Mechanical Alloying and Powder Consolidation in SiC and Hydoxyapatite

Abstract

The reaction ball milling can produce the solid state amorphization of covalent ceramic, SiC, including the mechanical alloying (MA) of the elemental crystalline powder mixture of Si and C and the mechanical grinding (MG) of the commercial β-SiC particle and MG of the nanocrystalline β-SiC powder as synthesized via ’high-energy’ MA. An increase in amorphous volume (X) by decreasing crystallite size (d) during MG is expressed by a relation of X= 1-{d/(d+∆)}3 with the intercrystal thickness (∆) of 1 nm. The rotating-arm reaction ball milling is used to synthesize nanocrystalline (nc) hydroxyapatite by MA of the powder mixture at 303 K, according to a reaction of 6CaHPO4･2H2O+4Ca(OH)2→nc-Ca10(PO4)6(OH)2+8H2O with JMA exponent of 1. By employing the pulse electric discharge consolidation, the amorphous SiC powder compact shows a rapid densification during Newtonian viscous flow as expressed by an Arrhenius relation with the activation energy of 495 kJ･mol-1, and then obtain the full densification at 2033 K under 100 MPa. The nanocrystalline hydroxyapatite powder with the crystallite size of 8 nm can be consolidated at full-density at 1023 K under 150 MPa, following a rapid shrinkage during superplastic flow from 900 K. The fracture toughness (KIC), as deduced from the indentation microfracture method, is the high level of 13 MPa･m0.5 for nanocrystalline SiC with 12 nm.