2. Thesis and Dissertations
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Item Studies on Wetting Behaviour, Microstructure Evolution and Solder Joint Reliability of Sn-Cu and Sn-Ag-Cu Lead-free Solders(National Institute of Technology Karnataka, Surathkal, 2014) Satyanarayan; Prabhu, K Narayana.The effect of substrate material, roughness and surface finish on wettability, evolution of intermetallic compounds (IMCs) and solder joint reliability of Sn-0.7Cu, Sn-0.3Ag- 0.7Cu, Sn-2.5Ag-0.5Cu and Sn-3Ag-0.5Cu lead free solders was investigated. Copper (Cu), Fe-42Ni, Cu with silver (Ag) finish and aluminium (Al) with nickel (Ni) finish were used as substrate materials. The relaxation behaviors of all solder alloys showed high spreading rates at the beginning and slower rates in the final stages. All solder alloys showed satisfactory spreading behavior with an area coefficient of spreading (Ac) ≥ 2 and the height coefficient of spreading (Hc) ≤ 0.5. Exponential power law (EPL) φ = exp(−Kτ n ) was used to model the relaxation behaviour of solder alloys, where ‘φ’ is the dimensionless contact angle and ‘τ’ is the dimensionless time. EPL parameters (K and n) decreased with increase in surface roughness. Spreading of solders exhibited capillary, gravity and viscous regimes. The increase in the surface roughness of Cu substrates improved the wettability of solders. The wettability was not affected by the Ag content of solders. The morphology of Cu6Sn5 IMCs transformed from long to short and thick needles for Sn-0.7Cu, Sn- 0.3Ag-0.7Cu and Sn-3Ag-0.5Cu solders solidified on rough Cu surfaces. However, with Sn-2.5Ag-0.5Cu solder alloy, needle shaped IMCs completely transformed to scallop morphology. The presence of thick Cu3Sn IMC at the interface of SAC solders indicated good wetting of the Cu substrate. Wettability of all solders on Fe-Ni surfaces was found to be better than that on Cu substrates. At the solder/Fe-Ni interface, Sn-0.7Cu and Sn- 0.3Ag-0.7Cu solders exhibited (Cu,Ni)6Sn5 IMCs. Higher Ag solders exhibited mainly (Cu,Ni)3Sn4 along with (Cu,Ni)6Sn5 IMCs. Solder bonds on smooth surfaces yielded higher shear strength compared to rough surfaces both for Cu and Fe-Ni surfaces. Fractured surfaces revealed the occurance of ductile mode of failure on smooth Cu surfaces and a transition ridge on rough Cu surfaces. Solder bonds of both smooth andrough Fe-Ni surfaces showed a transition ridge characterized by sheared IMCs. The increase in the integrity of solder joint on Fe-Ni substrates was due to the presence of (Cu,Ni)3Sn4 IMC at the interface. Wettability of all the solders on Cu with Ag finish was found to be similar. At the interface, all the solders exhibited predominantly Cu6Sn5 IMCs. With higher Ag solders, large amount of Ag3Sn precipitates were found. Wettability of Sn-0.7Cu and Sn-0.3Ag- 0.7Cu solders were found to be slightly better than higher Ag solders solidified on Al substrates with Ni finish. At the interface, Sn-0.7Cu solder exhibited faceted (Cu,Ni)6Sn5 IMCs whereas, Sn-Ag-Cu solders showed the presence of both (Cu, Ni)3Sn4 and (Cu,Ni)6Sn5 precipitates. Sn-3Ag-0.5Cu solder bonds yielded higher shear strength. Fractured surfaces of all solders revealed a transition ridge on Ag finished Cu substrates. With Ni finished Al substrates, the fracture was observed in the solder matrix. (Cu,Ni)3Sn4 IMCs at the interface increased the shear strength of Sn-3Ag-0.5Cu solder/ Ni finished Al substrate system. Although, rough surfaces exhibited better wettability, bond strength of solder/rough surface was lower than that of solder/smooth surface. Hence, smoother surface is preferable as it favors failure in the solder matrix.Item Studies on the role of HVOF coatings to combat hot corrosion, oxidation and erosion of materials used in turbine components(National Institute of Technology Karnataka, Surathkal, 2014) N, Jegadeeswaran.; K, Uday Bhat; M. R, RameshDegradation by high temperature oxidation, hot corrosion and erosion are the main failure modes of components in the hot sections of gas turbines, boilers, industrial waste incinerators, metallurgical furnaces, petrochemical installations, etc. The present research work explores the possibility of use of HVOF sprayed cermet coatings on the materials used in gas turbine systems. The coatings are investigated for their resistance to hot corrosion, oxidation and erosion, under laboratory conditions. Three types of feed stock powders, namely, 10% Al2O3+CoCrAlTaY , 25% (Cr3C2- 25(Ni20Cr)) + 75%NiCrAlY and Stellite-6 were sprayed on three alloys used in turbine related applications, namely Ti-6Al-4V (Ti-31), Cobalt based superalloy (Superco-605) and Fe-based special steel (MDN-121). The microstructure and mechanical properties of the coatings were characterized. It is followed by the investigation of their cyclic hot corrosion, cyclic oxidation and erosion of the coating behaviour is compared with the uncoated substrate alloys. Hot corrosion resistance of the coatings and substrates were investigated in a molten salt environment of Na2SO4-50%V2O5 at 800 C for 50 cycles. Each cycle consisted of heating at 800 C for 1 hour followed by 20 minutes of cooling in air. The analysis indicated that the carbide coated substrate alloys showed maximum resistance to hot corrosions, it was followed by alumina coating. The analysis also showed that the better resistance of carbide coating is due to the formation of oxides of alumina and chromium. Similarly, the resistance cyclic oxidation is investigated at 800 C for 50 cycles, Again each cycle consisted of heating at 800 C for 1 hour which is followed by 20 minutes of air cooling. The investigation indicated that the carbide coating exhibits maximum resistance to cyclic oxidation which is followed by Stellite-6 coatings. All three coatings showed better resistance compared to uncoated alloys both under cyclic oxidation and cyclic hot corrosion conditions. Solid particle erosion studies were conducted using silica sand as the erodent. Amongst three coatings, Stellite-6 coating performs better under sand erosion conditions. The 25% (Cr3C2-25(Ni20Cr)) + 75%NiCrAlY coating undergoes composite erosion mode, whereas the 10%Al2O3+CoCrAlTaY and Stellite-6 coatings undergo damage by brittle mode. Erosion behaviour of the substrate materials is ductile and resistance is better than the coating material.Item Preparation of preformed yarn to synthesize carbon-carbon composites(National Institute of Technology Karnataka, Surathkal, 2014) Naik, Padmayya Shaniyara; Surendranathan, A. O.The carbon fibre-reinforced carbon composites, popularly known as the carboncarbon (C/C) composites, are of interest because of their ability to retain strength and structural integrity till 30000C either in vacuum or in inert environment. C/C composites also possess outstanding specific strength and stiffness. Hence, the C/C composites are suitable for application in thermal protection systems used in nose cones and leading edges of hypersonic and re-entry type vehicles, which are exposed to elevated temperatures. Due to impressive high temperature properties, the applications of C/C composites in the aerospace industry have increased significantly in recent decades. Significant research has been carried out on the conventional C/C composites manufacturing methods and their properties. The conventional C/C composites synthesis requires many steps and consumes more time which leads to comparatively more cost. This research is mainly focused on a new method of C/C composite-synthesis by giving importance on preform preparation which includes reinforcement and matrix materials. In order to simplify the manufacturing of C/C composites, it was decided to develop a new production method, using preformed yarn, which contains the carbon fibre filaments as well as the matrix materials (coke and pitch binder).This method is named as preformed yarn (PY) method. This PY enables us easily to fabricate primary workpieces such as unidirectional (UD) sheets, cloth sheets, tapes and chopped yarns. Further, it is possible to prepare pipe and tube shaped standby preforms. From these workpieces and preforms, the C/C composites can easily be produced by hot press molding method. This investigation presents the construction of preformed yarn machine, and to produce preformed yarn bundles. In the beginning, it was decided to prepare proto-type PY model and three carbon fibre weight percentages of PY were prepared. Using this PY, unidirectional C/C composites were synthesized and various properties were analyzed. The C/C composites were prepared by varying the weight percentage of carbon fibre. The PY was prepared with carbon fibre (reinforcement) filaments surrounded byii coke and pitch (matrix materials), which were enclosed in nylon-6 as sleeving material for easy handling and processing. Three types of PY samples were prepared with carbon fibre fractions of 30wt%, 40wt% and 50wt% respectively and accordingly the composites were synthesized. In each case, the PY was chopped and filled unidirectional into a die of required shape and hot pressed at 600°C. Subsequently, impregnation of the carbon fibre preforms by pitch was carried at 2500C under a pressure of 0.1 MPa for 2-3 hrs. Then the pitch impregnated carbon fibre preforms was heated to 800◦C and hot isostatic-pressed at 90–100 MPa pressure for 24 hrs. This was followed by carbonization at 9000C for 48 hrs and graphitization at 25000C for 24 hrs, each under 1 atm. pressure. The process cycle from pitch impregnation to graphitization was repeated 2 to 3 times, until a density of 1.7 g/cc could be obtained in the investigated C/C composites. The characteristics such as microstructure (SEM images), XRD analysis, hardness, compressive strength, impact energy, creep, wear property, thermal degradation, have been studied. It is observed that, as the carbon fibre weight percentage increased the properties have also improved. The C/C composite made by the proposed PY technique is superior to any other conventional method. Among the three C/C composites containing different weight percentages of the fibre content, the one with 50wt% carbon fibre showed better properties. After developing a prototype model, it was further decided to design automatic (using PLC) machine for producing 50wt% carbon fibre-PY. The design is presented with relevant drawings. The sleeve weight percentage was reduced considerably in automatic PY technique as sleeve is not much important in composites except for holding and handling purposes. Due to this the weight percentage of matrix is proportionately increased against the reduction of weight percentage of the sleeve and weight percentage of carbon fibres would remain same.Item Processing of Commercial Purity Titanium, Aluminium and Al-5Zn-1Mg Alloy by Equal Channel Angular Pressing(National Institute of Technology Karnataka, Surathkal, 2014) Valder, James; Surendranathan, A. O.Severe plastic deformation (SPD) is a metal forming process in which a very large plastic strain is imposed on a billet in order to make an ultra-fine grained metal. Among all SPD processes, equal channel angular extrusion or pressing (ECAE/P) is an attractive processing method because of its simplicity and the possibility to scale up the technique for use in industrial applications. ECAE/P was originally developed by Segal et al. in the beginning of the 1980s’ to introduce a homogeneous simple shear deformation into billets without any change in its dimensions. There are various types of ECAP that have been developed and applied in the production of fine grained structures like ECAP of rods, bars, tubes etc. Many industrially important materials such as commercially pure (CP)-Ti and its alloys, CP-Al and its alloys, etc. have been processed by ECAP. In the present study, ECAP of CP-Ti rod in the wrought form, CP aluminium rod and tube in cast and wrought forms and Al-5Zn-1Mg alloy rod and tube in cast form using a die channel angle of 150˚ were investigated for various passes using four fundamental processing routes: route A where the sample is pressed repetitively without any rotation, route BA where the sample is rotated by 90˚ in alternate directions between consecutive passes, route BC where the sample is rotated in the same sense by 90˚ between each pass and route C where the sample is rotated by180˚ between passes. Mechanical properties of as-received and as-pressed billets after each pass were determined by Vickers hardness and tensile tests. Frictional property was determined by ring compression testing. The as-received microstructure and its evolution due to ECAP were characterized by optical microscopy. Failure analysis of fractured billets was characterized by scanning electron microscope (SEM). Compression testing was carried out for as-received and as-pressed billets to determine the flow properties before and after ECAP. Peak extrusion pressure was estimated for each pass for various routes by carefully recording the peak force for each pass.Processing of CP-Ti at room temperature resulted in improved strength with reduction in ductility. In spite of increased strength the peak punch pressure decreased as the number of passes was increased to three. Processing of CP-Al rod in the cast form at room temperature resulted in improved strength. Flow properties like strength coefficient (K) and strain hardening exponent (n) were also found to increase as number of passes was increased to two. The peak punch pressure increased for second pass compared to the first pass. CP-Al rod in the cast form failed in the third pass. A failure analysis of the same was carried out with the help of SEM. Processing of CPAl rod in the wrought form at room temperature resulted in improved strength with reduction in ductility. The peak punch pressure increased as the number of passes was increased to four. Al-5Zn-1Mg rod in the cast form failed during the second pass for all the temperatures selected for the study (303-673K). Friction factor (m) for Al-5Zn- 1Mg was determined in the temperature range of 303-673K. The maximum plasticity was observed in the temperature range of 373-573K where a hardness improvement is also seen. Processing of CP-Al tube in the wrought form at room temperature resulted in improved hardness. The peak punch pressure increased as the number of passes was increased to three. CP-Al and Al-5Zn-1Mg tube in cast form could not withstand even a pass. Failure analysis was carried out and crack propagation was observed clearly. Out of the four routes employed in the study route B (BA or BC) showed superior mechanical properties in all the chosen metals and alloy. As far as peak punch pressure is concerned route A showed the least punch pressure for CP-Ti after three passes, whereas for CP-Al, route C showed lowest punch pressure except in tubular form where route A showed the minimum punch pressure. From the present study it is clear that the different microstructural parameters for grain refinement criterion may give rise to different conclusions on the effectiveness of deformation route.Item Optimisation of Punch Pressure in Containerless Backward Warm Extrusion of Al-Zn-Mg alloys(National Institute of Technology Karnataka, Surathkal, 2014) M, Rijesh; Surendranathan, A. O.Open-die warm extrusion is an advanced forming technology which can not only reduce the machining time and material waste but also improves the properties of the products. Container wall – billet friction is eliminated in containerless extrusion, which leads to a large reduction in the total force required for extrusion. It is suitable