摘要:

AbstractThe relative surface energies for brittle fracture along grain boundaries or along crystal planes, at low temperatures, are estimated and used in a criterion for the relative strengths of boundaries and cleavages. It is concluded that the boundary is weaker than the crystal in a wide range of metals; that it becomes weaker as the ratio of shear modulus to bulk modulus increases; and that brittle pure metals, such as iridium and molybdenum, fracture preferentially on grain boundaries. The critical modulus ratio is in all cases lower than that for the ductile–brittle cleavage transition.MST/1154

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.12.1165

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractDifferences in the thermal stability of trapped lattice dislocations in interphase boundaries and grain boundaries in austenitic–ferritic steel have been studied. It was found that the distribution of diffusional properties ofα/γinterphase boundaries depends on the mutual orientation of phases and differs significantly from the distribution of diffusional properties ofα/αandγ/γgrain boundaries, which stems from the fact that interphase boundaries include a substantial fraction of boundaries of particularly low diffusivity. These are interfaces of austenite grains which nucleated inside ferritic grains and demonstrate Kurdjumov–Sachs or Nishiyama–Wassermann relationship with respect to the ferritic matrix.MST/1005

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.12.1168

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractPhase transformations in Ti–50V alloys containing oxygen in the range<0·095–0·36 wt-% have been studied at 750 and 400°C for times up to 1000 h. Results of electron microscopy, X-ray diffraction, and hardness testing indicate that oxygen widens theα+βphase field at 750°C and the metastableβphase miscibility gap at 400°C. The evidence is consistent with a phase diagram for high purity Ti–V alloys containing a stableα+βphase field with aβtransus decreasing with increasing vanadium content. No evidence was obtained consistent with aβmonotectoid form of diagram which has recently been proposed.MST/1039

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.12.1172

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractThe empirical rate equations of solid state reactions such as recovery of deformed metals, clustering, and transient creep are all of the same type, referred to here as recovery kinetics. For two systems, transient creep in fcc metal crystals and the first stage of tempering of Fe–C and Fe–Ni–C martensite, the rate equations were analysed 30 years ago using the increment technique. These results can be used to deduce the common physical principles which govern the mechanisms operating in the various systems. From this basis, it can be concluded that the densification kinetics in the intermediate stage sintering of certain ceramic green pellets is also a type of recovery kinetics. Initial experimental results are shown to support this conclusion.MST/1048

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.12.1178

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractCompression tests were carried out on fine grained copper at 870 K and at a constant true strain rate of 1·4×10−3s−1. Under these conditions, well defined flow stress oscillations followed by steady state flow stress are obtained. Grain size measurements of as deformed material revealed non-monotonic grain coarsening when stress oscillations appear. It was found that grain coarsening is most effective when the flow stress decreases after the first flow stress peak. Periodic flow stress is accompanied by periodic grain coarsening until the latter becomes practically independent of strain when the steady state flow stress region is attained. The structural effects of static processes (recovery and recrystallisation) in dynamically recrystallised material were examined closely. According to the model of periodic dynamic recrystallisation, one would expect periodic changes of the driving force for static restoration processes (mainly metadynamic and/or static recrystallisation). From the present work, conclusions are drawn that are contrary to this concept of structural softening. The critical strain leading to grain coarsening during post-deformation annealing of hot deformed copper was found to be significantly less than the strain corresponding to the first flow stress peak. For higher strains, the grain size of dynamically recrystallised copper was found to be highly stable during annealing for 7 h at 870 K.MST/978

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.12.1186

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractTorsion tests at strain rates of 10−3, 0·16, and 1 s−1and at temperatures between 850 and 1100°C have been carried out on an aluminium killed mild steel after either heating directly to the testing temperature or soaking for 30 min at 1200°C, then cooling the specimen to the testing temperature. During direct heating, a dispersion of small AlN particles was present and after soaking a coarser distribution of AlN particles was observed. Compared with the latter, the former microstructure seriously retarded the completion of dynamic recrystallisation. The effect of the two different particle distributions was examined for the following parameters: peak and steady state stress, peak strain, and dynamically recrystallised grain size. The retardation of completion of dynamic recrystallisation has the additional effect of impairing the hot ductility.MST/997

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.12.1191

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractComposite ferrite–lath martensite dual phase steel is an alternative to high carbon pearlitic steel for producing high strength wire and may be drawn with no intermediate patenting treatments because of its high work hardening rate and formability. This paper presents the study of the relationships between the void density in drawn wires, the drawing limit, and the initial structure. An Fe–2Si–0·1C (wt-%) dual phase steel was treated to produce three different martensite morphologies at constant volume fraction, then wire drawn. The void density varied linearly with total drawing strain in all three conditions. High magnification scanning electron microscopy revealed that voids were initiated by decohesion at ferrite/martensite interfaces and by shear cracking of martensite particles. The voids grow to form cracks parallel to the drawing direction and affect the drawing limit. The character of the martensite, either dislocated lath or twinned plate, was determined by transmission electron microscopy. The void density was least in the fibrous lath martensite structure, where the lath martensite has a high degree of initial structural coherency with the surrounding ferrite, which hindered void formation and hence delayed the drawing limit.MST/1024

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.12.1200

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractThe effect of Mg on the microstructure and properties of a high carbon cast steel (nominal composition, wt-%: 18Cr–2Ni–0·75Mo–Mn–Si–Febal.) is investigated. It is shown that the microaddition of Mg refines the primary carbide (Cr0·51Fe0·49)7C3and promotes an equiaxial dendritic structure, and the resulting structure refinement improves significantly the impact toughness of the alloy. Using Auger electron spectroscopy and electron probe microanalysis, it is shown that there is an unusually high Mg segregation (~70 at.-%) at the carbide interface region. It is proposed that the Mg enrichment at the carbide interface is primarily a result of the liquid phase separation that occurs in liquid Fe–Mg alloys when the Mg level attains a minimum value (~1–2 at.-%), and that this initial enrichment is a result of a combination of Mg rejection by the carbide and uphill diffusion of Mg to the carbide interface region. A thermodynamic analysis is presented to show the degree of component (Cr, Ni) segregation required for uphill diffusion of Mg to occur, which is in qualitative agreement with that observed.MST/1046

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.12.1207

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractThe hot ductility of normalised microalloyed steels having a variation in Mn and S content has been examined over the temperature range 700–1000°C after heating directly to the test temperature. Ductility troughs were generally found in the austenite and these became more severe on increasing the S content or decreasing the Mn content. The improvement in hot ductility on increasing the Mn content was found to be a result of grain refinement. Increasing the S content was also accompanied by grain refinement, but any improvement in the ductility associated with this refinement was offset by the detrimental effect of having a greater volume fraction of MnS inclusions at theγboundaries, thereby promoting grain boundary sliding and cavitation. The hot ductility in the hot rolled state before normalising was also examined. Behaviour was found to be similar, but hot ductility was lower than after normalising owing to a coarser grain size.MST/1010

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.12.1212

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractConventional nickel based hardfacing alloys deposited by arc welding usually have a nominally single phase microstructure and derive their hot strength primarily from solid solution strengthening. The present work is an attempt at designing improved alloys containing large volume fractions of ordered precipitates or intermetallic compounds. The alloy design has been carried out using a computer model capable of estimating microstructure and strength as a function of many variables. The results are tested experimentally against cast samples which simulate welding conditions during manual metal arc welding.MST/1035

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.12.1220

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor