Browsing by Author "Ramesh, M. R."

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Development and Characterization of Metal Injection Moulded Components in Improving Resistance to High Temperature Wear and Oxidation
(National Institute of Technology Karnataka, Surathkal, 2019) C, Veeresh Nayak.; Ramesh, M. R.; Desai, Vijay.
Metal injection moulding (MIM) is a near-net shape manufacturing technology for producing intricate parts, cost-effectively. MIM comprises combined techniques of plastic injection moulding and powder metallurgy. A wax-based binder system consisting of paraffin wax (PW), low-density polyethylene (LDPE), polyethylene glycol (PEG-600) and stearic acid is established for MIM of powder systems of Cr3C2- NiCr (30% Wt.) +NiCrSiB (70% Wt.), SS316L (70% Wt.) +WC-CrC-Ni (30% Wt.) and Tool Steel. The excellence of the MIM product depends on feedstock characteristics, process parameters of the injection moulding stage as well as debinding and sintering stage. Injection stage is most important as many defects such as phase separation, weld line, voids etc. may occur during injection stage due to improper selection of injection moulding parameters and these defects cannot be repaired in the subsequent debinding and sintering stages. The feedstock was characterized by rheological properties at different temperatures. Injection temperature was determined by the rheological investigation of the feedstock having the 56 % powder loading and 44% binder by volume. The solvent debinding temperature is optimized and defect-free MIM component is obtained at a temperature of 48°C. Sintering process was carried out with the temperature cycle in the range of 1150–1200 °C under hydrogen purged atmosphere. The sintering density achieved was 96%. The MIM components showed good and acceptable shrinkage in linear dimensions. Material behaviour at elevated temperature is becoming an increasing technological importance. Components working at higher temperatures like in land-based gas turbines, power generation boiler tubes, hot sections of aero engine, gas and steam turbine, propulsion bearings, materials processing, and internal combustion engines are subjected to surface friction, wear, oxidation conditions. Service conditions of such components in elevated temperature environments may compromise their mechanical properties resulting in a reduced life cycle. Components working in such adverse conditions demand suitable components processed through near net shape techniques. The proposed MIM compacts are investigated for their resistance to wear and oxidation under laboratory conditions.vi Three types of MIM specimens namely Cr3C2-NiCr+NiCrSiB, SS316L+WC-CrC-Ni, and Tool Steel are characterized using Scanning Electron Microscope (SEM), Energy Dispersive Spectroscopy (EDS) and X-ray diffraction (XRD). Further, microstructure and mechanical properties were characterized to evaluate their potential for hightemperature application. Dry sliding wear behaviour of MIM specimens are evaluated using a high-temperature pin on disc tribometer. The SS316L+WC-CrC-Ni and Tool Steel MIM specimens displayed a lower coefficient of friction and wear rate in comparison with Cr3C2- NiCr+NiCrSiB. Excellent wear resistance of the MIM specimens is attributed to the solid lubricants effect. Based on the wear rate data, the relative wear resistance of the MIM specimens under dry sliding conditions is arranged in the following sequence: (Tool Steel) > (SS316L+WC-CrC-Ni) > (Cr3C2-NiCr+NiCrSiB) Higher wear resistance of MIM Tool Steel specimens is attributed to the high hardness of Cr3Ni2 phase formed during the sintering process. Thermo cyclic oxidation behaviour of MIM specimens was carried out at 700 °C for 20 cycles. Each cycle consisted of heating at 700 °C for 1 hour, followed by 20 minutes of cooling in the air. The thermogravimetric technique is used to approximate the oxidation kinetics of MIM specimens. The Cr3C2-NiCr+NiCrSiB and SS316L+WCCrC-Ni MIM specimens reported lower weight gain as compared to the Tool steel. Cr3C2-NiCr+NiCrSiB MIM specimens registered less weight gain as compared to SS316L+WC-CrC-Ni which is attributed to the excellent oxidation resistance of NiCrSiB and formation of NiCrO4 along with NiO and Cr2O3 oxides on the surface of MIM specimens. In the present study, the powders of Cr3C2-NiCr+NiCrSiB, SS316L+WC-CrC-Ni, and Tool Steel are successfully metal injection moulded and sintered to achieve 96% density. Developed MIM components exhibit resistance to high-temperature wear and oxidation which is suitable for components subjected to elevated temperature service conditions.
Effect of Laser Processing on Surface Characteristics of Magnesium Based Rare Earth Element Alloys
(National Institute of Technology Karnataka, Surathkal, 2019) Rajan, Rakesh K.; Bontha, Srikanth; Ramesh, M. R.
