The intermetallic compound YbCu 2 Si 2 is a well-known nonmagnetic ͑NM͒ Yb intermediate-valent compound with a Yb valence of 2.9 at ambient pressure and 300 K. In the present work we have investigated the effect of high pressure on the ground state properties of YbCu 2 Si 2 on both microscopic and macroscopic levels by using the 170 Yb Mössbauer effect, electrical resistance, and x-ray diffraction techniques, respectively. High-pressure x-ray diffraction data indicate that the lattice structure of YbCu 2 Si 2 is stable up to 22.2 GPa. The value of the bulk modulus ͓B 0 ϭ168(10) GPa Ϫ1 ͔ is found to be close to the value expected for trivalent RCu 2 Si 2 compounds. The pressure dependence of the electrical resistance reveals evidence for a pressureinduced magnetic order for pу8 GPa. From our Mössbauer data, we conclude a crossover from the NM to a magnetically ordered state of localized Yb moments for pу8 GPa and below 2 K. The pressure-induced change of the electric quadrupole splitting indicates that this transition is accompanied by a valence change towards the Yb 3ϩ state. ͓S0163-1829͑99͒01729-4͔

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High pressure measurements on the nonmagnetic (NM) heavy fermion (HF) compound Yb 2 Ni 2 Al using the 170 Yb Mössbauer effect, electrical resistance, and x-ray diffraction techniques reveal for p . 8 GPa and below 2 K a crossover from the NM HF state to a magnetically ordered state of Yb͑4f͒ local moments ͑m Yb ഠ 1 m B at 1.8 K and 9 GPa). This crossover is not connected with a change of the Yb valence state. In the magnetic regime, we find a coexistence of discrete magnetic and nonmagnetic phases characteristic of a first order phase transition. [S0031-9007(98)

To extend the lifetime of the sinter grate used to crush the sinter cake into smaller pieces for steel fabrication, a study was undertaken to investigate which wear processes are primarily responsible for limiting the lifetime of the sinter grate. Several wear processes could be identified. The sinter temperature which is up to 800°C causes temperature-induced material ageing and oxidation. The falling of the sinter cake onto the sinter grate causes high impacts, erosion and abrasive wear. There is enormous economic pressure, which makes the most cost-efficient solution the most attractive one, not the technically ''best'' coating material; thus, Fe-Cr-C hardfacing alloys are mostly used. In view of the above, four different alloys which are promising for this application were studied with regard to their wear resistance. Each wear mechanism was investigated in a special test tribometer. Fatigue wear caused by multiple impacts and abrasion was tested in the high-temperature continuous impact abrasion test. Materials behaviour in heavy single impacts was evaluated in the single impact test. Characterisation of microstructure and wear behaviour was performed by optical microscopy and scanning electron microscopy. The results obtained with the help of the different measurement techniques were linked and set into comparison to calculate the volumetric wear of the specimen. Aim of this work was to investigate the influence of the material parameters such as macrohardness, hard phase content, microstructure coarseness on the wear resistance in impact loading and abrasive applications at high temperatures. Results also indicate that the matrix ability to bind carbides at high temperature as well as the matrix hardness at high temperatures strongly influence the wear resistance in the different tests. Those material parameters get correlated to the wear rates in different material demands. The test results indicate that at higher temperatures material fatigue becomes a major wear-determining factor which makes the matrix hardness and the matrix ability to bind carbides at high temperatures very important. Especially, in abrasive wear, a certain content of hard phases is also necessary to keep the wear to a lower level. It could also be shown that in impact loading applications, a coarse microstructure is a disadvantage.

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