http://localhost:8080/xmlui/handle/123456789/388 Sun, 26 Apr 2026 08:51:36 GMT 2026-04-26T08:51:36Z http://localhost:8080/xmlui/handle/123456789/3466 Title: Studies on microstructural and mechanical properties of Ti-15V 3Al-3Cr-3Sn electron beam and gas tungsten arc welds Authors: VAMSI KRISHNA, KARNI Abstract: The main aim of the current investigation was to study the microstructural features and mechanical properties, such as hardness and tensile strength of Ti-15V-3Al-3Cr-3Sn (Ti-15-3) weldments created through electron beam welding (EBW) and gas tungsten arc welding (GTAW) at varying welding speeds. Additionally, investigated the effect of Nickel (Ni) and Silicon (Si) modified fillers on microstructural and mechanical characteristics of Ti-15-3 welds during GTAW. The studies made on weldments in as-welded and post-weld heat treatment (PWHT) conditions. Ti-15-3 alloy sheets of 3mm thickness received in the form of solution treated condition, were used in the present investigation. Autogenous full penetration bead-on-plate EB welds (by varying welding speeds - 500, 700, and 800 mm/min) and GTA welds (by varying welding speeds - 15, 20, and 25 cm/min) were made on coupons. In order to obtain complete penetration several initial trails were made with varying heat input in both welding processes. Also, welds prepared using Ni and Si modified fillers on Ti-15-3 coupons by GTAW. The varying compositions of prepared fillers are Ti-15-3-xNi (x = 0.15, 0.3, 0.5) and Ti-15-3-xSi (x = 0.15, 0.3, 0.5), respectively. Tensile test specimens were fabricated by electric discharge machining (EDM). Few tensile test specimens were subjected to a PWHT of pre-aging at 300°C for 4 h, followed by aging at 500°C for 7 h in vacuum atmosphere and furnace cooled to room temperature. Microstructural observations were made by light microscope, scanning electron microscope (SEM) and transmission electron microscope (TEM). Mechanical properties were made by hardness and tensile testing. Hardness was measured across the weldments. Tensile tests were carried out on transverse weld samples at room temperature. The fractured surfaces of tensile tested samples were examined in a SEM. The microstructure of the fusion zone (FZ) in the as-welded condition, revealed a coarse columnar β grains and the heat-affected zone (HAZ) displays coarse equaixed β grains in both EB and GTA welds. Conversely, the base metal (BM) retains fine equaixed β grains across all welding speeds in both welding conditions. The average width of the fusion zone (FZ) decreased with an increase in welding speed in both cases, primarily due to reduced heat input and increased cooling rates. The EB welds produced at a higher welding speed of 800 mm/min iii resulted in greater ultimate tensile strength (UTS) at 751 MPa and increased hardness at 245 HV, surpassing the values obtained from welds produced at a lower welding speed of 500 mm/min, with UTS at 670 MPa and hardness at 235 HV. A similar trend has been observed in welds made subjected to GTAW. The GTAW welds prepared at a higher welding speed (25 cm/min) exhibited superior UTS of 654 ± 5 MPa and hardness measuring 240 HV, surpassing the performance of welds produced at a lower speed (15 cm/min), which had a UTS of 593 ± 5 MPa and hardness of 230 HV. The enhanced strength observed at the higher welding speed can be attributed to the reduced width of columnar β grains and the development of equiaxed grains at both the weld root and center in both welding conditions. The welds after PWHT exhibited a significant rise in UTS and hardness but expense of ductility. However, this increase in UTS and hardness attributed to the presence of uniform α precipitates within the β matrix, as confirmed by TEM analysis. Microstructural examination of welds with Ni and Si modified fillers revealed equaixed grains and refined prior-β grains and characterized by nonlinear grain boundaries within the FZ. The welds prepared using Ti-15-3-0.5 Ni filler exhibited a yield strength (YS) of 688 ± 6 MPa, UTS of 721 ± 5 MPa, and % elongation (%El) of 9 ± 0.5% and Ti-15-3-0.5 Si filler (YS = 693 ± 6 MPa, UTS = 725 ± 5 MPa, %El = 8 ± 0.5%) showed higher strength compared to autogenous weld (YS = 575 ± 4 MPa, UTS = 597 ± 4 MPa, %El = 11 ± 0.5%). The increased strength in welds produced using Ti-15-3-0.5 Ni