Abhijit Kar

Effect of Mn on Sn–Ag–Cu ternary lead free solder alloy–Cu assembly: a comparative study

Abstract In the present investigation, transition joints were produced by soldering Sn–Ag–Cu and Sn–Ag–Cu–Mn alloys to Cu substrate. Microstructure and mechanical properties of the assemblies were determined in reflowed condition and after aging at 100°C for variable time. The shear strength as well as the reaction layer thickness of Sn–Ag–Cu versus Cu is lower in comparison to Sn–Ag–Cu– Mn versus Cu solder assembly in reflowed condition. The reaction zone for Sn–Ag–Cu versus Cu is decorated with Cu3Sn and Cu6Sn5; however, in the case of Sn–Ag–Cu–Mn versus Cu assembly only Cu6Sn5 was observed. Mn is responsible for enhanced width of Cu6Sn5, which act as a barrier layer restricting the diffusion of Sn across the interface and Cu3Sn formation has not been found even after aging of 200 h. Aging treatment leads to growth of intermetallic layer for both the joints and decrement in shear strength of the assemblies. Still Sn–Ag–Cu–Mn versus Cu solder assembly exhibits superior mechanical strength than Sn–Ag–Cu versus Cu transition joint.

HySecNJoining: A hybrid secure node joining algorithm for wireless sensor network

A wireless sensor network consists of several sensor nodes strewn over a large geographic area and base station. Depending upon the routing model used data collected by the sensor node are routed through several hops of the network to the base station. Before a new node becomes operational the base station verifies its authenticity for security reasons. We call this phase as secure joining of a node. The process of secure joining can be as simple as allowing a new node to join by simply verifying its MAC-ID in plain text. However, this simple secure joining is prone to many attacks and therefore, not acceptable to many organizations requiring high grade of security. On the other hand stringent process of secure joining such as multi-level verification of authentication credentials in a secure channel comes with a cost in terms of energy consumption. In this paper we propose a stringent secure joining method which uses the concept of certificate less PKI and symmetric key and goes through multi-level authentication for prevention of flooding attack.

Secure self organization of wireless sensor network: A new approach

Self organization is an important phase of a wireless sensor network. Thousands of Sensors are deployed in a large geographical area randomly without considering the location factor. After deployment, sensors nodes are required to self organize themselves to form a network of their own. How well the network is formed determines the life of the whole network as well as the quality of data transmission. Also, security is an important aspect while forming the network initially. Only the authorized nodes should be allowed to join the network. In this paper, we discuss our secure self organization algorithm.

Damage Resistance of a Thermal Barrier Coated Superalloy for Combustor Liners in Aero Turbines During Fatigue and Creep

Abstract This paper deals with an evaluation of the lifetime of a thermal barrier coated (TBC) C263 superalloy under fatigue and creep loading. Results revealed that both TBC and bond-coated substrate had higher endurance limits than the base alloy, while the opposite was found for high stress, low cyclic lifetimes. At high stress, the premature failure for these two materials is possibly due to high stress crack initiation/growth in the TBC/bond coat layers. Oxidation is the cause of the reduced life of the bare substrate as compared to the coated substrate while fatigue and creep experiments are carried out in an oxidizing environment. During 800 °C fatigue, the bare specimens behave differently from the coated specimens, but both the bond-coated only and bond coat + TBC specimens seem to exhibit very similar results that are within experimental scatter. Delamination of the bond coat, oxidation of the substrate and spallation of the ceramic layer were evident at very high fatigue and creep stresses. Lateral cracks that grew in the ceramic layer parallel to the stress axis were responsible for spallation of the top coat (TBC) at a very high fatigue stress, whereas, at low creep stress, spallation of the top coat was due to the growth of alumina scale (of thickness >3μm) at the top coat (TBC)/bond coat interface.

Ceramic-Metal Joining Using Active Filler Alloy-An In-Depth Electron Microscopic Study

Joining of materials provides a means of fabricating structures, where difficulty is encountered to make one piece directly. Very often joining can be considered to be less expensive than making single piece structure for many intricate shaped components. Brazing is one of the most important techniques for joining various materials especially ceramics. To fabricate near net shape joined component or to make prototypes of intricate shapes, joining of ceramics to ceramics/metals, brazing has been considered as the most frequently used technique. Due to their excellent high temperature strength, resistance to corrosion and wear, application of ceramics in structural components, has received extensive attention in recent decades. However difficulties on joining ceramics with metals restrict their use in many occasions. The ability to produce a reliable ceramicceramic/metal and composite joint is a key enabling technology for many productions, prototype and advanced developmental items and assemblies. Thus it becomes an interesting challenge to the researchers for ceramic-metal joining.[1,2] Amongst several ceramic joining processes, active metal brazing is one of the most extensively used joining techniques for metal-ceramic joining. In this process, bonding is promoted by the use of an active filler alloy. The active filler alloy containing a small amount of an active element which is capable of reacting with the ceramic substrate facilitates joining.[3-12]. Characteristics of filler alloy play a significant role in obtaining unique joining properties. Filler alloy should have the liquidus temperature, below the melting point of the substrate to be joined and also must be capable of producing joint at a temperature where the properties of base materials are not degraded