Experimental and ab-initio study of the Zr- and Cr-enriched aluminide layer produced on an IN 713C Inconel substrate by CVD; investigations of the layer morphology, structural stability, mechanical properties, and corrosion resistance

Abstract

The paper discusses the effect of zirconium and chromium on the microstructure and properties of the aluminide layers produced on an Inconel 713C nickel superalloy substrate. The aluminizing process was conducted using the chemical vapor deposition (CVD) method in AlCl3 + ZrCl3 vapors and a hydrogen atmosphere as the carrier gas. This low-activity aluminizing process yielded a diffusive multi-component aluminide layer composed of three main zones: the outer zone, about 3 μm thick, chiefly built of AlNi2Zr, Ni3Zr and Al3Zr4, the intermediate zone, about 6 μm thick, containing the β-NiAl phase, and the inner zone, with a thickness of about 7 μm, mostly composed of the Cr2Al and β-NiAl grains. The substrate contained semi-coherent γ′-phases (Ni3Al) separated from the γ-austenite matrix by a dislocation net. DFT calculations have shown that Cr added to β-NiAl markedly increases the elastic constant C11 and the isotropic shear modulus G, whereas the addition of Zr decreases the C44 component. Moreover, zirconium added to β-NiAl increases its plasticity thanks to the formation of wide-spread metallic ZrNi bonds. It has been found that the Zr + Cr-modified aluminide layer formed on the Inconel 713C nickel superalloy improves its corrosion resistance (as measured in a 0.1 M Na2SO4 solution).