Prakt. Met. Sonderband 38 (2006) 239 
SEM AND TEM INVESTIGATIONS OF (W,Ti)C-(Co,Ni,Fe) 
: GRADED HARDMETALS 
2s during 
oxidation C. Barbatti***, F. Sket***, D. Eyidi*****. J. Garcig™**, A. Pyzalla*** 
geneous 
the lower * TU Wien, Wien, Austria 
particles * now: at Max-Planck-Institute fiir Eisenforschung GmbH, Dusseldorf, Germany 
esistance =+ now: at LMP, UMR 6630 CNRS - Université de Poitiers, Futuroscope-Chasseneuil 
usly and Cedex, France 
lentify: (i) *x* R&D, Boehlerit GmbH&Co.KG, Kapfenberg, Austria 
ation and 
ABSTRACT 
SEM/EDX and TEM/STEM/EDX techniques are combined to analyze the role of both 
opper by binder composition and a diffusion surface treatment (nitridation) on the microstructure 
a development of (W,Ti)C+(Ta,Nb)C hardmetals. Hardmetals with different compositions of 
Oxidation the binder phase (i.e., Co, Ni, Co+Ni, Co+Fe, and Ni+Fe) are compared. Quantitative 
98, 1970, image analyses reveal that the binder substitution does not affect the binder mean free 
path and the size of the hard phases in the bulk. In contrast, the thickness of the diffusion 
in Ag-Mg layers generated by the nitridation process strongly depends on the binder composition. 
The thickest layers are obtained in case of Fe-containing hardmetals. The WC hard 
London, phases are angular-shaped in the Co-binder hardmetals whereas they tend to have 
rounded edges in the Ni-binder ones. The average hard phase grain size within the graded 
6, 1988 near-surface zone is 500nm. The analyses on the dissolution of elements from the hard 
of Dilute phases in the binder show that the amount of dissolved W and Ta is higher in the Ni binder 
than in the Co one. The dissolution of W and Ta increases corrosion and wear resistance 
5, 1970, of the hardmetals. 
ochemie, 
x 1. INTRODUCTION 
Spheres - 
allurgical Hardmetals are multi-phase materials comprising a skeleton of refractory metal carbides 
> Allovs” embedded in a tough metal binder phase (e.g. Co, Ni, Fe). These materials are commonly 
7 yS employed in the manufacturing of cutting and drilling tools for machining of ferrous and 
Is” N non-ferrous alloys, wood, and rocks. The structural and physical-chemical properties of all 
is, NEW constituents are decisive influences on the performance and lifetime of the hardmetals 
‚Al allov” tools. Corrosion resistance of hardmetals, which is particularly important in wood cutting 
y applications, is known to be improved by an appropriate choice of the binder metal (e.g. 
a and substitution of Ni by Co-based alloys) [1-4] and/or by alloying of the binder phase [5]. 
9 72 Wear resistance and thus lifetime of hardmetal cutting tools can be increased by 
ST alterations of their surface microstructure. 
9 Surface modification techniques such as CVD and PVD deposition of hard surface layers 
are common production steps to increase wear resistance of hardmetal tools. An 
alternative method is the application of a nitridation treatment to Ti-containing hardmetals 
[6-11]. Depending on the applications, hardmetals containing not only WC but also mixed 
carbides e.g. TiC, TaC, and NbC are commonly used. These carbides form a cubic phase 
composed by (Ti, Ta,Nb)C, which is known as y-phase [10]. By reactive sintering of these 
hardmetals in the presence of a gas e.g. No, NH; a hard layer in the near-surface region is