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Fracture and fatigue resistance of Mo-Si-B alloys for ultrahigh-temperature structural applications

Description: Fracture and fatigue-crack growth properties are examined for a series of Mo-Mo3Si-Mo5SiB2 containing alloys, which utilize a continuous a-Mo matrix to achieve unprecedented room-temperature fracture resistance (>20 MPaAm). Mechanistically, these properties are explained in terms of toughening by crack trapping and crack bridging by the more ductile a-Mo phase.
Date: August 29, 2003
Creator: Kruzic, J. J.; Schneibel, J. H. & Ritchie, R. O.
Partner: UNT Libraries Government Documents Department
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Investigation into the joining of MoSi{sub 2} to 316L stainless steel

Description: Partial transient liquid phase joining and low temperature brazing were applied in joining MoSi{sub 2} to 316L ss. Exploratory studies were carried out on various interlayer materials. Mechanical, physical, and chemical compatibilities between various interlayers, brazing material, and substrate materials were investigated. Effect of thermal expansion mismatch between various components of the joint on the overall joint integrity was also studied. Preliminary findings are outlined.
Date: October 1, 1996
Creator: Vaidya, R. U.; Bartlett, A. H.; Conzone, S. D. & Butt, D. P.
Partner: UNT Libraries Government Documents Department
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Oxidation Behavior and Chlorination Treatment to Improve Oxidation Resistance of Nb-Mo-Si-B Alloys

Description: This thesis is written in an alternate format. The thesis is composed of a general introduction, two original manuscripts, and a general conclusion. References cited within each chapter are given at the end of each chapter. The general introduction starts with the driving force behind this research, and gives an overview of previous work on boron doped molybdenum silicides, Nb/Nb{sub 5}Si{sub 3} composites, boron modified niobium silicides and molybdenum niobium silicides. Chapter 2 focuses on … more
Date: December 19, 2004
Creator: Behrani, Vikas
Partner: UNT Libraries Government Documents Department
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Growth of Oriented C11(b) MoSi(2) Bicrystals Using a Modified Czochralski Technique

Description: Oriented bicrystals of pure C11<sub>b</sub> MoSi<sub>2</sub> have been grown in a tri-arc furnace using the Czochralski technique. Two single crystal seeds were used to initiate the growth. Each seed had the orientation intended for one of the grains of the bicrystals, which resulted in a 60&deg; twist boundary on the (110) plane. Seeds were attached to a water-cooled seed rod, which was pulled at 120 mm/h with the seed rod rotating at 45 rpm. The water- cooled copper hearth was counter-rotated… more
Date: June 2, 1999
Creator: Chu, F.; Garrett, J.D.; McClellan, K.J.; J.R., Michael; Mitchell, T.E. & Peralta, P.
Partner: UNT Libraries Government Documents Department
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Properties and challenges of nanolayer coatings

Description: A systematic study was made on MoSi{sub 2}-based nanolayer coatings. Alternating layers with thickness 1-20 nm were prepared by sputtering. Nitrided MoSi{sub 2} has a very high crystallization temperature, >1000 C, and MoSi{sub 2}Nx (x=3-4) can be used as a stable second phase reinforcement or diffusion barrier coatings. Mechanical properties depend strongly on phase and morphology of the layers: hardness and modulus is significantly increased in the crystallization. The nanolayers have much hi… more
Date: December 1995
Creator: Kung, H.; Nastasi, M.; Jervis, T.; Mitchell, T. & Hirvonen, J. P.
Partner: UNT Libraries Government Documents Department
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TEM characterization of invariant line interfaces and structural ledges in a Mo-Si alloy

Description: Two distinct <1{bar 1}0> lath morphologies of Mo{sub 5}Si{sub 3} precipitates observed in MoSi{sub 2} differ in their cross-sectional shape and lattice orientation. Type I laths exhibit a rectangular cross section, with interfaces parallel to low-index planes, while Type II laths are parallelogram-shaped, with their major interface at 13{degree} to the Type I precipitate. The corresponding orientation relationships differ by a 1.8{degree} rotation around the lath axis. In this study, the differ… more
Date: June 1995
Creator: Xiao, S. Q.; Dahmen, U.; Maloy, S. A. & Heuer, A. H.
Partner: UNT Libraries Government Documents Department
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Characterization of electrical resistivity as a function of temperature in the Mo-Si-B system

Description: Measurements of electrical resistivity as a function of temperature from 25 to 1,500 C were conducted on polycrystalline samples in the Mo-Si-B system. Single phase, or nearly single phase, samples were prepared for the following phases: Mo{sub 3}Si, Mo{sub 5}SiB{sub 2}, Mo{sub 5}Si{sub 3}B{sub x}, MoB, MoSi{sub 2}, and Mo{sub 5}Si{sub 3}. Thesis materials all exhibit resistivity values within a narrow range(4--22 x 10{sup {minus}7}{Omega}-m), and the low magnitude suggests these materials are … more
Date: December 10, 1999
Creator: Beckman, Sarah E.
Partner: UNT Libraries Government Documents Department
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Impression creep behavior of atmospheric plasma sprayed and hot pressed MoSi{sub 2}/Si{sub 3}N{sub 4}

Description: The use of MoSi{sub 2} as a high temperature oxidation resistant structural material is hindered by its poor elevated temperature creep resistance. The addition of second phase Si{sub 3}N{sub 4} holds promise for improving the creep properties of MoSi{sub 2} without decreasing oxidation resistance. The high temperature impression creep behavior of atmospheric plasma sprayed (APS) and hot pressed (HP) MoSi{sub 2}/Si{sub 3}N{sub 4} composites was investigated. Values for steady state creep rates,… more
Date: September 1, 1997
Creator: Hollis, K. J.; Butt, D. P. & Castro, R. G.
Partner: UNT Libraries Government Documents Department
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Thermal shock behavior of alumina/MoSi2 plasma sprayed laminated composites

Description: Alumina (Al{sub 2}O{sub 3}) is very susceptible to thermal shock, which leads to strength degradation. By reinforcing Al{sub 2}O{sub 3} with molybdenum disilicide (MoSi{sub 2}) layers, the tolerance to damage caused by thermal shock can be improved. The thermal shock resistance of plasma sprayed Al{sub 2}O{sub 3}/MoSi{sub 2} laminated composites were investigated. Three laminate microstructures having different layer thickness were fabricated by atmospheric plasma spraying while maintaining a 5… more
Date: January 1, 2001
Creator: Castro, R. G. (Richard G.); Petrovic, J. J.; Vaidya, R. U. (Rajendra U.) & Mendoza, D. (Daniel)
Partner: UNT Libraries Government Documents Department
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Measurement and modeling of residual stress in net-shape plasma sprayed tubes

Description: Residual stresses in net-shaped plasma sprayed MoSi{sub 2} tubes were measured by x-ray microdiffraction as a function of radial position in the sample. A tensile to compressive hoop stress profile was measured, ranging 200 MPa in tension at the outer diameter, to -125 MPa at the inner. A force balance model was used to explain the evolution of stresses when incrementally adding layers to the pre-existent material.
Date: September 1, 1996
Creator: Bartlett, A. & Castro, R. G.
Partner: UNT Libraries Government Documents Department
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Processing of Mo-Si-B intermetallics by extrusion and oxidation properties of the extruded Tl-MoSi{sub 2}-MoB System

Description: An extrusion process was developed that is able to consistently produce large quantities of Mo-Si-B rods without the presence of defects. Binder removal from the extruded rods was studied in detail and it was determined that heating rates on the order of 0.02{degree}/minute (1.2{degree}/hour) are necessary to remove the binder without the formation of defects. This low heating rate resulted in debinding times in excess of 70 hours (approximately 3 days). Wicking was investigated as a means to d… more
Date: November 8, 1999
Creator: Summers, Eric
Partner: UNT Libraries Government Documents Department
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Mo{sub 5}Si{sub 3} single crystals: Physical properties and mechanical behavior

Description: The materials processing, physical properties and mechanical behavior of an ultra-high temperature structural silicide, Mo{sub 5}Si{sub 3}, have been studied. High purity single crystals of Mo{sub 5}Si{sub 3} have been synthesized by both optical floating zone and Czochralski methods. The thermal and elastic properties of the MO{sub 5}Si{sub 3} single crystals were experimentally measured. Results show that Mo{sub 5}Si{sub 3} has significant thermal expansion anisotropy along the a and c direct… more
Date: December 1, 1998
Creator: Chu, F.; Thoma, D.J.; McClellan, K.J. & Peralta, P.
Partner: UNT Libraries Government Documents Department
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The thermal conductivity of silicon nitride with molybdenum disilicide additions

Description: Room-temperature thermal conductivity has been measured for a series of silicon nitride (Si{sub 3}N{sub 4}) matrix composites with molybdenum disilicide (MoSi{sub 2}) additions of 2, 5 10, 25 and 50 wt. %. Included in these measurements were a pure MoSi{sub 2} sample and a Si{sub 3}N{sub 4} sample containing only sintering aids. Aluminum oxide (Al{sub 2}O{sub 3}) and yttrium oxide (Y{sub 2}O{sub 3}) were added as the sintering aids, at approximately 6 and 2 respectively. When the amount of MoSi… more
Date: December 31, 1993
Creator: Beecher, S. C.; Dinwiddie, R. B.; Abeel, A. M. & Lowden, R. A.
Partner: UNT Libraries Government Documents Department
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Fracture and fatigue properties of Mo-Mo{sub 3}Si-Mo{sub 5}SiB{sub 2} refractory intermetallic alloys at ambient to elevated temperatures (25-1300 degrees Centigrade)

Description: The need for structural materials with high-temperature strength and oxidation resistance coupled with adequate lower-temperature toughness for potential use at temperatures above {approx} 1000 degrees C has remained a persistent challenge in materials science. In this work, one promising class of intermetallic alloys is examined, namely boron-containing molybdenum silicides, with compositions in the range Mo (bal), 12-17 at. percentSi, 8.5 at. percentB, processed using both ingot (I/M) and pow… more
Date: August 1, 2002
Creator: Choe, Heeman; Schneibel, J. H. & Ritchie, R. O.
Partner: UNT Libraries Government Documents Department
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Rapid fabrication of materials using directed light fabrication

Description: Directed light fabrication (DLF) is a rapid fabrication process that fuses gas delivered metal powders within a focal zone of a laser beam to produce fully dense, near-net shape, 3-dimensional metal components from a computer generated solid model. Computer controls dictate the metal deposition pathways, and no preforms or molds are required to generate complex sample geometries. The focal zone of the laser beam is programmed to move along or across a part cross-section, and coupled with a mult… more
Date: October 1, 1997
Creator: Thoma, Dan J.; Lewis, Gary K.; Milewski, John O.; Chen, Katherine C. & Nemec, Ronald B.
Partner: UNT Libraries Government Documents Department
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Aging model for solid lubricants used in weapon stronglinks: Oxidation chemistry and hardware review

Description: In support of efforts to model the performance of the MC2969 strong link for stockpile life extension, the kinetics of oxidation of the MoS{sub 2} based solid lubricant coating have been determined. The lubricant oxidation is primarily influenced by the extent of burnishing of the coating after application and curing. The activation energy for lubricant oxidation is low and agrees well with reported values for MoS{sub 2} coatings and particles. The type of substrate material and the amount of H… more
Date: September 1, 1997
Creator: Peebles, D. E.; Ohlhausen, J. A.; Dugger, M. T.; Varga, K. S. & Bryan, R. M.
Partner: UNT Libraries Government Documents Department
open access

Effect of 690 keV Xe ion irradiation on the microstructure of amorphous MoSi{sub 2}/SiC nanolayer composites

Description: The effect of 690 keV Xe ion irradiation at three different dosage levels, 1, 5 and 10{times}10{sup 15}/cm{sup 2}, on the microstructure of amorphous-MoSi{sub 2}/amorphous-SiC nanolayer composites has been studied using transmission electron microscopy. Results show that the depth of radiation damage in this multilayer material is {approximately}80 nm, which agrees qualitatively well with the calculated damage depth calculated by TRIM. A diffraction ring corresponding to the (10{bar 1}1) plane … more
Date: October 1, 1996
Creator: Lu, Y.C.; Kung, H.; Jervis, T.R.; Mitchell, T.E. & Nastasi, M.
Partner: UNT Libraries Government Documents Department
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A perspective on MoSi{sub 2} based composites

Description: MoSi{sub 2} based composites represent an important new class of ``high temperature structural silicides,`` with significant potential for elevated temperature structural applications in the range of 1200--1600{degrees}C in oxidizing and aggressive environments. The properties of MoSi{sub 2} which make it an attractive matrix for high temperature composites are described and the development history of these materials traced. Latest results on elevated temperature creep resistance, low temperatu… more
Date: June 1, 1992
Creator: Petrovic, J. J. & Vasudevan, A. K.
Partner: UNT Libraries Government Documents Department
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Brittle composites modeling: Comparisons with MoSi{sub 2}/ZrO{sub 2}

Description: We have calculated the mechanical properties of brittle composites with spring-network (SN) model. The composites that we studied involve the transformation toughening effects and the accompanying micro-cracking. Our simulation results are consistent with experiments of MoSi{sub 2} toughened with ZrO{sub 2}. We found that the continuum mechanics predictions on linear dependence in e{sup T} and f about the transformation toughening are correct except some differences in the critical transformati… more
Date: December 31, 1993
Creator: Chen, S. P.
Partner: UNT Libraries Government Documents Department
open access

Oxidation behavior of molybdenum silicides and their composites

Description: A key materials issue associated with the future of high-temperature structural silicides is the resistance of these materials to oxidation at low temperatures. Oxidation tests were conducted on Mo-based silicides over a wide temperature range to evaluate the effects of alloy composition and temperature on the protective scaling characteristics and testing regime for the materials. The study included Mo{sub 5}Si{sub 3} alloys that contained several concentrations of B. In addition, oxidation ch… more
Date: April 3, 2000
Creator: Natesan, K. & Deevi, S. C.
Partner: UNT Libraries Government Documents Department
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Synthesis and Design of Silicide Intermetallic Materials

Description: The overall objective of this program is to develop structural silicide-based materials with optimum combinations of elevated temperature strength/creep resistance, low temperature fracture toughness, and high temperature oxidation and corrosion resistance for applications of importance to the US processing industry. A further objective is to develop silicide-based prototype industrial components. The ultimate aim of the program is to work with industry to transfer the structural silicide mater… more
Date: May 14, 1999
Creator: Petrovic, J. J.; Castro, R. G.; Vaidya, R. U. & Park, Y.
Partner: UNT Libraries Government Documents Department
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