Plastic Deformation Conditions Research Articles

The research development of the structure in a-Fe Microcrystals with the Orientation deformed by compression with different values of the friction coefficient

The paper analyzes the change in the dislocation structure in a-Fe microcrystals with orientations <100> and <110> deformed by compression under conditions of limited flow with different values of the friction coefficient. The orientation stability of the microcrystal and texture is investigated when the compression axis deviates from the normal to the compression plane. Shooting and analysis of limited pole figures made it possible to establish that the operation of the OSS in the MC with the [100](001) orientation at different values of the friction coefficient at the sample-punch interface leads to a rotation of the latticework relatively to the MC axis. The specific conditions of plastic deformation under compression determined by the MC morphology prohibit displacement deyz., as the deformation is observed under conditions of limited flow. The operation of the OSS, consequently, leads to the MC partition with the [100] (001) orientation deformed by compression with the friction coefficient Kmax into parts and the rotation of the latticework around the growth axis. It is established the connection between the friction coefficient at the crystal-punch interface and the sliding geometry in a-Fe MCs deformed by compression under conditions of limited flow. The authors carried out the dimension of the friction ratio has a significant effect on the slip geometry and the dislocation structure formed in the MC of the [100] orientation deformed by compression along the (001) plane. Changes in the friction coefficient and the angle deviation of the compression axis from the normal to the compression plane in the MC with the [100] (001) orientation do not affect the slip geometry and the dislocation structure formed during plastic deformation.

Understanding local cutting features affecting surface integrity of gear flank in gear skiving

In gear skiving, large variations in cutting features significantly affect the cutting condition and surface integrity of a newly formed gear flank (NGF). This study aimed to improve the understanding of the effects of local cutting features on the surface integrity of approach and recess NGFs from the resulting microstructure produced by the multiple radial-infeed (MRI) strategy. For the first time, the boundary of the NGF regime and associated local cutting features were calculated from the uncut chip geometry (UCG) using a novel boundary-based level contour method. The theoretical and experimental results revealed that the local rake angle and uncut chip thickness are the most influential factors altering the plastic deformation conditions of the approach and recess NGFs. For the finishing pass, the uncut chip thickness developments within approach and recess NGFs were elucidated, showing the burnishing regime dominated the recess NGF formation. The strain–stress characteristics of the recess NGF show the strain-hardening effect due to the severe plastic deformation. Kernel average misorientation mapping showed a partial reduction in the misorientation angle under the recess NGF. This points to the accumulated deformation in the interaction between successive skiving passes further facilitating the localized recrystallization. Proposed local cutting feature calculations can be applied for further kinematic parameter optimization and MRI infeed rate design.

Extension of the Freiberg Layer Model by Means of Elastic–Plastic Material Behavior

Finite element method simulations offer deep and detailed modeling of complex processes, but with high effort of computation power and time. For the special purpose of flat rolling, a layer model was developed by Schmidtchen before based on the classic elementary theory of plasticity with the purpose to model inhomogeneous behavior with significant lower effort at computation. This model considered the layers only as rigid or in plastic deformation state. Herein, the model is extended by elastic material behavior to get closer to the depth of finite elements method (FEM) models. The results are first compared with a FEM simulation and measurements from the literature. The current model is found to fit well the FEM results as well as the measurements. Second, the results are compared with classic elementary theory and the layer model of Schmidtchen. From these comparisons is found, that the main elastic influences on the stress curve shape are due to the full elastic zones. Elastic deformations in the plastic regions are found to be smaller, but growing on transition from block rolling to thin sheet rolling.

Unique atomic structure of metals at the moment of fracture induced by laser shock

To effectively control the mechanical properties of structural materials and design their safety margins, understanding the properties of metal fracture is essential. However, it is difficult to experimentally investigate the atomic structures at the moment of fracture; therefore, the detailed fracture mechanism remains an active area of research. In this study, we in situ examined how the atomic structure of copper changes during the fracture process on the nanosecond scale using X-ray absorption spectroscopy and X-ray diffraction. The fracture was triggered by a shock wave induced by an optical laser and was examined with a single 100-ps synchrotron X-ray pulse with a delay time of 0–200 ns. This novel experimental approach provides insights into how the short- and long-range order of an atomic structure change on the nanosecond scale. The results showed that there was an irreversible change in the deformation state on the nanosecond scale. The initial elastic deformation state (0–20 ns) was superseded by a plastic deformation state (20–50 ns). Then, at the moment of fracture (50–320 ns), the plastic deformation state transformed into a state in which the heterogeneous atomic structures exhibited short-range disorder while maintaining long-range order (a “short-range-disorder-only” state). This unique “short-range-disorder-only” state, which has never been reported using conventional ex situ analytical techniques, triggered metal fracture; therefore, controlling the occurrence of this state could suppress fracture and allow the design of reasonable metal safety margins to avoid overengineering.

