Structural aspect of chemical reaction between components of mechanically alloyed Al-MoO2 and Al-MoO3 composites

Mechanical alloying of aluminum powder with additions of 5 wt% MoO2 and MoO3 powders was used for producing Al-MoO2 and Al-MoO3 composites. Mechanical consolidation of as-milled composite powders was performed by means of preliminary pressing followed by the KOBO extrusion at 573 K and lambda = 44 cross-section reduction ratio. Dilatometry and differential scanning calorimetry tests at the temperature range of 293-973 K were performed to study the chemical reactions between composite components in the solid/liquid state. Structural observations revealed the presence of Al12Mo intermetallic grains that result from a combined chemical reaction between the matrix and reinforcements. The phase transformation was studied using X-ray diffractometry as well as transmission and scanning electron microscopy methods. Structural observations performed for as-extruded composites revealed similar microstructures for Al-MoO2 and Al-MoO3 composites. Residual, coarse aluminum powder grains were surrounded with a mixture of nano-sized structural components containing heavily refined molybdenum and aluminum oxides uniformly distributed within nano-grained aluminum matrix. Some unrefined molybdenum oxide particles were also locally observed. It was concluded that the utilized alloying time, 34 h, was not long enough to complete the milling procedure. (C) 2016 Elsevier B.V. All rights reserved.