AbstractWe study the H NMR line shapes of a sample of a-Si:H under several conditions: 1) as grown, 2) light-soaked for 600 hours, and 3) light-soaked followed by annealing at different temperatures. At T = 7 K, the NMR line shape of the sample after light soaking exhibits an additional doublet compared to that of the sample as-grown. This doublet is an indication of a closely separated hydrogen pair. The distance between the two hydrogen atoms is estimated to be about (2.3 ± 0.2) Å. The concentration of these hydrogen sites is estimated to be between 1017 and 1018 cm-3 consistent with ESR measurements of the defect density after light soaking. This doublet disappears after the sample is annealed at 200°C for 4 hours.
Metastable austenitic steels react to plastic deformation with a thermally and/or mechanically induced martensitic phase transformation. The martensitic transformation to α’-martensite can take place directly or indirectly via the intermediate stage of ε-martensite from the single-phase austenite. This effect is influenced by the stacking fault energy (SFE) of austenitic steels. An SFE < 20 mJ/m2 is known to promote indirect conversion, while an SFE > 20 mJ/m2 promotes the direct conversion of austenite into α’-martensite. This relationship has thus far not been considered in relation to the hydrogen environment embrittlement (HEE) of metastable austenitic CrNi steels. To gain new insights into HEE under consideration of the SFE and martensite formation of metastable CrNi steels, tensile tests were carried out in this study at room temperature in an air environment and in a hydrogen gas atmosphere with a pressure of p = 10 MPa. These tests were conducted on a conventionally produced alloy AISI 304L and a laboratory-scale modification of this alloy. In terms of metal physics, the steels under consideration differed in the value of the experimentally determined SFE. The SFE of the AISI 304L was 22.7 ± 0.8 mJ/m2 and the SFE of the 304 mod alloy was 18.7 ± 0.4 mJ/m2. The tensile specimens tested in air revealed a direct γàα’ conversion for AISI 304L and an indirect γàεàα’ conversion for 304mod. From the results it could be deduced that the indirect phase transformation is responsible for a significant increase in the content of deformation-induced α’-martensite due to a reduction of the SFE value below 20 mJ/m2 in hydrogen gas atmosphere.
Abstract
The results of an experimental investigation of the effect of water vapor/hydrogen environments on the mechanical properties of niobium, B-66 niobium alloy, tantalum, and Ta-10W alloy are presented. Tensile tests were conducted on specimens of these materials in water vapor/hydrogen environments with water vapor/hydrogen mixture ratios of 1 and 3. The water vapor/hydrogen environment caused strength reductions on tantalum and Ta—WW and ductility reductions on all four materials. The degree and causes of embrittlement were a complex function of temperature.
Correction: Michler et al. Review and Assessment of the Effect of Hydrogen Gas Pressure on the Embrittlement of Steels in Gaseous Hydrogen Environment. Metals 2021, 11, 637