Structural Properties and Stability of Metastable Phases in the Zr-Nb System

AURELIO, G.; A. FERNÁNDEZ GUILLERMET; CUELLO, G. J.; P. B. BOZZANO

Badajoz, España

Conferencia; First International Meeting on Applied Physics; 2003

The  lattice  parameters  of  the  bcc  (¥â)  and  omega  (§Ù)  phases occurring metastably  in  a series  of  Zr-rich  Zr-Nb  alloys  have  been  determined  at  and  above  room  temperature (TR)  using neutron diffraction  techniques. In  the first place,  the effect of  temperature changes upon the lattice parameters of  the ¥â and §Ù phases  in alloys with 10 and 18 at.% Nb was monitored using neutron thermodiffraction.  A  method  of  analysis  is  applied  to  the  data  which  involves  a  confrontation between  the observed structural properties and an idealised -or ``reference''- behaviour (RB) which admits a simple mathematical description. A generalised form of Vegard's law is adopted as RB for the ¥â phase, whereas a specific RB is proposed for the §Ù structure. The experimental data are well accounted  for  by  this  interpretation  scheme,  leading  to  a  picture  of  the  isothermal  reactions occurring at high temperature which involves the transfer of Nb from the §Ù to the ¥â phase. Finally, the neutron diffraction data on the §Ù phase are combined with an electron microscopy study for the alloy with 10 at.% Nb aged at 773 K, which provides information on the composition of this phase and its evolution towards thermodynamic equilibrium.