Thermal Stability of Rapidly Quenched Ti-Ni-Al Amorphous Alloys
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MAL STABILITY OF RAPIDLY QUmaCm{D TI-NI-AL AMCPHOUS ALLOYS K. AOKI, K. HIRAGA AND T. MASUMOTO The Research Institute for Iron, Steel and Other Metals, Tbhoku University, Sendai 980, Japan
ABSTRACT Ti-Ni-Al alloys were rapidly quenched from a molten state by the melt spinning method. Three kinds of metastable phases, namely, amorphous,nonequilibrium and quasicrystalline phases are formed in these alloys. The amorphous phase is formed in the range of 35 to 70 at%Ti and 0 to 25 at%Al. The nonequilibrium phases are formed in the composition range of 25 to 33 at%Ti. On the other hand, fine quasicrystalline phases are distributed in the amorphous matrix of the Ti-rich alloys. Crystallization temperatures and the hardness of the amorphous alloys were also examined.
INTRODUcION In recent years, there has been an increased interest in the study of rapidly quenched metals and alloys. Among the products of rapid quenching, amorphous and nonequilibrium alloys occupy a prominent place because of the promise of industrial applications. The majority of amorphous and nonequilibrium alloys studied so far contain Fe, Ni, Co and/ or Cu. Rapid quenching has also been applied to Ti based alloys and amorphous phases have been obtained in some cases[l1]. Polk et al. were able to produce an amorphous phase in the Ti-Ni-Si system [2]. On the other hand, the present authors have been successful in preparing TiNi ribbons, which exhibit shape memory effect, by rapid quenching[3]. The aim of the present work is to investigate how rapid quenching affects the structure of the Ti-Ni-AIl alloys. EXPERIMTAL The Ti-Ni-Al alloys were arc melted from pure components. These alloys were then rapidly quenched using a single roller melt spinning technique in an argon atmosphere. The rotation speed of the copper roller( 200 mm in diameter) was 4000 rpm. Identification of the as-quenched phases were made by both X-ray diffraction analysis and transmission electron microscopy. Cu Kn radiation was applied in combination with an X-ray monochromator. Structural observations have been carried out by the JEM 200EX transmission electron microscope operating at 200 kV. Crystallization temperatures (Tx) of the amorphous alloys were measured in a differential scanning calorimeter(DSC) at a heating rate of 10 K/min. The Vickers hardness number(Hv) were measured by a Vickers microhardness tester with a 100g load.
Mat. Res. Soc. Symp. Proc. Vol. 58. c 1986 Materials Research Society
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20/ (M/18O)rad Fig.1
X-ray diffraction diagrams for the as-quenched Ti-Ni alloys
RESULTS AND DISCUSSION Amorphous and Quasicrystalline Phases Fig. 1 exemplifies the X-ray diffraction(XRD) diagrams for the binary Ti-Ni alloys. The Ti 7 0 Ni alloy is characterized by the diagram having no sharp diffraction peak but an extremely broad peak. On the other hand, sharp crystalline peaks are seen on the diagram for the as-quenched Ti 3 0 Ni 7 0 alloy. The XRD pattern for the as-quenched TisoNi50 alloy is an intermediate of the above two, exhibiting a superposition o? t!e broad amorphous p
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