Doctoral Dissertations

Date of Award

12-1992

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Metallurgical Engineering

Major Professor

Ben F. Oliver

Committee Members

C. Brooks, A. Mathew, C. McHargue

Abstract

One goal of this research was to expand the single phase γ-TiAI phase field to lower Al contents by microalloying TiAI with ternary and quaternary additions. This was done to examine whether or not lower Al single phase alloys would have improved ambient ductility. To this end, a series of ternary TiAI based alloys, with additions of Ag, Cr, Ga, Mn, and Zr, were arc melted and homogenized. Based upon this work, Mn and Ga appear to expand the r phase field to lower Al contents. Zirconium and Cr appear to shift this phase field to higher Al contents. Silver was found to embrittle TiAI. Both Ag and Cr have limited solubility in TiAI. The homogenized microstructures of the ternaries were observed and the number and composition of the phases present determined. This information was used to determine the ternary TiAI phase boundaries at room temperature. These data along with estimates of ternary ambient properties were used to decide which combination of solutes would yield the most promise for quaternary compositions. The main guideline that was followed for all these alloys, was to produce single phase, high purity, low Al content alloys. The properties of the quaternary alloys were compared to the properties for the stoichiometric binary alloy and the binary alloy having the best reported ambient ductility, 48 a/o Al. These quaternaries, as well as the binaries, were zone processed and four point bend specimens were electrically discharge machined from their processed regions. These specimens were subjected to four point bending. The outer fiber strain was measured with strain gages and this value along with the fracture stress used to compare properties between alloys. Based upon these test results, a Cr/Mn quaternary had the highest strength and ductility. However, this enhanced fracture stress and ductility was not substantial, 470 MPa and 0.6 percent, respectively. Although all of the quaternary alloys considered were slightly two phase, the variation in the extent of the γ single phase field was still determined.

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