Summary Cross‐sectional transmission electron microscopy and X‐ray phase analysis were used to study the structure of a layer formed during nitriding the AISI 316L stainless steel at temperature 440°C. It was found that the applied treatment led to the formation of 6‐μm‐thick layer of the S‐phase. There is no evidence of CrN precipitation. The X‐ray diffraction experiments proved that the occurred austenite lattice expansion – due to nitrogen atoms – depended on the crystallographic direction. The cross‐sectional transmission electron microscopy studies showed that the layer consisted of a single cubic phase that contained a lot of defects such as dislocations, stacking faults, slip bands and twins. The high‐resolution electron microscopy observations were applied to study the defect formation due to the nitriding process. It was shown that the presence of great number of stacking faults leads to formation of nanotwins. Weak, forbidden {100} reflections were still another characteristic feature of the S‐phase. These were not detected in the X‐ray spectra of the phase. Basing on the high‐resolution electron microscopy studies it can be suggested that the short‐range ordering of the nitrogen atoms in the octahedral sites inside the f.c.c. matrix lattice takes place and gives rise to appearance of these spots. It is suggested that the cubic lattice undergoes not only expansion but also slight rombohedral distortion that explains differences in the lattice expansion for different crystallographic directions.

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a r t i c l e i n f o a b s t r a c tTwo different tungsten limiters (castellated bulk metal block and W-coated graphite), subjected to high power loads in the TEXTOR tokamak, were examined in order to determine chemical composition of deposits inside the castellated grooves and on side surfaces of the coated limiter. Comprehensive analyses carried out by X-ray diffraction, ion beam analysis and other methods revealed: (i) the formation of tungsten oxide (WO 2 ) inside the castellated grooves; (ii) the formation of tungsten carbides (WC main phase and traces of W 2 C) on side surfaces of the coated limiter. Elemental tungsten was found in deposits on side surfaces only in trace quantities thus indicating that tungsten eroded from the limiter top and transported to the scrape-off layer reacted with carbon. Based on thermodynamic data, the pathways leading to the formation of compounds are discussed.

The synthesis and characterization of Ga 1-x Mn x N thick layers are reported. The layers were prepared by the modified sublimation sandwich method (SSM) from GaN powder and powdered Mn sources and reacted with ammonia. Ga 1-x Mn x N layers having a current maximum size of 60 µm thickness and 10 mm × 10 mm area were obtained. The crystals of best crystalline quality were obtained with a growth rate of 25 µm/h. SIMS measurements showed the presence of layers containing up to 4 atom % Mn. Measurements involving X-ray diffraction (structure refinement), rocking curves, map of reflections, and EXAFS confirmed good structural properties without phase separation. The measurements carried out by a superconducting quantum interferometer showed that the material revealed typical paramagnetic properties.