摘要:

AbstractThe variation of texture through the thickness and the average texture of sheet material of recrystallised AA 8090 and unrecrystallised AA 8090 (crossrolled) and AA 2090 AI–Li alloys have been investigated. Conventional (lithium free) AA 2024 alloy in the annealed condition was used as a reference material. The quantitative orientation distribution functions were determined via X -ray diffraction and neutron diffraction techniques. Using X -ray diffraction, textures of layers at various distances from the surface to the centre of the sheets were examined to achieve the texture gradients. The average textures were determined either via neutron diffraction using cylindrical stacked specimens or by summing the texture results obtained via the X-ray techniquefor the various layers. It is shown that the intensity of the common rolling textures, i.e. {112}, {123}, {110}, and shear texture {100}markedly varied through the thickness of unrecrystallised AA 8090 and AA 2090 AI–Li sheets. Also, in recrystallised AA 8090 AI–Li and AA 2024, a variation of the recrystallisation texture components {001}and {011}through the thickness was found. The quantitative texture data in conjunction with Taylor theory were used to predict the plastic anisotropy in terms of the plastic strain ratio as afunction of the angle a between the rolling and tensile directions. This prediction shows that the effects of texture can explain well the anisotropy in recrystallised AI–Li material (AA 8090). For unrecrystallised materials (AA 8090, AA 2090), a correct trend in plastic anisotropy is predicted; however, the calculated values in the 45°direction are larger than those determined experimentally.MST/1910

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.7.581

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractTwo 9Cr–1Mo steels containing 0·26 and 0·75 wt-%Si were subjected to different annealing treatments to vary the prior austenite grain size. When oxidised in air at 973 K, the grain boundaries oxidise at higher rates than the areas within the grains, and thus develop oxide ridges. In addition to this morphological difference these grain boundary ridges also show compositional dissimilarities from the oxides formed within the grains, as suggested by the results from analyses using scanning electron microscopy and secondary ion mass spectrometry (SIMS) at these locations. Both energy dispersive X-ray analysis and secondary ion imaging confirm the high Si content of the oxides in the ridges. Oxide ridges and the scales within the grains of the oxidised alloys having different grain sizes and Si contents have been extensively characterised by obtaining depth profiles for different elements using SIMS. An important observation is that there is a synergistic influence of the grain size and the Si content of the alloy that governs the chemical composition and morphological features of scales, which in turn governs the stability of the oxides growing within the alloy grains. As suggested by thermogravimetry, scales growing over the alloy having low Si content and fine grain size show the lowest stability and earliest onset of spalling, whereas the scale on the steel having high Si content and large grain size is most resistant to spalling.MST/1920

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.7.592

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractRetrogression and reaging produces coarsening of grain boundary precipitates and thereby improves resistance to stress corrosion cracking. At the same time it causes pronounced heterogeneous precipitation on dispersoids of E (Al18Cr2Mg3) phase inside the grain of 7075 alloy. Such heterogeneous precipitation does not occur on the coherent dispersoids of Al3Zr phase in 7050 alloy and its absence leads to higher strength compared with 7075 alloy. Supplementary examination of laboratory alloys 7075-Zr and 7075-Cr differing only in transition metal content supports the above result. This effect is probably the reason why retrogression and reaging (T77 heat treatment) is recommended for alloys containing zirconium but not for those containing chromium.MST/1898

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.7.599

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractThe influence of aluminium (0–0·3 wt-%) on the formability and mechanical properties of type 430 stainless steel was evaluated. Also, the effect of thermomechanical parameters such as hot band annealing and coiling temperature was examined at three different aluminium levels. Some comparisons are made between the processing routes for the deep drawing of carbon steel sheet andferritic stainless steel sheet. It is concluded that any influence that aluminium has on the engineering properties of these alloys depends on the thermomechanical processing treatment selected. Low hot finishing temperatures and no hot band annealing are detrimental to texture and sheet metal formability. Finishing temperatures of ~900 to 950°C coupled with relatively low coiling temperatures (~650°) result in the best formability, although the improvement in texture is not marked. The optimum aluminium levelfor the alloys studied appears to be about 0·1%. Fine dispersions of carbide and nitride precipitates are necessary to produce a relatively fine, uniformly equiaxed grain size, which is the optimum for deep drawing and stretching operations.MST/1931

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.7.604

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractThe effects of strain induced martensite formation and grain size on the room temperature low cycle fatigue behaviour of AISI 304LN austenitic stainless steel were considered. Two grain sizes, namely, 60 and 350μm, were developed via suitable solution annealing treatments. Microstructural changes before and after low cycle fatigue testing were identified. The martensitic transformation was studied using aferritescope, X-ray diffractometry, and optical microscopy. The mechanical response was correlated with the microstructural changes. Secondary hardening as well as a crossover in the strain–life plots for the two grain sizes resulted from martensite formation. Dislocation configurations depended on the strains imposed.MST/1902

