ISSN:0267-0836    

DOI:10.1179/mst.1996.12.10.793

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractThe microstructure and the thermal stability of rapid solidified centrifugally atomised AI–3Cr–X (X=1Ni, 3Ni, 0·3Mo, 1Si, or 3Si, at.-%) powders were studied. Three main types of microstructure were observed in the powders: cellular, globular, and rosettelike. Some powders exhibited a mixture of these. In the atomised state the alloys usually had two phases, intermetallic Al13Cr2andα-Al solid solution. Thermal stability was studied for a range of temperatures from 20 to 500°C. The phase Al3Ni appeared in the nickel containing alloys and grew upon heat treatment. The molybdenum containing alloy did not show any noticeable change upon heat treatment. With respect to the silicon containing alloys, the intermetallic Al13Cr2transformed into Al13Cr4Si4at high temperatures. On the basis of bibliographic information a nucleation map was calculated relating the prevalence of the intermetallic Al13Cr2phase and theα-Al phase to the particle diameter and the chromium concentration of powder obtained by centrifugal atomisation.MST/3273

ISSN:0267-0836    

DOI:10.1179/mst.1996.12.10.794

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractThe slow tensile straining of smooth specimens of mill annealed Ti6Al4V with different hydrogen contents revealed hydrogen induced slow strain rate embrittlement when the hydrogen content exceeded about 2000 ppm. The effect of hydrogen on the mechanical behaviour of the Ti6Al4V at lower hydrogen levels was not so pronounced and may be interpreted in terms of the partitioning of hydrogen between theαandβphases and the effect of hydrogen in solution on the lattice parameters of these phases. Hydrogen levels in excess of about 1200 ppm promote an increase in the amount ofβphase at the charging temperature employed and the effect of this on mechanical properties is discussed. The effect of hydrogen solubility and hydride precipitation at theα/βinterface on hydrogen induced slow strain rate embrittlement is also considered.MST/3431

ISSN:0267-0836    

DOI:10.1179/mst.1996.12.10.802

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractSimulations of industrial thermomechanical processing and on line accelerated cooling of a low carbon microalloyed strip steel were carried out using a quench deformation dilatometer. Effects of processing parameters, such as accelerated cooling rate T and accelerated cooling interrupt temperature TIon the critical transformation temperatures and final microstructure were determined. The most important on line accelerated cooling (OLAC) processing parameter is the accelerated cooling interrupt temperature, which controls whether the transformed microstructure is predominantly ferrite or bainite. A variety of (Ti, Nb, Fe) carbide, nitride, and carbonitride precipitates are present in the OLAC processed samples. The final precipitate distribution is developed at three stages of processing, namely: dissolution and coarsening of pre-existing precipitates at the reheat temperature, precipitation in deformed austenite during the deformation schedule, and precipitation in ferrite after the interruption of accelerated cooling. Maximum precipitation strengthening occurs for TI=700–640°C.MST/3424

ISSN:0267-0836    

DOI:10.1179/mst.1996.12.10.808

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractCombined quenching and tempering induced phosphorus segregation to prior austenite grain boundaries inα0·077 wt-%P doped 2·25Cr–1Mo steel was examined using field emission gun scanning transmission electron microscopy. The results indicate that combined equilibrium and non-equilibrium phosphorus segregation may play an important part in temper embrittlement of the steel caused by direct tempering after quenching. Non-equilibrium segregation requires the formation of sufficient quantities of vacancy–impurity complexes and their migration to grain boundaries is of great importance in the segregation. For this reason, the mechanism for migration of the complexes is discussed in detail.MST/3419

ISSN:0267-0836    

DOI:10.1179/mst.1996.12.10.818

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractA range of analytical techniques, including optical and electron microscopy, energy dispersive X-ray analysis, and X-ray diffraction were used to assess the extent of segregation in gas atomised Ti–48AI–2Mn–2Nb (at.-%). The secondary dendrite arm spacing was used as a measure of microsegregation in these powders. These undercooled powders were found to solidify as hexagonalα2dendrites, surrounded byγphase segregate. Depending on the degree of undercooling experienced by a dendritic region and its composition, the hexagonal phase was found to transform to equilibriumγphase by means of either a massive or a lamellar type reaction. The final relative phase distribution of theα2andγphases was a function of the powder particle size. The microstructure of the hipped powder reflected the inhomogeneity inherited from the starting powder material.MST/3470

