Phase Stability of the Al-Cu-Co Decagonal Phase Under Conventional Solidification
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Phase Stability of the Al-Cu-Co Decagonal Phase Under Conventional Solidification J.O. Téllez-Vázquez1, C. Patiño-Carachure1, A. Bedolla-Jacuinde1, E. García-De León2, R. Pérez3 and G. Rosas1 1
Instituto de Investigaciones Metalúrgicas, UMSNH, Edificio U, Ciudad Universitaria, CP 58060, Morelia Michoacán, México. E-mail: [email protected] 2
Facultad de Química, UNAM, Coyoacán, México D. F., 04510, MEXICO.
3
Centro de Ciencias Físicas, Universidad Nacional Autónoma de México, México, D.F., México.
ABSTRACT Al65Cu15Co20 and Al67Cu13Co20 (% at.) alloys with composition near to the quasicrystalline decagonal phase was produced by melting in an induction furnace and solidified at room temperature. The structural characterization was carried out by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM). For the structural model of decagonal quasicrsytals, it is important to know which crystalline phases have a structural relationship on the formation and decomposition of this type of phases. In the present investigation, the decagonal phase usually coexist with small amounts of the Al(Cu,Co) cubic phase of B2 type. Then, the quasicrystalline (QC) phase is outside of a single-phase region under equilibrium conditions at room temperature. DSC and TGA techniques showed the thermal stability of the alloy system up to 1000 oC. INTRODUCTION Since the discovery of the stable decagonal quasicrystal in the Al-Cu-Co system [1], several investigations have been carried out to explore the D-AlCuCo phase stability and their structure. For example, it has been demonstrated that D-phase transforms to crystalline phases for different processing conditions, including high-energy ball milling (HEBM), annealing temperature [2], and different synthesis methods [3]. Previous studies have shown that the D-phase is stable in the range of temperature between 550 and 1000 oC, [3]. Investigations about the solidification behavior of D-Al65Co15Cu20 and D-Al65Co20Cu15 alloys composition indicates that the D-phase melts incongruently. The D-phase is formed by a peritectic reaction between the B2 phase and the liquid at higher temperatures or it can grow directly from liquid [4]. Therefore, the cubic B2 phase has an important structural relationship with the D-phase. The presence of the decagonal phase in this ternary system has been found to be very sensitive to the amount of cobalt in the alloy composition [ 2,5]. However, these studies were obtained using a rapid solidification technique. The most interesting feature of this investigation is the disappearance of the cubic phase when the amount of cobalt is increased. This disappearance enhanced the presence of the decagonal phase. Few investigations have been focused to explain if the D-phase appears in a single-phase region or in a multiphase region at room temperature, as well as the stability of the phase or mixture of phases on heating. This data will be a contribution for the phase diagram at room temperature. Thus, i
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