Alloys containing yttrium

In particular, an alloy is mentioned whose registered trademark is FeCrAlloy. In the mentioned patent, reference is made to the fact that the alloy contains Yttrium, an element whose possible advantages we will examine later. 

Wukusick C S and Collins J F (1964), An Iron-Chromium-Aluminum Alloy Containing Yttrium, Mater Res Stndrd, 4, 637-646. 

Other detrimental factors which should to be taken into account in the materials selection process include temperature cycling and the presence of halide gases. Specialist alloys containing rare earth element additions such as cerium, lanthanum and yttrium have been developed for use in certain environments up to 130°C. 

A set of four iron aluminides (FA 49, FA 56, FA 57 and FA 58) was supplied by Shell Research, with compositions given in Table 1. These contained about 5 wt% Cr and aluminium concentrations from about 8% to 16 wt%.They all included a small amount of zirconium while three of them also contained yttrium, to assist in maintenance and retention of the protective A1203 scale. For comparison, two other Al203-forming alloys and two Cr203-forming alloys were included in the programme.The former alloys contained much more chromium than the aluminides but much less aluminium MA... 

Under these conditions, the presence of 0.2 to 0.3 wt% Y in the iron aluminides has little influence on the effectiveness of the thin A1203 scale in giving protection however, extensive intergranular precipitates, rich in yttrium and zirconium, are formed in alloys containing 0.3 wt% Y. 

The Fe-Cr-Al alloys have been used for some hme as heating elements (that is as material for resistors) for kilns, in competition with more expensive alloys with a high Ni content (Ni-Cr, Ni-Cr-Si, Ni-Cr-Fe-Si). The Fe-Cr-Al alloys normally have a chromium content of about 20-22% and an aluminum content of 5-5.5% while the content of yttrium, the most common alloying "auxiliary" element, is normally lower than 0.1%, if present. In comparison with the Ni-Cr and Ni-Cr-Fe alloys, the Fe-Cr-Al alloys have a lower linear thermal expansion coefficient. Mechanical resistance is sufficiently high for the alloys containing 22% of chromium and with an aluminum content of 4.5-5.5% and, therefore, 72.5-73.5 of iron. 

Gas turbine blades are essentially nickel-base or cobalt-base alloys containing substantial amounts of chromium, several percent aluminum, and a few hundredths percent yttrium. Their susceptibility to hot corrosion and sulfidation has already been discussed. Applied coatings of aluminum or of aluminum-chromium-yttrium increase resistance to attack. 

Markova et al. (1964) were in the process of investigating this system when the work of Beaudry and Daane was published. Markova et al. subsequently pubhshed some photomicrographs showing single-phase structure in scandium, yttrium and alloys containing 11, 43 and 67 at% yttrium, but did not show their phase diagram for the system. They stated that their measurements showed a continuous series of solid solutions of the isomorphous modifications of the components in this system, which confirms the work of Beaudry and Daane. 

In general, both cordierite and metallic monoliths are unsuitable as catalytic supports. To process a monolith into an active monolithic catalyst, a layer of porous catalytic support must be deposited on the walls between channels. y-Alumina appeared to be the most effective support for automotive catalysts. The alumina layer is deposited by sol-gel technique (so called washcoating). Adherence of 7-alumina to cordierite is relatively strong. However, to form the stable 7-alumina layer on a metallic surface, we need to use an appropriate alloy that is appropriately processed before the layer is deposited. Stainless steel containing chromium, aluminum, and yttrium subjected to thermal treatment under oxidizing conditions meets requirements of automotive converters. Aluminum in the steel is oxidized to form 7-alumina needles (whiskers) protruding above the metal... 

Work on one particular ferritic steel, Fecralloy, for fabrication of catalyst substrates was pioneered by the United Kingdom Atomic Energy Authority at Harwell and Johnson Matthey, in collaboration with Resistalloy, which developed technology for producing thin strip [32]. This and related alloys, in addition to iron, chromium, and aluminum, contain low levels of elements such as yttrium (0.1-3.0%), thought to enhance the protective properties of the surface alumina layer. Alumina forms by the oxidation of bulk... 

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