The microstructure evolution history and the underlying mechanism of an α/β dual phase titanium alloy during elastic-plastic deformation process

In this paper, in situ scanning electron microscope tensile test was carried out on the Ti-4.5Mo-5.1Al-1.8Zr-1.1Sn-2.5Cr-2.9Zn alloy, and the mechanism of grain rotation, shape change and micro-strain redistribution in macroscopic elastic deformation (stage I), macroscopic elastic-plastic transition (stage II) and macroscopic plastic deformation (stage III) stages were quantitatively investigated by electron backscatter diffraction and digital image correlation. In stage I, it was found that 10.1% of the viewing zone underwent grain rotation or shape change, and the micro-strain was mainly distributed in primary α phase (αp) and their intersection. The result of the separately designed elastic loading-unloading tensile test showed that the rotated αp no longer returned to the primary orientation. In stage II, the tensile plastic deformation regions reached 52.9%, and grains in βT regions continued to rotate and began to change shape. In stage III, 84.6% of the viewing zone got into the tensile plastic deformation state. Combined with geometrically necessary dislocation density distribution, it was found that some of the regions in low strain state (0 ≤ ε<1%) actually underwent complex tensile plastic deformation. In addition, the maximum micro-strain of the viewing zone was transferred to βT regions.

White etching structures in annealed 52100 bearing steel arising from high-pressure torsion tests

White Etching Areas observed in failed rolling bearings have been associated with the presence of Severe Plastic Deformation conditions, which can be achieved by High-Pressure Torsion tests; thus, this technique was selected to produce White Etching Structures in annealed AISI 52100. Their origin arises from two main phenomena: Firstly, the relative movement between anvil/samples creates instabilities and interruption to plastic flow close to the surface of the sample. Secondly, the presence of hard discontinuities such as carbide clusters and non-metallic inclusions interrupt plastic flow inside the samples. Both phenomena seem to promote carbide dissolution in the ferritic matrix and so could produce not only White Structures but also White Etching Areas.

Modeling the material of the cylindrical work with welded seam at compression distribution of vehicle parts

It is shown that the distribution of the ends of tubular billets, which are the main connecting elements of the vehicle brake system, is accompanied by a loss of stability in the circumferential and axial directions, as well as localization of deformations, followed by destruction in the form of a longitudinal crack that occurs at the end of the preform. The presence of the weld complicates the general conditions of deformation during crimping and distribution and leads to the destruction of the workpiece along the weld. To prevent cracking, it is necessary to tighten the crimping and distributing factors, which inevitably leads to an increase in the number of transitions, the complexity of the process and the cost of manufacturing the part as a whole. The issue of deformation of welded structures is of interest with the development of new materials for the automotive industry, such as joining two or more steel sheets with different mechanical properties, thickness or type of coating, which are important for reducing weight, minimizing costs and reducing scrap. It is shown that the deformation of the pipe billet will depend not only on the plasticity characteristics of the base metal and the weld metal, which is obvious, but also on the ratio of the squares of the pipe billet. The increase in the above modulus of plasticity is accompanied by hardening of the welded joint compared with the initial metal of the workpiece, respectively, a decrease in the value of the secant modulus in both directions – a decrease in the strength characteristics of the weld metal. Further analysis of the deformation of the welded workpiece should be carried out taking into account the local anisotropy caused by the welding seam, which will make it possible to determine the conditions of sustained plastic deformation and create an additional effect on the weakened area.

Analysis of self-loosening behavior of high strength bolts based on accurate thread modeling

The self-loosening of high strength bolt caused by vibration has been widely studied. However, the short-term self-loosening behavior of the high strength bolt when it is not subject to an external load has not received attention. This behavior will also lead the bolt preload to attenuate. Since the theoretical analysis of self-loosening behavior is difficult, this paper uses the finite element method to construct an accurate three-dimensions model with thread lift angle for numerical analysis. A new method is proposed to analyze the self-loosening behavior. The self-loosening behavior caused by the elasticity and plasticity of the bolted joint at different deformation periods is compared and analyzed. Besides, the evolution of the self-loosening behavior under different conditions is explored. The analysis results show that the torsional deformation of the thread leads to the relative slip of the internal and external threads. This results in the self-loosening of the thread in the elastic condition. In the elastic–plastic deformation condition, the self-loosening behavior is caused by the relative slip of the internal and external threads and plastic deformation. The weight of plastic deformation is greater. In addition, this behavior has the characteristics of increasing with increased tightening torque and decreasing with increased friction coefficient.

Functional materials under elasto-plastic deformation

A theoretical study of the factors affecting the workpiece accuracy under conditions of local plastic deformation has been carried out. The study has shown that when a two-support workpiece is bent by the force applied in the center along its length, plastic deformation occurs only at 1/3 of its length, and 2/3 remains under the elastic deformation. The paper analyzes the technologies and features of transient local plastic deformation, the factors influencing geometry fidelity are determined. The author gives the load function values under which the elastic deformation occurs as well as the carrying capacity loss load for the ideally plastic material unhardened. The function for calculating the values of elastic and plastic deformation zones is determined, which makes it possible to eliminate the need for additional calculations of the plastic deformation zone boundaries.

Investigation of nanocrystallization behaviour of AISI 316 stainless steel under adiabatic and non-adiabatic severe plastic deformation conditions

Abstract Of late surface nanocrystallization of steels has become an important topic for researchers due to the exceptional properties obtained after nanocrystallization. Austenitic stainless steel is very important alloy for industrial applications due to its corrosion resistance and versatile mechanical properties. However, austenitic stainless steel lacks in surface wear resistance. Surface nanocrystallization of austenitic stainless steel component can eliminate this drawback. This work involved fabrication of nanocrystallized layer on specimens of AISI 316 stainless steel. Nanocrystallized layer was synthesized by shot-peening process. Shots were propelled towards target surface by newly developed surface mechanical attrition treatment like process. The principal objective of the present work was to investigate nanocrystallization behaviour of AISI 316 stainless steel under adiabatic and non-adiabatic severe plastic deformation conditions. Two types of flow were used to propel the shots. In first method, only compressed air was used whereas in second method mixture of compressed air and water was used. Water is used to extract rapidly the heat generated during shot-peening so as to produce non-adiabatic conditions. After shot-peening, specimens were characterized by micro-hardness testing, optical microscopy, SEM and XRD. Results showed that nanocrystallized layer on AISI 316 stainless steel specimens can be easily synthesized by severe shot-peening. Hardness traverse as well as optical microscopy showed that with rise in velocity of shot, surface hardness, depth of nanocrystallized layer and total deformed layer increased for shot-peening with both types of flow. However, surface hardness, depth of nanocrystallized layer are higher for the specimen shot-peened using mixture of air and water. No strain induced martensite was observed when specimens were shot-peened by using only air, however, significant volume fraction of strain induced martensite (17.5 to 28.3%) was observed when shot peened with air/water mixture.

Some aspects of the behavior of metastable austenitic steels at high strain rates

Metastable austenite containing steels, i.e., steels capable of undergoing solid-state phase transformation from austenite to α´-martensite during plastic deformation, offer a very good combination of ductility, strength, and above all, exceptional strain hardening capability. In effect, in suitable plastic deformation conditions the relatively soft austenitic phase can transform to the harder α´-martensite, which increases the strain hardening rate of the material through various mechanisms. This special feature gives these kinds of alloys several beneficial properties, such as resistance against flow instabilities and increased capability to absorb deformation energy. For this reason, metastable austenite containing alloys have been extensively studied in the past. However, several open questions still remain, especially in the field of high rate deformation. This can be related to the great number and complexity of the related microstructural phenomena and their combined effects on the material response. The open questions affect both the metallurgy of the material and the numerical modeling of material behavior. The current contribution addresses some of these questions and their possible solutions, as well as gives an outlook on the possible future development directions.

Powerful ultraviolet laser pulse impact on polished metals and semiconductors

Laser treatment for samples of copper, its alloys and gold was carried out with a UV pulse of nanosecond duration. After irradiation at subthreshold values of the energy density (E ∼ 0.2 - 0.8 J/cm2) the noticeable changes in the surface layer were revealed. These are traces of thermoplastic deformation resulting from laser exposure. They appear as uneven rise of the irradiated sample surface area up to 1 μm. The effect is cumulative, because the height of the uplifts increases with increasing number of impact pulses. In addition, the characteristic features of high-temperature plastic deformation were observed in the form of crystallographic slip and grain-boundary slippage. At E ∼ 1 J/cm2 or more the optical breakdown occurred with the formation of a crater on the metal surface, that precludes the detection of described effects. The mechanical impulse of a laser plasma, when exposed to a metal surface, prevents the thermomechanical expansion of the material, and therefore, similar effects have not been previously observed. On the surface of materials with a significantly larger elastic limit (single crystals of germanium and silicon, a tungsten carbide) this phenomenon was not observed, because the generated thermomechanical stresses were insufficient to create conditions of plastic deformation.

Microstructures generated in AISI 316L stainless steel by Vickers and Berkovich indentations

Abstract The work aimes for studying the specifics of deformation of AISI 316L stainless austenitic steel under the conditions of micro severe plastic deformation (mSPD) created locally at the submicro and micro levels using Berkovich and Vickers indenters. The deformation was carried out by instrumented (depth-sensing), quasi-static indentation and microscratching methods in the load interval P = 10–2000 mN. Studies have shown that various mSPD methods (submicro-, microindentation and microscratching) create similar patterns of plastic deformation in thin surface layers of the material. The stick-slip nature of the scratching process has been demonstrated. It has been established that in the region of loads below 50 mN, the intragranular deformation mechanism has the main contribution to the formation of indentations, while at loads above 50 mN, intragranular and intergranular mechanisms participate in the process, and the role of the latter becomes greater with P increase. Load growth leads to a decrease in hardness under submicro-, microindentation and microscratching for all applied mSPD methods. The type of mSPD method, as well as the type of indenter and the magnitude of the applied load are the factors affecting the mechanical characteristics that should be taken into account depending on the practical purpose of the AISI 316L austenitic steel products.

Selection of Hot Plastic Deformation Regimes for Large Workpieces According to Mechanical Energy Distribution Criteria

Work is devoted to selecting parameters for a hot plastic deformation regime for alloy KhN55MVTs-ID on the basis of analyzing a distribution map for mechanical energy dissipation coefficients. The map is constructed from results of simulation modeling of deformation regimes for alloy samples in the temperature range 900–1140°C and strain rates of 10–3–10 sec–1. Metallographic analysis and a study of the sructure using electron microscopy are used for dissipation coefficients close to extreme values. The expediency of using a map for the process of finding favorable conditions for hot plastic deformation of alloy KhN55MVTs-ID is demonstrated.

STUDY OF THE DEFORMED STATE CONNECTION OF THE PISTON WITH THE ROD OF THE UNREGULATED PISTON PUMP

The technological processes of cold rolling of precision workpieces and ring parts, rolling of pipes, rolling of piston-connecting rod axial-rotor piston pump, which are a kind of processing of metals by pressure and contain changes in the shape of workpieces according to performing relative to the axis of the workpiece radial rotational motion. The workpiece can remain stationary or rotate. It is shown that by means of technological process of rolling of pipes, unrolling of preparations various hollow axisymmetric metal products receive, the specified processes are combined by the mechanism of deformation, namely: at them two deformations of compression and one - tension are realized. This mechanical deformation scheme creates favorable conditions for plastic deformation, because intercrystalline displacements are difficult, leading to the violation of mechanical bonds, and plastic deformation occurs mainly due to intracrystalline displacements. It is shown that in the process of connecting the piston-connecting rod in compliance with the process parameters (output supply pressure, feed rate, leaving time) the value of the specified gap either exceeds the maximum value or decreases to the value at which the next operation of the piston-connecting rod spell. The deformed state in the technological operation of rolling the piston-connecting rod pair at different stages of shape change is studied, the process control mechanism is revealed, which prevents the defect in the form of deviation from the regulated gap after rolling between the piston and the connecting rod. The used resource of plasticity at different stages of rolling is calculated, the deformability of the piston workpiece in the rolling process is estimated.

Reproducing rolling contact fatigue relevant loading conditions of railway operation on a test rig

ABSTRACT For the development of rail materials with improved properties regarding rolling contact fatigue and wear, it is at first important to know and understand the loading conditions in railway operation. Based on the loading conditions, crack initiation can be predicted. This has been done by a local analysis of the wheel/rail contact conditions with the so-called wedge model. This model takes the plastic shear deformation condition in a layer near the rail surface into account. Results for a specific railway operation scenario and test rig experiments are analysed to demonstrate how such different scenarios can be compared. The work contributes to the understanding of the transferability of test rig results to the behaviour in the field.

Strain-induced abnormal grain growth of Fe foils

Abnormal grain growth of polycrystalline iron (Fe) foil up to grains of 1 cm × 2.2 cm in size, is reported. Pre-strain generated by plastic deformation promoted the abnormal grain growth during post-strain annealing, resulting in large area regions close to single crystal within the foil. The number of nucleus/nuclei and maximum grain size for the abnormal grain growth were highly affected by the plastic deformation conditions as they cause different stored energies in the foils. These stored energies were estimated from the intragranular orientation spread using electron back scatter diffraction, and the relationship between this spread and the abnormal grain growth was investigated.

