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RECIPROCATING WEAR RESPONSE OF Ti(C,N)-Ni3Al CERMETSBuchholz, Stephen 05 December 2011 (has links)
Titanium carbonitride (Ti(C,N)) cermets have become more popular in recent research
due to their mix of high hardness, high hot hardness, good ductility, chemical stability,
and low densities. These mechanical properties make Ti(C,N)-cermets especially
desirable as a replacement for current ‘hardmetals’, such as tungsten carbide cobalt (WCCo),
as it is known that WC-Co exhibits poor mechanical behaviour at elevated
temperatures. Additional interest and research has been conducted in reference to binders
which enhance the cermet’s capability to retain strength at high temperatures while
remaining ductile. One such binder, Ni3Al actually increases in yield strength up to a
temperature of ~900°C. In this thesis, the production method utilizing melt infiltration for
TiC, Ti(C0.7,N0.3), Ti(C0.5,N0.5), and Ti(C0.3,N0.7)-based cermets with Ni3Al binder
contents of 20, 30 and 40 vol. % have successfully been developed and utilized. This
process produced high density samples at each nitrogen content for all binder contents,
excluding Ti(C0.3,N0.7). Ti(C0.3,N0.7)-Ni3Al samples at 20 and 30 vol. % suffered from
poor infiltration and could not be tested. The reciprocating wear mechanisms were
examined, using a ball-on-flat test, utilizing WC-Co spheres with a diameter of 6.35 mm
as a counter-face, and test parameters of 20 Hz, 2 hrs., and applied loads of 20, 40, 60 and
80 N. The wear tracks were examined using optical profilometry, SEM, and EDS to
determine the volumetric wear rate, and the dominant wear mechanisms. The wear
volume, and wear mechanisms were compared with the effect of binder content, nitrogen
content, and applied load.
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RESIDUAL STRESS AND MICROSTRUCTURAL EVOLUTION OF COMPOSITES AND COATINGS FOR EXTREME ENVIRONMENTSJohn I Ferguson (17582760) 10 December 2023 (has links)
<p dir="ltr">A current engineering challenge is to understand and validate material systems capable of maintaining structural viability under the elevated temperature and environmental conditions of hypersonic flight. One aspect of this challenge is the joining of multiple materials with thermal expansion mismatch, which can lead to residual stress, resulting in debits in component lifetime under in-service loading. The focus of this work is a series of studies focused on a ceramic-metal composite (WC/Cu), a zirconia coating applied to a carboncarbon (C/C) composite, and a silicide (R512E) coating applied to a Nb-based alloy (C103). Each of these material systems are candidates for elevated temperature applications in which dissimilar constituents result in residual stress in the material. Each study leveraged experimental residual strain measurements, with the primary focus on the use of synchrotron X-ray diffraction, in conjunction with representative models, and microscopy to illuminate the active mechanisms in the development and evolution of residual stress in the bulk material. The combination of experimental and modeling predictions provides a framework to inform the viability and lifing of material systems exhibiting dissimilar expansion properties.</p>
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