As-Fabricated and Heat-Treated Microstructures of the Ti-6Al-4V Alloy Processed by Selective Laser Melting
- PDF / 1,148,530 Bytes
- 10 Pages / 593.972 x 792 pts Page_size
- 34 Downloads / 199 Views
TRODUCTION
SELECTIVE laser melting (SLM) process appeared in the late 1990s and is inspired from the stereolithography technique emerging in the late 1980s.[1] These layer-bylayer processes were first used to produce prototypes, whereas the actual trend is to directly produce functional parts because of the permanent requirement of the industry to save manufacturing cost and time. The description of the process is done elsewhere and is not repeated here.[2–4] Its success is directly linked with its ability to manufacture complex structures from a computer-aided design model and a wide range of materials in short delays without the need of expensive tools such as molds. Another advantage is that the powder bed is selectively molten; therefore, the nonirradiated powder can be fully recycled for further fabrication (‘‘ecoconception process’’). In order to attain a high level of density (F99 pct) and mechanical properties comparable to the conventional fabrication routes such as foundry, the metallic powder is fully molten under the laser beam T. VILARO, Engineer of Research, is with Poly-Shape, 43, rue d’Yerres, 94440 Villecresnes, France, and also with the Materials Centre of Mines ParisTech, CNRS UMR 7633, BP87, 91003 Evry, France. Contact e-mail: [email protected] C. COLIN, Reader, and J.D. BARTOUT, Engineer of Research, are with the Materials Centre of Mines ParisTech, CNRS UMR 7633. Manuscript submitted August 23, 2010. Article published online May 19, 2011 3190—VOLUME 42A, OCTOBER 2011
in contrast to the selective laser sintering process, in which the melting point (Tm) or the solidus temperature of the material is never reached. This process is adapted more to the ceramic and polymer materials. Further, due to the high thermal gradient induced by the laser beam combined with high solidification rate, the resulting microstructure is out-of-equilibrium, very fine, and strongly textured whatever the nature of the material.[5,6] Finally, the parts contain several defects such as lack of melting, some problems of scanning strategy, entrapped gas in solidified material, or residual stresses.[7–9] The titanium alloys and especially the Ti-6Al-4V alloy are widely used in the aeronautical industry for their high specific strength (ratio between the ultimate strength and its low density) but also for their high corrosion resistance at temperatures up to 773 K (500 C). The high cost of the raw material has become an important driving force for the French aeronautical industry to manufacture near-net-shape components directly from additive processes. Nowadays, it exists in the literature in a few articles dealing with the as-fabricated microstructures of the titanium alloys by additive processes,[10,11] but none of them deals with the modification of this metastable microstructure through heat treatments in order to satisfy the industrial requirements as well as the resulting mechanical properties. This article is aimed at presenting the Ti-6Al-4V microstructure resulting from the SLM process. These microstructures are exa
Data Loading...
