Plastic Flow Phenomena Research Articles

THE EFFECT OF ANNEALING REGIME ON THE PRECIPITATION OF FeCoNiAl0.75Nb0.25 HIGH ENTROPY ALLOY

This paper investigates the effect of the annealing regime on the precipitation of FeCoNiAl0.75Nb0.25 high entropy alloy. The as-cast microstructure consists of coarse dendritic phases that are replaced by equiaxed morphology, and the distribution of the interdendritic phase becomes regularly better with increasing time and annealing temperature up to 825ºC. The precipitated process begins at 700ºC for 8 hours, shortening to 4 hours when the annealing temperature increases. The size of this phase is only a few μm. The fraction of the precipitated phase increases and the size of the dendritic phase is reduced as the annealing temperature is up to 825ºC, while this size rises in the 925ºC/16 hours regime. The microstructure is coarse, and the precipitated phase gradually disappears when the annealing is at 1000ºC. The HV3 hardness of the alloy increases with annealing time when the temperature is lower than 825ºC and reaches the highest value of ~ 614 kg/mm2 at 600ºC/ 24 hours; this value begins to decrease for the 925ºC/16 hours regime. Meanwhile, the hardness gradually decreases with increasing annealing time at 1000ºC. It can be expected due to the rapid coarsening of the dendritic phase, the decrease in the proportion of the precipitated phase in the alloy, and the appearance of plastic flow phenomena at grain boundaries.

Grinding subsurface damage mechanism of nickel-based single crystal superalloy based on stress-strain

This study investigates the microstructure damage mechanism of the difficult-to-machine material nickel-base single crystal superalloy DD5 by analyzing the working condition load and crystal deformation. The complexity of the macroscopic and microscopic deformation phenomena during the machining process makes it challenging to study the damage mechanism of the workpiece. Hence, crystal kinematics equation is established using true stress-true strain theory, and the internal force balance and constitutive model of the crystal are analyzed. The proposed theory is applied to finite element processing and experimental analysis of the workpiece, and the subsurface deformation behavior is studied from a mechanistic perspective.The stress model is employed to explore the plastic flow phenomenon of the material during the machining process, and the influence of stress and shear force on the subsurface of the workpiece is discussed. The theoretical analysis of crystal deformation, based on the principles of materials science and mechanics, uncovers the relationship between subsurface deformation curvature and stress. The study delves into the effects of the grinding process on subsurface damage and deformation by analyzing the phenomena of plastic flow, plastic slip, and plastic winding in the subsurface microstructure. The results indicate that at grinding speed vs = 25 m/s and grinding depth ap = 60 μm, the damage to the subsurface deformation layer is minimal. The grinding process considerably impacts the stress exerted on the workpiece, with an amplitude ranging from 1.255 × 103 to 1.286 × 103. Conversely, the strain on the workpiece is relatively less affected by the grinding process, exhibiting an amplitude of 2.366–3.568. Moreover, when the normal stress and shear force of the abrasive particles form 45° angle, the subsurface deformation of DD5 manifests a distinct slip distortion at an approximate 45° curvature.

Study on the influence of relative vibration between tool and workpiece on plastic side flow

The mutual vibration between the tool and the workpiece not only affects the surface roughness value, but also the vibration energy has a very important influence on the mechanical properties and plastic deformation of the material. Based on the interaction mechanism between the tool and the workpiece surface, the three-dimensional plastic deformation in the third deformation zone is studied. The analytical relationship among vibration and plastic side flow is explored, and the method of restraining plastic side flow is put forward. The change mechanism of flow velocity of materials under the influence of vibration is analyzed. Through analysis, vibration makes the material soften, which leads to more obvious plastic side flow phenomenon. Reducing vibration can effectively inhibit plastic side flow phenomenon. Finally, the influence of relative vibration between tool and workpiece on the formation process of surface cracks of workpiece is studied, and the number of cracks per unit area can be well reduced by reducing the vibration. The research content of this paper can provide theoretical basis for improving the surface quality of ultra-precision turning of spherical/aspherical surfaces, and is of great significance to the processing of high-quality spherical/aspherical mirrors.

