摘要:

AbstractThe characteristics of the hot deformation of Zr–2·5Nb (wt-%) in the temperature range 650–950°C and in the strain rate range 0·001–100 s−1have been studied using hot compression testing. Two different preform microstructures: equiaxed (α+β) andβtransformed, have been investigated. For this study, the approach of processing maps has been adopted and their interpretation carried out using the dynamic materials model. The efficiency of power dissipation given by [2m/(m+1)], where m is the strain rate sensitivity, is plotted as a function of temperature and strain rate to obtain a processing map. A domain of dynamic recrystallisation has been identified in the maps of equiaxed (α+β) andβtransformed preforms. In the case of equiaxed (α+β), the stress–strain curves are steady state and the dynamic recrystallisation domain in the map occurs with a peak efficiency of 45% at 850°C and 0·001 s−1. On the other hand, theβtransformed preform exhibits stress–strain curves with continuous flow softening. The corresponding processing map shows a domain of dynamic recrystallisation occurring by the shearing ofαplatelets followed by globularisation with a peak efficiency of 54% at 750°C and 0·001 s−1. The characteristics of dynamic recrystallisation are analysed on the basis of a simple model which considers the rates of nucleation and growth of recrystallised grains. Calculations show that these two rates are nearly equal and that the nucleation of dynamic recrystallisation is essentially controlled by mechanical recovery involving the cross-slip of screw dislocations. Analysis of flow instabilities using a continuum criterion revealed that Zr–2·5Nb exhibits flow localisation at temperatures lower than 700°C and strain rates higher than 1 s−1.MST/3103

ISSN:0267-0836    

DOI:10.1179/mst.1996.12.9.705

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractThe recrystallisation behaviour and its effect on the crystallographic texture during solution heat treatment of thick aluminium alloy 7010 plates has been studied both on commercially hot rolled plates and on laboratory specimens deformed in plane strain compression. In addition to X-ray macrotexture analysis, individual grain orientation measurements within the recovered subgrains and the recrystallised new grains were performed by means of electron backscattering diffraction. Significant recrystallisation takes place during the solution treatment with almost no change in the macrotexture. This behaviour is explained by the balancing effect of randomisation of the texture during recrystallisation and texture sharpening within the recovered matrix regions.MST/3433

ISSN:0267-0836    

DOI:10.1179/mst.1996.12.9.717

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractThe directional recrystallisation during zone annealing of a nickel alloy intended for high temperature use has been investigated. The material was processed from powder, by extrusion and rolling, to produce sheet. Zone annealing of that material led to a very coarse, directional grain structure with a distinctly different preferred orientation to that of the rolled and primary recrystallised material. There was no correlation between the preferred orientations of the large grains and their growth directions. The textures were related by a transformation close to that characteristic of a∑5 coincident site lattice. It is possible that this represents a rapid growth relationship in the case where the growth is controlled by the dissolution of the coherentγ′precipitate.MST/3436

ISSN:0267-0836    

DOI:10.1179/mst.1996.12.9.730

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractThe mechanical behaviour of an Al–Li–Mg–Cu–Zr 8090 alloy at a temperature of 515°C and strain rates in the range 10−4−10−2s−1was measured by tensile testing. The greatest strain rate sensitivity was measured in the middle of that strain rate range, and did not change significantly with strain. Large abrupt changes in strain rate during testing showed that the strain rate history had a significant effect, especially slow prestraining which gave a relative increase in flow stress and a reduction in rate sensitivity compared with testing at a constant rate to the same strain. The evolution of grain size was measured, and there was evidence that this aspect of the material microstructure could be used to explain the observed behaviour. This view was reinforced by the ability of a transition model of superplasticity, together with a simple model of the evolution of grain size distribution, to reproduce the essential features observed in testing with large changes in strain rate.MST/3351

ISSN:0267-0836    

DOI:10.1179/mst.1996.12.9.735

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractThe microstructures and age hardening behaviours of a series of Mg–Al–rare earth (RE) alloys that had been either pressure die cast or permanent mould cast were investigated by SEM and analytical TEM. Two types of phases, Al4MM and Al12Mg17, were found in the as cast alloys and no pseudoternary Mg–Al–RE phases were present. The Al4MM phase was thermally stable during solution treatment at temperatures as high as 500°C, whereas Al12Mg17partially dissolved in theα-Mg matrix during solution treatment at 420°C. No rare earth containing precipitates formed during heat treatment of the investigated alloys but two types of Al12Mg17precipitation took place. Colonies of discontinuous precipitation containing alternate lamellae ofα-Mg and Al12Mg17formed preferentially in regionsα-Mg with high aluminium content. Spheroidisation and coarsening of the discontinuous precipitates occurred after aging at 200°C. Continuous precipitation of Al12Mg17also occurred and these precipitates had a rodlike morphology and grew in preferred crystallographic directions.MST/3382

ISSN:0267-0836    

DOI:10.1179/mst.1996.12.9.741

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractSliding wear tests on SiC particle reinforced 2024 aluminium alloy composites fabricated by a powder metallurgy technique were carried out, and the effects of SiC particle content, size, and the wear load on the wear properties of the composites were systematically investigated. It was found that the wear resistance of the composites was about two orders of magnitude superior to that of the unreinforced matrix alloy, and increased with increasing SiC particle content and size. Under the conditions of sliding wear used, the effect of SiC particle size on the wear resistance was more significant than that of particle content.MST/3161

ISSN:0267-0836    

DOI:10.1179/mst.1996.12.9.751

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractA method of analysing the wear and friction properties of multiphase materials and composites in abrasion is described. The method is based on the pressure distribution between the phases in the contact zone. From wear and friction measurements, pressure distribution mode coefficients can be calculated. These give information about how the applied load is distributed between the phases, and thus describe the contribution of each phase to the overall tribological properties of a composite or multiphase material. The importance of the pressure distribution in the contact area, and its effect on wear and friction properties are discussed in detail. The technique described can be used to estimate upper and lower bounds for the wear and friction properties of a multiphase material from the tribological properties of the individual phases. It can also be used to predict whether a phase contributes optimally to the tribological properties of a composite when exposed in a specific tribosystem. The theoretical considerations are compared with experimental results obtained from aluminium matrix composites containing silicon carbide particulate reinforcements. The wear resistance and friction of the composites have been measured for several abrasive counterfaces and loads, and mode coefficients have been calculated in order to interpret the experimental results.MST/3408

ISSN:0267-0836    

DOI:10.1179/mst.1996.12.9.757

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractThe K2TiF6salt required for the production of Al–Ti and Al–Ti–B master alloys was synthesised in the laboratory and the dissociation behaviour of K2TiF6and KBF4salts at different temperatures was studied. An investigation was carried out of the mode of reaction of the salts with aluminium. The salts were found to react with aluminium directly without undergoing dissociation. The K2TiF6salt reacts with aluminium only when the aluminium is molten, while the KBF4salt reacts with solid aluminium. In the presence of KBF4, the reaction between K2TiF6and aluminium takes place below the melting point of aluminium.MST/3233

ISSN:0267-0836    

DOI:10.1179/mst.1996.12.9.766

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractPhosphide precipitation has been studied in a Ti modified type 316 stainless steel containing a 0·15 wt-%P addition during thermal aging in the temperature range 600–800°C and as a function of initial condition (solution treated or cold worked). Needle shaped M3P precipitates in well defined crystallographic orientations are observed to nucleate on either complex defects or dislocations resulting from the initial thermomechanical condition. The stability of the phosphides decreases with increasing aging temperature and in the presence of prior cold work.MST/3239

ISSN:0267-0836    

DOI:10.1179/mst.1996.12.9.771

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractElectroless nickel coatings cause a marked decrease in the fatigue strength of the base steel. For the 30CrMo4 steel used in the present work, the fatigue limit is reduced by electroless deposition by 39, 52, and 55% for heat treatment conditions of 200°C for 1 h, 400°C for 1 h, and 600°C for 3 h, respectively. Shot peening before deposition can increase the fatigue strength for material heat treated at 200 and 400°C, but reduces the fatigue strength for material heat treated at 600°C. Under all conditions, the loss of fatigue strength is primarily due to the poor fatigue properties of the coating and the weak interface between the coating and the substrate. The main factors which affect the fatigue properties of coated samples are the coating ductility, the interface bonding, and the residual stress within the coating.MST/3123

ISSN:0267-0836    

DOI:10.1179/mst.1996.12.9.776

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor