Fabrication and mechanical properties of ultra-fine grained gamma-Ni-20Fe/Al_2O_3 composites

摘要

High-dense (relative density D > 98 percent) ultra-fine grained gamma-Ni-20Fe/Al_2O_3 composites were fabricated by using a mechano-chemical process plus hot-pressing. Microstructure investigations revealed that fine gamma-Ni-20Fe particles with the dimensions of several hundreds of nanometers dispersed homogeneously at the matrix grain boundaries. Mechanical tests indicate that fracture toughness increases monotonously from 4.7 MPa m~(1/2) for monolithic alumina to 8.4 Mpa m~(1/2) for approx 19 vol. percent Ni-20Fe/Al_2O_3 composites. Fracture strength af increased with addition of Ni-20Fe phase as Ni-20Fe content was low (<5 vol. percent). However, sigma_f decreased with further increase of Ni-20Fe content, exhibiting a maximum strength of approx 600 MPa at approx 5 vol. percent Ni-20Fe. The improvement of the mechanical properties could be ascribed to the microstructure refinement of the composites and increase of cracking resistance introduced by the dispersed Ni-Fe phase, which was supported by fracture characteristic observations.