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The microstructural evolution, deformation modes, and fracture mechanisms of zirconium plate produced using ultrasonic additive manufacturing (UAM) are presented. In addition to conventional tensile testing techniques, digital image correlation captured highly variable strain accumulation in specimens loaded perpendicular or parallel to the build height (Z). When tested in parallel to Z, delamination at prior foil/foil interfaces creates strain localization noticeable in strain rate maps, whereas specimens loaded perpendicular to Z illustrate conventional strain hardening until necking accelerates delamination. Although bond strengths are statistically and spatially variable, in situ electron backscattering diffraction tests illustrate the ability for grains near interfaces to accommodate strain with twinning and slip modes consistent with conventionally produced zirconium alloys. Finally, mixtures of ductile and delamination-induced fracture highlight the interface-driven failure modes of UAM zirconium plate in the as-built condition. Graphic abstract

Third generation γ-titanium aluminides with nominal compositions Ti–45Al–5Nb–0.2B–0.2C and Ti–45Al–10Nb–0.2B–0.2C were investigated to identify the phase transformation and their morphological stability with temperature. Electron microscopy and differential scanning calorimetry were employed for the characterization of phases and for recording the corresponding transformations, respectively. It has been inferred that the order–disorder transformation temperatures α2 → α increased with increasing Niobium (Nb), while the α-transus temperature decreases. The stability of the microstructure for both alloys with temperature were also investigated. Mass change measured for the heating rates 20 °C s−1 and 30 °C s−1 reveals that the alloy Ti–45Al–10Nb–0.2–0.2C shows stability up to 1100 °C, and the alloy Ti–45Al–5Nb–0.2B–0.2C is stable up to 900 °C. The orientation relationship between the phases indicates that with the change in shape of the α phase from lamellar to equiaxed, it deviates from the Blackburn orientation relationship.

Hot deformation and softening response for the titanium aluminide Ti–48Al–2V–0.2B has been investigated. The deformation response to softening mechanisms has been examined. Deformation experiments were carried out in the strain rate range 0.01–10 s−1 keeping the temperature constant at 1200 °C and in the temperature range 1000–1200 °C at the strain rate 1 s−1. With an increase in strain rate, the microstructural changes associated with the softening mechanism include breaking of the lamellae, spheroidization of the broken laths and dynamic recrystallization. For the strain rate 1 s−1, deformation in the (α2 +γ) phase field leads to fine recrystallized grains, remnant lamellae and cavitation along the grain boundaries (for temperatures 1000 and 1100 °C). Deformation in the (α +γ) phase field leads to dynamic recrystallization at the shear bands, within the lamellae, breaking and rotation of the α phase during the continuous increase in the deformation strain.

The present investigation is aimed to find a thread between various surface textures of polycrystalline Cu–Ni alloys, in cold-rolled and annealed conditions, and the nature of graphene, grown by th...

The formation of shear bands during hot deformation of a two-phase (α2 + γ) titanium aluminide and its consequences on dynamics softening has been investigated. The starting material consists of a colony of lamellar grains along with the segregated vanadium and niobium which was subjected to hot deformation in the temperature range 1000–1175 °C at the strain rate 10 s−1. Microstructures of the deformed samples indicate that, with increase in the deformation temperature, the orientation of shear bands changes. Moreover, the extent of dynamic recrystallization also increases with deformation temperature. The softening behaviour and crystallographic orientation change within lamellae during hot deformation have been explored. The nucleation of newly recrystallized grains has been observed at twin–parent grain boundary and within the twined γ phase. Lamellae of the γ and α2 phase have been also observed to be twisted and tilted, leading to the band formations under the load, whose mechanisms have also been explored in the present study.

The hot deformation response of third-generation titanium aluminides with compositions Ti-45Al-5Nb-0.2B-0.2C and Ti-45Al-10Nb-0.2B-0.2C (hereafter referred to as Ti-45-5 and Ti-45-10, respectively) has been investigated through isothermal compression tests. The tests have been carried out in the $$ (\alpha_{2} + \gamma ) $$ and $$ (\alpha + \gamma ) $$ phase regions for both alloys. The flow response, kinetics and microstructural evolution during hot deformation have been analysed in detail, and the outcome of the investigation has been used to predict the processing window for the two alloys. The optimum processing domain for the Ti-45-10 alloy is situated 50°C higher than that of the Ti-45-5 alloy. The post-mortem analyses of the microstructures revealed that deformation in the $$ (\alpha_{2} + \gamma ) $$ phase field leads to dynamic recrystallisation of all the phases resulting in a distribution of very fine grains. Microstructural features of both alloys depict kinking and breaking of the lamellae for the equivalent temperatures. The higher strength of the Ti-45-10 alloy has been attributed to shifting of the order-disorder transition toward the higher temperature side. In the $$ (\alpha + \gamma ) $$ region, the fraction of $$ \alpha $$ phase increases more for the Ti-45-10 alloy compared with the Ti-45-5 alloy.

Surface severe plastic deformation (S2PD) of additively manufactured/three-dimensional (3D) printed metallic parts is gaining increased attention as a post-manufacturing operation to enhance the material performance in a wide variety of applications. Surface mechanical attrition treatment (SMAT) is an S2PD technique that can yield a nanostructured surface layer induced by compressive stresses and work hardening. In the present study, SMAT was performed on 316L (austenitic) stainless steel (SS) processed by selective laser melting (SLM), and the consequent effects on mechanical response were investigated. The underlying mechanisms of microstructural evolution leading to the formation of nanocrystalline grains resulting from SMAT in SLM 316L SS are elucidated. The interactions between twins and deformation bands act as potential sites for impeding the movement of dislocations, which in turn leads to the formation of stacking faults, twinning, and occasionally transform to a different crystal structure. Twin-twin and/or twin-deformation band intersections sub-divide the matrix grains into smaller cells or low-angle disoriented blocks, which result in the formation of low-angle grain boundaries and finally in nanocrystallization at the surface. The size of nanocrystalline grains increases progressively with depth from the surface to micrometer size grains in bulk. The gradient nanostructure in the additively manufactured alloy after SMAT imparts an unusual combination of strength and ductility that markedly exceeds that of conventional, bulk nanostructured, or even high-performance 316L SS (containing nanoscale deformation twins embedded in submicron-sized austenitic grains obtained by dynamic plastic deformation processes). Analytical models revealed that strengthening results from a combination of grain boundaries and dislocations. The results of the present investigation pave the way for engineering high-performance SS for a variety of engineering applications.

In the present study, hot deformation behavior of a FCC high-entropy alloy CoCuFeMnNi has been investigated to explore the stress-strain response for a wide range of temperatures and strain rates. The deformation response has been examined by plotting a processing map and examining the evolution of microstructure and texture in each of the temperature-strain rate domain. Hot compression tests were carried out in the temperature range 850-1050 degrees C at strain rates varying from 0.001 s(-1) to 10 s(-1). Stress-strain curves indicate characteristic softening behavior due to dynamic recrystallization (DRX). DRX has been observed along grain boundaries, shear bands, as well as in the interior of deformed grains. The size of dynamically recrystallized grains shows a strong dependence on deformation temperature and increases with temperature. A high degree of twin formation takes place in the DRX grains evolved inside the shear bands, and the extent of twinning decreases at high temperatures. The optimal processing window has been estimated based on strain rate sensitivity and has been validated with detailed analyses of microstructure and texture. The best region for thermo-mechanical processing has been identified as in the temperature range 850-950 degrees C at strain rate 10(-1) s-1.

The hot workability of gamma titanium aluminide alloy, Ti-48Al-2V-2Nb, was assessed in the cast condition through a series of compression tests conducted over a range of temperatures (1000 to 1175 °C) and at the strain rate of 10 S-1. The mechanism of dynamics recrystallization has been investigated from SEM Z-contrast images and from the Electron backscattered diffraction EBSD as well. It has been observed that volume fraction of the recrystallized grains increases with increasing the deformation temperature. The major volume fraction of the recrystallized grains was observed in the shear band which was forming at an angle 45 ̊ with respect to the compression direction. The mechanism of breaking of the laths and the region of the dynamic recrystallization were also investigated from the SEM Z-contrast image and EBSD. The dynamic recrystallization occurred in the region of the broken laths and shear bands. The breaking of the laths was because of the kinking of the lamellae. The shear band, kinked lamellae and dynamic recrystallized region where all investigated simultaneously.

The deformation mechanisms associated with uniaxial tensile testing are studied by conducting tensile experiments of an FeCrAl alloy using scanning electron microscopy (SEM) coupled with electron backscattered diffraction (EBSD). Prior to the deformation investigated alloy was consisting grain and precipitate size of ∼63 μm and ∼6.7 μm, respectively. The recorded SEM micrographs and EBSD data at increasing levels of strains revealed the complex phenomena of slip bands’ formation in the presence of surface grain morphology evolution and their (001), (110) and (111) crystallographic planes distortions. The grains with orientation (110)||tensile direction (TD) shows higher shape change; however, (001)||TD and (111)||TD oriented grains show higher lattice gradient formation. Extracted information from the EBSD indicates that the crystallographic rotations drive towards specific, fiber-like texture in relation to the loading direction. Postmortem analysis of the recorded microstructure during the tensile deformation explains the phenomena of crack formation in the hard-intermetallic particles before the ultimate tensile strength (UTS). However, after the UTS, pores were identified in the neck that resulted from extensive plastic deformation. In-depth analysis was carried out to identify the cause of cracks and pores formation phenomena during the tensile test.

In the present investigation, hot deformation behaviour of Fe–21Cr-1.5Ni–5Mn alloy was studied by performing isothermal unidirectional hot compression tests. The tests were carried out at strain rates of 0.01, 0.1, 1, 5 and 10 s−1 and at temperatures of 675, 750, 825, 900, 975 and 1050 °C. The samples were deformed up to 50% height reduction (e = 0.7). The flow softening behaviour was modelled using Arrhenius hyperbolic sine law approach. The predicted flow stresses and the experimental flow stresses were found to be comparable indicating that the developed model can accurately portray flow behaviour of Fe–21Cr-1.5Ni–5Mn alloy. As-received and deformed specimens showed elongated grain structure. The correlation coefficient (R2) of the experimental and predicted results for Arrhenius hyperbolic sine law model was ~0.97, while the average absolute relative error (AARE) was found to be 7.31%. The hot deformation activation energy for peak stress was found to be 508.3 kJ mol−1. The maximum value of ‘m’ (0.227) was obtained in the temperature range 975 °C–1050 °C and strain rates between 0.1 s−1 to 1 s−1. ‘m’ value between 0.1 and 0.2 is considered to be optimum for hot working. Deformation at 975 °C also gave the best match between experimental and predicted flow stress with m values between 0.1 and 0.2 and hence was considered optimum.

In the present work, evolution of microstructure and crystallographic texture during cold rolling of two phase Fe-Cr-Ni alloy was investigated. Fe-Cr-Ni alloy (in initially solution annealed condition) was uni-directionally cold rolled in a laboratory rolling mill to different thickness reductions. Scanning electron microscopy was used to observe the changes in microstructure, while X-ray diffraction was used to investigate changes in crystallographic texture of austenite and ferrite (through changes in orientation distribution function). Crystallographic texture was also simulated using different crystal plasticity models (Full constraint Taylor, relaxed constraint Taylor (lath and pancake) and co-deformation Visco Plastic Self Consistent (VPSC)). With the increase in plastic deformation, there were morphological as well as crystallographic changes in the microstructure. Strong a-fibre (RD//< 110 >) texture was developed in ferrite, while brass ({110}< 112 >) and Goss ({110} < 001 >) was dominant in austenite after 80% cold rolling. The formation of brass type texture after deformation has been attributed to the formation of shear bands and presence of strong crystallographic texture in the initial solution annealed material. Both Taylor as well as VPSC models could not capture the changes in texture with deformation accurately. For ferrite: gamma-fibre (ND//< 111 >) and for austenite: Cu ({112}< 111 >) component was always present in the simulated textures. Possible reason for this could be the pining effect of interface boundaries and non-incorporation of non-crystallographic shear banding in the Taylor and VPSC models.

