Vellore Institute of Technology (VIT) is a private university located in&nbsp;Tamil Nadu, India. Founded in 1984, as Vellore Engineering College, the institution offers 20 undergraduate, 34 postgraduate, four integrated and four research programs. It has campuses in Vellore, Amravati, Bhopal and Chennai.

VIT is one of the top ranked private universities in India according to NIRF, THE and QS Rankings.&nbsp;Govt. of India has recognized&nbsp;VIT, Vellore as an&nbsp;Institution of Eminence. This has allowed VIT to take independent quality initiatives and move up in world ranking.

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VIT University

AA5xxx alloys are widely used for different parts of marine appliances of low to moderate level of <a href="https://www.sciencedirect.com/topics/materials-science/mechanical-strength">strength</a>. However, these alloys are not suitable for high-strength marine parts because of its low mechanical strength, <a href="https://www.sciencedirect.com/topics/materials-science/elastic-moduli">elastic modulus</a>, and weld yield strength. Hence, with an aim to improve performance of these alloys for various high-strength marine components, the present study efforts to develop fine grained AA5083 alloy-based nanocomposites with uniform dispersion of nanosize <a href="https://www.sciencedirect.com/topics/materials-science/silicon-carbide">SiC</a> particles through stir casting followed by microstructural modification using friction stir processing (FSP). AA5083-SiC nanocomposites (1, 2 &amp; 3&nbsp;wt%) were produced by an indigenously designed bottom pouring stir casting setup reinforced with nanosize SiC (n-SiC, ∼80&nbsp;nm) particles. Then, FSP was performed with the optimized parameters (1216&nbsp;rpm rotational speed and 41&nbsp;mm/min traverse speed) to modify as-cast interdendritic structures of the nanocomposites. Microstructural investigation through optical and <a href="https://www.sciencedirect.com/topics/materials-science/electron-microscopy">electron microscopy</a> (SEM-EBSD, TEM-EDS) confirmed the evolution of fine recrystallized grains with a uniform distribution of n-SiC within the matrix after the FSP. The FSP is found more advantageous to attain better grain refinement (∼50 % more) for the n-SiC reinforced composites as compared to that of the FSPed pure AA5083 alloy. The <a href="https://www.sciencedirect.com/topics/materials-science/mechanical-property">mechanical properties</a> were found to improve up to 2&nbsp;wt% reinforcement significantly as compared to the as-cast counterparts. However, because of huge agglomeration of n-SiC particles in the 3 % reinforced composite, it showed inferior mechanical properties. Tensile yield strength (YS) and average hardness were recorded to be 224&nbsp;MPa and 84 HV, respectively, for the FSPed AA5083–2&nbsp;wt% n-SiC nanocomposite as compared to the YS-152&nbsp;MPa, hardness-75 HV for the FSPed AA5083 alloy without any reinforcement. The enhancement in the mechanical performance is attributed to the breakdown of interdendritic microstructure to evolve dynamically recrystallized fine grains (grain boundary strengthening) with uniform distribution of n-SiC particles (dispersion strengthening) and other secondary precipitate phases. Analysis of strengthening mechanisms’ contribution found to be in good agreement with the experimental YS up to 2 % reinforced nanocomposites. <a href="https://www.sciencedirect.com/topics/materials-science/fractography">Fractography</a> analysis of the tensile samples is found to correlate well in accordance with the <a href="https://www.sciencedirect.com/topics/materials-science/tensile-property">tensile properties</a>.

World University root node

Department of Manufacturing Engineering

School of Mechanical Engineering

Vellore Campus

Materials Today Communications

Effect of friction stir processing on microstructural evolution and mechanical properties of nanosized SiC reinforced AA5083 nanocomposites developed by stir casting

Tremendous growth has been witnessed in the field of <a href="https://www.sciencedirect.com/topics/materials-science/three-dimensional-printing">additive manufacturing</a> (AM) technology over the last few decades. It offers a plethora of applications and is already being utilized in almost every sphere of life. Owing to inherent differences between each AM technique, newer fields of research consistently emerge and demand attention. Also, the innovative applications of AM open up newer challenges and thus avenues for focused attention. One such avenue is AM materials. Raw material plays an important role in determining the properties of fabricated part. The type and form of raw material largely depend on the type of AM fabricators. There is a restriction on material compatibility with most of the established AM techniques. This review aims to provide an overview of various aspects of AM materials highlighting the progress made especially over the past two decades.

Journal of Materials Research and Technology

A review of various materials for additive manufacturing: Recent trends and processing issues

The sliding wear behavior of stir cast <a href="https://www.sciencedirect.com/topics/materials-science/silicon-nitride">silicon nitride</a> (Si3N4) and graphite (Gr) reinforced Al–Zn–Cu–Mg (Al alloy) <a href="https://www.sciencedirect.com/topics/materials-science/matrix-composite">matrix composites</a> were investigated under dry conditions. Al alloy/1&nbsp;wt.% Si3N4 composite, Al alloy/1&nbsp;wt.% Si3N4–xGr hybrid composites (x&nbsp;=&nbsp;1.5 and 3% Gr by weight) were separately developed to examine their wear behavior. Microstructure and <a href="https://www.sciencedirect.com/topics/materials-science/energy-dispersive-x-ray-spectroscopy">EDS</a> characterization were used to identify the reinforcement (Si3N4 and Gr) in casted composites. Experimental design with L–27 orthogonal matrix array was chosen to perform the wear experiments to examine the effect of various applied normal loads (15&nbsp;N, 30&nbsp;N, and 45&nbsp;N) and sliding velocities (0.523, 1.047, and 1.57&nbsp;m/s) at a constant sliding distance of 1000&nbsp;m. Results reveal that the wear rate significantly decreased after adding 1.5 and 3&nbsp;wt.% Gr in Al– Si3N4 composite and obtained a minimum wear rate for hybrid composites containing 3&nbsp;wt.% Gr particles. ANOVA results revealed that load is the most dominating factor in wear rate, followed by sliding velocity and Gr content. The worn surface study observed lesser micro-cracks and pits in the hybrid composite containing 3&nbsp;wt.% Gr compared to Al– Si3N4 composites. The uniform distribution of reinforcing particles in the Al alloy matrix was examined through SEM characterization of casted samples.

Optimization of dry sliding wear behavior of Si3N4 and Gr reinforced Al–Zn–Mg–Cu composites using taguchi method

In the present work, interstitial-free steel plates were joined using friction-stir welding. The weld integrity was found to be in excellent condition. This work emphasises the evolution of microstructure and the enhancement of mechanical properties by friction-stir welding. The microstructural characterisation using optical image microscopy revealed the refinement of grains in the nugget zone. Vicker's hardness test stopped to a maximum of ~91 VHN in the nugget zone compared to ~40 VHN in the base material. The tensile test of the welded sample concluded that the samples fractured in the region away from the nugget zone and towards the base material. The results are conclusive that friction-stir welding is an excellent approach for joining interstitial-free steel components for automotive applications.&nbsp;

IOP Conference Series: Materials Science and Engineering

Microstructure and mechanical properties of friction-stir welded interstitial-free steel using WC tool

In the present study, Fe-42% Ni, Fe-2% Y2O3, and Fe-42% Ni-2% Y2O3 (30-60 nm) were prepared by mechanical alloying using high energy SPEX8000M ball mill. Consolidation of the milled sample was done by spark plasma sintering (SPS) at 800, 900, and 1000 °C at a pressure of 60 MPa with a holding period of 5 min in an argon atmosphere. The sintered density was found to be higher at a higher temperature, e.g., 98% at 1000 °C as compared to 78% at 800 °C. The addition of nanosize Y2O3 in Fe or Fe-Ni system showed a strong influence on the formation of intermetallic compounds and final grain size of the resultant material. x-ray diffraction analysis of the sintered Fe-42% Ni-2% Y2O3 alloy indicates the presence of Fe-Ni phase with additional peaks of intermetallic phases (Fe17Y2, Ni5Y) and oxides (Fe3O4, NiO). The nanoindentation hardness of the sintered (at 1000 °C) alloys was found to be the maximum for the Fe-42% Ni-2% Y2O3 (7.9 GPa), followed by Fe-2% Y2O3 (7.2 GPa) and Fe-42% Ni alloy (5.8 GPa). Dry sliding wear resistance of the spark plasma sintered (SPSed) (sintered at 1000 °C) Fe-42% Ni-2% Y2O3 was found to improve due to higher hardness and formation of oxide rich layer at the contact surface. Moreover, the SPSed specimen of the Fe-42% Ni-2% Y2O3 alloy showed a better corrosion resistance (Icorr = 0.78 μA/cm2) as compared to the corrosion resistance (Icorr = 1.34 μA/cm2) of the Fe-42% Ni alloy, both sintered at 1000 °C. The corrosion tests were conducted in a freely aerated 3.5% solution of NaCl electrolyte. A significant amount of grain refinement (due to the addition of nanosize yttria), formation of intermetallic phases (Fe17Y2, Ni5Y) as well as uniform distribution of fine oxide particles (Fe3O4, NiO) played the pivotal role in the improvement of wear, corrosion and mechanical properties of the SPSed Fe-42% Ni-2% Y2O3 alloy. © 2021, ASM International.

Journal of Materials Engineering and Performance

Effect of Y2O3 on Mechanical and Corrosion Properties of Fe and Fe-Ni Alloys Prepared by Mechanical Alloying Followed by Spark Plasma Sintering

The present research aims to develop high strength Al7075–SiC nanocomposites by integration of stir casting and cryo-FSP. Al7075 alloy based nanocomposites reinforced with varying wt.% (2%, 3% and 5%) of nanosize SiC particles were produced through the bottom pouring stir casting technique. The cryo-FSP was successfully carried out using optimized parameters (i.e. 1025 rpm and 65 mm/min traverse speed) on as-cast samples. To understand the fundamentals of the deformation characteristics and microstructural evolution, a systematic study on microstructural evolution has been performed by SEM with EBSD and TEM. The mechanical properties were evaluated by Vickers hardness and tensile testing. Improvement in the mechanical properties is found to be the maximum for the Al7075-3 wt% SiC nanocomposite sample obtained through cryo-FSP (TS = 552 MPa, and %El. = 17%) as compared to other samples studied (Al7075 alloy/composites). Secondary processing through cryo-FSP not only refined the matrix grain size to 1–3 μm range, but also suppressed the coarsening of the strengthening η′ phase due to higher cooling rate. Moreover, the reinforced nanosize SiC particles distributed uniformly within the matrix thereby enhancing the particle/matrix interface characteristics. These modifications in microstructure drastically enhance the strength (YS, hardness) and ductility of the material simultaneously. The detailed strengthening mechanisms have been analyzed and correlated with the mechanical properties. © 2020 Elsevier B.V.

Journal of Alloys and Compounds

Effects of cryo-FSP on metallurgical and mechanical properties of stir cast Al7075–SiC nanocomposites

This study is aimed at understanding external cryocooling effects during friction stir processing (FSP) on mechanical and microstructural characteristics of cast solution-treated Al 5083 alloy. An indigenous cooling setup is designed to effectively draw out heat from stir zone during FSP. Microstructural characterization techniques like optical microscopy, EBSD and TEM are employed to ascertain the cooling effect on microstructural evolution. FSP of Al 5083 has resulted in dense distribution of complex precipitates of Mn and Mg depleting the solutes from the matrix grains. Despite the enhancement in strength due to the refinement of grains, there is a huge loss of solid solution strengthening after the FSP. External cooling has major role in the evolution of homogenous fine matrix grains by arresting the grain growth after recrystallization. On the other side, there is no change on precipitate size and its morphology due to external cooling as they form at peak temperatures during FSP and their growth kinetic is fast enough due to availability of deformation energy and thermal energy during FSP. Superior combination of mechanical strength (YS/UTS = 149/316 MPa) and ductility (el.% = 38.4) is achieved for the samples processed with external cryocooling condition. Different strengthening mechanisms involved to the enhancement of yield strength have been analyzed and discussed. © 2019, © 2019 Taylor & Francis.

Materials and Manufacturing Processes

Influence of cryocooling on friction stir processing of Al-5083 alloy

Friction stir processing (FSP) of heat treatable aluminum alloys is reported to deteriorate strength and hardness properties in spite of huge grain size refinement. The improvement in strength due to the grain size refinement after FSP could not be able to offset the reduction in strength due to coarsening or dissolution of the strengthening precipitate(s). To overcome this, the present work investigates an effective way of heat rejection from the FSP zone to control the precipitate evolution besides the grain size refinement during FSP of Al7075 alloy. The FSP was carried out with standardized process parameters (i.e. 720 rpm, 65 mm/min traverse speed) under two different cooling environments: (i) at normal air cooling and (ii) by rushing a chilled mixture (−30 °C) of liquid nitrogen and methanol through the bottom of the backing plate. Microstructural evolution was examined through optical, scanning and transmission electron microscopy and electron backscatter diffraction to confirm the grain size and morphology of precipitate(s) formed. The in-process cryocooling during the FSP led to 65 and 72% improvement in the Vickers hardness and tensile strength, respectively, in comparison to the solutionized base metal. The results have been analyzed in terms of precipitate interface characteristics and its strengthening effect, Hall–Petch strengthening due to grain size reduction and tradeoff between them. © 2018 Elsevier Inc.

Materials Characterization

Effects of in-process cryocooling on metallurgical and mechanical properties of friction stir processed Al7075 alloy

Aim of the present study is to investigate the effect of process parameters on microstructural evolution, mechanical properties and corrosion behavior of an age-hardenable Al 7075 alloy. The alloy plates (6 mm thickness) were friction stir processed (FSPed) at various traverse speed, namely 25, 45, 65, 85, 100 and 150 mm/min at 2 different rpm of 508 and 720. The optimized result in terms of defect-free processed zone with refined microstructure was obtained only at a rotational speed of 720 rpm for a traverse speed of 25, 45, 65 and 85 mm/min. The microstructural evolution was investigated using optical, scanning and transmission electron microscopy. The grain size of the nugget zone was found to decrease with increase in the traverse speed from 25 to 85 mm/min at a constant rpm of 720. The mechanical properties were evaluated by Vickers hardness measurements, tensile and wear testing. Yield strength was found to be the maximum (~366 MPa) for the FSPed sample processed at 85 mm/min. The hardness values also followed the similar increasing trend with increase in the traverse speed. The wear volume loss decreased by 38% for the sample processed at a traverse speed of 85 mm/min as compared to that of the sample processed at 25 mm/min. The friction coefficient was found to substantiate well with the wear track morphology. The improvement in mechanical properties is ascertained to the refinement of grain size at higher traverse speed (due to less heat input). The FSPed samples showed inferior corrosion resistance in contrast to that of the base metal. This is possibly due to the coarsening of precipitates and depletion of solutes in the matrix. The morphology of the corroded samples corroborated well with the corrosion behavior of the corresponding specimen. © 2017, ASM International.

Effect of Process Parameters on Microstructural Evolution, Mechanical Properties and Corrosion Behavior of Friction Stir Processed Al 7075 Alloy

Present work investigates the mechanisms of simultaneous improvement of tensile properties, wear properties and corrosion resistance of stir cast Al7075–2 wt.% SiC micro- and nanocomposites through microstructural refinement by friction stir processing (FSP). Optical, scanning and transmission electron microscopy were used to investigate the microstructural evolution. After the FSP, the nanoparticles reinforced composite showed better mechanical properties than that of the microparticles reinforced composite. Tensile strength (>3 times) and wear resistance were found to increase significantly with simultaneous enhancement of the ductility (10 times). The improvement is ascribed to the grain size reduction, distribution of SiC nanoparticles uniformly within the matrix, increase particle-matrix interface characteristics and elimination of casting defects such as porosity after the FSP. The corrosion potentials of the as-cast composites were found to shift towards noble direction after the FSP. Enhancement of corrosion resistance after the FSP is attributed to the decrease in the heterogeneity on the surface and uniform dispersion of the reinforced particles, which reduced the effective active surface area exposed to the corrosive solution. All such beneficial effects were found to be superior for the nanoparticles reinforced composite due to the improved particle/matrix interface characteristics and dispersion strengthening. © 2017

Journal of Manufacturing Processes

Simultaneous improvement of mechanical strength, ductility and corrosion resistance of stir cast Al7075-2% SiC micro- and nanocomposites by friction stir processing