Scandium aluminum nitride alloy (Sc x Al 1¹x N) thin films were prepared using rf magnetron sputtering with a scandium aluminum alloy (Sc 0.42 Al 0.58 ) target on n-type (100) silicon substrates. We have investigated the effects of 4 sputtering control factors, which are substrate temperature, sputtering pressure, nitrogen (N 2 ) concentration and cathode power, on the piezoelectric constant d 33 of Sc x Al 1¹x N films using design of experiments. Consequently, it is statistically proved that N 2 concentration in sputtering gas is the most important control factor. The piezoelectric constant d 33 indicates the maximum value of 19.0 pC/N at N 2 concentration of 25%. The composition of Sc x Al 1¹x N films prepared under optimized sputtering conditions is Sc 0.38 Al 0.62 N, and there is the composition difference between the ScAl alloy target and the thin film. However, the piezoelectric constant of the Sc 0.38 Al 0.62 N film is coincident with that of Sc 0.38 Al 0.62 N films prepared by dual co-sputtering. Thus, it is possible to prepare high piezoelectric Sc x Al 1¹x N films by using the ScAl alloy sputtering target. ScAl alloy targets are effective for keeping scandium concentration constant in Sc x Al 1¹x N thin films.
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.
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