PSI - Issue 16

Alexander Balitskii / Procedia Structural Integrity 16 (2019) 134–140 Alexander Balitski / StructuralIntegrity Procedia 00 (2019) 000 – 000

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strains and fracture localization (mainly intergranular) run in the investigated alloys at 1073 K so intensively that the coagulation of hardening phases is insufficient for the high – temperature plasticization observed in helium. Determination of Ni-Co alloys properties in the hydrogen with high parameters shows their strong dependence of accumulated hydrogen concentration in materials (Table 2 – 4). Table 2. Properties of Ni- Co alloys modifications Ni60Co15Cr8W8Al2Mo3 (І), Ni54Co15Cr9W7Al5Mo4 (ІІ) at the elongation velocity 1 mm/min. on air (numerator) and/ in hydrogen under the pressure 35 MPa (denominator), obtained on specimens without and with notching (n). Alloys modifications T [К] Mechanical properties σ В [MPa] σ 0.2 [MPa] δ [%] ψ [%] σ В n [MPa] ψ n [%] Ni60Co15Cr8W8Al2Mo3 (І) 293 1360/980 900/900 18/10 21/13 1510/1140 9/3 1073 940/810 820/780 10/7 16/10 980/920 10/8 Ni54Co15Cr9W7Al5Mo4 (ІІ) 293 1390/980 1170/1100 27/13 33/18 1570/1180 12/4 1073 970/960 890/870 17/12 29/22 990/960 14/10 Table 3. Properties of Ni- Co alloys modifications Ni62Cr14Co10Mo5Nb3Al3Ti3 (ІII), Ni61Cr14Mo6Nb3Al2Ti3 (ІV) at the elongation velocity 1 mm/min on air (numerator) and in hydrogen under the pressure 35 MPa (denominator). Alloys modifications T [К] Mechanical properties σ В [MPa] σ 0.2 [MPa] δ [%] ψ n [%] Ni60Co15Cr8W8Al2Mo3 ( І ) 293 1200/1010 810/760 13/5 16/10 1073 660/670 620/610 4/3 7/5 Ni54Co15Cr9W7Al5Mo4 ( ІІ ) 293 1330/1200 820/790 20/10 20/13 1073 980/880 840/820 11/7 14/11

Table 4. Dependence of hydrogen concentration in Ni60Co15Cr8W8Al2Mo3 alloy on hydrogen pressure during 36 h hydrogenation. Hydrogenated pressure, MPa Hydrogen concentration, ppm 1 4.5 10 19.5 35 26.9 60 31.2

One of major material descriptions is resistance to fatigue crack propagation. For the use of cyclic crack propagation diagrams in the engineering practice calculations of remaining durability they are described analytically. It is necessary to notice that most popular approach is based on the use of Paris equation (Dmytrakh (2011), Dmytrakh et al. (2013)):     n da C K dN , (2) where C і n – „materials - environment” system constants , which depend of materials, environment chemical composition and test circumstances;  K = ( K max – K min ) – SIF range per loading cycle; K max and K min – maximum and minimum SIF value in one loading cycle. Equation (2) has described the second part of da / dN curve. Take into account for the construction of fatigue crack growth diagrams and understanding the resistance of material for crack propagation we must to consider no only the electrochemical situation near crack tip (Dmytrakh (2011), Syrotyuk (2015)), but try to investigate and understand the changing the thin structure of materials near crack tip under the influence of working environment. It is known (Dmytrakh (2011)), that descriptions of metals and alloys crack resistance considerably more sensible for environment environments effect comparatively with standard mechanical and traditional fatigue tests.