摘要:

AbstractAuger electron microprobe observations on plasma nitrided 304 austenitic stainless steel samples have confirmed previous results obtained by scanning electron microscopy and wavelength dispersive X-ray spectroscopy and have also shown some marked differences in micrograin structure between NH3 and plasma nitrided samples. The N H3 nitrided layer appeared to consist of a single layer with precipitate grains, if any,>0.1μm size, nitrogen concentration decreasing exponentially with depth. The plasma nitrided layer, on the other hand, consisted of two layers: a near surface layer with constant nitrogen concentration and precipitate grains of B1 (CrN) 1-2μm in size, beneath which is a layer in which the nitrogen content decreases exponentially with depth, this layer being thinner than its equivalent in the NH3nitrided material. The differences in nitrogen depth profile and nitriding rate between the two processes are explained in terms of the different resultant microstructures.

ISSN:0267-0844    

DOI:10.1179/sur.1987.3.4.326

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractX-ray diffraction analysis can be very usefully applied in the field of surface engineering, since a depth of a few micrometres only is usually probed. This paper provides an overview of current X-ray diffraction methods for the analysis of surface layers. The treatment is illustrated by examples taken from recent work on nitrided iron and steels. Distinct ways to characterize the effective depth and layer thickness probed are presented. Composition-depth profiles can be measured accurately by tracing the lattice parameter (taking into account the possible presence of stresses) as a function of depth below the surface by successive sublayer removals. A correction for the penetration effect is required and methods for that are presented and demonstrated. The basis of the determination of (macro) stress (the sin2ψmethod) is indicated. Attention is paid to the determination of the strain free lattice spacing and (diffraction) elastic constants, to the effect of a concentration-depth profile, and to the comparison of theoretically predicted and experimentally determined strain values. A stress (profile) in a surface layer often originates from the thermal history (cooling after treatment) and the presence of a concentration profile, as is illustrated by examples. Further, the analysis of X-ray diffraction line broadening is discussed. It is shown that nowadays an easily applicable method exists for line profile analysis (the single line Voigt method), allowing the determination of crystallite size and microstrain parameters. As demonstrated by the examples, knowledge of in particular microstrain in conjunction with macrostress is of importance in understanding and predicting material behaviour.

ISSN:0267-0844    

DOI:10.1179/sur.1987.3.4.331

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractAtomic layer epitaxy (ALE) is a relatively new and generally poorly understood thin film growth technique which is likely to find application in high technology industries during the next decade. It can be used to grow high quality thin solid films with specific crystal structures or orientations and with very fine control of filn1 thicknesses to one atomic layer. Most thin film deposition techniques have, so far, simply involved material transfer from a suitable source to a suitable substrate via the vapour phase, e.g. vacuum evaporation, sputtering, or chemical vapour deposition. Nucleation takes place on the substrate surface, the molecules seeking the most energetically favourable position relative to one another and fonning n1icrocrystals that in later phases control thin film growth. This results in uncontrolled crystal boundaries, producing films whose average density can be considerably below that of the bulk crystal. Annealing is often employed to improve the quality of the deposited film. In ALE the compound thin film immediately achieves its final crystal form through sequential surface reactions in which one element of the con1pound reacts with the growing surface. This n1ethod is a self controlled process that automatically accepts only one atomic layer at a time.

ISSN:0267-0844    

DOI:10.1179/sur.1987.3.4.343

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor