Enhanced glass-forming ability and microhardness of Ti45Zr5Cu25Ni20Sn5 amorphous alloy by addition of TiC particles

Abstract

Recently there has been much interest in metal matrix composites (MMC) as a way to improve the mechanical properties compared to nonreinforced alloys [1–3]. MMCs are made by the addition of long or short fibers, whiskers, or particles. The addition of fibers or whiskers in a continuous uniaxial direction will result in anisotropic mechanical properties. However such composities with maximum strength and stiffness in one direction (anisotropic) are very costly. Discontinuously or random distribution of particles will result in MMCs with isotropic properties but also substantial improvements in strength and stiffness relative to those available with nonreinforced alloys [4]. Particulate reinforced MMCs have the further advantage of being machinable and workable using many conventional processing techniques as well as being relatively low cost. Nonferrous metals are often considered as matrix materials for the particulate reinforced MMCs. The most studied metal matrix for application at temperatures below 723 K is aluminum [5]. Titanium matrix MMCs are candidates for structural applications in the aerospace industry primarily because of their high specific strength and modulus, and good dimensional stability. Much attention has also been paid to particulate reinforced amorphous metal matrix composites. These amorphous MMCs are prepared by mechanical alloying [6, 7], melt spinning [8] and copper mold casting [9, 10]. It is concluded [6, 7, 9] that the addition of ceramic particles does not affect the thermal stability of the glassy matrix, i.e., the location and width of supercooled liquid region Tx(=Tx − Tg) (where Tg is the glass transition, Tx is the crystallization onset temperature of the metallic glass) of the alloy exhibits little change. It is also concluded from these references that the dispersion of second phase particles in the amorphous alloy causes a remarkable increase in the microhardness. In this paper, the multicomponent Ti45Zr5Cu25Ni20Sn5 amorphous alloy was used as the matrix material to be reinforced with TiC particles. This alloy was selected because it has very good glass-forming ability [11]. The aim of this paper was to investigate the influence of TiC particulate addition on glass-forming ability (GFA) of the multicomponent Ti45Zr5Cu25Ni20Sn5 amorphous alloy so as to see the necessity for particulate reinforcing of glassy alloys. The TiC particles with a diameter of about 1–5 micron was used as the dispersant because of its good wettability with the Ti45Zr5Cu25Ni20Sn5 alloy. The master ingot was prepared by arc melting the mixture of pure Ti, Zr, Cu, Ni and Sn metals on a water cooled copper boat under an argon atmosphere. The purity of the elements ranged from 99.5% to 99.9%. The alloy composition represented the nominal atomic percentage of the mixture. The master ingot was crushed into particles with a diameter of about 1–2 mm and then mixed with the TiC particles homogeneously. Subsequently, rapidly solidified composite ribbons with a cross section of 0.02×1.0 mm2 were prepared by single roller melt spinning the mixture of the crushed master Ti45Zr5Cu25Ni20Sn5 ingot with various volume fractions of TiC particles in an argon atmosphere. Bulk samples in a rod form with a diameter of 1 to 2 mm were also prepared by copper mold casting the mixture in an argon atmosphere. The structure of the composite materials was examined by X-ray diffractometry (XRD). Thermal stability associated with the glass transition, supercooled liquid region and crystallization of the amorphous matrix with various volume fractions of TiC particles were measured by use of a differential scanning calorimeter (DSC) at a heating rate of 0.67 K/s. The melting temperature was also measured with a differential thermal analyzer (DTA) at a heating rate of 0.33 K/s. Vickers hardness of the matrix alloy and composites was determined with an Akashi hardness tester using a load of 50 g. Fig. 1 shows the X-ray diffraction patterns of the melt-spun composites with volume fractions of TiC