Microstructure Control Using Precipitate Phases for the Development of Heat Resistant Fe3Al-based Alloys
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0980-II01-03
Microstructure Control Using Precipitate Phases for the Development of Heat Resistant Fe3Al-based Alloys Satoru Kobayashi1 and Stefan Zaefferer2 1 Osaka Center for Industrial Materials Research, Institute for Materials Research, Tohoku University, In Osaka Pref. University, Gakuen-cho Naka-ku, Sakai Osaka, 599-8531, Japan 2 Max Planck Institut fuer Eisenforschung GmbH, Max Planck Str. 1, Duesseldorf, 40237, Germany ABSTRACT A thermomechanical process (TMP) was performed to create a fine grained and recovered structure with a high density of fine particles in Fe3Al-Cr-Mo-C alloys. The TMP consists of two parts; the first part is to obtain fine recrystallised grains using coarse particles and the second to produce deformed/recovered structure using fine particles. It was found that κ-Fe3AlC (E21) carbide phase tends to precipitate coarsely, which is effective to refine grain size in the first process. In a special composition range, the κ carbide phase is thermodynamically stable in the Fe3Al matrix only at higher temperatures and fine M(Mo,Cr,Fe)2C (B81) carbide phase precipitates at lower temperatures. This fine M2C particles stabilize the recovered structure by inhibiting the migration of subboundaries in the second process. This result suggests that if the fine particle density remains high, the recovered structure can be maintained at 700°C. INTRODUCTION Fe3Al-based alloys with A2/B2/D03 structures have potential for high temperature applications because of excellent high-temperature corrosion, oxidation resistance and relatively low materials costs [1, 2]. A worldwide concern in material science is which materials will be chosen for ultra supercritical power plant components in the future [3]. Creep resistance and toughness should be improved to put Fe3Al-based alloys into that application. For the purpose of improving both the creep resistance and toughness, we proposed the following thermomechanical process (TMP) to create a fine-grained and recovered structure with a large amount of fine particles in Fe3Al-Cr-Mo-C alloys [4, 5]. The process consists of two parts; The first one is a process to obtain fine recrystallised grains using coarse particles to stimulate nucleation (PSN) of recrystallisation (Process 1) and the second one a process to produce a deformed/recovered microstructure using fine particles to promote extended recovery (Process 2). Currently, we try to realize the microstructure control through the proposed TMP [6]. In the present paper the latest results on this issue are presented. EXPERIMENTAL PROCEDURES Several Fe-26Al based alloys with additions of Cr, Mo and C were studied. Their alloy compositions are shown in Table 1. These alloys will be designated with their Cr, Mo and C content in atomic percent through this paper. 2 kg ingots of these alloys were prepared from 3N purity iron, 4N aluminium, 3N chromium, 3N molybdenum and 3N carbon by induction melting in an argon atmosphere. The surface of the ingot was machined and was then cut into blocks of 56 x 27 x 80 mm. The block
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