Plastic Deformation Method Research Articles

Fatigue crack growth behavior of a nanocrystalline low Young's modulus β-type Ti–Nb alloy

Low Young's modulus β-type titanium alloys, such as the Ti–45Nb alloy, with elastic properties close to that of human bone containing non-toxic elements are very desirable for load bearing implants. Their relatively low hardness and strength can be significantly increased by severe plastic deformation (SPD) methods, for example high pressure torsion (HPT). To gain a better understanding of the fatigue characteristics, the fatigue crack growth (FCG) behavior of Ti–45Nb was investigated in various microstructural states (as-received, HPT-deformed, HPT + cold-rolled, HPT + heat-treated). Compact tension (CT) specimens with different crack orientations were tested at different load ratios under tension-tension loading. The microstructure of the HPT and HPT + cold-rolled material shows highly elongated grains parallel to the principal deformation direction with grain sizes in the nanocrystalline regime. Compared to the majority of studies on FCG of SPD-processed materials this titanium alloy exhibits a remarkably weak anisotropy in the FCG-behavior in all material states but especially in the HPT and the cold-rolled state. This is mainly attributed to the transcrystalline fracture mode. The threshold of fatigue crack growth was found to decrease with increasing load ratio. This is related to a lower contribution of plasticity-induced crack closure at higher load ratios.

Conceptual Analysis on Severe Plastic Deformation Processes of Shape Memory Alloys: Mechanical Properties and Microstructure Characterization

Shape memory alloys (SMAs) are types of materials that can restore their original shape upon severe or quasi-plastic deformation, being exposed to specific external stimuli, including heating, electric current, magnetic field, etc. They are a category of functional materials that provides superelasticity as a significant material property. The roots of this unintentional discovery were in the 20th century, and later it attracted the attention of various industries, including aerospace, medical, mechanical, manufacturing industries, etc. Later developments mainly focused on improving the properties of these materials. One of the ways in which this is achieved is the application of intensive plastic strains on SMAs through severe plastic deformation (SPD) methods, leading to extreme grain refinement. Superelasticity is a key characteristic of SMAs and is known as the capacity of a polycrystalline material to display extremely high elongations before failure, in a typically isotropic way, with an approximate strain rate of 0.5. Utilization of SPD techniques can also affect and lead to superior superelasticity responses in SMAs. Several SPD methodologies have been introduced over the decades, to produce ultrafine-grained and even nanostructured materials, including constrained groove pressing, equal-channel angular pressing, high-speed high-pressure torsion, accumulative roll bonding, etc. This paper aims to present a clear view of the mechanical properties and microstructure evolution of shape memory alloys after processing by some SPD methods, and to show that SPD methods can be a great option for developing SMAs and expanding their industrial and technological applications.

Controllable gradient and concurrent improvements of strength-ductility in gradient-structured sheet fabricated by plastic flow machining

This paper reports a controllable gradient microstructure sheet fabricated at room temperature conditions by a severe plastic deformation method, called plastic flow machining (PFM). The forming mechanism, microstructure evolution, and mechanical properties of the gradient-structured sheet for different machining parameters were investigated in detail. Results show that the prepared sheet by the PFM process is stratified into three structured surface layers, deformed grains layer (DGL), transition layer (TI), and ultrafine grains layer (UGL) from top to bottom, whereas microstructures present layer-by-layer refinement. The gradient structure can be controlled by adjusting the constraint tool angle and extrusion thickness in PFM. The gradient-structured sheet exhibits the concurrent combination of strength and ductility by comparison with homogeneous counterparts. It confirms that the extraordinary strength-ductility balance comes from the gradient structural effect. The insights in this study show that the continuous sheet production by PFM has superior performance and application perspectives in the structural materials, which can offer an effective and practicable one-step approach for low-cost fabricating the gradient-structured material.

Improved fretting fatigue mechanism of surface-strengthened Ti-6Al-4V alloy induced by ultrasonic surface rolling process

Surface plastic deformation methods are prevalently applied to improve the fretting fatigue (FF) property of titanium alloys. Understanding the intrinsic relation between surface plastic deformation severity and the FF property is of great significance to the application of these methods. Here, the influence of surface plastic deformation severity on the FF behavior of Ti-6Al-4V alloy is investigated. Two different levels of surface plastic deformation severity are prepared at the surface of Ti-6Al-4V alloy by employing ultrasonic surface rolling process. Uniaxial FF tests illustrate that both of the deformed samples have improved FF properties and although their fatigue life is comparable, the influences of their refined microstructures and compressive residual stresses are different. Pre- and post-mortem microstructural analyses reveals that the grains are coarsened or crystallized from amorphous material at the topmost surface under the multiaxial stresses to accommodate the plastic strain for the high surface deformation severity, while the grains are refined at the subsurface for the low surface deformation during FF loading.

Microstructure, mechanical properties and fracture toughness of ECAPed magnesium matrix composite reinforced with hydroxyapatite ceramic particulates for bioabsorbable implants

Employing ceramic particles like hydroxyapatite to fabricate magnesium-based bio-composite has received incredible attention in orthopedic applications due to their bioactivity and biocompatibility. Besides, applying severe plastic deformation methods like equal channel angular pressing (ECAP), in addition to eliminating defects induced by casting, causes the metallurgical and mechanical behavior improvement of Mg/HA bio-composites. In this paper, the combined effects of HA particles and the ECAP process with Bc route on the microstructure, mechanical properties, and fracture toughness behavior of Mg/HA bio-composite fabricated through the electromagnetic and mechanical stir casting method were evaluated. Furthermore, a non-contact digital image correlation (DIC) method was adopted to accurately assess the elastic and plastic parameters and crack propagation during the fracture toughness test. Microstructural observation demonstrated that the addition of HA particles and, subsequently, applying four passes of the ECAP process on the bio-composites not only decreased the grain size by a considerable amount of 92%, but also resulted in a homogenous microstructure. Moreover, according to the results of the mechanical tests, after four-pass ECAP, although the compressive yield stress of Mg/HA bio-composite did not significantly change, the highest tensile yield stress, ultimate tensile, and compressive strength were accomplished. Among all elastic and plastic parameters, the elastic modulus and strength coefficient have continuously risen with adding HA and increasing the number of ECAP passes. However, the strain hardening exponent has decreased noticeably with the addition of HA, and the ECAP process compensated for some of this reduction. In addition, reinforcing magnesium with HA particles and improving the dislocation density caused by increasing the number of ECAP passes has led to increased material resistance against crack growth, wasted energy, and, consequently, fracture toughness. In this case, the four-pass ECAPed bio-composite showed the highest fracture toughness, approximately 28 MPa m0.5, 70% more than the pure Mg.

Study of Tribological Properties of Bulk Nanostructured Aluminum and Copper Samples Applicable in Automotive Bearing Application

Using lightweight systems and friction reduction approaches are two main contributors towards modern and efficient powertrains in the automotive industry. New materials and processes are required to achieve the demanding and ever-increasing performance requirement of automotive systems. Nanostructure induced by severe plastic deformation methods involves bimodal microstructures and hence, shows exceptional mechanical characteristics which can be exploited for automotive application. Through this study, samples were prepared using pure copper, aluminum alloy (series 7000) and were processed to attain bulk nanostructured samples using a Single Step High Pressure Torsion technique with appropriate dimensions applicable as the rolling elements of automotive bearings. The induced nanostructures resulted micro hardness and frictional characteristics of the bulk samples were assessed using transmission electron (TEM) and atomic force (AFM) microscopies as well as microhardness evaluations. The results revealed that a fully refined nanostructured samples were achieved with 90% increase in the hardness at the outer diameter of the sample. The AFM measurements indicated that the friction coefficient of nanostructured copper and aluminum samples were ~ 25 and ~ 45% less than that of both the unprocessed samples, respectively. Characteristics of treated samples suggest that these processes can be potentially used in demanding conditions of rolling element bearings with reduced weight and frictional losses.

Inclusive anisotropy and texture analyses of AZ91 Mg sheets subjected to various passes of elevated-temperature constrained groove pressing

Constrained groove pressing (CGP) is a kind of sheet severe plastic deformation method suitable for enhancing the strengths of light alloys for various applications such as aerospace and automotive industries. In this research, the annealed AZ91 Mg alloy sheets were subjected to three CGP cycles at 300°C. Subsequently, optical microscopy, scanning electron microscopy, x-ray diffraction, and tensile tests for various directions were performed. Initially, there was a basal texture with a maximum intensity of 3.4 multiple random distribution and several β-Mg17Al12 particles as the second phase in the annealed sheet. As an important achievement of employing the CGP operation, the 1-passed sample represented a superior elongation of 35.7%, maximum yield strength of 141.0 MPa, and maximum ultimate tensile strength of 231.0 MPa in the rolling direction. These were mainly due to, the grain refinement, enhancing the fiber texture in the transverse direction, and controlling the basal texture. However, the experimental results revealed that the basal texture during the second and third passes of the operation could not be controlled. The main preferred orientation was changed from [Formula: see text] fiber for the annealed sheet to [Formula: see text] fiber for the CGPed sheets. It is also interesting to note that based on an anisotropy analysis, the 1-passed sample was the most isotropic worksheet, making this specimen a suitable blank for secondary metal forming processes, in comparison with the other CGPed samples. Fractography also indicated that the fracture mechanism varied among ductile, brittle, and mixed modes for workpieces subjected to different passes of the process.

Concept for development of economically alloyed ausferritic (bainitic) ductile cast irons

The distribution of the castings production in the world, whose total output is more than 112 million tons, is considered. A steady trend to the replacement of rolled alloy steel, which is used for critical engineering products, by Austempered Ductile Iron (ADI) is outlined. The latter is ductile cast iron with globular graphite, which is austempered (isothermally quenched) to produce ausferritic (bainitic) structure. The dynamics of prices for main alloying elements in ADI (molybdenum, nickel and copper, whose total amount in the alloy reaches 5 %) is considered and their steady growth is outlined.The research goal is to develop a concept of economical alloying of ADI (the total content of Mo, Ni and Cu should not exceed 2 %) retaining sufficient hardenability and substantially decreasing the cost price. The goal is attained by decreasing the content of the most expensive alloying element, molybdenum, to a minimal level along with the use of microalloying and applying one of the methods of hot plastic deformation to the casting.The reduced content of the main ‘triad’ of alloying elements is compensated by microadditives of strontium or barium, vanadium, boron, niobium and the addition of misch metal. Several groups of economically alloyed cast irons are proposed: (1) low‑nickel and low‑molybdenum with increased content of copper (up to 1.8 %) and the addition of vanadium, (2) molybdenum‑free with microadditive of boron, (3) molybdenum‑free with microadditives of niobium and boron, and (4) molybdenum‑free minimally alloyed with nickel and copper.It is shown that plastic deformation, along with giving the product the required shape, affects the kinetics of structural‑phase transformations. and acts similarly to alloying with Mo and Ni, shifting the TTT‑curve to the right. Therefore, the ausferritic structure can be obtained at a lower cooling rate.The mechanical properties with such alloying and the use of plastic deformation are the following: ultimate tensile strength 1100–1500 MPa and elongation to failure 2–4 % for lower bainite; ultimate tensile strength 800–1100 MPa and elongation to failure is 4–7 % for upper bainite.

Comprehensive Estimation of Changes in the Microgeometry of Steel 45 by Ultrasonic Plastic Deformation with a Free Deforming Element

A method of ultrasonic surface plastic deformation is widely used to change the properties of the surface layers of metal products. Under the influence of this type of treatment, the structure of the material changes, microhardness increases, roughness decreases, internal tensile stresses are removed, and compressive stresses are created. Now many types of ultrasonic surface plastic deformation have been developed, which differ in the degree of impact on the material. The object of this paper is to study the change in the microgeometry of steel 45 (ASTM M1044; DIN C45; GB 45) under the action of ultrasonic plastic deformation by a free deforming element (indenter in the form of a surface rolling ball). During the study, factors that have the greatest influence on the change in the microgeometry of the sample during treatment were identified. These include the initial roughness of the sample, the number of passes of the indenter, the feed of the indenter, the force with which the indenter is pressed to the treated surface, and the amplitude of the oscillations of the ultrasonic horn. The paper presents the dependences of changes in the main roughness parameters on the above factors. The value of the initial roughness at which it is possible to obtain a uniform surface microrelief is determined. The optimization of treatment parameters providing a change in the height and step parameters of roughness was carried out. Recommendations for choosing the most effective technological modes of ultrasonic treatment of steel 45 with a surface rolling ball are given.

Improvement of the environmental safety of weaving equipment by reducing the wear of contact surfaces

The purpose of the work is improvement of the environmental safety of weaving equipment by reducing the wear of contact surfaces. For the environment, minimizing the wear during the operation of weaving equipment is of great importance. Nevertheless, the physical-chemical interaction of metal surfaces with the environment in its individual sections is uneven due to its polycrystalline structure and heterogeneity. At the same time, the value of their residual stresses (microstresses), the degree of plastic deformation, etc., have a significant effect on the physical and chemical activity of separate surface grains. The article covers the causes of wear of the batten mechanism of a shuttleless loom because of friction. In order to ensure the environmental safety of weaving equipment, methods of increasing the wear resistance of the batten mechanisms of shuttleless looms have been proposed. The article substantiates that an effective method for improving the efficiency of the batten mechanisms of shuttleless looms can be the method of surface plastic deformation of the inner surface of the batten teeth shed. As a result, the uniformity of the physical-chemical interaction of metal surfaces with the environment is ensured, as the resistance to wear and fatigue failure increases.

Justification of the method of surface plastic deformation to strengthen the surface of the shaft under the cuff during repair

The shaft-seal connection is a critical element of any unit, and its reliability is important to ensure the service life of the entire assembly unit. Treatment by surface plastic deformation makes it possible to provide hardening to a depth of up to 2 mm, microhardness increases on average by 150% relative to the initial value, and reaches a value of 6500 MPa. Residual stresses after SPD always have a negative value, the depth of their distribution exceeds the depth of distribution of increased microhardness by 1.5 times, which makes it possible to increase the service life.

Влияние отжига и дополнительной деформации на динамические свойства сплава АМг4.5 в ультрамелкозернистом состоянии

The possibility of increasing the static and dynamic strength of the aluminum-magnesium alloy AMg4.5 is shown by using methods of severe plastic deformation, a combination of annealing and additional deformation of ultrafine grained alloy. The strength properties of the material are evaluated using a structural-temporal approach to the analysis of experimental data on the dynamic tension of small samples obtained on split-Hopkinson pressure bar.

Effect of annealing and additional deformation on the dynamic properties of ultrafine-grained AMg4.5 alloy

The possibility of increasing the static and dynamic strength of the aluminum-magnesium alloy AMg4.5 is shown by using methods of severe plastic deformation, a combination of annealing and additional deformation of ultrafine grained alloy. The strength properties of the material are evaluated using a structural-temporal approach to the analysis of experimental data on the dynamic tension of small samples obtained on split-Hopkinson pressure bar. Keywords: dynamic strength, Incubation time criterion, Kolsky method, aluminum.

Effects of Hardening by Annealing and Softening by Additional Plastic Deformation in Ultrafine-Grained Al and Al-Based Alloys: Brief Review

This is a brief review of recent experimental and theoretical results on the influence of low temperature annealing and subsequent small plastic deformation on microstructure, strength and ductility of ultrafine-grained Al and Al-based alloys structured by high pressure torsion. Some earlier results on this problem for ultrafine-grained Al and Al-based alloys structured by different methods of severe plastic deformation are also shortly presented. The reasons for the effects of hardening by annealing and softening by additional small plastic deformation of the materials are suggested and discussed in detail. Moreover, the influence of the temperature of mechanical testing and the alloying elements are in the focus of the review. It is shown that in the physical origin of these effects are the transformations of the defect structure of grain boundaries in the process of low temperature annealing and subsequent small plastic deformation of the ultrafine-grained Al and Al-based alloys structured by high pressure torsion.

Substantiation of force and time of impact interaction of bodies performing translational motion in hardening process parts by cold plastic deformation method

The force and time of impact interaction of spherical surfaces of bodies that perform translational motion on the planar surface of the stop, at which elastic deformations occur in the process of hardening parts by cold plastic deformation, are substantiated.

PROPERTIES INVESTIGATION OF ALUMINUM-BASED COMPOSITES PROCESSED USING NEW METHODS OF SEVERE PLASTIC DEFORMATION AND THE FINITE ELEMENT METHOD

This paper aims to investigate the properties of aluminum-based composite Al2O3/SiC ceramics using new severe plastic deformation (SPD) methods and the finite element method. This research work also focused on the accuracy of the simulation results in manufacturing reinforced Al2O3/SiC ceramic. The latest method was developed by repetitive press-roll forming (RPRF) for processing ceramic-reinforced composite materials. The simulations were carried out to validate the experimental results of the strength testing conducted for composites with the hybrid reinforcement by having ultimate tensile strength (UTS) values that correspond to 123 N/mm2, 130 N/mm2, and 124 N/mm2 for the hybrid composites of two layers, four layers, and six layers, respectively. This is the best result among processes developed, such as accumulative roll bonding (ARB). The experimental results prove that the SPD of the RPRF process can significantly increase the UTS and hardness values in aluminum matrix-based composites type AA1100/5052. Samples with SiC reinforcements have the highest mechanical properties compared to the other reinforcements (Hybrid and Al2O3), with a resulting UTS value of 163 MPa and a resulting hardness value of 46.42 HV. The application of this experiment is a plate matrix attached where the surface of the end face is sprinkled with ceramic Al2O3/SiC material as reinforcement.

Functional gradation of aluminum alloy by impact of ballistics as severe plastic deformation process

In the present effort, impact of bullets fired at high speeds on a stationary target was used as a high strain-rate plastic deformation method to generate Functionally Graded Materials (FGMs). The bullet-shaped Aluminum alloy Al5052 specimens impacted the UHMWPE target at different projectile velocities ranging from 100 m/s to 750 m/s, to study the effect of the impact speed. Moreover, few of the projectiles impacted along the longitudinal axis whereas the remaining projectiles impacted with an obliquity to investigate the effect of leading-edge shape. The metallography of the projectile specimens fired at 750 m/s shows grain refinement from 70 ± 3 μm at the rear/ un-deformed point to 10 ± 1 μm at the front/ severely deformed point which is in the impact zone. Similar but of less magnitude variations were observed at other impact speeds also. The hardness variation was 45% (70 ± 3 HV at the rear surface to 102 ± 2 HV at the front face) at 750 m/s. Moreover, least variation in hardness and grain size was observed for projectile impacted at lowest velocity tested (100 m/s). Further, functionality in hardness and grain refinement was seen in graded direction due to shape of the projectile specimens, impact velocity, and target material. Depending upon the impact angles, axisymmetric (impacted normal to the longitudinal axis) or unsymmetrical (impacted at an angle) variation of grain refinement and hardness was observed.

Microstructural and Mechanical Evaluation of Pure Copper Rods Processed by Severe Plastic Deformation Method of Hydrostatic Cyclic Extrusion Compression

Microstructural and Mechanical Evaluation of Pure Copper Rods Processed by Severe Plastic Deformation Method of Hydrostatic Cyclic Extrusion Compression

Microstructure evolution and tensile property of deformed Al–Mg–Sc alloy: comparison of ECAP and FSP

In this paper, the effects of two severe plastic deformation (SPD) methods, ECAP and FSP, on the microstructure evolution and tensile strength of an Al–6Mg–0.4Mn–0.25Sc–0.1Zr (wt.%) alloy are comparatively studied. The microstructure was characterized by SEM, EBSD, T-EBSD, TEM and HRTEM, and the tensile strength of the material was tested by uniaxial tensile testing machine. The results show that ECAP has a stronger grain refining effect than FSP. ECAP can refine the average grain size of Al–Mg-Sc alloys to about 1 μm, while the grain size of the FSP samples is mostly 2–3 μm. In addition, the effects of the two SPD methods on the second phase particles in the Al–Mg–Sc alloy are also different, but both methods will change the distribution and morphology of Al3(Sc, Zr) particles, which is due to the different deformation mechanisms of ECAP and FSP. The yield strength of the ECAP sample is higher than that of the FSP sample, but the elongation after fracture is slightly less than that of the FSP sample.

Влияние деформационной обработки на микроструктуру и механические свойства сплава Ti-42Nb-7Zr

Introduction. The interest of modern medical materials science is focused on the development of beta-alloys of ternary systems (TNZ) based on titanium, niobium and zirconium with the low Young’s modulus, which is comparable with the elastic modulus of the bone. A wide application of the above alloys in medicine is limited by its insufficiently high strength properties, such as yield strength, ultimate strength, fatigue strength, fatigue life, etc. The formation of bulk ultrafine-grained structure in the alloys via deformation processing, including severe plastic deformation, ensures a considerable increase in the mechanical properties of alloys without toxic alloying elements. The aim of the work is to analyze the influence of deformation (multipass rolling and abc-pressing in combination with rolling) on the microstructure and mechanical properties of the alloy of the Ti-Nb-Zr system. The research methods. The Ti-42Nb-7Zr alloy cast blanks were made from pure titanium, niobium, and zirconium iodides by arc melting with a tungsten electrode in the protective argon atmosphere. It is shown that the cast blanks obtained have a high degree of uniformity in the distribution of niobium and zirconium alloying elements. To form an ultrafine-grained (UFG) structure, the cast blanks were subjected to deformation according to two schemes: 1) multipass rolling and 2) a combined method of severe plastic deformation, consisting in abc-pressing and subsequent multipass groove rolling. Results and discussion. As a result of deformation processing by rolling, an ultrafine-grained (UFG) structure is formed, which is represented by non-equiaxed -subgrains with cross-sectional dimensions 0.2…0.8 µm and length 0.2…0.7 µm, dispersion strengthened nanosized ω-phase, as well as subgrains of the -phase. Application of combined severe plastic deformation has promoted formation of a more dispersed UFG (+ω)-structure with an average size of structural elements equal to 0.3 μm. The UFG structure formed as a result of two-stage SPD has provided a high level of mechanical properties: yield strength – 480 MPa, ultimate strength – 1.100 MPa, microhardness – 2.800 MPa, with a low modulus of elasticity equal to 36 GPa.