There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

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

Additive manufacturing of metallic components – Process, structure and properties

Unlike conventional materials removal methods, additive manufacturing (AM) is based on a novel materials incremental manufacturing philosophy. Additive manufacturing implies layer by layer shaping and consolidation of powder feedstock to arbitrary configurations, normally using a computer controlled laser. The current development focus of AM is to produce complex shaped functional metallic components, including metals, alloys and metal matrix composites (MMCs), to meet demanding requirements from aerospace, defence, automotive and biomedical industries. Laser sintering (LS), laser melting (LM) and laser metal deposition (LMD) are presently regarded as the three most versatile AM processes. Laser based AM processes generally have a complex non-equilibrium physical and chemical metallurgical nature, which is material and process dependent. The influence of material characteristics and processing conditions on metallurgical mechanisms and resultant microstructural and mechanical properties of AM proc...

Laser additive manufacturing of metallic components: materials, processes and mechanisms

Beta phase decomposition in Ti-44Al-4Nb-4Hf-0.1Si during continuous cooling from β phase field has been investigated. A wide cooling rate range (0.3-1000°Cs-1) was provided by mainly using Jominy end quenching, which has been introduced into TiAl research recently, together with iced brine quench (IBQ) and furnace cooling (FC). At different cooling rates beta phase decomposes via different paths through diffusion or diffusionless mechanisms and lamellar transformation may occur after β decomposition at certain cooling rates.

Beta Phase Decomposition in a TiAl Alloy during Continuous Cooling

Solid samples about 20mm long, 20mm in breadth and about 2mm thick of Ti-6AI-4V have been produced from powder using direct laser fabrication. The temperature histories of individual layers have been measured by inserting thermocouples during laser fabrication. The changes in microstructure along the height of the laser fabricated samples have been characterized using optical, scanning electron and transmission electron microscopy, together with X-ray diffraction. A 3D-transient finite element model using ABAQUS has been developed which predicts thermal history during laser fabrication with reasonable accuracy. The thermal histories of different parts of the sample have been used to interpret the influence of the processing variables on the microstructures.

An Experimental and Modelling Study of Laser Fabricated Samples

A heat-treatable aluminum alloy A357 has been chosen in this study to obtain further understanding about the relative density and mechanical properties after selective laser melting (SLM) and subsequent heat treatment at an experimental stage. Although as one of the most important groups of industrial cast alloys with a high strength/density ratio and good thermal properties, aluminum alloy A357 has been less frequently studied in the SLM field. Also, since conventional casting and SLM are two different techniques, it is not known whether SLM procedures and parameters for heat-treated alloys can be directly transferred to Al alloy A357. From this perspective, this chapter investigates the influence of the parameters for SLM and post heat treatment on the tensile behaviors of Al alloy A357. The possibility of omitting solution heat treatment was also explored, assuming that a supersaturated Al matrix with precipitate-forming elements Si and Mg is already achieved in the as-built condition after high-temperature laser melting and subsequent fast cooling. This refers to direct ageing in this work. Through the application of various combinations of laser fabrication and heat treatment parameters, the corresponding properties of the SLMed materials can be modified, mainly determined by fractographic studies via scanning electron microscopy. An open question is whether these post heat treatment parameters can be properly tailored to avoid issues such as residual stress development during SLM process, and in the meanwhile to maintain the enhanced mechanical properties compared to conventional cast counterparts.

The processing and heat treatment of selective laser melted Al-7Si-0.6 Mg alloy

The influence of microstructure on the fracture toughness of Ti-23A1-9Nb-2Mo-1Zr-1.2Si (at. pct) and Ti-23A1-11Nb-0.9Si (at. pct) Ti3Al-based alloys has been investigated. Basket-weave microstructures comprising different volume fractions of α
 2 and retained β phases were produced by systematic heat treatments. Besides the volume fraction of the retained β phase, the average size of the β laths has also been used to characterize these microstructures. The toughness of both alloys was examined at room temperature, and the brittle transgranular fracture modes were found to be controlled by microstructure. However, the toughness is not determined solely by the volume fraction of the retained β phase, and a linear relationship has been obtained between the fracture toughness and the average size of the retained β laths. It appears therefore that the toughness of Ti3Al-based alloys at room temperature is controlled primarily by the width of retained β laths rather than by the retained β volume fraction.

Effects of microstructure on the fracture toughness of Ti3Al-based titanium aluminides

An extensive programme is being carried out in the IRC aimed at optimising the properties of a range of ordered Ti-based alloys. This paper will focus upon the work done on alloys based on TiAl and on alloys of the type Ti–25V–15Cr–(2–6)Al. The approach to alloy development, which is being used and the range of processing techniques, which have been used in an attempt to optimise the properties, will be described. The work has shown that whilst it is possible to make dramatic improvements in the ductility in the alloys based on Ti–25V–15Cr–(2–6)Al by specific alloying additions, only limited improvements in TiAl-based alloys appear possible through alloy development. In this case, property control is mainly obtained through the use of different processing routes. The significance of this and related work will be discussed.

Xinhua Wu

Papers

Beta Phase Decomposition in a TiAl Alloy during Continuous Cooling

An Experimental and Modelling Study of Laser Fabricated Samples

The processing and heat treatment of selective laser melted Al-7Si-0.6 Mg alloy

Effects of microstructure on the fracture toughness of Ti3Al-based titanium aluminides

Controlling the properties of some ordered Ti-based alloys