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Causes of the yield-point phenomenon in commercial beryllium products

Description: The variables of iron content, texture, and grain size are studied as a function of solutionizing, aging, and strain-aging heat treatments. Results show that the yield point is caused by precipitate pinning. Furthermore, precipitation is enhanced by pre-strain, which can be introduced by elevated- temperature working, rapid cooling, or tensile elongation at room temperature. Aging is effective between 400 and 760 deg C, depending on the type of pre- strain, iron content, and texture. Cottrell-type solute pinning is not observed, and the Rahn model for yield drops in bcc metals best explains these results. Texture increases the likelihood of a yield point occurring. In the case of extruded-flat stock, texture causes a 3-fold increase in the amount of hardening accompanying the yield point when compared to hot-pressed block. Yield points appear on aging and strain-aging for orientations favoring either prism or basal flow. Fine grain size is a necessary condition for the occurrence of a yield point. A yield point can occur if: the average grain size is less than 10 microns, the microstructure is duplex and has a large number of grains less than 5 microns in size, a substructure exists with subgrains less than 5 microns in size. Grain-growth anneals can irreversibly eliminate a yield point. Differences in the frequency of appearance of yield points can be explained by the above factors, and a strong yield point can be developed in material supplied by Brush and KBI by appropriate treatment. The solid-solution hardening effect of iron on yield stress is linear with a slope of 2.3 psi per ppM in the range of iron from 840 to 5850 ppM. The grain-size effect, in the range from 8 microns to 45 microns, is seen to be linear for a Hall--Petch plot of yield stress versus inverse square root of ...
Date: February 1, 1974
Creator: Floyd, D. R.
Partner: UNT Libraries Government Documents Department

Fatigue-crack propagation behavior of Inconel 718

Description: The techniques of linear-elastic fracture mechanics were used to characterize the effect of several variables (temperature, environment, cyclic frequency, stress ratio, and heat-treatment variations) upon the fatigue-crack growth behavior of Inconel 718 base metal and weldments. Relevant crack growth data on this alloy from other laboratories is also presented. (33 fig, 39 references) (auth)
Date: September 1, 1975
Creator: James, L.A.
Partner: UNT Libraries Government Documents Department

Effect of temperature on the fatigue-crack propagation behavior of A-286 steel

Description: The techniques of linear-elastic fracture mechanics were used to characterize the effect of temperature upon the fatigue-crack growth behavior of A-286 steel in an air environment over the temperature range of 75--1000$sup 0$F. In general, the fatigue-crack growth rate increased with increasing temperature. Two material forms were tested: 0.5 inch-thick strip material and 1.5 inch- diameter bar. Two different crack orientations were tested in each product form. In general, no significant differences in crack growth behavior were noted between product forms nor between the different crack orientations. (auth)
Date: April 30, 1976
Creator: James, L.A.
Partner: UNT Libraries Government Documents Department

Low-temperature brittleness

Description: From 3rd international conference on the strength of metals and alloys; Cambridge, UK (20 Aug 1973). Low temperature brittleness of materials is examined. Understanding the basic chemical forces that hold materials together as represented by potential functions still limits the understanding of the true fracture stress, inherent lattice resistance to dislocation mobility, and the origin of crystal types. Therefore, basic theoretical advancement on the role of alloying and crystal types on brittle fracture is limited by advances in theoretical and experimental work in the area of potential functions. The understanding of the role of dislocation mobility in determining fracture behavior has advanced well. The role of dislocation motion in energy adsorption at the crack tip and in defining the cleavage plane is a tractable problem, given the dislocation dynamics parameters for the given material. Calculations to estimate the drag stress'' due to inherent lattice resistance and defect interactions are well developed and useful. Limitntions, however, exist in the understanding of the rate of dislocation multiplication and in the sensitivity of dislocation motion to stress and since these appear to be important in determining the fracture behavior, full understanding will await determination of the origin of these parameters. Understanding of certain aspects of grain boundary fracture of materials is proceeding rapidly, primarily because of the development of new analytical tools for determining grain boundary chemistry. It is now possible to determine the chemistry within an atom layer of the grain boundary so the chemical composition of the fracture path can be accurately determined. However, the basic problem of predicting the fracture behavior is the same as that for cleavage and therefore the limitations previously described apply. Data are given for the metals Mo, V, Ta, Nb, and W. (auth)
Date: January 1, 1973
Creator: Stein, D.F.
Partner: UNT Libraries Government Documents Department

Ingot beryllium-microstructural and mechanical property changes during can- rolling

Description: Microstructural and mechanical property observations of ingotsource beryllium at selected points in the can-rolling process are reported. Recrystallization occur s concurrently with rolling at temperatures above 1800 deg F, and only partial recrystallization is observed during reheats at 1400 deg F. Most grain refinement induced by the rolling schedule occurs in the first 15 rolling passes. These represent 88 percent reduction from the ingot. A relatively small contribution comes from the final six passes which bring the total reduction from the ingot to 95 percent. Information was also obtained on the effects of the rolling schedule on the properties of the stainless steel can. (auth)
Date: December 21, 1973
Creator: Heiple, C. R. & Dolechek, L. F.
Partner: UNT Libraries Government Documents Department

Analysis of high-density areas in beryllium hemishells

Description: Small areas of high and low radiographic density in hot-pressed beryllium were studied by macroetching and optical and electron microscopy. The areas were either semispherical or wormlike in shape and were found to be agglomerates of grains markedly coarser or finer than the matrix. (auth)
Date: January 17, 1974
Creator: Lee, O. A. & Riefenberg, D. H.
Partner: UNT Libraries Government Documents Department

Thermal conductivity of high purity vanadium

Description: The thermal conductivity, Seebeck coefficient, and electrical resistivity of four high purity vanadium samples have been measured as functions of temperature over the temperature range 5 to 300$sup 0$K. The highest purity sample had a resistance ratio (rho/sub 273$sup 0$K//rho /sub 4.2$sup 0$K/) of 1524. The highest purity sample had a thermal conductivity maximum of 920 W/mK at 9$sup 0$K and had a thermal conductivity of 35 W/mK at room temperature. At low temperatures the thermal resistivity was limited by the scattering of electrons by impurities and phonons. The thermal resistivity of vanadium departed from Matthiessen's rule at low temperatures. The electrical resistivity and Seebeck coefficient of high purity vanadium showed no anomalous behavior above 130$sup 0$K. The intrinsic electrical resistivity at low temperatures was due primarily to interband scattering of electrons. The Seebeck coefficient was positive from 10 to 240$sup 0$K and had a maximum which was dependent upon sample purity. (auth)
Date: October 1, 1975
Creator: Jung, W. D.
Partner: UNT Libraries Government Documents Department

Fatigue of welded 5083 aluminum alloy

Description: A failure analysis was conducted on an aluminum (5083) structure subjected to fatigue testing. Failure occurred by fatigue in an electron-beam weld; the cycles to failure were reasonable for the loading conditions. (5 figures) (auth)
Date: December 19, 1973
Creator: Hanafee, J. E.
Partner: UNT Libraries Government Documents Department