Constrained Groove Research Articles

Effects of annealing on microstructure evolution and mechanical properties of constrained groove pressed pure titanium

Constrained groove pressing (CGP) is performed on pure Ti followed by intermediate annealing at 450–650°C to fabricate large-scale plate-shaped sheets with improved mechanical properties. The results reveal that intermediate annealing not only improves ductility, enabling the successful achievement of the three-pass CGP at room temperature, but also enhances the tensile strength during the subsequent passes. The process involving three CGP passes with intermediate annealing after the first pass (referred to as PAPP) is superior for strength improvement. Compared to that of pure Ti, the tensile strength of the PAPP specimen annealed at 550°C is improved by 67%. This is ascribed to the recovery of the secondary twins, 85° <11–20> during annealing at 550°C, resulting in the activated 29.5° <1–100> twin variant in the two subsequent CGP passes. Meanwhile, the dislocations within the shear bands recover and form dislocation networks or subgrains at 550°C, and thus the dislocations continue to entangle and pile up at these sub-grain boundaries in the subsequent pressing, which further contributes to the improvement in the tensile strength. However, recrystallisation occurs in the CGP-deformed pure Ti annealed at 650°C, leading to a decrease in the tensile strength.

Experimental and numerical study of the longitudinal and transverse residual stresses distribution in the constrained groove pressing process of pure copper sheets

In this research, the residual stresses distribution resulting from one of the severe plastic deformation methods called Constrained Groove Pressing in pure copper sheets has been studied experimentally and numerically. For this purpose, after the initial preparation of each sample, the mentioned process is applied to the samples up to three passes. After each pass, the residual stresses in these samples in both directions of their length and width have been measured experimentally. To measure the residual stresses in these samples, the contour method, which is a relatively new, effective, and accurate method in providing a two-dimensional residual stress map, has been used. The results indicate that the residual stresses on the surfaces of the samples are compressive and by moving towards the central layers of them, these stresses are converted into tensile residual stresses. The distribution of residual stresses along the length and width of the samples is reported to be relatively uniform. In another part of this research, numerical simulation of the Constrained Groove Pressing process in ABAQUS finite element software is discussed. In this simulation, Johnson–Cook model is used as a constitutive model. The average error of residual stress distribution between the simulation and contour method was about 18% which shown a good agreement.

Deformation Texture Evolution in ARMCO Iron Sheets During Constrained Groove Pressing Followed by Cold Rolling

Deformation Texture Evolution in ARMCO Iron Sheets During Constrained Groove Pressing Followed by Cold Rolling

Ultrafine Grain Structure Development in Aluminium Alloy by Strain Hardening using CCGP

Severe Plastic Deformation (SPD) processes are for developing ultrafine grained (UFG) structured materials for different Industrial applications. Cyclic Constrained Groove Pressing (CCGP) is a technique, produce fine grained structures in metallic sheets or plates in mass production. The objective of research work is to investigate the influence of CCGP processing on the super plastic behaviour of an Aluminium alloy. Samples in “ascast” materials processed by CCGP with as cast, 1, 2, 3 and 4 passes. Processed Material study for microhardness and Tensile strength mechanical properties test were done for different test specimens. Grain refinement, microhardness and Tensile strength increased with the number of CCGP passes.

Optical microscopic analysis of constrained groove pressed followed by cold rolled ARMCO iron sheet material

ABSTRACT This paper is entitled to investigate microstructure of ARMCO Fe after constrained groove pressing and further after merging of both constrained groove pressing and cold rolling processes. Optical microscopic studies revealed increased number of equiaxed grains as a function of constrained groove pressing cycles. Such grain morphology was later transformed into a complete elongated grain structure due to plain strain compression during different percentage cold rolling reductions. Cold rolling not only increased strain progressively in the constrained groove pressed samples, but also had a pronounced influence in bringing in ultrafine grained structures (less than ~1 µm) in the material.

Microstructure and Mechanical Behavior of ARMCO Fe Severely Plastically Deformed by Combination of Constrained Groove Pressing and Cold Rolling

Microstructure and Mechanical Behavior of ARMCO Fe Severely Plastically Deformed by Combination of Constrained Groove Pressing and Cold Rolling

Application of Novel Constrained Groove Pressing Routes on Austenitic Stainless Steel

Application of Novel Constrained Groove Pressing Routes on Austenitic Stainless Steel

Mechanical Behavior of Constrained Groove Pressed Stainless Steel and Pure Zinc

Constrained groove pressing (CGP), which is a severe plastic deformation technique, has been implemented on AISI 304 and commercially pure zinc samples in the present work. Four CGP passes were successfully applied to both materials providing a remarkable improvement in both strength and hardness values, despite reduced ductility. Average grain size values were diminished by around 45% for 304 stainless steel and 47% for commercially pure zinc. The highest levels of strengthening due to severe deformation were displayed after the initial passes for both materials. CGP was shown to be a viable method for strengthening based on deformation processing, whereby similar trends in microstructure and mechanical behavior were observed for both crystal structures.

Microstructural evolution and mechanical properties of 316 austenitic stainless steel by CGP

In the present work, 316 austenitic stainless steel was deformed employing constrained groove pressing (CGP). The processed samples of 316 austenitic steel were characterized using X-ray diffraction and electron backscattered diffraction. The analysis of XRD patterns confirms the transformation of the austenitic phase into the martensitic phase. The Rietveld refinement employing MAUD software on XRD patterns of deformed samples indicates the decrease in crystallite size with the increase in microstrain and dislocation density, which is also supported by electron backscatter diffraction results. CGP leads to an increase in strength and a decrease in ductility. The enhancement in yield strength, ultimate tensile strength and hardness after CGP is due to the combined effect of increased dislocation density, martensitic transformation, sub-structure formation and reduced crystallite size. The yield strength, ultimate tensile strength, and hardness values have increased from 428 to 1055 MPa, 702–1135 MPa, and 261 to 360 VHN in two passes of CGP, respectively. However, the toughness value is decreased from 566 to 205 J/m3. Modeled yield strength values in different conditions are in reasonable agreement with experimental results. The results of finite element analysis employing DEFORM-3D software are in good agreement with the theoretical analysis of CGP.

Microstructural, mechanical and strain hardening behaviour of NiTi alloy subjected to constrained groove pressing and ageing treatment

• Constrained groove pressing of NiTi alloy and its ageing at elevated temperatures. • Enhancement of YS, UTS and microhardness due to dislocation generation. • Effect of precipitation, growth and decay of NiTi intermetallic. • Effect of precipitates on strain hardening behaviour using modified K-M approach. • Strength, ductility and toughness modulation by ageing at different temperatures. Equi-atomic NiTi alloy is a versatile Shape Memory Alloy (SMA) with diverse applications emerging in the aerospace and biomedical sectors. Mechanical properties of NiTi can be transformed by severe plastic deformation (SPD) and heat treatments for a wide range of applications. In the present work, NiTi is subjected to severe plastic deformation by constrained groove pressing (CGP) followed by short term ageing treatments at 350℃, 450℃ and 550℃. Microstructural evolution confirms the grain refinement by CGP whereas post ageing at different temperatures leads to nucleation, growth, and decay of Ni 4 Ti 3 and Ni 3 Ti precipitates affecting the mechanical properties and strain hardening behaviour. CGP leads to an improvement of yield strength (YS) and ultimate tensile strength (UTS) by 200 % and 61 % respectively whereas the post-CGP ageing marks the yield strength and ultimate tensile strength improvement in the range of 112 % to 73 % and 25 % to 12 % respectively. Microhardness shows a similar trend of improvements in the CGP processed NiTi (92 %) and post-CGP aged NiTi (67 % to 22 %). The role of shearable and non-shearable precipitates in the strain hardening behaviour of NiTi is also captured by the modified Kock-Mecking hardening model. In addition to that, their role in changing the mode of fracture from ductile to ductile-brittle in NiTi and CGP processed NiTi is presented using fractography analysis. Finally, CGP and post-ageing treatment at 350℃ has been found to be very effective in improving the overall microstructural and mechanical properties. Thus, the enhanced and appropriately modulated mechanical properties of NiTi alloy after CGP and ageing treatments may enable to widen the domain of existing applications in aerospace and biomedical sector.

Microstructural characterization and electrochemical behavior of nano/ ultrafine grained pure copper through constrained groove pressing (CGP)

This study presents microstructural, electrochemical, and mechanical characterizations on pure copper fabricated using constrained groove pressing (CGP) in quiescent phosphate buffer solution (pH = 11.73). We tested the effect of surface modifications on electrochemical features using electrochemical impedance spectroscopy (EIS) and Mott–Schottky analysis. A three-dimensional simulation via finite element modeling evaluates the CGP effects on the maximum principal stress and the plastic strain distribution. The transmission electron microscopy (TEM) micrographs confirm that the increasing CGP cycles result in a nano/ultrafine grain microstructure. Our electrochemical study showed that the CGP process can positively impact the passive behavior of pure copper. Mott–Schottky analyses illustrated that the point defect densities decline in the p-type semiconducting passive layer upon receiving CGP. Besides, increasing the CGP cycles lowers the corrosion current density and produces less defective passive films.

Microstructural behaviour and electrochemical characterization of Nitinol alloy subjected to constrained groove pressing and heat treatment

Nitinol, owing to its excellent shape memory properties, superelasticity and high corrosion resistance is an ideal choice for orthodontic implants. Its mechanical and electrochemical properties can be further improved by suitable mechanical processing and heat treatment. The present work shows the effect of Constrained Groove Pressing (CGP) and post CGP heat treatment at three different temperatures of 350°C, 450°C and 550°C on the electrochemical behaviour of Nitinol. The Electrochemical Impedance Spectroscopy (EIS) and Potentiodynamic Polarization (PDP) studies of water quenched, CGP processed and CGP and heat treated specimens were analysed and it was observed that the heat treated samples showed an improvement in polarization resistance in the order of 15%–42%, with the highest resistance observed for the specimen heat treated at 350°C. An overall improvement in the microhardness, post CGP treatment was also observed. The microstructures of all the samples were observed using optical microscopy to validate the change in mechanical and electrochemical properties. The results of these studies showed that CGP led to an increase in dislocation density and grain refinement, which were responsible for improvement of mechanical properties. The post CGP heat treatment led to nucleation and growth of intermetallic compounds Ni4Ti3 and Ni3Ti whose presence was confirmed by XRD and were responsible for the modification in Nitinol’s electrochemical behaviour.

Effect of strain path on microstructure and mechanical properties of AZ31 magnesium alloy sheets processed by constrained groove pressing

Constrained groove pressing (CGP) is a novel severe plastic deformation (SPD) method suitable for fabricating ultra-fine grained (UFG) sheet metals. In this work, two passes of CGP were conducted to AZ31 magnesium alloy sheets at 523 K, and three routes including traditional CGP, 180° cross-CGP and 90° cross-CGP were employed to investigate the effects of pressing number and strain path on microstructure, texture and mechanical properties of the alloy sheets. The results show that, irrespective of CGP routes, a bimodal microstructure is developed in the deformed materials and the capability of CGP in fabricating UFG magnesium alloy sheets is confirmed by TEM observation. The superior grain refinement and microstructure homogenization is achieved in traditional CGP route from the as-annealed 9.85 μm–5.04 μm after one pass while no further improvement is observed after two passes. The average grain sizes are 5.69 μm and 5.18 μm after two passes of 180° cross-CGP and 90° cross-CGP, respectively. The average misorientation angle is mainly determined by the fraction of very high angle grain boundaries and texture and microstructure mechanisms dominate the generation of high angle grain boundaries in traditional and cross-CGP routes, respectively. The coexistence of strain free recrystallized grains and substructured/deformed grains is observed after one pass of traditional CGP due to incomplete dynamic recovery and dynamic recrystallization and promotes the subsequent activation of strain induced grain boundary migration, which may be postponed by employing cross-CGP routes. A double-peak basal texture with the basal poles inclined from ND to RD is developed in traditional CGP route while an inclination of the basal poles from ND to TD accompanied by a redistribution of the prismatic intensity toward RD is observed in cross-CGP routes due to the change of shear deformation direction. The texture softening plays a more important role in decreased strength than grain refinement in traditional CGP route while both grain refinement and texture modification contribute to the improvement of tensile properties in cross-CGP routes. Due to the inherent nature of CGP, the reverse loading condition between successive pressings cannot be changed even in cross-CGP routes. The relatively high processing efficiency in 90° cross-CGP route should be attributed to the unique strain accumulation sequence.

An experimental investigation on the influence of elevated-temperature constrained groove pressing on the microstructure, mechanical properties and hardening behaviour of Ti6Al4V alloy

Abstract Due to its high strength-to-weight ratio and remarkable resistance to corrosion, Ti6Al4V alloy finds its use in a wide range of fields such as defence, aerospace and biomedical applications. To further enhance its properties and widen its applications, this paper focuses upon the novel application of constrained groove pressing (CGP) on Ti6Al4V alloy at elevated temperatures as it is hard-to-deform at room temperature due to its HCP structure. Till date, CGP is reported mainly on FCC and BCC alloys which are relatively easier to deform as compared to HCP alloys and metals, especially at room temperature. In this work, CGP process has been successfully performed on Ti6Al4V at 750 °C and 550 °C. Mechanical and microstructural evolution in CGP processed (CGPed) material is characterized by tensile testing, microhardness testing, optical microscopy, SEM Fractography and XRD. Enhancement in mechanical properties at room temperature such as yield strength, ultimate tensile strength and microhardness is observed more for CGP at 550 °C as compared to CGP at 750 °C and as-received material. Further analysis of tensile test results revealed that CGPed specimens at 750 °C and 550 °C follow different hardening behaviour although hardening mechanism for both is governed by Voce hardening model. Optical microscopy revealed fine distribution of β-phase along the grain boundaries in CGPed specimens. Microstructural analysis showed evolution of grain structure due to dynamic recrystallization in CGPed specimen at 750 °C whereas work hardening and grain fragmentation was observed for CGP at 550 °C. As-received (AR) and CGPed Ti6Al4V were observed to follow the Hall Petch relationship. SEM Fractography was performed on broken tensile test specimens, revealing the change in mode of failure from ductile mode for AR to mixed ductile-brittle mode for CGPed specimen at 550 °C. No precipitates were observed in SEM images which confirmed strain hardening effect of CGP and inherent voids as the main reason of failure. XRD analysis confirmed bulk strain hardening in CGPed Ti6Al4V. Thus, CGP at elevated temperatures may effectively be used for tailoring the microstructure and mechanical properties of Ti6Al4V alloys for extending its application domain.

Influences of the constrained groove pressing on microstructural, mechanical, and fracture properties of brass sheets

Constrained groove pressing (CGP) was used for the production of fine-grained brass sheets in different conditions. The process was conducted up to two cycles on brass sheets at room temperature and then half cycle at the temperature of 200 °C. Optical microscopy (OM), scanning electron microscopy (SEM), microhardness measurement, and plane stress fracture toughness was used to investigate the microstructure, mechanical properties, and fracture behavior. Microhardness measurement showed the capability of the CGP process in increasing the hardness of the refined sheets. It also showed the inhomogeneity of the hardness along the thickness of the sample after the process. The Digital Image Correlation (DIC) technique was used to investigate the elastic and plastic factors of the sheets along with the major mechanical properties of samples. The results showed a slight increase and reduction in the Young modulus and Poisson’s ratios after the process, respectively. Moreover, after two CGP cycles applying half cycle at the temperature of 200 °C did not show any significant effect on these values. The strength coefficient was as like as yield and ultimate strengths increased by increasing the number of the passes. However, processing at a higher temperature of 200 °C showed lower values for the parameters, as mentioned earlier, compared to the specimens processed at room temperature. The strain hardening index experienced a major reduction after the CGP process due to the effects of strain hardening. The anisotropy coefficient, which plays a critical factor in the severe deformation of sheets, was increased after the CGP process. However, this ratio decreased in higher passes or elevated temperatures. The highest anisotropy coefficient was obtained after the first cycle of the process. Moreover, SEM observation of the fracture surface showed shearing ductile rupture mode in the processed samples rather than ductile mode due to appearing of small and elongated dimples.

Warm Tensile Deformation and Fracture Behavior of AZ31 Magnesium Alloy Sheets Processed by Constrained Groove Pressing

Constrained groove pressing (CGP), as a promising severe plastic deformation method suitable for processing sheet metals, was applied to AZ31 magnesium alloy sheets, and ultra-fine grained structure was achieved after two passes of CGP at 473 K. A bimodal structure was also developed due to partial dynamic recrystallization (DRX) and deformation homogeneity. Tensile tests at temperatures from room temperature to 523 K and strain rates from 1 × 10−4 to 1 × 10−1 s−1 were conducted to the processed alloy sheets, and their tensile deformation and fracture behavior were investigated in this work. The maximum elongation to failure of 38.7% is achieved at 1 × 10−4 s−1 and 473 K, and the yield strength and tensile strength are 37.0 and 43.0 MPa, respectively. The strain hardening ability increases gradually with increasing strain rate at elevated temperatures, and its dependence on strain rate is more significant at lower temperatures. The strain rate sensitivity coefficient gradually increases with increasing temperature, and the relatively high values of ~ 0.17 and ~ 0.14 are obtained at 473 and 523 K, respectively, indicating the absence of superplastic behavior. The fracture morphology shows that with increasing temperature, the fracture mode changes from brittle fracture to ductile fracture, which is closely related to the microstructural evolution during tensile deformation. The grain coarsening at 523 K may result in the slight decreases of elongation to failure and strain rate sensitivity coefficient as well as the recovery of strain hardening exponent. The apparent activation energy at 423-523 K is estimated to be 68.8-105.5 kJ/mol. Conclusively, DRX and grain growth should be the dominant mechanism accounting for the warm tensile deformation of AZ31 magnesium alloy sheets processed by CGP, while grain boundary sliding mechanism may contribute little, due to the developed bimodal structure during CGP and the relatively low temperatures for the tensile tests.

Microstructure and Mechanical Properties of a Two‐Phase Mg–Li Alloy Processed By Constrained Groove Pressing

Constrained groove pressing (CGP), as a novel severe plastic deformation method, is applied to a two‐phase Mg–Li alloy at room temperature, 373 K, 423 K, and 473 K. The microstructural evolution and mechanical properties of Mg–Li alloy sheets during CGP are investigated. The optimum mechanical properties are achieved at 373 K after two passes. The tensile strength and yield strength are 157 MPa and 145 MPa, respectively, with a moderate elongation to failure of 12.4%, and the average micro‐hardness is about 63 HV. At 373 K, high‐density dislocations induced by CGP are preserved to enhance the strength and microhardness. The cross‐orientation procedure improves the deformation homogeneity and results in strength increase and ductility recovery at later stages. Increasing temperature weakens the homogeneity improvement and grain refinement with strain accumulation. The β‐Li phase is refined faster than α‐Mg phase, and grain sizes about 1 μm are observed in β‐Li phase. Dynamic recrystallization (DRX) first occurs in the soft and ductile β‐Li phase at 423 K. The grain refinement induced by DRX in β‐Li phase is counteracted by grain coarsening in α‐Mg phase, which causes no obvious enhancement of mechanical properties at higher temperatures of 423 K and 473 K.

Development of new fiber textures for enhancing mechanical properties of 2024 Al alloy using elevated-temperature constrained groove pressing

Constrained groove pressing (CGP) is a type of severe plastic deformation (SPD) employed for sheet metal strengthening. In this investigation, the annealed 2024 Al alloy sheets were employed to conduct the CGP operation at 300 °C temperature and up to three cycles. Afterward, complementary experiments, namely metallography, texture, hardness, and tensile tests were conducted with various deformed and undeformed sheets. As an important observation, a new fiber texture was developed during the third cycle of the CGP operation, affecting the ductility enhancement of this sample besides certain improvement in its ultimate strength. Moreover, in the deformed sheets, existence of hardest orientation, i.e. [111] ‖ RD, in the 1-passed sample with high intensity and creation of some new and soft orientations, i.e. [104] ‖ TD and [326] ‖ ND in the 2-passed specimen and [718] ‖ ND in the 3-passed workpiece, during the CGP process resulted in production of worksheets having specific mechanical properties. It was found that the 1st pass of the CGP process increased the yield strength (YS), ultimate tensile strength (UTS), and hardness of the alloy by 45%, 21%, and 71%, respectively. The worksheets produced via the 2nd and 3rd CGP cycles had higher YS, UTS, and hardness in comparison with the annealed worksheets. The material elongation was improved in the 3rd pass significantly, namely 41%. The precipitations evolutions and the γ-fiber overall intensity are the two most important factors for increasing elongation in the 3-passed specimens. Fractography of the fracture surfaces, also, confirmed these mechanical properties changes in different CGPed samples.

Evolution of microstructure and mechanical properties of Ti6Al4V alloy by multiple passes of constrained groove pressing at elevated temperature

Constrained groove pressing (CGP) is one of the best available sheet material processing technique for grain refinement and improving material properties without changing the original dimensions of the specimen. In this work, CGP is successfully performed on 10 mm thick mill-annealed Ti6Al4V plates at a temperature of 550 °C up to three passes. Microstructure studies reveal that grain size decreased from 18.81 μm in as received (AR) sample to 9.24 μm after third pass. XRD studies confirm the lattice strain and grain refinement phenomenon by peak shifting and broadening. Work hardening and grain refinement lead to increase in microhardness from 346 HV in AR to 392.1 HV, 365.9 HV and 371.4 HV in one pass, two pass and three pass CGP processed (CGPed) Ti6Al4V respectively. CGP leads to improvement of YS from 964.75 MPa in AR to 1085.01 MPa, 1068.11 MPa and 1078.63 MPa in one, two and three pass CGPed Ti6Al4V respectively. Similarly, UTS is observed to improve from 1014.12 MPa in AR to 1118.26 MPa, 1015.21 MPa, 1098.05 MPa in one, two and three pass CGPed Ti6Al4V respectively. SEM fractography reveals change in the mode of fracture of Ti6Al4V from ductile to ductile-brittle mode before and after the CGP process. Work hardening behavior of CGPed Ti6Al4V changes from stage III and IV to purely stage III along with initial instantaneous hardening rate increases after the first pass and decreases for the subsequent passes. CGP on Ti6Al4V alloy at 550 °C is found to have a significant effect on the stabilization of its microstructure and mechanical properties which can be useful for extending CGP for HCP alloys and their applications in aerospace and defense sector.

Effect of the uncertainty of multi-cut contour method and friction coefficient on residual stresses of constrained groove pressing process

Constrained groove pressing (CGP) process is a severe plastic deformation (SPD) method that can create ultrafine-grained microstructure in the sheet metals. In this study, residual stresses of the CGP process and the effect of the friction coefficient on the residual stresses were investigated. The residual stresses were measured in two directions using a multi-cut contour method and a mathematical-finite element model was developed to estimate the uncertainty of results of the multi-cut contour method. In order to study the effect of the friction coefficient on the residual stresses, a 3D finite element model was employed and the results of it were validated with the experimental results of the CGP process. According to the results, residual stresses in the first pass of CGP are compressive on the surface and gradually change to tension at the center of the thickness. Investigation of the effect of the first cut on the residual stresses and uncertainty of the second cutting plane showed that the effect of the first cut is only confined to regions near the intersection of the two cuts. Distancing from the intersection of two cuts causes the effect of the first cut to be ineffective on the second cut. Also, evaluation of the effect of friction coefficient on the residual stress illustrated that friction has a direct relationship with the residual stresses.