Diffusional transport during the cyclic oxidation of ?+?, Ni-Cr-Al(Y, Zr) alloys

Failure of metals II: Fatigue

“…A second effect is the microstructural change in the bulk material beneath the oxide due to oxidation-linked diffusion and interdiffusion processes, which alters the phase composition of the material [134,[148][149][150]. In effect, the matrix and c 0 precipitates both contain elements that are prone to oxidation.…”

A coupled kinetic-constitutive approach to the study of high temperature crack initiation in single crystal nickel-base superalloys☆

“…7(b) is the predicted size of the g region for another single crystal nickel superalloy (SC16), which has a higher oxidation rate constant (k p ¼ 2:4 Â 10 À10 mg 2 =mm 4 =s) and a correspondingly thicker g region. Note that the value of k p ¼ 8:0 Â 10 À10 mg 2 =mm 4 =s used in the analysis of Dumoulin et al (2003) is relevant to the Ni-Cr-Al alloys with higher Al contents studied by Nesbitt (1982). Those analyses are expected to overpredict the rate of oxidation and the size of the g region for CMSX4.…”

“…Otherwise, D Al is taken to be zero and it is assumed that no diffusion takes place within this region (it has been seen (see e.g. Nesbitt, 1982) that the diffusivity of aluminium in the (g þ g 0 ) region is much less than that in the g region). In this way, the position of the interface is determined from the analysis as the location where the upper solubility limit is reached.…”

“…Therefore, the flux of aluminium from the metal into the oxide, J Al , at time, t, can be expressed as (Nesbitt, 1982):…”

“…MacLachlan and Knowles, 2001b;Ohtani et al, 2001). Second, due to oxidation-linked diffusion and interdiffusion processes in the bulk alloy, the phase composition of the material is altered, which introduces a microstructural change in the bulk material beneath the oxide (Nesbitt, 1982;Lerch and Antolovich, 1990;Ohtani et al, 2001). The local degradation in the material microstructure modifies the material constitutive behaviour which in turn can lead to a reduction in the time to crack initiation (Dumoulin et al, 2003).…”