Corrosion Behavior of Ti60 Alloy under a Solid NaCl Deposit in Wet Oxygen Flow at 600 °C

Abstract

The corrosion behavior of Ti60 alloy covered with a solid NaCl deposit in wet oxygen flow at 600 °C has been studied further by SEM, EDX, XPS, XRD, TEM and EPMA analysis. The results show that solid NaCl and H2O react with Ti oxides, which destroyed the Ti oxide scale to yield the non-protective Na4Ti5O12 and other volatile species. The resulting corrosion product scale was multilayered and contained abundant rapid diffusion channels leading to the fast diffusion which improved the corrosion rate. A possible mechanism has been proposed for the NaCl-covered Ti60 alloy, based on the experimental results.

Effects of pre-oxidation on the corrosion behavior of pure Ti under coexistence of solid NaCl deposit and humid oxygen at 600 °C: the diffusion of chlorine

“…Meanwhile, a corrosion scale is formed by the outward diffusion of Ti which results in a 15 μm loose layer that is observed under the corrosion products. Hence, the corrosion product scale is non-protective and the corrosion of pure Ti is greatly accelerated by solid NaCl in an O 2 + H 2 O environment at 600 ˚C, which is similar with the observation for several Ti alloy 11,[18][19][20] .…”

Degradation mechanism of Ti-6Al-2Sn-4Zr-2Mo-Si alloy exposed to solid NaCl deposit at high temperature

“…None of them proposed a clear mechanism. They only showed parabolic-like [21,22] or parabolic-then-linear [19] oxidation kinetics, whose weight gains appeared, in the first case, 6-10 times larger than those observed in dry air. In each case, damaged corrosion scales (porous, cracked and non-adherent) were observed.…”

“…Very few studies reported a degradation of the oxidation resistance of Ti-6Al-2Sn-4Zr-2Mo-Si alloy or close-composition alloys under solid NaCl deposits [19][20][21][22][23]. None of them proposed a clear mechanism.…”

“…In each case, damaged corrosion scales (porous, cracked and non-adherent) were observed. Corrosion scales also appeared layered, composed of a rather dense inner part and a rather porous outer part [19][20][21]. The external part of the corrosion scales was reported to be generally composed of rutile TiO 2 , surmounted by a mixed Na-,Ti-rich oxide (Na 4 Ti 5 O 12 [10,[22][23][24][25][26], Na 2 Ti 6 O 13 [23], Na 2 TiO 4 [27], Na 2 TiO 3 [5,20,28,29], NaTiO 2 [30]), whereas its internal part also included oxides of certain alloying elements (Al 2 O 3 , ZrO 2 and SnO 2 ) [19,22].…”

Robust tribo-mechanical and hot corrosion resistance of ultra-refractory Ta-Hf-C ternary alloy films

“…Thermal barrier or ultra-refractory materials have been widely used as protective coatings for components exposed to high temperatures (from 550 to 900 °C) in aerospace and applications such as turbine blades and steam generators in power plants 1 – 4 . Generally, the most used materials used for thermal barrier coatings are metal superalloys 1 , 5 and yttria-stabilized-zirconia (YSZ) and YSZ-based systems 2 , 6 , 7 . Those materials have excellent chemical stability at high temperatures, good anti-corrosion properties and low thermal conductivity 7 , however, most of the superalloys and YSZ-based materials are brittle and lack of high hardness and wear resistance which restrict the applications where the materials are subject to high stresses and loads.…”