Deformation Of Metallic Materials Research Articles

Micro-Mechanism Relations Between Deformation and Damage Behavior of Materials at Elevated Temperature

Deformation of metallic materials at elevated temperatures occurs by the movement of atoms either individually or in a group by diffusion, grain boundary sliding, and the slip processes as facilitated by vacancy, dislocations, and grain boundaries. The constitutive relationship for deformation is developed based on the contributions of external test conditions like temperature and strain rate or stress applied and the internal conditions like chemical composition, phases present, and the length scale of microstructures. Deformation can occur coherently by synergisms of all participating mechanisms, failing to which becomes a source for initiating the damage in the material. The same mechanisms that were initially responsible for deformation to occur then become the facilitators for void nucleation and its growth, which then go through cavity coalescence, and crack formation on the way to cause ultimate fracture of materials. The constitutive relationships for damage mechanisms then take the form that promotes the removal of atoms from the damaged part to a farther site, which further enhances the act of material damage. In the present work, the micro-mechanisms responsible for deformation and failure will be examined to evolve a relationship towards establishing connectivity between these two processes by integrating the effects of internal and external variables for a range of materials.

Basic Modelling of General Strength and Creep Properties of Alloys

There are excellent methods for modelling physical and elastic properties, for example, those based on ab initio atomistic procedures. For mechanical properties that are controlled by the motion of the dislocations, such methods have not been available in the past. One has been forced to resort to fitting the experimental data with empirical methods by involving a number of adjustable parameters. However, in recent years, methods based on physical principles have been developed for a number of mechanical properties. These methods can predict properties accurately without the use of fitting parameters. A review of such methods will be given, for example, for the modelling of creep deformation in metallic materials. It will be demonstrated that some properties can be described over a wide range of temperatures and strain rates. The advantage of these new methods is that they can be used for prediction, identification of mechanisms and extrapolation of results for new conditions.

Crack driving forces under creep conditions in presence of material inhomogeneity

ABSTRACT Under time-dependent creep deformation in metallic materials in the presence of a crack, the driving force is influenced at a distance in the presence of a zone (such as an interlayer, interface, hole, etc.) which deforms differently in reference configuration. This influence may increase or decrease the crack driving force based on the type of inhomogeneity (elastic, plastic, creep). The nature and extent of influence of material inhomogeneity are studied in this work with a configurational force-based rate of crack driving force definition for a crack in the presence of dissimilar metal weld zone, HAZ and second base metal.

Cutting Parameter Optimization based on Online Temperature Measurements

The deformation of metallic materials during the machining operation requires a significant amount of energy. During the chip formation process and due to the plastic deformation of the metal and the friction along the tool-part interface, the thermal loads generated are strongly impacted by the cutting factors. Thus, the choice of optimized cutting conditions is essential to control the quality of the work required. The aim of the present experimental study is to optimize the cutting parameters using temperature measurements. The average temperature of the cutting tool is studied using a FLIR A325sc type infrared camera. Optimal cutting parameters for each performance metric were obtained using the Taguchi techniques.

CRSS determination combining ab-initio framework and Surrogate Neural Networks

Critical Resolved Shear Stress (CRSS), fundamentally linked to the dislocation glide stress, is a crucial measure in dictating plastic deformation in metallic materials. A recent ab-initio predictive model for dislocation glide stress in Face-Centered Cubic (FCC) materials is developed which accurately predicts available experimental data, considering the anisotropic continuum energy, the atomistic misfit energy, and the minimum energy path for the intermittent motion of Shockley partials. The CRSS of a material is predominantly controlled by six parameters, namely, lattice constant, unstable/stable stacking-fault energies, and three anisotropic elastic constants for cubic materials, which are inputs to the predictive model. In this work, a large material dataset is produced incorporating properties of real materials and generating hypothetical combinations, subsequently calculating the CRSS for each combination using the predictive model. The hypothetical combinations of properties are employed to train a machine learning-based Surrogate Neural Network (SNN), and the ones of real materials are utilized to validate the SNN model yielding a 94% accuracy for 1,033 materials. The generated dataset is used to unravel the sensitivity of each material parameter to the predicted CRSS establishing a general trend for the FCC materials for the first time guiding the field in achieving superior mechanical properties.

