Ritwik Basu

Microstructural investigation on marforming and conventional cold deformation in Ni–Ti–Fe-based shape memory alloys

Abstract A hot-rolled Ni–Ti–Fe alloy was subjected to 50% cold rolling by laboratory rolling mill and was subsequently annealed at 800°C for 1.5 h. This sample was then deformed through another 10% reduction in thickness by two different routes (i) conventional cold rolling and (ii) marforming (rolling in liquid nitrogen) followed by annealing under identical conditions. The grain refinement during normal cold rolling was attributed to relatively large presence of dislocations in the ND // <110> grains in the starting microstructure. The regions of higher dislocation densities became gradually textured to ND // <111> orientation, with cold rolling. Marforming (deformation in liquid nitrogen following phase transformation) on the other hand led to more significant grain refinement and also change in the bulk texture. The objective of this study was to compare the grain refinement and microstructural modification produced through marforming with that obtained in conventional cold deformation.

Microstructural Aspects of TIG and A-TIG Welding Process of Dissimilar Steel Grades and Correlation to Mechanical Behavior

Abstract The present study reports microstructural characteristics of two grades of steels, stainless steel (SS 304) and carbon steel welded using tungsten inert gas (TIG) and activated flux-TIG (A-TIG) processes. Activated fluxes such as TiO2, ZnO and MnO2 are effective for A-TIG welding of dissimilar weld between carbon steel to stainless steel. Mechanical properties, joint efficiency of A-TIG welds are found to be higher than normal TIG Welds. This study attempts to establish a correlation between observed mechanical behavior (hardness and strength) and the microstructural characteristics of the weld samples. Significant differences in microstructures are recorded in terms of grain size, local misorientation, grain and phase boundary characteristics in distinct regions of the welded samples. The microstructural observations exhibit: (1) the presence of Widmanstatten ferrite structure at the heat affected zone of the carbon steel part in the A-TIG welded specimen and (2) differences in structure at the interface of stainless steel and weld metal region under the two conditions of welding. These structures are morphologically different and shows differences in the number fraction of 45° <114> phase boundary orientation relationship. The microstructure also displays significant heterogeneity in grain size and grain misorientation.

Vortex Pinning Properties of Dense Ti-Doped MgB 2 Bulks Sintered at Different Temperatures

We have studied the trapped field by field-cooled magnetization and microstructure of the Ti-doped MgB₂ bulks fabricated at 700°C by an in situ hot isostatic pressing method, which were compared with those at 900°C. The maximum trapped field B_T of 3.0 T at 19 K was realized at the Ti-doping level of 10%-20%. In spite of the lower filling factor of 700°C Ti-doped bulks, i.e., f ~80%, the obtained B_T = 3.0 T was 1.3 times larger than that of the nondoped bulk (f ~ 90%) and was comparable with those for the 900°C Ti-doped bulks (f ~ 90%) with the same Ti contents. The quantitative analysis of the chemical composition revealed that fine particles of higher borides, i.e., MgB_y (y > 2), existed in the MgB₂ matrix. The low sintering temperature of 700°C and the Ti doping strongly suppressed the grain growth of the MgB₂ matrix. The increase in both the grain boundaries of MgB₂ and the nonsuperconducting fine particles enhanced the trapped field of the present 700°C Ti-doped MgB2 bulks.

Marforming: A Novel Method for Grain Refinement in Ni-Ti Based Shape Memory Alloys

The study presents a comparative evaluation on microstructural modifications of a ternary Ni―Ti―Fe alloy deformed through two different routes of deformation through equal reduction in thickness. These deformation modes were (1) conventional cold rolling and (2) marforming (rolling in liquid nitrogen). The final annealing treatments were kept identical for both processes. Considerable differences in microstructures were brought out through aforementioned deformation modes. Marforming of the alloy led to significant grain refinement as against conventional cold rolling, revealed through electron backscattered diffraction (EBSD) studies.

Influence of Chloride Ion and Temperature on the Corrosion Behavior of Ni‐Fe‐Cr Alloy 028

Recently, the working condition of tubing systems used in oil and natural gas industries are severer than before with the increasing exploitation of acidic gas fields. The corrosion problems induced from the corrosive environment with chloride ion medium and high temperature have been much more concerned. The presence of chloride ion can accelerate the dissolution of metals. The corrosion performance is also sensitive to the operating temperature. Classic localized corrosions such as the pitting or the crevice type due to environmental temperature and chloride ion.