Nanoindentation behavior of nanostructured bulk (Fe,Cr)Al and (Fe,Cr)Al-Al2O3 nanocomposites

Abstract

The purpose of the present study was to design a new generation of FeAl-based intermetallic compounds with improved mechanical and oxidation properties. Synthesis of powders of FeAl, (Fe,Cr)Al and (Fe,Cr)Al in situ composites with 5 and 10% Al2O3 contents was reported elsewhere. In this paper the sintering behavior is reported. FeAl, (Fe,Cr)Al and (Fe,Cr)Al - Al2O3 powders were sintered by a hot-pressing method at 1600 °C and 5.5 GPa for 15 min to produce bulk specimens for mechanical and microstructural characterization. Microstructural characterization by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) of theses nanocomposites disclosed uniform distribution of Al2O3 nano-particles. XRD analysis indicated the presence of FeAl, (Fe,Cr)Al and Al2O3 phases. The presence of nano-sized Al2O3 particles effectively retarded grain growth by pinning the grain boundary during hot pressing. Nanoindentation tests indicated that with increasing content of Cr and Al2O3 reinforcement, the hardness and Young's modulus increased, and the fracture toughness reaches a high value of 19.6 ± 0.4 MPa m1/2 for the (Fe,Cr)Al-10%Al2O3 composition, with a hardness value of 21.7 ± 1.8 GPa. Nanoindentation creep tests at room temperature showed that composites with Al2O3 nanoparticles had higher creep rate than FeAl and (Fe,Cr)Al. It was found that improvements in the mechanical properties of FeAl intermetallic compound can be achieved by adding Cr and uniform distribution of Al2O3 nanoparticles.