Precipitation hardening of Cu – Ti – Zr alloys

Abstract

The influence of age hardening temperature and time on the hardness, tensile properties, electrical conductivity, and microstructure of Cu – 4Ti – 0.1Zr and Cu – 3Ti – 0.1Zr alloys has been investigated. The resulting microstructure of these alloys suggests that zirconium addition prohibited the formation of compositional modulations in the solution treated condition. These alloys exhibited maximum hardness and strength on peak aging at 450°C for 24 h by the formation of a coherent and metastable Cu₄Ti phase (β') in modulated structure while overaging occurred by the formation of equilibrium phase β-Cu₃Ti. The electrical conductivity of both the alloys increased moderately on aging. Unlike in an earlier study of binary Cu – Ti and some ternary Cu – Ti – X alloys, overaging did not cause any discontinuous precipitation in the Cu – Ti – Zr alloys investigated. Modulated structure formed on peak aging persisted on prolonged aging at 450°C for 80 h or at 500°C for 8 h.     

Preparation and Properties of Pb1 – xSnxTe1 – ySeyEpilayers

Pb_{1 – x} Sn _x Te_{1 – y} Se _y layers lattice-matched with KCl and BaF₂are grown by liquid-phase epitaxy. Epilayer compositions and growth temperatures are determined at which p- and n-type materials can be obtained without doping. The composition dependences of the Hall coefficient and carrier mobility are analyzed.     

Thermal aging of 16Cr – 5Ni – 1Mo stainless steel Part 1 – Microstructural analysis

Abstract

Specimens of 16Cr - 5Ni - 1Mo stainless steel were solution treated at 1050 ° C for 1 h followed by heating in the temperature range 400 - 750 ° C for different holding times (1 - 16 h). After heat treatment, optical microscopy, scanning (SEM) and transmission (TEM) electron microscopy, and X-ray diffraction examinations were conducted. The microstructure of all aged specimens was found to consist of martensite with variable fractions of δ ferrite and reversed austenite. Very fine precipitates of Mo carbides were revealed in the specimens aged at 475 ° C. The specimens aged at 625 ° C showed a decrease in the dislocation density and a high volume fraction of austenite and precipitation of Fe₂Mo Laves phase was detected by X-ray analysis. Above 625 ° C, Cr₂₃C₆ and TiC became the predominate carbides heterogeneously precipitated in the martensitic matrix. Partial transformation of reversed austenite to unaged martensite was observed at temperatures above 625 ° C.     

Near-IR Emitting InyGa1 – ySb1 – xBix Solid Solutions

Inorganic Materials - This paper examines the formation of InyGa1 – ySb1 – xBix isovalently (Bi) doped solid solutions under temperature-gradient zone recrystallization conditions. We...     

Thermal aging of 16Cr – 5Ni – 1Mo stainless steel Part 2 – Mechanical property characterisation

Abstract

Mechanical property characterisation has been carried out on specimens of 16Cr - 5Ni - 1Mo stainless steel, subjected to various aging cycles. The heat treatment cycles involved solution treatment at 1050 ° C for 1 h followed by heating in the temperature range 400 - 750 ° C for different holding times (1 - 16 h). After heat treatment, tensile, hardness, impact, and creep tests were conducted. Specimens aged at 475 ° C exhibited maximum values of tensile strength and hardness with minimum values of ductility and impact toughness, while specimens aged at 625 ° C had maximum values of impact toughness and ductility. The results were correlated with the microstructural data presented in Part 1 of this study. Softening of the martensitic matrix at 625 ° C occurs as a result of the elimination of internal stresses, the decrease in the dislocation density, and the high volume fraction of austenite which lead to the drop in values of tensile strength and hardness. The results of the study reveal that aging at 550 ° C for 4 h gives the optimum combination of strength, hardness, ductility and toughness for this steel.     

Effect of minor cerium additions on microstructure and mechanical properties of cast Al – Cu – Mg – Ag alloy

Abstract

A series of cast Al – Cu – Mg – Ag based alloys with minor cerium additions have been investigated using optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and transmission electron microscopy. It was found that increasing the cerium content from 0 to 0.45 wt-% increased the tensile strength at the test temperatures of 25°C and 300°C. The high strength of the casting alloys with cerium is attributed to the refined grains and the high density of fine ω precipitates. However, the addition of 0.2 wt-%Ce to the alloy with 0.25 wt-%Ti induced a detrimental effect on the mechanical properties. The cause of this was found to be the formation of the intermetallic compound Al_x Ti₆ Ce₃ Cu.     

Effect of thermomechanical treatment on spray formed Cu – Ni – Si alloy

Abstract

The heat treatment response of a spray formed Cu – 2.4Ni – 0.6Si (wt-%) alloy has been investigated. The spray formed alloy was given various thermomechanical treatments prior to isothermal aging. These treatments included solutionising and/or cold rolling with different reductions in original thickness. The variation in hardness and electrical conductivity of the alloys was measured as a function of the aging time. The results indicated the highest peak hardness value of ~250 kg mm^-2 for the alloy aged after solution treatment and cold rolling to 40% reduction in thickness, compared with the maximum hardness of 220 kg mm^-2 for specimens aged directly in the as spray formed condition. However, the electrical conductivity after aging was observed to be a maximum of 65%IACS (International Annealed Copper Standard) in specimens cold rolled to 80% reduction in thickness before aging. The aging response was observed to accelerate with the degree of cold working. Optical, scanning electron and transmission electron microscopy were used for microstructural characterisation of the materials. Precipitation of the second phase was observed to dominate in deformation bands. The alloy showed evidence of discontinuous precipitation, particularly when the alloys were cold rolled before aging. The onset of discontinuous precipitation led to a drastic deterioration in hardness of the alloys. The precipitation behaviour of the alloy is discussed in the light of microstructural characteristics associated with various processing conditions of the alloy.     

Turbulenz – ein problemhistorischer Abriss

Turbulence in Perspective In the beginning of the 20th century, the riddles of turbulent flow became articulated as “the turbulence problem”. It comprised two parts: the onset of turbulence, which was conceived as an instability of laminar flow; and fully developed turbulence, for which both empirical (mixing length) and statistical theories of turbulence were developed. Up until the present time turbulence research has been inter-and transdisciplinary, attracting scientists and engineers from a variety of specialties and with diverse scientific and technological orientations. For this reason, turbulence research is also an interesting case for the sociological study of knowledge production in technoscience. The article traces the history of the turbulence problem in the first half of the 20th century, when the major pathways for its attack were first outlined and explored. The ups and downs of the turbulence problem in different local and cultural settings provide a unique opportunity to study a technoscience in the making, beyond sweeping assumptions about science-technology relations. Present fluid dynamicists rate the turbulence problem still as unsolved, but this evaluation should not prevent historians of science and technology from tackling it by their own means: it safeguards the historical analysis against the pitfall of whig history.

Diese Studie entstand im Rahmen eines Projekts zur Geschichte der Str?mungsforschung, das von der Deutschen Forschungsgemeinschaft als Teilprojekt der Forschergruppe 393 gef?rdert wurde. Ich danke auch den Kollegen am Deutschen Museum, wo ich ein für dieses Forschungsthema an der Schnittstelle von Wissenschafts- und Technikgeschichte bestens geeignetes Milieu gefunden habe.     

Compositions of Two Morphological Forms of β-Si6 – zAlzOzN8 – z

Analysis of experimental data on the formation of -sialon (-Si_{6 – z} Al _z O _z N_{8 – z} ) at high temperatures (1300–1500°C) indicates that two morphological forms—fibers and spherical particles—differ in chemical composition:z = 3.58 in the fibers and 2.60 in the spherical particles. The formation of fibers is assumed to follow the whisker growth mechanism, while the spherical particles are likely to grow via diffusion.     

Transition metal oxides – Thermoelectric properties

Transition metal oxides (TMOs) are a fascinating class of materials due to their wide ranging electronic, chemical and mechanical properties. Additionally, they are gaining increasing attention for their thermoelectric (TE) properties due to their high temperature stability, tunable electronic and phonon transport properties and well established synthesis techniques. In this article, we review TE TMOs at cryogenic, ambient and high temperatures. An overview of strategies used for morphological, compositing and stoichiometric tuning of their key TE parameters is presented. This article also provides an outlook on the current and future prospects of implementing TMOs for a wide range of TE applications.     

Domestic product failures – Case studies

Every year in the UK more than 4000 people die in accidents in and around the home and nearly three million turn up at accident and emergency departments seeking treatment. Intrinsic in this number are many incidents of injury or death directly attributable to poor product design or manufacture of domestic products. In and around the home, commodities that dominate so much of every-day life are becoming more numerous and complex and could be mooted as an argument for such dire statistics. Moreover, society in general is becoming more litigious. These converging trends are responsible for an increasing significance of product liability. When property is damaged, personal injury sustained or loss of life occurs there is an understandable need to determine where any fault may lie. The forensic (or failure) engineer will glean relevant information through meticulous investigation and a reverse engineering process. Reconstructing the failure will uncover any inherent defect in product design, manufacturing, incorrect installation or maintenance. However, product failure can also be attributable to careless use or abuse by the individual, rather than to any specific defect or design shortcoming being inherent within a product. Ultimately the outcome of any investigation will be a sound finding and a conclusion that clearly describes what happened and why. To illustrate typical failure modes that are currently emerging in the home-based UK market, a range of domestic product failures are presented from the author’s forensic casebook.     

