Mechanical Behavior of Liquid Route Processed SiC f /Ti Composites Under Longitudinal and Transverse Loadings
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TITANIUM matrix composites (TMCs) reinforced with continuous SiC fibers offer exceptional specific strength in the fiber direction. This high specific property remaining acceptable under moderately high temperatures 823 K (550 C), the TMCs thus constitute good candidates for aircraft engine applications such as integrally bladed compressor rings (BLINGs). However, due to the high melting point and strong chemical reactivity of titanium alloys, TMCs are usually processed through solid-state routes such as hot isostatic pressing (HIP) of alternative layers of fibers and titanium alloy foils, i.e., the foil-fiber-foil (FFF) technique.[1–7] An alternative method consists in the deposition of the matrix on the fibers, the composite being thus obtained through HIP consolidation of a bundle of matrix-coated fibers. Plasma spraying[8,9] and physical vapor deposition (PVD) are methods commonly used for matrix coating. PVD processes include magnetron sputtering,[10] triode sputtering (TS),[11,12] and electron beam evaporation.[13] Even if these PVD processes allow the deposition of complex titanium alloys, the ROGER VALLE and JEAN-CLAUDE DAUX, Research Scientists, are with ONERA – The French Aerospace Lab, 92322 Chatillon Cedex, France. Contact e-mail: [email protected] Manuscript submitted December 22, 2015. Article published online November 28, 2016 METALLURGICAL AND MATERIALS TRANSACTIONS A
deposition rate is very low. On the contrary, liquid route processes are much more rapid coating techniques. Unfortunately, methods such as the conventional dip-coating process or methods involving only partial levitation of the liquid metal in an induction crucible[14] present a major drawback, essentially in the case of such high-reactivity alloys: contact with the crucible can lead to the contamination of the liquid alloy. However, the liquid route process developed by Madylam (Grenoble, France), Snecma-Moteurs (Safran Group, France), and Universite´ de Bordeaux (France)[15–23] allows the completely levitating liquid alloy sphere to be held in a cold segmented metal crucible. Such a liquid route process thus offers the advantage of avoiding any contact of the liquid alloy with the crucible and thus any contamination of the coating alloy. However, during the liquid route processing, the fibers are subjected to a very specific thermal loading: a very short thermal shock[15–23] at the very high temperature of liquid titanium alloys [e.g., >1978 K (1705 C) for Ti-6242S or >2223 K (1950 C) for Ti2AlNb (orthorhombic) matrix coatings]. Obviously, the commercially available SiC fibers have not been designed nor optimized for such thermal shock loadings. The SiC fibers used as a reinforcement for TMCs are fabricated by chemical vapor deposition (CVD) of SiC on a small-diameter carbon or tungsten filament.[24–28] SiC fibers deposited on a carbon core include SCS-6 (142 lm in diameter) and SCS-Ultra (142 lm) fibers VOLUME 48A, FEBRUARY 2017—883
produced by Speciality Materials (MA, USA), formerly Textron (MA, USA), and Trimarc 2 (142 lm) fiber produced
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