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.7.614

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractTo develop a high strength, high ductility steel, making use of transformation induced plasticity due to retained austenite, a 0·lC–5Mn (wt-%) steel was examined to ascertain whether a considerable amount of retained austenite is formed after simple thermal treatment consisting of heating, holding at temperatures in the intercritical range, and cooling. The amount of retained austenite passes through a peak with increasing holding time and is virtually insensitive to cooling rate. The maximum amount that can be retained is about 30 vol.-%. The ductility of the specimens tested is almost proportional to the amount of retained austenite.MST/1921

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.7.621

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractHigh strain fatigue experiments were carried out on thirteen different high temperature alloys at 550°C. By means of multiple step tests and interrupted tests in the steady state, the asymmetrical nature of the Bauschinger effect was examined, i.e. having regard to the magnitude and direction of the stress reversal point during the course of the hysteresis loop. The cyclic stress–strain curve was characterised using the well known Ramberg—Osgood deformation relationship, and distinction was made between actual curve shape and the locus approximation. The yield stress during the course of a cycle could be made to vary according to the reversal point in the interrupted tests, but even in steady state cycling, the cyclic yield point was found to decrease as the total strain range was increased. Limited investigations were also performed during evolutionary (hardening or softening) cycling and all results were interpreted in terms of the prevailing back stress and friction stress. A formula to predict yield was hence derived for engineering use.MST/1907

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.7.627

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractThe influence of alloy composition on cyclic stress response, cyclic strain resistance, and cyclic fracture behaviour is reported. Three Cu–Pb alloys containing 10, 25, or 40 wt-%Pb were investigated. Alloy composition, i.e. lead content, was observed to have an influence on cyclic stress response, cyclic ductility, and low cycle fatigue life. The cyclic stress response characteristics, fatigue life, and failure process are discussed in the light of the specific roles played by concurrent and mutually interactive influences of plastic strain amplitude, concomitant response stress, and intrinsic microstructural effects.MST/1918

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.7.640

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractSystematic characterisation of the behaviour of electron beam welded thin superplastic 8090 Al sheet has been carried out. The beam voltage, current, and travel speed were varied within 52·5–60·0 kV, 4·5–6·0 mA, and 50–80 mm S−lrespectively. The relationships of fusion zone depth, width, depth/width ratio, cross-sectional area, and postweld tensile properties versus voltage, current, velocity, and heat input were established. It was found that the beam current exerted the most pronounced effect. Based on microhardness values, electron probe microanalysis, and transmission electron microscopy, the fusion zone was harder in the as welded condition but weaker in the as welded + T6 tempered condition due to different distributions ofδ′, S′, T2, T1, and S phases. The porosity wasfound to increase with heat input, most likely as a result of the hydrogen enriched surface layer. The contribution from Li and Mg evaporation during welding is considered to be less important. Cracking was observed in superplastic 8090 under high heat input conditions, but not in 5083 (Al–Mg) or binary Al–Li alloys, which can be explained in terms of insufficient backfill effect, high thermal stress, and coarse grain boundary particles. The optimum postweld mechanical strength for full penetration welds enabled a joint efficiency of>85% to be achieved, thus the combination of electron beam welding and superplasticforming is thought to be a promising technique.MST/1973

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.7.647

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractFunctionally gradient materials exhibit a progressive change in composition, structure, and properties as a function of position within the material. Functionally gradient materials and conventional metal matrix composites have been manufactured from gas atomised aluminium alloy 2124 powders (matrix) and particulate silicon carbide (reinforcement) by mechanical mixing followed by hot pressing at 500°C at a pressure of 1·5 GN m−2. In this work the structure and mechanical properties of model functionally gradient materials consisting of two discrete layers are compared with those of composites of homogeneous composition. A careful microstructural investigation has revealed a uniform distribution of the reinforcing SiC and defect free interfaces between adjacent layers of the functionally gradient materials. The strengths of the functionally gradient materials and composites have been determined via three point bend tests and the fracture toughness properties assessed using single edge notch bend type specimens. In the tests the crack in the functionally gradient materials was propagated from a high SiC region into a low SiC region (generally more ductile) and retardation of the crack growth investigated. For most compositions the mechanical performance of the functionally gradient materials was superior to that of the conventional composite having a SiC content corresponding to the high SiC region.MST/1938

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.7.659

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor