Microstructure of Advanced TiC-Based Coatings Prepared by Laser Cladding
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JTTEE5 16:374–380 DOI: 10.1007/s11666-007-9045-4 1059-9630/$19.00 Ó ASM International
Microstructure of Advanced TiC-Based Coatings Prepared by Laser Cladding Anja Techel, Lutz-Michael Berger, and Steffen Nowotny (Submitted August 11, 2006; in revised form April 24, 2007) The specific advantages of TiC as a hard material are its low density, high hardness, and its high alloyability in metal matrix composites. Agglomerated and sintered core-rim structured TiC-based powders were intensively studied in the last few years for thermal spray coating solutions. In the work described in this paper a powder with cubic (Ti,Mo)(C,N) hard phases and Co binder were used together with mechanically mixed NiBSi and CoCrMo powders to produce wear resistant coatings by laser cladding. Coatings with fine-grained hard particles were obtained. Basic process parameters and coating microstructures are described.
Keywords
laser cladding, surface protection, system technology, TiC-based hardmetal coatings
1. Introduction Application of coatings by laser surfacing is widely used in order to increase the wear resistance of new machine components or for repair purposes. Typical hard materials and composites for laser surfacing are WC and WC/W2C (Ref 1-4). They are mostly applied together with mechanically mixed self-fluxing Ni-based alloys. In the result, composite structures with about 50% coarsegrained hard particles in a ductile binder are produced. These coatings are characterized by a very high resistance against abrasive wear with coarse particles. Multiple metallurgical reactions of WC and W2C in the molten bath prevent the realization of fine-grained welded structures. For this reason numerous development activities were directed to the realization of fine-grained structures by alternative hard phases, in particular by vanadium carbide (VC) (Ref 5-7). For different industrial applications VC is used with a steel-based binder matrix. Fine-grained carbides can be prepared by laser surfacing using agglomerated and sintered powders. Dissolved VC does not show metallurgical reactions and formation of new phases with the binder. It precipitates as monocarbide in the form of small dendrites. Therefore, VC is easily processable by welding processes. Coatings show a high ductility and a poor propensity to crack formation. A comparison of the physical properties of TiC with those of WC, and Cr3C2 (Ref 8) and results of Anja Techel, Lutz-Michael Berger, and Steffen Nowotny, Fraunhofer Institute for Material and Beam Technology (Fh-IWS), Winterbergstrasse 28, 01277, Dresden, Germany. Contact e-mail: [email protected].
374—Volume 16(3) September 2007
fundamental research on phase equilibria and metallurgical reactions of TiC-based composite materials (Ref 9) were the driving forces to use alloyed, core-rim structured TiC-based materials for the development of thermal spray coating solutions (Ref 10, 11). The core-rim structure is formed during the sintering step of spray powder preparation as a result of metallurgical reactions o
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