CC BY
19ISHS 2019 Moscow, Russia
MECHANICAL AND ADHESIVE PROPERTIES OF TITANIUM DOPED
Fe-Co-Ni BINDER FOR DIAMOND CUTTING TOOL
P. A. Loginov*", D. A. Sidorenko", and E. A. Levashov"
aNational University of Science and Technology MISiS, Moscow, 119049 Russia
*e-mail: pavel.loginov.misis@list.ru
DOI: 10.24411/9999-0014A-2019-10087
Designing of new binder compositions for diamond cutting and grinding tools is a crucial tusk in modern building and mining industries. Cobalt is well-known as the most suitable material for binder because of its excellent compatibility at relatively low temperatures, high mechanical properties, and fine interaction and adhesion to diamond monocrystals [1]. Nevertheless, its high cost forces diamond tool producers to work on low-cobalt binders. One of them, based on Fe-Co-Ni alloys, prepared by means of mechanical alloying (MA) and hot pressing (HP) techniques, has a strong potential for using in the tools dealing with highly abrasive materials [2].
Fe-Co-Ni binders demonstrate a combination of high mechanical properties and wear resistance. But improving of their adhesion to diamond monocrystals is still a major challenge. The method, applied in this work, is addition of adhesion-active elements, such as titanium [3, 4]. In this case problem complexity involves the facts that Ti has low solubility with basic matrix components. This may tend to development of brittleness due to intermetallic compounds formation. Ti is usually present in the world market by powders with high average grain size (usually several dozens of p,m). This feature leads to reducing of contact surface of Ti with diamond if used in diamond tool. But this problem can be solved using MA method to produce multicomponent powder binders [5]. Processing in planetary ball mills with high energies allows to redistribute Ti homogeneously in the matrix via their dissolution in the crystal lattice of basic component (Fe).
Thus, this study addresses the fabrication of nanocrystalline Fe-Co-Ni-Ti alloy using two operations: MA and HP.
Carbonyl iron powder (OOO Sintez-PKZh, Russia), carbonyl nickel powder (AO Kola Mining and Metallurgical Company), and reduced cobalt powder (Nanjing Hanrui Cobalt Co Ltd, China) were used as the initial materials. The doping agent titanium (AO Polema, Russia) had average grain size of 28 p,m.
Powder mixtures were prepared using an Activator-2s planetary ball mills (PBM) (Russia) with carrier rotation speed of 694 rpm and centrifugal factor of 90 g. Duration of ball milling was varied in the range of 5-20 min. The jars were filled with argon to prevent oxidation of the charge mixture during treatment.
Compacted samples 10 x 10 cm in size were prepared from the powder mixtures by hot pressing (HP). The HP temperature was 950°C; pressure at the maximum temperature, 350 kg/cm2; exposure time, 3 min. These preforms were used to cut out samples to measure the ultimate bending strength, hardness, and porosity. Residual porosity of the compacted samples was determined by hydrostatic weighing on an analytical balance (A&D, Japan). Weights were measured with an accuracy of 10-4 g.
The ultimate bending strength was measured using an LF-100 servo-hydraulic universal testing machine (Walter + bai, Switzerland) with an external digital controller (EDC). The ultimate bending strength values were determined using a DIONPro software enabling automated registration and statistical processing of the test results.
XV International Symposium on Self-Propagating High-Temperature Synthesis
The Rockwell hardness was tested using a Wolpert Rockwell Hardness Tester (Wolpert 600 MRD, USA).
The friction coefficient and the reduced wear of the samples were determined using the rolling sliding wear test on an automated Tribometer machine (CSM Instruments, Switzerland) using the rod-on-disk scheme under the following conditions: the wear track radius, 6.8 mm; applied load, 2 N; the maximum speed, 10 cm/s; a ball 3 mm in diameter made of sintered AhO3 used as a counterbody; path, 214 m (5,000 cycles); air used as the medium. The fractographic examination of the wear tracks on the samples was carried out by optic profilometry using a WYKO NT1100 optical profiler (Veeco, USA).
X-ray powder diffraction (XRD) analysis was performed using an automated DRON 4-07 X-ray diffractometer with monochromated CoKa radiation in the Bregg-Brentano geometry. A graphite monochromator was used to monochromatize radiation. Lattice parameters were measured with a relative error Aa/a = 10-4 nm.
The structure was studied by scanning electron microscopy on an S-3400N microscopy (Hitachi, Japan) equipped with a NORAN energy-dispersive X-ray spectrometer. Fine-structure features of the samples were studied by transmission electron microscopy using a JEOL JEM 2100 microscope. Samples 5*3 |im in size were prepared using a focused ion beam.
The challenge of using Ti as diamond to binder adhesion modifier is the relatively coarse grain size of the powders and consequently low surface area and probability of contact with diamond monocrystals.
The Ti-diamond surface area may be increased in the case of their uniform distribution in the binder. MA is a convenient method to solve this problem.
Fe-Co-Ni-Ti powder system demonstrated behavior at MA typical for the "ductile-ductile" systems. The powders were deformed after colliding with the grinding media and large composite granules were formed as a result of cold welding process. Thickness of the alternating layers varies between 1 and 10 |im. Layer thickness decreases as the MA duration rises to 10 min; the homogeneous structure is formed after MA for 15 min (Fig. 1a). Further increase in duration of MA had no effect on the structure.
(a) (b)
Fig. 1. Cross section image of Fe-Co-Ni-Ti binder after 15 min of MA (a) and titanium distribution (b).
The EDX analysis of obtained powder particles showed homogeneous distribution of Ti in the volume at this MA regime. According to XRD data all MA powder samples contained one phase - iron-based solid solution (bcc lattice).
The Fe-Co-Ni powder mixtures with addition of 0.5-5 mass % of Ti were prepared in PBM with MA duration for 15 min. They were used to obtain compact samples by means of hot pressing. The investigation of mechanical properties showed that 1% of Ti makes Fe-Co-Ni
-SIIS 2019_Moscow, Russia
binder 100 MPa stronger (up to 2000 MPa). The higher concentration of Ti leads to formation of brittle intermetallic phases Fe2Ti, resulting in decreasing the strength.
The diamond containing bits with Fe-Co-Ni and Fe-Co-Ni-Ti binders were hot pressed at 950°C. After that the fracture surfaces were examined. The surface of diamond in Fe-Co-Ni bits was clean and didn't contain areas of adhered binder. In opposition to it, diamond surface in Fe-Co-Ni-Ti bits was covered with large amount of small metallic chips (Fig. 2).
In order to confirm the positive role of Ti on adhesion the thin lamella from diamond-binder interface was made by means of focused ion beam. Both EDX data and diffraction patterns made from the interface regions indicated the presence of thin (50 nm) but solid layer of TiC (Fig. 3).
Fig. 2. Fracture surface of Fe-Co-Ni- Fig. 3. TEM-image of diamond/binder interphase Ti diamond composite. and titanium distribution.
An attempt to modify the Fe-Co-Ni binder for diamond cutting tool with adhesion active components (titanium) was made. It is shown that homogeneous distribution of Ti in Fe-Co-Ni matrix is possible by means of MA method using PBM, that ensures the highest possible contact areas of modifying agent with diamond. The best mechanical properties were found at samples containing 1% Ti. This composition was taken to produce diamond bits. The fracture surface analysis of the bits showed the presence of adhered metallic areas on diamond surface. The detailed investigation of diamond-binder interface proved formation of TiC layer, facilitating adhesion.
The authors gratefully acknowledge support from Russian Science Foundation (Project no. 17-79-20384).
1. F.A.C. Oliveira, C.A. Anjinho, A. Coelho, P.M. Amaral, M. Coelho, Met. Powder Rep., 2017, vol. 72, no. 5, pp. 339-344.
2. P.A. Loginov, E.A. Levashov, V.V. Kurbatkina, A.A. Zaitsev, D.A. Sidorenko, Powder Technol, 2015, vol. 276, pp. 166-174.
3. W. Tillmann, M. Ferreira, A. Steffen, K. Rüster, J. Möller, S. Bieder, M. Paulus, M. Tolan, DiamondRelat. Mater, 2013, vol. 38, pp. 118-123.
4. R. Chang, J. Zang, Y. Wang, Y. Yu, J. Lu, X. Xu, Diamond Relat. Mater, 2017, vol. 77, pp. 72-78.
5. P. Loginov, D. Sidorenko, M. Bychkova, M. Petrzhik, E. Levashov,Met., 2017, vol. 7, 570.
