Mechanical Properties of E2 1 Ti 3 AlC-base Alloy
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0980-II07-08
Mechanical Properties of E21 Ti3AlC-Base Alloy Hideki Hosoda, Tomonari Inamura, and Kenji Wakashima Precision and Intelligence Laboratory, Tokyo Institute of Technology, 4259 R2-27, Nagatsuta, Midori-ku, Yokohama, 226-8503, Japan
ABSTRACT Mechanical properties and phase constitution of an E21-type Ti3AlC-base alloy were investigated by compression tests in a temperature range from room temperature (RT) to 1273K, scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD). The unit cell of E21 Ti3AlC is constructed by “L12 Ti3Al” and a carbon atom occupying the body-center octahedralinterstitial-site surrounded by the Ti atoms. The nominal composition of the alloy was chosen to be the stoichiometric composition of 60mol%Ti-20mol%Al-20mol%C. The alloy was synthesized by mechanical alloying using high purity elemental powders followed by hot pressing at 1473K for 3hrs. It was found by XRD and SEM that the alloy was mainly composed of E21 Ti3AlC in addition to Cr2AlC-type Ti2AlC precipitates as a second phase. The density of Ti3AlC is calculated to be 4.29g/cm3 based on the lattice parameter of 0.4134nm of E21. The average grain size was 2µm by SEM. By the compression tests, the 0.2% flow stress at the temperature range from RT to 1073K exceeded 1GPa. The yield stress is comparably higher than those of other E21 intermetallic carbides: at 1073K, 1084MPa for Ti3AlC, 50MPa for Mn3AlC and 135MPa for Fe3AlC. Besides, a weak positive temperature dependence of strength was observed where the peak temperature was around 900K. This suggests that a Kear-Wilsdorf type dislocation pinning mechanism may be activated. It is concluded that E21 Ti3AlC-base alloy shows promise for a new high-temperature light-weight structural material.
INTRODUCTION E21-type intermetallic carbides and nitrides such as Co3AlC and Fe3AlN, which are often called κ phase, are candidate for high temperature structural materials [1,2]. This is partially because E21 intermetallic carbides possess Perovskite-type high symmetric crystal structure. The unit cell of an E21 carbide M3AlC (M: transition metals) is composed of (1) M atoms occupying the face center sites, (2) Al atoms occupying the corner sites and (3) C atoms occupying the body-center octahedral-interstitial-sites surrounded by M atoms. The crystal structure of E21 is similar to that of L12, rather, the interstitials stabilize the L12 structure [3]. Then, physical properties of E21-type intermetallic carbides are expected to be similar to those of L12 compounds [1,2]. Some E21 intermetallic alloys, e.g. Co3AlC alloy, exhibit positive temperature dependence of strength at intermediate temperatures similar to L12 Ni3Al [1]. The anomalous temperature dependence of E21 intermetallic carbides is thought to be related to a Kear-Wilsdorf mechanism [1, 4]. Recently, it was also reported that E21 compounds of Mn3AlC, Fe3AlC and Co3AlC and L12 Ni3Al widely form a continuous solid solution of M3AlC1-x in the multicomponent system of M (Cr-Mn-Fe-Co-Ni-Cu)-Al-C [5,6]. Some investigati
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