 alloy, the enhanced pyramidal slip plays an important role to accommodate plastic deformation.

The corrosion behavior of WE43 alloy with different rolling reductions (0%, 25%, 45%, and 80%) at 500 degrees C was investigated in 3.5 wt.% NaCl solution. The microstructure evolution of the rolled WE43 alloy was characterized in detail by means of optical microscopy (OM), transmission electron microscopy (TEM) and electron back-scattered diffraction (EBSD). The results show that with increasing reductions, basal texture is gradually enhanced and grain size gradually decreases. Only the alloy with 45% reduction exhibits dispersed dynamic precipitates. Immersion and electrochemical measurements demonstrate the decreasing order of the corrosion resistance of the rolled WE43 alloy: 45% reduction > 80% reduction > 25% reduction > 0 reduction. The best corrosion resistance of the WE43 alloy with 45% reduction is mainly related to a large number of finely dispersed precipitates, which are capable of promoting the formation of a compact corrosion product layer. The increased corrosion rate of the sample with 80% reduction is induced by the re-solution of the majority of precipitates into the matrix. The grain size, basal texture and deformation twins have a limited effect on the corrosion resistance of rolled WE43 alloy compared with the precipitates.

This research investigates the relationship between the microstructure and mechanical properties of electron beam welding joints, with a particular emphasis on the influence of varying electron beam currents on AISI 410L stainless steel plates and NS163 Co-based superalloy wires, which is a rare and novel form of welding. An increase in beam current led to a gradual transformation of the weld microstructure from columnar to equiaxed grains, creating finer and more homogeneous grains. Macrosegregation was also observed, a consequence of the liquidus temperature difference between the weld metal (WM) and base metal (BM). The segregation structure exhibited irregularly shaped beaches near the fusion line and islands of unmixed and partially mixed NS163 within the WM. This phenomenon was more pronounced in samples with a lower beam current. Given the limitations in BM shape and WM size, nanoindentation was employed to characterize the strength of welded joints. In conjunction with microhardness measurements, it was confirmed that the weld is strengthened under different electron beam currents, with higher current resulting in a more significant strengthening effect. This study also underscores the value of nanoindentation in evaluating the weld strength of brush seals without destruction.

The high-cycle fatigue behavior of the wrought superalloy GH4742 was studied at room-temperature (RT), 650 degrees C and 750 degrees C. The fatigue strength at 107 cycles of the GH4742 alloy increases with increasing temperature, which is mainly due to the different fracture modes at different temperatures. Fatigue cracks at room temper-ature originate from the specimen surface, including surface inclusions, surface carbides, surface slip and surface crystallographic facets. At 650 degrees C and 750 degrees C, the fatigue crack initiations originate from the subsurface or in-ternal crystallographic planes under lower stress levels, while the surface defects or surface crystallographic planes originate under higher stress levels. The dislocation density of the GH4742 superalloy is low at room temperature and 650 degrees C, and the deformation mechanism is mainly governed by APBs shearing primary gamma ' and Orowan bypassing secondary and tertiary gamma '. When the temperature rises to 750 degrees C, the deformation mechanism is mainly governed by stacking faults shearing primary, secondary and tertiary gamma '. Furthermore, antiphase boundaries (APBs) shearing primary gamma ' and Orowan bypassing secondary and tertiary gamma ' occur.

This study explicates the microstructural evolution and mechanical response of the joints of 304 stainless steel developed through micro-deformation diffusion bonding. The diffusion-bonded interface comprised the refined grains embedded with the intergranular M23C6 carbides and complex oxides, which was induced by dynamic recrystallization at 950 & DEG;C. The refined grains persisted at the bonding temperature of 950 & DEG;C due to the dynamic equilibrium of dislocations and pinning effect of intergranular particles. As the bonding temperature was raised to 1000 & DEG;C, the combination-grow up of grains was initiated caused by sufficient thermal activation and complete dissolution of M23C6 carbides. The interface was entirely migrated at 1050 and 1100 & DEG;C, and notably, the migration of interfacial grain boundaries played a greater role in diffusion bonding with an increase of bonding temperature. The interface with refined grains permitted a high joint strength (or impact load), while was incompetent to enhancing plasticity and particularly impact toughness. The migrated interface, in contrast, was provided with exceptional plasticity and impact toughness, attributed to its enhanced resistance to crack propagation. The joint prepared at 1050 & DEG;C for 60 min exhibited the optimum combination of ultimate tensile strength, fracture elongation, and impact toughness, and the ductile fracture was observed passing through the substrate instead of along the interface. In addition, the comprehensive performance of joints was degraded when the grains were excessively coarsened at 1100 & DEG;C for 60 min.

