Abstract: A method for enhancing the oxidation resistance of substrates fabricated from metallic molybdenum and alloys containing at least 50% molybdenum which comprises depositing silicon on the surface of the substrate under conditions which cause the formation of an outer layer of MoSi2. Also disclosed is a method for enhancing the oxidation resistance of other substrates, such as carbon-carbon and metals and alloys which show minimal reaction with molybdenum under the coating conditions, which comprises depositing a layer of molybdenum on the surface, then depositing silicon on the molybdenum layer under conditions which cause the formation of an outer layer of MoSi2.

Abstract: Gamma titanium aluminide alloys having the composition Ti-(45.5-47.5)Al-(0-3.0)X-(1-5)Y-(0.05-1.0)W, where X is Cr, Mn or any combination thereof, and Y is Nb, Ta or any combination thereof (at %), are treated to provide specific microstructures. To obtain duplex microstructures, the annealing temperature (T.sub.a) range is the eutectoid temperature (T.sub.e)+100.degree. C. to the alpha transus temperature (T.sub..alpha.)-30.degree. C.; to obtain nearly lamellar microstructures, the annealing temperature range is T.sub..alpha. -20.degree. C. to T.sub..alpha. -1.degree. C.; to obtain fully lamellar microstructures, the annealing temperature range is T.sub..alpha. to T.sub..alpha. +50.degree. C. The times required for producing these microstructures range from 0.25 to 15 hours, depending on the desired microstructure, alloy composition, annealing temperature selected, material section size and grain size desired.

Abstract: High temperature melting niobium-titanium-chromium-aluminum-silicon alloys having a wide range of desirable microstructures, excellent microstructural and morphological properties, superior oxidation resistance at temperatures from 1000.degree. C. to 1500.degree. C., and good low temperature toughness and good high temperature strength and creep resistance are described which comprise generally two- or three-or four-phase alloys systems having compositions (31-41)Nb-(26-34)Ti-(8-10)Cr-(6-12)Al-(9-18)Si. Two-phase beta+Nb.sub.5 Si.sub.3 -base alloys can be obtained by increasing the Nb/Ti ratio, while three-phase beta+Nb.sub.5 Si.sub.3 -base+Ti.sub.5 Si.sub.3 -base alloys or four-phase beta+Nb.sub.5 Si.sub.3 -base+Ti.sub.5 Si.sub.3 -base +Ti.sub.3 Si-base alloys can be obtained by decreasing the Nb/Ti ratio.

Abstract: High temperature melting molybdenum-chromium-silicon alloys having good high temperature strength and specific stiffness are described which comprise Mo--Cr--Si alloys in the Mo-rich (Mo, Cr)--(Mo, Cr).sub.3 Si two-phase field.

Abstract: Gamma titanium aluminide alloys having the composition Ti--(45.5-47.5)Al--(0-3.0)X--(1-5)Y--(0.05-1.0)W, where X is Cr, Mn or any combination thereof, and Y is Nb, Ta or any combination thereof (at %), are treated to provide specific microstructures. To obtain duplex microstructures, the annealing temperature (T.sub.a) range is the eutectoid temperature (T.sub.e)+100.degree. C. to the alpha transus temperature (T.sub..alpha.)-30.degree. C.; to obtain nearly lamellar microstructures, the annealing temperature range is T.sub..alpha. -20.degree. C. to T.sub..alpha. -1.degree. C.; to obtain fully lamellar microstructures, the annealing temperature range is T.sub..alpha. to T.sub..alpha. +50.degree. C. The times required for producing these microstructures range from 0.25 to 15 hours, depending on the desired microstructure, alloy composition, annealing temperature selected, material section size and grain size desired.

Abstract: High temperature melting molybdenum-chromium-silicon alloys having good high temperature strength and specific stiffness are described which comprise Mo--Cr--Si alloys in the Mo-rich (Mo, Cr)--(Mo, Cr).sub.3 Si two-phase field.

Abstract: Gamma titanium aluminide alloy articles having improved properties are produced by the following methods:The first of these methods comprises the steps of: (a) heat treating an alloy billet or preform at a temperature in the approximate range of T.sub..alpha. to T.sub..alpha. +100.degree. C. for about 0.5 to 8 hours, (b) shaping the billet at a temperature between T.sub..alpha. -30.degree. C. and T.sub..alpha. to produce a shaped article, and (c) aging the thus-shaped article at a temperature between about 750.degree. and 1050.degree. C. for about 2 to 24 hours.The second method comprises (a) rapidly preheating an alloy preform to a temperature in the approximate range of T.sub..alpha. to T.sub..alpha. +100.degree. C., (b) shaping the billet at a temperature between T.sub..alpha. and T.sub..alpha. +100.degree. C. to produce a shaped article, and (c) aging the thus-shaped article at a temperature between about 750.degree. and 1050.degree. C. for about 2 to 24 hours.

Abstract: A first method for producing articles of gamma titanium alumide alloy having improved properties comprises the steps of: (a) shaping the article at a temperature between the titanium-aluminum eutectoid temperature of the alloy and the alpha-transus temperature of the alloy, and (b) aging the thus-shaped article at a temperature between about 750.degree. and 1050.degree. C. for about 4 to 150 hours. Shaping is preferably carried out at a temperature about 0.degree. to 50.degree. C. below the alpha-transus temperature.A second method for producing articles of gamma titanium aluminide alloy having improved properties comprises the steps of: (a) shaping the article at a temperature in the approximate range of about 130.degree. C. below the titanium-aluminum eutectoid temperature of the alloy to about 20.degree. C.

Abstract: Methods are presented to produce duplex (DP) microstructures, nearly lamellar (NL) microstructures, and fully TMT lamellar (TMTL) microstructures in gamma titanium aluminide alloy articles. The key step for obtaining a specific type of microstructure is the post-hot work annealing treatment at a temperature in a specific range for the desired microstructure. The annealing temperatures range from Te+100° C. to T&agr;−25° C. for duplex (DP) microstructures, from T&agr;−25° C. to T&agr;−5° C. for nearly lamellar (NL) microstructures, and from T&agr; to T&agr;+60° C. for fully TMT lamellar (TMTL) microstructures, where Te is the titanium-aluminum eutectoid temperature of the alloy and T&agr; is the alpha transus temperature of the alloy. The times required for producing specific microstructures range from 2 min to 15 hours depending on microstructural type, alloy composition, annealing temperature selected, material section size, and desired grain-size.

Abstract: A heat treatment method for producing moderate .alpha. grain size (50-250 .mu.m) fully lamellar, microstructures in thin cross section near-.gamma. titanium aluminide alloy products is described, wherein a wrought, fine y grain starting microstructure is heated at a temperature high in the two-phase .alpha.+.gamma. phase field and 30-60.degree. C. below the .alpha. transus temperature to produce a structure of small equiaxed .alpha. grains (about 25 .mu.m dim) and fine .gamma. phase grains, which is then briefly heated to a temperature in the single-phase .alpha. field in order to complete dissolution of remnant .gamma. grains and to minimize growth of .alpha. grains. The material is then cooled to transform the microstructure to fully lamellar .alpha..sub.2 +.gamma..