摘要:

AbstractA review of the toughness properties of metal matrix composites (MMCs) is presented. It is shown that the toughness of MMCs is controlled by a complex interaction between the properties of the constituent phases and the processing route and that no single parameter is capable of describing all the features of their toughness response. It is proposed that the toughness of MMCs is best characterised by a combination of the fracture toughness and the energy values associated with the initiation and propagation of fracture. This approach is used to illustrate methods of optimising toughness in MMCs.MST/828

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.1.1

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractThe semicoherent interface is characterised between the matrix and a critical nucleus which has the same crystal structure and orientation, but a different lattice spacing. A coherency loss parameter C is introduced and is related to the interfacial energyγand volume strain energy∆Gɛaccompanying the formation of a second phase particle. It is found that the C value for a critical nucleus C*depends on both the driving force for nucleation∆Gchemand the lattice mismatch between the precipitate and the matrix. For a given alloy system, C*is a sole function of∆Gchem. The method is employed to calculate the C*values pertaining to the interface between an fcc Co nucleus and Cu in Cu–Co alloys and between a TiC nucleus and austenite. It is indicated by the results that there is a transition value of∆Gchemabove which a fully coherent nucleus/matrix interface is obtained. This value is 1 GJ m−3for Co rich nuclei in Cu–Co alloys and 18 GJ m−3for TiC in austenite. These predictions are consistent with experimental observations.MST/813

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.1.8

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractThe effects of precipitates formed by the addition of vanadium, nitrogen, and aluminium on the ferrite grain size of 0·15% C steels have been studied by cooling suitable steels at four rates ranging from 120 to 3·6 K min−lfrom temperatures giving a constant austenite grain size of 35μm. The undissolved particles present during austenitising have no role in determining the ferrite grain size. The precipitating particles of vanadium carbide (VC) and particularly vanadium carbonitride (V(C,N)) are excellent ferrite grain size refiners, while aluminium nitride (AlN) has little or no effect on ferrite grain size refinement. The presence of aluminium enhances the ferrite grain size refining effect of V(C,N). The volume fraction of precipitates and their size or distribution are responsible for ferrite grain size refinement.MST/773

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.1.13

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractThe microstructural response to normalising of commercial C–Mn–Al–Nb steels produced using various manufacturing routes and rolling schedules has been investigated over the range of normalising temperatures 840–940°C and the temperature required for optimum mechanical properties was identified. The morphological development of austenite was studied using reheat quench experiments by which it was shown that the morphology of coarse bainitic microstructures when present in the as rolled steels, was inherited by the austenite on normalising. The transformation behaviour on cooling from normalising temperatures close to the Ac3and the evolution of the grain refined ferrite–pearlite microstructure were studied using both dilatometry and electron microscopy. The variations in mechanical properties observed are explained in terms of microstructural features, such as ferrite grain size and volume fraction and distribution of pearlite, and there was found to be a strong relationship between the ferrite grain size before and after normalising. It can be inferred from the microstructural observations that the mode of austenite transformation (as determined by the as rolled ferrite–pearlite microstructure) confers a limited memory to these steels which is particularly evident at low normalising temperatures. From observations of the etching response of austenite grain boundaries at low normalising temperatures, it can be suggested that the memory may be a result of segregation of impurities to austenite/ferrite interfaces either during cooling after rolling or reheating during normalising.MST/673

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.1.20

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractFor low carbon acicular ferrite steels, niobium in solution may contribute to a low austenite to ferrite transformation temperature. Hot rolling schedules and steel compositions which could minimise the precipitation of niobium from the austenite as carbonitride are investigated. It is found that rather large quantities of niobium may be kept in solution under rolling conditions which favour rapid recrystallisation of austenite. Carbonitride precipitation in deformed austenite appears to be proportional to the precipitation potential at the deformation temperature which can be calculated by appropriate solubility equations taking into account actual compositions of steels. No precipitation of carbonitride during or after the austenite to ferrite transformation is observed in those specimens which exhibit acicular ferrite microstructures after air cooling.MST/805

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.1.29

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractAn analysis is presented of the influence of microstructure on the mechanical properties of austenitic–martensitic high Ni steels containing Ti. On the basis of data taken from the literature as well as the results of the present investigation, it is concluded that the properties of these steels are primarily dependent on the volume fraction and morphology of reversed austenite. Since it has been found that for many applications of duplex alloys the fracture toughness is an important property, further investigation of the interdependence of this property and the morphology of austenite is required.MST/728

