ISSN:0267-0836    

DOI:10.1179/mst.1992.8.4.289

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractIn this paper the potential and prospects of some intermetallic compounds for structural applications are discussed, with an emphasis on two specific aspects which seem to be of prime importance for future research and development activities. First, the benefits associated with the development of multiphase intermetallics are stressed and a novel approach for creating the two phaseγ–γ′type microstructure in different alloy systems is described. Second, the problem of stability of the constituent phases in these multiphase materials is considered. The superiority of nickel baseγ–γ′superalloys over the single phaseγ′is demonstrated by comparison of their creep behaviour, and advantages of multiphase alloys are also briefly reviewed with reference to other alloy systems. The discussion is frequently illustrated by reference to recent results obtained by the present authors for various alloy systems based on Ni3Al, iron, niobium, Ti3Al+X (X=Nb, V, or Mo), and NiAl.MST/1547

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.4.291

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractA national project aiming at the development of high temperature intermetallic compounds was launched in 1989. TiAl and some refractory metal aluminides and silicides such as Nb3Al are target materials for the project, which has aroused great interest in the technologies for processing of these intermetallic compounds and in their properties, particularly their mechanical and oxidation properties. This is an overview of the current research and development activities in Japan concerning TiAl and other intermetallic compounds recognised as potentially useful high temperature structural materials. A brief explanation of the project is also presented.

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.4.299

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractProcessing routes for intermetallic based materials are briefly surveyed and compared. For monolithic intermetallics the two main factors determining process routes both derive from the low room temperature ductility of most intermetallics. They are the need to maintain material cleanness, thus reducing fracture initiation sites, and the desire to achieve fine grain size to seek to improve ductility. For the titanium based aluminides there is also a need to minimise interstitial, particularly oxygen, pick-up during processing. For intermetallic based composites, a broad range of processes is already being investigated. In many of these, issues of cleanness may be more difficult to control than for the monolithic composites. With continuous fibre reinforced composites a further process impetus is the need to control interfacial interactions between the fibre and the matrix.MST/1560

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.4.308

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractA review is given of recent results obtained for discontinuously reinforced intermetallic matrix composites produced using the XD process. Intermetallic matrixes investigated include NiAl, multiphase NiAl+Ni2AlTi, CoAl, nearγtitanium aluminides (i.e. TiAl+Ti3Al), and L12trialuminides containing minor amounts of second phase. A judicious match of the matrix and reinforcement can enhance both physical and mechanical properties. Particulate reinforcements can affect properties directly by enhancing modulus and strength or indirectly by refining grain size, enhancing microstructural homogeneity in a casting, or providing additional nucleation sites which improve phase transformation kinetics. Such mechanical properties as low and high temperature strength, compressive and tensile creep, elastic modulus, ambient ductility, and fracture toughness are discussed as functions of reinforcement size, shape, and volume fraction. Microstructures before and after deformation are examined and correlated with measured properties. An observation of interest in many of the systems examined is‘dispersion weakening’at high temperatures and high strain rates. This behaviour is not specific to the XD process; rather similar observations have been reported in other discontinuous composites. Proposed mechanisms for this behaviour are presented.MST/1561

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.4.317

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractThe selective oxidation of intermetallic compounds is described. The effects of temperature on the development of protective external scales and on the occurrence of‘pesting’are considered. The influence of gas composition on oxidation rate and morphology and on the formation of volatile reaction products is described. Selected data for compounds of primary interest as high temperature materials (aluminides, silicides) are used to illustrate the effects discussed. Finally, the corrosion behaviour of intermetallics in more complex environments, such as those containing mixed oxidants or molten salts, are briefly discussed.MST/1544

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.4.331

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractThe phase NiAl with its wide homogeneity range, and especially when of high Al content, is a reliable alumina scale former and exhibits remarkable oxidation resistance at high temperatures. By contrast, the line phase NbAl3oxidises with formation of mixed layers of Al2O3and fast growing oxides. However, the mechanical strength of NiAl is not sufficient for application at high temperatures, but the strength is enhanced in multiphase alloys in the systems Ni–Al–Cr and Nb–Ni–Al. Increasing the Cr content of two phase NiAl–Cr alloys reduces the oxidation resistance, but for three phase NbAl3–NbNiAl–NiAl alloys the oxidation resistance is comparable to that of NiAl, since the Al content of the phases NiAl and NbNiAl is high in the phase equilibrium.MST/1570

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.4.339

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractRecent developments in the use of quantum mechanics to make structural predictions and provide insights at the atomic level are reviewed with respect to intermetallics. In particular, the question is addressed of why some tetragonal D022trialuminides (e.g. TiAl3) can be stabilised with the cubic L12structure by alloying additions but others (e.g. NbAl3) cannot, and why, if the cubic phase is stabilised, it remains brittle.MST/1543

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.4.345

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractOrdered intermetallic compounds based on transition metal aluminides have been proposed as structural materials for advanced aerospace applications. Development of such materials, offering benefits in density and/or operating temperature range, has concentrated on the aluminides of nickel, titanium, and iron, either as monolithic materials or as matrixes for composites. However, despite attractive elevated temperature properties, the utilisation of these materials has been hindered by their poor low temperature ductility and susceptibility to environmental embrittlement. This analysis of published work and current experimental results reveals a variety of environmental embrittlement mechanisms that afflict the three major aluminide types to varying degrees in either oxygen or hydrogen containing atmospheres at ambient or elevated temperatures. Embrittlement by hydrogen occurs in all the aluminide types at ambient temperature by loss of cohesive strength at interfaces, by interaction with dislocations (iron and nickel based), or by hydride formation (titanium based). The last mechanism is also operative at elevated temperature. In the presence of dissolved oxygen, titanium aluminides show little ductility, associated with pinning of 1/2〈110] dislocations through a deepening of the Peierls valley. This effect is operative up to about 600–800°C. Although unaffected at room temperature, Ni3Al based alloys exhibit ductility loss at 600–800°C in the presence of oxygen, owing to grain boundary oxygen diffusion and localised embrittlement at crack tips. Mechanisms are discussed that address the observed environmental embrittlement in aluminides. In all cases, suitable alloying attenuates the effect or offers the best prospect of so doing.MST/1563

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.4.350

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractAn elemental powder mixture of composition Ti–35 wt-%Al was cold extruded, reactive hot isostatic pressed at 1000°C, and subsequently annealed at 1250°C. A duplex microstructure was formed having elongated lamellar regions of Ti3Al/TiAl within a TiAl matrix. Specimens were tested in compression at temperatures between room temperature and 900°C. The material exhibits good deformability at 700°C and above. In this region, the typical stress–strain behaviour accompanying dynamic recrystallisation is observed. Matrix and lamellar regions both undergo deformation. Below 700°C, pseudoplasticity occurs, which is related to homogeneous formation of microcracks. The observed behaviour is compared with that of a cast material of similar composition.MST/1545

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.4.359

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor