Unveiling the Mechanism of Improved Oxidation Resistance for CaO Crucible Melting Using Ni-Al Alloy

Effect of Ca Addition on the Oxidation Resistance of Ni–Al Alloy

“…What appears to be inclusions formed within the voids, or inclusions promoting the formation of voids were found near the grain boundary and the eutectic γ′ phase, most likely in the inter-dendritic regions, for both Ni-Al (20 ppm Ca) and Ni-Al (100 ppm Ca) samples. The peaks of Ca and S were observed, indicating that CaS had formed, similar to the results for melting using a CaO crucible [16]. For each sample, the width and the height of 10 inclusions were measured, and the average size of the inclusions were calculated.…”

“…5(b). Judging from the SAED patterns and the crystal orientations of the substrate fcc-Ni3Al, mismatched fcc-CaS crystals have formed, similar to the ones detected when using a CaO crucible [16]. The inclusions likely form either at the voids or promote the formation of voids.…”

“…The chemical composition was analyzed using the same methods as our previous research [16]. For Ni and Al, an inductivity coupled plasma optical emission spectrometer (ICP-OES, Aligent, ICP-OES 720-ES) was used, while glow discharge mass spectrometry (GD-MS, Nu Instruments LTC.…”

“…ASTRUM) was used for S and Ca. Oxidation testing samples were also prepared following the same procedures as our previous research [16], where the samples were cut from the cylinders to be 5 mm in height and 9 mm in diameter, with the surfaces finished using U.S. Grid #600 SiC abrasive paper.…”

“…In order to simplify the reaction, similar tests were conducted for Ni-Al binary alloys. The usage of CaO crucible on Ni-Al alloy also proved to be effective, and the mechanism and location for the formation of CaS has been clarified [16]. According to Yokokawa et al, CaO pellets were also effective in the removal of S from the melt [17].…”