Tensile and fracture properties of type 316 stainless steel after creep

The effects of creep on the mechanical properties of type 316 stainless steel were studied. Tensile and Charpy specimens were machined from the oversize specimens crept at 750 °C and 103 MPa. The ambient fracture energy was found to deteriorate rapidly after creep. The ambient yield stress was increased moderately, but the tensile ductility was severely reduced. The effects of intergranular carbides alone on mechanical properties were studied with specimens thermal aged without load. These carbides were shown to cause a moderate reduction in fracture energy and tensile ductility but had little effect on yield stress. Extensive grain boundary separations were observed on the fracture surfaces. SEM studies showed that these grain boundaries were covered with micro voids initiated by the dense intergranular carbides. Frequently, large dimples on grain boundary joined up and initiated shear fracture into the grain. In the crept specimens additional microstructural changes in the form of intragranular carbides and subgrain boundaries were observed. Both are responsible for the increase in yield stress and the further reduction in tensile ductility and fracture energy. The intragranular carbides also modified the size and density of the dimples on the fracture surfaces. Formerly with Metallurgy and Materials Science Division, Brookhaven National Laboratory, Upton, NY 11973.     

Hardening mechanisms in a dynamic strain aging alloy,HASTELLOY X,during isothermal and thermomechanical cyclic deformation

Isothermal cyclic deformation tests were conducted on HASTELLOY X with a total strain range of ±0.3 pct at several temperatures and strain rates. Cyclic hardening exhibited a broad peak between about 200 °C and 700 °C, with a maximum near 500 °C of about 80 pct increase in stress amplitude, Δσ/2, at failure. The present work examines the mechanisms contributing to this marked cyclic hardening. Cr₂₃C₆ precipitation on dislocations contributed to hardening, but only with sufficient time above about 500 °C. The substantial hardening rate at lower temperatures or shorter times was attributed to solute drag. The contribution of solute drag was evidenced in tests at both 400 °C and 600 °C by a continually decreasing strain rate sensitivity of the AcrJ2. Solute drag alone produced very considerable cyclic hardening. The increase in AcrJ2 after 1000 cycles at 427 °C was 75 pct of the maximum observed at higher temperatures where carbides did precipitate. Additionally, thermomechanical tests were conducted between various temperature limits, but with the same ±0.3 pct mechanical strain range. Hardening was bounded by isothermal behavior at the temperature limits of the thermomechanical cycles, except for tests between 400 °C and 600 °C which exhibited extreme hardening. However, microstructural examination did not suggest a cause. Specimens subjected to thermomechanical cycles appeared similar to those isothermally cycled at the maximum temperature of the thermomechanical cycle, including those from the 400 °C to 600 °C tests.     

Effective grain size and charpy impact properties of high-toughness X70 pipeline steels

The correlation of microstructure and Charpy V-notch (CVN) impact properties of a high-toughness API X70 pipeline steel was investigated in this study. Six kinds of steel were fabricated by varying the hot-rolling conditions, and their microstructures, effective grain sizes, and CVN impact properties were analyzed. The CVN impact test results indicated that the steels rolled in the single-phase region had higher upper-shelf energies (USEs) and lower energy-transition temperatures (ETTs) than the steels rolled in the two-phase region because their microstructures were composed of acicular ferrite (AF) and fine polygonal ferrite (PF). The decreased ETT in the steels rolled in the single-phase region could be explained by the decrease in the overall effective grain size due to the presence of AF having a smaller effective grain size. On the other hand, the absorbed energy of the steels rolled in the two-phase region was considerably lower because a large amount of dislocations were generated inside PFs during rolling. It was further decreased when coarse martensite or cementite was formed during the cooling process.     

The effect of helium environment on the creep rupture properties of Inconel 617 at 1000°C

The effect of oxygen contents in helium and in vacuum on the creep rupture properties of Inconel 617 has been investigated at 1000°C under the stress of 3.5 Kg/mm². The main results are as follows. 1) The creep rupture properties in 99.9999 pct and 99.995 pct helium and in high vacuum are almost the same as those in air. 2) The oxygen in helium causes a remarkable decrease of the creep rupture time and similar effect of oxygen is also found in the controlled pressure of air. 3) The effect of oxygen on the creep rupture properties is attributable to the decarburization which tends to decrease the high temperature strength.     

Glycoprotein and ganglioside changes in human trophoblasts after exposure to pulsed Doppler ultrasound

Changes in glycoprotein and ganglioside composition in human trophoblasts (eighth week of gestation) after in vitro exposure to pulsed Doppler ultrasound (pulse duration 1.22 microseconds; repetition frequency 11.1 kHz; center frequency 4 MHz; ISPPA = 175.5 W/cm2; ISPTA = 0.59 W/cm2) were investigated. Evacuated trophoblasts were divided in two halves and insonated for 10 min on top of a 6-cm layer of 5% gelatin in 50-mL tubes (Falcon) at 37 degrees C. One half of each trophoblast was sham insonated and served as an internal control. After insonation trophoblasts were maintained at 37 degrees C for 24 h. Glycoproteins were detected using alpha-D-mannose specific lectins from Galanthus nivalis and Narcissus pseudonarcissus. A decrease in the expression of mannose containing glycoprotein mgp47 and an increase in expression of mgp54 were observed. Ganglioside composition was also significantly altered. Concentrations of two gangliosides migrating similarly to GM2, and one similarly to GQ1, decreased by more than 75%. At the same time, concentrations of one ganglioside migrating similarly to GM3, and two other unidentified gangliosides increased two- to fourfold.     

Equilibrium composition and thermodynamic properties of high-temperature gas-mixtures

The composition and thermodynamic properties of a gas plasma in thermal equilibrium can be computed from the partition functions of all particles in the plasma. Partition functions of atoms are determined from tabulated and extrapolated energy levels and under consideration of a so called cut-off criterion. The partition functions of molecules containing two atoms are evaluated from spectroscopic constants and with the assumption that the potential between the atoms can be described by a Morse-function. As an example, an oxygen-iron-plasma and an air-silicon-plasma in a temperature range from 2000 K to 35 000 K are computed with this procedure.     

Thyroid hormone changes in a cold air environment after local cold acclimation

Serum thyroid hormones (TH) and internal temperatures were investigated in 8 euthyroid men during a general standard cold air test (SCAT) (dry bulb temperature = 1 degree C, 2 h, nude, at rest) performed both before and after a local cold acclimation. Serum total thyroxin (TT4), total triiodothyronine (TT3), free thyroxin (FT4), free triiodothyronine (FT3), and thyrotropin (TSH) were studied during the SCT. The TH values were corrected following the plasmatic volume reduction (delta PV) calculated with Dill and Costill's formula. During SCAT, delta PV reached -9 to -11% (P < 0.05) without any effect of local cold acclimation. Slight TH changes were observed according to delta PV: TT4, TT3, and TSH increased during SCAT (P < 0.05) only before correction. FT4 and FT3 did not vary before correction but increased after correction (P < 0.05). After acclimation, a slightly decreased TT3 was observed both before and after correction (-18% and -11.7%, respectively; P < 0.05). Decreased internal temperatures after local cold acclimation suggested a hypothermic general cold adaptation. It was concluded that TH changes during SCAT differed if correction due to delta PV was applied and that the slight decrease in TT3 observed after local cold acclimation could suggest the presence of a "T3 polar syndrome."     

Tensile properties and microstructure of haynes 25 alloy after aging at elevated temperatures for extended times

The tensile properties of Haynes 25 alloy have been measured after various aging treatments, time, and temperature: as received; and aged at 600 °C for three months; 800 °C for 6 and 12 months; and 1000 °C for 3 and 6 months. Contour plots in temperature-ln (time) space were constructed based on the literature and our own data, detailing changes in yield strength, ultimate tensile strength, and tensile elongation. Scanning electron microscopy and transmission electron microscopy observations of the Haynes 25 alloy microstructure provided an explanation of why the properties changed with aging. Intense lattice distortions after aging at 600 °C, the presence of an α-Co₃W, a L1₂-ordered, fcc phase, a=0.357 nm, after aging at 800 °C, and the nucleation and growth of W₃Co₃C carbides from aging at 800 °C and 1000 °C produced the changes in tensile properties. We did not observe either the Co₂W Laves phase or Co₇W₆ γ phase in any of the material conditions we examined, using TEM of thin foils: as received and aged at 600 °C, 800 °C, and 1000 °C. Other researchers believe these phases cause a loss of ductility in the Haynes 25 alloy with prolonged high-temperature exposure.     

Thermodynamic properties and high-temperature evaporation of gadolinium silicides in vacuum

Using the methods of mass-spectrometric and x-ray diffraction analysis to investigate their high-temperature evaporation in vacuum, it was determined that gadolinium silicides undergo the sequence of phase transformations Gd₅Si₃ → Gd₅Si₄ → GdSi. The enthalpies of the phase transformations were calculated, as well as the enthalpies of formation of the silicides (?116.6, ?521.6, and ?502.5 kJ/mole for GdSi, Gd₅Si₄, and Gd₅Si₃, respectively). The results obtained are compared with data in the literature.     

Effects of environment on high-temperature fatigue crack growth in a superalloy

Fatigue crack growth rate measurements were made on Inconel alloy 718 samples at 650°C in fourteen different gaseous environments. Minor amounts of either oxygen or sulfur bearing species in the environment produced large increases in crack growth rates. Aggressive environments promoted intergranular crack growth. Kinetic factors rather than thermodynamic ones appear to be the variables dominating the effects of an environment on crack growth. Environments that markedly increased the crack growth rate did not produce significant corrosion attack on unstressed samples. Thus conventional high temperature corrosion tests may not be useful for predicting service performance of stressed components.     

The nature and impact of changes in home learning environment on development of language and academic skills in preschool children.

In this study, we examined changes in the early home learning environment as children approached school entry and whether these changes predicted the development of children's language and academic skills. Findings from a national sample of the National Institute of Child Health and Human Development Study of Early Child Care and Youth Development (N = 1,018) revealed an overall improvement in the home learning environment from 36 to 54 months of children's age, with 30.6% of parents of preschoolers displaying significant improvement in the home environment (i.e., changes greater than 1 SD) and with only 0.6% showing a decrease. More important, the degree of change uniquely contributed to the children's language but not to their academic skills. Home changes were more likely to be observed from mothers with more education and work hours and with fewer symptoms of depression. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perinatal exposure to morphine: reactive changes in the brain after 6-hydroxydopamine

The decapeptide H2N-Ser-Leu-Thr-Cys-Leu-Val-Lys-Gly-Phe-Tyr-COOH (termed immunorphin) corresponding to the sequence 364-373 of the CH3 domain of the human immunoglobulin G1 Eu heavy chain and displaying a 43% identity with the antigenic determinant of beta-endorphin was synthesized. Immunorphin was found to compete with 125I-beta-endorphin for high-affinity receptors on murine peritoneal macrophages (K = 2.5 +/- 0.9 x 10(-9) M) and with 3H-morphin for receptors on murine thymocytes (Ki = 2.7 +/- 0.6 x 10(-9) M) and murine macrophages (Ki = 5.9 +/- 0.7 x 10(-9) M). In particular two types of receptors to 125I-beta-endorphin with Kd1 = 6.1 +/- 0.6 x 10(-9) M and Kd2 = 3.1 +/- 0.2 x 10(-8) M were revealed on macrophages. The second type of receptors interacted with 125I-beta-endorphin, 3H-Met-enkephalin, 3H-Leu-enkephalin and 3H-morphin; the first displayed reactivity with 125I-beta-endorphin, 3H-morphin and immunorphin. The first type receptors are not present on murine brain cells nor are inhibited by naloxone. A minimum fragment of immunorphin practically completely retaining its inhibitory activity in the competition tests with 125I-beta-endorphin for common receptors on thymocytes was found to correspond to the tetrapeptide H2N-Lys-Gly-Phe-Tyr-COOH (Ki = 5.6 +/- 0.5 x 10(-9) M).