Veneering composites – a thermoanalytical examination

Differential thermal analysis and thermal gravimetric analysis were used to characterize veneering composites. Samples weighing 4–20 mg, made from the composite materials Visio-Gem (Espe, Germany), Sinfony (Espe, Germany), Artglass (Kulzer, Germany), Dentacolor (Kulzer, Germany) and Targis (Ivoclar, Liechtenstein), were examined. The samples were subjected to various thermal curing times of between 4 s and 25 min, using the relevant devices of the manufacturers. As a control group, samples of all materials were examined unreacted. In order to avoid post-curing during storage, all samples were subjected, immediately after manufacture, to the appropriate dynamic temperature programme of the thermoanalytical unit at a heating rate of 10 °C min-1. The materials showed specific material characteristics which can, for instance, be used to analyse the curing behaviour of the materials. The position of the glass transition, polymerization and post-polymerization peaks at temperatures between 30 and 100 °C, as well as 150 and 300 °C, and the filler and matrix content, allow the classification of the veneering composites. © 1999 Kluwer Academic Publishers     

Setup-oriented dispatching rules – a survey

This paper provides a survey of dispatching rules that explicitly take into account setup times in their decision making. Rules are classified into the categories of purely setup-oriented, composite and family-based rules, and the most promising rules from the three categories are identified from the literature. These rules are then compared empirically on various job shop problems with sequence-dependent setup times for their performance regarding mean setup time, mean flow time, mean tardiness and proportion of tardy jobs. The setup times are modelled using setup time matrices, and five different types of matrices are applied to assess the influence of this factor on the relative performance of a setup-oriented dispatching rule. Experimental results indicate that the choice of the best rule is often dependent on the setup time matrix structure. While good family-based rules exist for reducing the mean setup time and mean flow time, they are clearly outperformed by effective composite rules for due date-related criteria. Moreover, the better rules all seem to rely on queue information rather than only job attributes.     

Engineering ceramics – the process problem

Abstract

The main problem to be solved before advanced engineering ceramics can become industrial reality is that components having reliable and consistent properties cannot be made, and rejection rates can be as high as 95%, in stark contrast to the situation with metals and polymers. This results from the small size of defect sufficient to cause failure in a ceramic and the variability in the population density of such defects. It is unlikely that sufficiently sensitive non-destructive testing and diagnostic techniques will become available, and so success will depend on the development of intrinsically reliable process technology. The nature and origin of defects in ceramics are discussed and related to raw material characteristics and process technology. The changes that are needed in raw materials and processes are outlined, and the various approaches to intrinsically reliable techniques (such as the colloidal processing of submicrometre powders, sol–gel methods, etc.) are critically assessed in the light of the need for industrially realistic processes. An attempt is made to assess likely future developments such as ceramic fibre reinforced ceramics.

MST/409     

Influence of the surface mechanical pulsed treatment on the oxidation of Fe – 0.2C – 13Cr – 0.3Si steel in lead melts

We study the influence of mechanical pulsed treatment (MPT-1) on the corrosion resistance of Fe – 0.2C – 13Cr – 0.3Si steel in a lead melt containing 1.3 · 10^{– 3} wt.% of oxygen at a temperature of 550°C for 1000 h. It is shown that the MPT promotes the formation of micro- and macrodefects in the subsurface zone of the specimens, which intensifies the process of oxidation of steel. The oxidation resistance of steel after MPT-2 and MPT-3 (with adding aluminum and silicon) is attained as a result of the formation of a hardened zone with nanocrystalline structure and large lengths of grain boundaries intensifying the diffusion of chromium into the oxide films.     

Determination of the Melt Undercooling Required for Producing Al x Ga y In1 – x – y Sb1 – z Bi z /InSb Heterostructures

Conditions for temperature-gradient epitaxial growth of Al _x Ga _y In_{1 – x – y} Sb_{1 – z} Bi _z /InSb heterostructures are examined. The factors are established which determine the initial melt undercooling required for preventing the thermal degradation of the substrate.     

Marketing and operations research – a literature survey Marketing und Operations Research – Eine Literaturübersicht

Over the last decades the quantitative research based on Operations Research and Management Science (OR/MS) approaches has become one of the leading research paradigms in marketing. The aim of this article is, to give the reader of this special issue an overview of recent publications in OR/MS based marketing research. Its basis is a literature review of quantitative marketing publications with OR/MS orientation in the leading journals of marketing and management. The review reveals general differences in the quantity of the publications and the domain of research between those journals published in English and those in German. The review also provides an overview of research publications during the recent years and shows possible future trends in quantitative marketing research.     

PGE – Produktgenerationsentwicklung am Beispiel des Zweimassenschwungrads

Forschung im Ingenieurwesen - PGE – Produktgenerationsentwicklung – ist ein am IPEK entwickelter Ansatz, der erstmals eine zutreffende Charakterisierung von...     

Obsolescence – A review of the literature

Technology progress and fierce competitiveness between manufacturers creates intense pressues to innovatively develop and sell new products. These products could be household or industrial items, such as telephones, computers, machines, robots, unmanned aerial vehicle (UAV), motors, industrial processes, electronic devices, tools, and spare parts in general. The technological progress implies the use of the word “obsolescence.” The new products have higher performance metrics compared to the older units, such as reliability, resilience, memory capacity, improved material, precision, artificial intelligence, lower energy consumption, ergonomics, and safety. Therefore, obsolescence became a paradox in our daily life and industry. This paper presents a literature review of the main published works on obsolescence (1976–2020). Its typologies, consequences and replacement strategies are illustrated.