Aging behavior of Al-Li-(Cu, Mg) alloys processed by different deformation methods

Structural features and aging behavior of AlLi, Al-Li-Cu and Al-Li-Mg alloys under different equivalent strains (ε ) were investigated. Following solid-solution treatment, high-pressure torsion (HPT), asymmetric rolling (ASR) and cold rolling (CR) were adopted to introduce high, middle and low amount of strains to Al-Li-(Cu, Mg) alloys. After deformation, for the HPT processed alloys under high equivalent strains, the highest as-deformed hardness was obtained. Transmission electron microscopy (TEM) revealed that the grain size was refined to 210 nm, 120 nm and 150 nm, respectively. Under severe plastic deformation condition (ε > 30), the AlLi alloy lost age-hardenability, however, the aging of the asymmetric rolled AlLi alloys increased the hardness further and the highest hardness was obtained in this alloy. For the Al-Li-Cu and Al-Li-Mg alloys, a further increase in hardness was achieved by aging the as-deformed alloys, regardless of the equivalent strains. Meanwhile, the peak hardness increases with increasing the equivalent strains. During aging treatment, the behavior of the precipitates was discussed in the present work.

Effect of individual phase properties and volume fractions on the strain partitioning, deformation localization and tensile properties of DP steels

Deformation band localization modes, uniform tensile strength, and uniform elongation of Ferrite-Martensite Dual-Phase (DP) steels are analyzed by finite element (FE) study. Treating the microstructure inhomogeneity as the sole cause of imperfection, failure initiation is predicted as the natural fallout of plastic instability caused by load drop because of localized plastic strain in the Representative Volume Element (RVE) during straining. Strain partitioning between two phases (ferrite matrix and martensite island) are investigated on RVEs, and it reveals that the increase of martensite yield stress decreases the plastic deformation and increases the stress state in martensite. Whereas, a decrease in martensite island volume fraction (Vm) results in the reduction of plastic deformation and stress state in the island. Studies are then carried out to investigate the effects of the ferrite-martensite flow properties and martensite volume fraction on the macroscopic tensile deformation behavior and band localization of DP steels. Micromechanical based FE simulation results emphasize that an increase in initial yield strength and volume fraction of martensite increases the ultimate tensile stress (UTS) with the decrease in uniform elongation. Similarly, as the hardening rate of ferrite increases, it increases the ultimate tensile stress (UTS) and uniform elongation. Additionally, deformation band localization modes alter from inclined to perpendicular to the loading axis with an increase in martensite volume fraction and initial yield strength of martensite. The knowledge of this work can be used to design DP steels with desired mechanical properties.

Peculiarities of wear resistance of metal deposited by chromic flux-cored WIRE ПП12Х15

For surface hardening of a large range of engineering parts, surfacing is used with materials based on iron-chromium steel, which provide metal coatings with high strength and corrosion resistance. Based on them, flux-cored surfacing wires containing 13-17% chromium have been developed. At that, insufficient attention is paid to studies of the wear resistance of metal deposited by such wires. The structural features, wear resistance, and characteristics of the friction surface of the metal deposited by flux-cored wire ПП 12 Х 15 were investigated. Metallographic and durometric studies have shown that such a metal has a ferritic-martensitic structure with a hardness of 408-429 HV, as well as the presence of 5-ferrite and carbides in it, whose hardness is 358-376 HV and 551-609 HV. It was found that the mass wear of such a metal was 0.00753 g/m, the linear wear was 0.0235 mm/m, and the friction coefficient was 0.464. After friction loading, the topography of the surface was characterized by a grooved surface with deep tears, the relief of the wear surface with the presence of both small and large particles of wear products. The ПП 12 Х 15 coating with its relatively low hardness does not have sufficient resistance to the introduction of counter-microroughness vertices, which contributes to high wear rate and an increased friction coefficient due to the increased number of microcritical foci. For the microstructure of the surface layers after wear, a high degree of fragmentation of the investigated material was noted due to the formation of slip bands, characterized by a regular arrangement of dipole dislocation clusters. Friction loading turns these bands into foci of localized deformation in the form of mesa bands and leads to selective ejection of fracture products from the contact zone. The wear mechanism of metal deposited by a flux-cored wire ПП 12 Х 15 was due to the presence of chromium carbides, which act as obstacles for the sliding of dislocations under conditions of plastic deformation of the surface during friction.