Type of Document	Dissertation
Author	Al Ghaferi, Amal Abdulla
Author's Email Address	a.alghaferi@uaeu.ac.ae
URN	etd-11302006-132550
Title	Elastic Constants and Dislocations Image Simulations of L10-FePd
Degree	Doctor of Philosophy
Program	Materials Science and Engineering
School	School of Engineering
Advisory Committee	Advisor Name Title Jörg M.K. Wiezorek Committee Chair Anthony J. De Ardo Committee Member Ian Nettleship Committee Member Jean R. Blachère Committee Member John A. Barnard Committee Member
Keywords	TiAl Elastic Constants Image Simulations FePt FePd
Date of Defense	2006-12-04
Availability	unrestricted
Abstract A yield strength anomaly has been observed in intermetallic L10-ordered FePd alloys between about 300-700K. However, previous work did not provide clear explanations regarding the microstructural or mechanistic origins for this observation. FePd and ƒ×-TiAl have the same crystal sturtucre. YSA was studied intensively in ƒ×-TiAl system and its origin was related for the dislocation fine structure. In TiAl, the dissociation of the superdislocation [10-1] play an important role in the YSA phenomena and the existence of Yoo torque promote dissociated shockly partial to cross slip to another slip plane. This forms KW lock which is the reason of YSA in TiAl. The Elastic Constants of the tetragonal L10 phases describe the intrinsic elastic properties of the L10-FePd .Details of the dislocations fine structure, such as the details of dissociations and decompositions of dislocations and the relevant planar fault energies, are determined by the elastic constants , including the elastic interactions between partials dislocations and the effect of the Yoo torque. The elastic constants are required for the computer image simulations of WBDF TEM images of narrowly dissociated dislocation configurations. Elastic constants were calculated for FePd and were compared to Elastic constants of g-TiAl and FePt. Dislocations Image Simulation will provide contrast guidance for experimental studies in both FePd and FePt. Experimental TEM studies of the fine structure require extensive tilting of the thin crystal section within the magnetic field of the objective lens of the TEM instrument and are difficult to perform for the hard ferromagnetic FePd and FePt intermetallics since magnetic effects of the sample material on the electrons used for imaging lead to complicated artifacts in images upon tilting through significant angles. Hence, image simulations may assist in identifying appropriate imaging conditions under which significant and relevant differences in the dislocation image contrast may be expected for the dislocations in the two different intermetallics. This study builds the fundamental basic in the research of the origin of the YSA in FePd. Although the origin of YSA in L10 FePd has not been identified but the basic intrinsic elastic properties, i.e. elastic constants, has been measured experimentally for the fist time and these elastic constants were used in dislocations TEM image simulation .
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