Ultrasonic evaluation of the morphological characteristics of metallic powders in the context of mechanical alloying

• An ultrasonic method is presented for elastic probing of metallic powders.
• A non-monotonous variation of elastic parameters of powders at different stages of milling is revealed.
• We show that loose-packing elastic parameters are mostly influenced by the polydispersity.
• Our study provides some prospects for future numerical simulations and for the development of more advanced granular elasticity models.

An ultrasonic method is proposed to characterize the morphological (geometrical) aspects of powders through the elastic modulus dependence of their packing on the factors of polydispersity, coordination number and particle shape. During the mechanical alloying process, the variation in geometrical characteristics of powders provides critical information. Ultrasonic parameters are shown to be sensitive not only to the average contact number per bead (i.e. the coordination number) but also to characteristics of the bead size distribution, when given the same sample preparation and confining pressure. These parameters, in turn, are sensitive to both the granular medium polydispersity and particle shapes. A non-monotonic behavior of the ultrasonic velocity (and of the derived compressional wave modulus) is observed throughout the alloying process, which thus offers possibilities for powder structure monitoring.