Mechanically induced instability in Fe2Ti and mechanical alloying of Fe and Ti

Mechanical alloying (MA) of Fe and Ti elemental powder mixtures has been reported in studies mainly related to the preparation of nanocrystalline FeTi intermetallic compound [1–8]. In all these studies amorphous and/or nanocrystalline phases have been reported as end products of the milling process. The atomic composition 2Fe:1Ti has received less attention. For this composition the formation of amorphous phase on milling has been reported [2]. The amorphous phase was characterized by a broad X-ray diffraction peak and its crystallization was observed on heating above 800 K [2]. A more recent paper on mechanical milling (MM) of Fe2Ti reports the occurrence of certain structural disorder in the C14 hexagonal structure of this Laves phase but without the formation of an amorphous material [9]. The structural disorder is related to the occurrence, under milling, of planar defects such as stacking faults. According to X-ray diffraction (XRD) annealing at 873 K of this disordered phase restores the crystal structure of Fe2Ti. However, from theM¨ossbauer spectrum of the annealed of MM Fe2Ti sample about 5% of bcc iron is reported [9], which could be interpreted as an incipient decomposition process of Fe2Ti due to the milling process. In that case, on prolonged milling a higher amount of bcc ironwould be formed. In this contribution we report the resulting intermediate and end products of 2Fe:1Ti elemental mixtures and Fe2Ti powder samples when they were submitted to prolonged milling. In both cases in the end products a solid solution of Ti in α-Fe, α-Fe(Ti) (bcc), was detected. The intermetallic compound Fe2Ti was prepared by melting the appropriate mixture of elemental Fe (99.9% nominal purity) and Ti (99.9%) coarse powders in an electric arc-furnace under an argon atmosphere. After melting, the alloy was sealed in a quartz tube filled with argon and then annealed for 48 h at a temperature of 1173 K to aid homogeneity and crystallinity. Its elemental and phase composition was determined using energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD), respectively. Prior to milling, the Fe2Ti ingot was cut into small pieces using a diamond saw. The powder resulting from the cutting process was collected and used as representative of the starting Fe2Ti sample (without milling)