filler and Ti-15-3-0.5 Si filler can be ascribed to the reduced columnar width of β grains and the development of equiaxed grains within the FZ. A significant enhancement in both UTS and hardness were evident in samples that underwent PWHT of weldments, as compared to the as-welded specimens. Description: NITW Sun, 01 Jan 2023 00:00:00 GMT http://localhost:8080/xmlui/handle/123456789/3466 2023-01-01T00:00:00Z http://localhost:8080/xmlui/handle/123456789/3465 Title: Investigations on the Applicability of Pressure Slip Casting and 3D Printing for Alumina (Al2O3) and Aluminum Titanate (Al2TiO5) Systems Authors: RAJU, P Abstract: Since the previous few decades, researchers have tried to increase fracture toughness and microstructure modification in an effort to address the issue of ceramics intrinsic brittleness, which has limited its use in structural applications. Researchers have looked into how ceramic materials can be altered so that one or more mechanisms can be activated to improve the desired properties. Every facet of a ceramic component’s material performance is governed by the processing history, the inherent material qualities, and other variables. Colloidal forming is a common technique for shaping ceramics because it has the advantages of increased uniformity, densification at lower temperatures, and flexibility in complex design. The goal of the current study was to create oxide-based ceramic products using various ceramic processing techniques in order to achieve the necessary complicated shapes and densification levels for best mechanical properties. Pressure slip casting is a technique known in table ware industry for producing near net-shaped green bodies with shorter processing cycles and very good consistency. Of-late, the possibility of utilizing the pressure slip casting technique for making advanced ceramic components started being looked at to exploit the advantages associated with it such as the higher green densities, near net shaping, consistency and the productivity. The preparation and control of stable, well-dispersed ceramic slip is considered as key parameter to achieve the desired properties in the green bodies. An emerging preparation method for pressure-assisted casting of advanced ceramics allows for the use of colloidal slips during pressure-based shaping. In addition to good homogeneity, outstanding green density, strength, and high productivity, the application of pressure allows for flexibility in the formation of complex structures. The current study contrasts the methods used to prepare alumina green bodies, including conventional slip casting (CSC), pressure slip casting (PSC), and cold isostatic pressing (CIP). Additionally, the ceramic products were created using ceramic 3D printing and contrasted with colloidal techniques such as CSC, PSC, and CIP. Corresponding mechanical properties of the dense ceramics were also characterised, along with their microstructural characteristics. For this purpose, both the polymer based and Plaster of Paris moulds were fabricated by designing to cast objects in the standard shapes of a cylindrical disc ϕ 80 mm, square of 60 mm, and a spherical ball of ϕ 60 mm. Present work has been undertaken with a focus on studying the shaping of Al2O3 and its combinations by pressure slip casting process and understanding the results in comparison xi with that of the conventional slip casting method. Aluminum Titanate (Al2TiO5) and Alumina (Al2O3) products are prepared from powder state in a variety of proportions and to optimise slip preparation for appropriate rheological behaviour and colloidal ceramic processing processes (CSC, PSC). The same initial alumina powder produced by mixing powders with two different average particle sizes (7 µm and 1.43 µm) in the ratio of 65:35 was utilised in all three operations because to the fixed pore size of the mould. The average particle size (d50) of the mixture HM-mix powder is 3.18 µm. The optimization of slip/slurry has been done with solid loadings varying from 65% to 80% along with rheological behaviour of shear thinning which is required in pressure slip casting for better consolidation. The shear thinning behaviour that is a necessary characteristic in the development of casts is demonstrated by the rheological data stress-exponent n=0.5. The plot unequivocally