Degree Of Plastic Deformation Research Articles

Effect of Force and Heat Coupling on Machined Surface Integrity and Fatigue Performance of Superalloy GH4169 Specimens

GH4169 is one of the key materials used to manufacture high-temperature load-bearing parts for aero-engines, and the surface integrity of these parts in service conditions significantly affects their high-temperature fatigue performance. Under a coupling effect of high temperature and alternating load, the evolution process of the machined surface integrity index of superalloy GH4169 specimens was studied, and fatigue performance tests at 20 °C, 450 °C, and 650 °C were carried out to analyze the primary factors affecting the high-temperature fatigue performance of specimens. The results indicated that the surface roughness of specimens remained essentially unchanged. However, the value of surface residual stress decreased significantly, with a release of more than 60% at the highest temperature. At 650 °C, the surface microhardness increased, while the degree of surface plastic deformation decreased under alternating loads. Simultaneously, when the surface roughness was less than Ra 0.4 μm, surface microhardness was the main factor affecting the high-temperature fatigue performance of specimens. The influence of surface microhardness on low-cycle fatigue performance was not consistent with that on high-cycle fatigue performance. The latter increased monotonically, whereas the former initially increased and then decreased with increasing surface microhardness.

Influence of hot plastic deformation on properties of the carbon steel

Influence of hot plastic deformation on properties of the carbon steel

Role of nitrogen and helium gases on microstructure and anisotropic mechanical properties of cold-sprayed scalmalloy deposits

Aluminum alloys (Al) produced by fusion-based additive manufacturing techniques exhibit limited strength due to undesirable grain growth, porosity, and thermal gradient. To address these limitations, Scalmalloy (Al–Mg4.6-Sc0.72-Zr0.3 wt%) deposits of 5 mm thickness using helium and nitrogen gases were manufactured using a solid-state cold spray (CS) deposition. The microstructure of these deposits revealed a bimodal distribution of coarse and fine grains in the splat interior and jetting region, respectively, characterized by a higher degree of plastic deformation in the He-deposit. These bimodal grains resulted in a nanohardness of 1.2 GPa in the jetting region, 20% higher than that in the interior. The cumulative effect of these microstructural features resulted in a microhardness of 149 HV in the He-deposit, 1.1 times compared to that in the N2-deposit. The increased hardness is translated to a yield strength of 383 MPa and ultimate strength of 487 MPa in the He-deposit, 1.17 and 1.08 times of N2-deposit, respectively, estimated by Profilometry-based indentation plastometry (PIP). Across the hierarchical layers, profilometry-based indentation plastometry captured a consistent pile-up difference of ∼2 μm in the He-deposit and ∼3 μm in the N2-deposit on the plane perpendicular to build plane, a manifestation of in-plane anisotropy. This study advances the microstructural understanding and its relationship with observed mechanical properties, deformation behavior, and anisotropic response in high-strength Scalmalloy CS deposits.

Dilation and energy evolution mechanisms of sandstone under true-triaxial mining unloading conditions

The study of sandstone dilation characteristics under actual mining and excavation conditions promotes the safe and efficient development of underground engineering. Accordingly, this study employs true-triaxial testing to reveal the influence of intermediate principal stress and unloading action in the minimum principal stress directions on rock dilation. In the stress–strain analysis, with increasing intermediate principal stress, the maximum compression of the sandstone volume in the loading and unloading tests increases, while the onset of dilation is delayed under loading conditions and initially delayed and then accelerated under unloading conditions. The energy storage limit of sandstone under the unloading test tends to decrease with increasing intermediate principal stress, contrary to the results of the loading test, and the characteristic point at which the percentage of dissipative energy is greater than that of elastic energy occurs earlier. The energy of sandstone in the unloading test in the intermediate principal stress direction was smaller than that in the minimum principal stress direction, while the loading test showed the opposite trend. Combining these two analyses can elucidate the restraining effect and tensile stress effect of the intermediate principal stress, as well as the weakening and strengthening effects of the unloading action on the two effects. By further combining the average elastic energy and dissipative energy conversion rate under different test conditions, the weakening effect was manifested by shortening the compressive deformation course, and the strengthening effect was manifested by developing the degree of plastic expansion deformation. This study provides important guidance for deep mining projects.

Improvement in Fatigue Strength of Chromium–Nickel Austenitic Stainless Steels via Diamond Burnishing and Subsequent Low-Temperature Gas Nitriding

Chromium–nickel austenitic stainless steels are widely used due to their high corrosion resistance, good weldability and deformability. To some extent, their application is limited by their mechanical characteristics. As a result of their austenitic structure, increasing the static and dynamic strength of the components can be achieved by surface cold work. Due to the tendency of these steels to undergo intercrystalline corrosion, another approach to improving their mechanical characteristics is the use of low-temperature thermo-chemical diffusion processes. This article proposes a new combined process based on sequentially applied diamond burnishing (DB) and low-temperature gas nitriding (LTGN) to optimally improve the fatigue strength of 304 steel. The essence of the proposed approach is to combine the advantages of the two processes (DB and LTGN) to create a zone of residual compressive stresses in the surface and subsurface layers—the enormous surface residual stresses (axial and hoop) introduced by LTGN, with the significant depth of the compressive zone characteristic of static surface cold working processes. DB (both smoothing and single-pass hardening), in combination with LTGN, achieves a fatigue limit of 600 MPa, an improvement of 36.4% compared to untreated specimens. Individually, smoothing DB, single-pass DB and LTGN achieve 540 MPa, 580 MPa and 580 MPa, respectively. It was found that as the degree of plastic deformation of the surface layer introduced by DB increases, the content of the S-phase in the nitrogen-rich layer formed by LTGN decreases, with a resultant increased content of the ε-phase and a new (also hard) phase: stabilized nitrogen-bearing martensite.

Influence of microstructure on thermal fatigue effect of W-PFM with laminated structure

The response of tungsten (W) to thermal shock loading, as the best candidate for Plasma-Facing Materials, is an important issue in the research of future fusion devices. Under thermal loading, thermal irradiation damage, including brittle cracking and fatigue cracking, occurs on the surface of W-PFM. In this paper, a new scheme to suppress the thermal irradiation damage of W-PFM, i.e., the laminated structure W-PFM scheme, is proposed. Thermal fatigue experiments were conducted on laminated structures W composed of W foils with different thicknesses and heat treatment processes using an electron beam device. The samples were subjected to thermal pulses with a power density of 48 MW/m2 for 5000 cycles. The results indicate that the crack damage on the surface of the laminated structure W decreased with the decrease of the thickness of W foils under the same heat treatment conditions. The main cracks produced on the surface of laminated structure W after cyclic thermal loading were all approximately parallel to the foil thickness direction. The surface of W foils with smaller thicknesses has only main cracks, while the surface of W foils with larger thicknesses develops crack networks in addition to the main cracks, and the width of the main cracks is larger. For the same thickness, the laminated structure W in the rolled state has the weakest degree of surface plastic deformation. Scanning electron microscope images of the thermal damage area were finally selected, and the thermal fatigue crack damage on the surface was quantitatively analyzed using computer image processing software and analysis software. It was found that the de-stressed state W had the smallest crack area and the smallest number of cracks for the same thickness, indicating that the de-stressed state W had the strongest resistance to irradiation damage. The experimental results also show that, in addition to the effect of microstructure, both the uniaxial stress state and the crack-blocking mechanism of the laminated structured W-PFM contribute to the improvement of its thermal fatigue performance.

Grain-level mechanism of plastic deformation in harmonic structure materials revealed by high resolution X-ray diffraction

Materials with heterogeneous microstructures have been reported to have an attractive combination of strength and ductility. This is attributed to synergistic strengthening effects from the difference in strength of fine- and coarse-grained regions. Understanding the interaction of the regions is crucial for further optimization of the microstructures. In this work, we fabricated nickel of harmonic structure (HS) and a reference with homogenous coarse grains. The HS constitutes of an interconnected fine-grained network that surrounds regions of coarse grains. The interplay of the regions was studied by monitoring Bragg reflections from individual grains in situ during tensile deformation until approximately 2 % strain through synchrotron X-ray diffraction. The technique allows grain-level assessment of the degree of plastic deformation. Two grains were followed in the reference and two small grains (fine-grained region) and two large grains (coarse-grained region) in the HS. Three deformation regimes were identified: elastic deformation, onset of plastic deformation and significant plastic deformation. Our results reveal that the large grains in the harmonic structure onset plastic deformation during the macroscopic elastic stage. With increasing applied stress, the small grains yield plastically also and once a large fraction of the fine-grained network deforms plastically the large grains undergo significant plastic deformation. Notably, the onset of significant plastic deformation of large grains in the HS occurs at approximately 100 MPa higher applied stress than in the grains in the reference. This shows that fine grains constrain the large grains from deforming plastically in the HS.

