Nanoscale Cellular Structures at Phase Boundaries of Ni-Cr-Al-Ti and Ni-Cr-Mo-Al-Ti Superalloys

Abstract

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.

Alkaline corrosion resistance of slag‐free self‐shielded titanium‐added metal‐cored welding overlay

“…The procedure of flux-cored arc welding is extensively used for the recovery and prolongation of the service life of components of the heavy equipment owing to its costefficient and satisfactory wear resistance. The high chromium iron-based flux-core wires are used for the repairing of worn surfaces in order to restore their sizes and help performance even more [1][2][3]. Much attention has been focused on the chemical composition-microstructure-wear resistance relationships of high chromium iron-based weld overlay [4][5][6].…”

Oxidation and creep properties at 1200 °C of cast quaternary Ni-Cr-C-Ti alloys

“…Titanium is on the one hand the base of various alloys for biomedical [4] or structural aeronautical parts [5]. On the other hand one it also features among the key alloying elements, by playing a particularly important role in numerous superalloys [6][7][8] and Ti 3 Al or TiAl aluminides [9][10][11]. Titanium may notably be present in the γ' intermetallic compound [12][13][14] or ɳ phase [15] with often high benefit for the mechanical properties of the alloys at high temperature [16].…”