摘要:

AbstractThe effect of additions of TiO2and SnO2on the tetragonal phase of the ZrO2–Y2O3system has been investigated using complex impedance, X-ray, and transmission electron microscopy measurements. Neither addition acts to stabilize the tetragonal phase and SnO2increases the specific grain boundary resistance by a factor of 3. Additions of Al2O3improve the specific grain boundary conductivity of GPR (general purpose reagent) grade material to a level comparable to that of commercially available grades of tetragonal zirconia.MST/558

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.6.401

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractCarbon solubilities in iron at elevated temperatures (>1000 K) are analysed on the basis of statistical thermodynamics. A parameter Q which refers to the extent of stabilization of a carbon atom in the iron lattice is estimated forα-,γ-, and molten FeCxphases. The results suggest that the carbon atom is most stable in molten FeCxand least stable in (α-FeCx. In addition, the value of QCαfor (α-FeCxat high temperatures appears to be different from that at lower temperatures. This observation can be interpreted as the effect of the magnetic transition of the iron atom around the Curie temperature. The values for Q estimated for the other interstitial elements X (X = H, N, P, S) in iron lattices are compared.MST/586

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.6.404

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractThe increase in particle radius r during the coarsening ofγ′(Ni3(Ti, Al)) located at grain boundaries in Nimonic PE 16 has been found to vary as r3·6with time. Models for coarsening of intergranular and intragranular precipitates predict a dependence on grain boundary and lattice diffusion, respectively. The case investigated here, where coarsening is preferential to grain boundaries from precipitates in the matrix, is more complex since it will depend upon more than one diffusion regime. From the experimentally determined diffusion coefficient for the process, it is apparent that the out-diffusion of aluminium from dissolving precipitates is the rate controlling step. Convergent beam electron diffraction has been used to infer compositional changes within precipitates, particularly with respect to the boundary position. These results are used to argue that addition of atomic species to intragranular precipitates is via the grain boundary, rather than across the coherent precipitate/matrix interface.MST/615

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.6.411

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractTension–compression cyclic deformation behaviour in dual-phase steels has been studied. Three different ferrite (α)–martensite (α′) microstructures, i.e. isolatedα′-colonies dispersed inα-matrix (I), continuousα′(C), and laminatedα–α′(L), were prepared by appropriate heat treatments, keeping theα′volume fraction at ~0·3. The work hardening and the Bauschinger effect are found to be greater in microstructure C or L than in I when they are compared at an arbitrary forward (tension) prestrain level. An increase in the hardness ofα′enhances the Bauschinger effect and then narrows the stress–strain hysteresis loop. The stress evolved as a result of the Bauschinger stress (defined as the difference between forward prestress and backward (compression) 0·1% proof stress) is found to be almost independent of microstructure and hardness when it is compared at an arbitrarily fixed prestress level. The slip lines are very fine and relatively straight in microstructure C, but wavy in microstructure I. These findings are discussed from the standpoints of the accumulation of the average internal stress resulting from inhomogeneous plastic flow between two constituent phases and the plastic relaxation.MST/382

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.6.415

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractA detailed microstructural characterization of two silicon-containing low-alloy steels, Fe–0·2C–2Si–3Mn and Fe–0·4C–2Si–4Ni (nominal wt-%), isothermally transformed in the bainitic temperature range (~ 400–250°C), has been carried out using principally electron microscopy, X-ray diffraction, and dilatometry. Upper bainite in these silicon-containing steels consists of bainitic ferrite laths and interwoven thin films of retained austenite instead of cementite. Coarser granular regions of retained austenite may also be obtained. The bainitic ferrite laths (or plates) in lower bainitic structures contain intralath carbides, but the interlath morphology of retained austenite still occurs. The variations in these microstructures with isothermal transformation temperature, and the thermal stability of the retained austenite phase is described and discussed.MST/526

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.6.422

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractTwo silicon-containing low-alloy steels, Fe–0·2C–2Si–3Mn and Fe–0·4C–2Si–4Ni (nominal wt-%), isothermally transformed in the bainitic temperature range (~400–250°C) have been deformed in tension. The bainitic microstructures in these steels contain appreciable amounts of retained austenite (instead of interlath cementite), and the behaviour of this phase during tensile deformation, and its apparent influence on the mechanical properties, has been examined. In particular, it is shown that provided the retained austenite exists in an interlath, thin-film morphology it has appreciable mechanical stability. Larger volumes of retained austenite have less mechanical and thermal stability, forming plate martensite structures and also undergoing deformation twinning. The effects of these variations on tensile strength and ductility are discussed.MST/527

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.6.432

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractThe fracture toughness of two experimental silicon-containing steels in the bainitic condition has been measured and related to the microstructural state of the steels. The optimum bainitic microstructure for high strength and high toughness combinations consists of bainitic ferrite and thin interwoven laths of retained austenite instead of cementite, this condition being achieved through the silicon addition to the steels. The thin films of retained austenite are thermally and mechanically stable and act to reduce the effective fracture grain size and also possibly help to blunt propagating microcracks; blockier volumes of retained austenite are unstable and hence not beneficial to toughness. The two experimental steels achieved strength and toughness values equal to, or better than, some commercial steels in the martensitic condition.MST/528

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.6.441

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractThree different alloys of AISI Type 444 (18Cr–2Mo) ferritic stainless steel, stabilized to different levels with titanium and/or niobium, were melted as welds or weld simulations with deliberate additions of nitrogen to the argon shielding gas in order to simulate the effects of accidental contamination by nitrogen during production welding. The oxalic acid etch test (ASTM A262–A) was used to assess the susceptibility of the melts prepared in this way to intergranular attack, and the extent of attack was quantified. It is shown that a clear correlation exists between the extent of intergranular corrosion and the amount of nitrogen taken up by the steel on melting. The implications of sensitization by nitrogen contamination both for steel design and integrity of production welds are discussed.MST/415

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.6.450

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractA study has been made of the influence of uniaxial superplastic deformation on the ambient temperature tensile properties of Ti–6Al–4V sheet. Material was deformed to various strains up to 200% at temperatures from 850 to 970°C at strain rates in the range 1·1−18×10;amp;#x2212;4s−1(0·7−11% min−1). Tests were also performed on statically annealed material to separate the effects of high temperature exposure and superplastic deformation. Mechanical property changes were complex and depended on the relative contributions from the strengthening and softening mechanisms occurring during either superplastic deformation or heat cycling. Structural features influencing mechanical properties were phase size and morphology, dislocation density, and crystallographic texture. The strength after superplastic deformation was always less than that of as-received material but a significant reduction in strength was attributable to heat cycling. In some cases, the strength of the superplastically deformed material was greater than that after heat cycling.MST/593

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.6.455

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractRecent studies on the deformation of metals indicate that at relatively high strains the flow stress does not increase with further strain. The mathematical expressions usually used to derive the relationship between stress and strain (generally the Ludwik or Hollomon equations) do not predict such a plateau. A new expression (σ= K1mn(tanhε/m)nis proposed, where K and n have the same values as the original Hollomon equation and m is an additional disposable parameter. The new expression reduces to the Hollomon equation at low strains but, by adjusting the value of m, can be made to correspond to the high-strain behaviour. For copper and silver, using values of n = 0·5 and m = 2, the ratio of the flow stresses at unit strain to the saturation flow stresses corresponds to those observed experimentally.MST/455

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.6.462

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor