INCONEL 600 is extensively employed across various industries due to its remarkable resistance to both corrosion and elevated temperatures. The alloy’s superior high-temperature performance and extended service life are largely attributed to its stable single-phase microstructure, which remains intact up to 1703 K (1430 ℃). In this study, the microstructural evolution of INCONEL Alloy 600 was systematically examined under a range of thermal and thermomechanical treatments. These microstructural analyses were complemented by mechanical property assessments, including tensile and creep tests. Specimens were solutionized at 1200ºC for 1 h, resulting in a microstructure characterized by an average grain size distribution between 45–60 μm. Additionally, primary and secondary carbides rich in Cr, Nb, and Ti were observed within the γ matrix. The alloy was subsequently subjected to cold forging at room temperature, with varying levels of strain ranging from 20

This study reports the interplay between grain boundary morphology and mechanical behaviour using micropillar compression. Quantitative findings indicate that serrated grain boundaries with multiple curvatures exhibit notably higher yield strengths compared to their straight counterparts. In a bi-crystal system, 18 pct increase in boundary length, achieved through multiple curvature boundaries, results in 21 pct increase in yield strength. The quasi-in-situ electron backscatter diffraction (EBSD) investigations show the concentration of plastic strain within preferentially oriented slip bands, with grain boundaries offering resistance, and slip band leads to changing directions as they traverse from one grain to another, with secondary slips emerging post-yielding during micropillar compression. As compression levels rise, a prominent uniform strain hardening rate emerges in grain boundaries characterized by multiple curvatures. Local resolved shear stress at grain boundaries experiences a pronounced reduction under the applied load, particularly when the serration wavelength exceeds 0.4, and the amplitude ranges from 0.3 to 0.5 times the total grain boundary length. An attempt is made here to shed light upon the underlying microscopic mechanisms that govern grain boundary micromechanics through a comprehensive three-dimensional analysis. It becomes evident that both boundary curvature and inclination of interface plane play critical roles in enhancing material strength, collectively contributing to a 21 pct increase in yield strength in current case of boundary with curvature. Additionally, these morphologies notably reduce the likelihood of heterogeneous plastic deformation compared to straight grain boundaries.

This paper presents the mechanical behaviour of single crystal Ta (6.5 GPa-22 GPa) 1-D shocked along the three principal crystallographic directions [100], [110] and [111]. Room temperature mechanical testing was carried out on micropillars to make possible precise load and displacement measurements. The findings exhibit a marked variation in the flow curve and strain hardening between the three orientations, and relative changes are noticed with shock loading. The yield strength (YS) increases linearly as a function of shock load. The YS was highest along [111] (282 MPa) compared with the [100] and [110] orientations (194 and 206 MPa). The strain hardening rates without pre-shock loading are found to be in the order [111] > [100] > [110] and this is not altered by pre-shock loading. Deformation was accomplished by slip on {112} planes. Further, assessments are considered to identify effective plastic strain accumulation during shock loading. The accumulation of effective plastic strain was found to be similar for all directions for shock loading up to 6.5 GPa, however, above 15 GPa the effective strain was lower for [110] compared to [100] and [111] directions. An attempt is made here to assess the flow curve hardening behaviour and variation in yield strength based on a different combination of pair orientation to throw some light into materials response at high-pressure shock loading.

The formation of δ-ferrite in advanced structural materials is well known to impair mechanical and corrosion properties. In the present work, high-temperature phase stability and phase transformation characteristics of the γ → δ phase transformation of ferritic/martensitic steel were studied by differential scanning calorimetry (DSC) and electron backscatter diffraction (EBSD). The characteristics of martensitic transformation were studied by varying the temperature and time of austenitization. The results show that γ-austenite completely transforms to δ-ferrite during austenitization beyond 1523 K. The absence of martensite transformation was observed in the DSC thermogram for the sample annealed at 1523 K for 5 h. A detailed EBSD study of the time-dependent evolution of δ-ferrite revealed a significant reduction in low-angle and coincidence site lattice (CSL) grain boundaries of the martensite matrix. There was no reverse transformation (δ-ferrite → γ-austenite) observed during heating in DSC. Further, the Kolmogorov–Johnson–Mehl–Avrami (KJMA) model was employed to study the kinetics of the γ-austenite → δ-ferrite transformation. The activation energy and growth exponent obtained for this transformation were 335 kJ mol−1 and 2.1, respectively. Tis result has significant technological implications as it revealed an important fact that δ-ferrite, once formed in the material, does not dissolve by heat treatment. The characteristics of martensitic transformation were studied by varying the temperature and time of austenitization. It is observed that the γ-austenite completely transforms to δ-ferrite during austenitization beyond 5 h at 1523 K. A detailed EBSD study of the time-dependent evolution of δ-ferrite revealed a significant reduction in low-angle and coincidence site lattice (CSL) grain boundaries of the martensite matrix. For δ-ferrite, there was no reverse transformation (δ-ferrite → γ-austenite) observed during heating in DSC which signifies the difficulty associated with its dissolution by heat treatment. Further, Kolmogorov–Johnson–Mehl–Avrami (KJMA) model was employed to study the kinetics of the γ-austenite → δ-ferrite transformation. The activation energy and growth exponent obtained for this transformation were 335 kJ mol−1 and 2.1, respectively.

The high-temperature deformation behaviour of Al0.7CoCrFeNi alloy was studied at 800-1100 degrees C and 0.01-10 s 1. The alloy exhibited extensive softening via recrystallization and recovery with the examined temperature and strain rate domains. The recrystallization mechanism in the FCC phase was geometric dynamic recrystallization, and that in the BCC/B2 phase was continuous dynamic recrystallization. Further, the BCC/B2 lamellae underwent fragmentation via boundary splitting and termination migration. The amount of softening and subgrain morphology were dependent on the crystallographic orientation of the grains prior to deformation. Apart from lamellar fragmentation, dynamic globularization of BCC/B2 phase was found in certain grain colonies. Compared to heat treatment, hot deformation improved the globularization kinetics. Further, BCC/B2 precipitation occurred along the grain boundaries and at the triple points of the recrystallized FCC phase. However, the overall BCC/B2 phase fraction remained constant. Post-deformed alloy was also characterized by preferential cracking along the allotriomorphic FCC phase boundaries. The difference in strength between the idiomorphic and allotriomorphic regions was attributed to this grain boundary cracking. The activation energy for deformation showed a direct dependency on temperature and strain rate but an inverse relationship with strain.

Present investigation is aimed at understanding the deformation behavior and the development of damage in a type 316 LN austenitic stainless steel (SS) weld joint (WJ) under isothermal low cycle fatigue (IF) and thermomechanical fatigue (TMF). In-phase (IP) and out-of-phase (OP) TMF tests were carried out by maintaining a phasing relation of 0° and 180° respectively, between the mechanical strain and temperature cycles. Dynamic strain ageing (DSA) was found to exert a strong influence on the cyclic stress response (CSR) of the joint under both IF and TMF cycling. The CSR was observed to be higher under TMF compared to IF cycling due to the activation of additional hardening mechanisms in the former tests. The difference in fatigue life under TMF and IF is rationalized based on the development of deformation and damage through optical and scanning electron microscopy (SEM) coupled with electron backscatter diffraction (EBSD) studies. A clear demarcation of the strain distribution in the base metal (BM) and weld metal (WM) region of the joint is achieved through detailed EBSD analysis of the tested specimens. Cyclic plastic deformation and the associated development of damage take place independently in the BM and the WM parts of the joint, competing to cause the failure. The build-up of damage under IF and TMF cycling is dictated by a combination of DSA and δ-ferrite transformation, depending on the applied strain amplitude and the strain-temperature phasing employed. The observed life variations have been rationalized in terms of the substructural evolution and fracture behavior under different testing conditions.

Chromium alloyed Ferritic/Martensitic steels are widely used as structural materials in power plants, and considered for core applications of fast and fusion reactors. Characterization and fundamental interpretation of deformed microstructure through crystal plasticity principles are useful for tailoring desired microstructure by optimal processing methods. This study reports the characterization of plastic strain distribution in cold rolled 9Cr-1Mo steel using Electron back scatter diffraction (EBSD) technique. Small orientation changes within the individual grains were studied to gauge the accumulation of ‘geometrically necessary’ dislocations in deformed material, and correlate with the load geometry. The correlated misorientation angle distribution showed a significant presence of low angle boundaries in the deformed microstructure as compared to the annealed specimen. Crystal orientation map of deformation bands indicated significant intra-grain rotation, and the extent of rotation was distinctly different for different grains. A heterogeneous accumulation of plastic strain distribution is inferred from the grain maps of local misorientation angle (0.5º-5º) and orientation spread parameters. Analysis by Schmid factor criteria (0.4-0.5) showed more than 50% of the grains to exhibit favorable orientation for {110} <111> slip activity, whereas higher stress would be required for plastic deformation of remaining grains. Copyright © 2017 VBRI Press.

Ni coatings applied on structural alloys of molten-salt reactors have been shown to enhance corrosion resistance. Due to inherent advantages, the application of electrodeposited (ED) nanocrystalline Ni coatings could provide a progressive upgrade. The effectiveness, however, relies on the production of favorable microstructural attributes for corrosion resistance and their stability in a high-temperature radiation environment. The present study compares the annealed microstructure of electrodeposited nanocrystalline Ni of varying grain sizes: 20 nm, 50 nm, 100 nm and 200 nm. EBSD studies of samples annealed at 650 degrees C revealed a strong texture of < 001 >//ED fiber component accompanied by the formation of S3 twin boundaries. A high fraction of Sigma 3 twin boundaries desirable for corrosion resistance is found in samples with initial grain sizes of 20 nm and 50 nm. The irradiation stability of as-deposited 20 nm and 50 nm grain-sized samples was evaluated using ion irradiation at 550 degrees C and compared with unirradiated counterparts that had experienced annealing at the same temperature. Irradiation causes a marginal increase in grain growth and < 100 > texture, and a slight decrease in Sigma 3 twin fractions. The desirable microstructural attributes for corrosion resistance are largely preserved up to displacement damage of 18.5 dpa in 20 nm and 50 nm grain-sized samples.

Beneficial influence of prior thermal ageing on the cyclic life was demonstrated on a type 316 LN austenitic stainless steel weld joint under thermomechanical fatigue. Tests performed using different temperature intervals showed that the crack initiation occurs mostly in the heat affected zone in the as-welded joint. However, the failure location gets shifted to the weld region following thermal ageing. Mechanisms governing life variations between the as-welded and aged joints were identified. The localization of plastic deformation in different regions of the joints and its dependence on the microstructure was evaluated and explained on the basis of detailed EBSD investigations.

This paper presents the details on predicted and experimental microstructural evolution and high-temperature tensile behavior of a hot isostatically processed (HIPed) and heat-treated Ni-based superalloy EP741NP for aerospace applications. The phase prediction carried out using JMatPro® software from the composition of the alloy as a function of heat treatment has been found to agree with the results of characterization by scanning and transmission electron microscopy. Prediction has revealed the evolution of secondary and tertiary gamma prime (γ′) with phase fraction of ~46% during solutionization at 1483 K (1210 °C) for 8 h and ~12% during the course of aging treatment at 1144 K (871 °C) for 32 h, respectively. A uniform distribution of secondary γ′ with typical octocube morphology within a size range of 0.5–0.8 µm and a sparse distribution of tertiary γ′ of fine spherical particles with average size < 0.1 µm have been observed during study of microstructure. Electron backscattered diffraction (EBSD) studies showed epitaxial growth for γ′ phase within a grain with similar crystallographic orientation. Tensile tests conducted at room temperature and in the temperature range from 823 K to 1123 K (550 °C to 850 °C) have shown that yield strength (YS) and ultimate tensile strength (UTS) remain almost unchanged up to temperature 923 K (650 °C) due to microstructural stability of strengthening γ′ precipitate. Thereafter, it starts decreasing because tertiary precipitates cannot hinder grain boundary motion at high temperature, first because of their size and more importantly because they are usually dissolved back into the matrix at high temperature, which assist the annihilation and rearrangement of dislocations leading to reduction of dislocation density. Fractographic studies have revealed that the fracture mode is found to be mostly mixed in nature (both ductile and brittle fracture).

This article presents a systematic study to highlight micromechanisms associated with the grain interface character distribution of SS304HCu. The low-energy coincidence-site-lattice (CSL) boundary fraction is found to be increased (33 to 62 pct) with an increase in annealing temperature from 1073 K to 1323 K after 50 pct cold rolling. Furthermore, an increase in annealing temperature has shown reduction/saturation for CSL (~ 58 pct) due to diffusion-assisted grain boundary migration. Associated effective grain boundary energy has been calculated to rationalize the energy minimization process during annealing.

This study aims to quantify the improvement in the creep crack growth (CCG) resistance in the heat-affected zone (HAZ) of boron added modified 9Cr?1Mo (P91B) steel weld at 898 K. The crack growth rates in the HAZ of P91B weld have been compared with the crack growth rates in HAZ of without boron P91 steel weld. The creep crack growth rates are estimated as per ASTM E1457 using 7 mm thick compact tension specimens with a notch in the HAZ and test duration 248h-11,000 h. The CCG rate (a?) vs. C* correlation, commonly expressed as a? = D(C*)?, has been established. In comparison, the crack growth rate in the HAZ of P91 weld is found to be threefold as compared to HAZ of P91B weld; with the difference in CCG rate increasing towards a higher C* range. Creep damage assessment study has been done in the vicinity of creep crack in HAZ of a P91B weld specimen tested for 11,000 h. The extent of cavitation, cavities link-up, and micro-crack formation in HAZ of P91B weld is found to be relatively lower than HAZ of P91 weld. Most of the cavities appear to be discrete in nature. This testifies improvement in the creep crack growth resistance in the HAZ of P91B weld due to controlled boron addition of about 100 ppm to modified 9Cr?1Mo steel.

HCF-creep interaction in type 316LN stainless steel is investigated at 923 K by conducting HCF tests well below the endurance limit with high mean stress (high R-ratio). High mean stress inflicts creep damage at 923 K, which when imposed on a small alternating stress, leads to significant HCF-creep interaction. Depending on the magnitude of mean stress (R-ratio), three distinct regimes are identified, viz. (a) HCF regime (b) HCF-creep interaction regime and (c) creep regime. Detailed fractographic investigation revealed distinct fracture characteristics pertaining to each of the three regimes. HCF-creep interaction regime is marked by significant intergranularity at low values of mean stress which changes to predominantly dimpled fracture with increasing mean stress. The above observations are corroborated through detailed EBSD investigations which bring out the underlying deformation mechanisms responsible for failure under HCF-creep interaction.

This study reports the crystallographic analysis on sample extracted from the Creep Crack Growth (CCG) tested (873 K with a notch in the centerline of weld region) specimen in order to add further understanding to crystallographic slip initiation responsible for strain localization in a different zone of weldment in the vicinity of the crack tip. The microtexture evolution in the quest of strain distribution has been compared for creep cracked and weldment of the as-received specimen. A coarsening of dendrites in the thickness direction and intragrain strain localization are found to be evident in fusion zone (FZ) unlike a stable microstructure in the base metal region with strain distribution along the grain boundary. Further, an evolved procedure is adopted to assess the crystallographic slip plane in different regions of a weldment. It has been observed that slip plane of (111) type, with an average deviation angle of 6 degrees, is dominant in the base metal region of equiaxed grains microstructure. However, the grains grown epitaxially from the base metal to FZ has shown a preferential of slip plane transfer from (111) to (001) type in contrast to (001) type slip planes with average deviation angle 2 degrees in FZ.

This paper presents the results of an experimental study aimed to obtain an ultrafine equiaxed grain distribution in 18Cr oxide dispersion strengthened (ODS) ferritic steel through cold working and annealing starting with an initial columnar grain structure with a predominant α-fibre texture in a product consolidated from the alloy powders during extrusion at high temperatures. Deformation along the extruded direction (ED) resulted in the retention of α-fibre texture, while deformation in the transverse direction (TD) showed a shear banded structure with a reduced percentage of α-fibre texture. Differential Scanning Calorimetry (DSC) analysis of the deformed steel established the occurrence of two significant events during heating namely recovery and recrystallization, whose temperatures were influenced by the heating rate. The recovery and recrystallization domains have been distinctly observed at 1350 K and 1420 K respectively at a low heating rate of 7 K min−1. The resultant microstructure showed very coarse elongated grains interspersed with regions of ultrafine (<1 μm) equiaxed grains, due to the incomplete recovery. The deformed steel was subjected to a two step heat treatment designed based on the above inputs with an aim to reduce the microstructural anisotropy in longitudinal direction. The microstructure of the heat treated steel showed randomization of the initial <1 1 0>//ED α-fibre texture, which improved further with repeated deformation and two step heat treatment cycles. A gradual increase in hardness during the above cycles was observed reflecting the increase in dislocation density which offers the propensity to achieve an ultrafine grained microstructure.

9Cr-1Mo Ferritic/Martensitic (P9) steel was subjected to different heat treatments namely austenitisation followed by water quenching and air cooling and subsequently tempering. The changes in microstructures are studied using microscopy techniques. Hardness, elastic modulus and yield stress measurements through instrumented hardness testing have been carried out to evaluate the mechanical properties and correlated to microstructural changes.

The creep deformation and rupture behavior of P92 steel weld joint fabricated by narrow-gap TIG (NG-TIG) welding process have been investigated at 923 K over a stress range of 80-140 MPa. The prior-austenite grain size, M23C6 precipitate size and hardness have been found to vary significantly in the weld joint. The reduction in hardness from weld metal to base metal with a trough at the outer edge of heat-affected zone (HAZ) has been observed. Coarsening of M23C6 precipitate, recovery of martensite lath dislocation structure and formation of subgrain structure led to lower hardness in the intercritical HAZ. The creep rupture life of NG-TIG weld joint was lower than the base metal, the difference in creep rupture life between base metal and weld joint has been increased significantly with decrease in applied stress. The fracture location in the joint changed from base metal at high-stress regime to the fine grain (FG) HAZ (Type IV cracking) under lower stress level. Fracture in the FGHAZ evidenced the significant reduction in ductility, localized deformation and extensive localized cavitation. Extensive Laves phase formation with significant loss of solution strengthening contribution from tungsten and coarsening of M23C6 precipitate with prolonged creep exposure led to reduction in hardness and more extensive cavitation in the FGHAZ resulting in premature Type IV failure of the weld joint. Weld strength reduction factor about 0.59 has been evaluated for 105 h at 923 K.

This paper aims at understanding the texture evolution in extruded oxide dispersion strengthened 18Cr ferritic steel during high-temperature uniaxial compression testing at 1,423 K at a strain rate of 0.01/s based on extensive electron back scatter diffraction characterization. The α-fiber texture is observed along the extrusion direction (ED) in the initial microstructure. The flow curves generated during uniaxial compression test are used to determine the associated hardening parameters. In addition, the degree of texture evolution after deformation along the ED and the transverse direction (TD) with respect to the initial condition has been predicted using VPSC-5 constitutive model. The prediction shows that the deformation along the ED produces a dominant γ-fiber texture in contrast to the TD. This is in agreement with the experimental results where γ-fiber texture is observed, due to enhanced dynamic recrystallization at high-temperature deformation.

This paper presents the results of a study on microstructure and grain boundary character distribution (GBCD) in cold worked and annealed oxide dispersion strengthened 18Cr-ODS ferritic steel using electron backscatter diffraction (EBSD) technique. The steel in hot extruded condition shows anisotropy with respect to grain size distribution between the parallel and perpendicular axis of extrusion; however, the resultant GBCD was found to be comparable. Further, cold working and annealing was found to reduce the frequency of low-energy coincidence site lattice boundaries (CSL) due to diffusion assisted grain boundary migration during the annealing process. A statistical comparison has been made on the frequency of grain boundary character distribution and its theoretical predictions.

The study presents an EBSD based investigation on the nature of deformation occurring under different modes of cyclic loading viz. low cycle fatigue (LCF), creep-fatigue interaction (CF) and LCF-creep-HCF. Compared to LCF, cyclic life was found to decrease for CF or LCF-creep-HCF loading conditions. This was attributed to the additional damage contributions from creep in CF cycling and a combination of creep and HCF in LCF-creep-HCF loading conditions, as substantiated through a highly intergranular fracture observed in those cases. Local misorientation map derived from EBSD showed that the misorientation spread is highest for the LCF condition compared to CF and LCF-creep-HCF. This was attributed to the enhanced thermal recovery taking place during CF and LCF-creep-HCF conditions in comparison to LCF. The dislocations generated during cycling rearrange themselves into a stabilized substructure in the form of cells in the above loading conditions leading to a lower value of local misorientation in those cases. This was also accompanied by a significant decrease in number of twins in CF and LCF-creep-HCF conditions compared to LCF. The dislocation-twin interaction responsible for the process of de-twinning was found to be expedited in the former cases owing to a higher thermal recovery.