摘要:

AbstractExperiments have been carried out on coarsening ofγ″precipitates in Ni–Al and Ni–Al–Cr alloys and rate constants and particle size distributions have been determined as a function of volume fraction ofγ″. These results have been compared with those predicted by the various modified Lifshitz–Slyozov–Wagner theories. An important result obtained in this investigation is that the growth rate constant increases with volume fraction ofγ″in the Ni–Al system. The Brailsford–Wynblatt encounter model has been applied to the coarsening data obtained in the Ni–Al and the Ni–Al–Cr systems and values of interfacial energies and activation energies have been determined. By applying the growth path envelope analysis to theγ′coarsening data obtained in the Ni–Al system the ratio of the mean particle radius to the critical particle radius R/Rcand the variation of the growth rate of the particle with particle size have been determined.MST/1036

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.5.405

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractThe effect of austenitising temperature on the microstructure, mechanical properties, and dimensional stability of a spheroidal graphite iron containing copper and nickel has been investigated. It was found that as the temperature increased the amount of carbon taken into solution by the austenite increased thus reducing the driving force of the original austenite to bainitic ferrite and high carbon austenite. As a consequence, the amount of retained austenite increased, but its stability decreased. This placed an upper limit on the austenitising temperature and on the amount of retained austenite permissible. All properties other than hardness showed maximum values after austenitising at 900°C. It was also found that increasing the solution treatment temperature increased the dimensional stability.MST/1116

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.5.415

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractThe cleavage behaviour of plain carbon steels containing from 0·2 to 0·8%C has been investigated. It is observed that each steel displays two characteristic temperatures at which a transition in the mode of fracture occurs. These are the transition temperatures for cleavage Tcand for general yielding Tg. At temperatures below Tc,the steels fail by pure cleavage. This involves the generation of a cleavage crack nucleus in a carbide particle followed by cleavage crack propagation. The cleavage fracture stressσfis independent of temperature. Between temperatures Tcand Tg, the steels fail by quasicleavage. This involves the generation of a crack nucleus by a localised fibrous process followed by cleavage crack propagation. The crack nucleation stage is shear stress controlled and therefore the quasicleavage fracture stressσqincreases with decreasing test temperature. Above temperature Tg, failure occurs at or after general yielding.MST/1045

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.5.422

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractThe changes in structure and substructure occurring during homogenisation and hot rolling of an Al–5Mg alloy (AA 5083) have been investigated. It is shown that a homogenisation treatment is beneficial and that the resulting structure can be related to processing parameters. The results suggest that the substructure morphology is dependent upon the total strain, but this has not been quantified. The development of texture was also studied and it is shown to be almost invariant with temperature, but strongly strain dependent. The anisotropy so produced yielded plastic strain ratios that were found to be strongly dependent upon the rotated copper texture intensity. The deep drawing behaviour of the hot rolled sheet was investigated by employing cupping tests and it is shown that a relationship exists between the earing value and the subgrain size.MST/I086

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.5.428

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractSlow tensile straining of a series of specimens of 304L stainless steel after thermally charging with hydrogen at 31·0 MPa and 350°C resulted in a ductility loss compared with uncharged specimens. The susceptibility to embrittlement was shown to be dependent on the formation of martensite during deformation and, hence, the stability (and composition) of the austenite, but the interface between the austenite and any ferrite stringers acted as a nucleation site for cracking and as a weak propagation path for fracture.MST/1088

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.5.441

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractTo investigate the mechanical properties of a binary Al–2·8Li alloy at high strain rates in as received (solution treated) and aged conditions, quasistatic and dynamic torsion tests were carried out. With increasing strain rate, the strength and ductility of the as received alloy increased and a change of the fracture mode from intergranular to transgranular was also observed. However, in the aged alloy, the intergranular fracture mode was predominant at both quasistatic and dynamic rates. At the grain boundary offsets on the fracture surface of the aged alloy, a large number of very fine dimples were observed. This evidence suggests that a ductile precipitate free zone may be present there.MST/1043

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.5.447

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractPlane strain compression tests have been carried out at strain rates between 0·5 and 10 s−1and temperatures in the range 275–510°C, both under nominally isothermal conditions and with temperature decreasing. Also, temperature or strain rate have been changed in the interval between two deformations. In all cases, the stress–strain curves obeyed a mechanical equation of state, described by constitutive relationships in terms of strain and instantaneous value of Zener–Hollomon parameter Z. When the value of Z varies slowly during deformation, flow stress is uniquely related to subgrain size and to dislocation density within subgrains, but these relationships break down in transition structures developed after a change of Z between two deformations. The existence of an equation of state for mechanical behaviour, but not for microstructure, is considered to result from important contributions of both dislocation velocity and density to hot strength.MST/1066

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.5.453

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractIn an AA 8090 alloy, the microstructural changes that occur as a result of variation in the extrusion processing parameters have been investigated. Light microscopy revealed that under all processing conditions the surface layers of the extrudates are fully recrystallised, whereas the core is essentially unrecrystallised. The depth of the recrystallised surface layer, and recrystallisation at the core, are affected by changes in the processing conditions: recrystallisation is most sensitive to extrusion ratio and nucleates at prior grain boundaries. Transmission electron microscopy (TEM) revealed that a well recovered subgrain structure is produced under all deformation conditions and variation of both extrusion temperature and ratio affect the subgrain morphology. Examination of extrudates using TEM together with results from hot torsion and post-extrusion annealing, provide evidence of the recrystallisation mechanisms: at lower deformation rates recrystallisation occurs by the classical grain boundary bulging mechanism and at higher deformation rates this process is supplemented by rotation recrystallisation.MST/1072

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.5.461

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractWeight loss resulting from immersion in 3%NaCl solution buffered with Mg(OH)2has been determined for Mg alloy splats containing different levels of alloying with Zn or Al with and without ternary additions of Mn, Ce, Nd, and Si. The results show that additions of Zn increase the rate of dissolution, whereas an addition of 15 wt-%Al significantly reduces the dissolution rate. Ternary additions of Mn significantly reduce the dissolution rate of both Mg–Zn and Mg–Al alloys, whereas Ce and Nd reduce the dissolution rate of Mg–Al alloys. Additions of Si to Mg–Zn slightly increase the dissolution rate. These results are discussed in the context of other reported observations on the corrosion behaviour of rapidly solidified Mg alloys.MST/I098

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.5.469

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractThe localised corrosion behaviour of 17–4 PH (precipitation hardenable) stainless steel, in the solution annealed, aged, and overaged conditions, was studied in acidic chloride and sulphuric acid media using the potentiodynamic anodic polarisation method. Electrochemical potentiokinetic reactivation (EPR) studies and microstructural examination were also carried out. In the acidic chloride medium, the material in the solution annealed and overaged conditions corroded uniformly, whereas in the aged condition it exhibited passivity and pitting. In the sulphuric acid medium, the magnitude of anodic peaks changed significantly on varying the microstructural condition. The EPR charge and reactivation peak current density values, which were lower in the aged condition than in the solution annealed and overaged conditions, were in good agreement with the microstructural observations and results of polarisation studies.MST/1087

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.5.475

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor