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In this work, uniaxial tensile tests of Inconel-718 (IN718) sheets were performed at elevated temperature domain of 773-1023K and a deformation rate between 0.001-1s-1. A substantial reduction in m...

The Ti-5553 alloy has high strength close to that of the β Ti alloy for applications in high-strength structural components. In this article, results of detailed investigations of dilatometric responses of this alloy are presented. A Ti-5553 alloy ingot (150 mm diameter and 250 mm length) was double vacuum arc remelted (VAR), homogenized, forged and rolled. A very interesting dilatometric response was observed in this deformed material during heating in a dilatometer. Monitoring the sample length during continuous heating at a constant heating rate showed expansion and contraction in different temperature ranges. The observed contraction could not be attributed to any known phase transformation feasible in this alloy over the corresponding temperature range. Interestingly, the dilatometric contraction during heating was found to be orientation dependent. Precise lattice parameter measurements done on the basis of synchrotron data showed that the α to β phase transformation is associated with a slight expansion. To understand physical phenomena causing the dilatometric expansion/contraction, evolutions of microstructure and texture were investigated by intermittent sample removal at various intermediate temperatures along the heating path. Dilatometric responses were analyzed in terms of α phase dissolution, recovery, recrystallization of both α and β phases and release of anisotropic residual stress present in the starting material. The present investigation showed that the dilatometric examination coupled with microscopic observations can be employed for identifying the temperature ranges over which these processes occur—the information relevant for devising thermomechanical treatments of this alloy. This article also describes a method of assessing micro-residual stresses present in the two-phase Ti alloys from the dilatometric response of a small sample from the thermomechanically processed material.

Ti 5Al 5Mo 5V 3Cr alloy (Ti-5553) is a high strength near β titanium alloy for aircraft structural applications and has found its specific application in landing gear components. In the present paper a systematic approach was taken to generate and choose three distinct microstructures; one with full β, and the other two with two-phase lamellar α+β microstructures with distinctly different aspect ratios of α precipitates. Tensile behavior of these three microstructures was studied. Few of the distinct observations include 1) Even in the single phase β microstructure, yield strength (YS) was reasonably high, 2) For the two-phase lamellar α+β microstructure high YS and no work hardening were observed, 3) Among the lamellar microstructures, small aspect ratio of α showed much higher YS, but less ductility as compared to the larger aspect ratio of α. Detailed TEM based investigations of deformation micro-mechanisms along with study of eventual failure mechanisms were carried out to explain the above mentioned tensile responses of these microstructures. Differences between the microstructures with small vs. large aspect ratios of α were specifically addressed in terms of tensile behavior and underlying deformation micro-mechanism and failure mode.

Development of ultrahigh-strength steels having optimum combination of high ultimate tensile strength, fracture toughness and corrosion resistance has gained much importance due to emerging applications in the aerospace, medical and automobile industries. Indigenous development program of such steel has been started in India. Initial heats have been prepared following the standard processing route, and it was found that while they showed very high strength (1725–1757 MPa), ductility in the transverse direction (13–32% reduction in area) was lower than specification (minimum 35% reduction in area). Poor texture was initially believed to be the possible reason for this low transverse ductility. Hence, investigative characterization work was taken up to understand this effect in different heats of Aerospace Material Specification (AMS5936 C) steel samples. In this paper, it would be conclusively discussed how microstructural inhomogeneity and the presence of inclusions became overpowering reasons for poor transverse ductility as compared with the textural reasons in indigenous material.

Ti-5Al-5Mo-5V-3Cr (Ti-5553) is a high strength β titanium alloy. It is now commonly used in thick section aerospace components. In general, the thermo-mechanical processing (TMP) of β titanium alloys done at high temperature to obtain uniformly recrystallized fine grain structure is one of the major challenges. Through this work, a TMP window for Ti-5553 (through systematic variation in % reduction and post deformation annealing temperature) has been developed to obtain fine uniformly recrystallized β grains. Grain size has been quantified on EBSD generated orientation maps, by applying stereological methods, image processing and automated reconstruction. Effects of % deformation and post deformation annealing temperature, as well as that of initial ingot size prior to deformation and the capacity of the forge on the static and dynamic recrystallization behavior, which eventually determine the final grain size distribution, have been illustrated.

Elemental partitioning across the precipitate/matrix interface controls the kinetics of precipitate evolution, during growth and coarsening. We present the first integrated analysis of evolution of both the aspects of microstructure, i.e., the size of nano-scale, ordered, coherent γ′ precipitates as well as the lattice misfit at the interface, in light of elemental partitioning, applied to a Ni-based superalloy, Haynes 282. In this work, eexperimental analyses by atom-probe tomography, transmission electron microscopy, and x-ray diffraction are combined with thermo-kinetic modelling using ThermoCalc and TC-PRISMA. For the first time, rate controlling elements for growth and coarsening stages of γ′ precipitate have been identified: Ti diffusion into γ′ precipitate controls the growth rate; coarsening kinetics is controlled by the diffusion of Mo into the matrix. For identification of growth controlling element, a completely new approach has been adopted here that has not been reported earlier. For the coarsening kinetics, unlike most of the recent literature, we have used the thermodynamic parameter corresponding to the non-dilute, non-ideal γ solid solution phase in the modified LSW rate equation. This approach provides a much realistic prediction, as Ni-based superalloys show significant deviation from ideality. Misfit has been found to be positive and found to decrease with ageing time in the present alloy. Elemental partitioning explained quantitatively the variation in the lattice parameters and the misfit. Values of several important material properties, like interfacial energy, gradient energy coefficient at the matrix/ precipitate interface have also been determined.

IN718 sheets were separately solution treated to two different temperatures i.e. 970°C (HT970) and 1070°C (HT1070). Due to higher solution treatment temperature (1070°C), the microstructure...

We present the low-cycle fatigue behavior of a new nickel-based superalloy in the temperature range of 650 °C to 760 °C. Two initial microstructures having different precipitate distribution has been chosen for this. Low-cycle fatigue behavior of these two microstructures has been characterized using mechanical parameters. These parameters include cyclic anisotropy, plastic strain accumulation and back stress evolution. The deformation response has been substantiated by detailed electron microscopy studies. A deformation mechanism map illustrating defect activity at various testing conditions has been constructed based on the microscopy results.

A promising approach to decrease deformation load and improve ductility during forming of Inconel-718 (IN718) is through the use of solution treated blanks. In the present work, IN718 sheets were separately solution treated to different temperatures in the domain of 970 – 1070 ° C at an interval of 50 ° C to dissolve the strengthening precipitates ( γ ′ and γ ′ ′ ), and subsequently, were oil quenched to retain the microstructure. Due to significant difference in average grain size, the solution treated samples of 970 ° C (HT970) and 1070 ° C (HT1070) were selected for tensile characterization, deep drawing analysis, and micro-texture evolution. The tensile test response showed approximately 30% improvement in ductility and 27% reduction in load in case of HT1070 material with respect to that of HT970 material. The deep drawing process window was evaluated using flat bottom and hemispherical dome punch geometries, and it was found that the limiting draw ratio (LDR) improved marginally by 4.5% in case of HT1070 material. This improvement was due to the dominating presence of cube component in initial texture of HT1070 material. The high presence of cube and goss components in initial texture and the large difference in Taylor factor of individual grains at critical regions of deep drawn cups led to higher unsatisfactory surface roughness in the case of HT1070 material. Hence, it is suggested that the deep drawn components of HT970 material has better part performance in terms of surface roughness. Further, an attempt was made to correlate the fractographs with the fracture and formability behavior of sheet metal.

Two fundamental questions have been addressed on a recently developed high strength β Ti alloy, Ti-5Al-5V-5Mo-3Cr, with respect to two very different types of microstructures, one bimodal and the other fully lamellar, both having similar yield strength. Those are: 1) If and what would be the difference in their LCF response? 2) What would be the sequence of plastic deformation among the phases of different morphology, β, globular α and lath α? TEM based deformation micro mechanism explained the LCF response at various strain amplitudes. Crack path-microstructure interaction explained the difference in life, specifically observed at low strain amplitude.

Recently, aerospace industries have shown increasing interest in forming limits of Inconel 718 sheet metals, which can be utilised in designing tools and selection of process parameters for successful fabrication of components. In the present work, stress-strain response with failure strains was evaluated by uniaxial tensile tests in different orientations, and two-stage work-hardening behavior was observed. In spite of highly preferred texture, tensile properties showed minor variations in different orientations due to the random distribution of nanoprecipitates. The forming limit strains were evaluated by deforming specimens in seven different strain paths using limiting dome height (LDH) test facility. Mostly, the specimens failed without prior indication of localized necking. Thus, fracture forming limit diagram (FFLD) was evaluated, and bending correction was imposed due to the use of sub-size hemispherical punch. The failure strains of FFLD were converted into major-minor stress space (σ-FFLD) and effective plastic strain-stress triaxiality space (ηEPS-FFLD) as failure criteria to avoid the strain path dependence. Moreover, FE model was developed, and the LDH, strain distribution and failure location were predicted successfully using above-mentioned failure criteria with two stages of work hardening. Fractographs were correlated with the fracture behavior and formability of sheet metal.

Most engineering components used in gas/steam turbines are exposed to a range of complex loading conditions resulting from startup and shutdown procedures. These loading conditions involve superimposition of time-dependent creep on cyclic fatigue and can be simulated by properly designed high-temperature creep-fatigue tests. Creep-fatigue interaction is a function of duration and position of dwell in the loading waveform, and the material microstructure. The objective of this work is to investigate the creep-fatigue interaction response of a newly developed γ′-strengthened wrought nickel-based superalloy (HAYNES 282), which has a potential application in advanced ultra-supercritical steam turbines. Creep-fatigue tests are conducted at 760°C with strain dwell either at tensile peak or compressive peak or at both tensile and compressive peak positions for different dwell times of 100 and 1,000 s. The test results are analyzed with respect to evolutions of peak stress, stress amplitude, stress relaxation, hysteresis loop, inelastic strain energy density, and degree of softening. Degree of softening is found to increase with dwell position at tensile, compressive, and both peaks in that order. Tests with dwell at both tensile and compressive peak positions are found to be the most damaging, showing the least life. Between tensile dwell and compressive dwell tests, interestingly, those with compressive dwell show a significantly reduced life. Increasing dwell time aggravates the damaging effect manifold. The mechanism of fracture at the end of life is illustrated with fractographic characterization.

In this present work, we present an accumulated inelastic strain rate based methodology to predict creep fatigue life of two different superalloys i.e. Haynes 282 and IN 718. The evolution of differential strain rate during creep and fatigue respectively motivated the present work. As creep is the rate controlling damage process in creep fatigue interaction, present mean strain rate based approach considers creep strain rate as a kinetic variable controlling the process. The other variable considered for this approach is accumulative cyclic strain during Creep-fatigue interaction. Our prediction method is purely based upon a relative accumulation rate of creep and fatigue strain. This method correlates the creep fatigue life with rate of interaction in strain-controlled regions successfully from the data of creep fatigue tests on those superalloys at two temperatures, 650 °C and 760 °C. We found suitable microstructure sensitive constants in a lifing model.

The forming limit diagram (ε-FLD) was estimated by deforming IN-718 sheet metal in different strain paths using a sub-size limiting dome height test set-up. The bending strains induced due to the use of smaller punch were estimated in all the strain paths, and the corrected ε-FLD was evaluated. The mathematical models such as Hill localized necking, Swift diffuse necking and Storen-Rice bifurcation theories were implemented to predict the limiting strains. In-order to avoid the path dependency of the ε-FLD during multi-stage forming process, stress based forming limit diagram (σ-FLD) was estimated using von-Mises and Hill-48 anisotropy plasticity theory with incorporation of Hollomon power hardening law. It was found that the bending strain influenced the limiting strains and stresses in the forming limit diagram. However, IN-718 material has encouraging formability in stretch forming process. The plot of the equivalent strains versus triaxiality indicated increasing limiting strain of the material in tension-tension mode.

Commonly used 12.5Cr-5Ni consumable specified for welding of martensitic stainless steels is compared with newly designed 14.5Cr-5Ni consumable in terms of their suitability for repair welding of 410 and 414 stainless steels by gas tungsten arc welding process. Changes in microstructure and austenite evolution were investigated using optical, scanning electron microscopy, X-ray diffraction techniques and Thermo-Calc studies. Microstructure of as-welded 12.5Cr-5Ni weld metal revealed only lath martensite, whereas as-welded 14.5Cr-5Ni weld metal revealed delta-ferrite, retained austenite, and lath martensite. Toughness value of as-welded 12.5Cr-5Ni weld metal is found to be significantly higher (216 J) than that of the 14.5Cr-5Ni weld metal (15 J). The welds were subjected to different PWHTs: one at 923 K (650 °C) for 1, 2, 4 hours (single-stage PWHT) and another one at 923 K (650 °C)/4 h followed by 873 K (600 °C)/2 h or 873 K (600 °C)/4 h (two-stage heat treatment). Hardness and impact toughness of the weld metals were measured for these weld metals and correlated with the microstructure. The study demonstrates the importance of avoiding formation of delta-ferrite in the weld metal.

Ti–5Al–5V–5Mo–3Cr is one of the latest high strength β titanium alloys to be used for larger size components in aircraft structures replacing Ti–10V–2Fe–3Al. In the present study, a double VAR melted ingot was thermo-mechanically processed and it’s microstructure and tensile properties determined as a function of β as well as α + β solution treatment and aging. The β solution treatment and aging resulted in higher strength and α + β solution treatment and aging resulted in an optimum combination of strength and ductility. Its aging behavior was studied as a function of time and temperature and corresponding microstructure as well as fractographs of tensile tested specimens were recorded. This systematic study should help in further modeling its mechanical behavior.

Present paper discusses about a new methodology to quantify cyclic damage through ultrasonic measurement. Based on experimental results, correlations have been made between damage accumulated inside the material due to strain excursions and corresponding ultrasonic parameters. It has been proposed that based on the existing correlation between attenuation coefficient and number of cycles to failure, fatigue failure characteristics can be partitioned into two regimes (a) failures due to early nucleation and rapid propagation of cracks and (b) failures due to delayed propagation and crack coalescence. Plastic strain accumulation and surface crack density have been chosen as two physical parameters directly influencing attenuation coefficient and it has been observed that with increasing plastic strain accumulation, ultrasonic attenuation increases. Between two primary echoes of ultrasonic spectra, some secondary defect echoes have been found. A damage descriptor has been introduced by taking difference between the bandwidth of defect echo and backwall echo normalized by overall amplitude frequency distributions of backwall echo. It has been found to bear sensitivity towards surface crack density. This quantitative estimation differentiates between the classical descriptions of damage due to dislocation mediated plasticity, micro crack generation and coalescence.

The tensileanisotropy properties of Inconel-718 sheet metal were evaluated and the forming limit diagram (FLD) was established experimentally by deforming the material in different strain paths covering from tension-tension to tension-compression mode. Finite element model of the stretch forming process was developed successfully to predict limiting dome height (LDH) and strain distribution incorporating the Barlat-89 yield criterion and experimental FLD. It was found that the left side of FLD has higher forming limitscompared to right side. The IN-718 has encouraging stretch formability with uniform strain distribution in the cup compared to Ti6Al4 V alloy reported in previous literature.

A combined set of thermo-mechanical steps recommended for high strength beta Ti alloy are homogenization, deformation, recrystallization, annealing and ageing steps in sequence. Recrystallization carried out above or below beta transus temperature generates either beta annealed (lath type morphology of alpha) or bimodal (lath+globular morphology of alpha) microstructure. Through variations in heat treatment parameters at these processing steps, wide ranges of length scales of features have been generated in both types of microstructures in a near beta Ti alloy, Ti-5Al-5Mo-5V-3Cr (Ti-5553). 0.2% Yield strength (YS) has been correlated to various microstructural features and associated heat treatment parameters. Relative importance of microstructural features in influencing YS has been identified. Process parameters at different steps have been identified and recommended for attaining different levels of YS for this near beta Ti alloy. (C) 2014 Elsevier B.V. All rights reserved.

A physics-driven and microstructure-based model has been formulated for monotonic stress–strain behavior and applied to a polycrystalline nickel based superalloy, Rene 104. While the yield strength of this alloy is strongly dependent on size and distribution of the ordered γ׳ precipitate, the post-yield behavior is found to be fairly insensitive to the same. Additionally, post-yield hardening and softening rates are found to vary quite significantly within the narrow range of test temperatures examined. For a model to be able to consistently explain all these observations (a) it must explicitly account for microstructural effects and temperature dependence, and (b) it must be aware of the specific strengthening mechanisms unique to nickel-based superalloys. Accordingly, the present effort starts with Estrin׳s dislocation based framework (Estrin (1996) [4] ), and then extends the same to incorporate post yield strengthening/softening mechanisms. This paper presents details of this mechanism guided semi-empirical monotonic stress–strain model and its ability to describe flow behavior for different microstructures over a range of temperatures.

In this paper, total strain-controlled high temperature (760 °C) low cycle fatigue (HTLCF) behaviour (at 0.5% strain amplitude) of a new γ′-strengthened wrought Ni based superalloy (Haynes 282) for various ageing conditions is presented for the first time, emphasizing the microstructural effects. Haynes 282 is a promising material for hot gas path components of ultra-supercritical steam turbines due to its adequate fatigue property at elevated temperatures, along with high creep and oxidation resistance. Various microstructures were generated by varying ageing time (1 day, 6 days and 9 days) and temperature (650 °C and 760 °C). While continuous cyclic hardening behaviour was witnessed for lower aging temperature (650 °C), predominantly cyclic softening after initial hardening through few cycles was observed for higher aging temperature (760 °C), due to formation of more number of larger size voids and secondary cracks in the later specimen during the testing (as characterized by X-ray tomography). Underlying deformation mechanisms (characterized through TEM) and fracture modes (characterized through SEM, EDS) were correlated to alloy's microstructures under various HTLCF conditions; distinct differences were observed between the two ageing temperatures. While 650 °C, 9 days ageing condition showed primarily signatures of γ′ shearing, 760 °C, 9 days ageing condition showed primarily the Orowan mechanism of deformation. For 650 °C ageing condition, predominantly intergranular fracture mode has been observed, which is attributed to the presence of brittle primary MC particles on the boundaries. Whereas for the 760 °C ageing condition, the fracture mode remained predominantly transgranular because it involves less crack deflection through its path. Plastic strain energy density based life prediction model were used to predict fatigue life. Close agreement between calculated and measured life indicates validity of these models for the present material.

The fabrication of Inconel 718 (IN718) sheet metal components often requires larger deformation loads at room temperature. In this regard, deformation of the material at elevated temperature is a promising approach for reducing the forming load and enhancing the formability. Hence, the flow-stress behavior of IN718 sheets at elevated temperatures within the range of 773–973 K over wide ranges of strain rate (from 0.001 to 1 s−1) was studied by uniaxial tensile testing. The peak load reduced significantly by 75.6 and 8.5 % at 923 K and 0.001s−1 compared with room temperature and 773 K, respectively. Also, the total elongation improved by 65.4 and 16.5 % at 923 K with respect to room temperature and 773 K, respectively. In addition, a substantial improvement in the total elongation was observed with decrease in strain rate at higher temperatures. Seven different constitutive models, viz., Johnson-Cook (JC), modified-JC (m-JC), modified-Arrhenius equation (m-ARR), mechanical threshold stress (MTS), Rusinek-Klepaczko (RK), modified Zerilli-Armstrong (m-ZA), and the artificial neural network (ANN) were developed to describe the deformation behavior of IN718 sheet material at elevated temperatures and varying strain rates. Furthermore, suitability of these developed models was determined by comparing three standard statistical parameters, namely correlation coefficient (R), average absolute error (Δ), and standard deviation (SDA). The results showed that m-JC and m-ZA models predicted the flow stress very well in accordance with the experimental data. However, the trained ANN model could predict the flow-stress behavior more accurately throughout the entire testing condition. Though the ANN model was the best among all seven models, it was strongly dependent on an extremely good set of experimental data. Hence, the physical-based m-ZA model was considered to be the suitable model that could precisely predict the flow-stress behavior of IN718 sheet material.

Ti-5553 (Ti–5Al–5Mo–5V–3Cr) is a near beta Ti alloy with potential applications in structural components of aircrafts. In near beta Ti alloys, microstructural features can be varied over a wide range of length scales by changing different heat treatment parameters. Quantitative characterization of different microstructural features of each of those differently heat treated material is of considerable importance to eventually develop a model relating quantitatively, processing, microstructure and mechanical properties. In the present work, quantitative microstructure characterization, using stereological methods, has been performed on various microstructures developed through variations in separate heat treatment variables, as well as variation in each of the different individual variables of a set of sequential combined thermo-mechanical processing steps to obtain beta annealed microstructure. Quantitative effect of processing on microstructure is discussed and a TTT diagram is constructed for alpha precipitation in Ti-5553 alloy.

Alloys in the Mo-rich corner of the Mo-Ti-Zr-C system have found broad applications in non-oxidizing environments requiring structural integrity well beyond 1273 K (1000 °C). Alloys such as TZM (Mo-0.5Ti-0.08Zr-0.03C by weight %) and TZC (Mo-1.2Ti-0.3Zr-0.1C by weight) owe much of their high temperature strength and microstructural stability to MC and M2C carbide phases. In turn, the stability of the respective carbides and the subsequent mechanical behavior of the alloys are strongly dependent on the alloying additions and thermal history. A CALPHAD-based thermodynamic modeling approach is employed to develop a quaternary thermodynamic database for the Mo-Ti-Zr-C system. The thermodynamic database thus developed is validated with diffusion multiple experiments and the validated database is exercised to elucidate the effects of alloying and thermal history on the phase equilibrium in Mo-rich alloys.

Ti–5Al–5V–5Mo–3Cr alloy is a relatively new alloy developed for aircraft structural application where fracture toughness is an important property of consideration. A systematic variation of processing parameters has been carried out to generate different beta annealed microstructures, in terms of their dimensions in this alloy. Quantitative measurements of microstructural features have been carried out using stereological procedures. Different length scales of features have been correlated with the fracture toughness in order to optimize the processing parameters to develop desired microstructure that results in improved fracture toughness. The change in fracture mode associated with different microstructures has been investigated using fractographic analysis.

We present detailed analyses of dwell characteristics of various waveforms of creep fatigue interaction tests performed on the nickel-based superalloy IN 718. We discuss the effects of different dwell modes (strain, stress, and mixed) on creep fatigue properties. Strain dwell tests cause relaxation/accumulation of the mean stress, and stress dwell tests cause accumulation/relaxation of mean strain. True interaction of strain-controlled low cycle fatigue and creep takes place when stress-controlled dwell has been introduced within a strain-controlled cycling. In this article, the effects of pure and mixed modes have been compared in terms of the creep strain accumulation rate at dwell positions. It has been found, irrespective of creep and fatigue, that there is also a second competitive process that goes on, like tensile strain accumulation and compressive strain accumulation. These two processes compete with each other and show a difference in evolution with cycles. Mean strain rates for different stress and mixed control tests have also been determined; by comparing the creep strain accumulation rate and plastic strain rate, the competition of creep and fatigue processes has also been demonstrated in this article. The mechanism of cracking and cavity formation has also been illustrated by computed microtomography and subsequent fractography.

The evolution of recrystallized microstructure of cold-rolled aluminium alloy AA8011 is investigated with the help of optical metallography, orientation imaging microscopy (OIM), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), electrical resistivity and microhardness measurements at different annealing conditions. Tensile testing of the isochronally annealed specimens is performed to examine the effect of annealing temperature and microstructure on mechanical properties. Precipitates affect the grain growth behaviour and texture evolution. Normal grain growth takes place prior to abnormal grain growth. A wide range of grain size distribution and a combination of cube, rolling and random texture is observed at complete recrystallized condition. Our results provide not only new insight into aluminium packaging materials (i.e., foils, cans, and air conditioning ducts) but also a platform to better understand the recrystallization of a wide range of related alloys.

The solid-state β→β + α transformation in titanium alloys leads to complex microstructures with feature spanning across a range of length scales. In order to develop a better understanding of the microstructural evolution process, a detailed characterization of the crystallography of α laths formed from the β phase in a candidate α/β Ti alloy, Timetal 550, has been carried out. Specifically, the influence of the orientation relationship (OR) between the grain boundary α (GB α) and the adjacent β grains on the microstructural evolution has been investigated in this alloy employing orientation imaging microscopy (OIM) studies in a high-resolution SEM. The results indicate that the colony microstructure (clustering of α laths belonging to the same variant) tends to develop in the β grain that exhibits the Burgers OR with the GB α allotriomorph, whereas the basketweave microstructure (clustering of multiple variants) develops in the adjacent β grain. Additionally, the multiple variants of α laths forming the ...

Nb-Si alloys have gained much attention over the last decade as the next generation alloys for high-temperature aero-engine applications due to their low density and improved mechanical properties. However, the microstructures of these alloys are quite complex and vary significantly with the addition of elements such as Ti and Hf. Hence, an improved understanding of the phase stability and the microstructural evolution of these alloys is essential for alloy design for advanced high-temperature applications. In the present paper, we describe the microstructural evolution modeling results of the dendritic and eutectic solidification of the binary Nb-16 at.% Si alloy, obtained using a Phase-Field simulations performed with MICRESS. The effect of parameters; such as heat extraction rate, the ratio of the diffusivity of the solute in liquid to solid, and the interfacial energy of liquid and solid interface, on the microstructural evolution during dendritic solidification is discussed in detail.

The development of a set of computational tools that permit microstructurally based predictions for the tensile properties of commercially important titanium alloys, such as Ti-6Al-4V, is a valuable step toward the accelerated maturation of materials. This paper will discuss the development of neural network models based on a Bayesian framework to predict the yield and ultimate tensile strengths of Ti-6Al-4V at room temperature. The development of such rules-based model requires the population of extensive databases, which in the present case are microstructurally based. The steps involved in database development include producing controlled variations of the microstructure using novel approaches to heat treatments, the use of standardized stereology protocols to characterize and quantify microstructural features rapidly, and mechanical testing of the heat-treated specimens. These databases have been used to train and test neural network models for prediction of tensile properties. In addition, these models have been used to identify the influence of individual microstructural features on the tensile properties, consequently guiding the efforts toward development of more robust mechanistically based models. Based on the neural network model, it is possible to investigate the influence of individual microstructural features on the tensile properties, and in certain cases these dependencies can point toward unrecognized phenomena. For example, the apparently unexpected trend of increase in tensile strength with increasing prior β-grain size has led to the determination of the pronounced role of the basketweave microstructure in strengthening these alloys, especially in case of larger prior β grains.

The recrystallization behaviour of 92% cold rolled commercial pure aluminium has been studied. Annealing was done at different conditions to evaluate the effect of recrystallization temperature and time on the microstructure and texture of the alloy along with a study of subsequent precipitation. Variation of orientation between grains has been studied by the orientation imaging microscopy (OIM). During precipitation, cube component {001} has dropped and rolling texture component \(\{112\} \) has increased comparatively. Recrystallization texture is the combination of cube, rolling and random texture. However, during grain growth strong cube grains have formed. A significant number of dislocations are present during grain growth owing to the pinning effect of Al3Fe particles.

Microstructures, hardness, tensile properties and texture of cold-rolled AA1235 alloy are investigated under different annealing conditions. Precipitation of Al3Fe particles occurs during annealing of the alloy. These precipitates largely affect the microstructural behaviour, tensile properties and texture of the alloy. After complete recrystallization no change in mechanical properties is observed upon further annealing.

Mechanical properties of α/β Ti alloys are closely related to their microstructure. The complexity of the microstructural features involved makes it rather difficult to develop models for predicting properties of these alloys. Advances in stereology and microscopy permit rapid characterization of various features in Ti alloys including Widmanstatten α-laths, grain sizes, grain shapes, colony structures and volume fractions of different phases. This research documents the stereology procedures for characterizing microstructural features in Ti alloys, including the use of three-dimensional serial sectioning and reconstruction procedures for developing through material measurements. The resulting data indicate the powerful characterization processes now available, and the ability to rapidly assess microstructural features in Ti alloys. The processes were tested using Ti-62222 by serial sectioning the sample and conducting automated stereology protocols to determine features. In addition, three-dimensional reconstruction was completed on a Ti-6242 sample to evaluate lath interactions within the alloy. Results indicate the tremendous potential for characterizing microstructures using advanced techniques.

Mechanical properties of α/β Ti alloys are closely related to their microstructure. The complexity of the microstructural features involved makes it rather difficult to develop models for predicting properties of these alloys. Developing predictive rules-based models for α/β Ti alloys requires a huge database consisting of quantified microstructural data. This in turn requires the development of rigorous stereological procedures capable of quantifying the various microstructural features of interest imaged using optical and scanning electron microscopy (SEM) micrographs. In the present paper, rigorous stereological procedures have been developed for quantifying four important microstructural features in these alloys: thickness of Widmanstatten α laths, colony scale factor, prior β grain size, and volume fraction of Widmanstatten α laths.

We report the observation of a root-like structure at the interface between GaAs nanowires and the (100) single-crystal GaAs substrate. These nanowires were grown via the vapor-liquid-solid mechanism using metalorganic vapor phase epitaxy. The root-like structure extends from the base of the nanowires into the substrate and has been investigated in detail using transmission electron microscopy and high-resolution electron microscopy. While the nanowires predominantly exhibit the zinc-blende type diamond cubic structure with the growth axis parallel to ⟨111⟩ and growth twins perpendicular to the growth axis, the root regions have a CdTe type orthorhombic structure that has been reported to occur in GaAs only under high-pressure conditions.