High-Temperature Corrosion of AlN-Based Composite Ceramic in Air and in Combustion Products of Commercial Fuel. Part 2. Corrosion of Ceramic Composites in the AlN – SiC – TiB2 System in Air and in Combustion Products of Kerosene and Diesel Fuel

Corrosion resistance has been examined for composites in the AlN – SiC – TiB₂ ternary system. They have high corrosion resistance in air up to 1500°C because mullite and β-tialite are formed in the outer layer of scale. Their corrosion resistance substantially exceeds that of other ceramic materials because of the formation of the mullite phase on prolonged exposure (up to 200 h) to gaseous combustion products from kerosene and diesel fuel in the presence of sea salt at 900 and 1000°C. Also, AlN – SiC – TiB₂ ceramics have higher bending strength than does AlN – TiB₂ ceramic.     

AlN-W复合陶瓷的微波损耗研究

以AlN和W粉为原料,采用放电等离子烧结技术,在1 400～1 700℃、30MPa的工艺条件下制备了AlN-W复合陶瓷.采用扫描电镜、能谱分析仪、安捷伦精密阻抗分析仪4284A等对复合陶瓷的微观组织、介电常数、微波损耗进行了表征,研究了影响复合陶瓷微波损耗性能的因素.结果表明,AlN粉末颗粒细小、烧结保温时间增加,有...     

添加Y2O3的ZrO2增韧Al2O3陶瓷抗钢液腐蚀性能的研究

采用工业ZrO2和AlO3为原料,以Y2O3作为稳定剂,通过适当工艺制备出ZrO2增韧Al2O3(ZTA)陶瓷.主要研究了ZrO2和Y2O3稳定剂对ZTA陶瓷烧结性和抗钢液腐蚀性能的影响.实验结果表明:机械混合法引入的Y2O3在改善ZTA陶瓷的烧结性的同时,可以提高材料的抗钢液腐蚀性能;随ZrO2含量的增加,ZTA陶瓷的抗钢液腐蚀性能增强;材料中大量微裂纹的存在可以提高材料的韧性,但抗钢液腐蚀性能有所下降.     

氮碳化合物超细粉中氧的状态分析

用新开发的热抽取法，测定了超细粉中不同状态氧的含量。应用ＸＰＳ，ＡＥＳ和ＦＴ—ＩＲ表面分析技术鉴定粉末颗粒中氧的物种和分布。探讨了Ｓｉ３Ｎ４，ＡｌＮ，ＴｉＣＮ和ＳｉＣ超细粉中各状态氧含量与样品制备工艺、颗粒度及放置时间的关系。     

Manufacturing of Reinforced High Precision Forging Dies

The economical production of near‐net‐shape forging parts with the highest accuracy requires high precision dies with the lowest wear. Compared to metals, ceramics show an outstanding high wear and corrosion resistance accompanied by high thermal durability, which favours their application to hot forging. However, ceramics can not endure tensile stresses. In order to enhance die life, small ceramic inserts can be integrated into the steel die body by brazing, placed within the wear critical areas. In addition to this, alternative methods from the field of surface coating are introduced for reinforcing dies. On the other hand, thin Ti‐containing deposits from the gaseous phase, PVD‐ or PACVD, can increase the wear resistance when applied as a multilayer structure. An added top layer of TiBN or TiB₂ finishes the described batches of TiN‐TiCN‐TiC layers. Results are presented incorporating the expertise of material science, metal forming and production engineering. This includes the development of reinforced forging dies, their design and manufacture by active metal brazing of ceramic inlays or coating processes as well as investigations regarding the grinding of steel‐ceramic composite dies. The latter include parameter studies as well as grinding wheel development by performing thorough investigations of the wear mechanisms which lead to adapted and material‐specific grinding strategies.     

