دکتر مرتضی قدیمی

In this research, the method of mechanical alloying and subsequent sintering has been used to obtain Zr-based MAX Phases compounds with nanocrystalline structure. For this purpose, a stoichiometric mixture of high purity elemental powders of ZrH2, Al and C (Graphite) was subjected to intense mechanical alloying in a planetary high energy ball mill under different milling conditions (5, 10, 20, 40 and 60 h). The fabricated compounds were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and microhardness measurements. Experimental results exhibited that after an optimum milling time of 40 h, Zr2AlC MAX phase with the crystallite size of less than 25 nm and high microhardness of 971 HV can be obtained. Also with milling time, morphology of pre-alloyed powders changed from lamella to globular. Sintering of milled powders at 1300 °C for 2 h resulted in the production of nanometric Zr3AlC2 and Zr4AlC3 MAX phases, increase the crystallite size (grain growth), and release of internal strain. The results revealed that this route (high energy milling followed by sintering) is a powerful, cost effective and high productive technique for preparing Zr-based MAX phases compounds with nanometric structure and homogenies morphology.

NiTiCu intermetallic compound with nanocrystalline structure was successfully synthesized through mechanical alloying and subsequent annealing process. The X-ray diffraction (XRD) analysis revealed that after 60 h milling of high purity elemental powders mixture of Ni، Ti and Cu via a planetary high energy ball milling، the Cu dissolved into B2 structure and NiTiCu phase was obtained. Annealing of as-milled powders at 1173 K for 15 min leads to formation of nanometric NiTiCu (B19'') phase، grain growth and release of internal strain. Structural characterization was examined by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. The results demonstrated that this route result in preparation compounds with suitable morphology and homogeneous structure. Formation of nanometric structure enhances thermoelasticity and shape memory behavior in this compound by narrowing the thermal hysteresis.