Deformation Studies on Directionally Solidified Eutectic LaB6-ZrB2
Open Access
- Author:
- Phillips, Calista I
- Graduate Program:
- Materials Science and Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- September 09, 2009
- Committee Members:
- Sarah Elizabeth Dickey, Thesis Advisor/Co-Advisor
Elizabeth C Dickey, Thesis Advisor/Co-Advisor - Keywords:
- Deformation
Creep
Eutectic - Abstract:
- Directionally solidified eutectic LaB6-ZrB2 samples were studied for potential use as ultra-high-temperature materials. Novel ultra-high-temperature materials are needed to improve the efficiency of flight vehicles, turbine engines and rocket engines. In evaluation of LaB6-ZrB2¡¦s viability for high-temperature applications, room-temperature indentation and high-temperature creep studies were performed. A Vickers indenter was used to initiate room-temperature deformation at a 19.6 N load. The area directly under the indent was analyzed by TEM. Fracture and debonding at the interfaces was observed and samples showed numerous dislocations in both phases. Dislocations were observed to initiate and end in the bulk. Dislocations were not observed to initiate or end at the interfaces. Two beam conditions were performed in g200 LaB6 and g010 LaB6 orientations. Dislocations that were evident in the g200 LaB6 were not seen in the g010 LaB6 TEM studies. These results are consistent with the {100}/ ƒ¬ 110 ƒ® slip system being satisfied. Other dislocations appeared in both the g200 LaB6 and g010 LaB6 orientations. These results indicate that more than one slip system is operable at room-temperature in the LaB6 phase of the directionally solidified eutectic. An impression creep instrument was modified for controlled-atmospheric testing under high temperatures. Standard samples of SiAlON material were tested for validation of instrument performance. Standard samples yielded comparable results as samples run by a previous researcher. Samples of LaB6-ZrB2 DSE were run for 100hrs at temperatures between 1400-1600¢XC and stresses of -300, -400, and -420 MPa. Deformation did not occur at these temperatures and stresses. Oxidation occurred during creep testing and additional sample preparations and furnace modifications were performed to try to eliminate oxidation of the LaB6-ZrB2 DSE. Despite extra efforts to prevent oxidation of the surface, oxidation was still observed. This oxidation will limit LaB6-ZrB2 DSEs use as an ultra-high-temperature material in oxygen-containing environments.