University: Department of Metallurgical & Materials Engineering, IIT Madras,
Research Supervisors: Prof. B. S. Murty and Prof. Srinivasa Rao Bakshi.
Title: Effect of Scandium on the microstructure, mechanical and wear behaviour of A356 alloy and A356-5TiB2 in-situ composite.
Al–Si alloys and Al-matrix composites (AMCs) have received much attention for automobile, aerospace and structural applications due to their high specific strength, specific stiffness, higher hardness, wear resistance and good elevated temperature resistance. A356 alloys are used to manufacture sand cast and gravity cast automotive components. Usually, these alloys are used after the addition of grain refiners and eutectic Si modifiers to improve the strength. Only recently, researchers have started using Sc as eutectic Si modifier and grain refiner in Al-Si alloys. My Ph.D research was on the effect of 0.2 and 0.4 wt.% Sc addition on the microstructural modification and its effect on mechanical and wear properties in A356 alloy and A356-5 wt.% TiB2 in-situ composites.
Sc is known to be a grain refiner for Al alloys (Al3Sc particle will act as heterogeneous nucleation site for α-Al), as well as eutectic Si modifier in Al-Si alloys. Sc addition to A356 alloy resulted in grain refinement as well as modifies the eutectic Si morphology. Certain grain refiners settle down or dissolve with long holding of melt after the addition of grain refiners. It is necessary that for industrial practice in large foundries, grain refiner should last longer duration. Grain refinement test was performed by holding the melt after the addition of Sc (Sc added as Al-2Sc master alloy) with different time intervals 5, 30, 60 and 120 minutes and observed no change in grain size and eutectic Si morphology with even 120 minutes of melt holding. Hence Sc found to be an effective grain refiner and eutectic Si modifier in commercial A356 alloy.
The A356-0.2/0.4 wt.% Sc alloys were processed by adding Al-2 wt.% Sc master alloy to A356 melt. The A356-5 wt.% TiB2 composites were synthesized by the in-situ reaction between K2TiF6 and KBF4 salts added in proper stoichiometric ratio to form TiB2 in the A356 alloy melt at a temperature of 800°C. Addition of Sc reduced the secondary dendrite arms spacing (SDAS) by 50% and changed the Si morphology from needle-like to fine spheroidal particles. Al3Sc particles act as a heterogeneous nucleation sites for α-Al during solidification of A365-Sc alloy resulting in grain refinement. It was found that Sc addition of only 0.2 wt.% in A356 alloy modified eutectic Si by changing its morphology towards a rounded and fibrous shape.
In case of hypoeutectic Al-Si alloys, Si growth is by Twin Plane Re-entrant Edge (TPRE) growth mechanism and eutectic Si is in plate like morphology. Twins are the significance of TPRE growth and were found over the growth direction of Si in unmodified eutectic Si. Whereas with the addition of Sr and Na, the mechanism of modification was well known as Impurity Induced Twinning (IIT mechanism) and the Si morphology is fibrous and particulate. Branching of twins were observed in eutectic Si with Sr and Na addition, where the solute atoms (Sr and Na) absorbed over the growth direction and causes branching. The mechanism of eutectic Si modification with the addition of Sc in Al-Si alloys was not known. Addition of Sc modifies the eutectic Si from plate like to particulate and fibrous morphology. Twins were not observed in eutectic Si and for Sc added A356 alloy. This clearly indicate that the Si growth is not by TPRE mechanism. I proposed poisoning of TPRE growth or restricted TPRE growth is responsible for the modification of eutectic Si in Sc added A356 alloy.
Transmission electron microscopy (TEM) diffraction pattern, Energy dispersive spectroscopy (EDS) and XRD (X ray diffraction) analysis revealed the presence of β-Al5FeSi and π-Al8Mg3Si6Fe1 phases in A356 alloy. Addition of Sc to A356 alloy resulted in an additional V-AlSi2Sc2phase formation and changed β and π phases to Sc containing β-Al5Fe(Si.Sc), π-Al8Mg3(Si,Sc)6Fe1 phases. The β-Al5Fe(Si,Sc) phase is finer sized and irregular morphology compared with needle like morphology β-Al5FeSi phase. Addition of 0.4 wt.% Sc to A356 alloy improved its Vickers hardness, Ultimate tensile strength (UTS), Yield strength (YS) and Ductility by 20%, 25%, 20% and 30% respectively. Whereas, A356-5TiB2-0.4Sc in-situ composite showed a 30%, 24%, 33% and 7% improvement in Vickers hardness, UTS, Yield strength and Ductility respectively, compared with A356 alloy. Artificial aging treatment (T6) resulted in significant improvement in the tensile properties for both A356 and Sc added A356 alloys. Pin-on-disk dry sliding wear test results indicated that Sc addition improves the wear resistance of A356 alloy and A356-5 wt.% TiB2 composite at ambient, 150 deg.C and 250 deg.C temperature test conditions.
Title: Processing, characterization and mechanical properties of AZ91 Magnesium alloy reinforced with in-situ formed TiB2 and TiC particulate composites.
Mg matrix composites have great potential in automotive and aerospace applications due to their low density, high specific strength and good castability. AZ91-5 wt.% TiB2 and AZ91-5 wt.% TiC in-situ composites were synthesized by casting route by the addition of Al-Ti-B and Al-Ti-C powder compacts. I was successful in the synthesis of AZ91-in-situ 5 wt.%TiB2 and 5 wt.% TiC composites. This research work was carried out at CNPM in Ryerson University, Canada (March to July, 2012), funded by Canadian Commonwealth Scholarship from Canadian Bureau for International Education (CBIE) and Foreign Affairs and International Trade Canada (DFAIT) to carry out research work in Ryerson University, Toronto, Canada.
Title: Processing and characterization of silicon carbide (SiC) reinforced functionally graded aluminium matrix composites using centrifugal casting.
Functionally graded A356-15 wt.% SiC composite was synthesized by centrifugal casting. The outer periphery of the clutch plate requires high strength and wear resistance since these are continuously engaging/disengaging while operation. The processing parameters, pouring temperature and rotation speed were optimized to get a graded microstructure without porosity and shrinkage. The tensile and wear properties showed significant improvement to the outer periphery relative to inner periphery of the disk. This work was carried out in National Institute for Interdisciplinary Science and Technology (CSIR), Trivandrum, Kerala, India as a part of a project with Combat Vehicles Research and Development Establishment.
Multi-component Ni-Cu-Cr-Al High Entropy alloy coatings by plasma spraying, which can be used for wear resistant applications like cylinder liners.
Effect of carbon nanotube dispersion on mechanical properties of aluminum and aluminum-silicon alloy matrix composites.
Development of biodegradable Mg-HAP composites by powder metallurgy techniques.
Development of Al metallic foams by casting and powder metallurgy techniques.
Nanomechanical and nanotribological studies on nanocrystalline nickel coatings.
Leadership contributions:
Professional association: I was the chair for Material Advantage IIT Madras student chapter for a period two year during 2011-2013. During my tenure, the chapter won the most student recruitment and Chapter of excellence awards. We have organized K12 outreach for school students by giving talk to the selected schools on nanotechnology and invited school students to IIT Madras for showing the laboratories and facilities and demonstrating them on how to synthesize and characterize materials. I have initiated weekly technical fliers, where the recent trends in metallurgy and material science were chosen and made as a poster. I have also initiated A-quiz-A-day programme where every day a question based on the metallurgy and material science was posted in the webpage and those who gave most number of correct answer in a month were given rewards. This initiative helped me to interact with the material science community inside the institute and attract a large number of participants. I also invited the experts in the field of metallurgy and material science from industry and universities, from India and abroad to deliver technical talks and interactions with students. During my tenure, we conducted ISRS 2012 international conference along with Metallurgical and Materials Engineering department, IIT Madras and other professional associations and it was a great successful event and experience.
Assessment and review activities: I was the member of technical review committee for organizing ISRS 2012 and 2014 international conferences held in IIT Madras Chennai, India, where I was assigned to peer review and select the best papers in solidification and composite materials section. I also organized materials quiz programme for ISRS 2012 and 2014 international conferences.
Teaching and academic activities: I was in-charge for the Nanoindentation (Nano material property - Nano hardness testing) facility during 2011 to 2012 and X ray diffraction (Material Characterization) facility during 2013-2015 under the Nanotechnology laboratory facilities in Metallurgical and Materials Engineering department in IIT Madras, where I maintained the instrument and allocated test schedule. I also taught laboratory classes on Nanoindentation, Metal Casting and X ray diffraction to the graduate and undergraduate students as a part of their curriculum. I was also a co-mentor for 3 under-graduates and 2 post-graduate student’s thesis work, which was carried out in our nanotechnology laboratory.