exhibits a pseudoplastic behaviour appropriate for CSC and PSC processes. Under conditions of atmospheric pressure by CSC and external pressures of up to 35 bar by PSC casts for cylindrical discs, square, and Spherical Alumina balls samples were made. According to the results of the TG-DTA experiments, the samples sintering schedules developed over time at a slow heating rate of 10°C per minute up to the final sintering temperature of 1600°C.The green densities of the discs were calculated after drying and before subjecting them for sintered schedule with the peak temperature of 1600oC.It has been observed that green densities of 65%TD at 35 bar for PSC and 66%TD at 1200 bar following CIP were achieved which is attribute to interlocking nature. However, the density of the CSC samples was only 50%TD. Flexural strength and fractographic examinations were conducted and connected with the corresponding processes. Also, the samples were sintered at 1600 °C to test their sinterability. The PSC products have a high density due to the compact packing made possible by applying pressure to the slip, which complements the enhancement of the hardness. The PSC processed samples with refined grain structure and minimal imperfections/pores is found to improve the mechanical properties such as hardness, flexural strength, and fracture toughness, which are measured to be 14.92±0.15 GPa, 294.40 ± 2.5 MPa, and 4.06 ± 0.25 MPa m1/2 respectively in comparison of conventional cast sample’s respective values of 3.73 ± 0.25 MPa m1/2, 242.70 ± 2.5 MPa, and 11.77 ± 0.15 GPa, it is clear that the mechanical properties are improved. Alumina (Al2O3) is a favoured material for wear-resistant applications due to its high mechanical as well as chemical inertness. Owing to the mechanical properties, PSC alumina is shown to have a 56% lower wear rate than CSC alumina, with a wear rate as low as 2.35×10-18 m3/Nm (with 0.5 m/sec at 5N load). Commercial repercussions in the ceramic sector xii will result from PSC alumina’s improved wear rate. Successfully demonstrated that the physic thermal properties of Alumina and Aluminum Titanate were measured for a variety of geometrical shapes. Titania and Alumina MR-01 powders were combined dry in an equimolar ratio of 1 (TiO2): 1.27 (Al2O3) and ball milled for four hours. After blending, the dry mixture was heated to between 1350 -1440 degrees Celsius for two hours soaking, in order to calcinate the powder to generate the aluminium titanate phase using the solid-state reaction pathway. The X-ray diffraction method along with line scanning of FESEM Microstructures, will be used to confirm the phase. According to the same predictions, XRD patterns and FESEM results show the confirmed phase of aluminium titanate. Alumina, titanium, and aluminium titanate all had particle size distributions of 1.43 mm, 0.5 mm, and 1.27 mm, respectively. The slips have been prepared for calcined powder of Aluminum Titanate in varying proportionate ranging from 30 - 45 wt. % Solid loadings and with additions of remaining water in order to get best way of cast in both the processes. For the 45 wt.% of solid loading its giving the better required rheological behaviours and measured shear rate exponent around 0.5. The observed green, sintered densities in the cases of 3D-printed AL and AT ceramics are in the ranges of 55-57% and 65-70% of theoretical density, respectively. It is reported that the Al2TiO5 containing sintered samples made by CSC and PSC have a low thermal expansion coefficient. PSC, with a value of 1.88 × 10-6 K-1, and CSC, with a value of 2.20×10-6 K-1, have the lowest thermal expansion coefficients at 1100 °C and also the samples of sintered materials by 3D printed with a value of CTE is 2.58 ×10-6 K-1. Description: NITW Sun, 01 Jan 2023 00:00:00 GMT http://localhost:8080/xmlui/handle/123456789/3465 2023-01-01T00:00:00Z http://localhost:8080/xmlui/handle/123456789/3464 Title: DEVELOPMENT OF HIGH STRENGTH Mg-Ni-Gd AND Mg (Ni, Zn)-Gd-Li ALLOYS Authors: RAVIKANTH REDDY, C. Abstract: Mg-alloys, in spite of being the lightest structural metal, finds sparse industrial application due to low strength resulting from dismal values of critical resolved shear stress (CRSS) coupled with poor workability caused by its hcp structure devoid of sufficient independent slip systems. Grain