Effect of Water Washing Pre-treatment on the Properties of Glass-ceramics from Incinerator Fly Ash Using Electronic Arc Furnace

Production of glass-ceramics by sintering the molten slag obtained from electric arc furnace treatment of fly ash was investigated. The effect of washing pretreatment prior to melting the fly ash on the microstructure and properties of the glass-ceramics was examined. The results show that washing pretreatment of fly ash can decrease alkali metal chloride and increase network former in fly ash, which results in the increase of peak crystallization temperature of parent glass and strengthening of properties of bending strength and chemical stability of the glass-ceramics. The optimal heat treatment temperature for parent glass of washed fly ash is 1 173 K, at which the crystalline phase of glass-ceramics is composed of gelignite （Ca2A12SiO7） and akermanite （Ca2MgSi207）. Glass-ceramics produced at optimal heat treatment temperature are excellent in term of the physical and chemical properties and leaching characteristics, indicating attractive potential as substitute of nature materials.

Effects of B on the Microstructure and Oxidation Resistance of Nb-Ti-Si-based Ultrahigh-temperature Alloy

Nb-Ti-Si-based ultrahigh-temperature alloys concocted with boron ranging from 0 to 2 at% are prepared by arc-melting technology. The effects of adding boron on their as-melted microstructure and oxidation resistance are analyzed. The （Nb,Ti）ss, β-（Nb,Ti）5Si3 and γ-（Nb,Ti）5Si3 exist in Nb-22Ti-16Si-6Cr-3Al-4Hf alloy, while （Nb,Ti）ss, α-（Nb,Ti）5Si3 and γ-（Nb,Ti）5Si3 are present in Nb-22Ti-16Si-6Cr-3Al-4Hf-lB and Nb-22Ti-16Si-6Cr-3Al-4Hf-2B alloys. The oxidation of Nb-Ti-Si-based ultrahigh-temperature alloys is dominated by the diffusion of oxygen through （Nb,Ti）ss. Compared to boron-free alloys, the boron-containing alloys have significantly lower oxidation rate when oxidized at 1 200 ℃ for less than 50 h, but, for more than 50 h, their oxidation resistance deteriorates.

Mechanical properties and microstructure of in situ formed Ti_(2)AlN/TiAl(WMS)composites

The Ti_(2)AlN-reinforced TiAl(WMS)composites with different contents of Ti_(2)AlN were prepared by an in situ method of reactive arc-melting technique.According to the results of X-ray diffraction(XRD)analysis,the Ti_(2)AlNreinforced WMS composites consist ofγ-TiAl,α_(2)-Ti_(3)Al,and Ti_(2)AlN phases.Microstructure analysis results indicate that Ti_(2)AlN reinforcements with rod-like in shape form in the WMS matrix with aα_(2)/γlamellar structure containing some bulk y phases.With volume fraction of Ti_(2)AlN increasing,the grain size of the composites decreases significantly and the elasticity modulus(E)increases.The compressive strength and compressive fracture strain of the composite with 3 vol%Ti_(2)AlN have a maximum value of 1,654 MPa and 22.5%,respectively,which are approximately improved by 45.84%and 29.31%,respectively,compared with that of the unreinforced WMS alloy.

Microstructure, Mechanical Properties and Oxidation Resistance of Nb-22Ti-14Si-2Hf-2Al-xCr Alloys

Nb-22Ti-14Si-2Hf-2Al-xCr （x=2, 6, 10, 14, 17 at%） alloys are prepared by arc-melting under argon atmosphere. Microstructural characteristics, mechanical properties and oxidation resistance of the arc-melted alloys are investigated. At 2 at% Cr content, the microstructure is composed of Nbss, Nb3Si and a small quantity of Nb5Si3, when the Cr contents increase, Nb3Si disappears. For the high Cr content （x ≥ 10 at%） alloys, besides the Nbss and Nb5Si3, Cr2Nb is also detected. With the increase of Cr content, the volume fractions of Cr2Nb and Nb5Si3 increase, while that of Nbss increases firstly and then begins to degrade when the Cr content is higher than 6 at%. For the alloy with 2 at% Cr, the room temperature fracture toughness is about 14.5 MPa·m1/2, but badly decreases to about 8.5 MPa·m1/2, when the Cr contents increase. Vickers hardness of Nbss tends to increase linearly from about 400 to 500, while that of silicides is not sensitive to Cr contents, about 950. The appearance of Cr2Nb phase significantly improves the high temperature oxidation resistance of the alloys with high Cr contents. The isothermal oxidation tests show that the oxidation kinetics of the alloys with various Cr contents follows parabolic oxidation kinetics.