Microstructure of ball milled and compacted Co–Ni–Al alloys from the β range |
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Authors: | W MAZIARZ J DUTKIEWICZ ROGAL J GRZONKA & E CESARI† |
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Affiliation: | Institute of Metallurgy and Materials Science Polish Academy of Sciences, 30-059 Cracow, 25 Reymonta St., Poland;Departament de Física, Universitat de les Illes Balears, Cra. de Valldemossa, km 7.5, E-07122 Palma de Mallorca (Illes Balears), Spain |
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Abstract: | Two powder alloys from the β phase region of compositions Co28.5Ni36.5Al35 and Co35Ni30Al35 were ball milled for 80 h in a high energy ball mill. The formation of amorphous structure was observed after 40 h of milling and further milling did not change their structure. The analytical and high-resolution transmission electron microscopy (TEM, HREM) examination of powder structure showed that nanoparticles of L10 phase of size of about 5 nm were present within the amorphous matrix. The vacuum hot pressing of the milled powders under pressure of 400 MPa at 700°C for 12 min resulted in the formation of compacts with density of about 70% of the theoretical one. The additional heat treatment at 1300°C for 6 h followed by water quenching, led to significant improvement of density and induced the martensitic transformation manifested by a broad heat effect. The characteristic temperatures of the transformation were determined using DSC measurements, which revealed only small differences within the examined alloys compositions. TEM structure studies of heat-treated alloys allowed to identify the structure of an ordered β (B2) phase and L10 martrensite. |
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Keywords: | Co–Ni–Al alloys hot compacting powder metallurgy STEM-HAADF TEM |
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