In this study, tensile tests and interrupted experiments at different true strain levels were performed at 293 K and 77 K to reveal the deformation mechanisms of GH3536 superalloy during loading. The microstructure evolutions of the alloy with strain at both temperature were studied via Transmission electron microscopy (TEM), and dislocation densities were calculated by X-ray diffraction (XRD) for quantifying the forest hardening contribution to the flow stress. Deformation twins were rarely observed in the GH3536 superalloy specimens deformed at 293 K, where deformation occurred solely by dislocation slip. While twinning was initially found at a strain of similar to 7% at 77 K, and the corresponding stress at which twinning occurs is 808 +/- 46 MPa. The twin volume fractions, their widths and spacings were determined by electron backscatter diffraction (EBSD), which is used to investigate the twin evolution of GH3536 alloy at 77 K. The deformation mechanisms of GH3536 alloy, as well as its twinning behaviors, depend on the competition between the maximum flow stress and critical stress for twinning. The maximum flow stress is large enough to activate twinning at cryogenic temperature, resulting in the transition of deformation mechanisms for GH3536 alloy as SLIP (dislocation slip) at 293 K and TWIP+SLIP (deformation twinning and dislocation slip) at 77 K, and the improved combination of ductility and strength at 77 K compared to 293 K is derived from additional deformation mode provided by twinning during the process of deformation.

In this study, GH3536 superalloy was subjected to the cold rolling processing up to 60% of thickness reductions for meticulously investigating the evolutions of both microstructure and texture. Crucial findings of deformation microstructures such as the twinning of the grain with Copper orientation and the occurrence of shear bands in matrix were captured by electron backscatter diffraction (EBSD). Twin trace analysis (TTA) was concomitant with resolved shear stress (RSS) analysis for identifying active twin variants. Higher strength and lower ductility were developed with increasing reduction ratios, which was evaluated in mechanical properties tests implemented by using nonstandard miniaturized specimens. The RSS ratio analysis was carried out to predict the twinnability of the most compliant orientation and disclose the orientation dependence of deformation twinning. Experimental and calculated results proved the discovery of the deformation twinning in a Copper orientation.

In this study, the total stacking fault energy (SFE) of GH3536 superalloy was divided into three fundamental terms (chemical, magnetic and strain terms) for investigating the dependence of temperature via ab initio calculations. The present results imply that the incremental trend of SFE value is responsible for the increasing temperature, which indicates a significant temperature dependence for SFE. These results also account for the occurrence of twinning in GH3536 superalloy during plastic deformation at cryogenic temperature and shed light on the relationship between the SFE and deformation mechanisms. The estimated SFE at ambient temperature gains coincident conclusion with the experimental measurement of SFE obtained by using the line-broadening analysis of X-ray diffraction (XRD) in conjunction with the Rietveld method. The discovery provides an essential understanding of potential governing deformation mechanisms for face-centered-cubic (fcc) alloys with low SFE, paving the way for the development of novel materials with excellent resistance to cryogenic temperature.

In this study, the microstructure and mechanical properties of cobalt-based superalloys by internal nitridation at 1100 degrees C, 1150 degrees C, and 1200 degrees C were characterised in detail by transmission electron microscope (TEM), electron probe microanalysis (EPMA), electron backscatter diffraction (EBSD) and microhardness testing. The results show that with an increase in the internal nitridation temperature, the nitridation layer thickness of cobalt-based superalloys gradually increases to 898 & mu;m. Internal nitridation at 1200 degrees C for 10 h exhibits the densest nitrides and the thickest layer. The precipitates were then dispersed in the matrix. The precipitates are mainly cubic, spherical, and cruciform (Ti, Nb)(C, N). Small amounts of blocky AlN and Cr2N were observed in the outer nitridation layer. Internal nitridation significantly improves the mechanical properties of cobalt-based superalloys by precipitation and solution strengthening. The yield strength increased by 105 % at room temperature (RT). Compared with the yield strength of 100 MPa for the as-received alloy at 800 degrees C, the internal nitridation alloy could still maintain good mechanical properties: a yield strength 300 MPa and an elongation 32%. In addition, because of the low diffusion activation energy of nitrogen in cobalt-based superalloys, internal nitridation is suitable for strengthening cobalt-based superalloys, expanding their application prospects in engineering structural materials.

In this study, high-temperature nitriding was used to improve the surface hardness and wear resistance of Co-27Cr-22Fe alloy in a thermogravimetric analyzer. The high-temperature nitriding treatments were performed at 1200 degrees C for 3 and 10 h. Subsequently, at room temperature, the dry sliding wear test was carried out, and the possible effects of load on friction performance and microstructure of different specimens were investigated. The results show that the microstructure of as-received specimens is composed of g-Co and MC carbides, while the microstructure of the nitrided specimens contains g-Co, MC car-bides, acicular AlN, and granular (Ti, Nb)N. The thickness of the nitriding layer is 375 mm and 708 mm for nitriding 3 h and nitriding 10 h, respectively. An improvement in microhardness (-425 HV) was attained for nitrided specimens. For the as-received specimens, the wear rate decreases with increasing load. The as-received specimen exhibits better wear resistance than the nitrided specimen under a high load (-30 N). The wear mechanism under different loads was mainly abrasive wear, accompanied by adhesive wear. For the nitrided speci-mens, the specimens show different wear mechanisms under varying loads. Under low load (-5 N and-15 N), the high-temperature nitriding improves the wear resistance, and it exhibits abrasive wear and oxidative wear. Under high load (-30 N), the wear resistance of the nitrided specimen was significantly reduced, and the wear mechanism is mainly abrasive wear, fatigue wear, and oxidative wear.(c) 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

The interfacial behaviours of micro-deformed diffusion bonded joints were systematically revealed. There were two typical bonding interfacial characteristics: “bond line” and migrated grain boundaries. “Bond line” was featured as fine grains and phases on the interface. The critical temperature of joint characterized by “bond line” was 950 °C. The increased temperature 1000 °C was a critical temperature which interfacial characteristic “bond line” eliminated. The second type was characterized by interfacial migration over 1000 °C, in which the bonding interfaces were composed of straight grain boundaries, triple junctions, and protruding and expanding interfacial migrated grains. Additionally, two different interface migration and joint forming mechanisms were observed with elevated bonding temperature: recrystallization and grain recombination. The first one was the discontinuous dynamic recrystallization mechanism, which was observed in the joints bonded at 950 °C and 1000 °C. The second mechanism was the grain boundary migration mechanism based on the grain growth mechanism, of which the typical bonding temperature was 1050 °C. The joint was bonded under two kinds of grain boundary migration, including strain-induced interface grain boundary migration and interface grain boundary migration at triple junction.

In this study, the ratcheting fatigue behaviours of GH742 superalloy at 923 K were investigated through a series of symmetric and asymmetric stress-controlled tests. The effects of stress amplitude and mean stress on the fatigue behaviours were analysed through scanning electron microscopy, transmission electron microscopy and electron backscatter diffraction. The results highlight that the fatigue life significantly decreases with increasing mean stress or stress amplitude. Tensile ratcheting strain occurs and increases with the increasing number of cycles under both symmetric and asymmetric cyclic loading. The alloy initially exhibits a cyclic hardening response, followed by cyclic softening until fracture failure under symmetric and asymmetric cyclic loading. The increase in mean stress promotes the cyclic softening in the tensile strain direction to a certain extent. The fracture mode does not change with increasing mean stress. Multiple fatigue cracks initiate from the surface inclusions, crystallographic facets and slip bands, and propagate in mixed transgranular and intergranular modes. The modified Basquin equation, which considers the mean stress and stress amplitude, can accurately predict the fatigue life, and all the fatigue data are located within the 1.5X scatter band.

The reliable joining of DD5 single crystal superalloy and GH4169 polycrystalline superalloy was obtained by diffusion bonding method at 1120 ? for 90-180 min under 10 MPa with or without 730 ? /180 min aging process. The joint was divided into four distinct regions: GH4169 base metal zone, the diffusion zone, the structure affected zone, and DD5 base metal zone. The size, distribution and morphology of gamma' phases at the whole joint were distinguishing under different bonding conditions. The morphology of gamma' particles changed from nearly cubic shape into irregular sunflower shape, and nearly cubic shape growing up to cubic at the diffusion zone and DD5 base metal zone, which resulted from the operation of additional aging process at 730 ?for 180 min after bonded at 1120 ? for 180 min. Furthermore, the optimal tensile strength of the joint was 1058 MPa when the joint was bonded at 1120 ?/10 MPa/180 min and then heated at 730 ? for 180 min, of which the fracture was occurred at the base metal zone. The in-situ tensile test indicated the damage and fracture behavior of the joint resulted from the increasing slip lines and cracks in carbides.

This study focuses on diffusion bonding of WC-Co cemented carbide to a steel using Co and composite Ni/Co interlayers. The typical microstructure and microstructural evolution with variable bonding temperatures were investigated, and mechanical properties of the joint were evaluated. The results illustrated that increasing temperature promoted interdiffusion of interfacial atoms, leading to the elimination of interfacial voids and the enhancement of Fe-Co-Cr interdiffusion zone on steel side. As the temperature increased, so did the thickness of Co6W6C formed near the WC-Co substrate (using Co interlayer). On the other hand, the Co6W6C was inhibited due to the addition of Ni foil, and replaced by the WC and (Ni, Co) solid solution resulting in satisfactory shear strength of the diffusion-bonded joint, where referring to using composite Ni/Co interlayer. The maximum shear strength of 418 MPa was achieved when the joint was diffusion-bonded at 1100 degrees C for 60 min using composite Ni/Co interlayer. In addition, ductile fracture occurred in the joint indicating propagation of cracks in the Ni-Co interdiffusion zone, and passing through the WC-Co substrate. Added up, this study provided experimental support for reliable joining cemented carbides to Fe- or Co-based alloys.

Hydrogen permeation usually facilitates the corrosion of stainless steel remarkably. Herein, the corrosion behavior of a nickel-free high-nitrogen stainless steel (HNSS) containing 0.96 wt.% nitrogen with hydrogen charging is investigated by means of electrochemical measurements and x-ray photoelectron spectroscopy surface analysis. The results show that hydrogen charging not only increased the passive current density but also increased the pitting potential of HNSS. The increase in passive current density was attributed to the increased carrier density, depleted Cr content, and decreased O2−/OH− ratio in the passive film, while the increase in the pitting potential resulted from the enrichment of N element in the passive film and the replacement of Ni with Mn in HNSS.

The superalloy FGH98 was successfully diffusion bonded (DB) with medium-entropy alloy (MEA) Al3Ti3(CrCoNi)94 using pure Ni as the interlayer at a temperature range of 1050–1170 °C for 1 h under 5 MPa. The microstructure and mechanical properties of joints were investigated. The diffusion bonding seam was composed of an interlayer zone (IZ) and two diffusion-affected zones (DAZ). The IZ and DAZ beside the FGH98 consisted of cubic Ni3(TiAl)-type γ′ phases due to the diffusion of Ti and Al atoms. Meanwhile, the DAZ adjacent to the MEA consisted of spherical γ′ phases. Both of the γ′ phases with different morphology kept the coherent relationship with the matrix. Moreover, increase of bonding temperature led to the morphology of interlayer γ′ phase to transform from sphere to cube. Due to the strengthening effect of a mass of γ′ phase distributed evenly in IZ and the DAZ beside the FGH98, the microhardness and Young’s modulus of these two zones were higher than that of DAZ near the MEA. The maximum shear strength of DB joint, 592 MPa, was achieved in the joint bonded by 1150 °C, which was the typical ductile fracture feature confirmed by the shear dimples.

In this study, the effects of annealing on microstructures and the properties of GH3536 superalloy sheets were studied in detail by means of Electron Backscatter Diffraction (EBSD), Scanning Election Microscopy (SEM) and Transmission Electron Microscopy (TEM). The results show that a series of phenomena happened after annealing at 950 degrees C. The recrystallization occurs when the alloy is annealed at 950 degrees C, and new strain-free grains replace the strained grains. There is a significant reduction in grain size, low-angle grain boundaries and dislocation density. Meanwhile, a mass of M6C carbides precipitate along grain boundaries after annealing at 950 degrees C. And a large number of annealing twins are also formed during this process. The reduction of dislocation density due to the recrystallization of the alloy leads to a noteworthy decrease in strength and an obvious increase in plasticity, which means excellent reprocessing ability are obtained after recrystallization.