Severe Plastic Deformation Research Articles

Gradient microstructure formation in carbon steel bars

In recent years, severe plastic deformation has been one of the most popular methods of increasing the mechanical properties of bars. Obtaining an ultra or nanostructure in such bars provides high strength properties, but also reduces plasticity. This paper shows that gradient structure formation in carbon steel bars gives a simultaneous increase in strength properties and some decrease in plastic properties. A new combined technology is proposed for obtaining gradient microstructure. This technology consists of drawing medium carbon steel bars on a radial-shear broaching mill and subsequent drawing. Bars with 30 mm diameter were strained at room temperature to a diameter of 16 mm in 3 passes. As a result, during three straining cycles, the average value of microhardness in the central zone was 2085 MPa, in the neutral zone was 2505 MPa, and in the surface zone was 2915 MPa. This variation of microhardness confirms gradient microstructure availability. Also there was an increase in strength characteristics almost 2 times, plastic characteristics undergo reduction due to gradient microstructure obtained during straining, but remain at a fairly good level for steel AISI 1045. The validity of the results is confirmed by a large number of experiments using a set of standard and modern research methods, such as optical, scanning and transmission microscopy, EBSD analysis, microhardness changes, fractographic method and tensile tests of mechanical properties, as well as by the results reproduction in the joint use of methods.

Nanostructuring of Zn–Li-based alloys through severe plastic deformation: Microstructure, mechanical properties, and corrosion behaviors

To date, nanostructuring through plastic deformation has rarely been reported in biodegradable zinc (Zn) based alloys that have great potential in load-bearing conditions. Here, typical high-strength Zn–Li-based alloys were subjected to SPD processes, including equal channel angular pressing (ECAP) and high-pressure torsion (HPT), to achieve nanostructured microstructures. The effects of SPD on the microstructures, mechanical properties, and corrosion behaviors were generally investigated. The two SPD routes resulted in totally different microstructures. ECAPed samples processed at 150 ​°C exhibited a complicated multilevel structure (nm to μm) with mixed Zn equiaxed grains and lamellar-like eutectoid regions (Zn ​+ ​α-LiZn4), and HPTed ones (25 ​°C) possessed a fully dynamically recrystallized (DRXed) microstructure with an average grain size below 0.4 ​μm. The tensile strength of the SPD samples could reach 500 ​MPa. Meanwhile, HPTed samples exhibited extraordinary fracture elongations higher than 100 ​%, because of a different grain boundary sliding deformation mechanism. HPTed samples and ECAPed samples displayed different corrosion patterns, and the former exhibited a much higher corrosion rate in Hank's solution, possibly due to the accelerated corrosion at grain boundaries. In summary, SPD is an efficient way to refine the microstructure of biodegradable Zn-based alloys, possibly improving their performances and clinical applications.

Experimental study and finite element modelling of pure copper tube fabrication via the Parallel Tubular Channel Angular Pressing (PTCAP) Process

The Parallel Tubular Channel Angular Pressing Process (PTCAP) has emerged as a promising method for refining the grain structure and enhancing the mechanical properties of metallic materials through severe plastic deformation. This study focuses on a comprehensive investigation of the PTCAP process, combining experimental and numerical analysis to gain insights into its underlying mechanisms. Experimental investigations involve processing a commercially pure copper tube using PTCAP under controlled conditions. In parallel, an explicit numerical analysis is developed using ABAQUS software to simulate the deformation behavior during PTCAP. The model incorporates material constitutive equations and accounts to describe the material response under high strain rates and large deformations. The research aims to investigate how multi-pass PTCAP affects hardness, strain homogeneity, and stress distribution. A comparison between the load punch from the experimental and FEM is conducted to validate the FEM results, and there is a good correlation between both. Hardness measurements are conducted at various stages to quantify the changes in material hardness resulting from the successive PTCAP passes. The hardness of the Cu tube increased by 63.45, 94.51, 103.98, and 105.64% after 1 to 4 passes, respectively.

Development of Microstructure in Aluminum Single Crystal During Complex Shearing of Extruded Tube

The development of the microstructure during severe plastic deformation of an aluminum single crystal by complex shearing of the extruded tube (CSET) was studied in this paper. The research has demonstrated that even in a single crystal, an ultrafine-grained microstructure can be obtained during this one-step process. The size of the grains gradually changes and reaches the minimum size on the level of 1 μm at the inner surface of the resulting tube. Simultaneously, preferential orientations in individual parts of the deformed sample change in a complex way. The main mechanism affecting the final microstructure is continuous dynamic recrystallization. The microhardness also exhibits a gradient character with higher values at the inner surface of the tube compared to its center.Graphical

Microstructural transformation and corrosion–cavitation behavior of ultrasonic nanocrystal surface modified nickel aluminum bronze (NAB)

In this study, nickel–aluminum bronze (NAB) is optimized by ultrasonic nanocrystal surface modification (UNSM), and its surface microstructural evolution, surface hardness, electrochemical corrosion behavior, and cavitation erosion behavior are investigated. The potentiodynamic polarization curves and electrochemical impedance spectra before and after UNSM treatment of NAB are measured using a typical three-electrode system. The cavitation erosion process is simulated through the vibration of ultrasonic waves underwater, and the cavitation erosion resistance performance of various specimens is evaluated. UNSM significantly refines the coarse and heterogeneous multi-phase structure of the cast NAB, providing a relatively uniform and dispersed structure. Simultaneously, severe plastic deformation rapidly increases micro-strains on the NAB surface, which effectively improves its surface hardness from 211 to 360 Hv. After UNSM treatment, the corrosion potential increases slightly; and the passivation potential and current decrease considerably, dropping from 207 to 103 mV and from 5.23 to 2.41 mA/cm2, respectively. This is primarily because of the slowdown of selective-phase corrosion and the uniform formation of an oxide film. Additionally, UNSM parameters affect corrosion potential by regulating surface roughness. A smoother surface corresponds to a higher corrosion potential at the same load. UNSM treatment significantly improves the cavitation corrosion resistance of NAB, primarily because an increase in hardness and uniform distribution of structure effectively slows the speed of crack formation and propagation, which is a result of the synergistic improvement of mechanical and corrosion resistance properties.

Enhancing zero-valent iron (ZVI) pulverization during mechanical milling: FeSx as milling aids

A critical problem in the production of ultrafine zero-valent iron (ZVI) using mechanical milling is that the metallic iron (main component of ZVI) is ductile and can withstand severe plastic deformation, which leads to the slow pulverization of ZVI during its milling. In this work, we introduce non-ductile particle solids (FeSx) as milling aids to enhance the pulverization of the ductile ZVI, and find that the addition can improve the pulverization. The result is verified in three different ways through which the milling aids (FeSx) are introduced, namely, the addition of the FeSx solid directly, the use of the FeSx that is formed during the milling using aqueous sulfide solution as milling solvent with and without the addition of ferrous ion. The ZVI particles are pulverized to hundreds of nanometers using the milling aids, while the particles are deformed to flakes of a few microns without the milling aids. Such size difference is quantified using two sizing technologies independently and is verified by the study of the hydrodynamic performance at three flow conditions that are of practical interest for the environmental applications of ZVI. Mechanism of the FeSx as milling aids for the pulverization enhancement may relate to its wedge effects, its non-ductile texture that inhibits the cold welding and its fine bead function. The study provides a method to improve the efficiency of the production of ultrafine iron particles for environmental applications and it is also the 1st work reporting the enhancement of the pulverization of ductile ZVI.

Shot peening coverage effect on laser powder bed fused steel

Developing effective strategies for enhancing the damage tolerance of laser powder bed fusion (LPBF) components remains a formidable challenge in the disruptive additive manufacturing field. The typical shot-peening (SP) is a promising and efficient post-treatment procedure owing to its capability to introduce compressive residual stress, enhance the surface integrity, shrinkage the subsurface lack-of-fusion (LoF) defects of LPBF components. However, there is still a significant gap in understanding the appropriate utilization of the SP procedure to enhance fatigue performance, hindering its full potential in practical applications. This study systematically investigated the influence of surface coverage (150 %, 300 %, and 450 %) on surface characteristics, subsurface characteristics, and mechanical properties of LPBF 304L austenitic steel. Though evaluating the feasibility of severe shot peening and observing post-deformed microstructures, the process-microstructure-performance relationship of shot-peened LPBF austenitic steel was preliminarily established for the first time. The results indicated that increasing surface coverage up to a threshold (300 % in this work) could effectively enhance the strength and fatigue performance without significantly sacrificing ductility, primarily attributed to the increased gradient strain generated by the gradient deformation structures as well as the shrinkage of detrimental near-the-surface defects. The excessive surface coverage may be detrimental to ductility and fatigue performance, as it directly increases the severe plastic deformation and near-saturated micro-defects in the gradient deformation layer, substantially weakening the strain gradient's capability to accommodate dislocation flow during deformation. The findings suggested careful selection of shot peening coverage to balance enhanced mechanical properties and minimal introduction of detrimental defects.

Multiscale mechanical performance evaluation of L-DED Ti6Al4V by novel ultrasonic burnishing (UB)

Laser-directed energy deposition (L-DED), as a novel technology to produce titanium (Ti) alloys (e.g., Ti6Al4V), has potential impactful applications. However, Ti alloys by L-DED is largely compromised by defects (porosity, cracks, etc.) at or near surfaces, which prevents strength-ductility synergy. In this study, a new method for Ti6Al4V sample preparation using ultrasonic burnishing coupled with heat treatment (UB/HT) after L-DED has been suggested. The results show that UB/HT has a more positive effect than mere UB to overcome turning's disadvantages, when the roughness, porosity, microstructures, and multiscale mechanical performance of L-DED Ti6Al4V are considered. UB/HT transforms residual tensile stress into compressive stress and causes severe plastic deformation (SPD) within a depth of approximately 10 μm on the surface layer. With this, UB/HT improves multiscale mechanical properties, e.g., hardness to 428 HV and strength to 976.7 MPa, and the related failure modes and fracture features induced by the UB/HT crack inhibition effect are confirmed with the fatigue results. With these observations, this research provides a good theoretical and practical reference for multi-scale mechanical analysis and understanding of L-DED Ti6Al4V, which expand the UB/HT applications.

Microstructural and elemental analysis of flow lips of heavy haul curved rails affected by deformation driven phase transformation

A combination of optical imaging (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atom probe tomography (APT) was used to examine the white etching layer (WEL) and brown etching layer (BEL) formed in the flow lip region of a heavy haul curved rail. These flow lips eventually serve as crack initiating regions, leading to reverse detail fractures. OM distinctly identified the WEL/BEL region based on light contrast, while SEM micrographs identified a fine-grained structure within the WEL with intermittent patches of a deformed pearlitic structure. SEM images of the WEL/BEL indicate that the fraction of cementite patches was higher in the BEL region than in the WEL. TEM investigations revealed the presence of martensite/nano-crystalline ferrite along with newly formed austenite and cementite particles in the WEL and the BEL. The ferrite/martensite grain size was much finer in the WEL than in the BEL. The lath morphology of martensite was observed in the BEL, whereas a mixed morphology of lath and twinned martensite was observed in the WEL. APT studies show no Mn/Si partitioning in WEL/BEL along with C-concentrations ranging from 10 to 15 at.% and up to 20 at.% in the WEL and BEL respectively. The synergistic effect of elevated wheel-rail contact temperatures and severe plastic deformation dictated the overall microstructural evolution of the BELs and WELs on the outer rail surface in the flow lip.

Radial dependence of thermal, structural and micro deformation characteristics in Cu-Zr-Al bulk metallic glass subjected to high pressure torsion

Disk of a Cu38Zr54Al8 bulk metallic glass was subjected to severe plastic deformation by high pressure torsion up to 25 revolutions. X-ray diffraction was utilized to investigate the microstructure of the deformed sample, while the thermal behavior of the glass was analyzed by differential scanning calorimetry. To examine the effect of plastic straining on structural changes, micropillars were fabricated on the cross-section of the disk along the radius at specific locations, i.e. center, half radius and perimeter. Compression tests of these micropillars were conducted in a scanning electron microscope with simultaneous recording of continuous acoustic emissions. Present paper captures the effect of competition between thermal relaxation and deformation induced structural changes. Specifically, probability distributions were constructed for a series of acoustic emission events, revealing that the occurrence of acoustic emission bursts at larger deformations is in correlation with the shift of the X-ray diffraction halos and change in thermal characteristics. Accordingly, a transition was identified from random to correlated acoustic emission behavior parallel with a progressive increase in the accumulation of excess free volume from negative to positive values.

Multi-scale annealing twins generate superior ductility in an additively manufactured high-strength medium entropy alloy

Coherent twin boundaries (CTBs) are internal planar defects that offer a promising pathway for designing advanced metallic materials with superior strength-ductility synergy. However, incorporating nanoscale CTBs into additive manufacturing (AM) microstructures is highly challenging without severe plastic deformation. Here, by utilizing the intrinsic cellular structures in AM alloys, we for the first time achieved a high density of multi-scale annealing twins in a laser powder bed fusion (LPBF) Ni35Co35Cr25Ti3Al2 medium-entropy alloy. These multi-scale annealing twins, together with nanoprecipitates and dislocations, resulted in gigapascal strength (∼1.4 GPa) and substantial tensile ductility (∼25 %). We reveal that the AM-induced cellular structures, decorated with entangled dislocations and Ti segregation at the cellular boundaries, facilitate the abundant nucleation of multi-scale annealing twins through interactions with migrating recrystallization boundaries. Additionally, the cellular precipitation networks enhance the thermal stability of nanoscale annealing twins. Frequent dislocation-TB interactions during deformation contribute to superior strain hardenability and thus good ductility. Synergized multiple strengthening mechanisms, i.e., boundary strengthening, precipitation strengthening, and dislocation strengthening, are responsible for the excellent strength. Our present findings advance the design of AM microstructures by harnessing the beneficial effects of cellular structures and provide valuable guidance for developing alloys with exceptional mechanical properties.

EFFECTS OF PROCESSING AL-MG ALLOY BY SEVERE PLASTIC DEFORMATION: TENSILE PROPERTIES AT HIGH TEMPERATURES

Aluminum and wrought non age-hardenable such as Al-Mg alloys became interesting alternatives for various structural applications in spite of generally moderate strength, but relatively good formability and good corrosion resistance. Increasing overall strength while preserving or even improving ductility in special conditions without any any change in chemical composition that oppositely could alter other features of the material - such as weldability, becomes an objective worthy of research. A suitable way to increase the potential of Al-Mg alloys is the raising up the mechanical properties by structural refinement. Ultrafine grain size provides enhanced mechanical and/or physical properties such as strength and very good ductility – close to superplasticity at slightly higher strain rate and relatively lower temperatures – and better corrosion resistance. Well-known as one of the most encouraging and efficacious structure refining method amid other severe plastic deformation (SPD) techniques, equal channel angular pressing (ECAP) has been deeply investigated thanks to dramatic improvements in structure and therefore properties of bulk ultrafine grained/nanostructured materials. The aim of this study is to evaluate by tensile testing at higher temperatures the mechanical properties of an Al-3.4%Mg alloy previously processed by ECAP up to 8 passes, as a candidate for replacing AA5154 which contains different amounts of chromium. The tensile tests conducted at different temperatures using a computer-controlled testing machine with different strain rates showed in terms of engineering stress vs. engineering strain evolution that the ECAPed Al-3.4%Mg alloy have the potential to be used in technological processes at high temperatures, opening opportunities for industrial applications requiring high ductility.

Effects of broken β-Mg17Al12 and non-uniform Mg2Pb particles introduced by EX-ECAP on microstructure and mechanical properties of Mg–Pb-9.2Al-0.8B alloys

Mg–Pb-9.2Al-0.8B alloy faces a significant strength-toughness balance problem in applications. To address this challenge, severe plastic deformation was applied to the alloy by combining traditional extrusion with multi-pass equal channel angular pressing (EX-ECAP). The research delves into the microstructural evolution (including broken β-Mg17Al12 and non-uniform Mg2Pb particles) and its effects on the strengthening mechanisms. The synergistic effects of grain boundary strengthening due to grain refinement, Orowan strengthening, geometrically necessary dislocation strengthening, and coefficient of thermal expansion strengthening collectively enhance the tensile strength and ductility, balancing the strength and toughness. The results showed an impressive ultimate tensile strength of 386.1 MPa, which is 2.33 times that of the as-cast alloy. The altered fracture morphology clearly indicated a transformation from brittle to brittle-ductile fracture mode. During the deformation process, the activation of dislocations, atomic-scale ripples, minor lattice distortions, and kink bands enhance the macroscopic flexibility. The introduction of EX-ECAP presents new opportunities for manufacturing high-performance Mg–Pb-9.2Al-0.8B alloy through integrated deformation techniques.

Experimental investigations on the blast response of reinforced NSC, FRC and UHPC I-shape girders under contact explosions

