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Microstructure studies of ball milled and vacuum hot pressed NiZrTiAl powders

Dutkiewicz J., Maziarz W., Litynska L., Molnárová M., Kováčová A.

Archives of Materials Science and Engineering

2007

Vol. 28, nr 11

645-648

Purpose: To determine microstructure and hardness of hot pressed mechanically alloyed MA NiZrTiAl powders well known as a good glass formers. Design/methodology/approach: Powders has been ball milled r 40 hours starting from pure elements. Changes of particle's size and crystallographic structure of nanocrystals embedded in the amorphous matrix during milling has been determined using High Resolution Transmission Electron Microscopy HRTEM. Findings: The MA particles first grow, then decrease after 40 hours of milling, when powders possess amorphous structure. HRTEM studies of powders allowed to reveal small nanocrystals of NiTi2 within milled powders which were not detected using X-Ray diffraction. The powders show crystallization peak at temperature Tx near 553*C. Consolidation of powders was performed under vacuum using uniaxial hot pressing method at temperature slightly below Tx. Mean microhardness was determined near 430 HV and the mean Young's modulus as 81 GPa. Practical implications: It was shown a possibility of hot densification in vacuum of amorphous Ni base alloys allowing to obtain bulk amorphous compacts with embedded nanocrystals. Originality/value: The size and structure of nanmocrystals within the amorphous matrix after MA and after hot vacuum densification has been determined. The microhardness and Young's modulus of compacts show perspectives of application of such materials.