for Al-Zn-Mg alloys, which is difficult to extrude compared to other aluminum alloys. The high specific strength of Al-Zn-Mg alloys and the lower punch pressure for containerless extrusion promises to be a vital combination, which needs to be further explored upon, hence present investigation was to determine theoretically and experimentally the effect of containerless backward extrusion of Al-Zn-Mg alloys namely Al-5Zn-1Mg, Al-10Zn-1Mg, Al-15Zn-1Mg for different geometries under a lubrication condition. Theoretical analysis was carried out using elementary plasticity theory – Dipper model and experimental analysis by conducting containerless backward extrusion experiments. Friction was minimized by lubricating the billets with graphite powder. Experiments were carried out using a 40 T universal testing machine with ram velocity of 3.3 × 10-4 m/s. The effect of specimen geometry on the extrusion pressure at various temperatures after containerless backward extrusion were investigated and presented. Finally, an optimum ratio of lengths to diameters of billets was determined by finite element analysis software called LS. Dyna: Levermore Software Dynamic Non Linear Analysis. Flow and frictional properties of Al-Zn-Mg were determined at different temperatures from 303 K to 673 K by compression and ring compression tests. Force-stroke data were generated at temperatures 303 K to 673 K for strains 0.1, 0.15, 0.2, 0.29, 0.37 and 0.45 for conventional backward extrusion and containerless backward extrusion for theoretical analysis whereas experimentation was restricted only to containerless backward extrusion. During experimentation force stroke data were generated at temperatures 303 K to 623 K for the same strains. Variation of theoretical punch pressure against extrusion strain at selected temperatures was studied. From the results of flow stress and frictional analysis of Al-Zn-Mg alloys it was found that the flow stress and friction for forming all the three chosen Al-Zn-Mg alloys were least between 373 K and 573 K. From the theoretical investigation it was found that containerless backward extrusion requires less than half of the force compared to conventional container extrusion and the optimum warm extrusion temperature for Al-5Zn-1Mg and Al-15Zn-1Mg is 373 K and for Al- 10Zn-1Mg is 473 K. From the experimental investigation it was found that optimum warm extrusion temperature for Al-5Zn-1Mg is 423 K and for Al-10Zn- 1Mg and Al-15Zn-1Mg is 523 K which is in accordance with theoretical analysis. From the experimental investigation it is also found that initial height ho, of billet, should be as small as possible to make upsetting difficult and diameter (do) of the billet should be large in comparison to punch diameter (dp) to make extrusion strain smaller and extrusion process easier. From the finite element analysis it was found that for a billet of ho/ do ratio of 0.5 shows an absence of lateral displacement of material, which is a characteristic of containerless backward extrusion. In the present study dynamic strain aging was observed to occur in the temperature range of 573-673K. The domain where dynamic strain ageing exists must be considered when selecting operating conditions like working temperature and extrusion strain.Item Synthesis and Characterization of Mechanically Alloyed Nanostructured Al-Fe(National Institute of Technology Karnataka, Surathkal, 2014) Hegde, Rajath; Surendranathan, A. O.Elemental powders of Al and Fe with an atomic composition of 50 % each were mechanically alloyed in a high energetic planetary ball mill. Tungsten carbide milling media (MM) were utilized for ball milling. The milling vial was filled with toluene liquid to prevent contamination of the milled products from the milling media and atmosphere. Ball milling duration extended upto 185 hours; characterization of the milled powder was carried out by X-ray diffractometer (XRD), differential scanning calorimetry (DSC), vibrating sample magnetometry (VSM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The major objectives of characterization were to investigate phase transformation, morphology and topography, structural changes, determination of particle size and magnetic properties of the ball milled powders. Crystallite size was reduced to 86 nm at the end of one hour of ball milling and to 12 nm at the end of 65 hours of milling time. Simultaneously, mechanical alloying (MA) has occurred with the formation of Fe rich BCC Fe (Al) solid solution whose lattice parameter was 0.29316 nm at the end of 185 hours of ball milling duration. During the course of ball milling, slight amorphisation was observed at higher duration of ball milling time (> 125 hours). Heating the ball milled powders in the calorimeter showed the transition to ordering from a near ideal solid solution. The decrease (122 to 76.5 emu/gm) in saturation magnetization (MS) was due to progressive alloying of Al in Fe, moreover, powder samples ball milled for ≤ 20 hours of milling duration exhibited soft magnetic properties (coercivity, HC ≤ 125 Oe) and the remaining ones were magnetically hard (HC >125 Oe). Transition to intermetallic compound from solid solution has induced