CORROSION RESISTANCE OF COLD-ROLLED AISI 301 STAINLESS STEEL

: The performed investigations concerned on the effect of cold rolling on the corrosion behavior and microstructure of austenitic AISI 301 stainless steel. Samples of steel strip were cold-rolled within the degree of deformation 30%, 50% and 80%. The corrosion resistance test was examined using gravimetric and potentiodynamic method. Corrosion tests were conducted in acidic and alkaline corrosive environments. A light microscope and a scanning electron microscope were used to observe the surface morphology of the samples after corrosion testing. Corrosion tests by gravimetric method showed that investigated steel is not resistant to corrosion in 0.5N H2SO4 solution, while no significant weight loss was observed in artificial seawater solution (0.5N NaCl). Based on potentiodynamic tests carried out in 0.5N NaCl solution, it was found that the pitting corrosion resistance of the tested cold-rolled steel AISI 301 decreases with an increase in the degree of plastic deformation in the range of 30% to 80%. However, a decrease in the corrosion potential and an increase in the current density were observed on the polarisation curves. The propensity of the steel to initiation and propagation pitting was found to increase both with increasing degree of deformation and the associated increase in the volume proportion of martensite- in the material structure. The occurring of martensite- ’ in the investigated steel was confirmed by X-ray methods.

Strengthening Mechanisms of Rail Steel under Compression

The evolution of the structure–phase states and the dislocation substructure of rail steel under uniaxial compression to the degree of 50% was studied by transmission electron microscopy. The obtained data formed the basis for a quantitative analysis of the mechanisms of rail steel strengthening at degrees of deformation by compressions of 15, 30, and 50%. Contributions to the strengthening caused by the friction of the matrix lattice, dislocation substructure, presence of carbide particles, internal stress fields, solid solution and substructural strengthening, and pearlite component of the steel structure were estimated. Using the adaptivity principle, which assumes the independent action of each of the strengthening mechanisms, the dependence of the rail steel strength on the degree of plastic deformation by compression was estimated. A comparative analysis of the stress–strain curves σ(ε) obtained experimentally and calculated theoretically was performed.

Crack bifurcation behavior of coarse-grained copper under cyclic torsion combined with axial static loading

Because the growth behaviors of fatigue cracks are crucial for the safe assessment of structural components, the crack propagation behaviors of coarse-grained copper (CG Cu) subjected to cyclic torsion combined with different axial static stresses were studied. The crack bifurcation behavior is related to the strain amplitude applied. When the strain amplitude is lower, both the type and the magnitude of axial stress have no significant effect on the direction in which the primary crack branches, which is mainly determined by the position of the maximum normal plane. However, when the strain amplitude is higher, the bifurcated crack deviates visibly from the maximum normal plane, which can be attributed to the high degree of plastic deformation and microcracks caused by slip bands along longitudinal direction.

Влияние внутренних напряжений на интенсивность коррозионных процессов конструкционной стали

