摘要:

AbstractIn this paper–the first part of a two part review–the problems encountered and the materials used in the various aspects of adhesion in dentistry are briefly discussed. The areas covered are: adhesion to teeth; impression taking; capillary adhesion and denture retention; powder mixing, wettability, and bubble entrappment; porcelain–metal bonding; bioadhesion; composites; and abhesion. In the second part of the work, it is intended to cover adhesion to teeth in greater technical detail.MST/1081

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.7.621

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractSamples of Ti–24Al–11 Nb/TiC composites were heat treated at temperatures between 1000 and 1200°C for several hours and the extent of the reaction zone between the Ti–24Al–11Nb matrix and the TiC particulate was assessed using optical, scanning electron, and analytical transmission electron microscopy. It has been shown that there is an interaction zone surrounding each TiC particle caused by the diffusion of C from the TiC into the matrix and diffusion of Nb into the TiC. The extent of these interactions increases with increase of time and increase of temperature. The phases formed during heat treatment were shown to be Ti3(AlNb)C and (TiNb)C. The significance of these observations is briefly discussed in terms of recent work in which it has been shown that there is no detectable change in the matrix in similarly treated Ti–6AI–4V/TiC composites.MST/946

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.7.627

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractThe constitution of the Ti–Al–Ru system has been studied in detail. Metallography, X-ray diffraction, electron microscopy, and X-ray spectroscopy have been used to establish the phase diagram between 17 and 37 at.-%Al and 1 and 29 at.-%Ru in the temperature range 1250–770°C. Ternary isothermal sections within the range of investigation and selected phase composition data are presented and phase relationships are discussed. Results show only a small solubility (<1at.-%) of ruthenium in Ti3Al and TiAl which are involved in equilibria with a ternary intermetallic compound.MST/963

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.7.632

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractA high resolution quenched interface technique has been used to study the solid/liquid interface of the Al–Si eutectic solidified at extremely low growth rates. The interface morphology of the pure eutectic and also that of samples doped with Sr or P were studied. The observations were consistent with the twin plane re-entrant edge (TP RE) growth model for the pure eutectic and with a change to non-TPRE growth in the presence of Sr. On the other hand, P was found to have an effect on the relative tendencies towards faceting of the two phases.MST/923

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.7.645

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractThe presence of degenerate graphite in heavy section ductile iron causes a significant decrease in its mechanical properties. In this paper, two types of degenerate graphite are classified: large non-spheroidal graphite and small chunky graphite. The formation processes of degenerate graphite have been investigated by means of simulation quench experiments. With samples quenched in water, it was observed that the large non-spheroidal graphite forms directly from the degeneration of spheroidal graphite in an austenite shell. Some liquid channels were found in the austenite shell and at certain graphite/austenite interfaces. These channels link the graphite with the bulk liquid metal during the slow eutectic solidification process. The liquid channels form as a result of the temperature fluctuations and the segregation of certain elements. The existence of these liquid channels is an important factor in the formation of non-spheroidal graphite. Chunky graphite grows from the remains of molten iron in the middle or by the end of the eutectic reaction. This chunky graphite is actually an intercrystalline eutectic graphite.MST/970

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.7.657

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractIn many instances the use of neutrons for texture investigation offers advantages over well established X-ray methods, particularly when it is important to have the information averaged over the entire volume of the bulk sample or when it is necessary to obtain this information in a relatively short time. A neutron diffraction technique for texture investigation in low carbon cold rolled steel at ambient and elevated temperatures up to 700°C has been established. The use of the high intensity neutron beam from the ISIS pulsed neutron source and the application of the time-of-flight method made it possible to carry out in situ observations of texture formation during recrystallisation annealing. Pole density values were calculated from the integrated intensities of the diffraction spectra including values obtained for peaks at smaller d spacings than are observable with conventional X-ray machines or reactor based neutron instruments. Diffraction peak profile refinement enabled calculations of the line broadening, microstrains, and the elastic stored energies in various texture components to be made. In situ recrystallisation annealing was carried out at two mean heating rates: low (35 K h−l) and high (650 K h−l). Data obtained from in situ experiments give more reliable information and hence a better understanding of the recrystallisation kinetics in various texture components than is obtainable using 'off line' annealing.MST/959

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.7.665

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractThe continuous cooling transformation (CCT) diagrams for four C–Mn steels were constructed using dilatometry and metallography. All diagrams involved the formation curves of second phases and the formation curves of matrix structures. Between polygonal ferrite and martensite, acicularferrite and bainite were observed. The formation of acicularferrite was associated with a kinetic change which was an indication of the formation of second phases such as pearlite, pseudopearlite, and martensite. The pseudopearlite wasfound to form by separate precipitation of cementite and ferrite in austenite. It was thought that the transformation of martensite second phases followed a Kurdjumov–Sachs relationship. Three types of carbide, i.e. upper bainitic, lower bainitic, and Widmanstätten, were observed in continuously cooled bainite. An increase of manganese content suppressed the formation of polygonal ferrite, promoted the formation of acicular ferrite and bainite, and changed the second phase from pearlite to pseudopearlite and to martensite.MST/913

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.7.674

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractThe hot ductility of C–Mn–Al and C–Mn–Nb–Al steels with and without calcium additions have been examined over the temperature range 700–1000°C both after solution treating at 1330°C followed by cooling to the test temperature and directly after casting. Calcium additions invariably improved hot ductility. For hot rolled plate reheated to 1330°C and cooled to the test temperature, calcium is beneficial to hot ductility because it reduces the amount of sulphur able to redissolve and precipitate in a fine form at the newγ-grain boundaries produced on solution treating. For the C–Mn–Al steels, strain concentration occurred in the thin films of softer ferrite surrounding theγ-grains causing voiding around the sulphide inclusions that link up to cause intergranular failure. The removal of the sulphides by calcium addition therefore accounts for the improvement in hot ductility. Similar behaviour was observed for the C–Mn–Nb–Al steels, but for temperatures above the Ae3temperature calcium containing steels continued to give improved hot ductility over calcium free steels and this is believed to be due to the fewer sulphides present at the boundaries allowing an earlier onset of dynamic recrystallisation. For steels subjected to direct casting, interdendritic failure as well as intergranular failure by microvoid coalescence occurs. Calcium additions reduce the total amount of sulphur in the steel so that the volume fraction of sulphides precipitated at the interdendritic andγ-boundaries is low.MST/962

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.7.682

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractFatigue crack propagation has been studied in a series of Al–Sn bearing alloys as a function of microstructure and environment at stress intensity ratios R of 0·7 and 0·1. Fatigue thresholds of tin containing alloys increased with a reduction in content and in continuity of the tin phase in laboratory air. This is interpreted in terms of crack closure, crack growth along the Al/Sn interface, and crack tip blunting mechanisms. Mechanisms that retard fatigue crack growth through the aluminium phase (e.g. by an increase in the reversibility of slip or by an increase in the size of the reverse plastic zone) were found to increase fatigue thresholds. When tested in dry air, the Al/Sn interface shows reduced embrittlement. The consequence of this for fatigue thresholds is complex: at R=0·7, fatigue thresholds increase with a decrease in tin content, while the thresholds are constant at R=0·1.MST/927

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.7.689

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractThe prediction of long term creep properties from short term tests is discussed in terms of theθprojection method. The method has been shown to yield reasonable extrapolation functions and the present paper investigates the characterisation of creep scatter and the procedures required to give estimates of variability of creep predictions. The nature of errors in individual creep curves and in multiple curves obtained from various specimens under differing test conditions are discussed and formulae are developed that allow an assessment of the reliability of derived parameters. These methods are then extended to estimated creep properties (both interpolated and extrapolated) so that the variances of predicted quantities can be calculated. The analysis is carried out for general creep curve functions, but is illustrated with reference to the double exponential description of creep strainξwith time:ξ=θ1(1−e−θ2t) +θ3(eθ4t−1). Numerical examples relating to the creep properties of IN 100 are given and the significance of the procedures in relation to design for creep is discussed.MST/988

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.7.699

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor