Papers by Author: T.K. Sahoo

Abstract: Miniature specimen techniques viz. small-punch tests (SPT) have been carried out at room temperature in order to correlate the microstructural degradation of 2.25Cr-1Mo steel with that of SPT parameters. Microstructural degradation of this steel has been introduced as a result of thermal ageing corresponding to Larson-Miller parameters (LMP) values of 33,012, 35,402, 37,846 and 38,374. SPT parameters viz. total area and area under the region of plastic instability of the load-displacement curve have been found to decrease with an increase in LMP values. A strength parameter viz. UTS obtained using uniaxial tensile tests has also been found to decrease with an increase in LMP values. The results indicated that miniature specimen techniques viz. small-punch test could be successfully used to assess the degradation of microstructures in 2.25Cr-1Mo steel generated due to their exposure to high temperatures.

Abstract: Deformation of Titanium alloys close to optimal superplastic condition i.e. near superplastic regime of deformation leads to significant change in microstructures.VT-9 titanium alloy was used in order to find out those parameters of microstructure which are varying significantly during near superplastic regime of deformation. Tensile tests were carried out at 930°C up to fracture with a constant strain rate of 5*10^-4 s^-1 and a jump wise varying strain rate of 1*10^-4 s^-1 & 5*10^-4 s^-1 .The microstructural parameters of both air-cooled and water quenched portion i.e. size of alpha phase, percentages of alpha phase and parameter of non-uniaxiality of alpha phase were found to change significantly during near superplastic regime of deformation. It has been found that in the near superplastic regime of deformation percentage of α-phase decreased from 90% to 13%. As the β-transus temperature of this alloy is 970°C, this significant change in percentage of α-phase is attributed to deformation induced phase transformation. Optical microscopes, micro Vickers hardness test, XRD, FESEM have been used to characterize the microstructure of the material.

Abstract: The present paper investigates the effect of microstructural variations upon the wear properties of 2.25Cr-1Mo steel using a dry sliding wear test. Optical, Scanning and Transmission Electron Microscopy (TEM) together with Energy Dispersive X-ray analysis (EDX) have been used to characterize the microstructures and identify the evolution of various precipitates in terms of their shapes, sizes and morphologies. The wear behavior of this steel was investigated using a disc-on-roller multiple wear tester under dry sliding conditions, rubbing against EN-31 steel. Samples were tested at 100N load and 500rpm sliding speed at room temperature. A decrease in wear loss was measured continuously for up to one hour for all the samples. The results indicated that the wear behavior of this steel was highly influenced by microstructural variations taking place during service exposure. The precipitation of globular Cr- and Mo-rich carbides has been found to improve the wear behavior of this steel at room temperature. Scanning Electron Micrographs (SEM) of worn surfaces have been used to correlate the results obtained