SPD技术对锆及锆合金力学行为影响研究现状

综述了锆及锆合金剧烈塑性变形(SPD)后性能变化的研究进展,系统阐述了锆及锆合金经剧烈塑性变形后显微硬度、拉伸/压缩性能、高低周疲劳性能,重点介绍了SPD技术在纯锆、Zr-Nb系合金中的应用.经过剧烈塑性变形后,锆及锆合金的抗拉强度及屈服强度均显著提升,但依据剧烈塑性成形轨迹、合金成分、第二相分布、热处理制度不同,其提...     

核包壳管用HT9钢的600～1000℃空气氧化行为

HT9钢在核反应堆包壳管中具有巨大的应用前景。在失水事故下,包壳管材料的温度将远高于600℃。为此,研究了HT9钢600℃以上的空气氧化行为。用增重法测定其氧化动力学曲线,利用SEM、EDS和XRD分析氧化产物的形貌、成分和结构。基于对氧化动力学与氧化产物的分析,探讨其氧化机制。结果表明:在600~1 000℃范围内随着温度的升高和时间的延长,HT9钢氧化程度增加;氧化层呈双层结构,内层为(Fe,Cr)_2O_3,外层是Fe_2O_3;不同温度的氧化动力学遵循不同的规律,氧化过程主要受铁离子和铬离子的扩散共同控制。     

A signal-processing tool for non-destructive testing of inaccessible pipes

The design of Non-Destructive-Testing systems for fault detection in long and not accessible pipelines is an actual task in the industrial and civil environment. At this purpose, the diagnosis based on the propagation of guided ultrasonic waves along the pipes offers an attractive solution for the fault identification and classification. The authors studied this problem by means of suitable Artificial Neural Network models. Numerical techniques have been used to simulate the guided wave propagation in the pipes. In particular, the finite element method has been used to model different kinds of pipes and faults, and to obtain several returning echoes containing the faults information. Torsional wave modes have been used as excitation waves. The obtained signals have been processed in order to reduce the data dimensionality, and to extract suitable features. The features selected from the signals can be further processed in order to limit the size of the Neural Network models without loss of information. At this purpose, the principal component analysis has been investigated. Finally, the selected features have been used as input for the neural network models. In this paper, traditional feed-forward, multi-layer perceptron networks have been used to obtain the information on size and location of localized notches.     

Partitioning behaviour of oxygen in steam-oxidized Zircaloy

A model has been developed which describes the high temperature partitioning behaviour of oxygen in Zircaloy. The growth kinetics of the oxide/α and α/β layers are derived from a consideration of the material continuity requirements at the respective phase boundaries. It is shown that the rate of advance of the α/β interface in specimens of finite thickness will deviate from parabolic behaviour, a departure attributable to the progressive approach of the total oxygen content in the β phase towards its saturation value. This conclusion is significant since determination of the oxygen profile in the β phase is dependent on reliable evaluation of the α/β interface advance kinetics. The validity of the model is tested by comparing the observed oxide/α and α/β interface growth rates with those derived using basic oxygen diffusion and solubility data in conjunction with total oxygen uptake kinetics.     

Study on α-alumina precursors prepared using different ammonium salt precipitants

Nano-sized α-Al₂O₃ platelets have been produced by the precipitation method employing the starting material of Al(NO₃)₃·9H₂O and ammonium salt precipitants, such as the NH₄OH, (NH₄)₂CO₃ and NH₄HCO₃. The effects of chemical composition of ammonium salt precipitants and aging time of precipitated product on the formation of precursor and final product of α-Al₂O₃ particles were studied. The precursors with different crystal structures were formed depending on the chemical composition of precipitant and the agglomeration of final α-Al₂O₃ particles was found to be greatly affected by the precipitant. The aging time of precipitated precursor also influenced the agglomeration of final α-alumina particles.     

包覆工艺对微球形燃料相弥散燃料混合均匀性的影响

针对微球形燃料相颗粒与基体粉末的流动性相差较大、难于混合均匀,建立了一种微球的包覆工艺,并研究了包覆工艺对混合均匀性的影响。采用直径约为100μm的不锈钢微球代替燃料微球,研究结果表明,在微球表面物理包覆一层基体粉末,可增加颗粒表面粗糙度,降低两组元粉末的密度差及颗粒沉降的距离,包覆层还能使颗粒间保持一定的间距,微观上形成连续的基体网络,减少甚至避免发生偏聚,有效地改善了混合均匀性。包覆工艺的最佳参数为:保温温度,76℃;保温时间,6min;黏结剂添加量,1%;粉末粒径,小于25μm。该方法可用于改善(U-Mo)-Al、(U-Mo)-Zr等微球形燃料相弥散燃料的混合均匀性。     

FeCrAl铁素体不锈钢在压水堆水化学偏离工况下的应力腐蚀行为

采用慢应变速率拉伸（SSRT）试验方法,研究了FeCrAl铁素体不锈钢在偏离压水堆正常工况下的应力腐蚀行为。结果表明,在含有微量Cu²⁺与Cl^-的高温水介质中,应变速率为2×10^-7s^-1时,FeCrAl铁素体不锈钢将发生显著的应力腐蚀开裂;其在含Cu²⁺和Cl^-的高温水介质中的应力腐蚀开裂主要由点蚀导致。