The study of raw materials type on condition and production mechanism of nanocrystalline Zr-based MAX-phases

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.