Papers by Author: S.M.M. Hadavi

Abstract: Titanium Aluminide-based composites with Al2O3 reinforcement can be produced via reaction of Al with TiO2. These composites are considered as low-cost materials for high temperature applications. Addition of KClO4 to the TiO2/Al system was investigated in this research. On the basis of the results obtained, addition of KClO4 to the mixture of TiO2/Al and subsequent heating, results in titanium aluminide/alumina nanometric particle formation with dimensions of about 30 nm. Densification of this composite powder leads to production of a titanium aluminide-alumina nanocomposite body. Dimensions of the alumina phase are in the range of 100-150nm.

Abstract: Usual process for production of W-Cu nanocomposite is ball–milling and sintering of W and Cu mixed powder. Recently, mechanochemical process (MCP) using WO3 and CuO powders have been developed. In the present work, the influence of the ball-milling time from 1 to 30 hour, milling atmosphere such as Argon and Hexane as Process Control Agent (PCA) and weight ratio of ball to powder on characteristics of WO3-CuO was studied. The microstructure of WO3–CuO powder prepared by milling was investigated by x-ray diffraction (XRD) and scanning electron microscopy (SEM). Results show that, the grain sizes of the WO3 and CuO in the ball-milled powder mixture were significantly decreased with increasing the milling time. Those of each oxide ball–milled in Argon and Hexane atmosphere for 30 and 20 hour were about 98 and 84 nm, respectively. After milling of 20 hour in Hexane as PCA, the powder had a homogeneously mixed structure and the average size of WO3– CuO powders was determined to about 230nm.

Abstract: Aluminum-Lithium alloys are attractive choices for weight saving of aerospace structures. By addition of Lithium to Aluminum alloys, the mechanical and physical properties are improved, density decreases up to 10% and module of elasticity increases up to 15%. As-cast Al-Li ingots include some continues brittle phases in grain boundaries that decrease formability by crack initiation during hot rolling. In the present work, influence of homogenization on hot rolling of Al- Li alloys was studied. Homogenization temperature determined based on DTA test and homogeneity properties were characterized by microstructures observation. One specimen was cast in conventional method and the other was cast by direct casting (DC) method. Homogenization was performed at four different times: 10, 24, 50 and 100 hours at 500°C also no cracking has been observed in both ingots in 100 hr and 24 hr at 500°C respectively due to eliminate the brittle phases.

Abstract: In the present study, solidification and segregation of Al-Li-Cu-Zr alloys have been investigated. Results show that shape of ingots and amount of lithium can change solidification essence. Increasing solidification rate, not only eliminates grain-refining effect of zirconium but also causes coarse segregation of copper in grain boundaries (negative segregation). Increasing amount of lithium in Al-Cu-Li-Zr alloys can change the solubility of other alloying elements (Cu, Zr) and increase solidification range and microsegregation of copper in structure.