Polymer derived ceramic materials from Si,B and MoSiB filler-loaded perhydropolysilazane precursor for oxidation protection

Silica-based coating systems were developed using polymer derived ceramics (PDCs) technology. Ceramic composites on the base of a SiO₂ and SiNO matrix and homogeneously distributed Mo₅SiB₂, SiB₆, Si and B fillers were manufactured. The coating systems have low porosity and provide a high oxidation resistance up to 100 h at 800 °C and 1100 °C in air. The influence of temperature and atmosphere of pyrolysis on the polymer precursor, the volume fraction of filler materials on the chemical composition of compacts as well as their high-temperature oxidation protection was investigated.     

Synthesis of Mo5SiB2 based nanocomposites by mechanical alloying and subsequent heat treatment

In this study, systematic investigations were conducted on the synthesis of Mo₅SiB₂-based alloy by mechanical alloying and subsequent heat treatment. In this regard, Mo-12.5 mol% Si-25 mol% B powder mixture was milled for different times. Then, the mechanically alloyed powders were heat treated at 1373 K for 1 h. The phase transitions and microstructural evolutions of powder particles during mechanical alloying and heat treatment were studied by X-ray diffractometry and scanning electron microscopy. The results showed that the phase evolutions during mechanical alloying and subsequent heat treatment are strongly dependent on milling time. After 10 h of milling, a Mo solid solution was formed, but, no intermetallic phases were detected at this stage. However, an α-Mo-Mo₅SiB₂ nanocomposite was formed after 20 h of milling. After heat treatment of 5 h mechanically alloyed powders, small amounts of MoB and Mo₂B were detected and α-Mo-MoB-Mo₂B composite was produced. On the other hand, heat treatment of 10 h and 20 h mechanically alloyed powders led to the formation of an α-Mo-Mo₅SiB₂-MoSi₂-Mo₃Si composite. At this point, there is a critical milling time (10 h) for the formation of Mo₅SiB₂ phase after heat treatment wherein below that time, boride phase and after that time, Mo₅SiB₂ phase are formed. In the case of 20 h mechanically alloyed powders, by increasing heat treatment time, not only the quantity of α-Mo was reduced and the quantity of Mo₅SiB₂ was increased, but also new boride phases were formed. Finally, after 5 h heat treatment, the Mo phase completely disappeared and a Mo₅SiB₂-based composite was completely formed.     

Mo-Si-B系材料的性能及制备

综述了Mo-Si-B系材料的研究进展。主要就材料在各种环境中的氧化性能、单相和多相材料的力学性能、材料的电学性能和热学性能等方面的研究进展进行了介绍。通过无压烧结方法,在1600℃合成了7种不同原料配比的Mo-Si-B系材料。用X射线衍射仪分析了材料的物相组成,确定了最佳的B与Si的原子比为0．865。但是无压烧结法得到的材料致密度不够,还需要对合成工艺作进一步的研究。     

Mo—Si—B合金的制备及性能研究现状

综述了Mo—Si—B合金的研究现状,分别从制备工艺、抗氧化性、断裂韧性、微观结构等方面进行了综述。Mo—Si—B合金可以作为新一代的航空发动机用结构材料和高温抗氧化涂层材料。研究表明,Mo—Si—B合金具有更加优异的高温力学性能和高温抗氧化性能。最后讨论了Mo—Si—B合金未来的发展方向。     

Mo-Si-B系原位复合材料的研究

Mo-Si-B系原位复合材料是一族新型的高温结构材料,目前的研究主要集中在其中的α-Mo Mo3Si Mo 5SiB2(T2)、Mo 5Si3Bx(T1) Mo3Si Mo5SiB2(T2)和Mo5Si3Bx(T1) MoSi2 MoB 3个体系.详细介绍了Mo-Si-B系原位复合材料的研究进展及应用前景,并在此基础上提出了进一步研究的重点和方向.     

High-Temperature Oxidation Resistance of Mo-Si-B Alloys with Different B ContentsEI北大核心CSCD

The oxidation behaviors of the Mo-Si-B alloy with B content in the range of 5% to 17% (atomic fraction) were experimentally investigated at temperatures ranging from 1000 degrees Cto 1300 degrees C. The microstructures and antioxidant mechanisms were also analyzed. Results showed that the oxidation behaviors were affected by both B content and oxidation temperature. The formation and growth process of oxidation film were mainly influenced by the B element which could improve the fluidity of surface glass phase and adjust the volume fraction and microstructure of alpha-Mo, Mo3Si and Mo5SiB2. The Mo-Si-B alloy with the B content increasing was favourable for quick forming and uniform covering by improving the mobility of the glass, but which decreased the oxidation resistance due to the sufficient liquidity of the oxidation film at high temperature. The oxidation resistance of the Mo-Si-B alloy is controlled by B content at low temperature and alpha-Mo content at high temperature, respectively. A large quantity of Mo5SiB2 phase and a small quantity of alpha-Mo phase existed in the high B content of Mo-12Si-17B alloy, which could promote the oxide layer to form rapidly but also cover uniformly under the temperature range of 1000 similar to 1300 degrees C. The discussion illustrates that the fine-grained microstructure combining with the distributed intermetallics is a specific role to ensure the excellent oxidation resistance of Mo-Si-B alloy.     

Mo-Si-B三元硅化物显微组织及氧化行为研究

采用电弧熔炼法制备了4种不同成分的Mo-Si-B合金，利用XRD和SEM-BSE对其显微组织进行了分析，以及利用TGA，XRD和SEM-BSE对其在1200℃的氧化行为进行了研究。显微组织分析表明：4种合金均由Mo，Mo5SiB2（T2），Mo3Si三相组成。氧化结果显示：死相含量最多的合金有最好的抗氧化性；在Si含量相同的条件下，具有共晶组织的合金抗氧化性最好。氧化后的合金由表面氧化层、中间层和基体组成。对表面氧化层的相结构进行了XRD和BSE分析，发现表面氧化层主要由非晶SiO2组成。     

Oxidation mechanism of W substituted Mo-Si-B alloys

The oxidation mechanism of a Mo₅₅W₁₅Si₁₅B₁₅ alloy was established, and the effects of W content, oxidation temperature and microstructural length scale were determined. In addition to influencing the oxidation mechanism, the addition of W also destabilized the A15 phase which is consistent with our previous experiments in ternary Mo-W-Si alloys [1]. Microstructural investigation of the oxidized alloy revealed entrapped tungsten oxides at temperatures below 1300 °C, which volatilize above 1400–1500 °C. The presence of WO₃ in the oxide scale interrupts the surface coverage by the glassy borosilicate, thereby adversely affecting the oxidation behavior. In order to determine the effects of length scale, the microstructural evolution during the transient oxidation of cast and sintered alloys, with different microstructural length scales, was studied at 1100 and 1400 °C. Finer microstructure promoted faster borosilicate surface coverage at 1400 °C.     

Ultra-high temperature Mo-Si-B alloys — Synthesis, microstructural and mechanical characterization

Molybdenum boron silicides containing between 18 and 31 vol.% α-Mo are prepared by reactive hot-pressing from Mo-Si-B powder mixtures. Their microstructures and mechanical properties are investigated. The multiphase alloys consist of Mo₃Si, Mo₅SiB₂ and discontinuous α-Mo. The results demonstrate that the volume fraction of α-Mo and B content exerts a significant effect on the flexural strength and fracture toughness of the multiphase alloys.