Book•
Metallurgy of Welding
03 Apr 1980-
TL;DR: The effect of surface forces on the bonding of materials was studied in this article. But the authors focused on the behavior of welds in service and did not consider the effects of the weld thermal cycle.
Abstract: The effect of surface forces on the bonding of materials. Solid-phase welding and adhesive joining. Soldering and brazing. The joining of ceramics: microjoining. Fusion welding: processes. Fusion welding: mass and heat flow. Metallurgical effects of the weld thermal cycle. Carbon and ferritic alloy steels. Austenitic and high-alloy steels. Non-ferrous metals. The behaviour of welds in service.
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12 Mar 2014
TL;DR: In this paper, the effect of reflectivity of the surface, when a pure, monochromatic laser (6) is used, is remedied by the simultaneous application of a relatively shorter wavelength beam (1).
Abstract: In the laser treatment of a workpiece (9), e.g. for surface hardening, melting, alloying, cladding, welding or cutting, the adverse effect of reflectivity of the surface, when a pure, monochromatic laser (6) is used, is remedied by the simultaneous application of a relatively shorter wavelength beam (1). The two beams (1)(5) may be combined by a beam coupler (4) or may reach the workpiece (9) by separate optical paths (not shown). The shorter wavelength beam (1) improves the coupling efficiency of the higher- powered laser beam (5).
1,539 citations
TL;DR: An overview of laser-assisted forming, joining, machining and surface engineering can be found in this paper, where a review of the relevant literature is presented to highlight the recent advances and open questions.
Abstract: Light amplification by stimulated emission of radiation (laser) is a coherent and monochromatic beam of electromagnetic radiation that can propagate in a straight line with negligible divergence and occur in a wide range of wave-length, energy/power and beam-modes/configurations. As a result, lasers find wide applications in the mundane to the most sophisticated devices, in commercial to purely scientific purposes, and in life-saving as well as life-threatening causes. In the present contribution, we provide an overview of the application of lasers for material processing. The processes covered are broadly divided into four major categories; namely, laser-assisted forming, joining, machining and surface engineering. Apart from briefly introducing the fundamentals of these operations, we present an updated review of the relevant literature to highlight the recent advances and open questions. We begin our discussion with the general applications of lasers, fundamentals of laser-matter interaction and classification of laser material processing. A major part of the discussion focuses on laser surface engineering that has attracted a good deal of attention from the scientific community for its technological significance and scientific challenges. In this regard, a special mention is made about laser surface vitrification or amorphization that remains a very attractive but unaccomplished proposition.
420 citations
TL;DR: In this article, the authors identified the materials processing challenges in wire-arc additive manufacturing (WAAM), including high residual stresses, undesirable microstructures, and solute segregation and phase transformations at solidification.
Abstract: Wire Arc Additive Manufacturing (WAAM) is attracting significant attention in industry and academia due to its ability to capture the benefits of additive manufacturing for production of large components of medium geometric complexity. Uniquely, WAAM combines the use of wire and electric arc as a fusion source to build components in a layer-by-layer approach, both of which can offer significant cost savings compared to powder and alternative fusion sources, such as laser and electron beam, respectively. Meanwhile, a high deposition rate, key for producing such components, is provided, whilst also allowing significant material savings compared to conventional manufacturing processes. However, high quality production in a wide range of materials is limited by the elevated levels of heat input which causes a number of materials processing challenges in WAAM. The materials processing challenges are fully identified in this paper to include the development of high residual stresses, undesirable microstructures, and solute segregation and phase transformations at solidification. The thermal profile during the build poses another challenge leading to heterogeneous and anisotropic material properties. This paper outlines how the materials processing challenges may be addressed in WAAM by implementation of quality improving ancillary processes. The primary WAAM process selections and ancillary processes are classified by the authors and a comprehensive review of their application conducted. Strategies by which the ancillary processes can enhance the quality of WAAM parts are presented. The efficacy and suitability of these strategies for versatile and cost effective WAAM production are discussed and a future vision of WAAM process developments provided.
392 citations
01 Jan 2010
TL;DR: In this paper, a fresh look at the major non-renewable and renewable energy sources and examine their long-term viability, scalability, and the sustainability of the resources that they use.
Abstract: We take a fresh look at the major nonrenewable and renewable energy sources and examine their long-term viability, scalability, and the sustainability of the resources that they use. We achieve this by asking what would happen if each energy source was a single supply of power for the world, as a gedanken experiment. From this perspective, a solar hydrogen economy emerges as a dominant solution to the world's energy needs. If we globally tap sunlight over only 1% of the incident area at only an energy conversion efficiency of 1%, it is simple to show that this meets our current world energy consumption. As 9% of the planet surface area is taken up by desert and efficiencies well over 1% are possible, in practice, this opens up many exciting future opportunities. Specifically, we find solar thermal collection via parabolic reflectors - where focussed sunlight heats steam to about 600?C to drive a turbine - is the best available technology for generating electricity. For static power storage, to provide electricity at night, there are a number of viable options that are discussed. For mobile power storage, such as for fueling vehicles, we argue the case for both liquid and gaseous hydrogen for use in internal combustion engines. We outline a number of reasons why semiconductor solar cells and hydrogen fuel cells do not appear to scale up for a global solution. We adopt an approach that envisions exploiting massive economy of scale by establishing large arrays of solar collectors in hot desert regions of the world. For nonrenewable sources we argue that we cannot wait for them to be exhausted - we need to start conserving them imminently. What is often forgotten in the energy debate is that oil, natural gas, and coal are not only used as energy sources, but we also rely on them for embodying many crucial physical products. It is this fact that requires us to develop a solar hydrogen platform with urgency. It is argued that a solar future is unavoidable, as ultimately humankind has no other choice.
308 citations
01 Jan 2010
TL;DR: A solar hydrogen economy emerges as a dominant solution to the world's energy needs by exploiting massive economy of scale by establishing large arrays of solar collectors in hot desert regions of the world.
Abstract: We take a fresh look at the major nonrenewable and renewable energy sources and examine their long-term viability, scalability, and the sustainability of the resources that they use. We achieve this by asking what would happen if each energy source was a single supply of power for the world, as a gedanken experiment. From this perspective, a solar hydrogen economy emerges as a dominant solution to the world's energy needs. If we globally tap sunlight over only 1% of the incident area at only an energy conversion efficiency of 1%, it is simple to show that this meets our current world energy consumption. As 9% of the planet surface area is taken up by desert and efficiencies well over 1% are possible, in practice, this opens up many exciting future opportunities. Specifically, we find solar thermal collection via parabolic reflectorsV where focussed sunlight heats steam to about 600 � C to drive a turbineVis the best available technology for generating electricity. For static power storage, to provide electricity at night, there are a number of viable options that are discussed. For mobile power storage, such as for fueling vehicles, we argue the case for both liquid and gaseous hydrogen for use in internal combustion engines. We outline a number of reasons why semiconductor solar cells and hydrogen fuel cells do not appear to scale up for a global solution. We adopt an approach that envisions exploiting massive economy of scale by establishing large arrays of solar collectors in hot desert regions of the world. For nonrenewable sources we argue that we cannot wait for them to be exhaustedVwe need to start conserving them imminently. What is often forgotten in the energy debate is that oil, natural gas, and coal are not only used as energy sources, but we also rely on them for embodying many crucial physical products. It is this fact that requires us to develop a solar hydrogen platform with urgency. It is argued that a solar future is unavoidable, as ultimately humankind has no other choice.
283 citations