To improve the high-temperature strength of Nb-Mo-Ti-Si in-situ composites, alloying with W and a directional solidification technique were employed. The alloy composition of Nb-xMo-10Ti-18Si (x ϭ 10 or 20) was used as the base, and Nb was further replaced by 0, 5, 10 and 15 mol pct W. For samples without W, the as-cast microstructure was a eutectic mixture of fine Nb solid solution (Nb SS ) and (Nb, Me) 5 Si 3 silicide (Me ϭ Mo, W, or Ti), while large primary Nb SS particles appeared besides the eutectic mixture as a result of replacing Nb by W. The directionally solidified samples consisted of coarse Nb SS and (Nb,Me) 5 Si 3 silicides, and the microstructure showed a slight orientation in the direction of growth. The maximum compressive ductility ( max ) at room temperature decreased with increasing W content and was in the range of 0.8 to 2.3 pct, in contrast to the Vickers hardness (HV), which increased with W content. The 0.2 pct yield compressive strength ( 0.2 ) and the specific 0.2 pct yield compressive strength ( 0.2S ) ( 0.2 divided by the density of sample) at elevated temperatures were markedly improved by the W addition. The directionally solidified samples always showed higher 0.2 and 0.2S values than the as-cast samples. At elevated temperatures, the directionally solidified sample with 10 mol pct Mo and 15 mol pct W had the highest 0.2 and 0.2S values; even at 1770 K, 0.2 was as high as 650 MPa. The directionally solidified materials alloyed with W exhibited excellent compressive creep performance. The sample with 10 mol pct Mo and 15 mol pct W had a minimum creep rate ( m ) of 1.4 ϫ 10 Ϫ7 s Ϫ1 and retained steady creep deformation at 1670 K and an initial stress of 200 MPa. Under compression, the damage and failure of these in-situ composites were dominated by decohesion of interfaces between the Nb SS and silicide matrix.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.