Plastic Deformation Research Articles

Grain size gradient effect on grain boundary mediated deformation of nano-grained metals

The extraordinary mechanical performance of gradient nano-grained (GNG) structures is characterized by the heterogeneity of dislocation-based and grain boundary (GB)-based plasticity, where the grain size gradient effect on these deformation mechanisms even fracture process still remains unclear. Herein, molecular dynamics simulation is conducted on the GNG α-Fe structures to investigate the grain size gradient effect on the GB-mediated hetero-deformation mechanisms. The plastic deformation mechanism changes from GB motion (grain coarsening and merging) to GB-dislocation interaction when the grain size distribution extends from the Hall-Petch softening region to the strengthening region. With increasing grain size gradient, the ultimate tensile stress and flow stress increase in the GB motion-controlled samples, and strain partitioning between hard and soft zones is found to increase in the dislocation-GB interaction- controlled samples from an atomistic perspective. The increased strain partitioning and its accommodation process further contribute to the fracture resistance enhancement, which is demonstrated by the uniform hetero-deformation between coarse and fine grains of the GNG structure, and further avoids localized plastic deformation.

Hot deformation behavior of NiTiHf alloy under compression: Effect of deformation heating on flow softening

High-temperature shape memory alloys are suitable materials for substituting hydraulic elements in the aerospace industry due to light weight and high reactive stresses developing during thermoelastic martensitic transformation and acceptable recoverable strain. These properties may be improved by plastic deformation; however, the plastic deformation of NiTiHf alloys along with structure investigation has yet to be studied systematically. Here, the hot deformation behavior of a NiTiHf alloy with hafnium content >20 at.% has been investigated, and the processing map has been elaborated according to the dynamic material model (DMM) based on the Prasad instability criterion. The deformation heating effect has been shown to affect the flow curves and accounts for profound softening during deformation due to quasi-adiabatic deformation mode at high strain rates. NiTiHf alloys have a much higher activation energy of plastic flow, and the instability region of plastic flow is much larger compared to binary NiTi alloys. Microstructural observations have revealed that in the instability regions, oxide bands and crack nucleation occur, whereas outside this region, such defects are not observed. Electron-back scatted diffraction has demonstrated that at high temperatures and slow strain rates, discontinuous dynamic recrystallization occurs resulting in the neckless type structure, while at high strain rates, this phenomenon has not been observed. Based on the obtained results, the preferable deformation conditions are established to be 850–1000 °C and 0.003–0.05 s−1.

Effect of carbide refinement on high temperature erosive wear behavior of high chromium white cast iron with different titanium and carbon additions

It is known that better erosion wear resistance of high chromium (27wt.% Cr) white cast iron (HWCI) with titanium (Ti) addition can be achieved by controlling the size of M7C3 carbides. Nevertheless, it might not be directly applicable to high temperature conditions due to the more complex factors involved, especially the hot oxidation behavior. Therefore, the effect of 0-2wt.% Ti and 3-4wt.% carbon (C) addition on the high temperature erosion wear behavior of HWCI has be investigated in this research. The results show that there are TiC and M7C3 carbides precipitated in the material matrix. The size of M7C3 carbides decreases drastically as the amount of Ti increases. On the contrary, it is effectively enlarged with the addition of higher C. In addition, there is no significant difference in hardness among all specimens due to the relatively similar carbide volume fraction (CVF). The wear resistance of HWCI is improved by increasing the amount of Ti although it has a lower value as the C content increases. It means that hardness is not an important factor in evaluating the wear characteristics of HWCI at high temperatures. The worn surfaces and cross-sections show that the smaller M7C3 carbides are more likely to undergo plastic deformation rather than being directly peeled out. In addition, the effect of hot oxidation behavior was negligible because there is only a very thin oxidation layer on the worn surface. Therefore, it can be concluded that the erosive wear behavior of the material is greatly influenced by the size of M7C3, which the material with better erosive wear resistance contains finer carbides.

Wear behaviour of abrasive tools and its effect on surface integrity during polishing superalloy GH4169G with abrasive cloth flap wheels

In polishing nickel-based superalloys, the surface quality and dimensional accuracy of the workpiece are closely related to the wear of the abrasive tools. Over the years, several researchers have studied the wear of grinding wheels or abrasive belts, including the effects of various machining methods, abrasive materials, and machining parameters on the wear of abrasive tools. However, there is not enough research on the wear mechanism of the abrasive cloth flap wheel (ACFW). In this paper, during polishing GH4169G with ACFW, the wear evolution mechanism of ACFW and its effect on the surface integrity of GH4169G were investigated. First, the variations in material removal and ACFW wear amounts during the polishing process were analysed, and the different wear stages were divided based on the polishing ratio. Second, the mic-morphology and surface element distribution of ACFW at different wear stages were investigated using SEM and, EDS, and the wear evolution mechanism of ACFW was analysed. Finally, the effects of ACFW wear on the surface morphology, surface oxidation and microstructure of GH4169G were investigated by SEM, EDS, XRD, and EBSD. The results showed that the primary wear forms of ACFW were stepped fracture, cleavage fracture, blunt, pull-out, and adhesion wear. During the initial wear stage, the proportion of each wear form was relatively balanced. In the medium wear stage, fracture wear was the main wear form. Blunt and adhesive wear were the primary forms of wear during the final wear stage. In addition, with ACFW wear, the surface roughness tend to decrease first and then increase, however, the refinement level of the grains, the intensity of plastic deformation and the intensity of the oxidation reaction gradually increased. This study provides effective guidance for developing more wear-resistant abrasive tools and optimising the grinding and polishing processes.

Rebar-concrete bond behaviour in grouted sleeve connectors

Grouted sleeve connectors (GSCs) are commonly used in precast/prefabricated concrete structures. To ensure force transfer, connectors tend to be overdesigned, and this has a detrimental effect on the plastic deformation capacity of the connection region and the displacement ductility of the precast structure. To enable improvements in the design of precast RC connections involving GSCs, an accurate analysis of the bond behaviour of GSCs is required. This paper presents an analytical model for the local bond behaviour under the particular sleeve confinement. A representative cross-section of a GSC is treated as interconnected hollow circular tubes. Three stages are identified according to the state of the grout, namely elastic, partially cracked, and fully cracked. The confining pressure is formulated within the cross-section, and the bond stress is subsequently evaluated by a modified bond stress-slip law accounting explicitly for the confinement. Compared with traditional bond-slip laws, the model is capable of representing the evolution of confining stress in the loading process. Comparison with relevant experimental results show good agreement. A subsequent parametric study demonstrates the trends of influence of various parameters, and notably, within allowable limits, a reduction of the grout thickness tends to increase the bond strength in the connectors.

Effect of Prior Shot Blasting on Free Surface Roughening before Environmentally Friendly Lubrication during Plastic Deformation

Effect of Prior Shot Blasting on Free Surface Roughening before Environmentally Friendly Lubrication during Plastic Deformation

Investigating fretting wear mechanisms in Ti-6Al-4V: insights from residual stress and equivalent plastic strain analysis

Purpose The study delves into the influence of wear cycles on these parameters. The purpose of this paper is to identify characteristic patterns of σRS and εPEEQ that discern varying wear situations, thereby contributing to the enrichment of wear theory. Furthermore, the findings serve as a foundational basis for nondestructive and in situ wear detection methodologies, such as nonlinear ultrasonic detection, known for its sensitivity to σRS and εPEEQ. Design/methodology/approach This paper elucidates the wear mechanism through the lens of residual stress (σRS) and plastic deformation within distinct fretting regimes, using a two-dimensional cylindrical/flat contact model. It specifically explores the impact of the displacement amplitude and cycles on the distribution of residual stress and equivalent plastic strain (εPEEQ) in both gross slip regime and partial slip regimes. Findings Therefore, when surface observation of wear is challenging, detecting the σRS trend at the center/edge, region width and εPEEQ distribution, as well as the maximum σRS distribution along the depth, proves effective in distinguishing wear situations (partial or gross slip regimes). However, discerning wear situations based on εPEEQ along the depth direction remains challenging. Moreover, in the gross slip regime, using σRS distribution or εPEEQ along the width direction rather than the depth direction can effectively provide feedback on cycles and wear range. Originality/value This work introduces a novel perspective for investigating wear theory through the distribution of residual stress (σRS) and equivalent plastic strain (εPEEQ). It presents a feasible detection theory for wear situations using nondestructive and in situ methods, such as nonlinear ultrasonic detection, which is sensitive to σRS and εPEEQ. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-01-2024-0005/

