Effects of hardness on the solid particle erosion mechanisms in AISI 1060 steel

The mechanisms of mass loss were studied using impacts of single particles (WC spheres $\text{3}\text{16}$ in in diameter) for a 0.6% C steel (AISI 1060 steel) heat treated to give hardnesses of 12, 45 or 60 HRC. Both oblique and near-normal angles of impact were used. A new foil laminate was developed to measure rebound velocity and angle. Velocities of 100–200 m s^?1 were studied. A measurable mass loss was found only at 200 m s^?1. At a hardness of 12 HRC the mode of metal loss involved the loss of shear lips. At 60 HRC the dominant loss mode involves the intersection of adiabatic shear bands (ASBs) and shows a maximum mass loss at near-normal impact. The material with a hardness of 45 HRC shows both modes of mass loss and a maximum mass loss rate at oblique (30°) impact. ASBs on the surface and welding of target material to the impacting ball indicate a high temperature at the surface. However, the material welded to the particle is not a significant fraction of the material lost.     

Winds of change – Predicting water-based recreationists' support and opposition for offshore wind energy development in the Great Lakes

This study examined the factors influencing water-based recreationists' perceptions of support and opposition towards off-shore wind energy development (OWD) on Lake Erie. Much of the proposed or future Lake Erie OWD infrastructure may either be within or adjacent to public lands, waters, and protected areas, raising concerns about the potential environmental and social impacts upon recreation stakeholders. The limited body of OWD research within the United States has suggested there are numerous factors that may influence overall perceptions of support and opposition such as political orientation and beliefs in climate change. Moreover, recent research has proposed that the perceived recreation impact of OWD may be the most important predictor of support and opposition. This study confirmed this premise and found the perceived recreation impact of OWD to be the strongest predictor of support. Results of a multiple linear regression suggested that political orientation (β?=?0.135), beliefs in the anthropogenic causation of climate change (β?=?0.207), beliefs in the occurrence of climate change (β?=?0.213), and the perceived recreation impact of OWD among water-based recreationists (β?=?0.439) were significant predictors of support for OWD on Lake Erie (R²?=?0.46). Study findings corroborated previous research which suggested that regional climate change beliefs and political attitudes may influence support for OWD. From a policy and management standpoint, study results highlight the importance of assessing and communicating recreation experience and use impacts when planning, developing, and managing OWD and related decisions in the United States.     

Reducing Cr6+ emissions from gas tungsten arc welding using a silica precursor

Hexavalent chromium (Cr⁶⁺) emission from stainless steel welding operations poses a serious threat to worker safety and ambient air quality. In this study, tetraethyloxysilane (TEOS) was used as a silica precursor additive to welding shield gas during gas tungsten arc welding (GTAW) operations to determine the feasibility of using these chemicals for Cr⁶⁺ exposure reduction. Fume aerosol samples were analyzed for Cr⁶⁺ concentration using ion chromatography (IC) and for total Cr by inductively coupled plasma with atomic emission spectroscopy (ICP-AES).At high temperature, silica precursors are pyrolyzed to form amorphous silica (SiO₂) which can condense on the existing metal aerosols. The inert silica layer surrounding the aerosols can prevent further chromium oxidation by insulating chromium aerosols. Experimental results showed approximately 45% Cr⁶⁺ reductions when 3.0% TEOS was added to the shield gas. Nitrate concentration also decreased by 53%, indicating that reactive oxygen species were also reduced. Transmission electron microscopy (TEM) images of collected fume aerosols showed SiO₂ coating on metal particles, verifying the proposed mechanism.     

The enhancement of hydrogen attack in steel by prior deformation

An investigation has been made of the cause of enhancement of hydrogen attack (HA) by prior cold working. Bars of 1020 Si-killed steel deformed in three point bending were found to contain microcracks at ferrite/ferrite grain boundaries containing cementite inclusions and at ferrite/pearlite boundaries. Very long cementite plates crack, but shorter cementite inclusions (? ?2 μm) suffer decohesion from the matrix at or near the inclusion ends. The observed anisotropy of microcracking with respect to grain boundary orientation and sign of the deformation stress can be understood in terms of the stress state at the inclusion/matrix interface during deformation. The microcracks are not eliminated by an annealing treatment which is known to cancel the effect of deformation on HA. It is concluded that residual stresses arising from the difference in deformability between cementite particles and matrix are responsible for the influence of deformation on HA. Formerly with the Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60201     

A new model for the erosion of metals at normal incidence

A new theoretical model is proposed for the erosion of metals by particles at normal incidence. The model employs a criterion of critical plastic strain to determine when the material will be removed. This critical plastic strain is defined as the strain at which the deformation in the target localizes and hence results in the lip formation. It is shown that, under typical erosion conditions, the “localization” model is more appropriate than the “fatigue” models. Finally, it is demonstrated that the new model predicts quite well all the essential features of the normal impact erosion process.     

Unsuccessful retrieval attempts enhance subsequent learning.

Taking tests enhances learning. But what happens when one cannot answer a test question—does an unsuccessful retrieval attempt impede future learning or enhance it? The authors examined this question using materials that ensured that retrieval attempts would be unsuccessful. In Experiments 1 and 2, participants were asked fictional general-knowledge questions (e.g., “What peace treaty ended the Calumet War?”). In Experiments 3–6, participants were shown a cue word (e.g., whale) and were asked to guess a weak associate (e.g., mammal); the rare trials on which participants guessed the correct response were excluded from the analyses. In the test condition, participants attempted to answer the question before being shown the answer; in the read-only condition, the question and answer were presented together. Unsuccessful retrieval attempts enhanced learning with both types of materials. These results demonstrate that retrieval attempts enhance future learning; they also suggest that taking challenging tests—instead of avoiding errors—may be one key to effective learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Grain boundary cracking

A chronological summary is given of the various types of grain boundary fracture found in metals. In each case, there is an impurity that adsorbs at the new (fracture) surface being formed. For the case of Fe-P alloys, a quantitative argument can show that adsorption of phosphorous on the free surface greatly reduces the barrier to void nucleation compared to that in the absence of phosphorous. The same or larger reduction would appear for any other element, which adsorbs more strongly than phosphorous and displaces it at the surface. Such an argument is shown to explain a great many cases of dimpled grain boundary fracture in strong alloys undergoing creep or hydrogen attack. The reduction in surface energy can also lead to a smooth grain boundary fracture (no void nucleation), in which diffusion of solute to the new surface limits crack growth. Numerous examples of this are also discussed. Dr. Shewmon studied metallurgical engineering at the University of Illinois (B.S. 1952) and Carnegie Institute of Technology (Ph.D. 1955). His first job was at the Westinghouse Research Laboratory, where he studied thermal diffusion in alloys and surface diffusion. In 1958, he moved to the Carnegie Institute of Technology, where he served as a professor until 1967. The text “Diffusion in Solids” was published in 1963. An NSF Fellowship was used to study at Professor C. Wagner’s Max Planck Institute (Goettingen, Germany) in 1963. From 1968 to 1973, he was at Argonne National Laboratory, serving successively as Associate Director of the Metallurgy Division, Associate Director of the EBR-2 Project, and Director of the Materials Science Division. The text “Transformations in Metals” was published in 1969. Materials behavior in fast breeder reactors was the main theme of his work during this period. He was the director of the Division of Materials Research at the National Science Foundation from 1973 to 1975. From 1975 to 1993, he was Professor at Ohio State University in the Department of Metallurgical Engineering (later Materials Science and Engineering), serving as Chairman from 1975 to 1983. Research interests during this period were hard particle erosion and hydrogen-induced cracking of steel (“hydrogen attack”). From 1977 to 1993 he served on the Advisory Committee on Reactor Safety for the United States Nuclear Regulations Committee, serving as Chair for three of those years. Dr. Shewmon was elected to the National Academy of Engineering in 1979 and has been awarded the standing of Fellow in TMS, ASM, ANS, and AAAS. He has received several outstanding paper awards (Noble-AIME, Raymond—TMS, Mathewson—TMS, and Howe—ASM). He received the Distinguished Alumnus Award of the University of Illinois in 1981 and a Humboldt Foundation Senior Scientist Prize in 1984. The Edward DeMille Campbell Memorial Lecture was established in 1926 as an annual lecture in memory of and in recognition of the outstanding scientific contributions to the metallurgical profession by a distinguished educator who was blind for all but two years of his professional life. It recognizes demonstrated ability in metallurgical science and engineering. The Institute of Metals Lecture was established in 1921, at which time the Institute of Metals Division was the only professional division within the American Institute of Mining and Metallurgical Engineers. It has been given annually since 1922 by distinguished people from this country and abroad. Beginning in 1973 and thereafter, the person selected to deliver the lecture will be known as the “Institute of Metals Division Lecturer and R.F. Mehl Medalist” for that year.     

The migrational characteristics of the cusp-oriented α/κ interface in the Cu-Si system

The mobility of the coherentα/κ boundaries in the copper-silicon system was studied in a Cu plus 5.16 wt pct Si alloy with a lamellar microstructure. A new resistometric technique was employed to study the isothermal kinetics ofα/κ interphase boundary migration as a function of driving force at two reaction temperatures, 702° and 568°C. The driving force was shown to be linearly related to the temperature change, δT, and the experimental results show that the functional relationship between mobility and δT exhibits an initial linear dependence followed by a sharp rise in mobility at higher values of δT. Upquench and down-quench results were found to be equivalent, implying that the mechanism for boundary motion is independent of whether the boundary is moving into theα or into theκ phase. The results demonstrate that theα/κ interface does not move normal to itself by the long range bulk diffusion of silicon at low values of δT during the initial periods of the reaction times. A pole mechanism with its associated dislocation node configuration, consisting ofa/2〈112〉 andc[00.1] pole dislocations anda/6〈112〉 transformation partial, is proposed as the mechanism for the migration of the coherent fcc/hcp boundary in the range of small δT. The results obtained at the different reaction temperatures are consistent with the mechanism proposed, and quantitative agreement exists between the experimental and predicted mobilities. The sharp rise in mobility at larger values of δT could not be explained in terms of the pole mechanism. Attempts to rationalize this behavior in terms of a two dimensional nucleation model were not successful since unrealistically low values of surface energy would be required. Formerly with Carnegie-Mellon University Formerly Professor, Carnegie-Mellon University This paper is based on a portion of the Ph.D. Thesis submitted by J. K. TIEN to the Department of Metallurgy and Materials Science, Carnegie-Mellon University, in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Metallurgy and Materials Science.