refinement, alloying additions, and synthesizing composites aid in boosting mechanical properties. It is known that the Li addition to magnesium improves the formability of the alloy but at the cost of diminishing strength. The addition of transition elements along with rare earth elements formed a new type of phases called long period stacking ordered (LPSO) phases that effectively improved the strength without compromising the ductility of the alloys. Hence, in this thesis, efforts were made to synthesize low-density, high-strength, and ductile Mg-alloys using Li, Ni, Zn, and Gd as alloying elements via different processing routes, i.e., casting and powder metallurgy. Ni and Gd were selected as alloying additions due to their prolificacy towards forming LPSO phases. The effect of Li on the microstructural and mechanical properties of Mg-0.5Ni 2.5Gd (at. %) alloy was studied by varying Li content, from 0-25 at.%. The alloys were processed through casting in vacuum induction melting furnace and then hot extruded. In as-cast state, a eutectic phase consisting of α-Mg and Mg3Gd phase is present along the dendritic boundaries of α-Mg, Mg3Gd, and LPSO phases. In addition, high Li-containing alloys such as 15 and 25 at. % Li alloys contain β-Li phase as well, and its volume fraction is a direct function of Li content. The volume fraction of the LPSO initially increases up to 5 at. % Li and subsequently reduces. Extrusion at 400 ℃ led to grain size refinement due to dynamic recrystallization, eliminating the dendritic and eutectic network and forming lamellar LPSO/ blocky LPSO and Mg3Gd particles. High yield strength of 302 MPa, ultimate strength (UTS) of 347MPa, and 5% elongation was achieved in the 5 at. % Li alloy whereas a YS of 167 MPa, UTS of 188 MPa, and a tensile ductility of 37.5% were attained in 25Li alloy. To further enhance the precipitation/formation of LPSO phases even at high Li contents of 15, 23, and 30 at. %, a small amount of Zn was added, which induced formation of lamellar LPSO phases in 15 and 23 at. % Li alloys, whereas some blocky LPSO phase fraction was observed in the 30 at. % Li alloy. The alloys were cast, and solutionized at 510 ℃ for 48 h, which increased the amount of the LPSO phase compared to the cast alloys. Hot extrusion at 200 or 300oC led to viii dynamic recrystallization of matrix grains and refinement and uniform distribution of LPSO and Mg3Gd phases. A high UTS of 320 MPa and 18% elongation is attained with 15Li alloy extruded at 200 ℃. The alloys extruded at 200 ℃ performed better than the ones extruded at 300 ℃ due to the fine grain size and uniformly distributed second-phase particles. 30Li alloys exhibited initial strain hardening and after a critical amount, strain softening behavior at both the extrusion temperatures. This can be attributed to the dislocation annihilation by a dynamic recovery, owing to the presence of soft β-Li phase and lack of sufficient distribution of precipitates in the matrix. This investigation aims to achieve a YS of >600 MPa for a magnesium alloy. Introducing thermally stable and coherent secondary phases would boost the strength at elevated temperatures. A master alloy comprised of Ni and Gd was cast, and the compositions of Mg98.82Ni0.59Gd0.59 and Mg97.56Ni1.22Gd1.22 (at. %) were formulated using ball milling for 150 hours. Consolidation through sintering with 5, 7, and 9 h of exposure at 550 ℃ and subsequent extrusion at 500 ℃ resulted in the formation of Mg5Gd, Mg2Ni, Gd2O3 and MgO phases. The extruded samples possessed a high strength of 804 MPa and 3.75% elongation which can be attributed to ultra-fine grains and dispersoid strengthening by homogeneously distributed second-phase particles in the 100–200 nm range. The development of a high-specific strength Mg alloy has been attained via different processing routes and an exhaustive evaluation of the microstructure and mechanical properties has been carried out. Description: NITW Sun, 01 Jan 2023 00:00:00 GMT http://localhost:8080/xmlui/handle/123456789/3464 2023-01-01T00:00:00Z http://localhost:8080/xmlui/handle/123456789/951 Title: Synthesis of Borides Powder and Deformation behavior of Boride based Composites Authors: Gadakary, Saikumar Thu, 01 Jan 2015 00:00:00 GMT http://localhost:8080/xmlui/handle/123456789/951 2015-01-01T00:00:00Z