Thesis
The effects of external environments on the fracture of materials
Washington State University
Master of Science (MS), Washington State University
2003
Handle:
https://hdl.handle.net/2376/144
Abstract
This study develops a method to compare the strength of passive films present on 304 stainless steel in both the bulk and nanoscale. In addition, Vickers indentation is used to determine the effects of different heat treatments on silicon carbide. The mechanical properties of passive films formed on a 304 stainless steel have been measured using a bulk circumferentially notched tensile bar as well as with a nanoindentation technique. The nanoindentation method was coupled with scanning probe microscopy to isolate individual grains, which were free of any observable inclusions so as to probe only the properties of the base alloy. The mechanical response of the film was measured while anodically polarized in 0.1 M sulfuric acid, with various salt concentrations, as well as with respect to the applied potential. In both the bulk and nanoscale tests the passive film fracture strength was found to decrease with increasing salt concentration in solution. The passive film strengthened as the applied potential increased in the passive regime. The correlation between the bulk and nanoscale tests strongly suggests that both methods are viable options of measuring the mechanical properties of passive films on metals. The applied tensile stress at film fracture for an anodically grown passive film at 0 V vs. Ag/AgCl in 0.1% NaCl - 0.1M sulfuric acid tested using nanoindentation is estimate between 1 and 2 GPa. Vickers indentation was used to determine the effect of thermal shocks on polycrystalline silicon carbide samples. The rapid change of temperature was found to be responsible for a decrease in the material's fracture toughness. The temperatures tested ranged between 400 and 900 o C, and as the temperature increased, there was up to a 20 % decrease in fracture toughness (from 3.4 to 2.6 MPa m1/2). In addition, the effects of heat treatments on SiC were determined by using indentation techniques. Several samples were exposed to heat cycling between room temperature and 1000 o C, for various numbers of cycles. The effect of the heat treatment was determined using Vickers indentation coupled with a known applied strain. No visible changes in the fracture toughness were determined due to the heat cycling.
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Details
- Title
- The effects of external environments on the fracture of materials
- Creators
- Diego. Rodríguez-Marek
- Contributors
- David F. Bahr (Degree Supervisor)
- Awarding Institution
- Washington State University
- Academic Unit
- Mechanical and Materials Engineering, School of
- Theses and Dissertations
- Master of Science (MS), Washington State University
- Publisher
- Washington State University; Pullman, Wash. :
- Identifiers
- 99900525021701842
- Language
- English
- Resource Type
- Thesis