Papers by Author: Ramana G. Reddy

Abstract: The major reason that there is not more widespread use of titanium and its alloys is the high cost. In this paper, developments in one cost effective approach to fabrication of titanium components - powder metallurgy - will be discussed under various aspects of this technology. The aspects to be discussed are the blended elemental approach, pre-alloyed techniques, additive layer manufacturing, metal injection molding, spray deposition and microwave sintering. A brief review of a number of low cost powder production processes is also presented.

Abstract: A micro-DMFC is a promising power source to substitute the lithium battery and used in the portable electronic devices. In this study, the effect of four types of flow fields of bipolar plates in a micro-direct methanol fuel cells (micro-DMFCs) on their performance were experimentally investigated. MEMS technology was applied in fabrication of micro-channel for the micro-DMFCs. The effect of the type of flow field design on the performance of micro-DMFCs was electrochemically evaluated for the four types of flow fields. The micro-DMFCs with double-channel serpentine presented the highest maximum power density and the micro-fuel cells with mixed multi-channel serpentine with narrow channels had the lowest maximum power density.

Abstract: A thermodynamic model for the prediction of interfacial tension of liquid iron, inclusion and solid oxide substrate/refractory was evaluated. The combined Good’s and Young’s equations were used for high temperature liquid metal-solid oxide substrate-inclusion system to evaluate the interfacial tensions. The study predicts the liquid silicon (as model inclusion/impurity) adherence on the solid oxide substrate/refractory (MgO) in a liquid iron melt. The calculated results for interfacial tension between liquid iron-MgO values decreased from 1798 to 1026 ergs/cm2 as the temperature increases from 1823 to 1933 K, respectively. The Gibbs energy of adhesion for liquid silicon-MgO substrate was calculated shows that silicon adhesion to MgO substrate increases with increasing surface tension of liquid Fe/MgO and with decreasing temperature.

Abstract: Aluminum alloys were reinforced with AlN particles using a novel chemical in situ technique. Thermodynamic analyses were made to identify the conditions for the in situ formation of the AlN in Al alloys. Experiments were conducted in the temperature range of 1173-1473 K by injecting ammonia gas. The composites with AlN quantity varying from 5 to 51 wt % were produced. Effect of process variables such as gas injection time, flow rate of ammonia gas and temperature of the alloy melt on the formation of AlN was studied. Increase in either injection time or flow rate of the ammonia gas increased the nitride content. AlN particles with an average size of 500 nm were produced. The measured Vickers hardness of the composites formed increased with increasing AlN content. The amount of AlN experimentally formed is in good agreement with the thermodynamically predicted data.