Papers by Author: Hywel A. Davies

Abstract: The aim of this research is to clarify a quantitative evaluation in the structural relaxation processes focusing on the activation energy on the addition of B to Cu-based amorphous alloys. The activation energy for structural relaxation process in a metal type amorphous CuHfTi ternary and CuHfTiB 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. 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. In the present work on CuHfTi ternary and CuHfTiB quaternary alloys, the distributions for the Activation Energy Spectrum (AES) by calculation with derivative-type relaxed ratio function were observed almost 160 kJmol-1, whereas in difference for shape only in the CuHfTi-B3% quaternary alloy. Another result has been also established that the ‘reversible’ AES model energy distribution though the cyclically structure relaxation occurs even in amorphous CuHfTiB alloy system.

Abstract: The aim of this research is to clarify a quantitative evaluation in the structural relaxation processes focusing on the activation energy in Cu based amorphous alloys. The activation energy for structural relaxation process in a metal type amorphous CuHfTi ternary 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. Activation energies for structural relaxation with a spatial quantity in amorphous materials have been discussed by use of a relaxed ratio function that depends on annealing temperature and time. In the present work, the distributions for the Activation Energy Spectrum (AES) were observed almost 152 kJmol-1 (1.58 eV). Another result has been also established that the “reversible” AES model energy distribution though the cyclically structure relaxation occurs even in amorphous Cu60Hf20Ti20 alloy.

Abstract: In this paper, a rapid solidification (RS) method was employed to produce yttrium-containing TiAl based alloy ribbons. The microstructure evolution was investigated in terms of yttrium addition and RS parameters. For comparison, the conventionally cast counterpart alloys were studied as well. It was found that the microstructure of as cast alloys is sensitive to the Y content. The alloys with addition of 0 to 1.0at.% Y were of lamellar microstructures, but the alloy samples with 1.5 and 2.0at.% Y additioin were of strip-like microstructure. The yttrium-free alloy exhibited full γ phase, while the Y-bearing alloys contain γ phase, a small amount of α2, and yttrium containing phases. With increasing Y content, the secondary dendritic arm spacing (SDAS) gradually reduced. In the case of the rapidly solidified alloys, the microstructure was refined evidently when compared with the as cast counterparts. The fine Y-rich precipitates were homogeneously distributed in the matrix with a particle size of several tens of nanometers. A bcc phase (a=0.314 nm) was found in the alloys containing more than 1.5at.% Y, which was attributed to the extension of the solubility of Y in the matrix by rapid solidification.

Abstract: Powder injection moulding (PIM) is a cost effective powder metallurgical process for the fabrication of small, complex-shaped components for high performance applications. A binder system, which comprises a major fraction of polyethylene glycol (PEG) and a minor fraction of a very finely dispersed polymethyl methacrylate (PMMA), has been applied for tungsten carbide (WC) – cobalt (Co) hardmetal powders. PEG can be removed rapidly by water leaching and PMMA is removed by subsequent pyrolysis when the components are ramped up to the sintering temperature. In this work, the development of feedstock formulations and of the processing parameters for a successful injection moulding and to achieve high density has been investigated. The present study has demonstrated that the binder can be employed for the production of WC-Co hardmetal components by PIM process. The maximum density achieved thus far is 97% of the theoretical value.