The deformation mechanisms of neutron-irradiated 304 L stainless steel have been investigated using the in-situ electron backscattered diffraction (EBSD) technique. To decipher the role of irradiation, a detailed analysis was performed on irradiated miniature samples and compared with nonirradiated samples. At three levels of engineering strain, —0.0%, 4.8%, and 14.5%—microstructural features as well as EBSD were recorded at the identical location during in-situ deformation testing. Post-mortem analysis of the EBSD data revealed that the neutron-irradiated samples had higher fractions of the slip bands even at low amounts of deformation. Along with the slip bands, the neutron-irradiated sample showed the twins and martensitic phase formed almost parallel to the slip bands. In addition, the image results also indicated that the formation of twins and phases associated with the slip bands. A detailed mechanistic understanding has been investigated to identify the (111)γ planes orientation with respect to the loading direction associated with the formation of twins and martensite. The newly formed deformation twins and martensite were also found to maintain this relationship when they existed together.

Present work deals with modification of lamellar microstructure of a γ – TiAl alloy to globular concerning α2 phase. For this investigation, cast Ti-48Al-2Cr-2Nb alloy was subjected to cyclic heat treatment. This cycle was consisting of heating and cooling alternatively to order – dis-order (α2 ↔ α) regime. Thermal cycles led to the change of lamellar α2 phase to globular. Additionally, with time of globularisation, average micro-hardness was identified to be decreasing at the expense of grain coarsening with respect to γ and globularised α2 phase. Phase percentage of both phases was observed to be stabilizing with cycling time. Based on phenomena of globularisation with time, a possible mechanism was designed for understanding the mechanism of globularisation.

Two titanium aluminide (TiAl) based compositions with different niobium (Nb) contents, namely Ti–45Al–5Nb-0.2B-0.2C and Ti–45Al–10Nb-0.2B-0.2C, have been investigated for their hot deformation response. Prior to deformation, microstructural features were modified by a specially designed thermal treatment. The modified microstructures were intended to be equiaxed to facilitate the deformation response. Deformation responses of materials with modified microstructures were examined using isothermal hot compression tests. Strain rate sensitivity maps were generated from the stress-strain curves and suitable domains for optimal processing were identified. The strain rate sensitivity maps show that the workability of the alloys decreases with increasing strain rate and decreasing temperature. An increase in the proportion of dynamically recrystallized grains, which is indicated by deviation from the ideal orientation relationship between the phases, corresponds to the regions of high strain rate sensitivity. The processing domain for the alloy Ti–45Al–5Nb-0.2B-0.2C has been identified within the temperature range 1075 °C–1200 °C at the strain rate 0.1 s−1, whereas for the Ti–45Al–10Nb-0.2B-0.2C alloy, the temperature range of 1125 °C–1200 °C has been found to be most suitable processing domain at the same strain rate.

In an expansive field of metals, magnesium has been trending of late in automobile, aerospace, defense, sports, electronic and biomedical sectors as it offers an advantage in lightweighting. In the realm of Mg-based materials, Mg nanocomposites have a good combination of specific strength, thermal and damping properties, but lack a high ductility and do not typically undergo a large amount of uniform elongation. The current work bridges this gap by reporting a magnesium nanocomposite (Mg�1.8Y/1.5Y 2 O 3 ) that exhibits a significantly high tensile ductility of 36. Microstructural characterization of the nanocomposite revealed that the striking presence of micron-Mg�Y phases and nano-Y 2 O 3 particles in matrix led to a bimodal particle distribution which affected the dynamic recrystallization mechanism. It was also observed that the addition of Y 2 O 3 nanoparticles weakened the texture of nanocomposite. The dominating influence of texture weakening over other mechanisms (grain refinement and alleviated micro-strain) on the plastic deformation/ductility of the nanocomposite is highlighted, and the contribution of nanoparticles toward the enhancement of ductility is ascertained. In contrast to the previous studies where Mg-based nanocomposites are known to have improved strengths, this approach can be used to develop magnesium nanocomposites that are exceptional. © 2019, Springer Science+Business Media, LLC, part of Springer Nature.

