The Crystallization of (NiCu)ZrTiAlSi Glass/Crystalline Composite

Abstract

Until the present times many compositions of the amorphous alloys have been determined, commonly based on metallic components with some non-metallic additions. [1] Low critical cooling rates for crystallization of some such alloys allow the preparation of bulk metallic glasses. [2] The ability to achieve the quenching rate high enough in all the volume of the undercooled liquid determines size and shape of a potential amorphous constructional element for applications, in most cases not too large. [2,3] The other important factor in bulk metallic glasses production is a technology of production which should consider among others purity of the process. [4] From the mechanical point of view metallic glasses are characterized by a wide elastic range and high strength (around 2.0 GPa), lack of ductility and high hardness. [5][6][7] The ductility may increase in the range of nanocrystallization of undercooled liquid, at temperature between the glass transition and crystallization. [8] The increase of ductility in composite microstructure of a ductile dendritic phase in the amorphous matrix is also expected. To achieve such a microstructure both powder metallurgy [9] and "conventional" casting of BMGs with partial crystallization from the melt [10] could be applied. There is still need for knowledge on the crystallization process in order to achieve optimal phase composition and particles size.The alloys based on the Ni-Ti-Zr eutectic composition follow the criteria to obtain metallic glass. [10,11] Some additions like Si or Sn increase glass forming ability, [12][13][14][15] but Si also lowers mechanical properties of the alloys. [16,17] The Cu additions may increase the DT range of the supercooled liquid as well as the strength and corrosion resistance of the alloys. [16,17,18] The Al addition promotes a lower temperature of crystallization. [19] Amorphous or partially nanocrystalline, Ni-based alloys may reveal high strength and hardness, high thermal stability of the amorphous phase and especially good resistance against corrosive conditions similarly to Fe and Ti based to glasses. [20] The alloys of the compositions (Ni 1-x Cu x ) 50 -Ti 33 Zr 16 Si 1 containing more Ti than Zr were reported to make a potentially amorphous composite [7] revealing composite crystalline (dendritic)-amorphous microstructure, yield stress at the level of 1200 MPa and strength about 1900 MPa.The paper presents results of investigations of alloys of nominal composition (Ni 1-x Cu x ) 60 (Zr 18 Ti 13 )Al 5 Si 4 with copper content changing from 8 to 23 at.%, from the point of view of the phase composition and microstructure formed during partial crystallization of the massive samples in the copper mould, in dependence on different cooling conditions. Basic results concerning fully amorphous ribbons are presented for comparison. ExperimentalThe alloys were prepared from components of 3 M and 4 M purity, by melting in an induction furnace in a quartz tube, under an argon atmosphere. The alloys were re-melted several times by the levitation ...