13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- The Effects of Hydrogen on Mechanical Properties of Ni-base Alloys under the Static and Cyclic Loading. Alexander Balitskii*, Lyubomir Ivaskevich, Volodimir Mochulskyi. Department of Hydrogen Resistance of Materials Karpenko Physico-Mechanical Institute, 5 Naukova str., Lviv, 79601, Ukraine * balitski@ipm.lviv.ua Abstract The effect hydrogen on short-term strength, low-cycle durability and plane-stress fracture toughness of 04Cr16Ni56 and 05Cr19Ni55 alloys at pressure up to 35 MPa and temperature 293…1073 K was investigated. The modes of hydrogen action for which the mechanical properties of alloys are minimum were established: hydrogen pressure above 10 MPa (non-hydrogenated specimens of 04Cr16Ni56 alloy) and above 35 MPa (hydrogenated specimens of 05Cr19Ni55 alloy, hydrogen concentration CH = 19 wppm). The plane-strain state conditions and, correspondingly, the conditions of the evaluation of plane-strain fracture toughness (KІс) were fulfilled on compact tension specimens of 04Cr16Ni56 with a thickness of 20 mm at hydrogen pressure above 10 MPa in the temperature range 293…473 K. Plane-stress fracture toughness Kc of 05Cr19Ni55 alloys was decreased at 293 K from 116 MPa·m1/2 in helium to 78 MPa·m1/2 in hydrogen under the pressure 30 MPa and to 68 MPa·m1/2 in hydrogen under the pressure 30 MPa after preliminary high-temperature hydrogenation (with hydrogen concentration CH = 19 wppm). Keywords Hydrogen embrittlement, Fracture toughness, Alloy 1. Introduction The production of turbine equipment requires a wide usage of dispersive hardened heat-resistant Fe-Ni alloys. In these products heat-resistant alloys are exploited at high temperatures in the contact with high-pressure hydrogen containing gas mixtures. Therefore one of the most important requirements for such alloys is their resistance to hydrogen degradation. In other words their ability to keep high level of mechanical properties under the action of hydrogen in wide range of exploitation parameters. At the same time, age-hardening alloys are known to be rather sensitive to hydrogen embrittlement [1-3]. The serviceability of structures in hydrogen is, as a rule, estimated according to the results of testing at room temperature [4-7]. This is explained by maximum sensitivity of steels and alloys to hydrogen degradation and complexity of experiments at elevated temperatures. However, the operating conditions of the equipment for hydrogen power engineering include static and cyclic loading of the products in hydrogen in fairly broad temperature ranges [7, 8], whereas the available literature data on the temperature dependences of mechanical properties in hydrogen are quite poor and ambiguous. In most cases, the influence of gaseous hydrogen on mechanical properties weakens as temperature increases and, according to the data presented in [6], the upper temperature of embrittlement under the analyzed conditions was equal to 573 K. At the same time, we reveal a significant decrease in the plasticity of heat-resistant nickel alloys in hydrogen under a pressure of 35 MPa at temperature1073 K [3, 7, 9]. In what follows, we study the influence of high-pressure gaseous hydrogen on short-term strength, low-cycle durability, and static crack resistance of nickel based alloys in the temperature range 293-1073 K. 2. Materials and Experimental Procedure Two types of dispersion-hardened alloys were investigated: 04Cr16Ni56 and 05Cr19Ni55. Alloying
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