Faculty Publications
Permanent URI for this communityhttps://idr.nitk.ac.in/handle/123456789/18736
Publications by NITK Faculty
Browse
Search Results
Item Rotating bending fatigue tests were carried out on austempered ductile iron containing 1.5 wt% nickel and 0.3 wt% molybdenum. The ductile iron was austenitized at 900 or 1050 °C and then austempered at 280 or 400 °C for different lengths of time to obtain different microstructures. The fatigue strength was correlated with the amount of retained austenite and its carbon content, which were both determined by X-ray diffraction technique. While the tensile strength decreased with increasing retained austenite content, the fatigue strength was found to increase. Carbide precipitation was found to be detrimental to fatigue strength. Lower austenitizing temperature resulted in better fatigue strength. © 1994 Chapman & Hall.(Kluwer Academic Publishers, Effect of microstructure on the fatigue strength of an austempered ductile iron) Shanmugam, P.; Prasad Rao, P.; Rajendra Udupa, K.; Venkataraman, N.1994Item Austempered ductile iron containing 0.9 Ni and 0.3 Mo and subject to low stress dry sand abrasive testing shows that wear behaviour is very sensitive to heat treatment conditions. It is concluded that large retained austenite content promotes wear resistance.(Inst of Engineers (India), Low stress dry sand abrasive wear behaviour of austempered ductile iron) Prasad Rao, P.1995Item An alloy containing 49 at.% aluminium was heat treated at different temperatures within the ? + ? two-phase field to get five different volume fractions of lamellar constituent. Creep studies were carried out on these samples at five different temperatures in the interval between 1023 and 1223 K, by impression creep technique using four levels of stresses at each temperature. For a given temperature and stress, steady state impression velocity decreased with increasing volume fraction of lamellar constituent. Activation energy for steady state creep increased linearly with lamellar content from 185 kJ/mol at 22 vol.% to 362 kJ/mol at 100 vol.%. The stress exponent was found to be around 1.2 in all the cases. The results show that a fully lamellar structure has a superior behaviour where creep is an important factor.(Carl Hanser Verlag, Effect of microstructure on the impression creep of two-phase titanium aluminide) Prasad Rao, P.; Swamy, K.Shivananda1995Item Ductile cast iron samples were austenitized at 927 °C and subsequently austempered for 30 minutes, 1 hour, and 2 hours at 260 °C, 288 °C, 316 °C, 343 °C, 371 °C, and 399 °C. These were subjected to a plane strain fracture toughness test. Fracture toughness was found to initially increase with austempering temperature, reach a maximum, and then decrease with further rise in temperature. The results of the fracture toughness study and fractographic examination were correlated with microstructural features such as bainite morphology, the volume fraction of retained austenite, and its carbon content. It was found that fracture toughness was maximized when the microstructure consisted of lower bainite with about 30 vol pet retained austenite containing more than 1.8 wt pet carbon. A theoretical model was developed, which could explain the observed variation in fracture toughness with austempering temperature in terms of microstructural features such as the width of the ferrite blades and retained austenite content. A plot of KIC2 against ?? (X?C?)1/2 resulted in a straight line, as predicted by the model.(Minerals, Metals and Materials Society, Dependence of Fracture Toughness of Austempered Ductile Iron on Austempering Temperature) Prasad Rao, P.; Putatunda, S.K.1998Item Heat transfer during the solidification of an Al-Cu-Si alloy (LM4) and commercial pure tin in single steel, graphite, and graphite-lined metallic (composite) molds was investigated. Experiments were carried out at three different superheats. In the case of composite molds, the effect of the thickness of the graphite lining and the outer wall on heat transfer was studied. Temperatures at known locations inside the mold and casting were used to solve the Fourier heat conduction equation inversely to yield the casting/mold interfacial heat flux transients. Increased melt superheats and higher thermal conductivity of the mold material led to an increase in the peak heat flux at the metal/mold interface. Factorial experiments indicated that the mold material had a significant effect on the peak heat flux at the 5% level of significance. The ratio of graphite lining to outer steel wall and superheat had a significant effect on the peak heat flux in significance range varying between 5 and 25%. A heat flux model was proposed to estimate the maximum heat flux transients at different superheat levels of 25 to 75°C for any metal/mold combinations having a thermal diffusivity ratio (?R) varying between 0.25 and 6.96. The heat flow models could be used to estimate interfacial heat flux transients from the thermophysical properties of the mold and cast materials and the melt superheat. Metallographic analysis indicated finer microstructures for castings poured at increased melt superheats and cast in high-thermal diffusivity molds.(Effect of superheat, mold, and casting materials on the metal/mold interfacial heat transfer during solidification in graphite-lined permanent molds) Prabhu, K.; Suresha, K.M.2004Item Effect of thermal contact heat transfer on solidification of Pb-Sn and Pb-free solders(Elsevier Ltd, 2007) Chellaih, T.; Kumar, G.; Prabhu, K.N.The effect of thermal contact heat transfer on the solidification of spherical droplets of four solder alloys, namely, Sn-37Pb, Sn-9Zn, Sn-0.7Cu and Sn-3.5Ag, was studied using SOLIDCAST simulation package. A significant drop in the arrest time was observed for increase in heat transfer coefficient from 1000 to 2000 W/m2 K. Effect of contact conductance and thermal diffusivity of solder alloys on arrest time is quantified by the power relation, ? = m(?{symbol})n where ? and ?{symbol} are defined as arrest time and heat transfer parameters, respectively. Experiments were also carried out to investigate the effect of cooling rate on solidification behaviour of the solder alloys used in simulation. The results indicated the significant effect of mould material on interfacial heat flux and metallurgical microstructure. © 2005 Elsevier Ltd. All rights reserved.