Effect of trace Zn, P and Mg additions on microstructure and mechanical properties of Nb-Si-Ti alloys

The effects of Zn, P and Mg additions on the microstructure and mechanical properties of Nb-22Ti-3Si alloys were studied. The phases of Nbss and Nb3Si presented in Nb-22Ti-3Si (AC1), Nb-22Ti-3Si-0.2Zn (AC2) and Nb-22Ti-3Si-0.2Mg alloys (AC3). The Nb-22Ti-3Si-0.2P (AC4) alloy consisted of Nbss, Nb3Si network and eutectic cell of Nbss/alpha-Nb5Si3. By the addition of Zn, the Nb3Si network was broken and the volume fraction of Nbss increased from 92% to 96%. The values of fracture toughness of the alloy AC2 at ambient temperature increased from 22.58 MPa.m(1/2) to 26.41 MPa.m(1/2). The values of compressive strength for the Zn-added alloy at ambient temperature and 1 250 degrees C increased from 1 525.10 MPa to 1 652.44 MPa, and from 268.52 MPa to 284.18 MPa, respectively. Compared with the alloy ACI, the addition of P promoted the formation of alpha-Nb5Si phase but the values of fracture toughness and compressive strength of alloy at room temperature and 1 250 C decreased. In contrast, the addition of Mg improved the compressive strength at ambient temperature and 1 250 degrees C from 1 525.10 MPa to 1 618.08 MPa and from 268.52 MPa to 348.28 MPa, respectively. The relationship between the microstructure and the mechanical properties was discussed.