Plastic Deformation Process Research Articles

Biomedical devices surface functionalization through superfinishing processes to improve tribocorrosion

Permanent prosthesis surface conditions play a key role on the implants overall mechanical performance. Furthermore, the increased number of arthroplasty surgery represents a reason for the necessity of higher quality standards for the biomedical devices. Employing and optimizing severe plastic deformation processes represents a way to obtain implants with higher performance, therefore this work aims, through the application of burnishing process, to combine innovative machining finishing operations coupled with environmentally friendly cooling lubricant techniques to improve the surface integrity and the tribocorrosion resistance of biomedical devices in order to increase their quality, durability and reliability. Another phenomenon taken into account is the tribological behavior that could generates an irreversible transformation of the materials and the release of particles and metal ions in toxic concentrations in the biological environment in which the devices are implanted. One of the most used materials for permanent prosthetic implants is the Ti6Al4V alloy but its tribological behavior is still challenging for the application. In this work Ti6Al4V bars have undergone machining with semi-finishing parameters and burnishing processes, then the effects of sole machining and its combination with burnishing on surface quality and specific wear rate (SWR) have been assessed with respect to as received surface conditions.

Combined severe plastic deformation processing of commercial purity titanium enables superior fatigue resistance for next generation implants

Commercial purity titanium (cp-Ti) is considered for replacing Ti64 as an implant material in various applications, due to the potential toxicity associated with the release of Al and V ions. However, the mechanical properties of cp-Ti, particularly fatigue resistance, are inadequate for this purpose. In this study, cp-Ti grade 4 rods were processed using a combination of equal channel angular pressing and rotary swaging (ECAP/RS). Tensile and fatigue tests were conducted, along with detailed microscopy and evaluation of corrosion resistance and biocompatibility. An average yield strength of 1383 MPa was obtained while maintaining moderate ductility of 10 %. This represents the highest strength ever recorded for cp-Ti, even exceeding that of Ti64. Additionally, fatigue endurance limit increased by 43 % up to 600 MPa, almost obtaining that of Ti64. Strengthening mechanisms were attributed to the ultrafine-grained (UFG) microstructure generated by ECAP/RS, along with strong crystallographic texture and formation of sub-grain structure. Furthermore, the corrosion resistance and biocompatibility of cp-Ti were largely unaffected, potentially easing regulatory transition in future medical devices. Thus, these results demonstrate high potential of combined ECAP/RS processing to manufacture UFG cp-Ti grade 4 materials that prospectively allow for the substitution of questionable alloys and downsizing of medical implants.

Interfacial characteristics of multi-material SS316L/IN718 fabricated by laser powder bed fusion and processed by high-pressure torsion

This study focuses on investigating the microstructure and mechanical properties across the interface of a multi-material, Austenitic Stainless Steel 316 L (SS316L) and Inconel 718 (IN718), fabricated using laser powder bed fusion (LPBF) additive manufacturing (AM) technique. Challenges such as distortion, porosity, and intermetallic formation are common in such structures. To address these challenges, high-pressure torsion (HPT), a severe plastic deformation (SPD) process, was employed to eliminate porosity and create a homogeneous microstructure. The samples underwent HPT with varying numbers of turns, namely quarter, half, one, five, and ten turns, at room temperature and under 6 GPa of pressure at a speed of 1 rpm. The process aimed to create ultrafine and nano-grains in the microstructure and reduce the defects. A comprehensive characterization approach was adopted to analyze the interface. The results showed reduced porosity, improved bonding, and enhanced material density through HPT. X-ray diffraction (XRD) analysis confirmed the retention of the austenitic face-centered cubic (FCC) phase in both materials. The dislocation density reached a saturation point of 1.85 × 1015 m−2, while the crystallite size decreased to 26 nm. Transmission electron microscopy (TEM) analysis provided insights into the microstructure, showing dislocation networks at lower torsional strain and homogenous nano-grains at higher torsional strain. Vickers microhardness and nanoindentation measurements demonstrated an increase in hardness with increasing torsional strain, with the peripheral region exhibiting rapid hardness saturation and the central region showing lower hardness due to reduced strain. Overall, this study provides valuable insights into the effects of HPT on multi-material SS316L/IN718, contributing to the understanding of their interfacial characteristics and enhanced utilization of multi-materials in various engineering applications.

Design, Finite Element Analysis and Optimization of Helical Angular Pressing (HAP) Method as a Novel SPD Technique

Severe Plastic Deformation (SPD) processes improve the mechanical properties of materials by obtaining Ultra Fine Grained (UFG) materials, orienting the grains and reforming the grains. Helical Angular Pressing (HAP) is a newly proposed Severe Plastic Deformation (SPD) method. In order to improve the efficiency of the HAP method, its die geometry should be optimized first. In this context, four parameters (helical diameter, helical pitch, helical height and channel radius) were determined for the die channel geometry, each with four levels according to the literature. Then, thanks to Taguchi L16 combinations, 16 Finite Element Analyses (FEA) were carried out using Deform 3D software instead of 256 simulations, and effective strain values and maximum pressing load values were obtained. Later on, using the SPSS 16 software, Taguchi optimization was carried out to obtain the optimum HAP die channel geometries by minimizing the press load and maximizing the effective strain values. Next, the Finite Element Analysis (FEA) was repeated with these determined optimum die channel parameters. Finally, the efficiency of this novel HAP method was compared with conventional Equal Channel Angular Pressing (ECAP) and Twist Extrusion (TE) methods. As a result, HAP method provides effective strain values equivalent to 10 number of passes after processing with ECAP. And it is approximately 4 times higher than that achieved by TE processing. As a result of the Taguchi optimization, it is concluded that the values in the combination of diameter (d)=60 mm, height (h)=50 mm, radius (r)=4 and pitch (p)=1.25 are the optimum die geometry. In conclusion, these results indicate that the proposed novel HAP method is an efficient and applicable SPD technique.

Construction of a Two-Dimensional Discrete Dislocation Model to Describe the Plastic Deformation Process of a Single Crystal

Construction of a Two-Dimensional Discrete Dislocation Model to Describe the Plastic Deformation Process of a Single Crystal

Intelligent Online Sensing of Defects Evolution in Metallic Materials during Plastic Deformation

Metallic plastic deformation involves complex microstructural changes and defect evolution, posing challenges in predicting and controlling the quality and performance of formed parts. Therefore, a pressing demand exists for a proficient online defect‐sensing system to monitor defects evolution continuously within components during plastic deformation in real time. This article proposes an intelligent online sensing approach for detecting defects in metallic plastic forming based on acoustic emission (AE) and machine learning. A comparative analysis is conducted on AE amplitude signals, stress–strain curves, and defect evolution during the tensile process of TA15 titanium alloy specimens under different stress states. It is found that the defect formation process can be divided into four stages based on the AE amplitude signals. A convolutional neural network model for intelligent defect sensing is established. It leverages transfer learning and is grounded in the relationship between AE signals and the evolution of internal defects. The prediction accuracy using different pretrained models is investigated and compared. It is discerned that utilizing GoogleNet as the pretrained model offers the swiftest training pace with a prediction accuracy of 97.57%. This approach enables intelligent online sensing of internal defect evolution in metal plastic deformation processes.

Comparing the microstructural and mechanical improvements of AZ80/SiC nanocomposite using DECLE and MDF processes

The present study investigates the effects of two different severe plastic deformation (SPD) processes on an annealed AZ80/SiC nanocomposite. Specifically, the microstructure, texture, shear behavior, and hardness of the material were analyzed after being subjected to dual equal channel lateral extrusion (DECLE) for up to 5 passes, and multidirectional forging (MDF) for up to 8 passes, both carried out at a constant temperature of 300 °C. The effective strain was 1.44 and 0.5 in each DECLE and MDF pass. The annealed AZ80/SiC nanocomposite showed a reduction in average grain size from 68.4 μm to 2.7, 4.2, and 4.4 μm during 1, 3, and 5 passes of DECLE process, and to 8, 4.3, 2.3, and 5.4 μm during 2, 4, 6, and 8 passes of MDF process. Examination of the shear properties revealed that the ultimate shear strength (USS) of the nanocomposite increased after conducting both the DECLE and MDF processes. Specifically, the USS of the annealed nanocomposite increased by 23.1 MPa after 5 passes of the DECLE process and by 8.1 MPa after 8 passes of the MDF process. These results indicate that the DECLE process had a greater effect on the shear strength increase compared to the MDF process. The results of the hardness testing on the AZ80/SiC nanocomposite showed that the fifth pass of the DECLE process increased the hardness from 86.6 to 96.2 Hv, while the eighth pass of the MDF process increased this value to 90.1 Hv. The DECLE process was found to be more effective than the MDF process due to the simultaneous application of three types of shear deformation, pressing, and extrusion in each pass, as well as the higher effective strain.

Radial plastic flow machining: A new process for fabricating gradient-structured terminals in one step

Radial Plastic Flow Machining (RPFM) is a novel severe plastic deformation process. By designing a specific plastic flow channel, the material is allowed to flow radially into the predetermined channel under the combined action of extrusion and cutting. A restricting ring is placed in the channel to form a copper terminal structure in one step. This study investigates in detail the formation mechanism, mechanical properties, and thermal stability of gradient structured copper terminals generated under different extrusion angles. It was found that as the extrusion angle increased, the high strain region slightly decreased, while the low strain region increased, allowing more material to be radially extruded. This indicates that tensile strength and toughness can be balanced by controlling different extrusion angle parameters. In performance testing, the study showed that the hardness of the copper terminals prepared by RPFM was more than double that of the original copper material, and the maximum tensile strength also doubled. Moreover, the performance of the copper terminals annealed at 150∘C was similar to that of untreated copper terminals, demonstrating good thermal stability at this temperature. The study suggests that RPFM is not only an effective process for manufacturing gradient structured copper terminals in one step, but it also provides a new method for manufacturing copper terminals with excellent comprehensive performance.

Effective Strains Determination in Continuous Constrained Double Bending with Active Friction Forces

In this work, a new process for severe plastic deformation (SPD) with active friction forces - CCDB Conform R3D2, a variation of the so-called "active bending", which is a continuous two-stage bending in calibers with small relative bending radius, is analyzed. A mechanical scheme of a device for realization of the process with a bending roller is proposed, based on a developed 3D virtual tool for its realization. Using CAD/CAE software 3D simulation, two virtual solutions of the process were compared, differing in terms of the location of the bending roller relative to the axes of the feeding and output rolls. The distribution and magnitude of the effective strains in the volume of the deformed long workpiece in the two bending stages at small relative bending radiuses were analyzed. An analytical expression is developed to determine the effective strains achieved in the SPD operation by constrained continuous bending in calibers with grooved rolls. The strain calculation methodology is based on the results obtained by simulation modelling of the CCB Conform R3D2 process in trapezoidal calibers with a bending roller located above and below the rolls line.

CLASSFICATION OF WIRE PLASTIC DEFORMATION PROCESSES USING CONVOLUTIONAL NEURAL NETWORKS

ABSTRACT: Machine learning, particularly the convolutional neural network (CNN), is a potentially competent tool for image processing. In this work, the technique is ?rst utilized to perform an analysis of the di?erent wire plastic deformation processes. In particular, a CNN is established and trained using 3200 image fractions with a resolution of 80 × 80. The relevant architecture consists of three convolutional layers in conjunction with polling layers with relu activation. By properly tuning the network, we achieve good training and validation accuracies of 97.7% and 97.1% to identify between two underlying treatments by observing only an insigni?cant cropped fraction of the material’s cross-sectional pro?le. We argue that speci?c features of the architecture, such as the augmentation process’s rescaling parameter, are essential in guaranteeing a satisfactory accuracy rate. The possible implications of the present study are also addressed. Keywords: machine learning, convolutional neural network, image processing, wire plastic deformation processes

High Temperature Deformation of Harmonic Structure Designed CrMnFeCoNi High Entropy Alloy

