核电厂冷却水泵叶轮裂纹缺陷的成因及解决方法

针对冷却水泵叶轮出现裂纹缺陷的问题,以某工厂生产冷却水泵为例,从材料铸造工艺、力学性能、裂纹形貌等方面对裂纹缺陷产生的原因进行了分析,并对比了两种冷却水泵叶轮铸造工艺的区别。研究结果表明,该工厂生产叶轮的力学性能较差,在裂纹周围有沿晶面断裂特征,且其金属结构不均匀,造成叶轮裂纹缺陷的主要原因为铸造工艺存在问题。针对工艺方面存在的问题,分别从铸造工艺和热处理工艺两个方面提出改进方案,以期为相关人员提供参考。     

Design and simulation of bias-selectable few photon dual-colour photodetector operating in visible and near-infrared regions

In this paper, we report the design and simulation of a bias-selectable dual-band photodetector operating in the visible (VIS) and near infrared (NIR) regions. The photodetector consists of two back-to-back avalanche photodiodes (APDs) with InGaAs and Si absorption layers respectively. The structure and electrical and optical properties of the dual-color photodetector were designed and simulated by exploiting Silvaco software. The results obtained on the basis of numerical simulation include the current-voltage, capacitance-voltage, spectral response, etc. The optical simulation shows the detection capability in the VIS and NIR ranges, cut-off wavelengths of 1.0 µm and 1.8 µm depending on the applied bias polarity. Comparing with using the PIN structure as element device, the dual-band photodetector based on the APD configuration could detect the very weak signal, realizing few photons, even single photon detection.