Defect and deformation studies in transition metal trialuminide compounds

Wheeler, Robert, IV

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https://hdl.handle.net/2142/22470 Copy

Description

Title

Defect and deformation studies in transition metal trialuminide compounds

Author(s)

Wheeler, Robert, IV

Issue Date

1990

Doctoral Committee Chair(s)

Fraser, Hamish L.

Department of Study

Materials Science and Engineering

Discipline

Materials Science and Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Engineering, Metallurgy
• Engineering, Materials Science

Language

eng

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.

Type of Resource

text

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Copyright and License Information

Copyright 1990 Wheeler, Robert, IV

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