A novel in-situ synthesis technique has previously been proposed for the synthesis of magnesium based nano composites, by exploiting the thermodynamic reactions, to fabricate nanoparticles in-situ during the melt processing. Although the microstructural aspects of formation of such nanocomposites have been dealt with previously, the implications of the same on the texture and hence on mechanical properties are not certain. In the present work, the evolution of crystallographic texture and its influence on tension-compression asymmetry (Tensile yield strength divided by Compressive yield strength) and thereby, the impact on fatigue failure mechanisms is studied by comparing the behaviour of Mg-1.8Y/1.53ZnO nanocomposite and its monolithic alloy, Mg-1.8Y. The Mg-1.8Y/1.53ZnO nanocomposite revealed a very strong two component texture, not akin to the weak texture of Mg-1.8Y alloy. The texture was attributed to the loss of Y in the matrix and consumption of Y in formation of Y2O3 nanoparticles in-situ and the formation of the beta(1)' (Mg-Zn') rods during extrusion. Further, this texture exhibited by the nanocomposite favoured high twinning activity under compression, thereby causing strong asymmetry in the tensile and compressive yield strengths. The fatigue tests indicated a superior performance of the nanocomposite as compared to the alloy. The deformation and damage mechanisms, when studied in correlation with the asymmetry revealed that the asymmetric materials exhibit steeper S-N curves as compared to the symmetric materials.

Magnesium has been trending of late in automobile, aerospace, defense, sports, electronic and biomedical sectors as it offers an advantage in light-weighting. In aluminum, titanium, and steel dominated aerospace and defense sectors, applications of Mg were banned/restricted until recently due to perceived easy ignition and inability to self-extinguish immediately. Strength is generally inversely related to ductility, weak texture and unrelated to ignition resistance, making it challenging to optimize all four concurrently in a material. We address this challenge by designing a low density (~1.76 g.cm−3) in-situ Mg nanocomposite. It is a resultant of a sequence of in-situ reactions during melt processing and extrusion. The in-situ formed Y2O3 nanoparticles exhibit coherency with matrix and lead to development of large amount of elastic and plastic strain fields around them. These nanoparticles and secondary phases (Mg2Ca and Mg2Y) are responsible for the nanocomposite’s high tensile strength (~343 MPa). A weak texture mediated tensile ductility of 30% and compressive failure strain of 44% is observed. Further, the ignition temperature increased to 1045 °C (near the boiling point of Mg) due to the formation of protective surficial oxide layers aided by the presence of insulating Y2O3 nanoparticles, rendering the nanocomposite outperform other traditional commercial Mg-based materials.

In the present investigation, evolution of microstructure and texture was studied for a β titanium alloy during cold rolling (unidirectional rolling (UDR) and cross rolling (multi-step cross rolling (MSCR) and two step cross rolling). For both UDR and MSCR of initially hot rolled alloy consisting of elongated and equiaxed grain structure, the occurrence of shear bands inside the grains was the main feature of the microstructure. The density of these shear bands was dependent on the cold rolling reduction and strain path and was found to be orientation dependent. Shear bands preferentially occurred in γ-fiber (normal direction (ND)//〈111〉) oriented grains. The regions with shear bands had higher hardness than the regions without shear bands, and {111}〈112〉 component of the γ-fiber was found to be more susceptible to formation of shear bands. The orientation dependence of these shear bands was analyzed within the framework of Dillamore's plastic instability criterion. During UDR, strong α and γ-fibers were observed after highest strain (e = 1.6), while strong rotated cube ({100}〈110〉) texture developed after MSCR at highest strain (e = 1.6). The volume fraction of both α and γ fibers gradually increased with the increase in cold rolling reduction during UDR. For MSCR, the rotated cube component gradually increased with increase in cold rolling reduction. In solution annealed β-Ti alloy with equiaxed grain structure, α and γ fibers were formed after highest strain (e = 1.6) during UDR. However, due to large grain size, both α and γ fibers were discontinuous. The texture development was found to be more strongly dependent on the strain path than the initial microstructure during cold rolling.

Severe plastic deformation of the magnesium alloy WE43 (Mg-4%Y-2.3%Nd-0.5%Zr) has been carried out by multi-axial forging (MAF) in order to refine the grain size from 25 µm to 6 µm. Deformation behaviour of the as-processed material has been investigated. Compression tests were carried out in the temperature range 250–450 °C and in the strain rate range 10−3–10 s−1. Strain-rate sensitivity values were calculated from the stress-strain curves. A high value of strain rate sensitivity was noticed in the temperature range 350–400 °C and the strain rate range 10−4–10−2 s−1, which indicated the possibility of superplastic forming after multi-axial forging. The superplastic behaviour of MAF processed samples was further investigated by carrying out tensile tests. An excellent superplastic elongation of 470% was obtained at the temperature 375 °C and strain rate 3*10−4 s−1. The material also exhibited superplasticity at higher strain rates at this temperature.