An electron-transmission-microscope study has been ptade of the structural changes that occur in quenched niobium-nitrogen alloys on ageing at 535° C (808 K). Initially, nitride precipitate plates form on {100} planes in the matrix and when they reach a critical size, apparently defined by both diameter and thickness dislocation loops and segments are generated. The Burgers vectors of the dislocations are of the type ½〈111〉 and the loops are interstitial in nature. It is considered that the dislocation structure is generated to accommodate the misfit strain associated with the nitride platelets.
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