Assessment of different agricultural soil compaction levels using shallow seismic geophysical methods

A well-developed soil structure is crucial for a fertile soil and rules its influence on the ecosystem. Slight variations in the way soil components are organized and connected can greatly impact the soil mechanical and hydraulic characteristics. However, these features are challenging to measure at a scale that is relevant for agricultural management. In this study, we assess the capability of two seismic geophysical methods, i.e. Seismic Refraction Tomography and Multichannel Analysis of Surface Waves, to monitor the effects of compaction on agricultural bare soil. The purpose is to highlight the different mechanical response caused both by soil plastic deformation and soil water distribution due to increasing compaction. Results demonstrate that both geophysical techniques provide sufficient information to capture the effects of soil compaction and distinguish its significance, while traditional direct measurements, being punctual, lack sufficient spatial coverage. P-wave velocities carry a strong imprint of soil compaction, provided by seismic refraction, incorporating the information given by the multiphase medium in its entirety. On the other hand, S-wave velocity derived from Surface Waves discriminates the effect of solid matrix structure. This work, moreover, aims to pave the way for seismic methods to spatially characterize compaction at field scale, illustrating its potential and suggesting possible developments.

Investigation of the Strain–Stress Field in Nanoscale Multilayer Systems by the Phase Plane Method

This paper presents the results of the study of stress relaxation fields, deformation, and temperature of the system of nanostructured multilayer coatings. In the work, a nonlinear relationship between strain and stress was used to take into account nonlinear effects in the mechanism of nanostructure formation. The paper assumes that a friction surface is provided by the self-organization of shear components: both stress and strain on the one hand, and temperature on the other. The studied objects are described in the adiabatic approximation, taking into account the fact of the evolution of stresses and strains. With the help of phase portraits of the system, the dependence of the deformation processes on the stresses arising in the system without coating and with coating is shown. It is shown that the rate of change of deformation depends on the characteristics of the mechanical impact on the coating and on the amount of stress and deformation. A conclusion is drawn regarding the transition process in the presence of two regions (Hooke and plastic deformation) in the corresponding phase portrait of the strain–stress field of the system. The results of the work can be used to determine the effective parameters of a coating in the analysis of experimental time dependences of stresses.

Effects of multi-axial compression and double-step aging on the microstructure and mechanical properties of Al alloy 7075

This study investigates the combined effect of severe plastic deformation via multi-axial compression (MAC) and subsequent double-step aging on the microstructure and mechanical properties of annealed 7075 Al alloy. Three distinct processes were employed: (1) double-step aging on the annealed sample, (2) double-step aging on the six-MAC pass processed sample, and (3) double-step aging without solutionization on the six-MAC pass sample. Process (2) yielded the most significant improvements in mechanical properties. Compared to the annealed sample, the six-MAC pass, double-step aged sample exhibited an average ultimate tensile strength increase of 134% and an average Vickers micro-hardness (HV) increase of 209%. This superior performance is likely attributable to the synergistic effect of grain refinement induced by MAC and precipitate hardening achieved through double-step aging. A comprehensive analysis of microstructure evolution, mechanical properties, fractography, and the relationship between them was conducted for all three processes. This in-depth examination provided valuable insights into the mechanisms governing the observed property enhancements, particularly in process (2). Additionally, a variety of characterization techniques were employed to comprehensively evaluate the material's mechanical and microstructural characteristics.

Tailoring Mechanical Properties and Shear Band Propagation in ZrCu Metallic Glass Nanolaminates Through Chemical Heterogeneities and Interface Density

The design of high‐performance structural thin films consistently seeks to achieve a delicate equilibrium by balancing outstanding mechanical properties like yield strength, ductility, and substrate adhesion, which are often mutually exclusive. Metallic glasses (MGs) with their amorphous structure have superior strength, but usually poor ductility with catastrophic failure induced by shear bands (SBs) formation. Herein, we introduce an innovative approach by synthesizing MGs characterized by large and tunable mechanical properties, pioneering a nanoengineering design based on the control of nanoscale chemical/structural heterogeneities. This is realized through a simplified model Zr24Cu76/Zr61Cu39, fully amorphous nanocomposite with controlled nanoscale periodicity (Λ, from 400 down to 5 nm), local chemistry, and glass–glass interfaces, while focusing in‐depth on the SB nucleation/propagation processes. The nanolaminates enable a fine control of the mechanical properties, and an onset of crack formation/percolation (>1.9 and 3.3%, respectively) far above the monolithic counterparts. Moreover, we show that SB propagation induces large chemical intermixing, enabling a brittle‐to‐ductile transition when Λ ≤ 50 nm, reaching remarkably large plastic deformation of 16% in compression and yield strength ≈2 GPa. Overall, the nanoengineered control of local heterogeneities leads to ultimate and tunable mechanical properties opening up a new approach for strong and ductile materials.

Zr-based bulk metallic glasses in PBF-LB/M: near-polished surface quality in the as-built state

AbstractThis study investigates the relationship between varying contour scanning parameters and their impact on both surface characteristics and mechanical performance of the glass-forming Zr59.3Cu28.8Al10.4Nb1.5 produced via PBF-LB/M. Near-polished surface states with Ra values below 1 µm were achieved. The study identifies increased laser power as a key factor in reducing the surface roughness, while repetitive scanning exhibits only marginal improvements in surface quality. Partial crystallization on the surface of the amorphous samples is found on the as-built surfaces. However, it appears to be confined to depths below 50 µm. Impressively, the material showcases large mechanical strength in the as-built condition, evidenced by a high flexural strength of 2.2 GPa combined with approximately 1% plastic deformation. These findings offer initial insights into optimizing additive manufacturing processes for BMGs, guiding the enhancement of both surface quality and mechanical robustness in Zr-based metallic glass fabricated via PBF-LB/M techniques.

In Situ Electrical Resistance Measurement of Pure Titanium During Severe Plastic Deformation by High‐Pressure Sliding

In this study, in situ measurements of electrical resistance in pure Ti during severe plastic deformation (SPD) under high pressures are presented. The process of high‐pressure sliding (HPS) is adopted for the SPD so that straining is feasible under various pressures covering α to ω allotropic phase transformation in pure Ti. Anvil surfaces are coated by a plasma‐sprayed alumina layer to maintain electrical insulation between the sample and the anvils during HPS operation. The electrical resistance increases continuously with straining by the HPS processing but the increase in the electrical resistance is more pronounced as the applied pressure increases, particularly when the ω phase formation occurs. The phase transformation is evidenced by X‐Ray diffraction analysis as well as in situ static heating experiment. The continuous increase in the electrical resistance suggests that there is neither critical strain nor avalanche for the phase transformation to the ω phase.

Achieving high strength 316L stainless steel by laser directed energy deposition-ultrasonic rolling hybrid process

Laser directed energy deposition (LDED) has attracted as a progressive additive manufacturing technique in fabricating the stainless steel components. The rapid melting and solidification velocity under LDED process induces the appearance of pores and the columnar dendritic, which degrades the strength of alloys. Here, a self-developed LDED-UR (ultrasonic rolling) synchronous manufacturing equipment is developed to fabricate the 316L stainless steel, and the characterization of microstructure and mechanical properties are studied. Results show that the size and fraction of pores are significantly reduced by LDED-UR processing, and fine equiaxed grains are obtained under the combined effects of ultrasonic vibration and roller pressure. With the severe plastic deformation, the average grain size of LDED-UR sample is decreased from 76.10 μm to 26.23 μm (LDED sample), and high angle grain boundaries transforms to low angle grain boundaries. Meanwhile, the dislocation density in LDED-UR sample is increased compared to the LDED sample. Owing to the grain refinement and dislocation strengthening, the average microhardness, yield strength, ultimate tensile strength and elongation of the LDED-UR sample reach 268.18 ± 13.90 HV0.2, 442 MPa, 771.2 MPa, and 49.8 %, respectively, which are larger than those of LDED sample (214.13 ± 13.76 HV0.2, 396 MPa, 682 MPa, and 45.5 %). This implies that the superior mechanical properties are obtained by employing in-situ ultrasonic rolling under LDED process. The insight of the influence of microstructure on mechanical properties extends a new approach for enhancing the mechanical properties of LDED alloys.

Strain hardening behavior in T-carbon: A molecular dynamics study

T-carbon, a new carbon allotrope essentially composed of intra-tetrahedron bonds and inter-tetrahedron bonds, has attracted strong scientific interest in recent years due to its excellent mechanical performance for a wide range of applications. This study demonstrates that strain hardening can endow T-carbon with exceptional mechanical strength at a high compressive strain under plastic deformation, which is rarely observed in conventional carbon-based materials. Molecular dynamics simulations reveal that this behavior occurs in T-carbon nanowires and is caused by graphitization, where their original sp3-dominated carbon network transforms into a stronger sp2-network. Further analysis shows that graphitization occurs due to the breaking of intra-tetrahedron bonds, which is dominated by the deformation behavior of inter-tetrahedron bond angles. Particularly, when the deformation angle is small, only a small portion of the strain energy is stored in the tetrahedrons, while the remaining energy is released by breaking the intra-tetrahedron bonds of T-carbon, thus leading to graphitization. Moreover, such underlying mechanisms behind strain hardening and graphitization are found to occur in bulk T-carbon. This strain hardening potentially enables T-carbon to overcome the strength–ductility tradeoff issue of high strength leading to ductility loss.

Effects of fiber characteristics on tensile and impact properties of long fiber reinforced High‐Density Polyethylene

AbstractDue to the requirements of high stiffness and impact strength of HDPE pipes, in this article, long fiber reinforced HDPE were developed and the effects of fiber length, volume fraction, types, and matrix/fiber interface on the mechanical properties were investigated. Tensile properties, notched impact strength, as well as microstructures were tested. The results showed that fibers increased the tensile strength, modulus, and impact strength, but decreased their plastic deformation. Larger fiber fraction indicates more fibers are involved in load bearing, but easy agglomeration. With ascending fiber length, tensile, and impact strength first increased and then decreased, whereas tensile modulus first increased and then maintained an almost constant value. Carbon fibers showed no advantages over glass fibers and basalt fibers in reinforcing HDPE due to the relatively poor interface bonding strength. Interface modification with KH550 improved the mechanical performance of composites, but the enhancement was limited. More effective methods should be developed for better performance.Highlights Fiber increases strength and modulus, but decreases plastic deformation. Critical fiber length for basalt LFT is 2.6 mm obtained from SEM. Larger fiber volume and length lead to agglomerations. Difference in BF, CF, and GF reinforced HDPE is determined by interface. Interface modification enhances mechanical properties of LFT but limited.

Microstructural evolution in 12% Cr heat-resistant steel during compression deformation at 650°C

Microstructural evolution in 12% Cr heat-resistant steel during compression deformation at 650°C

Enhancing Surface Integrity and Quality through Roller Burnishing: A Comprehensive Review of Parameters Optimization, and Applications.

