DYNAMIC SHOCK COMPACTION OF NANOCRYSTALLINE BULK MAGNETIC AND THERMOELECTRIC MATERIALS

摘要

Dynamic shock compaction using an 80-mm diameter single-stage gas gun at impact velocities of 600-1000 m/s, is used to fabricate bulk nanocomposite Pr_2Fe_(14)B/α-Fe magnets with exchange-coupled hard/soft phases, as well as bulk nanocrystalline thermoelectric half-Heusler TiNiSnSb alloys. Compacts Pr_2Fe_(14)B/α-Fe nanocomposite powders (synthesized by melt spinning) showed retention of ct-Fe grain size of ≤ 25 nm, which ensured exchange coupling between the hard and soft phases. Magnetic measurements revealed an energy product of～13.9 MGOe. Shock consolidated compacts of TiNiSn_(0.95)Sb_(0.05) alloy with grain size of 20-30 nm were also produced and shown to exhibit reduction in total thermal conductivity to about 5.5 W/m-K and a lattice conductivity of about 3.5 W/m-K at room temperature. In this paper, the unique attributes of shock densification for forming and retaining nanocrystalline structure, and therefore leading to significantly improved magnetic and thermoelectric properties will be described.