摘要:

AbstractMicrostructural evolution in high purity nickel was investigated by comparing the dislocation substructures formed following torsion deformation with those following rolling. Results from transmission electron microscopy observations and measurements of microdiffraction show a common evolutionary path in rolling and torsion from (i) dislocation tangles to (ii) equiaxed cells bounded by dense dislocation walls (DDWs) which form cell blocks, then to (iii) microbands which, together with DDWs, bound smaller and smaller cell blocks, and, finally, to (iv) subgrains. During this evolution, grains are continually subdivided by the formation of new cell blocks. New cell blocks arise through the formation of new DDWs between cell blocks or of first generation microbands by the subdivision of a single DDW Since the dislocation content of a microband is principally derived from that of the parent DDW, microbands can take various forms, such as a string of small pancake shaped cells in highly recovered DDWs, short double walls in discontinuous DDWs, or long paired dislocation sheets from continuous DDWs which can be very straight if formed close to {111} planes. At moderate strains and subsequent to microband formation, localised shear and shear offsets were observed in some first generation microbands. A few second generation microbands, in which localised shear is part of the formation process, were also observed. Localised shear was much more prevalent in rolling than in torsion. These results provide evidence for the theory that grains are divided into regions in which slightly different slip systems operate. Collectively, these regions provide evidence for strain accommodation, although in individual regions the number of slip systems is less than that required by the Taylor criterion.MST/1333

ISSN:0267-0836    

DOI:10.1179/mst.1991.7.6.544

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractAchievement of good formability in aluminium sheet requires control of the final texture. Earing in deep drawing is a common problem in aluminium sheet and can be minimised by careful texture control. In practice, this means the control of recrystallisation during thermomechanical processing as well as control of particle size distributions and elements in solid solution within the material. Experiments have been carried out using aluminium alloyed with various amounts of iron and silicon. The alloys were characterised in terms of the size distributions of second phase precipitates and elements in solid solution. The materials were hot rolled at a rather low final temperature which resulted in a deformed structure after coiling. They were then heat treated to give different amounts of recrystallisation before further cold rolling and annealing. Earing measurements were made following a wide range of cold reductions in both cold rolled and annealed states. Texture development and recrystallisation behaviour were studied carefully in a few selected samples. The results showed that the presence of second phase iron rich particles is a dominant factor governing the texture and earing behaviour. Furthermore, it is of the utmost importance to control the hot worked structure before cold rolling and annealing. The reasons for this are discussed in more detail using well known theories for nucleation of recrystallised grains considering particle size distributions, deformed microstructure, and elements in solid solution.MST/1366

ISSN:0267-0836    

DOI:10.1179/mst.1991.7.6.554

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractThe evolution of the microstructure resulting (only) from the combination of diffusional phase transformations in Cu–In and Ni–Sn systems is described. For this purpose, discontinuous precipitation lamellar products in Cu–7·5In and Ni–8Sn alloys (both at.-%) have been subjected to dissolution treatments. Examination of the resulting microstructures has shown that, contrary to the precipitation transformation, the dissolution process involves volume diffusion and the grain boundaries remain stationary during dissolution. The most striking feature of the post-dissolution microstructure in these alloys is that new grains are generated in the transformation product, giving rise to a localised grain refinement. In the absence of any plastic deformation applied to the material, the role played by the (coherent) lamellar interfaces generated during the precipitation process is discussed, particularly as the energetic potential for the observed recrystallisation phenomenon.MST/1360

ISSN:0267-0836    

DOI:10.1179/mst.1991.7.6.565

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor