Deformation Behavior in Tubular Channel Angular Pressing (TCAP) Using Triangular and Semicircular Channels

Faraji, Ghader,Mashhadi, Mahmoud Mosavi,Kim, Hyoung Seop The Japan Institute of Metals 2012 MATERIALS TRANSACTIONS Vol.53 No.1

<P>In this paper, two different (triangular and semicircular) channel types were investigated in tubular channel angular pressing (TCAP) suitable for deforming cylindrical tubes to large strains without changing the tube dimensions. To examine the effects of the channel geometry on the strain distribution and deformation behavior during the TCAP process, finite element method (FEM) simulations and an analytical model were employed. The FEM results demonstrate that equivalent plastic strains of 2.15–2.9 and 2.35–2.6 were developed after applying one pass TCAP in the triangular and semicircular channels, respectively. The mean values of the equivalent plastic strains were almost identical for both cases, but the strain through the thickness with semicircular channel was more homogeneous than that in the triangular channel. Tube thinning in the early stages of the process was observed as a result of tensile circumferential strains, but this can be compensated by the back pressure effect resulting from the next shear zones and also compressive circumferential strain resulting from the decreasing tube diameter. While the strain values for both channel types were similar, the required load for the semicircular channel was lower than that of the triangular channel.</P>

Microstructure and Mechanical Properties of AM60 Magnesium Alloy Processed by a New Severe Plastic Deformation Technique

Siroos Ahmadi,Ghader Faraji,Vali Alimirzaloo,Ali Donyavi 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.8

The mechanical properties and microstructure of AM60 Magnesium alloy processed by a new cyclic extrusion channelangular pressing (CECAP) technique were investigated in this research. In this novel method, a low extrusion ratio stage wasadded at the end of the CECAP process to enhance the hydrostatic stresses and equivalent strain. The structure was refinedfrom the average grain size of ~ 76 μm for the annealed samples to 2.63 μm in the new CECAP after four passes. Whilefor the CECAP and ECAP processes, it was 3.43 and 6.98 μm, respectively. Experimental results of the proposed CECAPprocess showed an improvement in the mechanical properties after the second pass that were stopped for the ECAP process. However, the hardness of the CECAP-processed and proposed samples was constantly increasing. This increase in hardnesswas 196% and 175% for the proposed CECAP and CECAP processes after four passes compared to the unprocessedsample, respectively. Moreover, the compressive yield stress and ultimate compressive strength of the CECAP-processedsamples were higher in all passes; however, they were smaller than those of the proposed CECAP process. The hydrostaticcompressive stresses and higher plastic strain in the proposed technique helped in further refining of the grains, which caneffectively improve the mechanical properties.

Microstructure and Homogeneity of Semi-Solid 7075 Aluminum Tubes Processed by Parallel Tubular Channel Angular Pressing

Ramin Meshkabadi,Ghader Faraji,Akbar Javdani,Ali Fata,Vahid Pouyafar 대한금속·재료학회 2017 METALS AND MATERIALS International Vol.23 No.5

Semi-solid processing is a new developing technology for the fabrication of intricate parts at low temperatures incomparison with conventional casting routes. In this research, a parallel tubular channel angular pressing (PTCAP)was used as a pre strain-inducing process, and the influence of the number of PTCAP passes and semi-solid heatingparameters on the microstructural characteristics of Al7075 tubes was investigated. The results demonstratedthat PTCAP process could successfully be used as a best pre-straining method for tubular samples showing semisolidmicrostructures. As the temperature is increased, the solid particle size first decreased, then increased, andgradually became more spherical. The appropriate condition for the subsequent semi-solid forming process wasgained at reheating temperature of 620 oC. The suitability of this temperature was confirmed by the uniform distributionof grains. The grain size and shape factor both increased along with increasing the holding time. The distributionof the solid particles was strongly dependent upon the holding time and became uniform as the holdingtime increased. Comparison of the grain size and shape factor between ECAPed and PTCAPed samples revealed ahigh capacity of the PTCAP process as a strain-inducing stage. Also the two-pass PTCAP samples exhibitedhigher hardness than one-pass treated samples in the semi-solid state.

Processing and Properties of Biodegradable Magnesium Microtubes for Using as Vascular Stents: A Brief Review

Soheil Amani,Ghader Faraji 대한금속·재료학회 2019 METALS AND MATERIALS International Vol.25 No.5

Magnesium and its alloys have attracted a great deal of attention in the field of biomedical applications, especially biodegradablestents. However, they have not been extensively used because of some inherent limitations such as poor mechanicalproperties and high corrosion rate. During the last decade, the selected fabrication methods for producing stent precursors isof great importance and can significantly affect the final stent’s properties. In this paper, the progress of fabrication methodsand properties of Mg microtubes for using as biodegradable stents are reviewed. The paper will firstly classify the fabricationmethods, and then investigate produced microtubes’ properties from the perspective of mechanical, microstructural andbiocorrosion properties.

Electron Back-Scattered Diffraction and Nanoindentation Analysis of Nanostructured Al Tubes Processed by Multipass Tubular-Channel Angular Pressing

Mohsen Mesbah,Ghader Faraji,A. R. Bushroa 대한금속·재료학회 2016 METALS AND MATERIALS International Vol.22 No.2

Microstructural evolution and mechanical properties of nanostructured 1060 aluminum alloy tubes processed by tubular-channel angular pressing (TCAP) process were investigated using electron back-scattered diffraction (EBSD), transmission electron microscopy (TEM) and nanoindentation analyzes. EBSD scans revealed a homogeneous ultrafine grained microstructure after the third passes of the TCAP process. Apart from that the mean grain sizes of the TCAP processed tubes were refined to 566 nm, 500 nm and 480 nm respectively after the first, second and third passes. The results showed that after the three TCAP passes, the grain boundaries with a high angle comprised 78% of all the boundaries. This is in comparison to the first pass processed sample that includes approximately 20% HAGBs. The TEM inspection afforded an appreciation of the role of very low-angle misorientation boundaries in the process of refining microstructure. Nanoindentation results showed that hardness was the smallest form of an unprocessed sample while the largest form of the processed sample after the three passes of TCAP indicated the highest resistant of the material. In addition, the module of elasticity of the TCAP processed samples was greater from that of the unprocessed sample.

Specimen Size Effect on Behavior of Mg–3Al–1Zn Magnesium Alloy in Macro to Micro-scale Deformation

S. T. Khandani,Ghader Faraji,M. Karimpour 한국정밀공학회 2024 International Journal of Precision Engineering and Vol.25 No.1

Specimen size effect at a room-temperature uniaxial compression of an as-cast AZ31 Mg alloy was studied in detail using experiments and crystal plasticity finite element (CPFE) numerical simulations. The compression samples with a diameter of 1.2 to 15 mm and a height to diameter ratio of 0.8 were compressed at a strain rate of 0.01 s−1. As a result, the samples with lower diameters showed lower flow stress with not only higher standard deviation in terms of strength but also more sensitivity to the strain in terms of the standard deviation of the flow stress. Twin characterization analysis indicated that the specimen size could influence the twin average length and thickness. However, it did not affect the twin volume fraction. The experimental and CPFE simulation results for the flow stress were matched well, especially for the samples with larger diameters. The root sum square of the deviation between experimental and simulation results for flow stress and standard deviation of the flow stress showed a power law type relationship with sample diameter with a clear transition region denoting a micro-scale to macro-scale forming.

Microstructural, Mechanical and Corrosion Properties of AZ91 Magnesium Alloy Processed by a Severe Plastic Deformation Method of Hydrostatic Cyclic Expansion Extrusion

Armin Siahsarani,Farshad Samadpour,Mohammad Hossein Mortazavi,Ghader Faraji 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.8

This research investigates the microstructural evolution, mechanical properties, and corrosion behavior of AZ91 magnesiumalloy after the process of hydrostatic cyclic expansion extrusion (HCEE) at elevated temperature. The HCEE process is ableto produce long length ultrafine-grained rods by applying high hydrostatic pressure. The results showed that ultrafine-grainedmicrostructure appears after the consecutive passes of the process, which led to the higher hardness and strength with anincreased elongation to failure in the processed rods at room temperature. The ultimate tensile strength and elongation tofailure of the processed rod after two cycles of the HCEE increased more than 2 and 2.6 times, respectively. Moreover, anincrease in hardness was more than 100% after the second cycle of the process and its distribution was more uniform. Furthermore,the ultrafine-grained microstructure after the HCEE resulted in the movement of potentiodynamic polarizationderived curves to higher values of corrosion potential (Ecorr) and lower current density (Icorr), which shows the capabilityof the HCEE process in improving the corrosion resistance of AZ91 magnesium alloy rods. These increases in corrosionresistance were further indicated by the Nyquist diagram derived from the electrochemical impedance spectroscopy scanningand evolved hydrogen amount after 208 h of immersion in 3.5% NaCl solution. The novel HCEE process shows furtherits capability in producing long length ultrafine-grained rods with superior mechanical and corrosion properties rather thanother severe plastic deformation techniques.

Nano-Mechanical Properties and Microstructure of UFG Brass Tubes Processed by Parallel Tubular Channel Angular Press

Mohsen Mesbah,Firouz Fadaeifard3,Atefeh Karimzadeh,Bahman Nasiri-Tabrizi,Alireza Rafieerad,Ghader Faraji,A. R. Bushroa 대한금속·재료학회 2016 METALS AND MATERIALS International Vol.22 No.6

The production of the ultrafine-grained brass tubes was carried out by multi-pass parallel tubular channelangular pressing (PTCAP) as a severe plastic deformation process. In addition to that, the microstructuraland nano-mechanical features were investigated by EBSD and Nanoindentation for 0, 1, and 3 passes in acomparable mode. The elastic-plastic and micro scratch behavior were analyzed to show the enhanced features. Based on the obtained results, Young’s modulus and hardness of the specimens shifted to 1.62 and 1.7 times ofthe coarse-grained counterpart after the third pass respectively. The effects of the number of passes on the grainrefinement were also investigated to detect the applied changes through each step of the PTCAP experimental procedures. Moreover, based on the obtained results from EBSD, the grain size of 1 and 3 pass samples wererefined to 780 and 590 nm from its initial size of 75 μm. The fraction of the high-angle grain boundarieswas increased from 30% in pass 1 to 66% in pass 3 of the PTCAP process.