Weldability assessment of Al-SS dissimilar joints produced by ultrasonic spot welding route

Multiple materials are often used in the construction of modern vehicles to make them lighter and more affordable. Steel and aluminium alloys are the great building materials for these composite structures. Ultrasonic metal welding is an efficient solid-state joining technology that requires less energy and time than conventional welding methods while also eliminating the potential problems of distortion and shrinkage. In this research, stainless steel (UNS S30400) and aluminium (AA1100) sheets are ultrasonically welded with various surface treatments, including normally cleaned, electrolytically polished, and lubricated surfaces. The studies are carried out at various weld energies while maintaining constant vibrational amplitude and weld pressure parameters. The maximum lap shear and T-peel strength values are obtained as 621 N and 230 N at 2550 J of weld energy for the lubricated surface condition. According to the temperature profile, when weld energy grows, the weld interface temperature rises as well, reaching a maximum of 460 ˚C. It offers the perfect setting for the plastic flow phenomena to build strong bonds. The effects of natural aging and softening on the weld zone at each joint surface are studied through the microhardness test. Scanning electron microscopy and energy-dispersive X-ray spectroscopy investigations are also used to analyse fracture surfaces with various interface morphologies and characteristics.

Size Polydispersity Tunes Slip Avalanches of Granular Gouge

AbstractGranular materials have frequently been used as representations of natural fault gouges. Although they can reproduce proper avalanche behaviors, the universality of the scaling exponent of avalanche size remains debatable. As a core issue in both amorphous plasticity and geophysics, avalanche universality may help reconcile the avalanche behaviors of earthquake and granular materials into the same universality class. We examine numerically the signatures of stress avalanches emerging from quasi‐static shear of granular materials with different size polydispersity. A persistent serrated plastic flow phenomenon is observed in our models with varying polydispersity. The stress drop is well defined by a truncated power law distribution P(s) ~ s−τexp(−s/smax). The exponent τ and cutoff stress drop smax show a clear dependence on polydispersity, which reflects a tuned criticality. We further calculate the effective temperature from the statistics of energy fluctuations. The effective temperature volatility can be used to explain the tuned critical behaviors of granular gouge.

On the Cutting of Metals: A Mechanics Viewpoint

AbstractThe mechanics of large-strain deformation in cutting of metals is discussed, primarily from viewpoint of recent developments in in situ analysis of plastic flow and microstructure characterization. It is shown that a broad range of deformation parameters can be accessed in chip formation—strains of 1–10, strain rates of 10–105/s, and temperatures up to 0.7Tm—and controlled. This range is far wider than achievable by any other single-stage, severe plastic deformation (SPD) process. The resulting extreme deformation conditions produce a rich variety of microstructures in the chip. Four principal types of chip formation—continuous, shear-localized, segmented, and mushroom-type—as elucidated first by Nakayama (1974, “The Formation of ‘Saw-Toothed Chip’ in Metal Cutting,” Proceedings of International Conference on Production Engineering, Tokyo, pp. 572–577) are utilized to emphasize the diverse plastic flow phenomena, especially unsteady deformation modes that prevail in cutting. These chip types are intimately connected with the underlying flow, each arising from a distinct mode and triggered by an instability phenomenon. The role of plastic flow instabilities such as shear banding, buckling, and fracture in mediating unsteady flow modes is expounded, along with consequences of the flow modes and chip types for the cutting. Sinuous flow is shown to be the reason why gummy (highly strain-hardening) metals, although relatively soft, are so difficult to cut. Synthesizing the various observations, a hypothesis is put forth that it is the stability of flow modes that determines the mechanics of cutting. This leads to a flow-stability phase diagram that could provide a framework for predicting chip types and process attributes.

