摘要:

AbstractA theoretical prediction model is presented to estimate the in-flight velocity, temperature, and size of a ceramic particle traversing through a plasma flame. The model accounts for the various phenomena that can influence the transport rate calculations in plasma spraying operations, which typically involve very fine particles (<50μm) subjected to an extremely non-isothermal environment. The mathematical formulation simultaneously considers internal heat conduction in particles, accounts for the steep temperature gradients that prevail in plasma–particle systems, and incorporates the Knudsen discontinuum effects on both heat and momentum transfer. The significance of these factors is illustrated through some example calculations performed under typical plasma spraying conditions. Comparison with experimental data reveals that the present method, although simple and easy to use, enables accurate predictions to be made and can be a very useful tool in the model assisted development of various plasma–particle processing systems.MST/1533

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.6.481

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractThe variations of Young's modulus and temperature coefficient of resistance at room temperature of Co78−xMnxB22(2≥x≥14) as functions of manganese content x have been studied. The Young's modulus and the temperature coefficient of resistance are found to show maxima at x≍8.MST/1518

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.6.489

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractThe degree of reaction and dispersion achieved when TiB2powders are melted in contact with liquid iron based alloys has been assessed via a levitation dispersion test which had been developed earlier. Both Fe2B and TiC were observed to form as a result of dissolution and reaction of TiB2. The formation of TiC occurs during the reaction of commercial grade TiB2with liquid iron alloys containing as little as 0·08 wt-%C. The reaction of high purity TiB2with liquid iron alloys containing 0·24 wt-%C does not however lead to TiC formation. The formation of Fe2B was observed for all conditions tested, owing to the effectively zero solubility of boron in solid iron. The TiB2remaining after dissolution and reaction was found to produce relatively good dispersions in the iron matrix and therefore additions of TiB2to liquid iron alloys may provide a means of producing Fe–TiB2composite materials. However, the brittle properties of Fe2B will mean that, whereas such materials may be very hard, they are likely to lack toughness.MST/1477

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.6.491

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractA study has been made of the influence of the reinforcement/matrix interfacial strength on fatigue crack propagation in a powder metallurgy aluminium alloy 8090–SiC particulate composite. The interfacial region has been altered by two separate routes, the first involving aging of the 8090 matrix, with the subsequent formation of precipitate free zones at the boundaries, and the second consisting of oxidising the surface of the SiC particles before their incorporation into the composite. In the naturally aged condition, oxidation of the SiC leads to a reduction in fatigue crack growth resistance at higher values of stress intensity range∆K. This is due to a proportion of the crack growth occurring through voids formed in association with many of the weak SiC interfaces which have retained a layer of thick surface oxide after processing. On overaging no difference in crack growth rate is discernible between the oxidised and unoxidised SiC composites. It is proposed that this is due to similar levels of interfacial weakening having occurred in both composites, indicating that this is an important factor in the reduction of the high∆K crack growth resistance of the unoxidised SiC composite on aging.MST/1605

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.6.500

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractExperiments on stored energy have been carried out for three types of cold rolled aluminium and copper characterised by different texture and structure. In the first type, the shear texture has been obtained in the surface layers of the examined materials rolled in one pass at a high l/h ratio (where l is the projected length of contact between roll and material, and h is the mean thickness of the sample), characterising the geometry of the rolling gap. The second type of material has been deformed through a change of the deformation path in the final pass. Calorimetric measurements were also performed on the third type of material rolled unidirectionally with medium l/h. The amount of stored energy has been found to be much less in the material with shear texture than in that with rolling texture. The observed retention of shear texture during recrystallisation may be due to inherently low energy blocks caused by the orthogonal position of the Burgers vectors in the shear orientation, which led to a lower dislocation density. A change of the deformation path decreased the stored energy.MST/1514

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.6.510

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractTemperature and interparticle spacing measurements are presented for directionally solidified Al–CuAl2and Al–Si eutectic alloys. The results show that care must be taken to ensure that steady state heat flow conditions are established during directional solidification and that the correct definition of spacing is used to obtain interparticle spacing–growth velocity relationships that can be used to assess current eutectic solidification models. The results presented for the Al–Si eutectic show a strong temperature gradient dependence of the spacing–growth velocity relationship which is not predicted by the most recent detailed solidification models.MST/1516

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.6.516

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractSpecimens of the Bi–Cd–Sn ternary eutectic were solidified under closely controlled conditions and quenched during freezing to form a‘quenched interface’for subsequent observation. Very low growth rates, from 8 nm s−1to 1·1μm s−1, were used to produce a microstructure sufficiently coarse to show considerable detail at the quenched interface and thus reveal distinctly the mode of solidification of the alloy. The three phases formed on solidification of this eutectic alloy are Bi, Cd, and a–;βCd–Sn’phase derived from the hexagonal Sn rich phase of the Cd–Sn binary system. It was observed that the Bi and Cd phases both freeze in a faceted manner whereas theβCd–Sn phase is non-faceted. Under the growth conditions used, this eutectic showed a marked tendency to form regions of binary microstructure. At the higher growth rates examined, regions of Bi–βCd–Sn quasiregular binary microstructure, outlined by Cd flakes, were formed, whereas at the lower growth rates the Cd andβCd–Sn phases formed a nearly regular lamellar microstructure containing relatively large inclusions of Bi. It was observed that the Cd–Cd phase spacing varies only slowly, whereas the Bi–Bi phase spacing varies much more rapidly with growth rate in theβCd–Sn matrix phase. This variation is attributed to the different branching tendencies of the Bi and Cd phases and appears to account for the formation of regions of binary microstructure.MST/1551

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.6.523

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractSecondary recrystallisation has been studied in MA 957 oxide dispersion strengthened ferritic superalloy following heat treatment at a temperature of ~1320°C. Selected area channelling patterns in the scanning electron microscope were used to characterise the crystallographic texture of grains of large aspect ratio produced by zone annealing and microbeam electron diffraction was used to determine the orientations of submicrometre, equiaxed grains behind the (secondary) recrystallisation front. MA 957 exhibits a dominant〈110〉texture in the as extruded condition, but this texture is notably absent after recrystallisation. At high zoning speeds the material displays a〈113〉texture, but an increasing proportion of〈111〉texture component is evident as the zoning speed is reduced. The texture development can be tentatively rationalised in terms of the influence of solute segregation processes and grain orientation on interfacial mobility.MST/1555

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.6.531

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractA field ion atom probe study has been made of a low carbon steel after furnace cooling and rapid quenching from 700°C. Marked segregation of carbon to the boundaries was observed after furnace cooling, but not after rapid quenching. From comparison of previous and present results, it is concluded that the kyvalue of a steel can be related to the interstitial impurity content (mainly carbon) at the grain boundaries. Heat treatments that encourage grain boundary segregation of interstitials will result in steels having a high kyvalue.MST/1569

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.6.537

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractGrain boundary concentrations of phosphorus were determined using Auger electron spectroscopy in a 12Cr-Mo–V (wt-%) steel doped with 0·057%P after annealing at 450, 550, and 600°C for times up to 10 000 h. Data were calculated for the thermodynamics of the segregation equilibrium and diffusivities in the segregation kinetics and compared with the corresponding data for Fe–P alloys and with bulk and grain boundary diffusivities of phosphorus in the steel determined using a radioactive tracer method. It is concluded that segregation and diffusion in 12Cr–Mo–V steel is strongly affected by a high dislocation density, the dislocations are stabilised by fine carbide precipitates even after aging for long times at high temperatures and act as traps for phosphorus.MST/1525

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.6.541

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor