자료유형  

 학위논문

Control Number  

0017162506

International Standard Book Number  

9798383567623

Dewey Decimal Classification Number  

621

Main Entry-Personal Name  

Harris, Chad.

Publication, Distribution, etc. (Imprint  

[S.l.] : The University of Wisconsin - Madison., 2024

Publication, Distribution, etc. (Imprint  

Ann Arbor : ProQuest Dissertations & Theses, 2024

Physical Description  

150 p.

General Note  

Source: Dissertations Abstracts International, Volume: 86-01, Section: B.

General Note  

Advisor: Perepezko, John H.

Dissertation Note  

Thesis (Ph.D.)--The University of Wisconsin - Madison, 2024.

Summary, Etc.  

요약With current jet engines operating near the melting temperature of Ni-based superalloys, a solution to go beyond these temperatures is needed. As a result of complex cooling schemes and thermal barrier coatings, these turbine blade materials operate at ∼1150 °C, nearly 90% of the melting temperature (0.9 Tm). New materials must be developed that can operate at high (1300 °C) temperatures without the need for cooling. Refractory metal silicides, such as Mo‐Si‐B, are potential replacements for Ni‐based superalloys. A comprehensive Mo-Si-B coating system has been designed in our group's previous work; thus, optimization of the pack powder will allow for more efficient coating processes. Also, high temperature water vapor attack has been determined as a major contributor to turbine blade failure, which has necessitated the exploration of its effects on Mo-Si-B based coatings. To address the water vapor attack issue, an Al alloyed Mo-Si-B coating is designed and tested under high temperature, high-flow water vapor condition. To explore the Mo-Si-B coating application on a substrate other than Mo, a V substrate with Mo-Si-B coating is demonstrated and shows good oxidation performance at high temperature.In this study, silicide boron coating layers are created on a Mo substrate by pack cementation with NaF, Si, B, and Al2O3 powder. The silicide coating layer consists of MoB and MoSi2. The growth kinetics of the coating layers are estimated by identifying diffusion behaviors. The silicide coating layer growth constant (k0) is estimated to be ~86.04µm/h1/2, and the activation energy (Q) for the growth of the diffusion coating layer determined to be ~39.9kJ/mol for the examined coating temperatures of 900°C, 1000°C, and 1100°C. The thicknesses of the coating layers calculated by a formulated kinetic equation are compared with the experimental results. Although the 35Si:1B wt.% has the lowest activation energy, the values are too close to determine once standard deviation is taken into consideration. It has the largest thickness while still maintaining an appropriate amount of B in the coating. The growth kinetics of the coated layer and oxidation behaviors are discussed in terms of microstructure analysis and an equation to determine thickness is further developed.To extend the lifetime of the coating beyond its current limit, Al is diffused into the Mo-Si-B oxide layer to determine the effects it will have on the oxidation kinetics. The coating follows paralinear oxidation kinetics with a parabolic rate constant that is diffusion controlled and a linear rate constant that is interface controlled. The kP is 3.4x10-2 mg2/cm4h and the kL is 1.4x10-2 mg/cm-2h for the coating. This gives a 36% increase to lifetime vs the non-Al Mo-Si-B coating giving it 2560 hr. of estimated lifetime using the Opila model. The Al doped Mo-Si-B coating demonstrates excellent resistance to water vapor attacks at 1450 °C beyond what the current 35Si:1B Mo-Si-B coating is capable of. In high velocity water vapor testing, 60 m/s2, the estimated coating lifetime is 2589 hr., implying that the effects of the velocity of the water vapor may be negligible.Using the Mo-Si-B coating on other substrates is accomplished using a Mo slurry coating. V and V alloys are known to have very poor oxidation resistance, but when coated with a Mo coating and a Si:B coating, the substrates have shown a substantial increase in oxidation resistance. In water vapor, the V samples mass loss rate starts to equalize while in its uncoated form the samples fail through complete oxidation. With V and V alloy substrates being coated successfully, the possibility of success in other refractory metals will allow for broader applications of the Mo-Si-B coatings.

Subject Added Entry-Topical Term  

Mechanical engineering.

Subject Added Entry-Topical Term  

Materials science.

Subject Added Entry-Topical Term  

Engineering.

Index Term-Uncontrolled  

Coatings

Index Term-Uncontrolled  

High temperature materials

Index Term-Uncontrolled  

Molybdenum

Index Term-Uncontrolled  

Oxide resistant materials

Index Term-Uncontrolled  

Water vapor

Added Entry-Corporate Name  

The University of Wisconsin - Madison Materials Science and Engineering

Host Item Entry  

Dissertations Abstracts International. 86-01B.

Electronic Location and Access  

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Control Number  

joongbu:653948