Nano-scaled microstructure evolution of W-Ni-Fe-Co heavy alloy by mechanical alloying

The composition of 93W-3.0Ni-2.0Fe-2.0Co and 93W-3.5Ni-l.5Fe-2.0Co heavy tungsten alloys were selected for investigating the microstructure evolution of powder synthesis by mechanical alloying (MA) with Spex mill and Vibratory mill, respectively. The microstructure characterization of the MA powders was conducted by means of SEM, TEM and XRD techniques. The results reveal that the particle size of the alloy powder reaches about 2-3 urn when the heavy tungsten alloy mechanically alloyed 8 hours by Spex mill or 72 hours by Vibratory mill, respectively. In addition, the inner crystal size was found to be a nano-scaled cell structure with the dimension about 16nm. The sequence of microstructure evolution of these two heavy tungsten alloys by mechanical alloying was revealed as: the mixture of pure elements→micro-structured bcc solid solution7rerr; nano-structured bcc solid solution. The result of these refined heavy tungsten alloy powders after cold isostatic pressing (CIP) and solid phase sintering also verified the effect of nano-structured powders on decreasing the sintering temperature as well as increasing the densification.