Research status of Nb2O5 and Al coatings

       Wang Deqing et al. used differential scanning thermal analysis to study the in-situ reaction process of the A1-Nb2O5 system in the study of in-situ reaction preparation of particle-reinforced aluminum matrix composites. Mix 20wt% of Nb2O5 and Al powder on a vibrating rotary mixer for 6 hours, then cold-extrude it into a φ10mm×5mm sample under a pressure of 100MPa, and analyze the phase change during the reaction under the protection of argon by X-ray diffraction It is found that when the temperature reaches 650℃, the diffraction peak of Nb2O5 begins to weaken; it gradually decreases as the temperature further increases. When the temperature increased to 850℃, all the diffraction peaks of Nb2O5 disappeared, and the diffraction peaks of NbAl3 and Al2O3 appeared. The amount of NbAl3 and Al2O3 increases with the increase of temperature, but after 950℃, the amount of NbAl3 and Al203 basically does not change. This shows that the reduction of Nb and the formation of NbAl3 intermetallic compounds occur below the melting point of Al and complete at 939°C. At low temperatures, a small amount of in-situ reaction occurs locally in the sample; the simultaneous in-situ reaction in the entire sample is in the temperature range covered by the exothermic peak at 939°C.



SeottlM.Maurer et al. studied the acidity of Nb2O5/Al203 supported on silica by wet-impregnating Davjson952 silica (BET surface area -300m2/g) with a hexane solution of niobium ethoxide and s-butadiene alumina. The Nb2Os/Al203 sample supported by silicon oxide was heated to 1273K at a rate of 10K/min in flowing He (3L/h) for high temperature treatment, and XRD was used to detect the formation of AINbO4. Related literature reports that the Nb2O5/Al203 mixed oxide containing 50mol% niobium oxide has all the acid sites disappeared after the stoichiometric AINbO4 was formed.



Yang Zhibo and others analyzed the hot-pressing reaction process of Ti-Al-Nb205 system through DSC, XRD and related thermodynamic calculations. The results show that Al3Ti appears as the primary phase with the melting of Al at 700℃, and the substitution reaction between Nb205 and Al has not yet begun; when the temperature rises to 900℃, the TiAl phase has already existed stably as the main phase, and Al The reaction with Nb2O5 is also in progress, and the A2O3 produced by the replacement as a reinforcing phase exists in the material in the form of particles; the temperature continues to rise, and at 1100℃ the primary phase Al3Ti reacts with excess Ti further to form stable TiAl and TisAl phases. In the material; after 1h hot press sintering at 1100°C, the reaction of Al and Nb2O5 has also proceeded completely. Therefore, 1100°C is the optimal temperature for the reaction of the Ti-Al-Nb2O5 system, and the Al2O3-reinforced TiAl composite material was synthesized by in-situ reaction in a relatively short time. The substitution reaction of Al and Nb2O5 is mainly concentrated in the temperature range of 900~1100℃, and the reaction is carried out step by step.



Wang Fen and An Shiwu use the thermite reaction of Al and Nb205 to generate Al2O3 particles in situ to strengthen the high-niobium TiAl intermetallic compound. Relevant literature shows that the reaction free energy △G is the lowest when Nb2O5 reacts with Al to form NbO2, so the reaction is the easiest to proceed. During the reaction, part of Al is oxidized by replaced oxygen to form Al2O3; at the same time, the generated Nb reacts with part of Al to form NbAl3 Therefore, the Al content in the system is reduced, and the relative content of Ti is increased, and the resulting Ti3Al phase is increased accordingly. Therefore, the amount of niobium oxide introduced plays a role in regulating the relative content of TiAl and Ti3Al in the matrix phase. The contribution of the introduction of Nb element to material properties can be summarized into the following two aspects. First, it promotes the formation of adjustable dual-phase alloys, which contributes to the plasticity and strength of materials. When the second phase (Ti3Al) dispersed in the intermetallic compound (TiAl) is softer than the matrix, due to the gravitational interaction between the moving dislocation and the precipitated phase, the room temperature strength of the alloy is not only improved, but the high temperature strength is also improved. . Therefore, dual-phase alloys have great potential for development. At the same time, Nb is the element with the best effect to improve the plasticity of Ti3Al, and double 48% Al has the highest plasticity.



Zhu Ling, Huang Zhaohui and others used rutile, quartz and aluminum powder as the main raw materials to prepare corundum composite materials through reduction and nitridation at a temperature of 1500 ℃. They studied the thermal shock of the samples under the conditions of adding different powder contents and different sintering aid contents. The magnitude and rate of change of the residual flexural strength before and after the study showed that with the increase of the aluminum powder content, the change trend of the residual flexural strength of the sample after thermal shock is consistent with the change trend of the flexural strength of the sample before thermal shock. It increases with the addition of aluminum powder, and the strength retention rate is higher than 65%. The sample with 10% aluminum powder over the theoretical amount has relatively optimal thermal shock resistance; with the addition of sintering aid The change trend of residual flexural strength of the sample after thermal shock is roughly the same as that before thermal shock. At the same time, the strength retention rate of the sample with Y203 and La2O3 is higher than 69%, and the sample with 2.5% (Y203+La2O3) is added. It has relatively better thermal shock resistance; the fibrous, spine and long columnar crystals in the sample help to improve the thermal shock resistance of the material.



Wu Jiang et al. prepared aluminum niobate/mullite composite ceramic environmental barrier coatings on SiN substrates using atmospheric plasma spraying technology. The molar content of AlNbO4 in the feed was 5%, and the coating was placed at 1400℃. In an atmosphere of water vapor and air (half the volume), it will corrode for 100h, and the total pressure will be 1×105Pa. During the experiment, AlNbO4 formed a glass phase protective layer on the surface of the coating, which improved the corrosion resistance of the coating. However, due to the large difference in thermal expansion coefficient between the coating and the silicon nitride substrate, the coating was in the process of the experiment. Slight peeling occurred.