Statistical Approach to the Analysis of the Corrosive Behaviour of NiTi Alloys under the Influence of Different Seawater Environments

Nataša Kovač,Goran Vukelić,Špiro Ivošević,Rebeka Rudolf,Gyöngyi Vastag

doi:10.3390/app11198825

Abstract

Probabilistic models of corrosion rate estimation in the case of two NiTi alloys obtained by different technological processes are analysed in this paper. The depth of corrosion was measured by focused ion beam analysis on a metal surface that was not protected by an anti-corrosion coating. The samples were exposed to the influence of three different seawater environments, and empirical data were obtained in a systematic measurement procedure after 6, 12 and 18 months. Assuming that corrosion processes begin immediately after exposure of the samples to the influence of the seawater environment, and observing the corrosion rate as a random variable affected by various stochastic processes, the formed standard linear corrosion model was analysed by a statistical approach. The three best-fitted three-parameter distributions which can describe the changes in the corrosion rate for NiTi alloys exposed to the influence of the seawater environment adequately were obtained by fitting the continuous theoretical distributions. Adequate statistical tests showed similarities and differences in the behaviour of the two observed NiTi alloys from the point of view of corrosion processes caused by air, tide and sea.

Highlights

The possible exploitation of any material is implied by previous research of material behaviour in the environment in which it will be applied
Deviations in the measured values usually occur accidentally, due to measurement errors, or due to non-standard experimental conditions. Such data are not desirable in statistical analysis, because they can lead to poor interpretations of the results [42]
This paper proposes a statistical approach to the analysis and approximation of the empirical Cumulative Distribution Function (CDF) corrosion rate, defined by Equation (1) with two initial assumptions: H1

Summary

Introduction

The possible exploitation of any material is implied by previous research of material behaviour in the environment in which it will be applied. The usage of metallic materials, especially in the complex marine surroundings, or in the environment of the sea, atmosphere, semi-enclosed and closed spaces, certainly requires numerous studies on corrosion process causes, as well as predictions of the type, extent and rate of corrosion. In this regard, there are two types of methods for predicting the corrosion of metallic materials and structural elements. The first method is based on the application of statistical models and the analysis of empirical corrosion data of metallic materials in usage. The second method is based on the application of a model that predicts the probability of corrosion by identifying key variables and the mechanism of the corrosion process

Methods

Results

Discussion

Conclusion