Reaction of Composite Ceramic Materials with Corrosionally Active Media

The oxidation of composite powders and monolithic AlN SiC, AlN SiC TiB₂, and AlN SiC ZrB₂ ceramics in air up to 1600°C was studied by the methods of thermogravimetric, differential thermal, x-ray diffraction, and electron-probe microanalysis. The exceptionally high corrosion resistance of these materials was established. The corrosion resistance and possibility of using structural ceramics of the systems TiB₂ AlN, TiB₂ TiN, and TiC_0.5N_0.5 in sea water was demonstrated. The toxicity of Si₃N₄, AlN, BN, and TiN powders was analyzed on the basis of their reactions with biochemical media. It was proven that TiN based materials are highly stable in the oral cavity.     

Surface Modification of AL9 Alloy by Electric-Spark Alloying with Materials of the AlN – Ti(Zr)B2 – Ti(Zr)Si2System

Using x-ray phase, electron-probe microanalysis, and scanning electron microscopy, we have established that heterophase coatings based on an aluminum matrix with a quasi-layered finely dispersed structure reinforced with titanium (zirconium) diboride and borosilicide, and aluminum nitride (alloyed with oxygen) are formed by electric-spark alloying of AL9 alloy with A1N – Ti(Zr)B₂ – Ti(Zr)Si₂ composite ceramics. The wear resistance of the A1N – ZrB2-based coating approached that of the ceramic itself with the sliding speed increased to V ≥ l m/sec. The formation of secondary structures of oxide solid solutions on the coating surface during tribooxidation was investigated.     

Effect of Y2O3 and Dy2O3 on Microstructure and Mechanical Behaviors of Aluminum Nitride Ceramics

The effects of two types of additives, Y2O3 and Dy2O3, on the sintering and mechanical behaviors of AlN ceramics were investigated. The experimental results show that the sintering temperature can be decreased and the mechanical behavior can be improved by adding rare earth in AlN ceramics. The strength of AlN ceramics with Y2O3 and Dy2O3 are 326 and 320 MPa, respectively, which are 97.6% and 93.9% higher than the un-doped AlN ceramics. The fracture behavior on the fracture surfaces of rare earth oxide AlN ceramics was found to be a mixed mode of transgranular fracture and intergranular fracture. As a result, it is concluded that the improvement of bending strength of AlN ceramics with Y2O3 and Dy2O3 addition are mainly achieved by strengthening the grain boundary.     

直流等离子渗氮法对纯铝耐腐性的改善——时间和温度的影响

为了提高铝的耐腐蚀性能,在氮氢混合物（PN2/PH2=4/1）等离子体中用直流等离子体渗氮法对铝进行了处理。处理温度为673 K和723 K,处理时间为8 h、12 h和20 h。通过利用扫描电子显微镜（SEM）、X射线能量色散光谱仪（EDX）以及X射线衍射仪进行的表面分析发现,随着处理时间的延长和处理温度的升高,样品表面生成层的生长速度增加。为了考察样品的耐腐蚀性,在质量浓度为3.5%的氯化钠溶液中进行了电化学动态极化实验,结果显示,样品的腐蚀行为取决于生成AlN的质量。当处理温度为723 K、处理时间为20 h时,试样的耐腐蚀性最好。     

The Possibility of Dense Materials Based on Obtaining an AlN–SiC Solid Solution by Self-Propagating High-Temperature Synthesis Gasostating

Russian Journal of Non-Ferrous Metals - The synthesis and sintering of the (AlN)x(SiC)1 – x solid solution have been studied under conditions of self-propagating high-temperature synthesis...     

Studies and Properties of Ceramics with High Thermal Conductivity

The sintering technology of the AlN ceramics power were discussed. It is discussed that the compound sintering aids is consistent with the enhancement of the the thermal conductivity of AlN ceramics, and sintering technics is helped to the improvement of density. It is analyzed how to sinter machinable AlN ceramics with high thermal conductivity. And the microstructure of compound ceramics based on AlN was studied.     

Effect of Rare Earths on Mechanical Properties and Microstructure of TiCN/Al2O3 Ceramics

The effects of Y on mechanical properties and microstructure of TiCN/Al2O3 ceramics were studied in details. The experimental results show that the mechanical properties and microstructure can be improved by adding rare earth in TiCN/Al2 O3 ceramics, flexural strength and fracture toughness of the composites increased when Y is doped by 18.99% and 18.58% than those of the matrix, respectively. Microstructure of cracks extension was observed through SEM and TEM. The mechanics of particles bridge, cracks branch and cracks deflection are enforced obviously during the processes of cracks extension because strong interfaces and weak interfaces coexist, so manifold mechanics of enforcement of toughness act upon together to increase fracture toughness of TiCN/Al2 O3 doped with Y.     

Chemical compatibility of a TiAl-Nb melt with oxygen-free crucible ceramics made of aluminum nitride

The problem of uncontrolled oxygen contamination of intermetallic TiAl ingots is considered for the application of crucibles and molds based on traditional oxide ceramics. A synthesized Ti-45.9Al-8Nb (at %) alloy is solidified in alternative oxygen-free crucibles made of high-purity aluminum nitride (99.99% AlN) upon holding at 1670°C for 5, 12, and 25 min and subsequent quenching in a high-purity argon atmosphere. The initial material and the solidified ingots are studied by scanning electron microscopy, optical microscopy, X-ray diffraction, electron-probe microanalysis, and gas-content chemical analysis. The key features of the interaction of the TiAl-Nb melt with AlN ceramics are revealed. Partial thermal dissociation of the crucible material according to the reaction AlN → Al + N and the reaction of atomic nitrogen with the melt lead to the formation of a solid 6.4-μm-thick TiN coating on the ingot surface and provide perfect wettability of the crucible by the melt and easy removal of solidified casting items from the mold. The TiN coating serves as a diffusion barrier that hinders the diffusion of nitrogen and residual oxygen from the pores in the crucible toward the melt. As a result, no oxide particles are detected in the ingots. However, few single microprecipitates of two nitride phases ((Ti,Al) _x N _y , NbN) are detected in the near-bottom region, 300 μm thick, in the alloy after holding at 1670°C for 25 min. The total oxygen contamination in a two-phase α₂ + γ ingot does not exceed 1100 wt ppm, which is 1.5–2 times lower than that obtained in the experiments performed with modern advanced oxide crucibles made of yttrium ceramics Y₂O₃. AlN is shown to be a promising crucible material that can be considered as an alternative to oxide ceramics in the metallurgy of TiAl intermetallics.     

High-Temperature Corrosion of AlN-Based Composite Ceramic in Air and in Combustion Products of Commercial Fuel. Part 1. Corrosion of Ceramic Composites in the AlN – SiC System in Air and in Combustion Products of Kerosene and Diesel Fuel

We have established that scale formed upon oxidation of ceramic composites in the AlN – SiC system in air at temperatures up to 1550°C contains mullite 3Al₂O₃·2SiO₂ as the major phase of the outer layer, which provides its high protective properties. The inner layer of the scale contains β-SiO₂, α-Al₂O₃, and a fairly small amount of the oxynitride Al₁₀N₈O₂. In dry air, even at 1500°C with a long holding time (50 h), material of 50 mass% AlN – 50 mass% SiC retains extremely high corrosion resistance. We have shown that upon prolonged (up to 240 h) oxidation of the indicated ceramic in the combustion atmosphere of S- and Na-containing fuels (kerosene and marine diesel fuel) at 1200-1300°C, along with mullite in the scale we see formation (due to reaction of β-cristobalite with Al₂O₃ and gaseous Na₂O and NaOH) of low-viscosity silicate glass Na₂SiO₃ and NaAlSiO₄. Together with impurity Fe₂O₃ and gaseous Na₂SO₄, it partially destroys the protective mullite layer and leads to degradation of the protective properties of the scale.     

Methods of Protecting VKh-2K Alloy from High-Temperature Gas and Salt Corrosion

Heat resistance (1173-1573 K, 10-1000 h) has been examined for VKh-2K alloy together with the resistance to high-temperature sulfide and chloride corrosion (873-1273 K, 1-30 h). The alloy has high heat resistance up to 1473 K, but it falls substantially at higher temperatures. The alloy has higher resistance to sulfide corrosion than do high-chromium nickel alloys. In chloride melts, the alloy is subject to rapid corrosion. A two-layer YCrO₃ – ZrO₂ protective coating improves the resistance to oxidation and high-temperature corrosion in all media by more than two orders of magnitude.     

无压烧结SiC陶瓷研究进展

高硬度、高强度、耐腐蚀、耐磨损和高弹性模量等特性使SiC陶瓷成为航空航天、电力电子和机械工业等领域不可或缺的材料。然而SiC陶瓷超高的合成温度和难以烧结致密的特性限制了它的生产。近年来随着SiC陶瓷烧结机理的深入研究及添加剂的多样化,采用无压烧结工艺制备高性能SiC陶瓷材料已逐渐成为最常用的方法。本文主要阐述了近年来无压烧结SiC工艺添加剂的研究进展,综述了添加剂及其用量、烧结温度和时间对无压烧结SiC陶瓷性能的影响。     

Effects of Behaviors of Aluminum Nitride Ceramics with Rare Earth Oxide Additives

The effects of three types of additives, Y₂O₃, Nd₂O₃ and Er₂O₃ on the behaviors of AlN ceramics were investigated. The experimental results showed that the sintering temperature could be decreased and the mechanical behavior could be improved by adding rare earth oxide in AlN ceramics. The highest strength and fracture toughness of AlN ceramics with 2% Y₂O₃ addition were 311 MPa and 3.5 MPa·m^1/2, respectively. Second phase of AlN ceramics with Y₂O₃ addition was identified as Y₃Al₅O₁₂ formed by the reaction with Al₂O₃, meanwhile that with Nd₂O₃ was identified as NdAlO₃. The fracture behavior of AlN ceramics with Y₂O₃ and Nd₂O₃ were a mixed mode of transgranular fracture and intergranular fracture. Because of the high evaporation rates of Er₂O₃ (1.2 × 10⁻⁵ g·cm⁻²), no aluminium erbium oxide was found in the AlN ceramics doped with Er₂O₃. So the dielectric loss tanger(tanδ) and thermal conductivity of AlN ceramics doped with Er₂O₃ were best.     

热处理对马氏体不锈钢Fv520(B)组织及耐蚀性能的影响

采用透射电镜、Ｘ－射线衍射仪和金相显微镜,研究了Ｆｖ５２０（Ｂ）马氏体时效硬化不锈钢,经过１０５０℃固溶处理及１０５０℃固溶处理＋８５０℃调整处理,在４３０－６５０℃时效温度范围内显微组织变化及对耐蚀性能的影响。     

Effects of AlN Nanoparticles on the Microstructure,Solderability, and Mechanical Properties of Sn-Ag-Cu Solder

The addition of nanosized AlN particles to Sn-3.0 wt pctAg-0.5 wt pctCu (SAC305) lead-free solder alloy has been investigated. The various weight fractions of AlN (0, 0.03, 0.12, 0.21, 0.60 wt pct) have been dispersed in SAC305 solder matrix by a mechanical mixing and melting route. The influences of AlN nanosized particles on the microstructure, mechanical properties, and solderability (e.g., spreadability and wettability) have been carried out. The structural and morphological features of the nanocomposite solder were characterized by scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), and transmission electron microscope (TEM). The experimental results show that the best combination of solderability and mechanical properties is obtained at 0.21 wt pct AlN in the solder matrix. The reinforced composite solder with 0.21 wt pct AlN nanoparticles shows ≈25 pct improvement in ultimate tensile strength (UTS), and ≈4 pct increase in the spreadability. In addition, the results of microstructural analyses of composite solders indicate that the nanocomposite solder, especially reinforced with 0.21 wt pct of AlN nanoparticles, exhibits better microstructure and improved elongation percentage, compared with the monolithic SAC305 solder.

     

低温烧结氮化铝陶瓷烧结助剂的研究进展

分析烧结助剂在低温烧结制备高热导率AlN陶瓷过程中的作用和机理;综述AlN低温烧结助剂的研究实践;介绍烧结助剂的选择原则和几种不同烧结助剂体系对AlN陶瓷材料的烧结致密度与热导率的影响.