Intergranular attack and intergranular stress corrosion cracking of Alloy 690 TT in high temperature lead‐containing caustic solution

Immersion tests were carried out in high temperature lead‐containing caustic solution in a static autoclave. The results showed samples with three surface statuses of Alloy 690 TT suffered from intergranular attack (IGA) after immersion in 10% sodium hydroxide (wt%) with 10 g/L of litharge at 330 °C for different times. With the increasing immersion time, IGA became more severe. Wire cutting samples had the most serious IGA, ground samples followed and electro‐polished samples had the slightest IGA. IGA had developed into IGSCC only in wire cutting samples due to the existence of residual stress. All the specimens at different immersion time tests lost weight. To the same cold‐work samples, with the increasing immersion time, the weight loss increased. No IGA was found in 10% sodium hydroxide solution at 330 °C after 720 h immersion. When adding 100 ppm litharge into 10% sodium hydroxide solution, slight IGA was produced. IGA became more serious and the weight loss of the specimens with three surface statuses increased with the increase of lead concentration. As the results of 1% sodium hydroxide solution containing 10 g/L litharge and 4% sodium hydroxide solution containing 10 g/L litharge at 330 °C for 720 h immersion tests, only slight IGA occurred and the weight of samples with three surface statuses increased. The pH value played an important role in lead‐induced corrosion in caustic solution.     

Surface Oxidation and Subsurface Microstructure Evolution of Alloy 690TT Induced by Partial Slip Fretting Corrosion in High-Temperature Pure Water

The surface oxidation and subsurface microstructure evolution of Alloy 690 TT can occur during partial slip fretting corrosion in high-temperature pure water.Detailed characterization methods such as laser scanning confocal microscopy,scanning electron microscopy,electron probe micro-analyzer,and transmission electron microscopy were used to reveal the related mechanism.The results showed that Cr_2 O_3 oxides together with a small number of spinel oxides were formed in sticking region since a small quantity of high-temperature water could pass through the gaps between the asperities to oxidize the materials.Widespread distribution of oxides in microslip region consisted of(Ni,Fe)Cr_2 O_4,because Ni~(2+) and Fe~(2+) ions could react with Cr_2 O_3 to generate a small amount of non-stoichiometric spinel oxides.The oxides around micropitting in microslip region consisted of double-layer structure.The outermost layer contained(Fe,Cr)-rich oxides due to the effect of fretting leading to mechanical mixing between Cr_2 O_3 and(Ni,Fe)(Fe,Cr)_2 O_(4.)The inner layer consisted of(Fe,Ni)-rich oxides owing to the consumption of Cr_2 O_3 by the reaction with Ni~(2+) and Fe~(2+) ions.The reciprocating motion of oxide particles in microslip region resulted in the stress-strain supporting the recrystallization for the formation and development of a tribologically transformed structure in subsurface and plowing effect by fretting in surface.     

划伤690TT合金在高温含氧水中应力腐蚀裂纹萌生的研究

利用划伤技术研究了690TT合金在325 ℃高温含氧硼锂水中的裂纹萌生和生长情况。试样表面和截面显微分析的结果表明,划伤沟槽底部局部萌生了典型的沿晶应力腐蚀裂纹。由于应力集中,在慢速率拉伸阶段划伤沟槽底部产生了机械裂纹,而机械裂纹成为恒载过程中690TT合金沿晶应力腐蚀裂纹萌生和生长的先导。尖端非常接近晶界或者沿着晶界的机械裂纹可继续形成沿晶应力腐蚀裂纹。690TT合金在恒载荷条件下对应力腐蚀开裂仍有一定的敏感性。     

基于AR自编码扩频的卫星测控通信技术

文章介绍了卫星自编码扩频测控通信的原理和方案,提出了利用自回归滤波的方法从信源序列中提取扩频码的AR白编码扩频系统,并对该系统的误码性能进行了理论分析和仿真。分析与仿真结果表明,AR自编码扩频系统改善了普通自编码扩频系统的误码性能,降低了传输信号的截获率,为自编码扩频通信在卫星测控通信领域的应用提供了可选的方案。     

Thermohydraulics of turbulent flow through a round tube by a peripherally-cut twisted tape with an alternate axis

The effect of peripherally-cut twisted tape with alternate axis (PT-A) on the fluid flow and heat transfer enhancement characteristic in a uniform heat flux circular tube has been experimentally investigated. Experiments were conducted using water as a testing fluid in a turbulent tube where the Reynolds number was varied from 5000 to 20,000. Peripherally-cut twisted tape (PT) and typical twisted tape (TT) were also tested in similar conditions, for comparison. Evidently, the heat transfer rates in the tube fitted with the PT-A, PT and TT are respectively enhanced up to 184%, 102% and 57% of that in the plain tube. In the present Reynolds number range tested, the PT-A, PT and TT offer the maximum thermal performances at constant pumping power of 1.25, 1.11 and 1.02, respectively. In addition, the correlations of the Nusselt number, friction factor and thermal performance were developed for the tube equipped with the PT-A in terms of peripherally-cut tape width ratio (w/W), Reynolds number (Re) and Prandtl number (Pr).     

不容忽视的低压中性线

针对中性线接地系统,论述了由于对中性线接地重视不够而存在的缺陷和可能导致的严重后果,并提出了一些针对性建议和方法。     

测量船姿态误差影响分析

航天测量船在海上执行测控任务,其作业环境远比陆站复杂。安装在船上的测控设备的误差来源,也比陆站多,传播途径更为复杂,测量船姿态误差便是其中一项误差源。为了分析姿态误差对轨道的影响,进行了仿真试算,以任务中实测的姿态角作为真实值,对其添加一定的误差后进行仿真,比较分别利用实测数据和仿真数据进行处理后的定轨结果,考察姿态误差对轨道的影响。结果表明：姿态误差是测量船一项重要误差,对轨道的影响能基本在百米级,不可忽视,提高姿态测量的精度,能有效提高定轨的精度。     

锚泊状态下船载测控系统对塔相位标校研究

航天器海上测量船是搭载着船载测控系统的海上平台,主要完成对目标的海上测控任务。测量船在新建之时或大修之后均要对搭载的测控系统进行标校,主要是进行海上合作目标校飞。海上校飞过程中锚泊状态下天线对塔相位标校必不可少,对此进行研究有助于提高锚泊状态下对塔相位标校过程的认识,提升船载测控系统的标校精度。研究过程首先分析了我国测量船所采用的差模双通道单脉冲雷达的跟踪原理和天线对塔校相原理,然后再结合锚泊状态下大型海上测量船的运动规律,建立了船体运动对锚泊状态下对塔校相精度影响的数学模型,最后在远场条件下对数学模型进行了的仿真,分析了测量船锚泊时不同运动模式对相位标校的影响,并进一步给出了锚泊状态下船载测控天线对塔校相的建议。     

莱茵新Rhenosin TT100在轮胎胎面配方中的应用

研究了莱茵新Rhenosin TT100时NR／BR／SBR胎面胶硫化特性、物理机械性能和发黑与其它配合剂在肢料中的分散性以度耐磨性能的影响。结果表明，谈助剂加入NR／BR／SBR配方中可以明显改善炭黑等配合剂在胶料中的分散性，提高挤出胎面肢断面的致密性，提高了撕裂性能、耐磨性。轮胎实际里程试验表明，采用2份Rhenosin TT100的胎冠肢的轮胎耐磨性优异。     

关于住宅中照明回路增加PE线的思考

对PE线在TN系统与TT系统中的作用进行了分析,讨论了住宅内照明回路的特点及增加PE线后的优点．