Acoustic induced antifriction and its effect on thermo-mechanical behavior in ultrasonic assisted friction stir welding

The developed ultrasonic assisted friction stir welding (UaFSW) process can reduce the welding load and improve the joint quality, but the interaction mechanism between the exerted ultrasonic vibration and the thermo-mechanical behavior induced by friction stir welding is not yet elucidated. In this study, the classical Norton friction model is modified with the acoustic stress work, and the effect of ultrasonic vibration on the contact state at the tool/workpiece interface is analyzed. The relative velocity between the tool and its adjacent contacting material is taken as one of the main influencing factors to calculate the interfacial friction shear stress. A non-uniform interfacial friction model is combined with the modified constitution equation. And a fully coupled model of UaFSW process is developed to analyze the ultrasonic field, interfacial contact state, heat generation, plastic material flow and heat transfer phenomena. It is found that ultrasound can effectively reduce the interfacial friction stress, and this antifriction effect is more obvious in the welding direction which coincides with ultrasonic vibration. The ultrasound exerted along the radial direction of tool in UaFSW process results in acoustic softening of base material and friction reduction at the tool/material interface. Both effects change the heat generation, material flow and temperature field in UaFSW. Thus, the torque and traverse force are lowered with the ultrasonic induced reduction of interfacial stress, and the high quality of welds are obtained with the improvement of material flow. The model is experimentally validated by comparison of predicted and measured tool torque, heat input and thermal cycles.

Sand erosion of solar glass: Specific energy uptake, total transmittance, and module efficiency

Surface roughness, RZ, normal transmittance, ΤN, total transmittance, ΤT, and photovoltaic (PV) module efficiency, ηS, were measured for commercial solar glass plates and PV test modules identically sandblasted with different loads of quartz sand (200–400 μm), impact inclination angles, and sand particle speed. Measured data are presented versus the specific energy uptake during sand blasting, E (J/m2). Cracks, adhering particles, and scratch-like textures probably caused by plastic flow phenomena could be observed after sand blasting. Their characteristic size was much smaller than that of sand particles. After blasting and subsequent cleaning, the glass surface was still covered with adhering glass particles. These particles, cracks, and scratch-like textures could not be removed by cleaning. For sand blasting with α = 30° inclination angle and E = 30 000 J/m2, normal transmittance, total transmittance, and relative module efficiency decreased by 29%, 2% and ∽2%, respectively. This finding indicates that diffusive transmission of light substantially contributes to PV module efficiency and that the module efficiency decrease caused by sand erosion can be better estimated from total than by normal transmittance measurements.

Surface Damage Characteristics of BK7 Glass in Ultrasonic Vibration Machining Based on Scratching Experiment

To further explore the material removal mechanism in ultrasonic vibration machining, a diamond Vickers indenter was used to carry out scratching experiment for BK7 glass specimen. The morphologies of scratches and removal mechanism of material were analysed under different conditions. The results showed that the damage mode of scratch was plastic deformation when the scratching depth was small enough, and no crack was observed. With increase of scratching depth, the intermittent and continuous scratches appeared in plastic removal area, and plastic flow phenomenon was obvious. With further increase of scratching depth, the median/radial cracks and lateral cracks were induced, and the material was removed by plastic flow and brittle-plastic mixed mode. When the indenter arrived at the brittle fracture removal area, cracks in scratched surface became denser, the lateral cracks extended from inside of material to workpiece surface, and the material was removed by brittle fracture.

Research Status of the Pendulum High-Speed Single Grain Test

This paper has designed the pendulum type in high speed of single grit cutting equipment, discussed the material process of deformation and failure mechanism. During the investigation, compared with the abrasive cutting export and cutting entry based on the MP tool coating, which is badly broken when the cutting depth increases gradually at the entrance, and is broken less when the cutting depth gradually decreases at the export. Researched the MP tool coating of Surface and subsurface damages by indentation and scratching, it has demonstrated that on one side of the groove has appeared the crack and with severe plastic flow phenomena by scratching, and by indentation the cracks of the groove is not produce on both sides and bottom, but at the bottom of the trench existing extrusion phenomenon.

Methods for identifying dynamic parameters of clip-on extensometer–specimen structure in tensile tests

This paper presents the dynamic analysis of clip-on extensometer–specimen structure subjected to uniaxial tensile tests. The dynamic behavior of such structure is influenced by vibrations that can be caused by external factors, such as vibrations carried by the tensile test machine, “cold-welding” effect (typically at ultra-low temperatures) or internal factors arising from the plastic instability of testing materials. The Portevin–Le Chatelier effect (PLC), discontinuous plastic flow phenomenon (DPF) or Lűders band propagation effect are the most prominent modes of plastic deformations, that are characterized by an oscillatory behavior (plastic instability). Both factors are included in our analysis.

Wear phenomena of grinding wheels with sol–gel alumina abrasive grains and glass–ceramic vitrified bond during internal cylindrical traverse grinding of 100Cr6 steel

This article presents the results from a traverse internal cylindrical grinding process conducted using grinding wheels with sol–gel alumina abrasive grains and varying volumes of glass–ceramic vitrified bond. The aim was to determine how changing the bond volume within the range of V b = 11.5–14.5 % influenced the wear phenomenon of the microcrystalline sintered corundum abrasive grains and the ceramic bond bridges with glass-crystalline structure. The paper presents grinding wheels with conic chamfer and the most important wear phenomena of the grinding wheel components occurring in the area of contact between the tool and the workpiece material. The work includes the methodology of the experimental tests on the traverse internal cylindrical grinding of bearing rings made from steel 100Cr6 (62 ± 2 HRC). A wide range of test results were analyzed, including machined surface roughness parameters (Ra, Rz, Sm, Δa), grinding power, grinding wheel volumetric wear V s , material removal V w , G-ratio, root-mean–square roundness deviation from mean circle (Δ, rms), grinding wheel edge wear, grinding wheel microtopography parameters (Sa, St, Sdr, Sds), and SEM images of the wear marks on the grinding wheel active surface. The dominant wear phenomena of the grinding wheels with conic chamfer and the influence of the bond volume share on its intensity were experimentally determined. The results show that the decrease in bond volume from V b = 14.5 to 11.5 % increases the grinding wheel life by twofold. This was due to a decrease in abrasive wear and plastic flow phenomena and to a greater fracture wear (mostly fatigue and thermal-fatigue). These events led to a periodic shedding of the oxide layer and the plastically deformed grain layer and also revealed the crystals’ sharp edges, located below the plastically deformed surface layer.

Research on Plastic Flow Behaviors for Hole Flanging Part of Aluminum Alloy with Large Complicated Profiles by Electromagnetic Forming

Hole flanging part of aluminum alloy with large complicated profiles by electromagnetic forming is a complex metal forming process coupling electromagnetic field and constructive field. Due to the effects of large complicated profiles, plastic flow behaviors during the forming process are different from traditional flanging forming. A finite element model for hole flanging part of aluminum alloy with large complicated profiles by electromagnetic forming is established based on loose coupling simulation method, and then plastic flow behaviors on condition of one layer flat coil, two layers flat coil and three layer flat coil are investigated, and subsequently plastic flow rules of flange parts under different pressures are revealed by experiments. The results are as follows: Large complicated profiles are completed closed to female die surfaces on condition of three layer flat coil, flange parts are put into female die and plastic flow phenomenon is more obvious; flange parts are grown to different modes under different pressures, and obvious wrinkling phenomenon for flange parts appear when pressures are less; hole flanging part of aluminum alloy with large complicated profiles more closed to female die surfaces is obtained by controls of reasonable pressures.

Plastic Flow Localization Viewed as an Auto-Wave Process Generated in Deforming Metals

The localized plastic flow auto-waves observed for the stages of easy glide and linear work hardening in a number of metals are considered. The propagation rates were determined experimentally for the auto-waves in question with the aid of focused-image holography. The dispersion relation of quadratic form derived for localized plastic flow auto-waves and the dependencies of phase and group rates on wave number are discussed. A detailed comparison of the quantitative characteristics of phase and group waves has revealed that the two types of wave observed for the stages of easy glide and linear work hardening are closely related. An invariant is introduced for localized plastic flow phenomena occurring on the micro- and macro-scale levels in the deforming solid.