Introduction. The behavior of metal in a corrosive environment can be ambiguous, which is due to the peculiarities of the corrosion process. Both external and internal factors influence the corrosion process. External factors are determined by temperature, humidity, type of corrosive medium, etc., while internal factors depend on the parameters of the system (material): the presence of inclusions, phase composition, structure, and the magnitude of internal residual stresses. Internal factors ambiguously affect the behavior of the material in a certain aggressive medium, which ultimately affects the time of corrosion damage of the material and, as a consequence, the time of operation of objects made of this material. Therefore, differentiation of the influence of various internal factors on the rate of corrosion process in an aggressive environment is a priority area of research. The purpose of the present work is to consider the influence of the magnitude of internal residual stresses on the rate of corrosion process in an aggressive medium — 5% sulfuric acid solution. The object of research conducted in the work is sheet rolled steel St3 as received after different magnitude of plastic deformation, from which the specimens under study were made. The methods of investigation: microstructural study of deformed specimens was carried out on optical microscope Olympus GX53; software SIAMS 800 was used to compare the structure of the obtained material with the atlas of microstructures, determine the score of grain structure, determine the anisotropy of the structure after deformation of the material; X-ray diffractometer DRON-7 was used to register diffraction patterns and determine internal stresses; laboratory scales SHIMADZU UW620h was used to measure the mass of the specimens under study; tensile strength of the material’s specimens was measured. Results and Discussion. The obtained results show that the plastic deformation of the material in the rolling direction has an ambiguous effect on the structure anisotropy. When the degree of plastic deformation increases, there is an ambiguous change in the grain anisotropy value, which is associated with the internal effects of the processes occurring in the material structure during plastic deformation, such as: sliding of the crystal lattice in the {111} <110> directions; the occurrence of reverse residual internal stresses due to the presence of inclusions in the steel structure. However, the degree of plastic deformation correlates quite well with the magnitude of internal residual stresses. The increase in the magnitude of internal residual stresses leads to an increase in the corrosion rate of structural steel St3 in 5 % hydrochloric acid solution. The obtained dependence is described by a linear equation with a high coefficient of determination, which indicates that there is a strong relationship between the magnitude of internal residual stresses and the rate of corrosion of the material. At the same time, the coefficient of influence of internal stresses on the corrosion rate is equal to 0.72, which additionally proves the existence of interrelation between the considered parameters.

The Influence of the Deposition Speed during Friction Screw Extrusion Additive Manufacturing of AA6060

Solid-state additive manufacturing may solve critical issues typically arising during fusion-based additive manufacturing of high-strength aluminium alloys. In this work, the recently introduced Friction Screw Extrusion Additive Manufacturing (FSEAM) process was employed to manufacture wall-like rectangular builds of AA6060 T6 deposited with deposition speeds from 300 mm/min to 500 mm/min. All builds were manufactured at a tool rotation rate of 400 rpm with 1 mm layer thickness. The volumetric supply rates were adjusted to maintain constant build width. Solid builds were formed without major defects over the full range of deposition speeds. The process generated sufficient normal force and heat at all deposition speeds which resulted in manufacturing of defect free builds. The resulting average grain size was consistently below 5 micrometer throughout all builds independent of deposition speed or location through the height. Microhardness measurements revealed a decrease in hardness from a feedstock value of 80 HV to around 50 HV in all manufactured builds. Tensile tests in the building direction showed consistent results for all the samples as a result of defect-free parts, demonstrating a tensile strength of approximately 150 MPa, yield strength of 100 MPa, and uniform elongation of 12-15%. The fracture surfaces revealed large amounts of dimples at all deposition speeds in line with the high degree of plastic deformation preceding fracture observed from the tensile tests. The obtained results indicated that FSEAM is a promising process for solid-state additive manufacturing of aluminium alloys.

Effect of processing temperature and polymer types on mechanical properties of bamboo fiber composites

Bamboo fiber was extracted after alkaline treatment, and the mechanical properties of fibers and polymer composites were measured. The results showed that the strength of bamboo fiber was higher when the diameter was smaller. Smaller diameter bamboo fibers were dense, while larger diameter ones were composed of vascular bundles, which contained inside voids and outside parts having insufficient lignification. Tensile tests were conducted on bamboo fibers after heating at constant temperatures, and a significant decrease in mechanical properties was observed at heating temperatures above 250 °C. Bamboo fibers were compounded with PE, PA12, ABS, PA6, and biobased PC (Durabio), and injection-molded to prepare the composite specimens for flexural testing. The composite of polyethylene with 30 wt% bamboo exhibited considerably high flexural modulus compared to pure PE. Nevertheless, a large plastic deformation, which was equivalent to that of pure PE was observed. In other polymer composites, those flexural moduli increased, and degree of plastic deformation decreased dramatically, leading to brittleness. For PA6, which was molded above 250 °C, the increment in flexural modulus by fibers was less than the other composites due to the thermal decomposition of the fibers.

Strengthening mechanisms of rail steel under compression.

