摘要:

AbstractSuperplasticity, first observed some seventy years ago, remained a scientific curiosity until about twenty years ago. It is now recognized as a property which can be utilized in forming processes. There are two types of superplastic behaviour, known as fine–grained (or fine–structure) and internal–stress superplasticity. Fine–grained superplastic materials have a strain–rate sensitivity exponent of 0·5, and deform principally by a grain–boundary sliding mechanism. In this paper the microstructural features important in the development of fine structure super plasticity are discussed, and phenomenological equations for describing superplastic flow are presented. The superplastic properties of fine–grained materials can be optimized by promoting grain–boundary sliding and inhibiting slip. A number of fine–grained superplastic materials have been developed for commercial use, and their number is increasing. Internal–stress superplastic materials can have a strain–rate sensitivity exponent as high as unity, i.e. they can exhibit Newtonian viscous behaviour. Internal stresses can be generated by thermal cycling in materials that consist of two phases, or are anisotropic in their thermal–expansion coefficients, or are polymorphic. No commercial applications have yet been found for the superplastic forming of materials by generating internal stress.MST/169

ISSN:0267-0836    

DOI:10.1179/mst.1985.1.11.925

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractThe use of adhesives in civil engineering is reviewed by considering typical applications and experience gained, together with some results of research. The properties and requirements of structural adhesives as used to bond construction materials are discussed briefly. It is concluded that, with an appropriate design of joint, careful selection of a suitable adhesive, and adequate surface preparation, bonded connections may be used in structural applications–at least in the short term. However, caution should be exercised for longer–term applications, particularly if the joint is to be subjected to extreme environmental conditions under sustained load.MST/271

ISSN:0267-0836    

DOI:10.1179/mst.1985.1.11.937

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractThe type and nature of dislocations in oxide ceramics are reviewed and compared. Slip systems in these materials tend to be limited and difficult to activate, and Burgers vectors are often large. Thus, dislocation dissociation has been an important theme of research and climb dissociation has been frequently observed. Elasticity theory suggests that climb dissociation should be expected whenever diffusion can occur, and may be widespread in other materials deformed at elevated temperatures. Low temperature behaviour remains an area where much work needs to be done, particularly to assess the role of the Peierls barrier on the dislocation-core configuration.MST/270

ISSN:0267-0836    

DOI:10.1179/mst.1985.1.11.944

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractThe effect of microadditions of niobium, aluminium, and a combination of the two on the austenite grain coarsening behaviour of 0·08C–0·25Si–1·5Mn steels whose nitrogen content was varied/from 0·002 to 0·02 wt-% has been studied. Modified methods of surface oxidation and thermal grooving were used in order to determine the precise prior austenite grain size in these steels with low interstitial elements. The optimum concentration of niobium which could be effectively used for restraining austenite grain growth when steels are austenitized at high temperatures has been determined. It is also demonstrated that steels containing. NbC or NbN particles exhibit similar austenite grain coarsening behaviour. Increasing the nitrogen content from 0·002 to 0·02 wt-% to give nitrogen–rich Nb(CN) particles does not help restrain austenite grain growth. However, when nitrogen was added to steels containing aluminium or aluminium and niobium, significant improvement in grain restraining behaviour was observed.MST/120

ISSN:0267-0836    

DOI:10.1179/mst.1985.1.11.950

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractSilver has only slight solubility in low–carbon steel at elevated temperatures (~ 0·08 wt-% at the solidus) and precipitates on cooling as fine particles (<10 nm) in the interphase mode. When present in as-cast steel at an estimated volume fraction of ~ 0·0006, silver can cause precipitation strengthening of up to 50 MN m−2. In as–rolled and in normalized steels, silver (0·02 wt-%) improves both strength and toughness mainly through grain refinement, with only a small influence from precipitation hardening. An important observation is the improvement to the heat affected zone toughness of high heat input welds which can result from small silver additions (0·02 wt-%) to C–Mn–AI–V steels. However, because of its relatively high cost, it remains to be demonstrated whether silver will impart sufficient benefit to steel properties to be commercially acceptable as an alloying addition.MST/44

ISSN:0267-0836    

DOI:10.1179/mst.1985.1.11.954

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractSolution treatment of 12Cr–Mo–V steels below the specified temperature range leads to the development of spheroidized microstructures with dramatically reduced creep resistance. This is known to have resulted in the premature service failures of superheater tubing. Compositional and mechanical property checks currently specified in the relevant standards may not be sufficient to reveal deficiencies. Steels with Cr–Ni equivalents at the uppermost extreme of the range possible within the compositional limits of the tube steel standards show enhanced susceptibility to bothδ–andα–ferrite formation. The significance of this is discussed in relation to creep strength, with particular reference to the differences between the effects ofα- andδ-ferrite.MST/147

ISSN:0267-0836    

DOI:10.1179/mst.1985.1.11.961

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractSpecimens of a 9Cr–1 Mo steel have been deformed in tension at room temperature and the concentration and size distribution of deformation–induced carbide–nucleated voids was established as a function of strain. Additional specimens were annealed, after deformation, at 600 and 750°C, respectively; thin foils prepared from these specimens were used to monitor void shrinkage and the consequent reduction in void density as a function of annealing time. The results are compared with the behaviour predicted by an equation previously used by Volin and Balluffi to account for the shrinkage of‘quenched-in’voids in aluminium.MST/213

ISSN:0267-0836    

DOI:10.1179/mst.1985.1.11.968

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractA new method of calculating stress–strain curves from torsion measurements is described. Contrary to the usual calculation of stress and strain at the surface of the specimen–where the material properties are distorted by microcracks, notch effects, etc.–stress and strain are determined at a‘critical radius’inside the specimen. For this purpose an initial approximation for the flow curve of the typeσf~ΦnΦmis improved by calculating a‘correction function’from the test results. This calculation is based on a Taylor series expansion which converges more strongly if tubular specimens are used instead of solid ones. Tubular specimens are therefore used if the flow curve appears to deviate strongly from the exponential law. The new method of test evaluation makes use of the fact that contrary to tensile and upsetting tests, in torsion tests the measured curve gives an almost undistorted linear projection of the flow curve. In fact the test evaluation consists only of‘calibrating’the measured torque and angle of twist in terms of yield stress or equivalent strain, respectively.MST/94

ISSN:0267-0836    

DOI:10.1179/mst.1985.1.11.972

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractThe constitution of the 75 at.%Ni section of the Ni–Cr–Al–Ta system has been determined at 1523 and 1273 K. Alloys annealed at these temperatures have been studied using electron probe microanalysis and X–ray diffraction, and their microstructures and associated hardness values have also been examined. The isothermal sections at 1523 and 1273 K contain the following phases:γ+γ′+Ni3Ta, and Ni6TaAI, with the following three–phase equilibria between them:γ+γ′+Ni6TaAI andγ+Ni3Ta+Ni6TaAl. Theγ′–phase contains up to ~9 at.–%Ta. Some observations on as–cast structures have also been made.MST/208

ISSN:0267-0836    

DOI:10.1179/mst.1985.1.11.978

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractThe past twenty to twenty–five years has been a period of considerable change for the foundry industry during which established practices and ingrained attitudes have required critical re–appraisal and occasionally drastic revision. The energy related industries, demanding higher quality components of proven integrity as service conditions have become progressively more exacting, have played an important role over this period as castings specifications have been subject to frequent revision to reflect changing requirements. Founders have been required to respond, first in order to exploit the buoyant market of the 1960's and early 1970's, and second to survive in the depressed international market of the late 1970's and early 1980's. This paper reviews developments in ferrous castings for large steam turbines during this period, and outlines the manner in which specifications for this type of casting have become progressively more stringent. The impact of these changes on the foundry industry is reviewed, and an outline is given of the response of one UK castings manufacturer to the challenge of competing in the international marketplace of the 1980's.MST/164

ISSN:0267-0836    

DOI:10.1179/mst.1985.1.11.986

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor