An analytical electron microscopy study of the role of La and Y during high-temperature oxidation of selected Ni-base alloys

Journal Article · Wed Sep 01 04:00:00 EDT 1993 · Scripta Metallurgica et Materialia; (United States)

DOI:https://doi.org/10.1016/0956-716X(93)90420-W· OSTI ID:6326773

Tawancy, H M; Abbas, N M ^[1]

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1. King Fahd Univ. of Petroleum and Minerals, Dhahran (Saudi Arabia). Materials Characterization Lab.

Minor but critical additions of active elements such as Y to Al[sub 2]O[sub 3]-forming alloys and La to Cr[sub 2]O[sub 3]-forming alloys are known to have beneficial effects on their high-temperature oxidation resistance. Several mechanisms, sometimes opposing, particularly in the case of Al[sub 2]O[sub 3]-forming alloys have been proposed to explain the active element-effect. A number of extensive reviews have dealt with these mechanisms. In the case of Cr[sub 2]O[sub 3]-forming alloys, however, it is generally agreed that the role of active elements is to promote selective oxidation of Cr, reduce the scale growth rate, and improve its mechanical strength. For a better understanding of the active element-effect, it is essential to determine its atomic-scale distribution within the oxide scale. Using thin-foil analytical electron microscopy techniques, it has been shown that in some Al[sub 2]O[sub 3]-forming alloys and Cr[sub 2]O[sub 3]-forming alloys, Y tends to segregate at grain boundaries of the oxide scale resulting in modification of its transport properties and mechanical strength. Also, it has been suggested that other elements such as Ce and La may segregate to grain boundaries of oxide scale in Cr[sub 2]O[sub 3]-forming alloys. It was the objective of this study to determine the atomic-scale distribution of active elements in wrought Ni-base alloys of commercial grade using the techniques of analytical electron microscopy. Two alloys representing Al[sub 2]O[sub 3]-forming and Cr[sub 2]O[sub 3]-forming alloys were selected for the study. Haynes alloy no. 214 is a Y-containing alloy capable of developing Al[sub 2]O[sub 3] scale upon exposure at temperature exceeding 1,000C and Haynes alloy no. 230 is a La-containing alloy protected by Cr[sub 2]O[sub 3] scale.

• OSTI ID: 6326773
• Journal Information: Scripta Metallurgica et Materialia; (United States), Journal Name: Scripta Metallurgica et Materialia; (United States) Vol. 29:5; ISSN 0956-716X; ISSN SCRMEX
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360105* -- Metals & Alloys-- Corrosion & Erosion
ALLOYS
CHEMICAL REACTIONS
DATA
ELECTRON MICROSCOPY
ELEMENTS
EXPERIMENTAL DATA
INFORMATION
LANTHANUM
LANTHANUM ADDITIONS
LANTHANUM ALLOYS
METALLURGICAL EFFECTS
METALS
MICROSCOPY
NICKEL ALLOYS
NICKEL BASE ALLOYS
NUMERICAL DATA
OXIDATION
RARE EARTH ADDITIONS
RARE EARTH ALLOYS
RARE EARTHS
TRANSITION ELEMENTS
YTTRIUM
YTTRIUM ADDITIONS
YTTRIUM ALLOYS