Papers by Author: Parameshwar Prasad Sinha

Abstract: Copper - multiwall carbon nanotubes (MWCNT) composite was processed by powder metallurgical processing technique. Pure copper powder and MWCNT were mechanically alloyed by high energy milling to produce Cu-MWCNT composite powder. The composite powder was subsequently consolidated by vacuum hot pressing. Characterization studies were conducted along axial (hot pressing direction) and radial (transverse) directions. Microstructural observations of the processed composite revealed random distribution of MWCNT in axial direction and aligned distribution in radial direction. The structure property correlation was established and it revealed certain degree of anisotropy in mechanical and electrical properties of the composite.

Abstract: Investment casting has emerged as the foremost casting process for manufacturing of intricate parts where better dimensional accuracy is required. Use of rapid prototyping polymer patterns is one of the major advancements in investment casting process. Elimination of die making step as required in the traditional wax process makes it quicker and a cost effective process. The direct conversion of 3D CAD data into rapid prototyping pattern decreases development time, chances of costly mistakes, minimizes sustaining engineering changes and extend product lifetime by adding necessary features and eliminating redundant features early in the design.

Abstract: In the present study, thermal treatments for homogenizing cast structures of Al-Cu-Li alloy AA2195 for improved workability are developed chiefly by empirical methods and detailed Differential Scanning Calorimetry (DSC) and microstructural characterization. DSC has been carried out on as-cast samples to establish the homogenization temperatures and avoid incipient melting. Homogenization time has been calculated empirically and microstructural characterization and DSC has been carriedout to after each cycle to validate the empirically established homogenization cycle. Homogenization cycle (435°C/8hrs+495°C/12hrs+525°C/32hrs) has been established for AA2195 alloy having an average grain size of 500μm based on calorimetric studies and microstructural examination.

Abstract: Al-Cu-Mg (Russian grade V65) alloys are used for riveting applications in aerospace industries due to relatively high shear strength of the order of 25 kg/mm² combined with a high plasticity. The main advantage of using V65 aluminum alloy for rivet application comes from its significantly slower natural aging response, which gives flexibility to carryout riveting operation even after 4 days after solution heat treatment and natural aging at room temperature. This very valuable feature is not found in its counterpart alloy AA2024 where due to rapid aging kinetics of this alloy, the riveting operation must be completed within 30 min of the solution treatment, which is many times impractical. This paper presents the processing of V65 aluminium alloy by Direct Chill (DC) casting followed by subsequent secondary processing through extrusion and forging to realize feedstock for caliber rolling. These ingots were caliber rolled to 12 mm diameter rods at different temperatures and mechanical properties were evaluated in T6 and T4 tempers. Detailed microstructural examination using optical microscopy and fractography of the tensile tested samples using scanning electron microscopy were carriedout to correlate microstructure and mechanical properties.

Abstract: A novel technique of pure Lithium addition has been adopted for the processing of Al-Cu-Li alloy AA2195 cast ingots (7-8 kg each) in VIM under dynamic inert atmosphere, which gives more than 95% recovery of Lithium. The cast billets were homogenized, forged and converted into 12mm diameter rods by caliber rolling in the temperature range of 250°C, 300°C, 350°C and 400°C. The caliber rolled rods were treated to T8 (Solution Treatment+WQ+CW+Aging) condition. Mechanical properties were evaluated for T8 tempered bars at room temperature and correlated with microstructural observations. Highest mechanical properties in T87 temper have been obtained for rods caliber rolled at 350°C temperature.

Abstract: Missile and rocket motor cases are often fabricated by welding process. The replacement of welded hardware with the flow formed construction eliminates many problems associated with welded joints. Data on the cold workability of the material in different heat treatment conditions is essential for the flow forming of the material. The cold workability of a 0.3C-CrMoV grain refined steel processed by air melting and electroslag refining was studied in annealed and Q&T conditions through cold rolling process. The effect of heat treatment on the strength properties of the rolled materials was also studied. The observed behaviour is explained in the light of the results of the microstructural characterization.