The Harmonic Structure (HS) is a recently introduced concept that paves the way for engineering metallic materials to achieve superior mechanical performance. They consist of soft, coarse-grained regions surrounded in three dimensions by an interconnected network of hard, ultra-fine grained regions. In addition, from a structural materials point of view, high entropy alloys have attracted attention due to their unique mechanical properties. In the present study, the HS design was applied to a high entropy CrMnFeCoNi alloy (also called "Cantor alloy"). The HS-designed Cantor alloy was successfully fabricated by mechanical milling, which is one of the surface severe plastic deformation processes, and the subsequent sintering process. The mechanical properties of these HS and homogeneous (Homo) Cantor alloy compacts were investigated by high-temperature compression tests in the temperature range of room temperature (RT) and 1173K, under initial strain rates of 0.01 s-1, 0.001 s-1, and 0.0001 s-1. The stress-strain curves of the HS compacts showed a large initial increase in stress and then a rapid decrease with strain, while that of the Homo compact showed a gentle increase and a gradual decrease. EBSD observation of the deformed compacts revealed that the HS compacts were probably deformed not only by dynamic recrystallization, but also by grain boundary sliding during deformation. The strain rate sensitivity value m of the HS compacts was 0.541 (true strain: 0.2) at 1173 K. In other words, the HS compacts exhibited pseudo-superplastic deformation at these temperatures.

Preparation, Microstructure, and Mechanical Properties of Aluminum Matrix Composite by Accumulating Roll Bonding Method

The ARB (Accumulative Roll Bonding) method is greatly watched as a new severe plastic deformation process that uses only a conventional general rolling machine. The ARB method is a preparation method of ultra-fine-grained, high-strength thin metal and alloy sheets by repeated rolling. The purpose of this study was to clarify the effectiveness of the ARB method as a metal matrix composite manufacturing process. At first, alumina particles and short carbon fibers were used as dispersoids, and pure aluminum was used as the thin plate. Then, the dispersoids were deposited on a pure aluminum plate to 2 vol.% dispersoids. Six of these aluminum sheets were stacked to form a multi-layer composite sheet, which was then cold rolled at a rolling reduction of 67%. After rolling, the sheet composites were cut in half, overlapped, and rolled again. The composites were obtained by repeating this process. When the repetition exceeded 6 times, the dispersoids tended to disperse in the aluminum matrix. In addition, uniform dispersion progressed through further repeat rolling. By repeated rolling, the tensile strength of the composite sheets was greatly improved. In addition, the tensile strength of the composites was higher than that of the ARB-processed monolithic aluminum sheet. The improvement in strength was caused by the refinement of aluminum grains rather than the particle dispersion.

Crystallographic Textures of Al and Al-Mg Alloy Formed by Shot-Peening

Shot-peening (SP) is one of the severe surface plastic deformation (SSPD) processing techniques. Due to large plastic strain by the SP, the SP for metallic materials forms crystallographic texture on the peened surface. Since the crystallographic texture formed by the SP depends on the dislocation slip, it can be expected that this texture is affected by stacking fault energy (SFE) of the materials. However, effects of the SFE on the crystallographic texture formed on the peened surface by the SP is not clear. In this study, crystallographic textures of pure Al (higher SFE) and Al-10 mass%Mg alloy (lower SFE) formed by the SP are investigated. When the pure Al is SPed, {001}+{111} double fiber texture with the <001> and <111> directions parallel to the plane normal direction of the peened surface is obtained. On the other hand, in the case of Al-10 mass%Mg alloy with the SFE close to the pure Cu, {110} fiber texture is formed as well as the pure Cu. Therefore, it is found that the crystallographic texture formed by the SP is influenced by the SFE.

Effect of Process Condition and Test Environment on Tensile Properties in Cold-Rolled Al-Cu-Mg Alloys

Severe plastic deformation processing and subsequent aging treatment have been known to be effective for achieving higher strength than the conventional aging treatment in aluminum alloys. This study prepared the Al-Cu-Mg-based alloy sample, Al-5.3Cu-2.8Mg (mass%). The alloys were solution treated at 480, 495 and 505°C, and cold-rolled by 90%. The effect of process condition and test environment on tensile properties in cold-rolled Al-Cu-Mg alloys was investigated. Results confirm that strength and ductility were improved with increasing the solution heat treatment temperature regardless of test environment. 0.2% proof stress and ultimate tensile strength were higher than aging treatment specimens, but elongation to failure was lower than aged one. Hydrogen embrittlement susceptibility increased with increasing solution treatment temperature. Ductile fracture with many dimples is observed in both cold-rolled and aged specimens. Second-phase particles were observed at the bottom of the dimples. There was no significant difference in fracture surface between the different test environments.

INVESTIGATION OF STAMPING BY WRAPPING PROCESSES THROUGH MATERIAL DEFORMATION MODELING ANALYSIS

This scientific article addresses the pressing issue of material deformation modeling in the context of stamping by wrapping processes (SWP). The main challenges in the development of these processes include the likelihood of workpiece failure due to insufficient material plasticity and unfavorable stress-strain states, determined by technological process parameters. Thus, effective SWP process development requires the utilization of material deformation modeling. The article indicates that any material deformation model in plastic deformation processes comprises three main elements: Analytical representation of the curve or surface of boundary plastic deformations during stationary deformation: This element describes how the material's plastic deformation changes during stationary deformation with alterations in the invariant stress state indicators. Mathematical model of the deformation path in coordinates of stress state indicators - accumulated plastic deformation. This model determines the path along which material deformation develops with changing stress state indicators and is dependent on accumulated plastic deformation. Damage accumulation model: This element takes into account accumulated damage in the material and can be used to predict workpiece failure. Specifically, the article analyzes the surface of boundary plastic deformations during stationary cold deformation and employs terminology to describe the dependence of accumulated plastic deformation until failure on invariant stress state indicators. The term "stationary deformation" is used to denote material deformation under unchanged values of these indicators.

Effects of P segregation on deformation mechanism in Ni-P nanocrystalline by atomic simulations

By using hybrid Monte Carlo-molecular dynamics (MC-MD) simulations, the segregation behavior of solute P atoms in the grain boundaries (GBs) of nanocrystalline (NC) Ni-P alloy was studied under different temperatures. The effects of P segregation on the mechanical properties and quantitative deformation mechanism of the Ni-P alloy were also investigated at high temperatures (800 K). The results show that the temperature strongly influences the segregation behavior of P atoms. Uniform P segregation occurs along GBs at 300 K, while at elevated temperatures (e.g., 1000 K), P atoms are concentrated at triple junctions (TJs), forming Ni-P precipitates. The uniform grain boundary segregation of P leads to Ni-P alloy with larger grain sizes and higher strength, while Ni-P precipitates at TJs result in alloy with smaller grain size, higher yield and flow stresses, which could be attributed to the Zener pinning effect. Moreover, quantitative analysis of the deformation mechanisms reveals that for NC Ni-P alloy with small grain size, Ni-P precipitates show significant effect on the competition between intracrystalline deformation and grain boundary deformation. A low percentage of elastic strain on the GBs was observed in the elastic deformation stage. The plastic deformation process of the non-segregated sample with grain size of 5 nm is dominated by grain boundary deformation, whereas for non-segregated samples of 10 and 15 nm, the strain is accommodated by both intragranular dislocation slip and grain boundary deformation. Importantly, Ni-P precipitates can reduce the degree of grain boundary deformation in alloys with small grains and thereby stabilize the GBs. The less grain boundary deformation caused by uniform grain boundary segregation of P and the more dislocation slip play a major role in improving the mechanical properties of the alloy with large grains. The results and findings of this study provide further insights into the segregation-induced strengthening mechanisms of NC Ni-P alloys.

Modeling of Stainless Steel Bending Force on CNC Press Brake

Bending processing is one of the most common plastic deformation processing procedures. It is widely represented in the metal processing industry. In this paper, sheet metal bending on a CNC press with a tool that has two basic parts is analysed: the lower-die and the upper-punch. The sheet metal material is stainless steel, which is one of the most commonly used materials. During the bending process on presses, one of the main challenges is the experimental determination of the bending force. The methodology used in this work is based on the experimental stochastic method, that is, design of experiment. A rotatable plan for three input parameters: material thickness, bending angle and bending line length, are varied at five levels. The output parameter is precisely the bending force. No special devices are needed to measure the bending force as an output parameter, because the bending force is measured and registered on the CNC press via the control panel. After the experiment, using the experimental design matrix, the coefficients of an adequate nonlinear mathematical model were determined. Such a mathematical model is suitable for analysis and optimization of the bending force.

Investigation of Microstructure and Mechanical Properties of the Repaired Precipitation-Strengthened Ni-Based Superalloy via Laser Melting Deposition

In this study, a typical γ′ phase precipitation-strengthened Ni-based superalloy DZ411 was repaired using an LMD-based repairing technique with an IN738LC superalloy, and crack-free samples were acquired. The mechanical properties and microstructure of different areas inside the repair sample were investigated, including the IN738LC deposit, the DZ411 substrate, and the interface between these two parts. The differences in mechanical properties between different areas were explained via analyzing fractography and KAM maps. It was found that the coarse carbides of the DZ411 substrate might lead to rapid cracking of grain boundaries, resulting in the worst mechanical properties of the DZ411 substrate. The IN738LC deposit demonstrated significantly superior mechanical properties in comparison to the DZ411 substrate. Its tensile strength exceeded that of the substrate by over 250 MPa, while its relative elongation after fracture was twice as great as that of the substrate. The excellent mechanical properties of the IN738LC deposit could be attributed to its fine microstructure, which resisted rapid cracking and generated a large number of GNDs during the plastic deformation process. For the interface between the deposit and substrate, although its hardness before the tensile test was low, it could also generate many GNDs during the plastic deformation process, hence exhibiting commendable mechanical properties. The research results show that using an LMD-based repairing technique with IN738LC superalloy to repair γ′ phase precipitation-strengthened Ni-based superalloy DZ411 is a feasible solution.

Constrained Constant Radius Pressing (CCRP) process to improve mechanical properties and microstructural homogeneity of pure copper sheet

Constrained groove pressing (CGP) is a well-known severe plastic deformation (SPD) process used to improve the mechanical properties of metallic sheets by forming the ultrafine grain (UFG) structure. The conventional CGP process employs 45° grooved dies to impart good amount of plastic strain on the specimen without altering the specimen's initial dimensions. The literature indicates that conventional CGP-processed sheets have inherent strain inhomogeneity. In the present investigation, an effort was made to minimize the inherent strain inhomogeneity by modifying conventional CGP dies into symmetric constrained constant radius pressing (CCRP) dies. Three distinct CCRP dies with varying radius of curvature and die parameters were designed to attain the optimal combination of mechanical properties. It was found that metal sheets processed by new modified dies (CCRP) exhibit improved ductility and significantly enhanced toughness, in contrast to the sheets processed by conventional CGP dies. The improvement in mechanical properties could be attributed primarily to homogeneous grain refinement. In addition, the finite element analysis (FEA) was used to simulate the influence of different die designs on the strain distribution across the sheet, and it showed that lower die angle of CCRP lead to more homogeneous distribution of strain across the arc of the CCRP die.

Subloading-elastoplastic constitutive equation of glass

Elastoplastic constitutive equation of glass is proposed in this article, which is formulated based on the subloading surface model which possesses the various distinguished advantages for the description of the plastic deformation, i.e., the smooth elastic-plastic transition, the continuous variation of the tangent stiffness modulus tensor, the automatic controlling function to attract the stress to the yield surface during the plastic deformation process, etc. It would be the firstly proposed three-dimensional elastoplastic constitutive equation of glass, which is furnished with the basic properties, e.g. the ellipsoidal yield surface with the dependence of the third deviatoric stress invariant, undergoing the flattering to the deviatoric direction with the plastic compression and the plastic volumetric hardening with the associated flow rule. The validity of the description of the deformation behavior of glass will be verified by comparisons with some test data for silica glass specimens.