Showing papers by "Gary S. Was published in 2001"

Combined effect of special grain boundaries and grain boundary carbides on IGSCC of Ni–16Cr–9Fe–xC alloys

Abstract: Susceptibility to intergranular stress corrosion cracking in Ni–16Cr–9Fe– x C alloys in 360°C primary water is reduced with increasing fraction of special grain boundaries, i.e. coincident site lattice boundaries (CSLB) and low angle boundaries, and grain boundary carbides. Intergranular stress corrosion cracking (IGSCC) was investigated using interrupted constant extension rate tensile tests in a primary water environment at 360°C. Thermal–mechanical treatments were used to increase the fraction of special boundaries from approximately 20–25% to between 30 and 40%. In a carbon-doped heat, further heat treating was used to precipitate grain boundary carbides preferentially on high-angle boundaries (HAB). Orientation imaging microscopy was used to determine the relative grain misorientations and scanning electron microscopy (SEM) was used to identify specific grain boundaries after each interruption. After each strain increment, the same regions in each sample were examined for cracking. Results showed that irrespective of the microstructure condition, CSLBs always cracked less than HABs. Results also showed that IGSCC is reduced with increasing solution carbon content, and for the same amount of carbon in solution, the addition of grain boundary carbides reduced IGSCC still further. The best microstructure was the one consisting of an enhanced CSLB fraction and chromium carbides precipitated preferentially on high-angle boundaries.

Combined out-of-plane and in-plane texture control in thin films using ion beam assisted deposition

Abstract: Complete control of the texture of a film during growth requires the ability to determine the in-plane and out-of-plane texture simultaneously. We present both computer simulation and experimental evidence for the simultaneous establishment of out-of-plane and in-plane texture during ion beam assisted deposition of aluminum. Channeling along 〈110〉 directions (60° from the normal) creates a {220} out-of-plane orientation rather than the thermodynamically preferred {111} orientation. The ion beam also aligned 〈220〉 directions within the plane of the film. Measured x-ray pole figures confirmed the presence of a strong out-of-plane texture and the presence of two main, twin-related, in-plane texture components. We theoretically demonstrated that it is impossible to completely control both the in-plane and out-of-plane texture with a single ion beam in high-symmetry crystals and two ion beams must be employed to ensure complete texture control.

A priori determination of the sampling size for grain-boundary character distribution and grain-boundary degradation analysis

Abstract: The objective of this work was to formulate a simple model that can be used for assessing the statistical significance of the grain-boundary character distribution in a material. Increased interest in the control of the grain-boundary character distribution to influence grain boundary properties has led to numerous studies on the characterization of grain-boundary type without regard to the statistical significance of the results. Specifically, the model was developed to determine, a priori, the number of boundaries that need to be characterized such that the fraction of boundaries of a particular type is known to within a specific fractional error. The inclusion of experimental error in the model accounts for the misidentification of boundary type in the characterization process. The model also addresses the statistical significance of boundary degradation by boundary type. This is a more restrictive application of the same formalism in that a low probability of degradation (e.g. cracking, corro...

Stress and temperature dependence of creep in Alloy 600 in primary water

Abstract: The stress and temperature dependence of creep of commercial nickel-base Alloy 600 was investigated through constant load, step-load, and step-temperature creep tests in deaerated primary water containing 40 to 60 cc/kg hydrogen To analyze creep rates for Alloy 600 in the mill-annealed (MA) condition, effective stresses were estimated using applied stresses and instantaneous strains The apparent activation area was determined to be 7b 2 by the multiple regression analysis of creep rates The apparent activation energy for creep has a weak stress dependence and was determined to lie between 188 and 281 kJ/mole for the effective stress range of 117 to 232 MPa Creep rates were better correlated with effective stress than applied stress and the stress exponent of Alloy 600 MA was determined to be 22 at 337 °C and 51 at 360 °C The magnitudes of the stress exponent, activation energy, and activation area can be interpreted to support a creep mechanism controlled by dislocation-climb and nonconservative motion of jogs in commercial Alloy 600 MA The activation area agreed with that determined from carbon in solution, implying thermally activated dislocation glide as another possible creep mechanism

A high intensity radiation effects facility

Abstract: The facility of the Michigan Ion Beam Laboratory at the University of Michigan has been upgraded to conduct high intensity radiation effects studies on materials. This upgrade is necessary to pursue higher radiation damage levels than the studies previously conducted. To achieve this capability a new volume ion source was installed which can produce several times more H− current than the previous duoplasmatron. We will describe the objectives of the research and the facility as well as applications to a variety of radiation damage problems.