Laser surface alloying

In addition to many industrial and laboratory techniques developed to apply hydroxyapatite onto metallic substrates, Lusquinos et al. (2002) presented a new approach to bind calcium phosphate solidly to Ti alloy that is related to a well-known technique in the metallurgical field laser surface alloying. The analysis of the results obtained and the description of the phenomena that take place in the coating process has been outlined in this explorative study. 

Multiwall carbon nanotube (MWCNT)-reinforced hydroxyapatite composite coatings (80% HAp/20% MWCNT) were deposited on austenitic stainless steel AISI 316L by laser surface alloying (LSA) with a 2.5-kW CW Nd YAG laser (Kwok, 2007). EIS of unprotected AISI 316L and HAp/MWCNT-coated steel obtained at open circuit potential are shown in Figure 7.60 after immersion in 0.9% NaCl solution for 2 h. The Bode plot shows that the total impedance Z has noticeably increased for the steel substrate coated with HAp/MWCNT. While the thin passive oxide film on the stainless steel surface was rendered less protective... 

Ari] Ariely, S., Bamberger, M., Hugel, H., Schaaf, P., Phase Investigation in Laser Surface Alloyed Steels With TiC , J. Mater. Sci., 30(7), 1849-1853 (1995) (Crys. Structure, Experimental, Morphology, 11)... 

Bab] Laser surface alloying (LSA), optical pyrometry and microscopy Fe rich comer... 

Bab] Babu, S.S., Martukanitz, R.P., Parks, K.D., David, S.A., Toward Prediction of Microstrac-tural Evolution During Laser Surface Alloying , Metall. Mater. Trans. A, 33(4), 1189-1200 (2002) (Morphology, Phase Diagram, Thermodyn., Calculation, Experimental, Kinetics, 31)... 

Moore P. G. and McCafferty E. (1981), Passivation of Fe/Cr Alloys Prepared by Laser-Surface Alloying. JEfecfroche/n Soc, 128,1391-3. 

Laser and electron beam processing are effective methods for preparing amorphous surface alloys covering conventional crystalline bulk metals... 

The Pt(l 11) surface alloyed by a small amount of Ge is a nice alloy substrate for studying the origin of the desorption activity in UV laser-induced desorption [87]. This surface alloy is prepared by repeated cycles of deposition of a few ML Ge and subsequent annealing to 1100°C until a constant Ge Auger electron signal was obtained. The total amount of Ge contained in several surface layers of this alloy is 0.1 ML and the Ge coverage in the top layer is 0.04 ML due to a 5 x 5 structure observed by STM [88]. Fukutani et al. call this surface the Pt(l 1 1)-Ge surface alloy. 

When ArF excimer laser irradiates the Pt( 111 )-Ge surface alloy saturated by NO or CO at 80 K, desorbed NO molecules are detected by the REMPI method, while no CO desorption is observed [87]. Only a little modification of the Pt(l 1 1) surface brings such a remarkable change of the desorption activity. TDS of NO from the alloy at various NO coverages is shown in Fig. 29. Every spectrum has a prominent peak at 220 K, and NO is saturated at 0.2 L exposure in contrast with Pt(l 1 1), on which NO is saturated at 2 L exposure and saturation coverage is 0.75 ML. 

Averback, R.S., Kirk, M.A. Atomic displacement processes in ion-irradiated materials. In Rhen, L.E., Picraux, S.T., Wiedersich, H. (eds.) Surface Alloying by Ion, Electron, and Laser Beams, p. 91. American Society for Metals, Metals Park, (1987)... 

The demands of practical applications led to attempts to overcome the high electric resistance of thin ribbons by a new technical solution of laser-induced surface vitrification (105, 106). First an amorphous alloy ribbon was adhered uniformly to a nickel plate by heat treatment. Subsequently, this surface alloy layer was transformed to the amorphous structure by laser surface melting and self-quenching (107). A sample consisting of Pd56Rh23P oSi9 adhered to bulk crystalline nickel exhibited anodic characteristics very similar to those of the melt-spun amorphous ribbon (102). Clearly, similar improvements forced by practical demands will be a part of the future use of amorphous alloys. 

The planar Fe-Fc3C eutectic in C-Fe-Si alloys during laser surface re-melting on alloys containing small amount of Si (1-3 mass%) and C (3.2-4.2 mass%) is destabilized widi respect to primary austenite dendrites for a velocity of the laser impulsions of die order of several mms (0.44 mm s for Fe-1 Si-4.2C (mass%)) [1998Lim]. 

O.V. Akgun and O.T. Inal, Laser surface modification of Ti-6A1-4V alloy . Journal of Materials Science, 29, 1159-1168 (1994). 

The laser surface melting can be combined with a simultaneous controlled addition of alloying elements. These alloying elements diffuse rapidly into the melt pool, and the desired depth of alloying can be obtained in a short period of time. By this means, a desired alloy chemistry and microstructure can be generated on the sample surface and the degree of microstructural refinement will depend on the sohdification rate. The smfaoe of a low-cost alloy, such as low carbon steels, can be selectively alloyed to enhance properties, such as resistance to wear and corrosion (Davis, 2001). 

Anthony TR, Cline HE. (1977) Surface rippling induced by surface-tension gradients during laser surface melting and alloying. JApp Phys 48 3888 3894. 

SZ. Lee and H.W. Bergmann, Laser Surface Aloying of Titanium and Titanium Alloys, Sixth Wortd Conference on Titankjm, P. La-combe, R.TricoLandG.Beranger,Ed.,LesE(ftionsdePl sique, Paris, 1988, p 1811-1816... 

Key words recycling alloys, amorphous alloys, alloy coatings, laser surfacing, laser alloying. 

The technique of laser surface melting (LSM) is well known and has been in use for many years for modifying the surfaces of both ferrous and non-ferrous substrates (Liu et al., 2006). LSM of the engineering alloys, in general, is aimed at improving the corrosion resistance by modifying the... 

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