AFM and XPS Corrosion Research on Rock Bolt for Yucca Mountain Repository
EMSL Project ID
2548
Abstract
Conventional electrochemical studies performed to understand corrosion behavior of metals do not give dynamic structural feedback due to presence of causing hydrogen embrittlement. We propose to perform in-situ microscopic studies using AFM and STM at PNNL that will elucidate hydrogen embrittlement (HE) and stress corrosion cracking (SCC) effects. We would like to incorporate the mechanistic information obtained from PNNL and combine with our University of Nevada, Reno (UNR)-SSRT studies; these will give more comprehensive results. For long-term drift stability of the rock bolts, it is very important to know the surface chemistry and the changes in phases during the electrochemical charging of the rock bolts. Chemical composition, thickness, and where possible, the phase composition of the corrosion layer on steel surfaces and iron plate immersed in electrolyte will be determined under conditions of in situ AFM and STM and possibly use XPS for chemical analysis. The following are proposed experiments: 1.Obtain time-resolved AFM data for iron/steel specimen in electrolyte (for hydrogen charging) to obtain crack nucleation mechanism. The specimen may be bent using a simple bending device to initiate the crack and to observe the micro-structural changes occurring in crystal lattice during the incubation period of the crack. Preparing medium carbon (ASTM-A-432) steel specimens for AFM and STM studies from the rock bolts. Also as a reference, we would like to perform tests on pure a-Fe [3]. 2. Obtain STM results in presence of hydrogen to study dynamic behavior of hydrogen in crystal lattice. 3. Possibly obtained XPS results will be used to obtain the surface chemistry. The behavior of the metal-hydrogen systems can be classifieds in various ways; one of the most useful being based on whether the systems forms second phases such as hydrides under the stress, below the yield stress. Hydride formers such as Zr, V, Nb and others are severely embrittled by hydrogen when it is present as a solute element. The other category of metals is non-hydride formers, such as Fe, Mo, W, Cr, at low pressures. The alloys of Fe are severely embrittled while others such as Mo and W, have reduced strain to failure in the presence of a high hydrogen fugacity. The embrittlement behavior of iron and steels is important as they do not easily form hydrides under normal conditions [3]. However, the embrittlement effects for Mo and W are not so dramatic. Brongers et al. [4] have shown the parameters involved in the AFM studies on austenitic stainless steel and observed crack initiation and propagation, dislocation motion, we will follow these procedures to obtain results for appropriate samples. To predict the life component, one needs to consider both crack nucleation and propagation stages of the crack life. There is an incubation period required in which hydrogen-induced cracking (HIC) and stress corrosion cracking (SCC) nucleates. Wilde [5] suggested that this incubation time represents a considerable portion, possible 90 %, of this life of any engineered propagation. In order to gain a fundamental understanding of the nucleation process of HIC and IG-SCC in carbon steel and (pure) a-Fe, the crack nucleation process should be examined at its earliest stage. We can obtain following information with regards to mechanisms HE and SCC from the experiments: 1. AFM time resolved data for the microstructural changes occurring before and after the initiation and propagation of crack due to stress applied under hydrogen charging. 2. AFM will give the physical and topographic surface properties of the samples. 3. STM studies will be conducted to evaluate electronic properties at the specimen surface by monitoring tunneling current by controlling the separation between the tip and the surface. 4. XPS can provide surface chemistry information as well.
Project Details
Project type
Exploratory Research
Start Date
2002-06-17
End Date
2003-07-14
Status
Closed
Released Data Link
Team
Principal Investigator