Plastic Deformation Of Alloys Research Articles

In-situ study of microstructure and mechanical properties of GH3536 alloy manufactured by selective laser melting at 750 °C

Nickel-based GH3536 alloy exhibits high strength but low ductility when produced by selective laser melting (SLM), which hinders its widespread application in aerospace. This paper employed a ‘two-step’ method of heat treatment to optimize the microstructure of the SLM GH3536 alloy and investigated the mechanical properties. Tensile tests were conducted on SLM GH3536 alloy before and after heat treatment at 750 °C, using an in-situ high-temperature tensile stage. The relationship between the microstructural evolution and deformation behavior of the alloys was investigated by combining the in-situ tensile experiments and crystal plasticity finite element method (CPFEM). The results suggested that the elongation can be increased by 80% without a significant reduction in tensile strength. The improved elongation is attributed to the complete recrystallization, formation of annealed twins and serrated grain boundaries after heat treatment. The study also investigated the deformation behavior and fracture mode of the alloy before and after heat treatment. Discussion was done on the influence of the microstructure, particularly the twin and serrated grain boundaries on the alloy's plastic deformation. This study enhanced the understanding of plastic deformation of SLM GH3536 alloy and provided a valuable reference for the design and post-treatment of superalloy.

Atomic-Scale Insights into the Deformation Mechanism of the Microstructures in Precipitation-Strengthening Alloys

Clarifying the deformation behaviors of microstructures could greatly help us understand the precipitation-strengthening mechanism in alloys. However, it is still a formidable challenge to study the slow plastic deformation of alloys at the atomic scale. In this work, the phase-field crystal method was used to investigate the interactions between precipitates, grain boundary, and dislocation during the deformation processes at different degrees of lattice misfits and strain rates. The results demonstrate that the pinning effect of precipitates becomes increasingly strong with the increase of lattice misfit at relatively slow deformation with a strain rate of 10-4. The cut regimen prevails under the interaction between coherent precipitates and dislocations. In the case of a large lattice misfit of 19.3%, the dislocations tend to move toward the incoherent phase interface and are absorbed. The deformation behavior of the precipitate-matrix phase interface was also investigated. Collaborative deformation is observed in coherent and semi-coherent interfaces, while incoherent precipitate deforms independently of the matrix grains. The faster deformations (strain rate is 10-2) with different lattice misfits all are characterized by the generation of a large number of dislocations and vacancies. The results contribute to important insights into the fundamental issue about how the microstructures of precipitation-strengthening alloys deform collaboratively or independently under different lattice misfits and deformation rates.

Mathematical Modeling of Fragmentation Under Plastic Deformation in Alloys with the L12 Structure

Mathematical Modeling of Fragmentation Under Plastic Deformation in Alloys with the L12 Structure

The Strength of Inconel 625, Manufactured by the Method of Direct Laser Deposition under Sub-Microsecond Load Duration

This paper presents the results of measurements of the spall strength and elastic-plastic proper-ties, under dynamic and static loads, of the high-strength heat-resistant nickel-chromium alloy Inconel 625, obtained by the direct laser deposition method. The structural parameters of the obtained samples and the mechanical properties during static tests were studied. According to our information, anisotropy in the structural parameters operates primarily at the level of plastic deformation of alloys. Shock compression of the additive alloy Inconel 625 samples in the range of 6–18 GPa was carried out using a light-gas gun, both along and perpendicular to the direction of the deposition. The strength characteristics were determined from the analysis of the shock wave profiles, which were recorded using the VISAR laser velocimeter during the loading of samples. It was found that the value of the spall strength of additive samples does not depend on the direction of deposition, and the Hugoniot elastic limit of samples loaded perpendicular to the deposition direction is about ~10% higher. With an increase in the maximum compression stress, the material’s spall strength increases slightly, but for both types of samples, a slight decrease in the Hugoniot elastic limit was observed as the compression stresses increase. On the basis of the measured wave profiles, shock Hugoniots of the samples of the alloy Inconel 625, loaded both along and perpendicular to the direction of deposition, are constructed in this pressure range.

Transformation of structure during friction stir welding

In comparison with low carbon steels, there is increased interest in the use of aluminium-based alloys as materials for the manufacture of welded structures rolling stock of railway transport. During friction stir welding aluminium-based alloy, against the background of the analysis structural transformations, issues of development hardening processes are considered. Under conditions of existence, a temperature gradient at zone of weld formation, shown degree approximation alloy to the conditions of superplastic flow and influence from presence particles of the second phase on grain size of matrix is estimated. Evaluation of the separate influence grain size of matrix and state of solid solution at total hardness of the weld showed dependence of their contributions on temperature of hot plastic deformation. As the temperature of plastic deformation of alloy at area of the weld increases, contribution to the total hardness from grain size increase and on state of the solid solution decreases.

Mechanism of dislocation evolution during plastic deformation of nitrogen-doped CoCrFeMnNi high-entropy alloy

Abstract In this study, the evolution of statistically stored dislocation (SSD) and geometrically necessary dislocation (GND) during tensile tests was investigated in CoCrFeMnNi high-entropy alloys (HEAs) with 0 and 0.52 at. % nitrogen. The microstructure characterization indicated that the plastic deformation of the alloys was dominated by dislocation slip below 20% true strain. Nitrogen alloying increased the total dislocation density and the strain-hardening rate during deformation, which could be explained by the interaction between nitrogen atoms and dislocations. The higher fraction of soft orientation zones for 0.52 N HEA was conducive for strain accommodation, resulting in a reduced GND density. Hence, SSDs contributed primarily to the increase of the total dislocation density and the higher strain-hardening rate of nitrogen-doped CoCrFeMnNi.

Влияние прокатки и кручения под высоким давлением в камере Бриджмена на количественные характеристики полос сдвига в аморфном сплаве на основе Zr

Amorphous alloys based on metal components demonstrate a unique ability to realize plastic deformation under the influence of external mechanical stresses. Influenced by substantial degrees of plastic deformation in alloys, one can observe shear bands (SB) in the form of rough lines on the polished surface of the sample. The concept of shear band formation in amorphous metallic glasses varies greatly from plastic deformation processes in crystalline metals and alloys. Unlike crystalline metals, amorphous metallic glasses can exist in a spectrum of structural states with accompanying mechanical, thermodynamic, and physical properties of materials. The formation and evolution of shear bands control the fluidity and plasticity of almost all metallic glasses at room temperature, and in many cases, the formation of dominant shear bands rapidly leads to failure. The literature does not contain any rigorous quantitative description of SB main parameters, which could adequately describe in the analytical form the process of plastic deformation of amorphous alloys, similar to the dislocation and disclination theories of plastic deformation of crystals. An open question remains how the transition from macroscopic deformation to severe plastic deformations of amorphous alloys affects the key SB characteristics. In this work, using the method of optical profilometry, the author studied in detail the quantitative characteristics of the steps formed by shear bands on the surface of deformed samples of the massive amorphous alloy Zr60Ti2Nb2Cu18.5Ni7.5Al10 after high-pressure torsion (HPT) and after rolling. The study identified that the design of shear bands depends on the deformation method and showed that the magnitude of deformation had the controlling effect on the shear bands thickness (the height of the steps). The transition from deformation by rolling (e=0.4) to plastic deformation during HPT (e=2.6) leads to the threefold increase in the power of shear bands and the average distance between them.

ИНТЕРМЕТАЛЛИДНОЕ СОЕДИНЕНИЕ AlxTi – ПЕРСПЕКТИВНЫЙ МАТЕРИАЛ ДЛЯ ПОВЫШЕННЫХ ТЕМПЕРАТУР (обзор) Часть 1. Кристаллическая структура и свойства интерметаллидного соединения Al2Ti

The Al2Ti intermetallic compound is the most promising base for high-temperature alloys designed for advanced power plants. This work provides an overview of the structures of binary alloys concerning to the Ti–Al system, as well as the phase transformation mechanisms and the peculiarities of plastic deformation of alloys. The alloys which phase composition is represented by a mixture of r-Al2Ti+γ-TiAl with a lamellar structure show anomalous mechanical properties depending on texture formation and grain size. These alloys possess increased strength and decreased plasticity at elevated temperatures.

Fracture behaviour of SiCp/Al composites with network architecture

It is found that, for discontinuous metal matrix composites (MMCs) with an inhomogeneous network reinforcement distribution, a thin network layer and large alloy cells are favorable for the toughness.. The network layers contribute to the high modulus and strength, while large alloy cells work in deflecting crack propagation and thus enhancing the toughness. Furthermore, mutually coordinated and restricted deformation behaviors of alloy cells may create a three-dimensional tensile stress state, which induces the anomalous brittle fracture of intrinsically ductile aluminum matrix in some alloy cells. These phenomena have weakened the matrix alloy plastic deformation capacity, constrained the crack propagation and improved the toughness of network composites.

Enhancing Toughness of Particulate Aluminum Composites Via Tailoring Inhomogeneous Particle Distribution

It is found that thin network layer and large enough alloy cells are favorable for the toughness of inhomogeneous network metal-matrix composites (MMCs). The thin network layers contribute to the high modulus and strength, while large alloy cells work in deflecting crack propagation and thus the toughness. Furthermore, mutually coordinating and restricted deformation behaviors of alloy cells may create a three-dimensional tensile stress state, which induces the anomalous brittle fracture of intrinsically ductile aluminum matrix in some alloy cells. These phenomena weaken matrix alloy plastic deformation capacity and restraint crack propagation and toughness of network composites.

Localization of plastic deformation in HCP-, BCC- and FCC-alloys at indentation

Using instrumental indentation, we studied the regularity of elastoplastic deformation of workpieces from alloys aluminum AMc, titanium VT23 and steels 45, HVG with FCC, HCP and BCC lattices, respectively. It was shown that with increasing indentation depth, instrumental hardness (H1T), elastic modulus (E1T), their ratios (HIT/EIT) tend to the values of classical microhardness Hµ, Young’s modulus E and their ratio (Hµ/E). The nature of localization of plastic deformation of alloys near the surface of the indenter is determined. The reason for the hard workability of titanium-based alloys is determined.

Stability of Homogenous Plastic Deformation in Alloy Single Crystals with L12 Structure Under Tension and Compression

The paper studies the loss of stability of high-temperature, homogenous plastic deformation of alloys with L12 structure during the super-localization process. Using methods of mathematical simulation, a joint effect of geometric and physical factors on the stability loss of plastic deformation is analyzed under the tensile and compressive stresses. The properties of elements of the deformable medium are detected, at which the macroscale loss of stability is observed in relation to homogenous plastic deformation. It is found that super-localized plastic compressive deformation occurs when physical softening is ahead of the geometric strengthening. Under the tensile stress, the loss of stability of homogenous plastic deformation always occurs due to necking because the geometric softening begins before physical.

Plastic deformation of magnesium alloy with different forming parameters during ultrasonic vibration-assisted single-point incremental forming

The research of forming parameters on the ultrasonic vibration single-point incremental forming of magnesium alloy plastic deformation can provide a theoretical basis for the establishment of the forming parameters. According to the forming characteristics of magnesium alloy sheet, a new method of ultrasonic vibration-assisted single-point incremental forming was proposed. The influence of forming parameters on the plastic deformation of magnesium alloy was studied by finite element simulation and experimentation. The influence of vibration frequency, amplitude, friction coefficient, and tool head size on stress and thinning rate of magnesium alloy during ultrasonic vibration-assisted single-point asymptotic forming was studied. The results show that the vibration frequency of 20 kHz and forming tool radius of about 5 mm are beneficial for plastic deformation magnesium alloy in ultrasonic vibration-assisted single-point incremental forming. With vibration amplitude increasing, the maximum shear stress tends to decrease as a whole, but at the amplitude of 0.16 mm, the thinning rate is large and fracture occurs easily. With friction coefficient increasing, the maximum shear stress tends to increase, and there is a good linear relationship between the maximum thinning rate and the friction coefficient.

Rheological properties of EP742-ID alloy in the context of Integrated Computational Materials Engineering (ICME). Part 1. Results of experimental research

The article covers rheological properties of the EP742-ID alloy in high-temperature compression tests of cylindrical samples with different ratios of similar initial diameters and heights (d0 /h0). The results of experimental research in the temperature range t = 1000÷1150 °C and initial deformation rates e · 0 = 3·10–2÷3·10–4 s–1 have shown that an increase in compression flow stress with the growth of the d0 /h0 ratio is observed at all temperatures and deformation rates with a linear dependence on the e · 0 value and the d0 /h0 ratio. The method is proposed to recalculate deformation resistance indicators to the set ratio of similar sizes. Higher compression flow stress is connected with an increase in the coefficient of rigidity of samples and their specific contact surfaces. The dependence of apparent activation energy of alloy plastic deformation (Qdef), its relationship with the phase structure and conditions of the process of γ solid solution dynamic recrystallization is established. In the temperature conditions of the beginning of γ solid solution dynamic recrystallization process (1000–1050 °C) the Qdef value for d0 /h0 = 0,75 samples is 959 kJ/mol. The highest Qdef values for d0 /h0 = 0,75 samples of 1248 and 1790 kJ/mol are observed in the range of temperatures of intensive grain boundary γ ′-phase dissolution and coagulation (1050–1100 °C). Samples with d0 /h0 = 3,0 in this temperature range have Qdef up to 2277 kJ/mol. The apparent activation energy of plastic deformation decreases to 869 kJ/mol in the range of temperatures of homogeneous γ solid solution with grain-boundary primary and secondary carbides (1100–1150 °C). The paper provides the results of alloy sample compression at single and repeated consecutive loading with various times of pauses between deformations. It is shown that meta dynamic recrystallization under experimental conditions does not occur in the γ + γ ′-range, and occurs inertly in the γ-range.

Anomalous Strain Rate Sensitivity of Flow Stress in Ni3Ge Single Crystals. The role of Point Defects

The paper considers the strain rate sensitivity of flow stress in Ni3Ge single crystals having high-energy antiphase boundaries detected in experiments for the strain rate variation. The concentration of point defects is estimated by the model of plastic deformation of alloys having L12 structure. These point defects generated by plastic deformation, annihilate both mutually and on dislocations. It is shown that at higher temperatures of deformation, the anomalous strain rate sensitivity of the flow stress observed during the strain rate variation, can be caused by the migration of and interaction between the point defects and dislocations.

Dislocation-dynamics-based dynamic constitutive model of magnesium alloy

Since the dynamic plastic deformation of magnesium alloy, a hexagonal close-packed metal, consists of dislocation slipping and twinning, it is assumed that the dynamic plastic deformation of magnesium alloy is controlled by the mechanism with lower resistance, i.e., dislocation slipping or twinning. So, the evolution law of dynamic plastic deformation of the alloy can be determined by that of the resistance of dislocation slipping or twinning. After the evolution equations of the deformation resistances are deduced, the dynamic constitutive model of magnesium alloy is developed in this work. The proposed model is further verified by describing the dynamic tensile and compressive deformation of AZ\(_{31}\)B magnesium alloy obtained by the split Hopkinson pressure bar device. It is observed that the simulations agree well with the experimental results.

Creep behavior and deformation feature of TiAl–Nb alloy with various states at high temperature

By means of creep properties measurement and microstructure observation, an investigation has been made into the creep behaviors and deformation features of TiAl–Nb alloy with various states at high temperature. Results show that the microstructure of as-cast alloys consists mainly of lamellar γ/α2 phases with various orientations, the boundaries located in between the ones consist of single γ phase. The bigger plastic deformation of alloy during forging may refine the grains and increase the volume fraction of boundaries which consists of the fine block-like γ/α2 phases with weaker strength. During creep, the bigger volume fraction of boundaries increase the probability of crack initiated and propagated along boundaries, which is thought to be the main reason of the forged alloy displaying a lower creep resistance. Compared to the forged alloy, the as-cast alloy displays a better creep resistance and longer creep life at high temperature. The deformation mechanism of as cast alloy during creep is significant amount of dislocations shearing into the lamellar γ/α2 phases in the form of dislocations rows and rings. Compared with α2-Ti3Al phase, the γ phase possesses a weaker strength, therefore, the crack is easily initiated and propagated along the inclined boundaries. Wherein, the propagation of crack along the direction parallel to the lamellar γ/α2 phases displays the smooth surface of fracture, while the tearing edges appear on the surface of fracture in one side of the inclined boundaries relative to lamellar γ/α2 phases, which is attributed to the α2-Ti3Al phase with better strength hindering the propagation of crack during creep.

Lattice strain framework for plastic deformation in complex concentrated alloys including high entropy alloys

Alloys involving multiple solutes where the concentrations are such that it becomes difficult to identify a “solvent”, such as the so called “high entropy alloys”, have the potential for interesting combinations of properties. A key question relates to the fundamental mechanisms of plastic deformation in these alloys. A simple lattice strain framework is proposed for complex concentrated alloys to address the energetics and kinetics of dislocations and twins. It is argued that the lattice strain in highly concentrated alloys raises the base energy of the crystal and thereby reduces the additional energy required to nucleate dislocations and twins. However, the kinetics of dislocation motion are dampened by the lattice strain and local energy variations. This is reflected in lower values of activation volume. This framework can be used to design non-equiatomic high entropy alloy matrixes that enhance the properties achieved thus far.

Effect of equal channel angular pressing on the Portevin–Le Chatelier effect in an Al3Mg alloy

Plastic deformation of alloys is often accompanied with discontinuous flow known as the Portevin–Le Chatelier (PLC) instability. Recent studies of mechanical behavior of alloys subjected to severe plastic deformation (SPD) revealed different forms this phenomenon can take as a result of grain refinement. In the present work, it is reported that SPD may effectively suppress the macroscopic stress serrations characteristic of the PLC effect. At the same time, small-scale stress fluctuations can still be resolved on the deformation curves. To investigate their nature, stress vs time curves for an Al3Mg alloy processed by equal channel angular pressing (ECAP) are compared with those obtained for the initial coarse-grained (CG) material, using statistical and multifractal approaches to multi-scale analysis of time series. An interpretation of the results in terms of the concurrency of phenomena of self-organized criticality and synchronization in the dislocation system is proposed.

Microstructure and creep behaviors of a high Nb-TiAl intermetallic compound based alloy

By means of heat treatment, creep properties measurement and microstructure observation, an investigation has been made into the influence of heat treatment on microstructure and creep properties of the high Nb-TiAl alloy. Results show that the microstructure of as-cast high Nb-TiAl alloy consists of lamellar γ/α2 phases with various orientations. The irregular serrated boundaries with single γ phase are located in between the lamellar γ⧸α2 phases with various orientations. After solution and aging treatment, the microstructure of alloy consists of uniform and regular lamellar γ⧸α2 phases, and the regular boundaries are located in between the lamellar γ⧸α2 phases. Under the applied stress of 200MPa at 800°C, the creep lifetime of the as-cast high Nb-TiAl alloy is measured to be 147h, the one of the alloy after heat treatment is measured to be 297h. In the ranges of the applied temperatures and stresses, the creep activation energy of alloy after heart treatment is measured to be Q=432kJ/mol. The deformation mechanism of alloy during creep is dislocations slipping in the lamellar γ⧸α2 phases, the creep dislocations may be decomposed to form the configuration of the partials plus stacking faults. The deformation of as-cast alloy during creep occurs mainly in the irregular serrated boundary regions with single γ phase. For the heat treated alloy, the primary/secondary slipping systems of dislocations are alternately activated during creep, which results in the bigger plastic deformation of alloy to contort the lamellar α2/γ phases. In the latter stage of creep, the cracks are firstly initiated along the boundaries parallel to the lamellar γ⧸α2 phases, and propagated along the boundaries vertical or at about 45° angles relative to the stress axis up to the occurrence of creep fracture.