PSI - Issue 42

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Petr Dymáček et al. / Procedia Structural Integrity 42 (2022) 1576–1583 Author name / Structural Integrity Procedia 00 (2019) 000–000

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2. Experimental 2.1. Material processing of the FeAlOY

Many trials with Cr, Mo, V, Ti, Nb... (nearly 20 metallic elements) as alloying elements and also Al, Y, La oxides have been done to optimize the chemical composition of the FeAlOY with the aim to improve the cohesive strength of the grain boundaries (as strength limiting factor at high temperatures) and to achieve coarse grains after secondary recrystallization. Optimal chemical composition of the FeAlOY with top creep and oxidation resistance was found as Fe-10Al-4Cr-4Y 2 O 3 in wt. %. The main tasks of the processing are as follows: 2.1.1. Preparation of the FeAlOY powder by mechanical alloying The mix of powder is prepared as following: 82 % Fe powder, 10 % Al powder, 4 % small Cr granules, 3 % Y 2 O 3 powder, 1 % Y granules compensating for O introduction by oxidized powder surfaces are used as inputs (wt. %). The following processes happen during the ball milling: (i) When the balls collide, small particles of powder are forged onto the balls and form larger and larger protrusions on their surface. When they grow sufficiently, they break off as large particle. (ii) The large particles are gradually broken and small particles are forged onto the balls to grow the protrusions. (iii) The process (i) and (ii) are continually repeated and the powder is more and more homogenized. 2.1.2. Consolidation of the FeAlOY powder Canned FeAlOY powder is hot consolidated by forming as rolling, or rotary swaging to the extent that the porosity is completely removed. After stripping a compact material is obtained with an ultrafine grain microstructure (typically 100 nm in size) reinforced by nanodispersion (typically 5 nm in size) of Y 2 O 3 . The material is very brittle and practically unusable, see Fig. 2.

(a)

(b)

Fig. 2 Microstructure after hot consolidation by rolling (a) ultrafine grains (b) Y 2 O 3 precipitates

2.1.3. Secondary recrystallization of the ODS alloy At 1200 °C, few grains grow rapidly at the expense of the ultrafine grains until the ODS alloy completely recrystallizes, see Fig. 3. The ODS alloy thus becomes relatively ductile and easy to machine at room temperature and has excellent creep and oxidation resistance at temperatures of 1100-1300 °C.