A new model of localized plastic flow and failure of solids

The localized plastic flow auto-waves observed for the stages of easy glide and linear work hardening in a number of metals are considered. The propagation rates were determined experimentally for the auto-waves in question with the aid of focused-image holography. The dispersion relation of quadratic form derived for localized plastic flow auto-waves and the dependencies of phase and group rates on wave number are discussed. A detailed comparison of the quantitative characteristics of phase and group waves has revealed that the two types of wave are closely related. An invariant is introduced for localized plastic flow phenomena occurring on the micro- and macro-scale levels in the deforming solid

Evidence for the existence of localized plastic flow au-to-waves generated in deforming metals

The localized plastic flow auto-waves observed for the stages of easy glide and linear work hardening in a number of metals are considered. The propagation rates were determined expe- rimentally for the auto-waves in question with the aid of focused-image holography. The dispersion relation of quadratic form derived for localized plastic flow auto-waves and the dependencies of phase and group rates on wave number are discussed. A detailed comparison of the quantitative characteristics of phase and group waves has revealed that the two types of wave are closely related. An invariant is introduced for localized plastic flow phenomena occurring on the micro-and macro-scale levels in the deforming solid.

Evidence of plastic flow and recrystallization phenomena in swift (∼100 MeV) Si 7+ ion irradiated silicon

Surface modifications caused by a swift heavy ion irradiation on a crystalline p-type silicon crystal have been reported. ∼100 MeV Si 7+ ions from a 15UD Pelletron source has been employed with varying fluence of 10 12 and 10 13 ions cm −2. Atomic force microscopy has been extensively used to study these surface modifications. Significant observation includes the evidence for a plastic flow upon irradiation. Attempts have been made to explain the results on the basis of radiation-induced amorphization followed by recrystallization. The observation confirms the occurrence of these types of effects in such irradiations and is in line with the models based on thermal spike approach.

Numerical study of vortex pinning and plastic vortex flow in disordered Josephson junction arrays

Pinning and plastic flow phenomena of superconducting phases of current-driven Josephson junction arrays (JJAs) in magnetic fields are studied numerically. Using the resistively shunted junction (RSJ) model of ladder-type JJAs with positional disorder, we calculate the time evolution of the phases. We focus on two characteristic threshold currents. One is the threshold current between pinned and plastic flow regimes, and the other is that between plastic flow and elastic flow regimes. Even in a strong disorder limit, it is found that the two threshold currents show weak pinning behavior against the change in the strength of a junction critical current. We discuss pinning and plastic flow phenomena on the basis of the scaling theory of pinning of density waves, emphasizing a close relationship between the RSJ and the random field XY models.

Plastic deformation modelled as a self-excited wave process at the meso- and macro-level

A self-excited wave model is developed to describe plastic flow phenomena in crystalline solids. Experimental observations suggest that by plastic flow in single crystals and polycrystalline materials, different underlying mechanisms are responsible for key features of strain localisation corresponding to different stages of the deformation curve. The major autowave (self-excited wave) types manifest themselves in plastically deforming materials. The self-excited wave model could explain plastic flow pattern behaviour corresponding to different physical mechanisms.

Modelling of heat transfer, plastic flow and microstructural evolution during shape rolling

The paper describes investigations on the development of an integrated model allowing for the prediction of heat transfer, plastic flow, and microstructure evolution during shape rolling. Finite element method was adopted to describe the heat transfer and plastic flow phenomena. Generalized plane strain method is applied to modelling the 3D problem using 2D finite element formulation. In consequence, significant savings of the computing time and required memory can be obtained. A computer program in FORTRAN 77 was written according to the developed mathematical model. Data on temperature, strain and strain rate relevant to the rail rolling process were computed and employed to model microstructure evolution in austenite.