Hydrogen internal friction peak and thermal desorption spectrum in amorphous Cu50Zr50

Abstract

The hydrogen internal friction (HIF) peak and hydrogen thermal desorption spectrum in amorphous Cu50Zr50 (a-Cu50Zr50) were investigated for hydrogen concentrations CH below about 50 at.%. Features of the HIF peak very similar to those in a-Cu50Ti50 were obtained here, i.e. St ∝ N(μ) and n(E; μ) were composed of seven constituent gaussian distributions in E where St denotes the total relaxation strength of the HIF peak, N(G) the site energy G distribution for hydrogen atoms where G is the free energy of occupation of a site, n(E; μ) the activation energy E distribution in N(μ) and μ the chemical potential of hydrogen in the specimen. N(G) appeared to consist of the gaussian distributions N1(G) forCH ⩽ 16 at.%, N2(G) for 16 at.% ⩽ CH ≲ 35 at.% and N3(G) for 30 at.% ≲ CH. We surmised N1(G), N2(G) and N3(G) to correspond to the 4Zr, 3Zr + 1Cu and 2Zr + 2Cu sites respectively. From the thermal desorption spectra, g∗ − G ≈ 0.7 eV (H atom)−1 near the bottom of N3(G) and g∗ − G ⩾ 1.0 eV (H atom)−1 for N2(G) were estimated, where g∗ denotes the energy of the transient state for the formation of an H2 molecule at the specimen surface. The close similarity of the HIF peaks found in a-Cu50Zr50 and a-Cu50Ti50 suggests that these features reflect the common properties of amorphous alloys of an early transition metal with a later transition metal and that the model proposed for the HIF peak in a-Cu50Ti50 might apply to a-Cu50Zr50.