Enhanced plastic deformability of copper single crystals under low-frequency vibrational loading

Tensile tests on copper single crystal ([110]) foils using low-frequency vibrational loading of frequencies ranging from 0 to 50 Hz were performed at room temperature to explore the mechanisms of vibration-facilitated plastic deformation in metallic materials. It was found that the total elongation of copper single crystal foils under vibrational loading increased gradually with increasing vibration frequency, indicating enhanced plastic deformability. This behavior could be rationalized with the formation of equiaxial dislocation cells (EDC) in copper single crystal ([110]) foils under vibrational loading, which reflects the activation of multiple codirectional slip systems induced by the approximate biaxial tensile stress state during the unloading stage of vibrational loading. Additionally, the formation of Lüders bands under vibrational loading at high frequencies validates their dislocation-proliferation-mediated nucleation mechanism. This work would help to understand the vibration-lowered forming resistance in metallic materials of FCC lattice structures.

A dual-scale elasto-viscoplastic constitutive model of metallic materials to describe thermo-mechanically coupled monotonic and cyclic deformations

Thermo-mechanical coupling effect often occurs during the deformation of the metallic materials, especially when they are subjected to cyclic loadings at a high loading rate. On one hand, the internal heat generation and accumulation originated from the energy dissipation during plastic deformation lead to the change of temperature field in the material. On the other hand, the variation of temperature field further changes the dissipation property of the material, since the stress-strain response depends on the temperature. These two factors influence with each other and result in a complex thermo-mechanical coupling effect. In this work, a dual-scale thermo-mechanically coupled elasto-viscoplastic constitutive model is developed to predict the monotonic, cyclic deformation and temperature field evolution of metallic materials under monotonic and cyclic loadings. At the mesoscopic scale, the polycrystalline representative volume element (RVE) is considered as an aggregation of individual grains. For an individual grain, a crystal plasticity model accounting for the internal heat generation is developed based on the fundamental laws of irreversible thermodynamics. A nonlinear kinematic hardening rule extended from the Ohno-Abdel-Karim model is adopted to capture the evolution of resolved shear back stress for each slip system, and the classical Bassani-Wu latent hardening rule is utilized to describe the interaction of dislocation slipping. To calculate the thermo-mechanical interactions among the grains, and obtain the overall responses of the polycrystalline RVE, a self-consistent (SC) homogenization scheme accounting for material nonlinearity and thermo-mechanical coupling effect is developed. At the macroscopic scale, the thermo-mechanical responses for the specimen are obtained by solving the equations of force balance, deformation compatibility, thermodynamic equilibrium and constitutive relationship through an approximation method. Finally, the proposed model is validated by predicting the monotonic, cyclic stress-strain responses and temperature evolution of 316L stainless steel.

Theoretical insights into dislocation-induced deformation in metallic materials

Theoretical insights into dislocation-induced deformation in metallic materials

МНОГОУРОВНЕВОЕ МАСШТАБНОЕ КОМПЛЕКСНОЕ ИССЛЕДОВАНИЕ ДЕФОРМИРОВАНИЯ МЕТАЛЛИЧЕСКИХ МАТЕРИАЛОВ

The paper considers the theoretical and experimental questions connected with researches of elastic and plastic deformation of metal materials. The article shows that joint multilevel large-scale study performed by physics-mechanics and material engineers of the patterns connecting characteristics of stress-strain state with parameters of a structural condition of a metal material will allow to develop modern physical and mathematical models of a material. For this purpose in-depth study of the shift deformations forming plastic properties of a material and processes formation of defects and a new free surface is necessary. The paper presents the examples of such a research, and provides methods of analysis of structure and physical and mechanical characteristics at different structural levels of a polycrystalline metal material.

Strain rate sensitivity of titanium matrix composites: In the presence of laminated structure

The strain rate sensitivity (SRS) plays an important role in the deformation of metal materials. We presented SRS studies of a kind of thick-layer-laminated Ti–TiB/Ti-6.58Al-1.76Zr-0.89Mo-1.04V composites to give an insight into the deformation mechanism. The SRS of the laminated composites decreased with increasing plastic strain, and the strength and SRS both agreed with the rule of mixture. The strain hardening exponent of the laminated composites was also higher than the TiB/TA15 composite but lower than the pure Ti. After the onset of necking, it is believed that stress redistribution would occur in the necking area of the laminated composites due to the SRS differences between adjacent layers. This stress redistribution resulted in the post-necking deformation ability enhancement of the laminated composites.

