Microstructure mechanical behavior and thermal stability of in situ polymer derived ceramic reinforced Al based composites

Abstract

Al-based metal matrix composites (MMCs) show a high strength-to-weight ratio which makes them attractive for the aerospace and automobile industries. The reinforcements for the same have conventionally been micron-sized ceramic particles (ex-situ MMCs). These MMCs show high strength, elastic modulus, and resistance to wear. However, there is also a severe reduction in their ductility. These MMCs also do not possess strong particle-matrix interfaces which adversely affect the ductility. If the particle-matrix interface is strong, ceramic nanoparticles, when used as ex-situ reinforcements, have shown improvement in strength and relatively lower loss in ductility as compared to using micro-particles. However, these nanoparticles, tend to agglomerate which deteriorates the mechanical properties. Additionally, they are also expensive and can be hazardous to health during handling. Polymer Derived Ceramics (PDCs) based composites can potentially overcome these shortcomings. Such ceramics are obtained from the preceramic polymers after pyrolysis. These polymers are inexpensive, can be fragmented to the nanoscale, and pyrolyzed in-situ within the matrix. Initially, friction stir processing (FSP) was used to fragment and disperse the polymer within an Al-Mg alloy. The PDC particles pinned the dislocations and grain boundaries. The composite exhibited a microstructure resulting from continuous dynamic recrystallization aided by the PDC particles. It also exhibited both high strength (96% and 24% improvement in the yield and ultimate tensile strength (UTS), respectively) and good ductility (18%)... newline