摘要:

AbstractThe directional recrystallisation process which leads to the growth of highly anisotropic‘new’grains in an oxide dispersion strengthened nickel base superalloy is investigated to elucidate the mechanism of recrystallisation and the process variables important in controlling microstructural evolution. It is found that after extrusion and hot deformation, the alloy consists of an ultra fine equiaxed grain microstructure characteristic of a material which has undergone dynamic primary recrystallisation. Thus, the directional recrystallisation which follows when the hot rolled sample is annealed in a moving temperature gradient (zone annealed) is really a secondary recrystallisation phenomenon. By comparing grain boundary mobility with the rate of zone annealing, it was theoretically predicted and experimentally observed that directional recrystallisation should give way to equiaxial recrystallisation when the interface velocity is less than the speed of zone annealing. The variables involved in the anisothermal zone annealing process appear to rationalise when the effects of temperature and time are consolidated into a single parameter, the kinetic strength of the heat treatment. Directional recrystallisation is found to occur only when a critical value of the kinetic strength is exceeded, irrespective of the peak temperature or traverse speed during zone annealing.MST/1268

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.12.1236

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractA series of hot rolling textures of steel sheet with different compositions and hot rolling parameters have been compared. The observed hot rolling textures all belonged to a limited number of different types. These types seemed to depend on the composition, the hot rolling parameters, and the local deformation mode. The influence of these hot rolling textures on the properties of commercial sheet steels after cold rolling and continuous annealing is critically evaluated. For steels with a low content of high temperature precipitates, the texture and microstructure after intercritical hot rolling often appeared to be the result of a transformation induced recrystallisation process with a specific nucleation mode. Understanding of the nature of this type of recrystallisation may facilitate an improvement in the material properties by optimisation of the hot rolling texture.MST/1327

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.12.1247

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractThe dislocation substructures developed during dynamic recrystallisation (DRX) were studied by means of tensile tests and metallographic observations on polycrystalline nickel. The average cell size in the homogeneous substructures decreased rapidly with straining to about half the peak strain, whereupon DRX nuclei began to form. The average cell size then approached a constant value for increasing strain. Full DRX substructures were distributed heterogeneously throughout all areas, and were classifiable into three categories: (i) DRX nuclei, (ii) growing DRX grains containing a dislocation density gradient, and (iii) large DRX grains with a fairly homogeneous substructure. The average cell size in region (iii) could be expressed as a function of either the peak flow stress or the DRX grain size. The relationship between these microstructures and flow behaviour under DRX are discussed in detail.MST/1285

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.12.1251

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractThe microstructural evolution during mechanical alloying of Ti and Al powders has been investigated by X-ray diffraction, scanning electron microscopy (SEM)–energy dispersive spectroscopy, and transmission electron microscopy (TEM). Observations by SEM showed a progressive change of the powders' morphology as a function of milling time. Observations by TEM, performed on a sample milled for 20 h, revealed the simultaneous occurrence of amorphous zones and nanocrystalline domains. The observed amorphous phase is not the final milling product. After 34 h of milling it was possible to identify by TEM fcc (a=0·41 nm) nanocrystalline zones, with a mean size of about 10 nm. By irradiating the powder milled for 20 h with high density electron beams, a suddenin situcrystallisation took place. The crystallite (fcc with a=0·41 nm) size was between 0·1 and 0·5μm.MST/1281

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.12.1258

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.12.1263

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor