Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Phd by thesis

Principles of equal-channel angular pressing as a processing tool for grain refinement

1. Introduction 2. The physical metallurgy of nickel and its alloys 3. Single crystal superalloys for blade applications 4. Superalloys for turbine disc applications 5. Environmental degradation: the role of coatings 6. Summary and future trends.

The Superalloys: Fundamentals and Applications

This article presents an overview of the developments in stainless steels made since the 1990s. Some of the new applications that involve the use of stainless steel are also introduced. A brief introduction to the various classes of stainless steels, their precipitate phases and the status quo of their production around the globe is given first. The advances in a variety of subject areas that have been made recently will then be presented. These recent advances include (1) new findings on the various precipitate phases (the new J phase, new orientation relationships, new phase diagram for the Fe–Cr system, etc.); (2) new suggestions for the prevention/mitigation of the different problems and new methods for their detection/measurement and (3) new techniques for surface/bulk property enhancement (such as laser shot peening, grain boundary engineering and grain refinement). Recent developments in topics like phase prediction, stacking fault energy, superplasticity, metadynamic recrystallisation and the calculation of mechanical properties are introduced, too. In the end of this article, several new applications that involve the use of stainless steels are presented. Some of these are the use of austenitic stainless steels for signature authentication (magnetic recording), the utilisation of the cryogenic magnetic transition of the sigma phase for hot spot detection (the Sigmaplugs), the new Pt-enhanced radiopaque stainless steel (PERSS) coronary stents and stainless steel stents that may be used for magnetic drug targeting. Besides recent developments in conventional stainless steels, those in the high-nitrogen, low-Ni (or Ni-free) varieties are also introduced. These recent developments include new methods for attaining very high nitrogen contents, new guidelines for alloy design, the merits/demerits associated with high nitrogen contents, etc.

Recent developments in stainless steels

The precipitation sequence in Al–Mg–Si alloys

Fine-scale precipitation of the metastable Zn- and Mg-rich η′ phase and its precursors is essential for the mechanical properties of Al–Zn–Mg alloys. However, at present neither the precipitation sequence nor the structure and composition of the intermediate precipitate phases are completely clear. This paper deals with an investigation of precipitation in an industrial Al–Zn–Mg alloy at various stages of a conventional two-step ageing treatment at 100° and 150°C. Studies were performed using both transmission electron microscopy and atom-probe field ion microscopy. Transmission electron microscopy (TEM) analysis revealed two parallel precipitation paths; one involving formation and dissolution of the ordered GP (I) zones, the other involving formation of clusters (type II), having a different atomic arrangement compared to the Al-matrix, which transform to the η′ phase. Atom-probe study of the material after short time ageing at 100°C did not show any observable distinction between GP (I) and type II precipitates. In the peak-aged material the best classification of precipitates was obtained using their morphology (the cigar-like and the plate-like) because there was significant overlap in the range of total solute contents of each type of precipitate. Generally the Zn:Mg ratio in all observed types of precipitates was close to 1:1 and the total solute atom content increased with ageing time. Distribution of alloying elements in the precipitates and in the surrounding matrix is discussed.

Investigation of precipitation in an Al–Zn–Mg alloy after two-step ageing treatment at 100° and 150°C

http://publications.lib.chalmers.se/records/fulltext/138057/local_138057.pdf

Quantitative atom probe analysis of carbides.

Transmission electron microscopy and atom probe field ion microscopy have been used to study the effect of heat treatment at 150 °C and material composition on precipitation in Al–Zn–Mg alloys. Two Cu-free materials with different Zn:Mg ratios (1.7 and 3.2) and one material with low Zn:Mg ratio but with small additions of Cu have been investigated. Selected area electron diffraction patterns of Cu-free materials revealed the presence of GP II zones for all heat treatments used. The number of η particles increased for longer ageing times, but η′ is the dominant precipitate phase up to 6 h at 150 °C. In the material containing Cu, occurrence of GP I zones was also observed. One dimensional atom probe analyses showed that Zn:Mg ratio in the precipitates decreased with heat treatment time increase and that particle number density got lower. Investigation also revealed that Cu is incorporated into the precipitates. An attempt to estimate the contribution of Al excess into η′ due to ion trajectory aberration has been made. The influence of Cu and excess Zn on the precipitation process is discussed.

Investigation of fine scale precipitates in Al–Zn–Mg alloys after various heat treatments

Atom-probe tomography (APT) is in the midst of a dynamic renaissance as a result of the development of well-engineered commercial instruments that are both robust and ergonomic and capable of collecting large data sets, hundreds of millions of atoms, in short time periods compared to their predecessor instruments. An APT setup involves a field-ion microscope coupled directly to a special time-of-flight (TOF) mass spectrometer that permits one to determine the mass-to-charge states of individual field-evaporated ions plus their x-, y-, and z-coordinates in a specimen in direct space with subnanoscale resolution. The three-dimensional (3D) data sets acquired are analyzed using increasingly sophisticated software programs that utilize high-end workstations, which permit one to handle continuously increasing large data sets. APT has the unique ability to dissect a lattice, with subnanometer-scale spatial resolution, using either voltage or laser pulses, on an atom-by-atom and atomic plane-by-plane basis and to reconstruct it in 3D with the chemical identity of each detected atom identified by TOF mass spectrometry. Employing pico- or femtosecond laser pulses using visible (green or blue light) to ultraviolet light makes the analysis of metallic, semiconducting, ceramic, and organic materials practical to different degrees of success. The utilization of dual-beam focused ion-beam microscopy for the preparation of microtip specimens from multilayer and surface films, semiconductor devices, and for producing site-specific specimens greatly extends the capabilities of APT to a wider range of scientific and engineering problems than could previously be studied for a wide range of materials: metals, semiconductors, ceramics, biominerals, and organic materials.

Krystyna Marta Stiller

Papers

The precipitation sequence in Al–Mg–Si alloys

Investigation of precipitation in an Al–Zn–Mg alloy after two-step ageing treatment at 100° and 150°C

Quantitative atom probe analysis of carbides.

Investigation of fine scale precipitates in Al–Zn–Mg alloys after various heat treatments

An atom-probe tomography primer