A New Experimental Method for Determining the Thickness of Thin Surface Layers of Intensive Plastic Deformation Using Electron Backscatter Diffraction Data

It is, in general, essential to investigate correlations between the microstructure and properties of materials. Plastic deformation often localizes within thin layers. As a result, many material properties within such layers are very different from the properties in bulk. The present paper proposes a new method for determining the thickness of a thin surface layer of intensive plastic deformation in metallic materials. For various types of materials, such layers are often generated near frictional interfaces. The method is based on data obtained by Electron Backscatter Diffraction. The results obtained are compared with those obtained by an alternative method based on microhardness measurements. The new method allows for determining the layer thickness of several microns in specimens after grinding. In contrast, the measurement of microhardness does not reveal the presence of this layer. The grain-based and kernel-based types of algorithms are also adopted for determining the thickness of the layer. Data processed by the strain contouring and kernel average misorientation algorithms are given to illustrate this method. It is shown that these algorithms do not clearly detect the boundary between the layer of intensive plastic deformation and the bulk. As a result, these algorithms are unable to determine the thickness of the layer with high accuracy.

Quasi-Static and Dynamic Testing of Metallic Materials

Understanding the deformation of metallic materials at different states is essential in forming operations and under working conditions [...]

Optimization of Crystallographic Texture for Sheet-forming Applications Using Taylor-based Models

Plastic deformation of metallic materials is an inherently anisotropic process as a result of the presence of preferential orientations in their crystallographic texture. Crystal plasticity modeling, which allows simulating the response of polycrystal aggregates taking into account their texture and other microstructural parameters, has been extensively used to predict this behavior. In this work, crystal plasticity models are used to deal with the opposite problem: given a desired behavior, determine how to modify a texture to approximate this behavior in the most efficient way. This goal can be expressed as an optimization problem, in which the objective is to find the texture with the best formability properties among all the possible ones. An incremental optimization method, based on the gradient descent algorithm, has been developed and applied to different initial textures corresponding to typical steel and aluminum sheet products. According to expectations, the textures found present a stronger gamma fiber component. Moreover, the method sets the basis for the development of more complicated optimization schemes directed toward optimizing specific materials and forming processes.

Universal Mechanism of Viscoplastic Deformation of Metallic Materials Far from Thermodynamics Equilibrium

The article gives results of structure formation in metallic materials after different types of deformation: tungsten after rolling, nickel after thermal cycling and nickel single crystal after rolling, aluminum single crystal after cyclic tension and aluminum alloys (D16, 2024-T3) after impulsive load. We used optical and electron microscopy methods for investigation of deformation structure formation and molecular dynamics method for computer modeling of the processes of plastic deformation (LAMMPS software). The following quantitative parameters were calculated during the simulation: energy of pair interaction, temperature, total cumulative pressure, stress tensor and pressure tensor. The study shows that the plastic flow of metallic materials with any initial structure at certain loading stage can be carried out by homogeneous mass transfer through channels with a liquid-like structure, from which follows that the dislocation mechanism of plastic deformation of crystals has a limited field of application. The main role has a synergistic structure formation in the conditions of distance from thermodynamic equilibrium. The relaxation processes proceed intensively after and during the process of destruction. The results of modeling have shown the possibility of forming channels of hydrodynamic flow without the participation of defects in the initial material.

Generation and accumulation of atomic vacancies due to dislocation movement and pair annihilation

ABSTRACTGeneration and accumulation of atomic vacancy due to pair annihilation of edge dislocations during plastic slip deformation of metallic materials are numerically evaluated by crystal plasticity analysis. Dislocation density-based models are utilised in the deformation analysis and a theoretical model for the generation of atomic vacancies is introduced. Purely uniform single- and double-slip deformations are analysed and results show that the evolution of the vacancy density depends largely on the microstructure length scale and multiplication of slip activity on different slip systems.

Stress-strain dependence and the evolution of dislocation structure in Cu-Mn polycrystalline concentrated solid solutions

Deformation of metallic materials results in dislocations occurrence and accumulation, with establishment of their definite distribution (dislocation substructure). The type of dislocation substructure (DSS) defines largely resistance to deformation and fracture of materials. Quantitatively the interrelation of DSSs and resistance to deformation are studied on a limited number of alloys. Foreign literature lacks studies referring to those issues. The given paper investigates the stress-strain dependences in Cu-Mn polycrystalline solid solutions. Mn concentration in the alloys varied within the range of 10…25 at.%. Polycrystals with 10 and 240 μm mean grain size were investigated. Deformation was applied by means of tension at the velocity of 2.10-2 s-1 and the temperature of 293 K. Using transmission electron microscope at the accelerating voltage of 125 kV, microstructure of the samples was investigated when they were deformed up to various deformation degrees. The types of DSSs were defined. The connection of the deformation stage under tension with the formed types of DSS was discussed. The sequence of transition of DSSs during the process of alloys deformation was defined. Appearance of the new stage of deformation hardening is attributed to the occurrence of the new type of substructure. The occurring “new” DSS develops during the deformation process, while “the old” DSS gradually disappears. Each of the stage of plastic deformation generally has two types of DSSs. The connection of the deformation stage and the strain hardening coefficient with the DSS was defined and it was shown to possess the definite dislocation density.

A Review of Electrically-Assisted Manufacturing With Emphasis on Modeling and Understanding of the Electroplastic Effect

Increasingly strict fuel efficiency standards have driven the aerospace and automotive industries to improve the fuel economy of their fleets. A key method for feasibly improving the fuel economy is by decreasing the weight, which requires the introduction of materials with high strength to weight ratios into airplane and vehicle designs. Many of these materials are not as formable or machinable as conventional low carbon steels, making production difficult when using traditional forming and machining strategies and capital. Electrical augmentation offers a potential solution to this dilemma through enhancing process capabilities and allowing for continued use of existing equipment. The use of electricity to aid in deformation of metallic materials is termed as electrically assisted manufacturing (EAM). The direct effect of electricity on the deformation of metallic materials is termed as electroplastic effect. This paper presents a summary of the current state-of-the-art in using electric current to augment existing manufacturing processes for processing of higher-strength materials. Advantages of this process include flow stress and forming force reduction, increased formability, decreased elastic recovery, fracture mode transformation from brittle to ductile, decreased overall process energy, and decreased cutting forces in machining. There is currently a lack of agreement as to the underlying mechanisms of the electroplastic effect. Therefore, this paper presents the four main existing theories and the experimental understanding of these theories, along with modeling approaches for understanding and predicting the electroplastic effect.

Flow Stress Modelling and Microstructure Development during Deformation of Metallic Materials

A constant strain hardening rate is characteristic for large strain deformation at low temperatures and often observed during wire drawing. This stage of deformation, in the following referred to as stage IV, is determined by the microstructural evolution of dislocation cells. At elevated temperatures, rapid stress saturation is typically reached and no stage IV behavior is observed. This behavior is modelled in the present work, following the concept of state-parameter based plasticity, evolving dislocation density and subgrain formation as functions of strain rate, strain and temperature. It is demonstrated that the temperature dependence of state parameters at different deformation stages is closely related. The present model is compared to a series of compression tests carried out on a Gleeble 1500 thermo-mechanical simulator. EBSD micrographs of the same material reveal the microstructural evolution during plastic deformation. It is shown experimentally that the transition from cell forming behavior to subgrain formation correlates well with the disappearance of stage IV and the overall change in the dominant mechanism for overcoming obstacles. In combination with thermally activated yield stress prediction, this model, recently implemented in the software package MatCalc, offers a powerful tool for flow-curve simulation.

A numerical solution for a closed die forging process

One of the manufacturing processes that can be permanent improved is plastic deformation of metallic materials, as incorporating reserves on the manufacture of products with reduced material and energy consumptions. This paper presents finite element analysis for a closed die forging process, showing the stresses, strains and temperature into deformed part and stresses in the working tools. The analysis of obtained results for different flash dimensions of the working tools has enabled optimization of the forging process studied. To be able to validate the numerical results obtained, experimental tests were conducted. The compared data series show a good agreement between the numerical and experimental data.

Modelling plastic deformation in a single-crystal nickel-based superalloy using discrete dislocation dynamics

Abstract Background Nickel-based superalloys are usually exposed to high static or cyclic loads in non-ambient environment, so a reliable prediction of their mechanical properties, especially plastic deformation, at elevated temperature is essential for improved damage-tolerance assessment of components. Methods In this paper, plastic deformation in a single-crystal nickel-based superalloy CMSX4 at elevated temperature was modelled using discrete dislocation dynamics (DDD). The DDD approach was implemented using a representative volume element with explicitly-introduced precipitate and periodic boundary condition. The DDD model was calibrated using stress–strain response predicted by a crystal plasticity model, validated against tensile and cyclic tests at 850 °C for <001 > and <111 > crystallographic orientations, at a strain rate of 1/s. Results The DDD model was capable to capture the global stress–strain response of the material under both monotonic and cyclic loading conditions. Considerably higher dislocation density was obtained for the <111 > orientation, indicating more plastic deformation and much lower flow stress in the material, when compared to that for <001 > orientation. Dislocation lines looped around the precipitate, and most dislocations were deposited on the surface of precipitate, forming a network of dislocation lines. Simple unloading resulted in a reduction of dislocation density. Conclusions Plastic deformation in metallic materials is closely related to dynamics of dislocations, and the DDD approach can provide a more fundamental understanding of crystal plasticity and the evolution of heterogeneous dislocation networks, which is useful when considering such issues as the onset of damage in the material during plastic deformation.