Our group has been involved in the study of mechanical properties of hardmetals for almost 20 years becoming a recognized center of competence. The aim of this research is to understand the deformation processes leading to cutting tool wear and failure during machining. The analysis of high temperature deformation tend to demonstrate that in all cemented carbides based on WC or TiCN hard phase three behavior domains can be observed as a function of temperature:
1) Brittle where both the metal and ceramic phase are not deformable
2) Tough where the metal phase (cobalt or nickel) starts to deform. As this phase generally constitutes a small fraction of the hardmetal, the overall deformation remains negligible since the cermaic skeleton only deforms elastically
3) Creep where the ceramic skeleton deforms by grain boundary sliding
At present we focus our attention on the grain boundary sliding mechanism occurring in ceramic-metal composites. Grain boundary sliding is determined by the wetting of the ceramic (WC or TiCN) by the metal binder (cobalt) and it is characterised by an internal friction peak.
Collaborations with major industries in the field have been established in particular with the company Sandvik AB, Stockholm, the major world producer of cutting tools. Colaborations are also established with Prof. Andrén ans Prof. Wahnström at Chalmers University Göteborg and and with the Los Alamos Natl. Lab. for the measurement of residual stress by neutron diffraction.
Several PhD thesis work have been dedicated in our group to these research:
J.J. Amman, PhD Thesis n. 861 (1990), D. Mari PhD Thesis n. 938 (1991), T. Viatte PhD Thesis n. 1371 (1995), G. Feusier PhD Thesis n. 1659 (1997), S. Bolognini PhD Thesis n. 2161 (2000), K. Buss PhD Thesis n. 3095 (2004)
G. Östberg, K. Buss, M. Christensen, S. Norgren, H.-O. Andrén, D. Mari, G. Wahnström, I. Reineck, Mechanisms of plastic deformation of WC-Co and Ti(C,N)-WC-Co, Int. J. Refr. Metals Hard Mater. 24, (2006) 135-144.
G. Östberg, K. Buss, M. Christensen, S. Norgren, H.-O. Andrén, D. Mari, G. Wahnström, I. Reineck, Effect of TaC on plastic deformation of WC-Co and Ti(C,N)-WC-Co, Int. J. Refr. Metals Hard Mater. 24, (2006) 145-154.
L. Llanes, D. Mari, V.K. Sarin, « Science of Hard Materials 7 », Elsevier Science, 2005.
D. Mari, S. Bolognini, G. Feusier, T. Cutard, T. Viatte and W. Benoit, TiMoCN based cermets part II. Microstructure and room temperature mechanical properties, Int. J. Refract. Metals Hard Mater. 21, 47-54 (2003).
D. Mari, S. Bolognini, T. Viatte and W. Benoit, Study of the mechanical properties of TiCN-WC-Co hardmetals by the interpretation of internal friction spectra, Int. J. Refract. Metals Hard Mater., 19, 257-265 (2001).