Effect of Titanium Addition on the Elemental Partitioning Behavior of Silicon in Ni-19 At. Pct Al- x Si- y Ti Alloys
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TRODUCTION
ADVANCED Ni-based superalloys usually contain many alloying elements to promote solid-solution and c¢-precipitation strengthening. The elemental partitioning behavior between the c and c¢ phases can affect the properties of superalloys, and it is an important area of investigation.[1–5] Some solutes have distinct partitioning characteristics, for example, Cr, Co, Mo, and Re tend to partition in the c matrix, whereas Al, Ta, Ti, and Nb tend to partition in the c¢ phase.[1,3,6] The partitioning behavior of elements can affect the lattice misfit between the c and c¢ phases, which could be related to the high-temperature strength of Ni-based superalloys.[7] However, the partitioning behavior of some solutes may be affected by other alloying constituents. For example, Walston et al.[8] reported the reverse partitioning effect of Ru addition, where Cr, W, Mo, and Re more strongly partition in the c¢ phase and more Al and Ta partition in the c phase. However, Reed et al.[9] did not observe the same effect with Ru addition in different alloy systems. Another example is the reverse partitioning phenomenon of Ta and W reported by Amouyal et al,[10,11] where Ta atoms can replace W atoms in the
LI-YIN KUO, YAO-JEN CHANG, and AN-CHOU YEH are with the Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan, ROC. Contact e-mail: [email protected] Manuscript submitted April 3, 2016. Article published online May 30, 2017 3920—VOLUME 48A, AUGUST 2017
c¢ lattice and reject W atoms into the c lattice, causing a change of the partitioning characteristic of W owing to Ta addition. High Si content was reported in some early Ni-based superalloys.[12–15] Although the oxidation resistance could be improved, the mechanical properties dramatically deteriorated.[14] Small Si addition (around 1.0 at. pct) has recently been shown to improve the resistance against thermomechanical fatigue,[16] and it can increase the oxidation resistance owing to an increase in the Al activity.[15] Therefore, small Si content has become important for developing advanced Ni-based superalloys. Yeh et al.[17] developed Si-containing Ni-based single crystal superalloys (TMS-138A-based alloys) and directionally solidified KC-series Ni-based superalloys.[18] These studies suggested possible reverse partitioning behavior of Si induced by Ti addition, although this phenomenon has not yet been extensively studied. Chandrasekaran et al.[19] reported that Si partitions in the c¢ phase of Ni-Al-Si ternary alloys containing 2.5 to 17.5 at. pct Si. Muralidharan et al.[20] also reported that Si partitions in the c¢ phase of Ni-Al-Si ternary alloys containing 4 to 11 at. pct Si. However, the effect of Ti on Si partitioning has not been investigated. Because both Si and Ti addition are important for advanced Ni-based superalloys, it is important to understand their partitioning characteristics. In this work, the elemental partitioning behavior of several Ni-based alloys with varying Si and Ti contents was investigated by electro
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