The fifth WINTEREV meeting was at T-U Wien on 19-20 February 2009. Hosted by Professor Wolf-Dieter Schubert, the WINTEREV was attended by 25 people from 18 organisations from across industry, academia and RTOs. The subject of WINTEREV 09 was a review and discussion of the various methods used to characterise the physical and mechanical properties of hard tool materials with an emphasis on the role played by the binder phase, its internal characteristics and its interface with the hard phase.
The majority of the world’s production of hard tool materials are multiphase with the predominant hard carbide or carbonitride phase toughened by a secondary binder-phase. For the most part the binder-phase is based on a transition metal or alloy using Fe, Co and Ni as the major constituents. Economic drivers and health concerns are continually putting demands on producers and users to optimise, or even consider the replacement, of current binder phase constituents. The purpose of this most recent one day WINTEREV meeting was to bring together researchers and industrial colleagues to discuss the possibilities and limitations of current characterisation methods and debate emerging new techniques such as orientation imaging. For local mechanical characterisation there are indentation methods for plastic and fracture behaviour (often on a very fine scale, such as microscratch and nanoindentation testing methods), depth sensing indentation for elastic property measurement plus possible knowledge of residual stresses, since they are thought to have a role in interpreting performance. Recent research has reinforced the importance of modelling of each phase’s mechanical behaviour to the application of global stresses and consequently presentations on models and their predictions regarding phase chemistry and deformation characteristics were included.
The meeting subject matter was introduced with a resumé of property maps and deformation/ microstructure maps with an emphasis on the role played by the binder phase. In particular historical aspects of the development of models by Gurland, Fischmeister, Exner, Sigl, Chatfield, Luyckx and Shatov as well as contributions by the NPL group were assessed. The interrelation between carbide and cobalt size measurements by intercept was emphasised and insights provided by mechanical testing of synthetic binder phase alloys promoted as a route to fit-for-purpose binder phases. Further research opportunities were emphasised, including modelling to account for the complexities in microstructural characterisation such as phase shape and distribution as well as size, and elucidation of local chemistry and texture effects. Additional knowledge is required of the effects of studying fault energy, twinning and martensitic structures in alloyed binder phases. Finally, gaps in knowledge about high temperature behaviour and response to environmental effects were emphasised. Some questions that arose in discussion concerned the effects of constraint on binder phase mechanical properties, effects of WC shape on deformation of the binder phase and curiosity regarding the effects of small amounts of other refractory (such as Ruthenium and Molybdenum) and rare earth elements.
Professor Schubert provided an overview of the role of the binder phase in hardmetals summarising the reasons for the dominance of Co (wettability, superior mechanical properties, tolerance to variations in C content, etc) and opportunities for making changes with Ni(Co,Cr,Mo), FeCoNi, and other alloyed phases. Particular attention was paid to technological investigations of Co and Ni powders, especially aspects of milling to distribute the binder phase uniformly. Contrasts were drawn with different thermodynamic drivers for various alloying systems and the possibility of precipitation hardening as a strengthening mechanism was noted with reference to Japanese and Swedish research in the 1960s and 1970s. Also, the importance of C control and WC grain growth inhibition through additives was discussed. It was noted in discussion that grain growth enhancements and shape control through additives was less well researched and worthy of further study. For some products brazeability was important and this affects the choice of suitable binder phase through effects of interaction, such as wettability, with Cu base materials. From the perspective of mechanical property measurements Palmqvist data were shown to cluster at specific toughness values dependent on binder-phase type and very high TRS values were noted in materials with an alloy binder phase in the fully martensitic state. It was also noted that many properties reported for non-Co bonded hardmetals in the older literature underestimate their real property values since inconsistencies in the raw materials in past decades (such as binder agglomerates and large grain inclusions) degrade bulk properties. Modern raw materials and sintered alloy binder hardmetals exhibit much high homogeneity and therefore higher property values.