Microstructural Evolutions, Hot Deformation and Work Hardening Behaviour of Novel Al–Zn Binary Alloys Processed by Squeezing and Hot Extrusion

S. Sivasankaran,K. R. Ramkumar,Hany R. Ammar,Fahad A. Al‑Mufadi,Abdulaziz S. Alaboodi,Osama Mohamed Irfan 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.4

The main goals of this work were to manufacture novel Al–Zn extruded alloys by varying the Zn content (0, 10, 20, 30 wt%),investigate the microstructural evolutions, hot deformation, and work hardening behaviour by hot compression test at differenttemperatures (25 °C, 75 °C, 150 °C, 225 °C, 300 °C). Al–20Zn alloy microstructure revealed α-Al and uniform distributionof (α + η) phases, coherent (α + η) crystals in GBs with casting defect-free surfaces, and effective interactions of pinningdislocations which led to improve mechanical performance of Al–20Zn alloy, as compared to the other alloys. The observedengineering stress–strain curve results revealed the decrease of stress with increasing of temperature due to flow softening,dynamic recovery and dynamic recrystallization. These results displayed also an increase of stress value with increasingof Zn content due to the precipitation of high density (α + η) phase in the matrix and GBs, increasing of forest and mobiledislocations density with strain fields, and the formation of fine dendrites. Work hardening rate (WHR) of extruded samplesdisplayed three stages: stage I, WHR decreased slightly with increasing of temperature up to 75 °C and decreased drasticallyfrom 75 °C to 300 °C due to softening; stage II, WHR maintained constant due to balance between dislocation generationsand dislocation annihilation; stage III, WHR slightly increased due to strain hardening of (α + η) phase. WHR was observedto increase considerably with increasing of Zn content due to the formation and dispersion of high density of (α + η) phasein the Al matrix and GBs. Deformation micro-localization in terms of different characteristics was examined and reportedon the deformed samples after hot-compression test through SEM micrographs.

Effect of Partition and Species Diffusivity on Double Diffusive Convection of Water Near Density Maximum

( S Sivasankaran ),( P Kandaswamy ) 한국산업응용수학회(구 한국산업정보응용수학회) 2007 한국산업정보응용수학회 Vol.11 No.1

EFFECT OF PARTITION AND SPECIES DIFFUSIVITY ON DOUBLE DIFFUSIVE CONVECTION OF WATER NEAR DENSITY MAXIMUM

S SIVASANKARAN,P KANDASWAMY 한국산업응용수학회 2007 Journal of the Korean Society for Industrial and A Vol.11 No.1

The double diffusive convection of cold water in the vicinity of its density maximum m a rectangular partitioned enclosure of aspect ratio 5 with isothermal side walls and insulated top and bottom is studied numerically, A thin partition IS attached to the hot wall. The species diffusivity of the fluid is assumed to vary linearly with concentration. The equations are solved by finite difference scheme, The effects of position and height of the partition, variable species diflusivity and enclosure width arc analyzed for various hot wall temperatures, It has been found that adding partition on the hot wall reduces the heat transfer. The density inversion of the water has a great influence on the natural convection. When increasing species diffusivity parameter heat, and mass transfer rate is decreased.

Effect of a Partition on Hydro-Magnetic Convection in an Enclosure

Sivasankaran, S.,Lee, J.,Bhuvaneswari, M. KING FAHD UNIVERSITY OF PETROLEUM MINERALS 2011 Arabian journal for science and engineering: AJSE Vol.36 No.7

Effect of TiB2/Gr Hybrid Reinforcements in Al 7075 Matrix on Sliding Wear Behavior Analyzed by Response Surface Methodology

S. Sivasankaran,K. R. Ramkumar,Fahad A. Al‑Mufadi,Osama M. Irfan 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.6

Al 7075 alloy matrix reinforced with different weight percentage of titanium borides (TiB2, 0, 1.5, 3, 4.5 and 6 wt%) and1 wt% graphite (Gr) hybrid composites were synthesized by in-situ liquid metallurgy route, then the sliding wear characteristicswere performed and investigated in this research work. TiB2reinforced as 0, 1.5, 3, 4.5 and 6 wt% by the in situchemical reaction of KBF4and K2TiF6salts and 1 wt% Gr with the Al 7075 matrix were added constantly in the melt. Severalexperiments were carried out to examine the wear behavior of the fabricated composite specimens through a tribometer atambient temperature. The weight percentage of reinforcement (TiB2 particles), the applied load, the sliding velocity (SV),and the sliding distance (SD) were selected as process parameters at five different levels. The response surface methodology(RSM) was used to conduct the experiments as RSM is the feasible and accurate method employed for optimizing to set theparameters. To check the significance of the developed model by RSM, ANOVA and confirmatory tests were also accomplished. FESEM surface morphology was also carried out to illustrate the uniform dispersion of the TiB2–Gr particulatesin Al 7075 matrix. The predicted wear characteristics from the developed model were well agreed with the experimentalresults. The obtained results were explained that both the increase in the percentage of RF and SV have dropped the wearloss (WL) curve whereas the load at all SVs and the SDs were uplifted the WL. The worn surface morphology explainedthat the adhesive mechanisms were dominated during the sliding wear test. Further, severe and mild wear occurred duringhigher load and lower load respectively.

EXISTENCE OF SOLUTIONS FOR DOUBLE PERTURBED IMPULSIVE NEUTRAL FUNCTIONAL EVOLUTION EQUATIONS

V. VIJAYAKUMAR,S. SIVASANKARAN,M. MALLIKA ARJUNAN 한국산업응용수학회 2011 Journal of the Korean Society for Industrial and A Vol.15 No.4

In this paper, we study the existence of mild solutions for double perturbed impulsive neutral functional evolution equations with infinite delay in Banach spaces. The existence of mild solutions to such equations is obtained by using the theory of the Hausdorff measure of noncompactness and Darbo fixed point theorem, without the compactness assumption on associated evolution system. An example is provided to illustrate the theory.

Effect of heating location and size on mixed convection in lid-driven cavities

Sivakumar, V.,Sivasankaran, S.,Prakash, P.,Lee, J. Pergamon Press ; Elsevier Science Ltd 2010 COMPUTERS & MATHEMATICS WITH APPLICATIONS - Vol.59 No.9

A numerical study is performed to analyze the mixed convection heat transfer and fluid flow in lid-driven cavities with different lengths of the heating portion and different locations of it. The left wall has been heated fully or partially to a higher temperature, whereas the right wall is maintained at a lower temperature. Three different lengths of the heating portion and three different locations of it are used along the hot wall. The remaining portions of the left wall, and the top and the bottom walls of the cavity are insulated. The finite volume method is used to discretize the governing equations which are then solved iteratively. The velocities and pressure are coupled by the SIMPLE algorithm. Results are presented graphically in the form of streamlines, isotherms and velocity profiles. It is concluded that the heat transfer rate is enhanced on reducing the heating portion and when the portion is at middle or top of the hot wall of the cavity.

Synthesis, Microstructures and Mechanical Behaviour of Cr0.21Fe0.20Al0.41Cu0.18 and Cr0.14Fe0.13Al0.26Cu0.11Si0.25Zn0.11 Nanocrystallite Entropy Alloys Prepared by Mechanical Alloying and Hot-Pressing

Yaser A. Alshataif,S. Sivasankaran,Fahad A. Al‑Mufadi,Abdulaziz S. Alaboodi,H. R. Ammar 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.1

Four component Cr0.21Fe0.20Al0.41Cu0.18medium entropy alloy (Quaternary, 4C-MEA) and six componentCr0.14Fe0.13Al0.26Cu0.11Si0.25Zn0.11high entropy alloy (sexinary, 6C-HEA) were designed and developed in non-equiatomicratio to attain improved mechanical properties. These 4C-MEA, and 6C-HEA were synthesized via mechanical alloying(MA), and consolidated by hot pressing (HPing) at 723 K. For comparison, the same atomic ratio of four and six componentsof coarse grain alloys (4C-CGA and 6C-CGA) were also manufactured by conventional blending method. Nanocrystallitesize powders of 27 ± 5.20 nm and 38 ± 3.7 nm were achieved for 4C-MEA and 6C-HEA respectively after 20 h MA. Thephase evolutions, structural properties, and powder surface morphologies were characterized using X-ray diffraction andseveral electron microscopes. The 4C-MEA has possessed more quantity of body centred cubic (BCC) and less amountof face centred cubic (FCC) phases due to the more solid dissolution of 4 components. However, 6C-HEA exhibited morequantity of FCC and a small amount of BCC phases due to the incorporation of more FCC components compared to 4C-MEAand less solid dissolution due to more atomic radius difference among the mixing elements (atomic radius of Cr = 166 pm,Fe = 156 pm, Al = 118 pm, Cu = 145 pm, Si = 111 pm and Zn = 142 pm). The HPed samples produced ultra-fine crystallitesize of 177 nm and 499 nm for 4C-MEA and 6C-HEA respectively. Further, 4C-MEA and 6C-HEA exhibited the ultimatecompressive strength (UCS) of 365 MPa and 456 MPa respectively due to dissolution and lattice distortion of mixing elements. Also, 6C-HEA possessed Vickers hardness strength of around 1.97 GPa which was 2 times higher than 4C-MEA. The theoretical background of various strengthening mechanisms, various physicochemical, thermodynamic parameters, andfour core effects behind the improved properties in entropy alloys was discussed and reported. The dislocation strengtheningand solid solution strengthening were the major factors in exhibiting more UCS in 4C-MEA and 6C-HEA than 4C-CGAand 6C-CGA.

Manufacturing Methods, Microstructural and Mechanical Properties Evolutions of High‑Entropy Alloys: A Review

Yaser A. Alshataif,S. Sivasankaran,Fahad A. Al‑Mufadi,Abdulaziz S. Alaboodi,Hany R. Ammar 대한금속·재료학회 2020 METALS AND MATERIALS International Vol.26 No.8

High entropy alloys (HEAs) are being attracted recently by several researchers, scientists, and academicians to achieveextraordinary and outstanding properties that cannot be obtained from conventional alloys. HEAs are multicomponent alloysin which a minimum of five metallic elements are mixed in an equal molar or non-equal molar ratio. The rapid growth ofthis field produces a huge amount of scientific papers over the last decade. However, still, there is a need to review variousmanufacturing methods and their results. Also, the outcome of the scientific articles related to HEAs has ignored the variousmethods of synthesizing and manufacturing. In this review article, an attempt was made and largely concentrated on themethods and techniques that can be used in the manufacturing and synthesizing of the HEAs. Recently, the properties ofHEAs become much better when compared to conventional alloys. Some techniques have succeeded in producing ultrafinemicrostructure grains which become a leap in industrial fields. Now, the manufacturing methods of conventional alloys arealmost familiar and implemented according to the suggestions given by the researchers and academicians based on their work. Therefore, the present review article has demonstrated various methods of manufacturing of HEAs with novel schematicswith a preview description for more understanding of the basic work criteria. Besides, this article has reviewed the outcomesof several research articles related to several methods, then compared the outcome of each method with the correspondingmechanical properties, and major challenges of HEAs are discussed and reported.

Microstructural and Wear Behaviour of Al 6063–W Nanocomposites Developed Using Friction Stir Processing

L. Feroz Ali,N. Kuppuswamy,R. Soundararajan,K. R. Ramkumar,S. Sivasankaran 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.12

The goal of the present research is to introduce the Tungsten (W) nanoparticles as reinforcement into Al 6063 alloy to produceAl–W nanocomposites by the FSP technique. The vol% of the reinforcement was varied from 3 to 12 with a step of 3,besides the unreinforced Al matrix was considered as 0 vol% for comparison. The role of W nanoparticles in the Al 6063matrix has been exhaustively investigated using advanced characterization techniques such as XRD analysis to observe thephases, FESEM to detect the distribution of reinforcements with their interparticle spacing and the average grain sizes, TEManalysis to study the strengthening factors, new phase formation at the interface between AA 6063 matrix and W particles,the morphology of the W nanoparticles. The achieved average matrix grains size was 42, 2, and 0.9 μm for 0, 6, and 12vol% W nanocomposites, respectively. The obtained results disclosed the uniform dispersion of W nanoparticles, withoutany agglomeration, and with the absence of intermetallic compounds. The hardness and wear resistance of the fabricatednanocomposites were increased incommensurate with the incorporation of heavy metallic W element as reinforcementparticle; which was due to the proper dispersion of W nanoparticles, refinement of matrix grains to ultrafine level, generationof dislocations, and clear interface between Al 6063 matrix and W nanoparticles. In a nutshell, AA 6063–12 vol% Wnanocomposite has achieved the higher hardness (120 HV), lower wear rate (0.13 mm3/m), and friction coefficient (0.33)than other nanocomposites.