- Chezheng Cao, The University of California, Los Angeles
Solidification processing of metals, such as casting, welding, and laser-based additive manufacturing, is of paramount significance for the mass production of high-performance metals and alloys, which offer tremendous potential to improve energy efficiency and system performance for numerous applications. Effective phase control during solidification is vital to yielding desired microstructures with enhanced performance for materials. However, conventional phase control methods have gradually encountered certain technical and/or fundamental limits. Recent studies start to show that the integration of emerging nanotechnology and conventional metallurgy provides new opportunities to break these limits. The speaker will present work on processing of bulk metal matrix nanocomposites and nanocomposite powders through a novel molten-salt-assisted incorporation method and then will focus on the studies of nanoparticle-enabled phase control in solidification processing of Al and Cu alloys. The results revealed that nanoparticles are very effective to control the grain size of primary phase and the morphology, size, and distribution of the secondary phase, breaking the existing limits of processing metals. Specifically, a new discovery that nanoparticles can refine primary metal grains to ultrafine (< 1 μm) or even nanoscale during regular casting process (cooling rate < 100 K/s) and can deliver exceptional thermal stability and mechanical properties will be discussed. In addition, nanoparticle-assisted casting of immiscible Al-Bi alloy for self-lubricating bearings, welding of Al 7075 alloy (which is susceptible to hot cracking), and laser processing of Al-TiC nanocomposites will be introduced. These findings pave a new pathway to further promote the solidification processing of metals to the next level. In summary, possible applications of this nanoparticles enabled phase control approach on development of high temperature Al alloys for additive manufacturing will be proposed.