The evolution of structural-phase states and dislocation substructure of rail steel under uniaxial compression to the degree of 50% was studied by transmission electron microscopy. The obtained data formed the basis for a quantitative analysis of the mechanisms of rail steel strengthening at degrees of deformation by compression 15, 30, 50%. Contributions to the strengthening caused by the friction of matrix lattice, dislocation substructure, presence of carbide particles, internal stress fields, solid solution and substructural strengthening, pearlite component of the steel structure are estimated. Using the adaptivity principle, which assumes the independent action of each of the strengthening mechanisms, the dependence of rail steel strength on the degree of plastic deformation by compression is estimated. A comparative analysis of the stress-strain curves σ(ε) obtained experimentally and calculated theoretically is performed

Experimental research on milling of TC11 by scCO2-MQL and edge morphology

Titanium alloy is widely used in typical aerospace structural parts because of its excellent mechanical properties and corrosion resistance. However, the serious problem of tool wear in the machining process of titanium alloy often leads to the decline of machining quality. In this article, scCO2 MQL cutting experiment and dry cutting experiment of TC11 are carried out. The machined surface morphology, plastic deformation, residual stress and tool wear were analyzed. The results show that scCO2 MQL can effectively reduce the surface defects on the machined surface. The increase of cutting edge structure and blunt radius of the composite increases the plastic deformation degree of the material, as well as the residual stress and work hardening degree. The scCO2 MQL can effectively improve the cutting contact area and reduce tool joint wear.

Tailoring polyamide 6 to exhibit super‐tough behavior and high thermomechanical stability: The role of AES and EPDM‐MA hybridization

AbstractHigh‐performance blends based on polyamide 6 (PA6) were prepared using a hybrid mixture of acrylonitrile/EPDM/styrene (AES) and maleic anhydride grafted ethylene–propylene–diene (EPDM‐MA). Samples were processed in a twin‐screw extruder and injection molded. The torque curves of the PA6/AES/EPDM‐MA blends shifted to higher torque values with added EPDM‐MA, suggesting a chemical interaction between the components. The melt flow index (MFI) results for the PA6/AES/EPDM‐MA blends confirmed the intensification of the flow resistance. Intense infrared absorption peaks for NH and CO indicated that the amine groups of PA6 reacted with the maleic anhydride in EPDM‐MA. The 60/25/15 wt% PA6/AES/EPDM‐MA blend showed an impact strength over 800 J/m, heat deflection temperature (HDT) of 62.3°C, elongation at break of 115%, and contact angle of 59.1°, corresponding to increases of 1718%, 10.5%, 297%, and 10%, respectively, compared to neat PA6. When examined by scanning electron microscopy, the morphology showed a fracture surface with a high degree of plastic deformation and the formation of elastic microfibrils, contributing to the super toughening of the PA6/AES/EPDM‐MA (15%) system. These results indicate the technological potential of the PA6/AES/EPDM‐MA (15 wt%) blends for application in industrial sectors that require super‐tough plastics.

Shaking table test and cumulative deformation evaluation analysis of a tunnel across the hauling sliding surface

AbstractTo explore the cumulative deformation effect of the dynamic response of a tunnel crossing the hauling sliding surface under earthquakes, the shaking table test was conducted in this study. Combined with the numerical calculations, this study proposed magnification of the Arias intensity (MIa) to characterize the overall local deformation damage of the tunnel lining in terms of the deformation characteristics, frequency domain, and energy. Using the time‐domain analysis method, the plastic effect coefficient (PEC) was proposed to characterize the degree of plastic deformation, and the applicability of the seismic cumulative failure effect (SCFE) was discussed. The results show that the low‐frequency component (f1 and f2 ≤ 10 Hz) and the high‐frequency component (f3 and f4 > 10 Hz) acceleration mainly cause global and local deformation of the tunnel lining. The local deformation caused by the high‐frequency wave has an important effect on the seismic damage of the lining. The physical meaning of PEC is more clearly defined than that of the residual strain, and the SCFE of the tunnel lining can also be defined. The SCFE of the tunnel lining includes the elastic deformation effect stage (<0.15g), the elastic–plastic deformation effect stage (0.15g–0.30g), and the plastic deformation effect stage (0.30g–0.40g). This study can provide valuable theoretical and technical support for the construction of traffic tunnels in high‐intensity earthquake areas.

Raptorial appendages of the Cambrian apex predator Anomalocaris canadensis are built for soft prey and speed.

