Hot corrosion behaviour of yttrium and aluminium modified wear resistance coating alloy in mixed sulphate at 900 °C

Optimization of pre-oxidation time for corrosion resistance of cobalt based coating alloy in mixed sulphates

“…Whereas, previous research suggested that increasing Co oxide concentration in outer layer tend to increase the hot corrosion resistance as well as protection from internal sulphate formation (Qiao and Zhou, 2012;Zhao and Zhou, 2014;Liu et al, 2015). The mechanism of outward growth of Ni and Mo oxides on non-pre-oxidised specimens has already been discussed in our previous study where, outward diffusion of Mo formed the MoO 3 with tendency of outward growth and followed by reaction with Na 2 SO 4 to promote the acidic fluxing reaction (Rehman et al, 2019c).…”

“…Whereas, few spots of plate-like Ni and blocky Mo oxides could be observed on the surface of specimen shown as region B (Figure 2a). The region A represents the corresponding matrix phase, which is rich in chromium concentration as reported in previous study (Rehman et al, 2019c) and helps to form a continuous layer of Cr 2 O 3 immediately during 1 h of preoxidation.…”

“…Thus, thermodynamically, Cr 2 O 3 supposed to be more stable than other oxides and could be preferable for better hot corrosion resistance. Our previous study also explained the mechanism of MoO 3 acidic fluxing, which played critical role for the catastrophic failure of non-oxidised Tribaloy T-900, where, the outward growth of NiO and MoO 3 also contributed to compromise the mechanical stability of Cr 2 O 3 and prevention of protective oxides layer formation (Rehman et al, 2019c).…”

“…Whereas, 10-h pre-oxidised surface oxides was only porous Cr 2 O 3 layer, which shows that less stable Ni and Mo oxides completely dissolved because of the salt attack during initial 10 h of hot corrosion. Our previous studies reported that the non-oxidised alloys showed severe internal oxidation of Si and internal sulphidation during cyclic oxidation and hot corrosion, respectively (Rehman et al, 2019a(Rehman et al, , 2019b(Rehman et al, , 2019c. Thus, the present study was conducted to improve the hot corrosion behaviour by eliminating the internal precipitation of oxides, nitrides and sulphates.…”

“…Whereas, remaining surface of specimen marked as region A was Cr and Co oxides. As the pre-oxidation time increased to 10 h, the Ni rich matrix phase and Mo rich Laves phase(Rehman et al, 2019c) acted as reservoir and higher amount of NiO and MoO 3 , which could be observed on the specimen's surface in Figure2(b).…”