Nano and microstructural design of advanced materials: a by M. A. Meyers, M Sarikaya, R. O. Ritchie

By M. A. Meyers, M Sarikaya, R. O. Ritchie

The significance of the nanoscale results has been famous in fabrics learn for over fifty years, however it is barely lately that complex characterization and fabrication equipment are allowing scientists to construct constructions atom-by-atom or molecule-by molecule. the knowledge and keep an eye on of the nanostructure has been, to a wide volume, made attainable by means of new atomistic research and characterization tools pioneered via transmission electron microscopy. Nano and Microstructural layout of complicated fabrics specializes in the powerful use of such complex research and characterization strategies within the layout of fabrics. * Teaches potent use of complex research and characterization tools at an atomistic point. * comprises many aiding examples of fabrics during which such layout ideas were effectively utilized.

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Ion-assisted coatings, ion implantation, thermal spraying, as well as electron and laser beam treatments) [ 1,2]. Not all of these methods involve hardening of the surface layer. The change of the 35 J. Kusinski and A. Woldun 36 surface layer properties can also be obtained by changing its microstructure and/or chemical composition. Laser surface melting found many practical applications, as a method of formation of rapidly resolidified surface layers with many advantageous properties. Indeed, laser melting can harden alloys that cannot be hardened so effectively by laser transformation hardening.

9: TEM micrographs: (a) - bright field; (b) - dark field images and related electrc n diffraction pattern taken from the laser-alloyed zone. Laser surjuce alloying of carbon steels with tantalum, silicon and chromium 41 Such structure is characterized by a relatively high hardness level ranging from 700 - 1600 pHV, depending on quantity of silicon in the alloyed layer [8] The TEM microscopy studies revealed that there were three structural components acicular martensite, femte and retained austenite in the LA2 As was already mentioned, femte and austenite crystals were formed during crystallization of the silicon rich laser melted zone Microprobe analysis showed that silicon distnbution in that zone was not uniform The highest Si quantity was measured in the central areas of the alloyed zone (about 6 5% of Si), whereas, near the surface and near the bottom of the alloyed zone Si concentration was = 4% [8] Ihe I b M examinations did not show presence of SIC powder particles It seems that SIC dissolved completely in the melted pool Figure 8b shows a thick plate of retained austenite present between two martensitic needles Presence of retained austenite was confirmed by SAD patterns Figures 9 are the bright (9a) and dark field (9b) images presenting, interlath, thin films of retained austenite Alloying with chromium Similar to the case of laser alloying with tantalum and silicon, the influence of laser output power and scanning velocity on dimensions and microstructure of the chromium laser-alloyed layer (LML) was Figure 10: a) - Optical image of the crosssection of the surface alloyed layer and SEM images of b) - the laser-alloyed zone (LAZ) and c) - the heat affected zone (HAZ), laser surface alloying with chromium using non-organic binder in the slurry evident With increased scanning velocity, the laser beam-sarnple interaction time decreases and less laser energy is absorbed by irradiated matenal The same was observed with decreased output power Indeed, the size of the laser-alloyed (LAZ) and heat-affected zones (HAZ) decreased too In such case, the laser beam melts only the pre-deposited layer of Cr and a limited, thin layer of the base material As a result, the melted zone was highly enriched with chromium and carbon (in the case of using an organic binder in the slurry) The OM and SEM micrographs in rigure 10 show typical cross-section of the surface layer after laser alloying Lath martensitic structure, coarser than that observed in the heat-affected zone, was characteristic for the matenal alloyed with chromium (for pre-deposited chromium layer with non-organic binder) Figures 11 a - c are the microprobe line scans showing chromium distribution in the laser-alloyed layers The analysis was done for samples laser treated at constant g = 0 13 mm and V = 12 mmis, and with variable laser power (a) - P = 1 35 kW, (b) - P = 1 5 kW and (c) - P = 1 8 The depth of the substrate melted layer increase with the laser power, hence, for the same scanning velocity and the same thickness of the pre-deposited chromium powder layer, the alloyed zone was thicker and contained less chromium The dendritic structure of the melted zone was again evident when an organic binder was used (Figures 12a and b) The chemical compositions in the dendritic and the interdendritic regions at the middle part of the J.

S. L. (1999)J. Nucl. Mat. 274,299. B. Williamset al. Wynblatt, P. and Takashima, M. (2001) Interface Science 9, 265. Krauss, G. (2001) Metall. and Muter. Trans. A 32A, 861. M. (1997). Interfaces in Materials. Wiley, New York, NY. P. W. (1995). Interfaces in Crystalline Materials. Oxford University Press, Oxford, UK. B. W. (1976) Acta metall. 24, 323. R. B. (1986). In: Interface Migration and Control of Microstructure, pp. H. and Walter, J. ). American Society for Metals, Metals Park, OH. Doig, P.

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