Surface integrity is a critical aspect in ensuring the quality of components or products, particularly in industries such as automotive, aerospace, and machinery where superior surface finish and prolonged functionality of cylindrical parts are essential. Burnishing, a chip-less cold working finishing process, enhances the surface finish of machined workpieces through plastic deformation. This review paper delves into various aspects of the burnishing process and its impact on surface properties, drawing insights from multiple research projects. It explores topics including residual stresses, surface roughness, microhardness, cooling strategies, and modeling techniques. Key findings underscore the influence of burnishing parameters such as speed, feed rate, penetration depth, and number of passes on surface roughness and microhardness. Moreover, the process induces compressive residual strains on the workpiece surface, with their magnitude varying based on operational parameters. The choice of cooling methods, including kerosene, minimum quantity lubrication (MQL), cryogenic cooling, and hybrid cooling, significantly affects surface integrity. Various modeling approaches, such as Artificial Neural Networks (ANN), Adaptive Neuro-Fuzzy Inference Systems (ANFIS), and Response Surface Methodology (RSM), aid in predicting and optimizing surface characteristics. Despite the extensive discussion on surface roughness, microhardness, residual stresses, cooling methods, and modeling, out-of-roundness in the burnishing process remains understudied and warrants further investigation. This review contributes valuable insights for enhancing surface qualities in manufacturing applications and deepening our understanding of the burnishing process.

Effects of Strain Rate on the GND Characteristics of Deformed Polycrystalline Pure Copper

Geometrically necessary dislocations (GNDs) play a pivotal role in polycrystalline plastic deformation, with their characteristics notably affected by strain rate and other factors, but the underlying mechanisms are not well understood yet. We investigate GND characteristics in pure copper polycrystals subjected to tensile deformation at varying strain rates (0.001 s−1, 800 s−1, 1500 s−1, 2500 s−1). EBSD analysis reveals a non-linear increase in global GND density with the strain rate rising, and a similar trend is also observed for local GND densities near the grain boundaries and that in the grain interiors. Furthermore, GND density decreases from the grain boundaries towards the grain interiors and this decline slows down at high strain rates. The origin of these trends is revealed by the connections between the GND characteristics and the behaviors of relevant microstructural components. The increase in grain boundary misorientations at higher strain rates promotes the increase of GND density near the grain boundaries. The denser distribution of dislocation cells, observed previously at high strain rates, is presumed to increase the GND density in the grain interiors and may also contribute to the slower decline in GND density near the grain boundaries. Additionally, grain refinement by higher strain rates also promotes the increase in total GND density. Further, the non-linear variation with respect to the strain rate, as well as the saturation at high strain rates, for grain boundary misorientations and grain sizes align well with the non-linear trend of GND density, consolidating the intimate connections between the characteristics of GNDs and the behaviors of these microstructure components.

Size dependent scaling law of plastic flow in FCC Nanolattices: A Dislocation Dynamics Study

Micro- and nanolattices can achieve simultaneously both lightweight and ultra-high strength due to a combination of resilient architecture and enhanced mechanical properties of small-scale unit constituents. However, understanding the fundamental deformation mechanism for these novel materials remains intriguing due to the intricate interplay of various geometric characteristics and intrinsic microscopic defects. Here, we investigate the fundamental mechanism of plastic deformation in terms of dynamic evolution of defects and corresponding mechanical responses in aluminum nanolattices using a mesoscale defect dynamics model which couples three-dimensional dislocation dynamics and finite element method. Our concurrently coupled model could capture detailed dislocation motion under complex loading conditions and predict the plastic flow stress of the nanolattices. We demonstrate that the size of individual constituent beam plays a critical role in the properties of nanolattices through small-scale strengthening, showing the strength of the nanolattices increases with decreasing beam size with the scaling law of σ∝db−0.89. As a result, the scaling law of plastic yielding with material density drastically increases from the continuum prediction. In addition, our modeling could allow us to study the geometric effect with various nanolattices. These findings establish a foundation for the fundamental understanding of the governing mechanism of plastic deformation, allowing access to a new regime in designing optimal structures using nanolattices.