Magnesium (Mg) based alloys have attracted considerable interest in the biomedical field as materials for temporary implants, primarily due to their dissolution in physiological environments and absorption by the human body. However, several problems such as inadequate strength and rapid degradation must be addressed before Mg alloys can be used as bone implants. These inadequacies of Mg alloys can be addressed either by alloying or through surface modification. The first part of this work aims to develop Mg based alloys containing zinc (Zn) and rare earth elements such as gadolinium (Gd), dysprosium (Dy) and neodymium (Nd) for temporary implant applications. Three different alloys with compositions such as Mg-1%Zn-2% Gd, Mg- 1%Zn-2%Dy and Mg-3%Zn-1.5%Gd-1.5%Nd (all in wt.%) are developed via casting route and investigated for microstructure, mechanical properties, in vitro corrosion behavior and cytotoxicity. The microstructure results indicate that apart from major α-Mg phase and few binary phases, Mg-Zn-Gd and Mg-Zn-Dy alloys consist of lamellar long period stacking ordered (LPSO) phases. The in vitro degradation behavior were studied by immersion and electrochemical methods in hanks balanced salt solution (HBSS). The corrosion rate obtained from both the methods are in the order of Mg-Zn-Gd < Mg-Zn-Gd-Nd < Mg-Zn-Dy. The MTT (methylthiazoldiphenyl-tetrazolium bromide) assay study revealed that all the three alloys had no adverse effect on cells and proves the good cytocompatibility of these alloys. The ultimate tensile strength of Mg-Zn-Gd-Nd is better than the Mg-Zn-Gd and Mg-Zn-Dy alloys due to the uniform distribution of the precipitate phase. In order to tailor the surface properties of these alloys, the second part of this work proposes to understand the effect of laser surface melting (LSM) of Mg-Zn-Gd, Mg-Zn-Dy and Mg-ZnGd-Nd alloys on microstructural changes, hardness variation, wettability and in vitro degradation behaviour. Different ranges of laser energy densities have been adopted to alter the surface characteristics of all the alloys and proper correlations have been drawn with respect to the un-altered surface. The surface modified samples showed fine grain structure in the melt zone compared to the untreated substrate. The surface remelting of material at lower energy density conditions promoted the formation of micro cracks in the meltpool zone. Crosssectional microhardness was observed after laser surface melting. Hardness increase of nearly two times was observed in laser melted region due to the grain refinement and solid solution strengthening. In vitro degradation study showed clear improvement in corrosion resistance of LSM samples at certain range of energy densities. At higher energy density, removal of materials from the surface is enhanced, resulting in deeper grooves and higher surface roughness. The wettability studies indicated that the variations in surface chemical composition, grain size and surface roughness of LSM samples strongly influence the surface energy and hydrophilicity
Investigation on Elevated Temperature Adhesive Wear Behavior of Microwave Fused Thermal Spray Tribaloy Composite Coatings
(National Institute of Technology Karnataka, Surathkal, 2019) C, Durga Prasad; Joladarashi, Sharnappa; Ramesh, M. R.
Metallic materials that operate under high speed, high temperature and harsh chemical environments are prone to wear and corrosion degradation. This leads to the failure of metallic components and results in huge economic loss to industries. The amorphous alloy or metallic glasses exhibit superior properties like high hardness, good wear, and corrosion resistance. Metallic glasses eliminate an ordered crystalline structure, hinders plastic deformation. The Co-based amorphous alloy is the best example of bulk metallic glassy structure alloy and presence of primary intermetallic laves phase’s exhibits good mechanical as well as chemical properties. This is mostly employed as coatings because they are too brittle to be used in bulk form. Co-based metallic glass coating depositing on metallic materials could positively eliminate the failure of the working component caused by serious wear and erosion issues. In the present study, CoMoCrSi superalloy powder (Tribaloy-T400) comprising of a primary intermetallic laves phase of Co-rich solid solution has shown better mechanical and tribological properties. Processing of CoMoCrSi feedstock powder is carried out through a high-energy ball milling (HEBM) technique to obtain a higher volume fraction of intermetallic laves phases. The hard phases of 30% Cr3C2, WC-CrC-Ni and WC-12Co are reinforced into milled CoMoCrSi feedstock. The four different feedstock powders CoMoCrSi, CoMoCrSi+30%Cr3C2, CoMoCrSi+30%WC-CrC-Ni and CoMoCrSi+30%WC- 12Co are sprayed on pure titanium grade-15 substrate using High-Velocity-Oxy-Fuel (HVOF) and flame spray methods. The as-sprayed coatings are subjected to post heat treatment to refine their metallurgical and mechanical properties using microwave hybrid heating technique. Characterization of feedstock, as-sprayed and microwave fused coatings is done by using Scanning Electron Microscopy (SEM), Energy dispersive spectroscopy (EDS) and X-ray Diffraction (XRD). Porosity, surface roughness, microhardness, and adhesion strength of as-sprayed and fused coatings are evaluated. The substrate, as-sprayed and microwave fused coatings are subjected to elevated temperature sliding wear test against alumina disc under dry conditions. The