Prajish Prasad

The effect of ultrasonic vibration on nickel electrodeposition

Abstract The effect of ultrasonic vibration on microhardness, residual stresses and surface finish of nickel electrodeposits was investigated. A comparison was made between the results obtained with an ultrasonically agitated bath and those with a still bath. Ultrasonic agitation increased the deposition rate and limited current density. The deposit from the bath with ultrasound gave a smoother surface and exhibited increased microhardness. The residual stresses of the deposits were reduced with an ultrasonically agitated bath.

Fatigue strength of nickel electrodeposits prepared in ultrasonically agitated bath

Nickel coatings are widely used 1:o prevent wear of structural steels resulting from abrasion and corrosion. When used for this purpose it may be expected that the coatings should also influence other characteristics such as mechanical woperties. As the plating alters the surface characteristics of the base metal, the fatigue properties of steels may be markedly affected by the presence of such coatings. Fatigue crack initiation generally occurs at the surface of a specimen. The internal stress of the deposit, its inherent fatigue strength relative to that of the substrate, its hardness and its thickness have all been shown to affect the fatigue limit [1-3]. In recent years, the effect of ultrasonic agitation during electrodeposition has gained popularity [4-6]. Because of the catastrophic failure due to hydrogen embrittlement in many plated highstrength steels, any effort to improve plating should attempt reduction, if not total eJimination, of this undesirable feature. Research is being continuously carried out with this as the main objective. Ultrasonics provide a solution to this problem. The present work is concerned with studying the effect of ultrasonics of the fatigue properties of nickel electrodeposits. A comparison has been made between the deposits obtained from a still bath and an ultrasonically agitated bath. The composition of a nickel Watts bath used for the present study is given in Table I. Fatigue tests were carried out in a rotating, bending fatigue testing machine of type PUNZ. Mild steel specimens prepared according to DIN 50113 standards (Fig. 1) and coated with nickel (thickness 20/~m) were employed. The mechanical properties of the base metal were: yield strength 475 MPa, tensile strength 650 MPa and hardness 194 Vickers Hardness Number (VHN). All the fatigue tests were carried out in air at room temperature (25 °C). The thickness of deposit was measured using the gauge, Mikrotest III. The surface roughness of the plated specimens was measured by a perthometer, Perthon S5P. Fig. 2 shows the fatigue life of the specimens at different applied stresses. Three samples were tested

Carbide precipitation in 2.25 Cr-1 Mo steel and its weldments during creep testing

Abstract Elevated temperature behaviour of 2.25 Cr-1 Mo steel (UW — unwelded) and weldments, namely, manual metal arc (MMA) and induction pressure (IP) welded joints, was assessed. The creep rupture time was found to follow the order: IPW>UW>MMAW. The nature, size and distribution of carbides, as evidenced by transmission electron microscopic (TEM) studies, were found to have a bearing on the rupture time of the specimens.

A comparative study of hot corrosion of welded and unwelded 2.25 Cr-1Mo steel

Abstract Hot corrosion of unwelded and welded 2.25 Cr-1Mo steel coated with a potassium sulphate and sodium chloride mixture is discussed. The coating composition is a eutectic mixture with 40 wt% K 2 SO 4 and 60 wt% NaCl. Weight gain studies were done for welded specimens containing only weld metal and composite specimens containing both weld metal and heat-affected zone. The results indicated that the coated specimens were more corroded than uncoated specimens. Also welded samples showed less attack than unwelded samples.

A System for Developing Operationalization Skills through Problem Decomposition

Novice researchers have difficulties in operationalization (breaking down of abstract concepts to measurables) and generalization (generalize the findings to make claims). We have designed a system called OPeD (Operationalizing using ProblEm Decomposition), for teaching learning of operationalization. OPeD trains novice researchers in operationalization through problem decomposition. OPeD is based on pedagogical theories of guided inquiry, problem visualization and adaptation. In order to visualize the operationalization process, OPeD guides the learner to create a decomposition tree and construct meaningful hypotheses based on the tree. The gradual and iterative construction of this tree can help learners develop their operationalization skills. In this paper we present the design of OPeD and provide an exemplar of a learner path in the context of educational research.

Game Based Learning of Blood Clotting Concepts

In this paper we describe the architecture of virtual clot (vCLOT), a virtual world system designed to teach procedural knowledge of blood clotting process, in a game based learning environment. vCLOT utilizes virtual world to give learners an immersive learning experience while actively participating in tasks that require them to apply the procedural knowledge they have learned. Design of vCLOT combines the immersivity of virtual worlds with the power of knowledge structures. Immersivity provides learners with the opportunity to make decisions at every level of the game. This transfers control of interaction to the learner, enabling the learner to be actively engaged in knowledge construction process. Knowledge structures are a neat way to represent domain and learner data. The user interface of vCLOT is designed and implemented with Open Wonderland which is an open-source 3D toolkit. The learning goal which is to learn about blood clotting process, is aligned with the game goal, which is application of blood clot process steps to heal an injury. The game goal is presented as a quest in which the learner interacts with concepts by either dragging them or synthesizing them from other concepts. Learners complete the quest on successful formation of blood clot which in turn implies that they have learnt the blood clot process. We plan to do a usability study to improve the system before starting actual intervention.

Acceleration of high-temperature oxidation of manual metal arc welded 2.25Cr-1Mo steel by sulphate-chloride mixture

Abstract The oxidation behaviour of manual metal arc welded (MMA) 2.25Cr-1Mo steel was studied in a potassium sulphate-sodium chloride salt mixture. The presence of this salt mixture accelerated the attack. The variation of weight gain with time indicated a parabolic growth of oxides. The outer layers consisted of oxides whereas inner layers showed the presence of sulphides. This is an example of hot corrosion attack wherein the degradation resulted in internal oxidation and sulphidation of the material.