ISSN:0267-0836    

DOI:10.1179/mst.1996.12.10.823

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractThe wire electrical discharge machining behaviour of alumina particle and short fibre reinforced aluminium based composites was studied. Under the two cutting conditions of this study, namely coarse and fine cutting, the average surface roughness Raof the particle reinforced composite was found always to be higher than that of the corresponding machined matrix surfaces, however, the opposite was found to be true for the fibre reinforced composite. Comparing the surface quality of the two composites, in terms of roughness measurements, the fibre reinforced composite was superior to the particle reinforced composite. Although cutting conditions have little effect on the overall Raof the two composites, their corresponding surface topographies were found to be intrinsically different. Surface banding was observed on the fine cut surfaces of the particle reinforced specimens, which was believed to be caused by shifting of the wire. Based on the machined surface morphology and the measured surface profiles, the material removal mechanism for the two reinforced composites is discussed.MST/3412

ISSN:0267-0836    

DOI:10.1179/mst.1996.12.10.831

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractAn important and challenging aspect of the development of a system for fully automated electron backscattering pattern (EBSP) analysis is the design of reliable digital image processing routines for automatic detection and localisation of the bands in the digitised patterns. Procedures based on the Hough transform which permit precise localisation of a large number of bands in digital EBSPs are described in detail. Special attention is paid to the analysis and post-processing of the Hough space which ensure a high insensitivity to noise and a high precision of the measured band positions. The possibilities for further improvements and extensions of the procedures are also discussed, including the possibility of extracting band width information from the Hough transform. To demonstrate these possibilities, a new procedure is outlined and shown to be capable of providing high precision estimates of the EBSP band positions and, in addition, fairly precise estimates of the band widths.MST/3672

ISSN:0267-0836    

DOI:10.1179/mst.1996.12.10.837

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractCurrent methods of data representation for electron backscatter diffraction (EBSD) measurements are reviewed. Obtaining diffraction data from microstructures using EBSD has become a relatively straightforward procedure, and EBSD software packages are used to represent these data as qualitative statistics in the form of ideal orientations, pole figures, inverse pole figures, Euler space, and Rodrigues–Frank space. Quantitative statistics in the form of secondary computations allow full microtextural analysis. Additionally, the power of EBSD is demonstrated through positional information representation. Through experimental examples, the conversion of EBSD data to statistical information to facilitate interpretation of results is demonstrated.MST/3678

ISSN:0267-0836    

DOI:10.1179/mst.1996.12.10.844

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractHot deformation is a critical step in the production of high quality aluminium alloys, because it frequently controls the grain sizes, orientations, and substructures. These microstructural parameters are particularly amenable to quantitative analysis by electron backscattered diffraction, so that systematic studies of the influence of processing conditions on microstructural evolution are now possible. To understand the effects of temperature, strain, strain rate, and crystallographic orientation on microstructural evolution within the grains during hot rolling, single crystals of aluminium, Al–Mn, and Al–Mg have been hot compressed in a channel die and their substructure characterised using scanning electron microscopy and electron backscattered diffraction. This continuing work has demonstrated the following features: (i) the cube orientation undergoes a transition between unstable and stable deformation at a temperature that is a function of the strain rate and composition; (ii) the dislocation substructure in the crystal orientations corresponding to the typical fcc rolling texture components (Cu, S, and Bs) depends strongly not only on temperature but also on grain orientation. The results are compared with previous and current studies of hot worked aluminium polycrystals and discussed in terms of the influence of grain substructure on recrystallisation texture development.MST/3674

ISSN:0267-0836    

DOI:10.1179/mst.1996.12.10.851

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor