The nitriding of iron-nickel-niobium alloys

Abstract

A modulated structure is formed in nitrided Fe:35Ni:Nb alloys at 500 to 750°C in NH 3:H2 gas mixtures when the niobium and nitrogen concentration exceed critical values associated with a metastable zone solvus. The modulated structure is formed by substitutional-interstitial solute-atom clusters on {10O} matrix planes and it, overages to give a fine dispersion of homogeneous precipitates of Y-NbN. The initial spheroidal particles of Y-NbN coarsen at 800°C by forming octahedr& with their faces parallel to the {111} matrix planes. After prolonged ageing these niobium nitride octahedra transform to platelets parallel to the {100} matrix planes. The interfacial -surface energy of Y-NbN is determined*as approximately 600 ergs/cm2. Stacking fault precipitation of Y-NbN in nitrated Fe-35Ni:Nb alloys occurs when the niobium concentration exceeds the nitrogen concentration. The dislocation-particle interaction of Y-NbN in nitrided Fe:35Ni:Nb alloys occurs by the Orawan mechanism. The nitriding kinetics are dependent upon nitrogenatom diffusion in Fe:35Ni.