A multi-scale correlative investigation of ductile fracture
Journal: Acta Materialia
Publication Date: 15 May, 2017
Department of: Materials
Zooming in on the cause of failure: understanding safety-critical parts
Understanding the failure of metals is critical to the performance and safety of many engineering structures. Researchers at The University of Manchester and the National Nuclear Laboratory have used a novel approach to understand the failure of the steel used to produce reactor pressure vessels for nuclear power plants. These are safety-critical parts, and with the lifetimes of nuclear power plants being considered for extension, and improvement being sought in new reactors, a better understanding of the possible failure mechanisms of such components is needed. Using a multiscale 3D approach combining state-of-the-art X-ray computed tomography imaging and plasma-focused ion-beam machining, it has been possible to quantify the damage accumulated in large, statistically meaningful, volumes of the material, and relate this to particular microstructural features at a much finer scale. This has enabled us to confirm a strong link between the macroscale properties and the micro- and nanoscale mechanisms of damage formation, allowing for greater understanding of the material failure processes. This work has identified some key relationships that will be used to improve the current models used to predict the performance of metallic materials in crucial engineering applications.
- In X-ray computed tomography, X-rays are used to create X-ray images called radiographs, which are the same as an X-ray image taken in hospitals. Thousands of these images are collected as a sample is rotated through 360 degrees. All these radiographs are reconstructed using a computer-based algorithm to produce a 3D image, creating a virtual replica of the sample.
- Plasma-focused ion-beam (PFIB) technology uses a xenon plasma to provide the ions for nanometre- and micrometre-scale machining of specimens – the ions are used to bombard the sample, milling away small amounts of material from it. The PFIB can be used to sequentially slice material from a prepared block. Each newly revealed surface is imaged using the scanning electron microscope to build up a stack of images thus creating a 3D volume. The PFIB is capable of machining material in the hundreds of microns range whereas traditional FIB only operates up to the tens of microns scale.
- The ‘microstructure’ of a material refers to its structure at the micrometre-scale (one thousandth of a millimetre). The structure of metals and alloys at this length scale, which we can see using microscopes, determines their macroscopic properties, such as strength and toughness.