A Study on Stochastic Models for Localized Corrosion

局部腐蚀随机模型的研究

基本信息

批准号：
63470053
负责人：
SHIBATA Toshio
金额：
$ 3.26万
依托单位：
OSAKA UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1988
资助国家：
日本
起止时间：
1988 至 1989
项目状态：
已结题

项目摘要

For corrosion resistant materials such as stainless steels, more than half cases of corrosion failure had been known to be caused by localized corrosion. It is well known that data of localized corrosion show wide scatter in space or in time, namely statistical and probabilistic variations. For this reason, statistical and probabilistic nature of localized corrosion shckild be studied in more detail in order to evaluate failure life of materials for various structures with more confidence.This study aims to refine the birth and death stochastic model of pitting corrosion which had been proposed previously and to simulate the actual pit foreation process by using Monte Carlo similation based on the proposed model. Simulated distributions of pitting potential and induction time for pit generation were compared with the observed distributions by the experiments in order to establish the confidence of the proposed model. The basic assumptions for the birth and death stochastic model are as … More follows: 1) Pit generation obeys a Posson stochastic process, so that the distribution of pit senation time follows exponential probability distribution.Transition probability corresponding to the pit generation rate is given by a function of potential. 2) The size of pit nucleus increases with time and the proportional constant of the rate law is expressed as an exponential function of potential. 3) Below a critical size, the growth of pit nucleus will stop due to repassivation. Death process of pit nucleus obeys also Poisson process, so that the distribution law for life time until death follows also exponential probability law. 4) Large pit which grows over a critical size will not die and continue to grow.Based on the above model and assumptions, Monte Carlo simulation provided the following results: 1) The distribution of pitting potential obeys normal probability distribution as a first approximation. 2) Median of pitting potential is proportional to the square root of potential sweep velocity. 3) The probability distribution of induction time for pit generation obeys distorted distribution. The above results were found to simulate the results observed in the experiments with a high confidence. Increase in heterogenuity due to recrystalization of amorphous alloys by heat treatment was analyzed based on the model. Less

对于耐腐蚀的材料，例如不锈钢，已知一半以上的腐蚀失败是由局部腐蚀引起的。众所周知，局部腐蚀的数据在空间或时间上显示出较大的散射，即统计和概率变化。因此，更详细地研究了局部腐蚀Shckild的统计和概率性质，以评估材料对各种结构的失败寿命。本研究的目的是以前提出的，并基于Monte Carlo Simulation基于提出的模拟模型来模拟实际的PIT进程。将PIT电位的模拟分布和凹坑生成时间的诱导时间与实验观察到的分布进行了比较，以建立所提出的模型的置信度。出生和死亡随机模型的基本假设是……更多以下：1）坑的生成遵守可能的随机过程，因此凹坑传感时间的分布遵循指数概率分布。过渡概率对应于凹坑的产生率，与电势函数给出。 2）PIT核的大小随时间增加，速率定律的比例常数表示为电势的指数函数。 3）低于临界大小，由于重新激活，坑核的生长将停止。坑核的死亡过程也要服从泊松过程，因此终生的分布定律也遵循指数概率定律。 4）在临界大小上生长的大凹坑不会死亡并继续生长。基于上述模型和假设，蒙特卡洛模拟提供了以下结果：1）点蚀势遵守正常概率分布作为第一个近似值。 2）蚀势的中值与潜在扫描速度的平方根成正比。 3）凹坑发电的诱导时间的概率分布遵守扭曲的分布。发现上述结果以高置信度模拟了实验中观察到的结果。根据模型分析了由于热处理的无定形合金重结晶而增加的异质性。较少的