Reactive element effect

W. E. King, ed.. The Reactive Element Effect on High Temperature Oxidation After Fifty Years, Materials Science Forum, MRS, 1991. 

A small addition of Y to the coating resulted in flat A1203 scales [48] as has often been discussed in terms of the so-called reactive element effect. However, the protectiveness of the coating was not improved rather it was slightly decreased. A variation in the nature of the coating by the Y addition may be a reason for this. 

B. A. Pint "Study of the Reactive Element Effect in ODS Iron-Base Alumina-Formers, Materials Science Forum, in press (1996). 

Another complication with chromia formers is that surface application of yttria (and ceria) has been shown to produce the same effects as a reactive element incorporated into the alloy, but this precludes the operation of many of the mechanisms proposed for the reactive-element effect. The application of MgO has been shown to be ineffective, at least with regard to altering the growth rate of the chromia. ... 

Ion implantation is less expensive than VPS or HVOF and can be used in environments that are slightly less corrosive. A concentration of 1016-1018 ions/cm drastically improves corrosion resistance. Rare earth (RE) metals also improve the corrosion resistance. Rare earth metals such as Y improve oxide scale formation on alloys. This improvement is based upon the reactive element effect (REE), which improves resistance in several ways According to Hussey et al. [63], the observed increase in corrosion resistance is due to ... 

In high-temperature corrosion, the protective oxide hlms—usually either chromia, Cr203, or alumina, AI2O3—that form between the metal and the environment are of critical importance. One of the major advances in corrosion science over the past few decades has been the characterization of the reactive element effect (REE), which identifies the role of small additions of reactive elements, such as yttrium, hafnium, lanthanum, zirconium, and cerium, to improve high-temperature oxidation resistance. 

OXIDATION-RESISTANT ALLOYS 11.13.1 Reactive Element Effect (REE)... 

The reactive element effect (REE) is obtained when lwt.% or less of a reactive element, such as yttrium, hafnium, lanthanum, zirconium, or cerium, is added to... 

D. P. Moon, "The Reactive Element Effect on the Growth Rate," Oxidation of metals, pp. 47-66, 1989. 

According to the reactive element effect, the reactive element ion, such as beryllium, diffuses in to the native oxide grain boundaries and prevents the outward diffusion of substrate metal cations (Czerwinski and Smeltzer, 1993 Czerwinski and Szpunar, 1998 Czerwinski, 2000, 2004). The inhibitory effect of boron on aluminum alloy oxidation is clearly a surface phenomenon given the effectiveness of very low levels of boron. This could occur through a combination of boron migration into the MgO lattice and/or boron bonding to the defect-rich MgO surface (Choudhary and Pandit, 1991). 

Y ions into an aluminide ((3-NiAl) on a nickel-base alloy and confirm that while initially the implanted reactive element effectively imparts increased scale adhesion, both in air and oxygen at 1000 -1200 C, the beneficial influence is not long lasting. They attributed this loss to the influence of the substrate Ni-base superalloy, since lasting benefits of reduced rates of oxidation and improved scale adherence were maintained when Y was implanted into bulk 3-NiAl (Jedlinski and Mrowec 1987). 

The reader is directed to three comprehensive reviews and a conference publication, dealing with the reactive-element effects on oxidation Whittle and Stringer (1980), Stott and Wood (1987), Moon and Bennett (1989) and Lang (1989), thus only a broad summary of proposed mechanisms, classified as either chemical, physical or mechanical effects is presented here. These may be further, or even alternatively, sub-divided into effects relating to (i) initial oxidation, (ii) growth-rate, (iii) scale adhesion, or (iv) cracking. 

B.A. Pint, Experimental observations in support of the dynamic segregation theory to explain the reactive element effect. Oxidation of Metals, 45, 1/2, 1-31 (1996). 

The reactive element effects on the transition can also be explained by the present model. Application of reactive elements or their oxides onto the alloy surface or into the alloy substrate can change the growth mechanisms of oxide scales [12]. For undoped M-Cr alloys, the growth of Cr203 scales is sustained mainly by the outward diffusion of Cr" ions, resulting in the... 

Pint B A, Garratt-Reed A J and Hobbs L W (1995), The Reactive Element Effect in Commercial ODS FeCrAl Alloys, Mater High Temp, 13, 3-16. 

Pint B A (1996), Experimental Observations in Support of the Dynamic Segregation Theory to Explain the Reactive Element Effect, Oxid Met, 45, 1-37. 

Pint B A (2003a), Progress in Understanding the Reactive Element Effect Since the Whittle and Stringer Literature Review, in Tortorelli P F, Wright I G, and Hou P Y, Proc. John Stringer Symposium on High Temperature Corrosion, Materials Park, OH, ASM International, 9-19. 

Quadakkers J and Singheiser L (2001), Practical Aspects of the Reactive Element Effect, Mater Sci Forum, 369-372, 77-92. 

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