Abstract: High yield strength and good wear resistance of hypereutectic steels in hardened and tempered condition made them attractive to manufacture rotating parts of mechanical systems. However, they suffered with poor corrosion, owing to high carbon content. The need for a material with improved strength, wear resistance and corrosion resistance for bearing application resulted in the design of a new steel having 17 wt.% Cr, up to 0.75 wt.% Mo and 1 wt.% C, which was christened as 440C. This martensitic grade of stainless steel was surface hardened by laser transformation hardening (LTH) technique using Pulsed Nd: YAG laser. Optimised process parameter could result in 300 µm thick hardened layer consisted of martensite, retained austenite and fine carbide with an average hardness of 540 VHN, while it was about 220 VHN in the core. Laser process parameter like energy/power density, pulse width, scanning speed and overlap ratio were responsible in influencing the microstructural constituents, hardness achievable and in turn dictates the wear resistance capability of the material. Experimental results such as temperature distribution, depth of hardening have been verified analytically. A reasonable agreement between the theoretical and experimental measurements was obtained. This paper highlights the details of experimental work.

Abstract: nconel 718 is an age hardenable nickel base supper alloy with high strength at elevated temperatures, and excellent creep properties. It is used extensively in turbine discs, blades where components experience elevated temperatures for prolonged duration, leading to coarsening of the microstructure. To evaluate the life of such components after prolonged exposure to service conditions, LCF properties at such large grain sizes are essential. For this purpose, low cycle fatigue (LCF) behavior of forged Inconel 718 turbine rotor disc having large grain size was studied at room temperature. Total strain controlled fatigue tests were conducted in air at ambient temperature on this alloy in solution treated and aged condition. The results indicated that the material exhibits cyclic strain softening and the cyclic yield strength is lower by 40% compared to the monotonic yield strength. The deformation takes place by multiple planar slip.

Abstract: Aluminium alloy AA 2219 has been selected for fabrication of both earth storable and cryogenic propellant tanks of launch vehicles due to its high specific strength, compatibility with liquid propellants, good resistance to stress corrosion cracking (SCC), excellent properties at cryogenic temperatures and good fabricability including weldability. Propellant tanks are fabricated by welding sheets in T87 and rings in T851 temper conditions. Microstructural characterization was carried out on the weldments with sheet-sheet and sheet-forge configuration using optical microscopy and electron microscopy with energy dispersive spectroscopy. Microstructure of weld pool had dendritic pattern, typical of weld cast structure. Fine recrystallised grains were observed near fusion line. Heat affected zone on either side of the weld revealed thickened grain boundaries. EDS on these thickened grain boundaries indicated composition of eutectic. Microhardness and tensile strength for both the configurations was evaluated. Fractures surface of tensile tested specimens were examined for fracture morphology and to understand the role of eutectic film in fracture. Presence of the eutectic film along the grain boundaries was explained with the help of liquation mechanism and Al-Cu phase diagram. This paper brings out details of the investigation carried out.

Abstract: 0.3C-CrMoV(ESR) steel is an ultra-high strength low alloy steel indigenously developed by ISRO for space applications. The steel is used in the form of rings of 2.8 m diameter also. In this paper, the effect of tempering temperature on ring rolled steel for the best combination of fracture toughness and strength properties is studied. The tensile properties and fracture toughness of the steel were evaluated in the as quenched and tempered conditions through the specimens drawn in radial direction of the ring segment. Five tempering temperatures were used in the study: 200, 450, 475, 500 and 510°C. Tensile strength of the steel showed continuous decrease with increasing tempering temperature, but yield strength increased reaching maximum when tempered at 450°C and further decreased with increasing tempering temperature. The elongation was higher for higher tempering temperature. The strain hardening exponent decreased with increasing tempering temperature. The fracture toughness test results showed that tempering between 475 and 510°C exhibited better combination of fracture toughness and strength.