ISSN:0267-0836    

DOI:10.1179/mst.1987.3.9.681

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractThe development of what are now termed superalloys is reviewed from the early days of high-temperature alloys in the light of the demands of engineers for materials to serve under differing conditions of stress, temperature, and environment. Before the introduction of the aircraft gas turbine the main interest lay in the field of low-alloy creep resisting steels for steam raising plant or in heat resistant alloys for relatively low-stressed furnace components. Piston aeroengines posed two problems–the exhaust valve and the turbo supercharger rotor–and special materials for these components were introduced, largely on the basis of high-temperature tensile strength. The gas turbine demanded high creep resistance and two main lines of alloy development were followed: carbide-hardened iron or cobalt-base alloys andγ′-hardened nickel-base alloys. The latter type has surpassed the former and now, either in wrought form or, predominantly for the most severe conditions, as castings, is the mainstay of superalloy applications. In recent years, progress has mainly been sought by the improvement of macrostructure: in castings by directional solidification to give columnar crystals or single crystals and in wrought products by powder technology. Severe hot corrosion has been combated by the application of protective surface coatings and the development of a series of wrought and cast high-chromium nickel-base alloys. It is anticipated that future progress in high-temperature materials technology will be sought in the application of a variety of metallurgical and physical techniques to specific engineering components in much the same manner as was done with the aeroengine exhaust valve of 50 years ago.MST/511

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.9.682

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractThe outstanding performance of current military and civil aero gas turbine engines is linked closely to the way in which modern design and manufacturing techniques have become totally integrated with materials designed specifically for operation within the hostile environment of a gas turbine. Advanced titanium alloys are used extensively throughout the compressor and nickel-base superalloys dominate materials application in the turbine. In spite of current achievements, the engine designer is still under severe competitive pressure to improve engine performance still further and this will inevitably lead to even more demanding material requirements. The present paper outlines the continuing trends in engine development and describes the impact these are having on materials technology in general and the mechanical property requirements of nickel-base superalloys in particular.MST/512

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.9.695

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractA new approach to creep data analysis, termed theθ-projection concept, is shown to offer a material constitutive relationship which is ideally suited to modern computer-base procedures for high-temperature design. The concept is illustrated by reference to high-precision constant-stress data obtained for the conventionally cast turbine blade superalloy IN 100.MST/515

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.9.701

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractThe low-cycle-fatigue (LCF) behaviour of superalloys has been examined with particular emphasis on their early stage strength changes and their response to complex cycling. Using steels and a titanium alloy as comparators, it has been possible to establish some general guidelines regarding their LCF performance. In the normal testing domain (700–1000°C) a high yield strain results in predominantly elastic conditions and cyclic stability. Under strain controlled dwell testing superalloys are fatigue dominated and generally more sensitive to compressive hold periods, whereas under stress control shortest lifetimes result from tensile dwells. Environmental influences are strong especially at temperatures where oxides remain brittle, but at high temperatures (>900°C) overaging effects may be beneficial. During thermal–mechanical cycling in-phase testing appears most deleterious.MST/516

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.9.706

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractThe main factors influencing high temperature fatigue crack growth in superalloy blade materials are discussed. The significance of temperature, frequency, environment, and minimum to maximum load ratio R are considered in turn. Transgranular cycle dependent and intergranular time dependent controlled cracking processes are identified. Conditions favouring each mechanism are clarified and it is shown that cumulative damage concepts can be applied to predict interaction effects. It is found that cycle controlled processes are most likely to dominate at high frequency and low values of R. Creep and oxidation mechanisms, which are favoured by low frequencies, high temperatures, and high values of R, have been identified as contributing to the time-dependent component of cracking. It is shown that creep and oxidation can enhance crack growth/cycle significantly and reduced blade lifetimes.MST/517

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.9.716

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractRecent developments in superalloy technology for turbine aerofoil applications are reviewed, such as single crystals (SC), oxide dispersion strengthening (ODS), and rapid solidification (RS). Single crystal and ODS superalloys are in production use in aircraft turbine engines. While ODS superalloys exhibit higher strength at high temperatures, SC superalloys are somewhat stronger at intermediate temperatures. It will depend on engine design which alloy can give greater advantage. The strength potential of RS superalloys is probably less than or equal to SC superalloys which does not justify the complicated processing. If SC or ODS technology is to be applied to industrial engines of high power, more corrosion resistant alloys must be developed and component fabrication methods will have to be scaled-up.MST/518

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.9.726

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractDiscs have always been the life- and reliability-limiting components of the gas turbine engine. Progress in disc materials development has been enhanced through the interaction of superalloy materials and metallurgical process development. Disc service environment, property requirements, and physical metallurgy are reviewed. Historically, the introduction of stronger, more heat- and fatigue-resistant alloys has depended upon process developments such as vacuum induction melting, inert gas atomization, and thermomechanical processing. Current developments and future directions are reviewed, including new melting practices for the manufacture of clean metals, the forging of fatigue resistant microstructures and dual property discs.MST/519

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.9.733

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractThe failure mechanisms that can occur in a component in service are discussed. The mechanisms are categorized into three major classes: low-life failures, macroscopically non-localized damage accumulation, and macroscopically localized damage accumulation. The methods used to avoid these failure mechanisms are discussed in detail. The problem of fatigue life prediction is highlighted and the‘traditional’initiation life calculation method is compared and contrasted with fracture mechanics based methods. The importance of performing full scale component tests for highly stressed gas turbine parts is highlighted, both from the traditional lifing viewpoint and to validate fracture mechanics based calculations. Finally, some examples are given of the comparison of fracture mechanics fatigue life predictions with full scale component rig test results.MST/520

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.9.743

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractThe current state of knowledge and understanding of the long fatigue crack propagation behaviour of nickel-base superalloys are reviewed, with particular emphasis on turbine disc materials. The data are presented in the form of crack growth rate da/dN versus stress intensity factor rangeδK curves, and the effects of such variables as microstructure, load ratio R, and temperature in the near-threshold and Paris regimes of the curves, are discussed.MST/521

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.9.750

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor