Effect of Ti addition on density and microstructure development of MoSiBTiC alloy
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Effect of Ti addition on density and microstructure development of MoSiBTiC alloy Joung Wook Kim1, Kyosuke Yoshimi1, Hirokazu Katsui2, Takashi Goto2 1 Department of Materials Science and Engineering, Tohoku University, Sendai, Miyagi 9808579, Japan 2 Institute for Materials Research, Tohoku University, Sendai, Miyagi 980-8577, Japan ABSTRACT The effect of Ti addition on the density and microstructure development of MoSiBTiC alloy was investigated. Two kinds of MoSiBTiC alloys with the composition of Mo-5Si-10B10Ti-10C (10Ti alloy) and Mo-5Si-10B-15Ti-10C (15Ti alloy) (at. %) were prepared by conventional arc-melting. The primary phase of as-cast 10Ti and 15Ti alloys was (Ti,Mo)C, and there were two eutectic phases of Moss + (Ti,Mo)C and Moss + T2 + (Ti,Mo)C in the alloys. In addition, 10Ti alloy had a Moss + T2 + (Mo,Ti)2C eutectic. There was no Moss + T2 + (Mo,Ti)2C eutectic in the 15Ti alloy, and thus it is apparent that the (Mo,Ti)2C formation was suppressed by 5 at. % Ti addition. The volume fraction of (Ti,Mo)C increased and thus the density reduced from 8.78 to 8.43 g/cm3 with the Ti addition. In all constituent phases, Ti concentration increased while Mo concentration decreased. In spite of the changes, hardness, Young’s modulus and shear modulus were hardly changed. Therefore, Ti addition seems to be effective to further lower the density without deteriorating mechanical properties of the MoSiBTiC alloy. INTRODUCTION In order to increase energy efficiency, raising working gas temperature and pressure and weight-saving are required to combustion engines such as jet-engines and gas-turbines. Currently, Mo-Si-B alloy has attracted a great deal of attention as a new ultrahigh temperature material able to replace Ni-base superalloys because of their excellent high temperature (creep) strength, and moderate oxidation resistance in the ultrahigh temperature range [1–2]. However, its low fracture toughness and density higher than that of Ni-base superalloys are their drawbacks [3–4]. To improve those material properties, attempts have been made to add a fourth element and control their microstructure. Quite recently, our research group has developed MoSiBTiC alloy by adding TiC to Mo-Si-B alloys [5]. The density was significantly reduced comparable to that of Ni-base superalloys as a result of the TiC addition. The MoSiBTiC alloy is composed of four constituent phases such as Mo solid solution (Moss), Mo5SiB2 (T2), (Ti,Mo)C and (Mo,Ti)2C, and its microstructure was very composition-sensitive. For further improvement, the optimization of their microstructure is necessary, and besides, further reduction in the density makes it more attractive. Therefore, in this study, the effect of Ti addition on the density, microstructure development and elastic modulus of MoSiBTiC alloy was investigated. EXPERIMENT MoSiBTiC ingots with nominal compositions of Mo(65-x)Si5B10Ti(10+x)C10 (x = 0, 5)(at. %) were prepared by conventional arc-melting in an Ar atmosphere. These alloys are referred to as 10Ti and 15Ti, respectively through
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