Insight into a high temperature selective oxidation of HP40 alloy under a H₂–H₂O environment

Abstract

A MnCr2O4 spinel coating initially forms at grain boundaries under a H2–H2O gas mixture at high temperature.

A novel spinel coating on cobalt‐based Superalloy GH605 via an in‐situ oxidation approach

“…Large differences exist among representative peaks, and the oxide phases are determined by the position of the peaks. Raman spectra assigned to Cr 2 O 3 centered at 553 cm −1 , with another 2 weak peaks exist at 530 and 625 cm −1 . A weak peak at 511 cm −1 and a strong peak at 685 cm −1 assigned to MnCr 2 O 4 phase are also observed .…”

“…Raman spectra assigned to Cr 2 O 3 centered at 553 cm −1 , with another 2 weak peaks exist at 530 and 625 cm −1 . A weak peak at 511 cm −1 and a strong peak at 685 cm −1 assigned to MnCr 2 O 4 phase are also observed . The strongest peak of 685 cm −1 is assigned to A 1g mode, the structure mainly generated by the bonds in Cr 3+ O 6 octahedral .…”

“…Among them, the peaks of 575.6 and 576.6 eV are corresponding to Cr 3+ ions which mainly exist in MnCr 2 O 4 and Cr 2 O 3 multiple oxides . The peak located at 577.4 eV is attributed to Cr 6+ ions, and the peak assigned to 578.1 eV is attributed to chromium hydroxide . Previous studies show that evaporation of chromia occurred in the intermediate reactions under H 2 ‐H 2 O low oxygen partial pressure, and the reaction produces chromium hydroxide, which is probably responsible for Cr 6+ ions and chromium hydroxide.…”

“…The EDS analysis results show that both needle‐like oxides and small granular oxides are rich in Cr, O, Mn, and lacking of Co, Ni, W (Figure 4). According to the previous studies, the growth of alloy oxides is determined by oxygen affinity, which has large disparity for different alloying elements . Equilibrium oxygen partial pressures of different oxides and gas mixture at different temperatures are calculated and shown in Figure .…”

“…Each Cr 2p spectrum is deconvoluted into 4 peaks, which are located at 575.6, 576.6, 577.4, and 578.1 eV, respectively. Among them, the peaks of 575.6 and 576.6 eV are corresponding to Cr 3+ ions which mainly exist in MnCr 2 O 4 and Cr 2 O 3 multiple oxides . The peak located at 577.4 eV is attributed to Cr 6+ ions, and the peak assigned to 578.1 eV is attributed to chromium hydroxide .…”