Oxide pegging is a widely accepted mechanistic model explaining the reactive element effect on the improved adherence of scale.However,previous models for the oxide peg formation process have not considered the effects of more than one active element added into the alloy during the peg formation.This study proposes a new model of oxide peg formation and growth for the doping of two reactive elements in an alloy(the precipitated Y and solid solute Ti).Different amounts of Ti and Y were added to a Co Ni Cr Al alloy,and the characteristics of the resulting oxide pegs,such as their linear density,size,and forming process,are obtained by examining alloy samples subjected to an isothermal oxidation operation at a temperature of 1150℃.It is found that the amount of Y determines the density of the oxide pegs,and Ti does not form a Ti-rich oxide core if a Y-rich oxide exists in the sample.In samples with the same Y content,the oxide pegs primarily grow in length,and with increased Ti content,they grow along the b-phase boundary and into the alloy.Based on these results,a three-step model for oxide peg formation and growth is conceived.
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