Effect of Zr and Mg on microstructure and fracture toughness of Nb-Si based alloys

The alloy ingots with the compositions of Nb-16Si-22Ti-3Cr-3Al-2Hf (at.%) and Nb-16Si-22Ti-3Cr -3Al-2Hf (at.%)+1.5at%Zr+0.01 at.%Mg were prepared by the electric arc melting technique. The ingots were heat treated in argon atmosphere at 1450 °C for 100 h and with furnace cooling. The phases in the two alloys were investigated by X-ray diffraction (XRD), and the result showed that the main phases in both alloys were Nbss and Nb ₅Si ₃. The microstructure of the two alloys was determined by electro probe micro analyzer (EPMA). The results showed that the amount of large Nb ₅Si ₃ blocks in the alloy with the addition of Zr and Mg was obviously less than that in the alloy without Zr and Mg, and the small Nb ₅Si ₃ particles surrounded by Nbss matrix existed in both alloys. The results of the fracture toughness tests indicated that the room temperature fracture toughness of the alloy with the addition of 1.5 at.%Zr and 0.01 at.%Mg was about 30% higher than that of the alloy without Zr and Mg. The propagation behavior of the cracks was also studied in the present investigation.