Schichten aus kubischem Bornitrid. Teilprojekt: Beschichten von Wendeschneidplatten mit kubischem Bornitrid durch chemoreaktive Verfahren und deren Erprobung Abschlussbericht

The deposition of thin layers of cubic boron nitride requires a ion bombardement of certain energy. For flat substrates high biased PVD methods are well established. Using substrates of complicated shapes like indexable inserts CVD methods are more suitable. In this project the plasma activated CVD for the deposition of boron nitrid were investigated. The experiments were based on thermodynamical calculations of the CVD processes. Adherend coatings of boron nitride were deposited on indexable inserts and other substrate materials at temperatures of 650 C to 880 C. The coating properties depends on different parameters, especially from the voltage and the density of the ion current. The coatings have a amorphous structure with nanocristalline particles of the hexagonal and cubic phase. The cutting performance of inserts coated with these boron nitride were improved considerably in machining stainless steel. (orig.)Available from TIB Hannover: RN 3212(2170)+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman

Timing and nature of the penultimate deglaciation in a high alpine stalagmite from Switzerland

The timing and nature of the penultimate deglaciation, also known as Termination II (T-II), is subject of controversial discussions due to the scarcity of precisely-dated palaeoclimate records. Here we present a new precisely-dated and highly-resolved multi-proxy stalagmite record covering T-II from the high alpine Schafsloch Cave in Switzerland, an area where climate is governed by the North Atlantic. The inception of stalagmite growth at 137.4 ± 1.4 kyr before present (BP) indicates the presence of drip water and cave air temperatures of above 0°C, and is related to a climate-induced change in the thermal state (from cold- to warm-based) of the glacier above the cave. The cessation of stalagmite growth between 133.1 ± 0.7 and 131.9 ± 0.6 kyr BP is most likely related to distinct drop in temperature associated with Heinrich stadial 11. The resumption of stalagmite growth at 131.9 ± 0.6 kyr BP is accompanied by an abrupt increase in temperature and precipitation as indicated by distinct shifts in the oxygen and carbon isotopic composition as well as in trace element concentrations. The mid-point of T-II is around 131.8 ± 0.6 kyr BP in the Schafsloch Cave record is significantly earlier compared to the age of 129.1 ± 0.1 kyr BP in the Sanbao Cave record from China. The different ages between both records can be best explained by the competing effects of insolation and glacial boundary forcing on seasonality and snow cover extent in Eurasia

Termination II record, stable isotopes and trace elements of Stagamite MF-3 from Schafsloch Cave

The timing and nature of the penultimate deglaciation, also known as Termination II (T-II), is subject of controversial discussions due to the scarcity of precisely-dated palaeoclimate records. Here we present a new precisely-dated and highly-resolved multi-proxy stalagmite record covering T-II from the high alpine Schafsloch Cave in Switzerland, an area where climate is governed by the North Atlantic. The inception of stalagmite growth at 137.4 ± 1.4 kyr before present (BP) indicates the presence of drip water and cave air temperatures of above 0 °C, and is related to a climate-induced change in the thermal state (from cold-to warm-based) of the glacier above the cave. The cessation of stalagmite growth between 133.1 ± 0.7 and 131.9 ± 0.6 kyr BP is most likely related to distinct drop in temperature associated with Heinrich stadial 11. The resumption of stalagmite growth at 131.9 ± 0.6 kyr BP is accompanied by an abrupt increase in temperature and precipitation as indicated by distinct shifts in the oxygen and carbon isotopic composition as well as in trace element concentrations. The mid-point of T-II is around 131.8 ± 0.6 kyr BP in the Schafsloch Cave record is significantly earlier compared to the age of 129.1 ± 0.1 kyr BP in the Sanbao Cave record from China. The different ages between both records can be best explained by the competing effects of insolation and glacial boundary forcing on seasonality and snow cover extent in Eurasia

Nanocrystalline diamond coatings: Effects of time modulation bias enhanced HFCVD parameters

Nanocrystalline diamond NCD coatings could improve the performances of cutting tools if the adhesion on cobalt-cemented tungsten carbide WC–Co substrates was optimized and maintained during diamond deposit. In this study, a time modulated polarized growth process during diamond hot filament chemical vapor deposition (HFCVD) method was used. NCD coatings were deposited on cobalt-cemented tungsten carbide (WC–10% Co) substrates previously coated with tantalum or zirconium nitride–molybdenum bilayer as interlayer systems to control carbon and cobalt diffusion. Continuous films consisted of diamond clusters. Their size decreased when the applied bias voltage increased and substrate temperature decreased. Raman analyses confirmed the reduction of crystallite size and formation of nanocrystalline diamond films by time modulated biased substrate HFCVD process. Scratch tests showed that the NCD/interlayer systems/WC–10% Co displayed very good film adhesion interesting for cutting tools applications compared to NCD/WC–10% Co. In addition using an interlayer system could offer additional protection when diamond coating was deteriorated. This technique seems to be promising for industrial applications in the field of machining tools when increasing the thickness of the diamond layer by only extending the time modulated deposition process