The stem-group euarthropod Anomalocaris canadensis is one of the largest Cambrian animals and is often considered the quintessential apex predator of its time. This radiodont is commonly interpreted as a demersal hunter, responsible for inflicting injuries seen in benthic trilobites. However, controversy surrounds the ability of A. canadensis to use its spinose frontal appendages to masticate or even manipulate biomineralized prey. Here, we apply a new integrative computational approach, combining three-dimensional digital modelling, kinematics, finite-element analysis (FEA) and computational fluid dynamics (CFD) to rigorously analyse an A. canadensis feeding appendage and test its morphofunctional limits. These models corroborate a raptorial function, but expose inconsistencies with a capacity for durophagy. In particular, FEA results show that certain parts of the appendage would have experienced high degrees of plastic deformation, especially at the endites, the points of impact with prey. The CFD results demonstrate that outstretched appendages produced low drag and hence represented the optimal orientation for speed, permitting acceleration bursts to capture prey. These data, when combined with evidence regarding the functional morphology of its oral cone, eyes, body flaps and tail fan, suggest that A. canadensis was an agile nektonic predator that fed on soft-bodied animals swimming in a well-lit water column above the benthos. The lifestyle of A. canadensis and that of other radiodonts, including plausible durophages, suggests that niche partitioning across this clade influenced the dynamics of Cambrian food webs, impacting on a diverse array of organisms at different sizes, tiers and trophic levels.

Nano-cutting deformation characteristics and atomic-scale behavior of two-phase γ/γ′ nickel-based single crystal superalloy

The γ/γ′ interface has an important influence on the nanoscale deformation of nickel-based single crystal superalloy. In this paper, nano-cutting simulations of nickel-based single crystal superalloy are performed by molecular dynamics methods, and the mechanical properties, atomic displacements, dislocation evolution, temperature, surface quality and Al atom precipitation behavior of the workpiece are analyzed in depth. We found that: the γ/γ′ interface will hinder the force conduction and dislocation development, resulting in fluctuation of processing force and dislocation density. In addition, the special two-phase structure will affect the deformation of the material, and the dislocation motion will stay in the γ phase for a long time and occur dislocation accumulation and work hardening, meanwhile, there are more displacement atoms in the γ phase than in the γ′ phase, and the degree of plastic deformation in the γ phase will be more drastic. It is also found that there is always a difference in the temperature distribution of the two phases of the material, and the uneven cutting surface always appears at the junction of the two phases, and the Al atoms on the subsurface will precipitate and form an Al film covering the surface after being influenced by the cutting temperature.

Effects of K2CO3 addition on the physicochemical properties of goethite composite pellets with different basicities (CaO/SiO2)

In this study, the effects of K2CO3 addition (0, 1, 2 wt%) on the physicochemical properties (moisture content, liquid saturation, plastic deformation degree, drop number, compressive strength) of green and (crystalline phase, fraction of melt phase, morphology, compressive strength and reduction behavior) of sintered composite pellets with varying basicities (CaO/SiO2 = 0.04, 0.40, 0.83, 1.24) were examined. The moisture content of cured green pellet with higher K2CO3 addition was greater at the same basicity. The corresponding results had a positive effect on the development of capillary state, which enhance the drop number and compressive strength up to approximately 14, 28.40 N/Pellet respectively above moisture content of 12.41 wt%. However, it was also confirmed that excessive moisture content (above 13.22 wt%) induced over liquid saturation and has negative effects on physical properties. The magnetite phase predominantly observed with increasing K2CO3 addition at fixed basicity of 0.40–1.24. Intraparticle porosity (pore size = 6.4 nm to 5 μm) decreased with higher K2CO3 addition and showed below 5% at 0.40–1.24 basicity. Interparticle porosity (pore size = 5–1100 μm) showed various behavior with K2CO3 addition at a basicity 0.04–0.40 but increased up to approximately 30% at a basicity 0.83–1.24. Compressive strength of sintered pellet tends to have negative effect on porosity. However, reduction behaviors have positive effects on higher fluxed sintered pellet due to advantageous reduction condition by impurities (alkali and alkaline earth metal cations). Obtained results help elucidate the physicochemical properties of composite pellet-containing alkali metal oxides with varying basicities.