Acta Metallurgica Sinica (金属学报) 2013/49:12 PP.1567-1572
The Ni-based single crystal superalloy is the primary material for the manufacture of blades of the advanced areoengine and gas turbine. As the alloying design theory improved, the concentration of refractory elements increased and some new elements were introduced. Among these refractory elements, Ru became a fresh and sign element which was introduced into the fourth gen- eration Ni-based single crystal superalloy. A large amount of research had indicated that Ru, as a member of Platinum group metals (PGMs), had played a significant role on the enhancement of phase stability and rupture life for Ni-based single crystal superalloy. Inspired by these works, other PGMs like Pt have been suggested to be the major alloying elements of the next generation advanced Ni- based single crystal superalloy. But the research for the effects of Pt addition on solidification behavior or creep property of the single crystal superalloy is rare. To explore the possibility of Pt using as a major alloying element, the present work investigated the influence of Pt on the solidification be- havior of the Ni-based single crystal superalloy. Directional solidification method was used to grow the single crystal. DTA and EPMA were used to determine the effect of Pt on the phase transition temperatures and composition variety, respectively. In addition, OM and SEM were used to show the phases morphology. Some results are described as follow. Firstly, it has been found that the addition of Pt changes the eutectic morphology and increases eutectic fraction. Grid-like eutectic increases with the addition of Pt. Secondly, Pt promotes not only the segregation of refractory elements but also the eutectic-forming element Al. In addition, Pt prefers to segregate to the interdendritic region and is able to form an ordered Pt3A1 phase with A1 which may be a reason for the increase of eutectic fraction. But Pt reduces the segregation of Mo element whose content is a sensitive factor for the for- mation of the topological close-packed (TCP) phase. Thirdly, Pt decreases initial melting temperature and enhances γ phase precipitation temperature; thereby reduces the solution heat treatment window of the alloys. The solution heat treatment of the alloys therefore becomes more difficult. Since the element segregation is hard to be eliminated饰heat treatment in the Pt-containing alloys, Pt addition may be harmful for the mechanical properties of single crystal superalloy. The effects of Ru addition on the solidification behavior of the Ni-based single crystal superalloy will be also discussed for comparison.
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