Papers by Author: Brajendra Mishra

Abstract: This study deals with the evaluation of self-healing ability of conducting polymer corresponding to a corrosion process. Poly ortho-anisidine (PoA) was doped with Phosphomolybdic acid (PMA) and Tungstosilicic acid (TSA) and incorporated in polyvinyl butyral (PVB) coatings. The self-healing abilities of coatings were evaluated using open circuit potential (OCP) in 0.1 M NaCl solution for 45 hours of immersion. The coatings containing doped PoA showed increased positive potential of OCP after 45 hours of immersion as compare toblank PVB which showed a constant profile of OCP over the time indicating uniform corrosion under the coating.Thermogravimetric analysis (TGA) showed that PoA doped with TSA is more stable and more effective in the coating. High resolution Transmission Electron microscopy (HR-TEM) and Energy dispersive x-ray spectroscopy (EDX) confirms the doping of PoA.

Abstract: In the present study, corrosion behavior of a diffusion bonded interface formed between micro-duplex stainless steel (MDSS) and a mixed titanium alloy (Ti6Al4V) formed at 900°C for 60 minutes under 4MPa uniaxial pressure in vacuum has been investigated in 1M HCl and 1 M NaOH solutions using various electrochemical measurements such as Equilibrium Potential (EP), Electrochemical Impedance Spectroscopy (EIS) and Potentiodynamic Polarization (PD). For comparison, corrosion behavior of base metal alloys, MDSS and Ti6Al4V have also been also characterized. Bonded interface has been characterized in light optical microscopy and scanning electron microscopy using back scattered electron. The layer wise σ phase and λ+FeTi phase mixture has been observed at the bond interface and the bond tensile strength and shear strength were ~556.4MPa and ~420.2MPa, respectively. The corrosion rates of the bonded joint are intermediate to the corrosion rates of MDSS and Ti6Al4V alloy.

Abstract: The purpose of this investigation is to develop the nondestructive tools for microstructure assessments in carbon alloyed steels. The role of carbon in steel and its effects on electromagnetic property and also the free electron model have been reviewed. The fundamental electromagnetic principle behind low frequency impedance measurements has been included. The systematic analysis of phonon vibration and ultrasonic resonance spectroscopy for elastic wave perturbation in T22 Cr-Mo steel has been presented. A brief examination of nondestructive microstructure evaluation techniques has been described. The induced microstructure variations in Grade T22 Cr-Mo steel, including the correlations of changes in physical (microstructure) and mechanical (hardness data) properties during annealing have been measured. The explanations of aged carbide precipitates, martensitic and pearlitic nucleation and growth have been illustrated. The possibility of simultaneous use of two nondestructive wave techniques is discussed. The electron model and electron interactions are associated and are shown to support the results of low frequency impedance measurements enhanced elastic wave perturbations.

Abstract: Ti6Al4V titanium alloy has been characterized for its prospective applications as an implant material. The surface treatments performed have brought about enhanced surface properties of these alloys and have produced corrosion resistant oxide films with increased bioactive properties. Characterization of the alloy surface has revealed the presence of a duplex oxide structure over the surface treated specimens, composed of an inner barrier layer and an outer porous layer. The inner barrier layer has imparted a high corrosion resistance to the alloy while the outer porous layer which is responsible for the increased roughness of the surface treated alloy specimens, has encouraged formation and deposition of apatite into the oxide pores and further resulted in an increase in cell adhesion over the alloy surface. Anodization and heat treatment procedures have proved advantageous to titanium alloys in terms of producing oxide films that can offer these alloys an improved biological performance.

Abstract: High power pulsed magnetron sputtering (HPPMS) is an emerging thin film deposition technology that generate high ionization plasma by applying a very large amount of peak power to a sputtering target for a short period of time. HPPMS is also known as High Power Impulse Magnetron Sputtering (HiPIMS). However, HPPMS/HiPIMS exhibits decreased deposition rate as compared to continuous dc magnetron sputtering. Modulated pulse power (MPP) magnetron sputtering is an alternative HPPIMS deposition technique that overcomes the rate loss problem while still achieving a high degree of ionization of the sputtered material. In the present work, the principles and some important characteristics of MPP technology were presented. Technical examples of CrN coatings were deposited using MPP and continuous dc sources. The positive ion mass distributions were characterized using an electrostatic quadrupole plasma mass spectrometer. The structure and properties of MPP and dc CrN coatings were characterized using x-ray diffraction, scanning electron microscopy, nanoindentation tests, and ball-on-disc wear test. It was found that the MPP CrN coating exhibits denser microstructure and improved mechanical and tribological properties as compared to the dc CrN coating.

Abstract: Thermoelectric power coefficient measurement techniques have been developed for numerous applications to guarantee material integrity by providing a non-destructive electronic property correlation to material microstructure, phase stability, specific solute additions, and lattice strain. How the electron concentration, the effective mass, and the dominating scattering mechanisms allow for non-destructive evaluation of materials will be described. Because thermoelectric power (TEP) is dependent upon numerous variables, additional non-destructive techniques are necessary to further characterize or classify the material or weldment. The concept of an electronic metallography laboratory is developed using additional collaborative NDE technologies.

Abstract: TiC/a:C nanocomposite thin film has proven to be a worthy material selection as a thin film for tribological applications due to its low coefficient of friction, good wear resistance and high hardness. In the current study TiC/a:C thin films with carbon concentration near 55-62 at % were deposited via pulsed closed field unbalanced magnetron sputtering (P-CFUBMS) in pure argon atmosphere with different substrate bias voltages and onto 440C stainless steel substrate with different substrate roughness. It was found that the TiC/a:C film hardness and elastic modulus were increased from 18.5 GPa to 33.8 GPa by increasing the substrate bias from floating to -150 V. However higher substrate bias can also decrease the film tibological properties. The substrate roughness has a strong effect on TiC/a:C film wear behavior. When the Ra (Mean surface roughness values) is less than 110 nm, the COF values are in low range (0.18-0.28). Further increase the Ra value to above 300 nm will result in a higher COF (>0.33). Films deposited on higher surface roughness substrate need longer time to reach the sliding equilibrium state.

Abstract: Thermoelectric power has demonstrated a capability for rapid hydrogen assessment and can achieve the equivalent of the pressure-composition-temperature (activity) diagram. Effective use of hydrogen storage materials occurs in the alpha+beta two-phase region of the activity diagram. A thorough assessment of the content of each phase in this two-phase region can optimize the performance of hydrogen storage materials. The use of thermoelectric power measurements as a hydrogen sensor for reversible batteries is discussed.

Abstract: Ti–B–C–N and Ti–Si–B–C–N nanocomposite coatings were deposited on AISI 304 stainless steel substrates by DC unbalanced magnetron sputtering from two (80mol% TiB2–20mol% TiC and 40mol% TiB2–60mol% TiC) composite targets in various Si target powers. The relationship among microstructures, mechanical properties, and tribologiacal properties was investigated. The synthesized Ti–B–C–N and Ti–Si–B–C–N coatings were characterized using x–ray diffraction (XRD) and x–ray photoelectron spectroscopy (XPS). These analyses revealed that the Ti–Si–B–C–N coatings are nanocomposites consisting of solid-solution (Ti,C,N)B2 and Ti(C,N) crystallites distributed in an amorphous TiSi2, SiC, and SiB4 matrix including some carbon, BN, CNx, TiO2, and B2O3 components. The addition of Si to the Ti–B–C–N coating led to percolation of amorphous TiSi2, SiC, and SiB4 phases. The Ti–Si–B–C–N coatings exhibited high hardness and H/E values, indicating high fracture toughness, of approximately 35 GPa and 0.098, respectively. Furthermore, the Ti–Si–B–C–N coatings exhibited very low wear rates ranging from ~3×10-7 to ~16×10-7 mm3/(N·m). The minimum friction coefficient of the Ti–Si–B–C–N coatings was approximately 0.15 at low Si target power between 25W and 50W. A systematic investigation on the microstructures, mechanical properties, and tribological properties of Ti–Si–B–C–N coatings prepared from two TiB2–TiC composite targets and one Si target is reported in this paper.

Abstract: The paper will present the methodology used to design optimized die coatings employed in material forming processes in an effort to extend the life and effect efficient operation of the dies. An optimized die coating 'architecture' requires that the coating system be essentially non-wetting with the material (metal, glass, polymer) being formed in the die, coupled with good wear and oxidation resistance Other factors, such as delaying the onset of thermal fatigue cracking (heat checking), and an acceptably low coefficient of friction. And, possibly, self-lubricating, also need to be considered based on the processing and forming conditions that include both liquid and solid materials. Many different die coatings have and are being used with different levels of success. This paper presents the current understanding that has been gained in laboratory testing, in-plant trials, and modeling in an effort to generate a fundamental understanding of how such optimized die coating systems may be designed for specific forming operations and conditions, with examples based on dies used in aluminum pressure die casting, glass molding, and metal forming operations.