paramagnetic behavior when ball milled powders were heated beyond 520 0C. Further, ball milled powder (185 hours of milling time) was compacted, sintered and annealed, due to which annealed compact started exhibiting a fully ordered (long range order, LRO, parameter ‘S’ of 0.7) structure. Such an ordered compact was subjected to plastic deformation by various compressive stresses for a very short duration of time. The highly ordered compact transformed into a fully disordered (LRO, ‘S’ = 0.20) structure when plastically deformed with stresses ≥ 4 GPa. Increase in compression stresses caused crystallite size refinement, increased hardness and MS in the deformed compact. In another set of experiments, the role of milling media (MM) was investigated. Elemental powders of Al and Fe with an atomic % of 50 each were ball milled in high energetic planetary ball mill utilizing stainless steel MM. The milling vial was filled with argon inert gas to avoid atmospheric and MM contamination of the milled products. Milling was carried out for a maximum duration of 400 hours. It was inferred that Longer duration of milling was required to achieve MA, crystallite size refinement and amorphisation to certain extent using stainless steel MM compared to that of ball milling with tungsten carbide MM. Metastable amorphous solid solution of Fe (Al) was found to be formed at the end of 400 hours of milling time which has alattice parameter of 0.2934 nm, crystallite size refinement to the tune of 5 nm and lattice strain of 2.215%. Equilibrium phases (AlFe/AlFe3 intermetallics) have precipitated when metastable amorphous solid solution was thermally activated in the temperature range of 500 0 to 700 0C. Ball milled powders exhibited soft magnetic properties with the sole exception of powder milled for 300 hours which behaved as a hard magnetic material. MS of 400 hour ball milled powder was 21.37 emu/gm. Ferromagnetism at room temperature decreased notably with increase in temperature reaching a paramagnetic phase in the temperature range of 620 0 to 720 0C for most of the ball milled powders. Transmission electron microscopy (TEM) with selected area diffraction pattern (SADP) images has authenticated the XRD results of indexing, the presence of amorphous phase and nanocrystalline domain which appeared to be less than 20 nm. Further, ball milled powders which have been mechanically alloyed using stainless steel MM was consolidated to bulk pellet form using equal channel angular pressing with back pressure (ECAPBP). Such pellets have been characterized by XRD, optical microscopy (OM), SEM, nanoindentation, TEM, DSC, VSM and texture analysis. Slight increase in crystallite size (13.4 nm) occurrred as a result of elevated temperature consolidation; though back pressure assisted ECAP-BP consolidation has decreased the diffusion coefficient thereby restricting the grain boundary mobility. Depending on the consolidation temperature and back pressure, either transitional (not fully ordered) AlFe alloy or a combination of AlFe/AlFe3 intermetallics coexisted in a few pellets. Pellets consolidated at higher temperature (450 0C) and back pressure (480 MPa) possessed better densification compared to those pellets processed at lower temperatures and back pressures. Metallurgical events like grain refinement, nucleation of nanopores, and precipitation of second phase particles were noted from SEM images of the pellets. Mechanical properties at the nano level measured by load induced nanoindentation are dominated by the local phase composition rather than the bulk mechanical properties of the pellets. Intermetallic phases provided greater nanohardness and elastic modulus values than those regions where transitional alloy and elemental phases were present. In addition, finer crystallite sizes in the nano level in the pellets promote higher nanohardness and elastic modulus. Comparision between the magnetic parameters of ball milled powders and ECAP-BP consolidated pellets, MS of the pellets is lower while HC is higher with most of the pellets possessing hard magnetic properties. Steep increase in LRO ‘S’ (0.45 to 0.85) and similar decrease in lattice parameter (0.28987 nm to 0.2882 nm) beyond 450 0C caused a transition to paramagnetic (≤ 2 emu/gm) behavior in the pellets. In addition to ECAP-BP consolidation, powders ball milled in stainless steel MM were consolidated by compaction followed by sintering in a nitrogen atmosphere. Sintered compacts exhibited coarser crystallites (120 nm) and reduced lattice strain (0.232 %) compared to ball milled powders and ECAP-BP consolidated pellets. Larger lattice parameter (0.2949 nm) of AlFe intermetallic is noted in addition to the presence of AlN and traces of Al, Fe and Fe4N phases in the sinteredcompacts. However, stronger texture (Maximum Intensity of 703.500) coupled with the presence of AlFe intermetallic and AlN phases caused sintered compacts to possess higher mechanical properties than the ECAP-BP processed pellets. In another set of experiments, elemental powders of Al and Fe (initial composition of 90 atomic % and 10 atomic % respectively) were ball milled in argon atmosphere using stainless steel milling media. Milling caused