Electron microscopy and diffraction of ordering in Ni---W alloys

Mishra, N. S. ; Ranganathan, S. (1995) Electron microscopy and diffraction of ordering in Ni---W alloys Acta Metallurgica et Materialia, 43 (6). pp. 2287-2302. ISSN 0956-7151

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Official URL: http://linkinghub.elsevier.com/retrieve/pii/095671...

Related URL: http://dx.doi.org/10.1016/0956-7151(94)00417-X


Electron microscopy and diffraction studies of ordering in stoichiometric Ni-20%W and off-stoichiometric Ni-15%W alloys have been carried out. The specimens of Ni-20%W were first disordered at 1398 K for 4 h and then quenched rapidly into water. Short range order (SRO) spots were observed at {1½0}* positions. Two hitherto unknown metastable phases: D252h-Ni2 W and D022-Ni3 W were observed in the diffraction patterns. Long range order (LRO) transformations were studied at 1103 and 1213 K. Kinetics and mechanism of transformations have been identified. Ni-15%W specimens were solution treated at 1523 K for 1 h followed by quenching in water. SRO spots similar to those found in Ni-20%W were observed in this alloy as well. The transition to LRO was studied at 1093 K. Distinct Ni4 W precipitates could be observed after 5 h of annealing at this temperature. After 100 h of annealing precipitates were found to grow into faceted shape coherent with the disordered matrix. After prolonged annealing for over 150 h the Ni4 W precipitates began to lose coherency by the generation of misfit dislocations. The microstructural observations have been compared for the stoichiometric and off-stoichiometric alloys.

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