Increasing surface hardness of austenitic stainless steels by pack nitriding process

This paper investigated the possibility of increasing the surface hardness of austenitic stainless steels under very low nitrogen dissociation pressures of metal nitride powders using pack nitriding process. Thin sheet of 304 type of stainless steel of approximately 1 mm in thickness was used as a substrate for the study. Based on the results of thermochemical calculations, Cr₂N powder was selected as a nitrogen source from a series of metal nitride powders considered for the pack nitriding process, which included Si₃N₄, Mn₄N, BN, AlN and TiN. The pack nitriding was carried out in a sealed alumina retort at temperatures of 860 °C and 910 °C for up to 48 h. The surface was then characterised using techniques of SEM, XRD and microhardness testing. It was observed that the process used increased the surface hardness of the steel, but it also induced precipitation of chromium nitrides in the matrix even under the nitrogen dissociation pressures below 50 Pa. It was also observed that, in the nitrided layer, the γ phase of the steel was partially transformed to the α phase under the pack nitriding process conditions studied.     

Boroaluminide coatings on ferritic-martensitic steel deposited by low-temperature pack cementation

In this study, new boroaluminide protective coatings were deposited on ferritic-martensitic steel substrates (P91) using the pack cementation technique, at moderate temperatures in order not to influence the substrates' mechanical properties. Extensive thermodynamic calculations were performed initially, using the Thermocalc Computer program, so as to optimize the process parameters. The most important gas-precursors for successful deposition of the coatings were identified. The effect of pack composition on the formation and growth of boroaluminides at 715 °C, using pack powders containing Al and B as element depositing sources, two halide salts as activators, and Al₂O₃ as inert filler, was investigated. Three distinct regions were found in the coatings consisting of an outer Al-rich layer, a transition region containing Al, B and Fe and an inner layer containing mostly B, Cr and Fe. The layers were characterized by means of optical and Scanning Electron Microscopy (SEM) in terms of coating morphology and thickness. X-ray diffraction (XRD) was used in order to detect the phases formed and the presence of iron aluminide and boride phases in the coatings due to the boroaluminizing process.     

高性能移动电话电池制造方法

采用按充放电特性曲线分进单体可充电电池,其容量、内阻、表面温升、充放电电压平台、出现时间、自放电率、寿命等主要性能参数趋于一致,将这些性能一致的单体电池配对,组装成移动电话电池,较按容量分选组装的移动电话电池寿命、待机时间和连续通话时间等性能有大幅度提高。     

Cf/SiC 复合材料的 ZrB2-SiC/SiC 超高温陶瓷涂层研究

采用两步包埋法在Cf/SiC复合材料表面制备了Zr B_2-SiC/SiC超高温陶瓷涂层。借助SEM、XRD对涂层的微观结构及物相组成进行了分析研究,并进行了高温静态氧化和热震测试。研究表明,1500°C氧化5 h后,涂层表面覆盖有平整的玻璃相氧化层,氧化失重率为6.4%;热震测试10次后涂层的氧化失重率为14%。Zr B_2-SiC/SiC涂层能有效提高Cf/SiC复合材料的高温抗氧化性能。     

GCr15销轴固体渗Cr层的生长机制及孔隙成因探索

低扩渗效率和渗层孔隙是困扰着渗铬生产的两个重要难题。本文采用固体包埋法在GCr15表面制备渗Cr涂层,重点探讨了渗层的生长机制、孔隙成因及不同稀土氧化物的催渗作用。结果表明,加入稀土氧化物后渗层厚度明显提高,三种稀土氧化物的催渗效率依次为Y2O3>CeO2>La2O3。渗Cr层明显的分为双层结构,外层是以（Cr,Fe）23C6相为主的多孔层,内层为（Cr,Fe）7C3相为主的致密层。扩渗初期在基材表面首先生成的（Cr,Fe）23C6相层阻碍了表面活性Cr原子向内扩散,其自身作为Cr源向内扩散促进了致密层的生长,Cr原子扩散速度的差异及渗层中的应力是产生孔隙的主要原因。发现降低基体碳含量抑制（Cr,Fe）23C6相层的生成或细化该相层晶粒增加Cr原子扩散通道可有效降低孔隙率,这为改进渗铬层质量提供了一个重要思路。     

基于GA-WPA优化的BP神经网络目标威胁估计

在防空作战中,目标威胁估计是指挥控制过程的重要一环,是决策和指挥的重要依据。BP神经网络能够解决目标威胁估计问题,但存在收敛速度慢、易陷入局部最优等缺点。提出将遗传算法(Genetic Algorithm,GA)的选择、交叉和变异操作融入到狼群算法(Wolf Pack Algorithm,WPA)中,提出了GA-WPA算法,以提高狼群算法的收敛速度。在此基础上,利用所提出的GA-WPA算法对BP神经网络进行优化,确定最优初始权值和阈值。最后,将优化后的BP神经网络解决地面防空系统目标威胁估计问题。仿真实验表明,所提算法能够有效克服BP神经网络收敛速度慢、易陷入局部最优等缺点,能够提高目标威胁估计的准确性和适应性。     

八面河油田稠油热采井出砂机理及循环充填防砂工艺

八面河油田两大稠油区块均为弱胶结成岩相。胶结疏松是造成油井出砂的主要原因,注蒸汽热采亦对储层造成了一定程度的伤害,加剧了油井的出砂。循环充填防砂工艺具有二级拦截过滤体系,较好兼顾了产能和控制出砂要求,防砂强度高,有效期长,工艺适应范围广。     

A study on the microstructure and cyclic oxidation behavior of the pack aluminized Hastelloy X at 1100 °C

A pack aluminizing process at 950 °C for 9 h has been employed on the nickel-base superalloy Hastelloy X to deposit a 75 μm thick β-NiAl aluminide layer on the surface. A nanoscale dendritic structure is observed on the surface of the aluminide coating. A finger-like interdiffusion zone is found between the aluminide layer and the substrate. Fine precipitates with complex phases are distributed in the NiAl layer. The cyclic oxidation tests of aluminized alloys and untreated substrates were conducted at 1100 °C for 196 h. It was observed that the aluminizing process greatly enhances the cyclic oxidation resistance of Hastelloy X at 1100 °C due to a dense and protective alumina layer formed on the surface. Complex phase transformation reactions occurred in the aluminide layer. Owing to the oxidation and interdiffusion reactions at high temperature, the Al content of the NiAl layer was depleted to form some low Al containing γ-substrate grains on the surface and a continuous γ layer between the aluminide layer and substrate. Thermal stress induced, transverse cracks in the interdiffusion zone, were observed possibly due to the difference of thermal expansion coefficients among the substrate, aluminide layer and interdiffusion zone.     

静压钢套筒护壁灌注桩技术的研究与应用

本文在分析全套筒贝诺特施工灌注桩理论的基础上 ,提出了利用静压沉管技术 ,在干作业条件下施工钢套筒护壁成孔灌注桩理论。通过施工过程内力分析 ,指出施工技术关键。分析表明 :该种灌柱桩较其它类型灌注桩有更突出的优点和显著的经济性