Preparation of Ultrafine-Grained and Nanocrystalline Materials by Mechanical Alloying and Spark Plasma Sintering
Department of Metals and Corrosion Engineering, University of Chemistry and Technology, Prague
Keywords: mechanical alloying, spark plasma sintering, microstructure, hardness, compressive strength
Mechanical alloying and subsequent compaction via spark plasma sintering belongs to prospective combination of two methods capable to produce materials with enhanced mechanical properties, as compared with their conventionally cast equivalents. During this processes, a maximum effort is focused to maintain refined microstructure and to preserve this character even after compaction. Resulting materials are characterized by high hardness, compressive strength or excellent thermal stability. From several materials prepared at our Department, the Al-20Si-16Fe and Al-10Si-21Fe alloys achieved hardness of 400 HV 30 and compressive strength of ca. 1000 MPa; moreover, these materials exhibited quite a unique anomaly of the yield drop during the compressive test at elevated temperatures. The cobalt-based alloy represented by the Co 26Cr-6Mo-0,25C alloy showed an even higher hardness (650 HV 30) and compressive strength reaching 3100 MPa. The positive influence of short-term mechanical alloying was demonstrated by the first observation of quasicrystaline phase present in the Al-24Cu-13Fe alloy, which arose after 90 minutes of the process. The procedures mentioned can be used even to prepare the Ni-Ti alloys, till now usually prepared by vacuum induction or arc melting, with required phase compositions and intensively refined microstructure with a very low value of porosity.
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