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Title:Defect and deformation studies in transition metal trialuminide compounds
Author(s):Wheeler, Robert, IV
Doctoral Committee Chair(s):Fraser, Hamish L.
Department / Program:Materials Science and Engineering
Discipline:Materials Science and Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Engineering, Metallurgy
Engineering, Materials Science
Abstract:Defect studies have been performed on the intermetallic compounds $\rm Al\sb3Ti$, $\rm Al\sb3V$ and $\rm Al\sb{67}Ni\sb8Ti\sb{25}$ which were deformed at elevated temperatures. Test materials were prepared via the rapid solidification route. TEM characterizations indicated that the microstructure of the asatomized Al-25at.%Ti alloy powder consisted of primary dendrites of the $\rm Al\sb3Ti$ phase (DO$\sb{22}$ structure) and $\alpha$-aluminum. The as-atomized Al-25at.%V alloy exhibited a microstructure composed of primary $\rm Al\sb8V\sb5$ dendrites with interdendritic $\rm Al\sb3V$ (DO$\sb{22}$) and $\alpha$-aluminum. The Al-8at.%Ni-25at.% Ti alloy exhibited dendrites of $\rm Al\sb{67}Ni\sb8Ti\sb{25}$(L1$\sb2$) and small $\rm Al\sb3Ni\sb2$ particles.
The consolidated Al-25at.%Ti alloy contained $\rm Al\sb3Ti$ with numerous small particles. Three types of second phases were noted: TiAl particles, oxide streamers at prior particle boundaries; and small TiC particles within certain grains. In the consolidated Al-25at.%V powder, large $\rm Al\sb8V\sb5$ particles were identified within a matrix of $\rm Al\sb3V$. The Al-8at.%Ni-25at.%Ti alloy contained $\rm Al\sb2NiTi$ particles (fcc, a$\sb0$ = 11.94A) in a matrix of $\rm Al\sb{67}Ni\sb8Ti\sb{25}$.
Compression testing was carried out at 300$\sp\circ$C, 600$\sp\circ$C and 800$\sp\circ$C. The weak-beam darkfield technique was employed to determine the Burgers vector, slip plane and dissociation reactions of dislocations responsible for plastic deformation.
In $\rm Al\sb3Ti$, microtwins on the close packed $\{112)$ planes formed by the repeated passage of 1/6 $<$ 111) partial dislocations on successive $\{112)$ planes were identified. Partial dislocations with b = 1/2 $<$ 110) which bound APB's on the (001) plane were also characterized at 300$\sp\circ$C and 600$\sp\circ$C. Dislocations with b = $<$100) were found to glide on (001) and shown to climb at the higher temperatures ($\geq$600$\sp\circ$C). $\rm Al\sb3V$ appears to deform by glide of b = $<$110) dislocation son the $\{112)$ planes. At 800$\sp\circ$C, again climbing $<$100) dislocations were found. In $\rm Al\sb{67}Ni\sb8Ti\sb{25}$, dislocation glide of the type $\langle 110\rangle\{111\}$ was identified. At 300$\sp\circ$C, the dislocations were undissociated, while at 600$\sp\circ$C and 800$\sp\circ$C, considerable APB-type dissociation on the $\{001\}$ planes was noted.
Defect structures in the two DO$\sb{22}$ compounds have been explained using a new model of accounting for energies related to the dissociated configurations. This model relies on quantum mechanical calculations for total crystal energies of various other crystal structures, similar to DO$\sb{22}$, which are present locally within the faulted region of the dissociated dislocations. A possible extrapolation to the case of $\rm L1\sb2$ compounds is also given.
Issue Date:1990
Rights Information:Copyright 1990 Wheeler, Robert, IV
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9026350
OCLC Identifier:(UMI)AAI9026350

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