Paul R. Howell

The pearlite reaction in steels : Mechanisms and crystallography. Part I. From H. C. Sorby to R. F. Mehl

Abstract The mechanisms for the formation of pearlite in steels are reviewed with particular reference to the work of R. F. Mehl and colleagues. The role of crystallography in the early theories, and inherent in the mechanisms of Mehl et al., is also discussed. Certain inconsistencies are shown to exist between Mehl’s ideas and more current concepts. A description of Mehl’s pioneering work on quantifying the pearlite reaction in terms of nucleation and growth rates and of interlamellar spacings also is presented.

The application of metallographic techniques to the study of the tempering of HSLA-100 steel

Abstract A study of a quenched, and a quenched and tempered low-carbon, copper-containing steel (HSLA 100) was conducted. The primary investigative technique employed was transmission electron microscopy. Quenching the steel from the austenitizing temperature yielded a microstructure that was predominantly lath martensite. However, a significant amount of retained austenite was also present. Niobium carbide particles were also documented in the as-quenched structures. Tempering at 605°C for 1–3 h yielded a heterogeneous distribution of eCu, much of which was associated with the lath boundaries. The austenite was highly resistant to decomposition during tempering at 605°C and, as a consequence, little evidence of cementite precipitation was found.

On the origin of deformation twinning in electrodeposits and the phenomenon of cross-twinning

On observe des morphologies de macles interessantes avec des intersections de macles multiples dans des echantillons de depots electrolytiques de palladium

Archaeological Copper Smelting at Itziparátzico, Michoacan, Mexico

Mesoamerican copper metallurgy emerged in West Mexico sometime between A.D. 600 and 800. Over a period of approximately 900 years a wide variety of artifacts, typically decorations and other valuable non-utilitarian goods, were produced. By A.D. 1450, the Tarascan kingdom in the state of Michoacan had become the most important center of pre-Hispanic metalworking. Metallurgy played a significant role in the structure of political and economic power in the Tarascan Empire. Metal adornments used as insignia of social status and public ritual became even more associated with political power. While metal was used for an array of goods, virtually nothing is known about the manufacture and the organization of production of this material. Archaeological research at the site of Itziparatzico, near the modern Tarascan community of Santa Clara del Cobre, has recently located potential production areas where concentrations of smelting slag were recorded. The smelting of ores is almost invariably related to the formation of slags, which form from the various impurities introduced into the smelting process, such as gangue minerals, furnace wall material, and fuel ash. Slag analysis thus has the potential for revealing important information about metallurgical technology. Copper smelting slag recovered from the excavations at Itziparatzico has been analyzed for microstructure and compositional properties using light microscopy, x-ray fluorescence spectrometry (XRF), and scanning electron microscopy with energy-dispersive x-ray spectrometry (SEM/EDS). Preliminary results indicate a smelting technology that used sulfidic ores and highly efficient furnaces. While further archaeological investigations are required to precisely date these activities, this technological information is important for establishing the context and scale of production of copper at the site.

Transmission electron microscopy of electrodeposits

Commercial electrodeposits are usually fine grained and highly stressed. Conventional transmission electron microscopy (TEM) studies reveal defect-free structures except for the presence of twins. However, high voltage TEM studies of thick specimens show a high concentration of dislocations and lack of twins, which suggests a restructuring of electrodeposits during TEM specimen thinning.

Dopant Enhanced Grain Growth During Crystallization of Amorphous Silicon Using Rapid Thermal Anealing

PECVD a-Si deposited at 250oC on 7059 glass was used as precursor material to produce low resistivity large grain doped poly Si. The films doped in the range of 10 20 −10 21 cm -3 with P during growth or by ion implantation wereannealed at 700oC for times 2 to 5 minutes using RTA. A dopant enhanced grain growth was observed with grain sizes of the order of 3 μm for films of only 2000A thickness. Resistivity as low as 6x10 -4 Ω-cm and mobility as highas 34 cm 2 /V-sec. were obtained using this low thermal budget process.These values are comparable to those obtained in the literature using significantly higher annealing temperatures.

Techniques for the production of thin foils from the interfacial regions of iron-zinc couples

Abstract In an effort to characterize interfacial microstructures in FeZn bimetallic couples, various techniques for the production of thin foils for examination with the transmission electron microscope (TEM) were developed. Microcrystalline arrays were observed in bright-field transmission electron microscopy images in the vicinity of the FeZn interface. Selected-area diffraction pattern analyses of these microcrystalline regions indicated the presence of several intermetallic phases and/or mixtures of these phases. These phases might originate during ion-beam thinning. However, it is argued that they could also form during room temperature aging.

A Preliminary Characterization of the Defect Structure of the Zeta Phase in the Interfacial Region of Fe-Zn Couples

A preliminary investigation of the defect structure of the monoclinic zeta phase, within the interfacial region of Fe-Zn couples, has been performed using cross-section transmission electron microscopy (TEM). Twin boundaries and dislocations have been unambiguously identified, however, examples of defects which, as of yet are unknown, are also presented. The monoclinic zeta phase was found to twin by a rotation of 180° about the normal to the (110) plane.

The Role of Dislocations in the Superplastic Deformation of a Duplex Stainless Steel

Transmission electron microscopy (TEM) has been employed to examine the role of dislocations in the superplastic deformation of a duplex stainless steel. In particular, matrix, grain boundary and interphase interface dislocation distributions have been documented after testing in region II. It is concluded that dislocation activity is of importance during superplastic flow and both loop sources and dislocation pile-ups have been observed. The presence of highly distorted dislocation arrays also suggests that grain and interphase boundary sliding is intimately linked to the motion of grain and interphase boundary dislocations. Finally, it is argued that dislocation multiplication in interphase interfaces can involve the operation of loop sources.

The Design, Implementation and Assessment of an On-Line, Open-Book Quizzing Environment for an Introductory Materials Science Course.

The authors have developed, implemented and assessed an on-line, open-book quizzing environment for the introductory materials science course, “Materials In Today’s World”. The course is offered as an E-Education course and students may complete the course from anywhere that permits access to our course management system, ANGEL. For reasons that were both pragmatic and philosophical, we decided that the exams/quizzes would not be proctored, they would be delivered wholly on-line, and would be open-book. In the current paper, we will present and justify our philosophy, of on-line, open-book quizzes: the rich feedback, which is a feature or our quizzing system, Question Mark Perception, is used both as a teaching tool, and as a means to refine the quiz database. We have replaced the original “high-stakes” midterm and final exam, with a series of lower-stakes, weekly quizzes, which are generated from a large question database. Student response to the quizzing environment is generally very positive.