Mo effect on the phase stability and room-temperature fracture toughness of Nb/Nb_5Si_3 in-situ composites

摘要

Nb/Nb_5Si_3 in-situ composites are very attractive structural materials because these materials perform a good balance in mechanical properties, including high strength at high temperature (>1000 deg C) and reasonably high fracture toughness at room temperature. Metastable phase Nb_3Si plays an important role in the properties of Nb/NbsSis composites by affecting the volume fraction of ductile phase. The addition of Mo affects on the microstructure of ductile phase and the stability of metastable phase Nb_3Si. In this paper, Nb-10Si-xMo and Nb-18Si-xMo (x = 0, 5, and 15) alloys were prepared by arc melting and annealed at 1473 K for 100 h. Single edge-notched bending (SENB) test was used to study the fracture toughness of Nb-Si-Mo alloys. The room temperature fracture toughness of Nb-10Si is 10.48 MPa centre dot m~(1/2) and higher than that of binary Nb-18Si alloys at near-eutectic composites. The addition of 5 at. percent Mo improved the fracture toughness of as-cast Nb-Si alloys from 4.1 MPa centre dot m~(1/2) to 9.99 MPa centre dot m~(1/2) at near-eutectic compositions and reduced it from 10.48 MPa centre dot m~(1/2) to 8.86 MPa centre dot m~(1/2) at hypoeutectic compositions.