Mechanical crystallization of Fe-based amorphous alloys

Abstract

Mechanical alloying of a number of blended elemental powders of Fe-based alloy systems containing four or five components was undertaken to determine if amorphous phases could be produced and also to compare the glass-forming ability achieved by mechanical alloying and that obtained by solidification-processing methods. Amorphous phase formation was achieved in all the alloy systems investigated, the time for the amorphous phase formation being a function of the glass-forming ability of the alloy system investigated. However, in some alloy systems it was noted that on milling, beyond the time required for the formation of the amorphous phase, the amorphous phase started to crystallize, a phenomenon designated as mechanical crystallization. The present paper specifically discusses the results of mechanical crystallization obtained in the Fe 42 Ge 28 Zr 10 B 20 and Fe 42 Ni 28 Zr 10 C 10 B 10 alloy systems as representatives of the typical quaternary and quinary ͑five-component͒ systems, respectively. In the case of the quaternary system, mechanical crystallization led to the formation of a supersaturated solid solution of all the solute elements in Fe, while in the quinary system, a mixture of the solid solution and intermetallic phases has formed. The possible reasons for mechanical crystallization and the reasons for the differences in the behavior of the quaternary and quinary systems are discussed.

Microstructural evolution characterization of Fe–Nb–B ternary systems processed by ball milling

“…However, very long milling could imply recrystallization processes [22]. Results obtained in the present work show that even far beyond the time considered for stationary state using global techniques B inclusions are detected.…”

Influence of milling time on microstructure and magnetic properties of Fe80P11C9 alloy produced by mechanical alloying

“…3) and total area of the main diffraction peak. As the figure indicates, the fraction of the amorphous phase abruptly increases up to 30 h of milling, then gradually increases up to 90 h of milling and finally decreases by increasing the milling time up to 120 h. The observed mechanically-induced amorphization for the current alloying system is attributed to different mechanisms, such as severe plastic deformation, grain refinement and particularly, the increase in the strain energy due to significant size difference between the constituent atoms [13,24]. Such parameters can increase the free energy of the crystals beyond that of hypothetical amorphous phase and consequently decreases the energy barrier for crystal-to-amorphous transformation [13,24,36].…”

“…The mechanically-induced crystallization and the formation of different phases including solid solutions and intermetallic compounds has been observed for other mechanically alloyed Fe-based amorphous powders [24,37]. It has been demonstrated that the temperature rise upon milling, powder contamination, introduction of mechanical energy and the corresponding variations in the thermodynamic stabilities of the different competing phases are the main causes of mechanical crystallization [13,24]. Moreover, it has been shown that the atomic displacement and enhancement of atomic mobility as a result of severe deformation upon milling contribute to deformation-induced crystallization [38].…”

“…It is obvious that the ball milling of the powders beyond 90 h gives rise to formation of small amount of Fe 2 P nanocrystals, as a result of mechanically-induced crystallization. The mechanically-induced crystallization and the formation of different phases including solid solutions and intermetallic compounds has been observed for other mechanically alloyed Fe-based amorphous powders [24,37]. It has been demonstrated that the temperature rise upon milling, powder contamination, introduction of mechanical energy and the corresponding variations in the thermodynamic stabilities of the different competing phases are the main causes of mechanical crystallization [13,24].…”

“…This process is capable to produce amorphous powders in diverse alloy systems, even when they are far from the eutectic composition or they consist of elements with positive heat of mixing [13]. It has been reported and demonstrated that the glass formation occurs during MA in some of the Fe-based alloying systems like Fe-B [17,18], Fe-Si-C [19], Fe-Cr-Mn-N [20], Fe-Ni-(Zr,Nb,Ta)-B,C [21][22][23], FeGe-Zr-B [24], Fe-Al-P-C-B [25], and Fe-Nb-B [26].…”