The EPMA Hard Materials Group (EHMG) held the next three meetings of its WINTEREV (in fact the first of the three was a SUMMEREV!) series on the theme of Fracture, Fatigue and Damage characterisation at NPL, CEIT and finally UPC, Barcelona. The meetings were attended in total by more than 80 research and technical leaders and students.
Hardmetals, also referred to as cemented carbides, are composite materials with two interpenetrating crystalline phases with widely differing properties. The performance and reliability of hardmetal components are controlled by the materials internal microstructure over a wide length scale range. Detailed knowledge of the in-service degradation mechanisms will clearly lead to improved performance. Effective implementation of relevant microstructural effects on critical design parameters requires further research and applied work, both experimental and modelling, on damage and damage evolution, particularly as related to behaviour of intrinsic (short) flaws and surface behaviour. Cemented carbides are heterogeneous in nature, and modelling of their mechanical behaviour (especially in the presence of damage) will require a multi-scale approach. At the microscale the initial processes relate to the size dependence and discrete behaviour of plastic deformation (often under constraint), strain hardening and fracture within individual phases. At the macroscale continuum mechanical models are based on homogenised material parameters. At all levels, molecular dynamics, crystal plasticity models and finite element approaches may be effective tools for quantifying the relevance of representative size effects. Capturing microscopic phenomena and bringing them to the macroscale, will be essential for the correct simulation of strength, toughness, wear and fatigue degradation phenomena in hardmetals.
Identification and quantitative description of physical mechanisms which control defect and damage development in hardmetals is a continuing challenge. It is particularly important to take advantage of advanced characterisation techniques such as in situ scanning electron microscopy (SEM) testing, nanoindentation, electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), focussed ion beam (FIB), and 3-D tomography to provide equivalent information to that yielded by electron microscopy (mainly by means of fractographic analysis) to current knowledge. Extensive and detailed use of these techniques will help to characterise the deformation behaviour and operative mechanisms at the microstructural scale for cemented carbides.
It was intended that these three SUMMEREV/WINTEREVs would address as many of these issues as possible. At the first meeting, the SUMMEREV at NPL in June 2010, the emphasis was on experimental issues. The second meeting in the set was at CEIT, San Sebastian with continuing assessment of experimental issues but also an introduction to the role that modelling can play. The third meeting was at UPC, Barcelona and addressed key issues tackled in Parts I and II with an added emphasis on elevated temperature characterisation.