O. Knotek

Das Dreistoffsystem Nickel—Chrom—Bor

The ternary system Ni−Cr−B was established at 1000°C by X-ray diffraction and metallographic examinations. Binary chromium resp. nickel borides and two ternary borides Cr3NiB6 and Cr2Ni3B6 were confirmed. Differential thermoanalysis of binary Ni−B-alloys showed the possibility of a metastable solidification according the partial system Ni−Ni2B up to 19 at % B. The melting temperatures of ternary alloys were established.

Investigation of the mechanical and structural properties of Ti-Hf-C-N arc PVD coatings

Abstract Nowadays, a few coating systems are commercially available (TiN, TiCN, CrN, TiAlN, WC/C, ADLC). These coating systems are used for various applications. In the range of cutting procedures, TiN-coated tools are widespread. Further developments have led to coatings based on the systems Ti–C–N and Ti–Al–N possessing improved properties. In interrupted cut machining, for example, the lifetime of Ti–C–N-coated cemented carbides is four times higher than that of TiN-coated ones (O. Knotek, F. Loffler, G. Kramer, Vacuum 43 (5–7) (1992) 645–648). This is a result of the favorable thermophysical and tribological properties of Ti–C–N (O. Knotek, E. Lugscheider, F. Loffler, G. Kramer, H. Zimmermann, Surf. Coat. Technol., 68–69 (1994) 489–493; E. Lugscheider, O. Knotek, H. Zimmermann, in T.S. Srivatsan, J.J. Moore (eds.), Processing and Fabrication of Advanced Materials IV, TMS Warrendale, PA, 1996). The high hardness of TiC is the reason for the excellent low flank wear. TiN possesses higher formation enthalpies than TiC and therefore a better resistance to crater wear. The binary combinations of HfN and HfC possess similar properties to TiN and TiC, but their thermal stability is better. Thus HfN and HfC possess higher melting points than TiN and TiC, respectively (R. Keiffer, F. Benesovsky, Hartstoffe, Springer, Vienna, 1963; W. Konig, Fertigungsverfahren, Band 1, 4. Auflage, VDI, Dusseldorf, 1990). Because of this, the substitution of Ti atoms by Hf atoms can be expected to lead to an improvement of wear behavior. First coatings from the system Ti–Hf–N were deposited with the arc PVD process. Based on these investigations, coatings in the quaternary system Ti–Hf–C–N were developed. Beside the number of layers (Ti–Hf–N/Ti–Hf–C–N), the composition of the reactive gas comprising nitrogen and the carbon carrier gas ethane was varied. During deposition with a high carbon carrier gas flow share (total pressure=constant), the coatings chipped off. Lower shares of carbon carrier gas, e.g. C2H6:N2=1:4, led to smooth and dense coatings with good mechanical properties. With regard to different number of layers, the values of microhardness were around 2900 HV 0.05.

Das Dreistoffsystem Nickel-- Bor-- Silicium*

The ternary system Nickel-Boron-Silicon was established at 850°C by means of X-ray diffraction, metallographic and micro-hardness examinations. The well known binary nickel borides and silicides resp. were confirmed. In the boron-silicon system two binary phases, SiB4-x withx≈0.7 and SiB6 were found the latter in equilibrium with the β-rhombohedral boron.Confirming the two ternary silicon borides a greater homogeneity range was found for Ni6Si2B, the phase Ni4,6Si2B published byUraz andRundqvist can better be described by the formula Ni4.29Si2B1.43.In relation to further investigations we measured melting temperatures in ternary Ni-10 B−Si alloys by differential thermoanalysis.