Low Cost In-Situ Formation of AIN - B- SiC

AIN-a-SiC composite powders have been prepared by in-situ high temperature reaction process. By appropriate mixing of Charred Rice Husk (CRH) and aluminium powder, samples containing 30-70% A1N (balance SiC) have been produced. Nitridation has been done by high purity N, gas at temperatures ranging from 1400-17000C.Amorphous SiO, and carbon present in CRH have been utilized for the formation of [i-SiC. At about 1550°C the reaction products are only [3-SiC and AIN, whereas,below 1550°C other phases, like a-A1,03, Al, Si are the reaction products. It has also been observed that above 1600°C SiC starts going into the solid solution of A1N. The final products have been identified and characterized by XRD, SEM and EDX analysis

Development and Characterization of Ag-Cu-Ti Alloys for Ceramic Brazing

In the present investigation, silver and copper base alloys with varying compositions of Ag:Cu = 72:28, 60:40, 50:50 and 30:70 (by wt%) are prepared. In each set, 1, 2 and 3w1% of active filler element, i.e. titanium is incorporated by powder metallurgical route. The samples are characterised by XRD, DTA-TGA, SEM and EDX. The XRD results show that titanium and its related phases are not present due to the lower concentration of Ti in these samples. Energy dispersive X-ray analyses reveal that most of the titanium is present in the copper rich phase and very little in the silver rich phase. The rolled brazing alloys are used for./pining the alumina to alumina, that showed excellent joining characteristics

Evaluation of interface microstructure for friction stir welded aluminium-stainless steel plate

In the present study, commercially pure aluminium has been joined with 304 stainless steel by friction stir welding. Microstructural characterization was carried out using scanning and transmission electron microscopes. Diffusion of Fe, Cr and Ni is substantial within Al; however diffusion of Al within 304SS is limited. Owing to inter-diffusion of chemical species across the bond line, discrete islands of Fe3Al intermetallic phase forms within the reaction zone. The rubbing action of tool over the butting edge of 304SS removed fine particles of 304SS and got embedded in the stirring zone of Al matrix. At the latter stage austenite underwent phase transformation to ferrite due to large strain within its grain. Fracture path mainly moves through stirring zone of Al alloy under tensile loading; however in some places, presence of Fe3Al compound has been found

Remaining life assessment of service exposed reheater and superheater tubes in a boiler of a thermal power plant

This paper presents the high temperature tensile and the stress rupture properties of 150,000 hours service-exposed superheater and reheater tubes made of 2.25Cr-1 Mo steels in a 120 MW boiler of a thermal power plant. These were used to estimate the remaining life for safety. Experimentally determined yield strength and ultimate tensile strength as well as estimated 10,000 hours - 100000 hours rupture strength as obtained from experimental data in the temperature range of 793 to 853K exhibit a decreasing trend with increasing temperature. Microstructural study did not reveal any significant degradation in terms of creep cavities, cracks, graphitization etc. In general, analysis of tensile and stress rupture data reveal that the service exposed superheater and reheater tubes can remain in service for a length of more than ten years at the operating hoop stress level 40 MPa / 813K, provided no localised damage in the form of cracks or dents has been developed. It is recommended that a similar health check should be carried out after 50,000 hours of service exposure at 813K

Application of Multivariate Adaptive Regression Spline-Assisted Objective Function on Optimization of Heat Transfer Rate Around a Cylinder

The present study aims to predict the heat transfer characteristics around a square cylinder with different corner radii using multivariate adaptive regression splines (MARS). Further, the MARS-generated objective function is optimized by particle swarm optimization. The data for the prediction are taken from the recently published article by the present authors [P. Dey, A. Sarkar, A.K. Das, Development of GEP and ANN model to predict the unsteady forced convection over a cylinder, Neural Comput. Appl. (2015) 1–13]. Further, the MARS model is compared with artificial neural network and gene expression programming. It has been found that the MARS model is very efficient in predicting the heat transfer characteristics. It has also been found that MARS is more efficient than artificial neural network and gene expression programming in predicting the forced convection data, and also particle swarm optimization can efficiently optimize the heat transfer rate

Acoustic emission studies during indentation on ceramic and ceramic composite

Acoustic emission (AE) activity during indentation fracture toughness tests on 25 wt% silicon carbide whisker(SiCw) reinforced alumina composite and an alumina based wear resistant ceramic has been investigated. It has been shown as to how the emitted AE signals may characterize the crack growth during loading and unloading of an indentation test. The AE results indicate that in the case of the composite the amount of crack growth during unloading was higher than that during loading. The reverse is true in the case of wear resistant ceramic and in this case overall less AE activity was observed compared to that of the composite

Self-Stabilizing Algorithms in DAG Structured Networks

International audienceThis paper describes a parameterized protocol applicable to directed acyclic graph (DAG) topologies. The function parameter of the protocol is instantiated twice to design two specific protocols: (i) the topological sorting of the successor list at every node, and (ii) a shortest path routing table construction. Both protocols are self-stabilizing and thus they are resilient to transient failures and guarantee system recovery in a finite time linear in the network diameter. From the fact that a DAG topology can be imposed on a more general topology through graph labeling protocols, the solutions presented in this paper are expected to be quite useful for a large class of distributed systems, where an optimal routing along with the robustness and fault tolerance are key factors. Read More: http://www.worldscientific.com/doi/abs/10.1142/S012962649900052

Aging Characteristics of Sn-Ag Eutectic Solder Alloy with the Addition of Cu, In, and Mn

In the present investigation, three types of solder alloy, i.e., Sn-Ag-Cu, Sn-Ag-In, and Sn-Ag-Cu-Mn, have been prepared and joined with Cu substrate. In the reflowed condition, the joint interface is decorated with Cu6Sn5 intermetallic in all cases. During aging at 100 C for 50 to 200 hours, Cu3Sn formation took place in the diffusion zone of the Sn-Ag-Cu and Sn-Ag-In vs Cu assembly, which was not observed for the Sn-Ag-Cu-Mn vs Cu joint. Aging also leads to enhancement in the width of reaction layers; however, the growth is sluggish (~134 KJ/mol) for the Sn-Ag-Cu-Mn vs Cu transition joint. In the reflowed condition, the highest shear strength is obtained for the Sn-Ag-Cu-Mn vs Cu joint. Increment in aging time results in decrement in shear strength of the assemblies; yet small reduction is observed for the Sn-Ag-Cu-Mn vs Cu joint. The presence of Mn in the solder alloy is responsible for the difference in microstructure of the Sn-Ag-Cu-Mn solder alloy vs Cu assembly in the reflowed condition, which in turn influences the microstructure of the same after aging with respect to others

Effect of nickel on sintering of self-propagating high-temperature synthesis produced titanium carbide

A detailed study of the sintering behavior of titanium carbide (TiC) powder synthesized by the self-propagating high-temperature synthesis (SHS) route was carried out with varying percentages of nickel. With an increase in the nickel content, porosity was found to increase along with Ni2.67Ti1.33 secondary phase at grain boundary. A 90-92% dense sintered body of TiC was produced from SHS-produced powder at 1800 degrees C with 10 wt% nickel