High-purity Zirconium under Niobium ion implantation: possibility of a dynamic precipitation?
AK Revelly and HW Becker and B Vishwanadh and KVM Krishna and R Tewari and D Srivastava and GK Dey and I Samajdar and AS Panwar, PHILOSOPHICAL MAGAZINE, 95, 3727-3744 (2015).
High-purity (6N purity) Zirconium was subjected to different Niobium ion (Nb+) fluences in a particle accelerator. Grazing incidence X-ray diffraction confirmed subsurface phase transformation. While an approximate scaling was noted between Nb+ fluence and quantum of phase transformation, the sample subjected to the highest ion irradiation also showed significant subsurface shear residual stresses ((13)). Molecular dynamics simulations, considering momentum transfer, revealed a drop in (13) beyond a critical displacements per atom or Nb+ fluence. High- resolution cross-sectional transmission electron microscopy (HRXTEM) confirmed formation of bcc (body-centred cubic) phase and also linked (13) with such transformation. HRXTEM revealed, at about 100nm depth, presence of 10-15% with 2-15nm size. The particles and the surrounding also had significant microscopic shear strains. The dynamic nature of the Nb implantation is expected to create fluctuations in temperature, Nb concentration and relative lattice damage. Such fluctuation, on the other hand, is/was hypothesized to dynamically alter the critical nuclei size: a clear possibility of dynamic precipitation'.
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