The Effects of Residual KNO3 and Ion Exchange Induced Crack Closure on Indented Glass
Date
2023-11
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Publisher
New York State College of Ceramics at Alfred University. Inamori School of Engineering.
Abstract
The objective of this body of work is to investigate the fatigue response of ion - exchanged aluminosilicate glass containing pre-exchange indentation flaws. Previous work found that residual potassium nitrate (KNO3), the ion exchange material, remained in the flaw after an initial washing of the parts. The remaining material at the flaw tip is thought to prevent humidity or water from penetrating to the crack tip and slows crack propagation thus increasing the failure load. To test this hypothesis two flaw depths of 25μm and 90μm, and three washing conditions were tested after the parts were ion-exchanged at the same time and temperature. The first condition is the control set where the samples just underwent an initial washing to remove salt on the surface post ion exchange. The second condition was ultrasonic cleaned. The third condition was also ultrasonic cleaned and mineral oil was added to the flaw to act as a humidity barrier. The fatigue response for each condition was evaluated using a ring-on-ring method at varying strain rates to calculate the fatigue response. The sample with small flaws around 25μm in depth showed no difference in fatigue response between the control and just ultrasonic cleaned. The driving force for the increased strength is from the ion exchange at the flaw tip and not the material left in the flaw acting as a humidity barrier. The samples with the larger flaws around 90μm did show some variation in the failure mechanism and failed at low loads that were closer to the non-ion-exchanged failure loads. When these parts were looked at under SEM NaCl was found on the surface of the flaws, which led to some exploration in diffusion time, expansion, and contamination during the ion exchange process. The crack width was estimated to evaluate the volume of salt in the flaw as well as determine the feasibility of the crack closure. The two most plausible hypotheses were the salt refresh rate or contamination. Further testing is needed to answer these questions.
Description
Thesis completed in partial fulfillment of the requirements for the degree of Master of Science in Materials Science and Engineering at the Inamori School of Engineering, New York State College of Ceramics at Alfred University
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Keywords
Glass--fatigue, Ion exchange