test is carried out at 200°C, 400°C, and 600°C temperatures for 10 N and 20 N normal loads. Microwave fused coatings exhibit higher wear resistance than the as-sprayed coatings and substrate. The hard intermetalliclaves phases which are amorphous (bulk metallic glass) in nature strengthen the coatings at high temperatures. Co3Mo2Si, Co7Mo6, Mo3Si, Co3Mo, and Co2Mo3 are the intermetallic laves phases generated in CoMoCrSi feedstock during HEBM process. The coatings produced from HVOF and flame spray process exhibits heterogeneous structure by showing cracks and pores, also cohesive strength between splats is low. The microhardness and adhesion strength of as-sprayed coatings is lower than fused coatings. Microwave fused coatings exhibit homogeneous structure with less porosity, and surface roughness. The posttreated coatings reveals the inter-diffusion of atoms near substrate-coating interface region, these results in formation of metallurgical bonding leads to increase in microhardness and adhesion strength. The as-sprayed coatings exhibits higher wear rate and coefficient of friction due to lower microhardness. The worn surface of as-sprayed coatings reveals detachment of splats with severe deformation results in adhesive wear mechanism. Microwave fused coatings exhibits lower wear rate and coefficient of friction due to higher microhardness obtained from intermetallic laves phases and also formation of homogeneous structure. The fused coatings exhibits tribo-oxide layers during sliding action which is the main phenomenon for improving the wear resistance of the fused composite coatings. CoMoCrSi+WC-12Co composite coating showed better mechanical and tribological properties compared to other types of coatings.
Investigations on Characteristics and Performance of Hard Thin Films Developed by Cathodic Arc Evaporation
(National Institute of Technology Karnataka, Surathkal, 2019) Badiger, Pradeep V.; Desai, Vijay H.; Ramesh, M. R.
The fretting and adhesive wear behavior of Ti, Al and Fe based thin solid films deposited on MDN121 steel substrate are studied. Plasma-assisted cathodic arc evaporation technique is used to develop TiC-C, Ti/TiN/TiCN/TiN/TiCN, AlCN/AlC and FeCrN coatings. FESEMEDS, nanoindentation and Raman spectroscopy are used to characterize the coatings. The fretting and adhesive wear tracks are investigated using an optical profiler, confocal microscopy and electron microscopy. The diamond-like carbon (DLC) is observed in both the coatings. Developed coatings exhibit better mechanical properties with increase in hardness by 24.5 % in TiC-C and 29.4 % in Ti/TiN/TiCN/TiN/TiCN, 8.70 % in AlCN/AlC and 50.79 % in FeCrN coatings compared to the uncoated SNMG120408 WC substrate. During fretting wear analysis, TiC-C coating is exhibited lower coefficient of friction (COF) compared to Ti-multilayer coating. Similarly, FeCrN coating exhibited lower coefficient of friction (COF) compared to AlCN/AlC coating. The volumetric wear loss of TiC-C monolayer coating is better than the multilayer coating. The volumetric wear loss of FeCrN coating is better than AlCN/AlC coating. The wear surface morphology revealed abrasive form of fretting wear mechanism in all coatings whereas galling failure in the substrate. During adhesive wear analysis, TiC-C coating exhibited lower coefficient of friction (COF) compared to Ti-multilayer coating. Similarly, FeCrN coating exhibited lower coefficient of friction (COF) compared to AlCN/AlC coating. TiC-C, Ti/TiN/TiCN/TiN/TiCN, AlCN/AlC and FeCrN coatings exhibited low friction and high wear resistance. Tungsten carbide cutting tool inserts are coated with customized composition of Ti/TiCN/TiN/TiCN/TiN (multilayer), TiC-C AlCN/AlC and FeCrN (monolayer) thin films using cathodic arc evaporation technique. Quality characteristics of coatings are evaluated using calo and VDI3198 tests. Thickness of the coatings are found to be in the range of 1.1-1.8 µm and adhesion quality of HF1 is attained. Machinability of highly alloyed steel MDN431 is studied using the coatings developed on SNMG120408 inserts. The iiiperformance of coated tool inserts are evaluated using cutting speed (59-118 m/min), feed rate (0.062-0.125 mm/rev) and depth of cut (0.2-0.4 mm) as process parameters in turning MDN431 steel. Experiments are conducted based on full factorial design and regression analysis is used to analyze the cutting forces and surface roughness. Optimization of the process parameters has been done with the combination of desirability approach and PSO technique. Optimum machining condition for least cutting force and least surface roughness are obtained at the condition of Vc=118 m/min, f=0.063 mm/rev and ap=0.2 mm for Ti-multilayer coatings, Vc=59 m/min, f=0.063 mm/rev and ap=0.2 mm for TiCC coatings, Vc=75 m/min, f=0.063 mm/rev and ap=0.3 mm for AlCN/AlC coatings and Vc=118 m/min, f=0.063 mm/rev and ap=0.2 mm for FeCrN coatings. ANN modeling has been adopted in order to improve the coefficients of determination (COD) and capability of predictive regression models. ANN trained model and mathematical regression models predict the responses, which follows the experimental data with minimum absolute error. The predicted results are validated with minimum error and developed models are adequate for further their usage. Tool wear was reduced by 3 times in Ti-multilayer, 3 times in TiC-C, 3.62 times in AlCN/AlC and 1.63times in FeCrN coated tools compared with commercially available uncoated WC-Co inserts (SNMG120408).
Studies on End Milling of Maraging Steel Using Cryogenic Treated and PVD Coated Cemented Carbide Inserts Under Dry
(National Institute of Technology Karnataka, Surathkal, 2019) Varghese, Vinay; Ramesh, M. R.; Chakradhar, D.
Maraging steel MDN 250 is an ultra-high strength steel which is developed to meet the large demand for high strength materials. The high strength of maraging steel is due to the precipitation of intermetallics during aging. Maraging steel finds wide applications in tool dies, a piston rod in heavy vehicles, rocket parts etc. The high strength combined with good hardness makes maraging steel difficult to machine material. Excessive tool wear, high heat generation, high power consumption, larger cutting forces, poor surface quality and/or difficulties in chip formation are some of the difficulties faced while machining difficult to cut materials. It is difficult to overcome these difficulties by the use of conventional cutting methods and tool materials. As the conventional cutting tools cannot withstand the high cutting temperature and cutting forces and results in tool wear while machining these difficult to cut materials. This early failure of cutting tools reduce the surface finish, increase the idle time and production cost. Some of the techniques used to overcome these difficulties are cryogenic treatment of cutting tools, coating of cutting tools, using sustainable cutting fluids like cryogenic liquid nitrogen etc. The cryogenic treatment is a new technique which improves the physical and mechanical properties of existing cutting tool in the most economic and sustainable way. It is reported that cryogenic treatment can improve some of properties of cutting tool like tool life, micro hardness, wear resistance, fatigue life, rupture strength and compressive residual stress. The cryogenic treatment use liquid nitrogen at -196°C for cooling the samples to cryogenic temperature and generally held for 24 hours to improve the properties of cutting tool. The present study investigates the effect of cryogenic treatment of cemented carbide (WC-Co) inserts at the different soaking period of 18 h (CT-18), 24 h (CT-24) and 32 h (CT-32) at a sub-zero temperature of−196 °C. The cryogenically treated inserts exhibited higher tool life, better surface finish and lower cutting forces during machining at different spindle speeds. The optimum soaking time for cryogenic treatment of WC-Co inserts is found to be 24 h (CT-24) beyond which there is no improvement in microhardness and wear resistance. However, as the spindle speed increased the effect of cryogenic treatment diminished. Hence the machining performance of cryogenic treated WC-Co inserts at a soakingvi period of 24 hours under three different environment of dry, wet and cryogenic has been investigated. The machining performance and tool life extended under cooling environments and highest tool life and machining performance is found to be during cryogenic machining. Coatings on the cutting tools are one of the outstanding strategies developed to avoid the difficulties in machining like rapid tool wear and lower tool life. A large number of PVD coatings are developed for the milling operations to have better performance. Aluminium and silicon based coatings find most promising applications in the end milling. Thus aluminium based coatings like AlTiN and AlCrN coatings synthesized by cathodic arc deposition (CAD) and silicon nitride based coatings like TiSiN and TiAlSiN synthesized by magnetron sputtering were studied for end milling performance. The coated tool along with the use of cutting fluid can minimize the tool wear and extend the life of the cutting tool. Also considering the environmental hazards, operator safety, recycling, and the disposal issues, use of conventional cutting fluids should be minimized. The liquid nitrogen is used in the experiment as nitrogen is abundant in the atmosphere and causes a rapid reduction in cutting temperature and quickly evaporates into the atmosphere. The tool life is maximum using AlCrN coated tool (125 min) compared to cryogenic treated and other coated tools at a spindle speed of 270 rpm under cryogenic environment. AlCrN > TiAlSiN > AlTiN > TiSiN > CT-24 is the order of tool life of cutting tools.