ISSN:0267-0836    

DOI:10.1179/mst.1986.2.5.425

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

AbstractThe current status of precision vacuum casting technology is reviewed in outline and the historical background of the subject is briefly covered. Particular reference is made to its application to the manufacture in nickel-base superalloys of aerofoil and associated components for gas turbine engines, and possible directions for further development of the process and ancillary technology are examined. The current state of progress in both alloy technology and casting process development is reviewed. In connection with the latter, both the scope of currently available product geometries, from small solid equiaxed components through complex hollow shapes to integrally cast multi-aerofoil components, and the extension of the technology to include large, integrally cast, near-net-shape structural components, are discussed. Specific brief reference is made to the main contributory changes and developments which have taken place in each sector of the process from pattern technology to post-casting processing. The more recently adopted and now increasing utilization of multi- and monocrystalline directionally solidified aerofoils in gas turbine engines is addressed with reference to its impact on alloy chemistry and to the conflicting opinions on the relative merits of the diverse process technology. Also addressed are the increasingly important favourable effects on product quality and casting design flexibility of post-casting coating processes, thermal and thermomechanical treatments, advances in non-destructive testing, and the steady trend of progressively improving product quality assurance technology. Finally, consideration is given to the degree to which the casting of superalloys has reached maturity, and what, if any, prospective further improvements may be developed from which gas turbine engines could derive benefits in performance, weight, or operating efficiency in the future.MST/243

ISSN:0267-0836    

DOI:10.1179/mst.1986.2.5.426

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

AbstractIn order to achieve the very high dimensional and metallurgical standards demanded of precision cast gas turbine components, a large number of factors must be considered during the initial design of the component and the tooling, and in planning the processing technique to be followed. Similarly, during manufacture very precise process controls must be rigorously applied at all stages. In this paper the major variables involved are described, and some of the remedies that are adopted to avoid failures and meet required standards are outlined.MST/262

ISSN:0267-0836    

DOI:10.1179/mst.1986.2.5.436

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

AbstractThis approach has required work in the three broad areas of process development, material development, and quality assurance. The first has led to the development of an automated casting facility, and the adoption of the technically more difficult seeding technique, as a result of its greater process and design flexibility. The second has been met by the development of a series of three alloys to meet specific turbine applications and the economies necessary to make the complex shapes to the required precision. The third has been met by the development of SCORPIO, a real-time rapid-orientation measurement system for the production environment, and the understanding and development of the process controls necessary to control wall section measurements and heat treatment. By the involvement of multidisciplined teams, this approach has led to a demonstrated technology with little or no cost penalty.MST/244

ISSN:0267-0836    

DOI:10.1179/mst.1986.2.5.442

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

AbstractIn this paper the authors compare the creep and low-cycle fatigue properties of conventional, directionally solidified, and single-crystal castings produced from nickel-base superalloys. A brief historical review describes the reasons for the evolution from wrought to cast product through directionally solidified to modern single-crystal (‘monocrystal’) castings. The influence of microstructural variations produced by the casting conditions, such as porosity and grain size, on creep and low-cycle fatigue properties are illustrated. The important aspects of postsolidification heat treatment, hot isostatic pressing, and the damaging effects of impurities are described for conventional castings. The results of controlling the microstructures produced by directional solidification especially by high temperature gradient solidification are demonstrated by comparing the creep properties of directionally solidified materials with those of the conventionally cast alloys in long-term tests. The creep and low-cycle fatigue properties depend on the stress direction relative to the crystallographic directions of the material for both directionally solidified and single-crystal castings. For single crystals, individual alloys show variable dependences of properties on the crystallographic directions. Directionally solidified materials show advantages in thin sections and are less sensitive to the effects of impurities compared to conventional castings.MST/329

ISSN:0267-0836    

DOI:10.1179/mst.1986.2.5.461

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

AbstractThe mechanical design of hot turbine blading has two main phases: (i) optimization, which yields the choice of material, number of blades, and general configuration, and (ii) detailed design of the particular features of the blades. The first phase makes use of the data available, which are usually limited, to provide an outline mechanical assessment of commercial viability. At this stage maximization of the lifetime to failure is considered in terms of the temperature and stress at each radial position; in the second phase failure modes are considered in more detail. The methods used in both stages are discussed, with emphasis on material and manufacture, taking as an example the blading in civil aircraft gas turbines. Particular attention is paid to the problems of designing with single-crystal cast superalloys.MST/222

ISSN:0267-0836    

DOI:10.1179/mst.1986.2.5.476

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

AbstractIt is shown that the mechanical properties of single-crystal superalloys can be optimized through appropriate solidification conditions and heat treatments. A comparison of the creep behaviour of low- and high-gradient processed single crystals of CMSX-2 alloy shows that minimizing porosity improves the creep strength at intermediate temperatures. The optimum creep resistance is achieved by alignedγ′-precipitates, about 0·5μm in size. It is shown that in high-cycle fatigue the solidification conditions have a dramatic effect on the fatigue strength. The improvement in fatigue behaviour is attributed to the extremely low density and small size of pores achieved by using a very high-gradient process. The strain–controlled low–cycle fatigue properties of CMSX-2 at intermediate temperatures are also greatly improved by using the high-gradient process. Elimination of porosity in‘industrial’single crystals by hot isostatic pressing restores their creep and especially their fatigue performance to the level of the high-gradient solidified material.MST/224

ISSN:0267-0836    

DOI:10.1179/mst.1986.2.5.486

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

ISSN:0267-0836    

DOI:10.1179/mst.1986.2.5.493

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

AbstractThe influence of parent phase chemistry on the marmem behaviour of Cu–Al–Ni and Cu–Zn–Al alloys has been studied. The essential differences in the nature of thermoelastic martensites in the two systems were observed metallographically and it was attempted to improve the imperfect shape recovery of Cu–Zn–Al alloys by thermal cycling. It was observed that both aluminium and nickel raised the recovery temperature of the alloys under investigation. The lattice invariant deformation mode in the Cu–Al–Ni system was found to be twinning, but in the Cu–Zn–Al system it was found to be stacking faults. Improved marmem behaviour of Cu–Zn–Al alloys was achieved by thermal cycling.MST/231

ISSN:0267-0836    

DOI:10.1179/mst.1986.2.5.496

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor

摘要:

AbstractUseful properties of eutectic alloys have been found to relate to the presence of granulated discontinuous phase, and its formation is encouraged during solidification; although difficulties are encountered in some alloy systems. In the present paper it is suggested that discontinuous phase granulation can be achieved through either solidification processing or heat treatment. The kinetics of granulation during heat treatment and the factors affecting it have been analysed and examined for eutectic silicon in Al–Si alloys and for graphite in cast irons during heat treatment, using the techniques of high-temperature and quantitative metallography. The concept of combined control of the size and morphology of the discontinuous phase through solidification and heat treatment was developed.MST/254

ISSN:0267-0836    

DOI:10.1179/mst.1986.2.5.500

出版商:Taylor&Francis    

年代:1986

数据来源: Taylor