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.1.36

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractData are presented from fatigue and creep–fatigue crack growth rate tests carried out at 650°C on an aged type 347 stainless steel weld. Fully reversed tests were carried out under displacement control, with constant displacement hold periods, to simulate closely the thermally induced straining relevant to power plant applications. Tensile hold periods of up to 192 h were used in the creep–fatigue tests; a 1 h hold period was sufficient to induce internal intergranular cracking in the test specimens. In the creep–fatigue tests, crack growth occurred during both the cyclic excursions and the hold periods. Cyclic rates were also dependent on hold time, the acceleration in fatigue crack propagation rates being associated with the extent of creep damage produced ahead of the main crack as a result of the hold periods. Such an interaction between fatigue and creep was supported by a sequential creep–fatigue crack growth experiment. Empirical equations were obtained which describe the total crack growth rates as the sum of a cyclic and a dwell contribution. The cyclic contributions were described in terms of a stress intensity factor range, while the dwell components were correlated with a creep crack growth correlating parameter C*. It was shown that the reference stress approximation to C*accurately predicts measured values as long as creep strain rate data were derived from constant displacement stress relaxation data rather than from forward creep data.MST/782

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.1.40

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractThe precipitation behaviour in Al–1·52Cu–0·75Mg alloys containing 0, 0·23, 0·49, and 1·03%Si has been investigated by scanning electron microscopy, transmission electron microscopy, and differential scanning calorimetry. In the solution treated condition, the Si free and 0·23%Si alloys had a single phase structure, but on aging precipitation of the S′(Al2CuMg) phase was observed. In the higher Si alloys, completely different precipitation behaviour and the presence of other phases, such asθ′(CuAl2), were observed. These alloys contained up to 1·34 vol.-% of the insoluble phase Q(Al5Cu2Mg8Si6). The formation of the insoluble phase was found to change the solute contents of the matrix such that the Cu/Mg ratio changed from 2 in 0·23%Si alloy to 23 in 1·03%Si alloy. In the Al–1·52Cu–0·75Mg alloy, which retains up to ~0·3%Si in solid solution, precipitation of S′phase was observed. At concentrations above ~0·3%Si, the matrix becomes depleted in solute as a result of the formation of the insoluble Al, Cu, Mg, Si bearing quarternary Q phase. The significant change in precipitation behaviour due to small changes in the Si content of the alloys is attributed to this rapid depletion of the matrix in solutes as a result of the formation of insolubles.MST/714

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.1.52

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractExperiments have been carried out to determine the relationship between processing, microstructure, and mechanical properties of an Al–6Mg–3Cr powder alloy consolidated by extrusion. Attention is focused on the microstructure of the powder and the subsequent changes that occurred during thermomechanical consolidation to a fully dense product. The powder microstructure was composed of aggregates of three equilibrium phases (Al18Mg3Cr2, Al3Mg2, and Al13Cr2) which were uniformly distributed within an Al matrix. Preheating to the extrusion temperature by induction had very little effect on the microstructure. However, consolidation of the powder accompanied by significant structural changes occurred during passage through the extrusion shear zone. The extruded microstructure was found to be inhomogeneous with coarse and fine bands of precipitates throughout. The inhomogeneities of extrudate microstructure have been related to the original powder and were caused by the wide range in powder particle size. The structural heterogeneities adversely influenced the extrudate properties, in particular, fracture behaviour, which was highlighted in poor toughness and ductility in a direction transverse to the working orientation.MST/840

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.1.56

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor

摘要:

AbstractThe effects of surface treatments on the fatigue lifetime of 8090 (Al–Li–Cu–Mg–Zr) and 7010 (Al–Zn–Mg–Cu–Zr) alloys have been assessed, using a rotating bend fatigue testing machine at a stress ratio R =−1. It was found that the fatigue performance of alloy 8090 was less susceptible to chromic/sulphuric pickling than alloy 7010 and shot peening was more beneficial for the lithium containing alloy. Excellent fatigue properties were also exhibited by alloy 8090 in the anodised condition. These observations are discussed in terms of the physical properties of the lithium bearing alloys and of their microstructure.MST/833

ISSN:0267-0836    

DOI:10.1179/mst.1989.5.1.65

出版商:Taylor&Francis    

年代:1989

数据来源: Taylor