DEVELOPMENT OF HIGH-STRENGTH NIOBIUM ALLOYS FOR ELEVATED-TEMPERATURE APPLICATIONS

A study to improve the elevated-temperature strength of niobium by solloving has resulted not only- in greatly improved strengths at 1200 and 1470 deg F but also in the development of improved fabrication techniques for these alloys. The most important step in the fabric:ition procedure of niobium and niobium-base allows is the initial breakdown of the cast structure. The cast structure of 1.84 wt. 4 chromium, 3.21 wt.% chromium. 4.33 wt. ' zirconium, and 20.5 wt.% titanium-4.28 wt. = chromium allovs and unalloyed niobium was broken known by- forging ingots (protected from oxidation by molybdenum ciins) at 2550 deg F and rolling at 800 deg F. After the initiai breakdown of the cast structure, the alloy-s were coid roiied to a total of 95 per cent reduction with no difficulty .A second fabrication technique was employed for a second set of alloys. Unalloyed niobium and 1.29 wt. % chromium, 2.74 wt. 3 zirconium, 4.5 wt.% molybdenum, and 10 wt. % titanium-3 wt.% chromium alloys were forged and rolled at 1000 deg F to break down the cast structure and then cold rolled to 0.030-in. sheet. the sheet obtained by this technique showed moderate edge cracking. Tensite tests on the coid-worked materiais at 1200 and 1470 deg F indicate that chromium and zirconium.ire both potent strengtheners of niobium: the 1.84 wt.% chromium alloy- hiid a 0.2 per cent offset yield strength of 107,000 psi at 1200 deg F and 69,000 psi at 1470 deg F, and the 4.33 wt. % zirconium alloy had a 0.2 per cent offset yield strength of 69,000 psi at 1470 deg F. Limited welding studies indicate that strong and reasonably ductlle welds can be produced both by arc and spot welding. (auth

CREEP AND CORROSION PROPERTIES OF ZIRCALOY-2 IN STEAM AT 750 F

Test equipment to determine the creep properties of Zircaloy-2 in a 750 deg F 500-psi steam atmosphere was designed and constructed. Duplicate tests were performed at stresses to produce failure in approximately 1, 10, 100, and 1000 hr. A comparison between these data and data obtained in vacuum-test equipment showed that a corrosive test atmosphere does not alter ductility or failure times appreciably. (auth

HIGH-TEMPERATURE OXIDATION RESISTANCE OF THIN IRON-CHROMIUM-ALUMINUM ALLOY SHEET

S>The oxidation resistance of thin sheets of Fe - 28 wt. % Cr - 2.67 to 10.0 wt. % Al alloys, nominally 0.004, 0.006, 0.008, 0.012, and 0.016 in. thick, was determined by exposure in static air for 100 hr at 2100 and 2300 deg F. A minimum of 3.67 and 9.37 wt.% Al was necessary to prevent excessive oxidation of 0.004-in. thick sheet material at 2100 and 2300 deg F, respectively. Specimens of lower Al content and greater thickness withstood oxidation attack. Oxidation of Fe - Cr - Al alloys apperars to be related to the diffusion of Al to surfaces of the sheet to form an adherent protective layer of Al/sub 2/ O/sub 3/.(auth

DEVELOPMENT OF HIGH-STRENGTH CORROSION-RESISTANT ZIRCONIUM ALLOYS

Approximately 100 ternary and quaternary spongezirconium alloys were screened for structural and cladding applications in a natural-uranium-fueled heavy-watermolerated power reactor. The alloy additions studied included2 to 4 wt.% Sn, 0.5 to 2 wt.% Mo, and 1 to 3 wt.% Nb. The effect of 0.1 wt.% Fe and 0.05 wt.% Ni additions to the experimental alloys was evaluated. All compositions were are melted, rolled at 850 ction prod- C from a helium- atmosphere furnace, vacuum annealed 4 hr at 700 ction prod- C, and furnace cooled. Room- and elevated-temperature hardness measurements were used to estimate the tensile strengths of the alloys, while corrosion resistance was evaluated by 1000-hr exposures to static 300 ction prod- C water. (auth

The Mechanical Properties of Beta-Quenched Uranium at Elevated Temperatures

The creep strength and tensile properties-were determined in vacuum for beta-quenched, derby uranium. The stresses to produce a secondary creep rate of- 0.0001 per cent per hr at 100, 250, 400, and 500 deg C were 48,000, sile strengths were 114,500, 35,100, 11,100, and 8,500 psi at temperatares of 28, 300, 500, and 700 deg C, respectively. The creep and tensile strengths decrease quite rapidly with increasing temperature in the temperatare range 250 to 400 deg C. (auth

Linking soil microbial community structure to potential carbon mineralization: A continental scale assessment of reduced tillage

Potential carbon mineralization (Cmin) is a commonly used indicator of soil health, with greater Cmin values interpreted as healthier soil. While Cmin values are typically greater in agricultural soils managed with minimal physical disturbance, the mechanisms driving the increases remain poorly understood. This study assessed bacterial and archaeal community structure and potential microbial drivers of Cmin in soils maintained under various degrees of physical disturbance. Potential carbon mineralization, 16S rRNA sequences, and soil characterization data were collected as part of the North American Project to Evaluate Soil Health Measurements (NAPESHM). Results showed that type of cropping system, intensity of physical disturbance, and soil pH influenced microbial sensitivity to physical disturbance. Furthermore, 28% of amplicon sequence variants (ASVs), which were important in modeling Cmin, were enriched under soils managed with minimal physical disturbance. Sequences identified as enriched under minimal disturbance and important for modeling Cmin, were linked to organisms which could produce extracellular polymeric substances and contained metabolic strategies suited for tolerating environmental stressors. Understanding how physical disturbance shapes microbial communities across climates and inherent soil properties and drives changes in Cmin provides the context necessary to evaluate management impacts on standardized measures of soil microbial activity

The Winchcombe meteorite, a unique and pristine witness from the outer solar system.

Direct links between carbonaceous chondrites and their parent bodies in the solar system are rare. The Winchcombe meteorite is the most accurately recorded carbonaceous chondrite fall. Its pre-atmospheric orbit and cosmic-ray exposure age confirm that it arrived on Earth shortly after ejection from a primitive asteroid. Recovered only hours after falling, the composition of the Winchcombe meteorite is largely unmodified by the terrestrial environment. It contains abundant hydrated silicates formed during fluid-rock reactions, and carbon- and nitrogen-bearing organic matter including soluble protein amino acids. The near-pristine hydrogen isotopic composition of the Winchcombe meteorite is comparable to the terrestrial hydrosphere, providing further evidence that volatile-rich carbonaceous asteroids played an important role in the origin of Earth's water

EFFECTS OF YTTRIUM ON THE FABRICATION AND TENSILE PROPERTIES OF TWO MODIFIED STAINLESS ALLOYS

Alloys containing 55 wt.% iron--22 wt.% nickel-- 17 wt.% chromium--2.5 wt.% molybdenum- 1.0 wt.% niobium-0.03 wt.% carbon-- 0.5 wt.% manganese-- 0.5 wt.% silicon with nominal additions of from 0 to 1.5 wt.% yttrium, and 36 wt.% iron-37 wt.% nickel--18 wt.% chromium--2.5 wt.% molvbdenum- 1.5 wt.% niobium-- 1.0 wt.% aluminum-0.05 wt.% carbon--0.5 wt.% manganese-- 0.5 wt.% silicon with nominal additions of from 0 to 2.0 wt.% yttrium, were prepared by vacuum- induction melting. Alloys containing 55 wt.% iron were successfully forged in air at 1900 deg F, rolled at 1850 deg F to 0.060-in. sheet and cold rolled to 0.015in. sheet. Fabrication of alloys containing 36 wt.% iron with more than 0.5 wt.% yttrium was unsuccessful. Addition of yttrium had relatively no effect on the yield and ultimate strength from room temperature to 1850 deg F. The ductility of fabricable alloys studied was increased at elevated temperatures by increasing yttrium contents. The greatest increase in ductility occurred at 1.5 wt.% yttrium. (auth