Microstructural evolution during high-temperature oxidation of spark plasma sintered Ti2AlN ceramics

Microstructures of Ti₂AlN ceramics synthesized and simultaneously consolidated from starting mixtures of Ti/Al/TiN powders by spark plasma sintering (SPS) were characterized using X-ray diffraction, scanning electron microscopy, focused ion beam (FIB) and transmission electron microscopy (TEM). When sintered for 10 min at 1300 °C, nearly single-phase Ti₂AlN ceramics with elongated (∼22 × 6 × 6 μm) grains were obtained. After sintering for 10 min at 1200 °C and chemical etching, Ti₂AlN nanowhiskers (150-200 nm dia., 1-5 μm long) were exposed in pores coexisting with TiAl, TiN and Ti₂AlN grains. FIB-TEM studies revealed single-crystal Ti₂AlN nanowhiskers in a TiAl matrix with orientation relationship [1 1 −2 0]_H//[−1 0 1]_γ, (0 0 0 1)_H//(1 1 1)_γ, γ = TiAl, H = Ti₂AlN. The nanowhiskers are believed to form by diffusion of TiN into TiAl during SPS and to be exposed during the chemical etch. Microstructural development during high-temperature oxidation of dense Ti₂AlN ceramics for 1 h at <1200 °C involves gradual formation on the surface of layered microstructures containing anatase, rutile and α-Al₂O₃. After 1 h at >1200 °C, more complex layered microstructures containing Al₂TiO₅, rutile, α-Al₂O₃ and continuous voids layers form. After heating to 1100 °C for 1 h and cooling to room temperature, planar defects are observed in surface TiO₂ grains identified as stacking faults bounded by partial dislocations. After heating for 1 h at 1400 °C and cooling to room temperature, cracks propagate in TiO₂ grains. It is believed that planar defects and cracks arise from stress generation in the oxide scale. Thermal stresses formed on cooling may arise from thermal expansion mismatch of phases (TiO₂, Al₂O₃ and Al₂TiO₅) in the oxide scale, the high anisotropy of thermal expansion in Al₂TiO₅ and thermal expansion mismatch between the oxide scale and Ti₂AlN substrate. Growth stresses formed during the isothermal oxidation treatment may arise from the volume changes associated with oxidation reactions of Ti₂AlN. An oxidation mechanism for Ti₂AlN ceramics is proposed, which involves initial reaction with atmospheric oxygen to form oxide phases, demixing of the mixed oxide phases, void formation due to the Kirkendall effect and gaseous NO_x release. Oxidation of Ti₂AlN <1200 °C with 1 h hold times is limited, while above this temperature the oxide scale grows rapidly, and Ti₂AlN ceramics undergo heavy oxidation.     

MAX相Ti3SiC2管材在高温高压水和过热蒸汽中的腐蚀行为

MAX相材料有作为事故容错燃料(accident tolerant fuel,ATF)包壳材料的潜力,为了全面了解MAX相材料在模拟正常工况下的腐蚀行为,使用基体为Ti₃SiC₂的MAX相陶瓷管材于400℃/10.3 MPa过热蒸气,360℃/18.6 MPa去离子水、3.5μL/L Li+1000μL/L B溶液和70μL/L Li溶液4种不同的水化学条件中进行腐蚀试验,采用XRD、SEM和FIB/TEM观察分析腐蚀前后样品的显微组织、晶体结构和成分。结果表明,Ti₃SiC₂管材在4种条件下的腐蚀速率均远高于参比Zr-4合金,腐蚀后主要检测到腐蚀产物TiO₂,且其表面疏松多孔,未形成保护性的氧化膜。     

串行数据采集无线数据传输模块的设计

以AT89C2051单片机为核心,设计了一个用串行A/D转换器MAX1226进行数据采集,单片无线收发芯片PTR2000进行数据传输的模块,给出了硬件构成,软件设计及部分程序.该模块电路简单、使用方便,有采样精度高、可靠稳定、功耗低等优点,能较好地实现数据的串行采集和无线传输,应用在工业数据采集、工业控制、医疗监护等场合.     

一种新型快速的机器人三维图形仿真建模方法

以MOTOMAN-SV3X机器人为原型,在3DSMAX中进行机器人各部件的实体建模,编制了CpenGL导入3DSMAX模型文件的接口软件.借助OpenGL图形库,使用Visual C＋＋6.0编制了MOTOMAN机器人的图形仿真和控制软件.这种方法在PC机上可以快速建模并满足仿真形象逼真的要求.     

基于VHDL的出租车计价器设计

采用VHDL编写出租车计费器系统程序,采用MAX＋PLUSⅡ软件作为开发平台,进行了程序仿真,验证设计实现了出租车计价器的相关功能。     

基于嵌入式以太网的煤矿安全智能监控系统设计

针对煤矿安全存在的问题,设计了一种基于微控制器MAX7651和AX88796的嵌入式以太网智能监控系统,该系统不但有功能易于拓展、组态灵活的特点,而且具有很高的性价比,可很好地满足中小型煤矿安全监控的需要。     

Medium-entropy (Ti,Zr, Hf)2SC MAX phase

Medium- and high-entropy alloys or ceramics for tuning the physicochemical properties of materials by the combination of multiple principal elements have received much interest. Herein, a medium-entropy (Ti, Zr, Hf)₂SC phase was synthesized attributing to the structural and chemical diversity of MAX phases. The crystal structure of (Ti, Zr, Hf)₂SC was determined by the Rietveld refinement of XRD, SEM, and atom-resolved TEM along with EDS elemental analysis. Phase evolution of X-ray diffraction patterns and TG/DSC curves were employed to reveal the synthesis mechanism of (Ti, Zr, Hf)₂SC from 2TiC–Zr–ZrC-2HfH₂-3.2FeS reactant system. The Vicker's hardness and the electrical resistivity of (Ti, Zr, Hf)₂SC were found higher than those of Ti₂SC, but the thermal conductivity of (Ti, Zr, Hf)₂SC was lower.     

Mechanical properties and wear behavior of Tin+1(Al,A)Cn (A = Ga,In, Sn,n = 1, 2) via quasi-high-entropy of single atomic thick A layer

The strengthening method of multi-element M-site solid solution is a common approach to improve mechanical properties of MAX phase ceramic. However, the research on capability of multi-element A-site solid solution to improve mechanical properties has rarely been reported. Thereupon, quasi-high-entropy MAX phase ceramic bulks of Ti₂(Al_1?xA_x)C and Ti₃(Al_1?xA_x)C₂ (A = Ga, In, Sn, x = 0.2, 0.3, 0.4) were successfully synthesized by in situ vacuum hot pressing via multi-elements solid solution. The multi-elements solid solution in single-atom thick A layer was confirmed by X-ray diffraction and X-ray photoelectron spectroscopy as well as by energy dispersive X-ray spectroscopy mappings. Effects of doped multi-elements contents on the phase, microstructure, mechanical properties, and high temperature tribological behaviors were studied. Results demonstrated that the Vickers hardness, anisotropic flexural strength, fracture toughness, and tribological properties of Ti–Al–C based MAX ceramics could be remarkably improved by constitution of quasi-high-entropy MAX phase in A layers. Moreover, the strengthening and wear mechanisms were also discussed in detail. This method of multi-element solid solution at A-site provides new way to enhance mechanical properties of other MAX phase ceramics.     

利用VHDL语言设计数字电路

介绍在MAX＋PlusⅡ软件开发平台下利用VHDL硬件描述语言和CPLD器件,实现一个具体的数字电路功能,给出具体设计原理和各功能模块VHDL语言程序,通过软件的方式设计硬件,设计方法更加灵活、高效,并具有调试方便、故障率低、修改升级容易等特点。     

CATIA V5 环境下水电工程三维可视化仿真场景中的应用研究

在水电工程三维可视化仿真场景实现过程中,针对水电工程的设计特点与视觉特征,提出CG知识库的概念,并以CATIA与3DS MAX软件为应用平台,从环节分解、要素分类、建立方法、关键问题等方面探讨了水电工程三维参数化模型库与三维网格模型库、材质库等CG知识库的实现思路及采用的主要技术,并阐述了通过CG知识库的运用,可快速搭建三维可视化仿真场景,缩短同类项目的制作周期,提高应用自动化的程度。