Al lattice dilation to the tune of 0.4088 nm forming Al rich solid solution (Al (Fe)) resulting in crystallite size refinement to as low as 6 nm. Quantitatively, 9 % of unalloyed Al was present after 400 hours of ball milling duration. Due to amorphous structure, distinct glass transition temperature prior to crystallisation and a narrow supercooled liquid like region could be observed in all the powder samples. Hard magnetic properties (HC ≥ 294.10 Oe) with low MS (≤ 8.432 emu/gm) were observed in all the ball milled powders. Appearance of grain boundaries, dislocations and amorphous structure was evident from the TEM analysis. Further, the ball milled powders (Al90-Fe10 category) were consolidated by ECAP-BP as well as by compaction and sintering. Metastable Al rich solid solution transformed into a stable Al76Fe24 compound of monoclinic structure in all the pellets due to consolidation of the ball milled powders. DSC analysis indicated the slight amorphous structure in the pellets. Pellets exhibited soft magnetic (HC≤ 107.63 Oe) properties with a very low paramagnetism MS (≤ 0.6582 emu/gm). Pellets with excellent bonding between the particles were produced with a low back pressure (300 MPa) and temperature (450 0C), which is much lower than the sintering temperatures. Nanosized grain boundaries, amorphous and Al76Fe24 compound phases were distinctly visible in the SEMFEG micrographs of the pellets. Sintered compacts exhibited crystalline phases of Al76Fe24 compound, AlN and unalloyed Al. Larger quantity (74 %) of Al76Fe24 crystallized in the 400-h sintered compact, although the lattice dilation of Al in the 250-h sintered compact was to the tune of 0.4109 nm. Maximum size of the crystallites in the sintered compact was 135 nm, which was much larger than that of ECAP-BP consolidated pellets (D = 11 nm). Among all the consolidated materials of both the categories (Al50-Fe50 and Al90-Fe10), 400-h sintered compact of Al90-Fe10 system possessed strongest texture (Maximum intensity of 6556.00), coupled with highest nanohardness and elastic modulus caused by larger quantities of Al76Fe24 intermetallic and AlN phases. The present investigation unambiguously brings out the fact that mechanical alloying followed by consolidation in different modes (ECAP-BP and sintering) and conditions produces nanomaterials with spectrum of structure and properties from which a choice of industrial product can be developed.Item Development of Austempered Ductile Iron as a Grinding Media Material in the Ball Mill: Microstructural Aspects and Influence of Surface Coating(National Institute of Technology Karnataka, Surathkal, 2014) H, Raghavendra; Bhat, K. L.; Udupa, K Rajendra.In the present investigation an attempt has been made to evaluate the suitability of austempered ductile iron (ADI) as media material for grinding iron ore, chalcopyrite and coal in a laboratory sized ball mill. The spheroidal graphite (S.G) iron balls having 2.5 cm diameter of required composition were produced by sand casting method. In the first case, single step austempering was given on each set of 200 balls after austenitising at 900ºC for one hour and austempering at 280ºC and 380ºC for different time duration of 30, 60 and 90 minutes. In the second case, each set of 200 S.G.iron balls were austenitised at 9000C for 60 minutes and given low to high stepped austempering treatment (ATLH) at 2800C for 15, 30, 45 and 60 minutes followed by 3800 C for 60 minutes. Similarly in the third case, each set of 200 S.G.iron balls were austenitised at 9000C for 60 minutes and given high to low stepped austempering treatment (ATHL) at 3800C for 15, 30, 45 and 60 minutes followed by 2800C for 60 minutes. Altogether, 14 sets of 200 S.G.iron balls, each were austempered at different time and temperatures to obtain ADI. A selected set of ADI balls were given surface coating to improve their wear and corrosion resistance. The materials such as titanium nitride (TiN), titanium aluminium nitride (TiAlN) and aluminium chromium nitride (AlCrN) are coated by Plasma physical vapour deposition (PPVD) on ADI balls. Also, the nitriding was carried out by gas nitriding process to increase the surface hardness of the ADI ball material. These materials were characterised by measuring hardness, studying microstructure using optical and scanning electron microscope (SEM) and analysing the X-ray diffraction (XRD) profiles. Grinding experiments were carried out in a ball mill using these ADI balls as media material for the comminution of different ores namely, iron ore, chalcopyrite and coal. Grinding wear behaviour of these materials was assessed for wear loss in wet condition at different pH value of the mineral slurry. For the sake of comparison the grinding experiments were carried out with the conventionally used forged En31 steel balls as media material in the ball mill.The wear rate of all the category of ADI were compared with that of forged En 31 steel balls and found that the wear resistance of ADI was superior to forged En31 steel balls. Among ADI balls ones austempered in conventional single step at 2800C for 30 minutes with hardness of 497 BHN, 26% by volume of retained austenite and 1.90% by weight carbon content of retained austenite offered highest grinding wear resistance. Further, the wear rate of ADI balls decrease with increase in duration of grinding and it was found to be 39 X 10-8 cc/revolution after 40 hours of grinding which is less than that for any category of ADI balls. Corrosive wear behaviour of ADI and forged En31 steel balls were analysed by carrying out the grinding experiment using water and kerosene as slurry media separately. In both the cases it was found that the wear resistance of ADI is superior to that of forged En31 steel balls. However, this experiment revealed that the corrosion plays an important role in wear of grinding media balls. The mechanism of wear is conceived to be corrosive wear occurring by delamination phenomenon and aided by impact fatigue crack growth. The results of the investigations reveal that the surface coated ADI balls possess very high wear resistance during the initial few hours of ball milling but decreases suddenly after particular duration of grinding. A term called relative efficiency index (REI) has been developed to compare grinding efficiency of ADI balls with that of forged En 31 steel balls. The REI values of 3.7 as recorded by ADI balls compared to that for forged En 31 steel balls indicated the superior nature of ADI balls. Hence, even without surface coating the ADI balls offered very high wear resistance and can be a suitable substitute for conventionally used forged En31 steel balls as grinding media in the ball mill. Results of the investigations were discussed in detail.Item Utilization of Nanostructured Fly Ash in Polymer Matrix Composites(2016) Patil, Akshata G.; Anandhan, S.Fly ash (FA) is a by-product generated during the combustion of pulverized coal in power generating thermal stations. In this study, a class-F FA was subjected to mechano-chemical activation by high energy ball milling. Mechano-chemical activation was carried out in presence of a surfactant and an inert liquid medium to obtain nanostuctured FA. The morphological, compositional, spectral and structural properties of the mechano-chemically activated FA (MCA-FA) were characterized using scanning electron microscopy, transmission electron microscopy, x-ray diffraction, Fourier transform infrared spectroscopy, dynamic laser scattering and Brunauer-Emmett-Teller surface area analysis. The fresh FA and MCA-FA were incorporated as fillers in ethylene-octene random copolymer and poly(vinyl alcohol) matrices. Morphological studies revealed that interfacial adhesion between the polymer and MCA-FA was good, which accounted for the improvement in mechanical properties of these composites. Thermal properties and flammability of ethylene-octene random copolymer and poly(vinyl alcohol) composites were enhanced on the addition of fresh FA and MCA-FA. The design of statistical analysis by Taguchi methodology was used to study the influence of milling parameters to obtain nanostructured FA. Ball milling parameters, such as ball-to-powder weight ratio, type and quantity of surfactant and type of medium were varied as guided by the Taguchi design. An orthogonal array and analysis of variance were employed to analyze the effect of milling parameters. According to the results obtained from analysis of variance, the factors ball-to-powder weight ratio and surfactant type emerged as the major contributing factors. Also, a fractal approach was used to characterize the lacunarity of the agglomerates in the MCA-FA. The MCA-FA was characterized by various techniques. Later, chitosan and poly(vinyl chloride) composites were prepared using fresh FA and MCA-FA. The key parameters for the enhancement of the properties of these composites and compatibility between MCA-FA and matrices were interfacial adhesion and morphology of these fillers.Item Solidification Analyses and Heat Treatment of Modified And Refined Al-Si Alloys -A Study(2016) V, Vijeesh; Narayan Prabhu, K.The present work involved the study of the effect of addition of cerium (Ce), phosphorus (P) and strontium (Sr) on cooling curve parameters, heat transfer characteristics, microstructure and mechanical properties of Al-8Si, Al-13Si, Al-14Si and Al-22%Si alloys. Melt treated alloys were solidified against sand base and against stainless steel, brass, and copper chills to assess the effect of cooling rate on silicon morphology. Thermal analysis parameters of melt treated alloys were determined by recording the temperature of the liquid metal solidifying against the chill. The addition of Ce significantly influenced both primary and eutectic phase nucleation temperatures and increased the undercooling temperatures. Newtonian and Fourier analysis techniques were used for the calculation of solid fraction and latent heat of solidification. The heat flux across the casting/chill interface was estimated using inverse modeling technique. The interfacial heat flux between the chill and the alloy increased with Ce and Sr melt treatment and decreased on addition of P. The effect of melt treatment and chilling on microstructure was assessed by measuring (i) the grain size (ii) roundness of eutectic silicon (iii) fineness of primary silicon. Ce treated alloys solidified against sand base at a slow cooling rate resulted in refinement of eutectic silicon along with the formation of AlSi-Ce ternary intermetallic compound. The addition of Ce to alloys solidified against chills resulted in complete modification of the eutectic silicon. The addition of Ce also resulted in fine equiaxed grains in Al-8Si alloys and refined the primary silicon in hypereutectic Al-Si alloys. The addition of Ce simultaneously modified and refined both primary and eutectic phases, whereas, Sr and P modified eutectic silicon and refined primary silicon respectively. On addition of Ce, P and Sr there was a significant improvement in the mechanical properties of the alloys. The combined addition of Ce with Sr to Al-Si alloys resulted in further improvement of mechanical properties. Al-8Si, Al-14Si and Al-22Si alloys were subjected to T6 heat treatment. The ageing temperature and time were selected based on a series of trial experiments. The tensile strength of all untreated alloys increased when subjected to heat treatment, whereas, the heat treatment had deleterious effect on the mechanical properties of melt treated alloys except on P treated alloys.Item Study on the Material Engineering aspects of Microwave sintered Aluminum– Cenospheres Composites(2016) Ananda Kumar, M. G.; Nayak, Jagannatha; Seetharamu, S.The thesis brings out the findings from the study undertaken on development of Aluminium based Metal Matrix composite through Powder Metallurgy route. The composite has been fabricated reinforced with various volume percentages of Fly ash Cenospheres particulates ranging from 0 to 50 vol %. The densification of the composites has been achieved through a non conventional sintering route known as Microwave sintering which is different from the well known conventional processing routes. The microwave sintering process appears rapid and economical. The Aluminium composites reinforced with Cenospheres and sintering through Microwave sintered composites have been later characterized for physical properties such as Density, Porosity, Hardness and Water Absorption, Chemical characteristics and Morphology of the synthesized composites and that of the raw materials through Scanning Electron Microscopy and Energy Dispersive X-ray Fluorescence methods. The Phase Analysis of the composites has been carried through Powder route X-ray Diffraction. The composites have also been studied for Mechanical properties such as Compression Strength with Finite Element Analysis and Modulus of Rupture. The composites have been studied for Tribological properties such as Wear and Erosion Resistance, Thermal properties such as Co-efficient of Thermal Expansion, Thermal Shock Resistance and Fusion Temperatures. The above test results have been compared with the results of conventionally prepared AMCs. The study on the various properties on the PM based Aluminium Cenospheres composites sintered in Microwave at 6650C have indicated that Apparent Porosity was about 35% compared to conventionally sintered ones which was around 40.7%. The Bulk Density was seen to reduce from 2.2 to 1.75 g/cc and the BHN values were found decreasing from 46 to 24% for the Microwave sintered samples. The conventionally sintered sample showed Bulk Density reducing from of 2.1to 1.75 g/cc and BHN values were found decreasing from 46 to 24. The BHN values were better than the conventional ones by about 26 %. The CTE of the composites decreased from 25.6 to 7.4 x 10-6/0C with increase in cenospheres content from 0 to 50 vol % forx the conventionally sintered composites. For the microwave sintered composites, the CTE of the composites decreased as the cenospheres content from 25.6 to 3.6 x 10- 6/0C which is much lower than the conventionally sintered samples by 51%. The microwave sintered composites showed lesser erosion loss by about 12-15% compared to conventionally sintered samples. The slide wear data shows that conventionally sintered samples has higher slide wear losses compared to conventionally sintered ones by about 86%. The Flexural strength of the conventionally sintered composites was seen decreasing from 52 to 8.8 MPa while Flexural strength of microwave sintered composites were decreasing from 71.9 to 31.5 MPa with increase in cenospheres content from 10 to 50 vol %. MW sintered was better by about 40% in Flexural Strength compared to the conventionally sintered composites. The Compression strength of the composites containing Cenospheres from 10 vol. % to 50 vol. % was found to decrease from 140.3 to 71.7 MPa with the increase in Cenospheres content, for microwave sintered samples. For the conventionally sintered composites the strength reduced from 140.3 to 71.7 MPa. The compressive strength of microwave sintered samples was more by 17.4 % compared to the conventionally sintered samples. Aluminium metal matrix composites can be fabricated through powder metallurgy route sintered in microwave sintering which is found to be adoptive & effective rapid sintering method. It is possible to fabricate Aluminium Cenospheres ‘Syntactic Foams’ through powder metallurgy microwave sintering and the properties for the same match with those materials for applications in automotives.