Development of Heat-Resistant Displacement Sensitive Sensor and Mechanism Elucidation of Environmental Assisted Cracking at Elevated Temperature by Inverse Processing of Dissipative Elastic Wave

本研究旨在研制一种在600 ℃左右工作的面外位移敏感、耐热的声发射传感器，并研究环境辅助断裂的机理和动力学。我们开发了两种类型的耐热传感器。一种是采用红外激光PVD沉积的非晶氧化铝薄膜（3 μ m）电容式传感器，该传感器在600 ℃以下的温度范围内具有较宽的测量范围，并能准确地测量离面位移。在此基础上，研制了一种居里温度在1000 ℃以上的铌酸锂圆锥形位移传感器。该传感器的频带较电容式传感器窄，但在600 ℃以下仍能以较高的灵敏度测量离面位移。由于传感器的尺寸减小，使多通道监测成为可能。使用所研制的传感器，我们首先测量了热奥氏体不锈钢AISI 340中纵波的速度色散和波衰减。我们还监测了304钢在600 ℃熔融氯化物和熔融银基钎料作用下的声发射信号，并利用所研制的声发射系统监测了大量快速断裂的声发射信号。通过对监测到的面外位移进行源模拟来估计断裂动力学或断裂运动学和动力学。开发的源模拟包括匹配的第二类理论绿色函数的卷积积分计算的位移与延迟功能和假设的源动态的监测。首次阐明了极快速断裂与熔盐应力腐蚀开裂和熔融焊料脆化有关。

Research aims to develop a out-of-plane displacement sensitive and heat resistant acoustic emission transducer which serves at temperature around 600C,and to study the mehanism and dynamics of environmentally assisted fracture. We developed two types of heat resistant transducer. One is the capacitive transducer with thin (3 micrometer) amorphous but stoichiometric alumina film which si deposited by the IR laser PVD.This sensor was demonstrated to be broad band and accurately measure the out-of-plane displacement at temperature below 600C.Disadvantage of this transducer is noise-generation due to its high bias voltage. Then we developed another conical-type transducer with a LiNbO3 element whose Curie temperature is above 1000C.Frequency band of this transducer is narrow compared withjthat of capacitive one, but it measures the out-of-plane displacement at high sensitivity below 600C.As the transducer size was minimized so as to make the multi-channel monitoring possible.Using the transducers developed, we first measured the velocity dispersion and wave attenuation of the longitudinal wave in hot austenitic atainless steel AISI 340. we also monitored AE signals from type 304 steel subjected to molten chlorides and fused silver-based solder at 600C.A number of AE signals from fast fracture were monitored by the developed AE system. The fracture dynamics, or the fracture kinematics and kinetics, were estimated by the souce simulation to the monitored out-of-plane displacement. The source simulation developed consists of matching the displacement computed by the convolution integral of the theoretical Green's function of the second kind with the retardation function and the assumed source dynamics to the monitored one. It was first elucidated that extremely fast fracture are associated with the molten salt stress corrosion cracking and fused solder embrittlement.