To investigate the blast response and evaluate the structural resilience of reinforced I-shape girders, seven reinforced normal strength concrete (NSC), fiber reinforced concrete (FRC), and ultra-high performance concrete (UHPC) specimens are subjected to multiple contact explosions in this study. With the test results, the concrete damage regions and plastic deformation of steel bars are used to recognize the damage mechanism of the test specimens. The experimental results show that the damage modes of I-shape girders are mainly dominated by vertical punctures and transverse shear failures. Due to fragile characteristics, nearly 35 % of the punching crater in concrete webs, the entire shear failure of top plates, and severe plastic deformation of steel bars are discovered in NSC specimens. Polyethylene fibers improve ductility, allowing for smaller steel bar deflection and a reduction in punching depth to 21.6 % in FPC specimens. However, due to the oversized impact energies and the insufficient material strength, the transverse shear failure cannot be significantly mitigated. By contrast, not only significantly reduced punching depth but also greatly mitigated transverse shear failures are observed in UHPC specimens. Under 50 g∼200 g contact explosions, the punching depth ratios are reduced to 3.3 %, 16.6 %, and 25.8 %, merely. Apart from that, after explosions, the transverse shear failure and plastic deformation of steel bars can be effectively reduced. Due to the remarkably decreased damage regions, the UHPC specimens exhibit better structural resilience after blast loadings.

Ultimate compressive strength and severe plastic deformation of equilibrated single-crystalline copper nanoparticles

Mechanical properties and deformation mechanisms of defect-free copper nanoparticles are investigated by combining experiments with atomistic simulations. The compressive strength of the particles increases with decreasing size and tends to saturate near the theoretical strength in the small-size limit. In this limit, the intrinsic size dependence of the strength is governed by the stochastic nature of dislocation nucleation near the particle surface. The particle deformation process evolves from the initial strain softening to strain hardening as the particle accumulates residual damage. The normalized strength-size relation for Cu is compared with those for Au, Ni, and Pt. The lack of universal behavior among the four FCC metals is discussed. Heavily deformed Cu nanoparticles develop polycrystalline structures and change the lattice orientation from [111] to [110]. The experiments and simulations reveal the twinning mechanism of the lattice rotation leading to the new grain formation.

Evaluation of microstructure and mechanical characteristics of 2024 aluminum alloys with μ-Al2O3 additives produced via hydrostatic cyclic expansion extrusion with back-pressure

Grain refinement techniques are commonly used to produce enhanced materials with micro- and nanoscale grain sizes. This study investigates the severe plastic deformation of 2024 aluminum alloys reinforced with microparticles of alumina (Al2O3) using a new method based on hydrostatic cyclic expansion extrusion. Cuboid samples of aluminum 2024 were subjected to severe deformation at 20 °C through the pressing of a steel punch from the top and the application of back-pressure to the bottom part of the workpiece after the addition of the reinforcing powder. The mold design was created to facilitate both modes of operation. The experimental results were used to examine deformation behavior and flow patterns in the samples. Furthermore, the mechanical properties and microstructure of the processed samples were analyzed to determine the effects of the applied strain.

Exploring Refinement Characteristics in FeTi‐Cux Composites: A Study of Localization and Abrasion Constraints

FeTi‐Cu composites with varying Cu contents are subjected to high‐pressure torsion, and their deformation behavior is explored systematically using scanning electron microscopy, microhardness, and nanoindentation. The study identifies the limiting factors influencing the refinement during severe plastic deformation. The pronounced strength differences between phases lead to fragmentation primarily through hard‐hard (FeTi‐FeTi) contact points, promoted by homogeneous, i.e., non‐localized, and possibly turbulent material flow. These conditions are prevalent in Cu‐rich composites and during high‐temperature deformation. Conversely, Cu‐lean composites exhibit deformation localization, hindering the fragmentation process. Abrasion becomes an efficient refinement mechanism at the submicron‐/nano‐scale, particularly for composites containing higher concentrations of nanocrystalline FeTi and exhibiting homogeneous plastic deformation. Consequently, deformation localization in Cu‐lean composites inhibits both refinement mechanisms, while Cu‐rich compositions and higher temperatures result in efficient refinement but at the risk of coarsening at the nano‐scale. Refinement is localization‐limited in the former case and abrasion‐limited in the latter. Optimized processing conditions can overcome these constraints, yielding a uniform nanocomposite. This study sheds light on the intricate interplay of the mechanical properties of the respective phases in a composite, emphasizing the importance of tailored compositions and deformation conditions to optimize nanocomposites, particularly when dealing with challenging material pairings.This article is protected by copyright. All rights reserved.

Термическая стабильность микроструктуры сплава MG-Y-ND в экструдированном состоянии

Introduction. Today, bioresorbable magnesium alloys possessing the required physical, mechanical, corrosion, and biological properties, are promising materials for orthopedic and cardiovascular surgery. The addition of rare earth elements such as yttrium, neodymium, and cerium to magnesium alloys improves its properties. Compared to widely used titanium alloys, magnesium alloys have a number of advantages. Bioresorbable materials slowly dissolve in the body, and recurrent operation to remove the implant is not needed. Biocompatible magnesium alloys have a fairly low elastic modulus (10 to 40 GPa), approaching to that of cortical bone, that reduces the contact stress in the bone-implant system. At the same time, strength properties of magnesium alloys alloyed with rare earth elements do not always meet the requirements for medical applications. Severe plastic deformation, for example, equal channel angular pressing, torsion under quasi-hydrostatic pressure, uniaxial forging, extrusion, is therefore very promising technique to gain the high level of mechanical properties of metals and alloys. Severe plastic deformation of magnesium alloys improves its structural strength by 2.5 times due to the generation of an ultrafine-grained and/or fine-grained structure. The issues related to the study of heat resistance, structure and phase composition of magnesium alloys with appropriate strength are relevant. Purpose of the work is to determine the influence of thermal effects on the microstructure of the extruded Mg-Y-Nd alloy. Methodology. The extruded Mg-2.9Y-1.3Nd alloy (95.0 wt. % Mg, 2.9 wt. % Y, 1.3 wt. % Nd,  0.2 wt. % Fe,  0 wt. % Al) is investigated in this paper. The thermal stability of the alloy microstructure is studied after annealing at 100, 300, 350, 450 and 525 °С in argon for one hour. The microstructure and phase composition are investigated using optical, transmission and scanning electron microscopes and analyzed on an X-ray diffractometer. Results and discussion. The extruded Mg-2.9Y-1.3Nd alloy has the bimodal fine-grained microstructure. It is found that along with the stable α-Mg phase, the alloy structure consists of Mg24Y5 intermetallic particles and -, -, and 1-phase precipitates. Annealing in the temperature range of 100–450 °С for one hour has no effect on the structure of the Mg-2.9Y-1.3Nd alloy, but promotes the growth in the linear dimensions of -, -, and 1-phases precipitates. In the temperature range of 300–450 °С, the morphology of -, ,- and 1-phases changes, while the average grain size of the major -phase remains unchanged. Annealing at 525 °С leads to a notable transformation of the bimodal microstructure of the alloy, which is associated with the intensive growth in the grain size of the -phase, Mg24Y5 particles, and -, -, and 1-phases precipitates. Annealing in the temperature range of 100–450 °C leads to an increase in the linear dimensions of Mg24Y5 particles, -, -, and 1-phases precipitates and bimodal microstructure of the Mg-2.9Y-1.3Nd alloy remains unchanged.

Characterization of material flow behavior in friction stir welded AA2014 aluminum alloy joints

Abstract Steel rivets serve as a substitute material for connecting similar and dissimilar materials within the structural fabrication industries. However, the use of steel rivets can result in a significant increase in the structure’s weight and may trigger corrosion at the interface due to galvanic coupling. Combining dissimilar alloys through the fusion welding process poses numerous challenges for manufacturers and designers. A solid-state welding technique called friction stir welding (FSW) has been developed. FSW can effectively join materials without reaching their melting points, relying on severe plastic deformation and recrystallization to form a welded joint. The proper selection of the tool and process parameters is essential for achieving a sound weld. The findings of this study indicate that plastic deformation, material flow, and recrystallization play pivotal roles in the strength of the joint. This implies that FSW represents an ideal joining process for high-strength alloys and serves as a viable alternative to replace permanent joints like rivets.

Multiscale simulation combined with experimental investigation on residual stress and microstructure of TC6 titanium alloy treated by laser shock peening

The evolution behavior of residual stress and microstructure of TC6 titanium alloy under laser shock peening (LSP) were investigated using finite element (FE) and molecular dynamics (MD) simulations combined with experiments. The propagation process of laser-induced stress wave and plastic deformation behavior of TC6 titanium alloy model were studied using FE software with ABAQUS. The FE simulation results showed that increasing laser energy and impact time could increase the amplitude of compressive residual stress (CRS) to a certain extent, while a higher overlapping rate improved the CRS uniformity. The experimental results of residual stress testing based on XRD technology were consistent with the FE simulation results. Based on the piston shock method, the microstructural evolution process of α phase of titanium alloy under different shock velocities was simulated using MD software with LAMMPS. Laser shock wave promoted the transformation of hexagonal close-packed (HCP) structure to body-centered cubic (BCC) and face-centered cubic (FCC) structures in titanium alloy, and the generated dislocation density increased with increasing shock velocity. The severe plastic deformation caused by laser shock wave induced the formation of mechanical twin, subgrain and stacking fault, which was consistent with the (transmission electron microscope) TEM characterization results.