Microstructure and high-temperature mechanical properties of Nb-silicide based in-situ composites

Nb-15W-18Si-xHf （x = 0, 5, 10 and 15, mole fraction, %） alloys were prepared by arc melting and then homogenized at 1 750 ℃ for 50 h. The microstructure and mechanical behaviors, such as Vickers hardness, fracture toughness, room- and hightemperature strength of the alloys were investigated. The microstructure of the annealed Nb-15W-18Si-xHf alloys is composed of large primary Nbss dendrite and fine eutectic mixture of Nbss and MsSi3 silicide. Both the hardness and the fracture toughness show an increase tendency at room temperature with increase of Hf content. The 0.2% compressive yield strength, σ0.2 of the alloys with 5 %Hf and 10%Hf are larger than 960 MPa at 1 200 ℃, and about 500 MPa even at 1 500 ℃.     

从2G网优经验看3G网络的优化

3G网络优化既有与2G网络优化相同的一面,也有其特殊的方面,因此本文主要从2G出发来分析3G网络的优化,主要借鉴2G网络优化的经验对3G的无线网络的优化进行分析。     

High-temperature oxidation behavior of Nb67-xW15Si18Hfx（X=0.5 and 10） alloys

The oxidation behaviors of Nb67-xW15Si18Hfx （x=0, 5, 10） alloys were studied at 1 250 ℃ in air. It is found that the Nb67W15Si18 alloy has the best oxidation resistance among the three alloys; and Hf addition is harmful to the oxidation resistance of the Nb67W15Si18 alloy. The oxides formed on the Nb67W15Si18 alloy are mainly Nb12WO33 and NbO2, and that on the Nb62W15Si18Hf5 and Nb57W15Si18Hflo alloys is Nb2O5. Effect of Hfon the oxidation behavior of the Nb67-xW15Si18Hfx alloys has been discussed based on mierostructures and kinetics of oxidation.