Nanoscale Cellular Structures at Phase Boundaries of Ni-Cr-Al-Ti and Ni-Cr-Mo-Al-Ti Superalloys
نویسنده
چکیده
The microstructural evolution of Ni-20 pct Cr wires was studied during pack cementation where Al and Ti, with and without prior cementation with Mo, are deposited to the surface of the NiCr wires and subsequently homogenized in their volumes. Mo deposition promotes the formation of Kirkendall pores and subsequent co-deposition of Al and Ti creates a triple-layered diffusional coating on the wire surface. Subsequent homogenization drives the alloying element to distribute evenly in the wires which upon further heat treatment exhibit the c+ c¢ superalloy structure. Unexpectedly, formation of cellular structures is observed at some of the boundaries between primary c¢ grains and c matrix grains. Based on additional features (i.e., ordered but not perfectly periodic structure, confinement at c+ c¢ phase boundaries as a cellular film with ~100 nm width, as well as lack of topologically close-packed phases), and considering that similar, but much larger, microstructures were reported in commercial superalloys, it is concluded that the present cellular structure solidified as a thin film, composed of eutectic c+ c¢ and from which the c¢ phase was subsequently etched, which was created by incipient melting of a region near the phase boundary with high solute segregation.
منابع مشابه
Microstructure Evolution During Al, Ti, and Mo Surface Deposition and Volume Diffusion in Ni-20Cr Wires and Woven Structures
Ni-20 wt pct Cr wires, as individual wires or within 3D woven structures, are alloyed with Mo, Al, and Ti by gas-phase surface deposition and volume interdiffusion. Mo deposition creates Mo-rich coating and Kirkendall pores. Al+Ti co-deposition creates uniform triple-layered coating. The resulting homogenized and aged Ni-(17.4-19.6)Cr-(1.6-1.8)Al-(2.5-3.6)Ti-(1.54.5)Mo(wt pct) wires exhibit c+ ...
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