Formation and Thermal Stability of Cu‐Hf‐Ti‐M Glassy Alloys

Abstract

Since 1995, Cu has been shown to be a good base element for bulk glass-forming alloys, with fully glassy sections up to 7 mm being reported. [1] For instance, Lin and Johnson [2] produced 4 mm thick glassy strips of Cu 47 Ti 34 Zr 11 Ni 8 alloy by copper die injection casting. The introduction of 1 at.% Si increased the critical thickness for glass formation to 7 mm. [1] Binary Cu -(Zr or Hf) alloys have been found to form an amorphous phase [3][4] over a wide composition range. However, addition of Ti in both these binary systems greatly increased the glass forming ability (GFA), [5][6][7][8] with the critical diameter for fully amorphous rods being at least 4 mm for Cu 60 Zr 30 Ti 10 , Cu 60 Hf 20 Ti 20 and Cu 55 Hf 25 Ti 20 . On the other hand, it has been shown that small additions of B and Y [7] and of Nb, Ta and Mo [9] reduce the GFA for Cu-Hf-Ti alloys.One of the empirical rules for high GFA in a metallic alloy is that the heat of formation from the constituent elements is negative. Nevertheless, although addition of alloying elements with positive enthalpy of solution should reduce the GFA, there have been some reports that the addition of elements with positive heats of mixing enhances GFA, [10][11][12][13] though Xu et al. [10] show that this occurs only when they decrease the melting temperature of the alloy. The objective of the present study was to investigate the effects of small concentrations of Al, Mo, Si and V on the GFA and thermal stability for Cu-Hf-Ti-based alloys.Cu-based alloy ingots of composition Cu 55-x Hf 25 Ti 20 M x (M = Al, Mn, Si, V, where v = 1, 2, 4 and 7 at.%) were prepared by argon arc melting mixtures of Cu (99.99 % pure), Hf (99.8 % pure), Ti (99.98 % pure), Al (99.99 % pure) Mn (99.99 % pure) Si (99.99 % pure) and V (99.98 % pure). The alloy compositions represent the nominal values but the weight losses in melting were negligible (< 0.1 %). The alloy ingots were inverted on the hearth and re-melted several times, to ensure compositional homogeneity. Conical alloy shapes, of length ∼ 50 mm and having a minimum diameter of 1 mm and a maximum of 10 mm, were produced by copper mould suction-casting within the argon arc furnace. [6] Additionally, ribbon samples of each alloy, with cross sections of typically 0.03 mm × 2.0 mm, were produced by chill-block melt spinning in a sealed argon atmosphere. The structures of the conical and ribbon samples were studied by XRD and the glass transition (T g ) and crystallisation (T x ) temperatures determined by DSC (using a Perkin Elmer DSC-7) at a heating rate of 0.33 K/s. The initial melting (T m ) and liquidus (T l ) temperatures were measured by DTA (Perkin Elmer DTA-7) at a heating rate of 0.33 K/s. Both, the DSC and the DTA instruments were calibrated at the respective heating rates using the known melting temperatures of pure metals. The measured T l corresponding to the completion of the melting transformation were adjusted to allow for thermal lag, using a correction factor determined earlier by Donald and Davies. [14] Initiall...

Structural Relaxation Solutions Formetallic Amorphous Condensed Lattice with Activation Energy Spectrum Model Applied Computational Physics

“…An additional consequencewas also recognized that the reversephenomena AES classical energy distribution nevertheless the cyclically nano-structural relaxations were in good covenant with the presented experimental results of transition metallic type amorphous alloys. There wasfreshly considerable as to whether the glassy alloys are archetypal of the bulk formed ultra-fine structure [4]. Predominantly Cu has been shown to be good base element for bulk glassforming alloy with fully glassy sections lately by custom of die injection casting [4].…”

“…There wasfreshly considerable as to whether the glassy alloys are archetypal of the bulk formed ultra-fine structure [4]. Predominantly Cu has been shown to be good base element for bulk glassforming alloy with fully glassy sections lately by custom of die injection casting [4]. Alloys for Cu system have been initiatedto form an amorphous phase over a wide configuration collection.…”

Numerical Solutions for Structural Relaxation of Amorphous Alloys Studied by Activation Energy Spectrum Model

“…Particularly Cu has been shown to be good base element for bulk glass-forming alloy with fully glassy sections recently by use of die injection casting [2,3]. Binary Cu -(Zr or Hf) alloys have been found to form an amorphous phase over a wide composition range.…”

“…Binary Cu -(Zr or Hf) alloys have been found to form an amorphous phase over a wide composition range. However, addition of Ti in both these binary systems greatly increased the glass forming ability (GFA), with the critical diameter for fully amorphous rods being at least 4 mm for Cu60Zr30Ti10, Cu60Hf20Ti20 and Cu55Hf25Ti20 [2,3]. Meanwhile the understanding of the structural relaxation process is essential in the development of stability for amorphous alloys, as well as in establishing stable working temperature to avoid the degradation of strength.…”

“…Activation energy for structural relaxation process in a metal type amorphous ternary and quaternary alloys, with cross sections of typically 0.03 mm x 2.0 mm, prepared by chill-block melt spinning has been investigated by Differential Scanning Calorimetry (DSC) with a cyclically heating technique [1,2,3]. Activation energies for structural relaxation with a spatial quantity in amorphous materials have been discussed by use of a total relaxed ratio function that depends on annealing temperature and time.…”