Pack cemented silicon carbide interlayer for plasma sprayed yttria over graphite. Issue 6 (26th April 2019)

• Record Type: Journal Article
• Authors: Vetrivendan, E.; Madhura, B.; Rao, Ch. Jagadeeswara; Ningshen, S.
• Is Part Of: Materials and manufacturing processes. Volume 34:Issue 6(2019)
• Page Start: 681
• Page End: 688
• Publication Date: 2019-04-26
• Subjects: Plasma spraying -- yttria coating -- pack cementation -- SiC interlayer -- thermal cycling; Manufacturing processes -- Periodicals; Materials -- Periodicals; Manufactured Materials; 670.5
• DOI: 10.1080/10426914.2019.1566961
• Languages: English
• ISSNs: 1042-6914

Abstract

ABSTRACT: Thermodynamically stable and non-reactive yttrium oxide is proposed to be the coating material on high-density graphite (HDG) crucible for melting and consolidating uranium in the pyrochemical reprocessing of spent metallic nuclear fuels. Yttria deposited over HDG by atmospheric plasma spray (APS) process without interlayer cannot withstand temperatures above 1400°C because of large thermal expansion mismatch and high-temperature partial oxidation of underlying graphite substrate through pores and openings in the plasma sprayed yttria layer. To overcome this limitation, a stable oxidation-protective intermediate layer of SiC was developed over graphite by conventional pack cementation process using two different precursor powders. The coated samples were characterized with respect to coating thickness, microstructure, and phase composition. Experimental results revealed that the optimum pack composition for obtaining thick and diffused coating was 70 wt. % Si – 20 wt. % C – 10 wt. % Al2 O3 . Subsequently, yttria top coat was deposited over pack cemented HDG coupons by APS process with optimized process parameters. The interlayer of SiC developed by pack cementation for yttria top coat facilitated to extend the thermal cycling life of the coating in inert argon environment significantly. The onset of micro-cracking in the top coat with SiC interlayer occurred after 45, 25 and 13 thermal cycles at 1400°C, 1450°C and 1500°C, respectively.