Mechanical Properties of E2 1 (Mn, Fe) 3 AlC-Base Alloys
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L1 2 aluminides and silicides, such as Ni 3 AAand Ni3Si, are promising to be high temperature structural materials due to their superior mechanical properties. Some features, such as good ductility and mechanical anomaly [1], of Ni 3AA come from the nature of L1 2 crystal structure itself. Unfortunately, in the third-period transition-metals (M) and Al binary systems, NiaA1 is the only one L12 M3AL. Third-period transition-metals are beneficial on the balance of melting points, density and production cost. Thus, new L12 compounds have been tried to be produced by crystal-structure control [2,3]. Another viewpoint is that compounds having crystal structures similar to L12 may behave like L1 2 compounds. The most promising candidate in the latter case is E21 : E2 1 crystal structure is constructed by M at the face-center sites, Al at the corner sites and C (interstitials) at the body-center (octahedral interstitial) sites. Thus E2 1 M3A1C could be said to be L12 M3AAcontaining interstitials. Recently we found that some E2 1 compounds form a continuous solid solution to L12 Ni 3Al [4]. Moreover, it was found that some Co 3AIC alloys show positive temperature dependence of strength around 1000K [5]. E21 M3A1C have a large potential to be structural materials. However, relatively small number of studies have been reported for E21 M3 AAC: Fe3 AAC [6,7], Mn-added Fe3AAC [8], Co 3A1C-base alloys [3,9] and Ni3A1C [6]. No study seems to have been done for Mn3 AAC. In this study, to reveal the nature and potential of E2 1 M3A1C compounds, we have systematically investigated mechanical properties of E21 (Mn, Fe) 3A1C alloys: Mn 3A1C and Fe 3AAC form a continuous solid solution [4]. Alloys were made using powder metallurgy because it is difficult to fabricate carbiderelated materials by ingot metallurgy such as arc-melting. Results are discussed in connection with Fe and interstitial contents.
KK8.32.1 Mat. Res. Soc. Symp. Proc. Vol. 552 0 1999 Materials Research Society
EXPERIMENTAL PROCEDURE Concentrations of transition metals were systematically changed from 60mol%Mn to 60mol%Fe stepped by 10mol% under the constant aluminum and carbon contents of 20mol%Al and 20mol%C (stoichiometric composition of E2 1). Using transition metal content, these alloys are called such as 40Mn2OFe alloy. Starting materials were elemental powders of 99.9% purity. The sizes of powders are less than 75ltm for Mn and Fe, 20gm for Al and 5[.tm for C. Alloys of lOOg were mechanically alloyed using a planetary ball mill made from stainless steel and chromium steel balls at RT for 604.8ks in Ar. Bulk specimens were produced using MA powders by hot pressing under 69 MPa for 7.2ks at 1473K using carbon dies. Alloy compositions were determined by ICP chemical analysis, as shown in Table 1. Scanning electron microscopy (SEM), X-ray diffractometry (XRD) and quantitative electron probe microanalysis (EPMA) were carried out to identify microstructure and constituent phases. Compositions by quantitative EPMA were averaged for at least 5 point measurements. Mi
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