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Tham khảo tài liệu 'high temperature strain of metals and alloys part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 6.6 Composition of the y Phase and Atomic Vibrations 103 Tab. 6.5 Compositions of B3A y phases and the mean-atomic displacements. square Phase 723 K Ilf. pm2 723 K uA pm2 873 K 1023 K 873 K 1023 K Ni2.96Fe0.02 All.00 330 470 660 380 580 810 Ni2.95Fe0.05 Al0.85Ti0.15 380 440 600 290 370 460 Ni2.83Fe0.04 Cr0.07Mo0.06 Al0.51Ti0.31Nb0.07Mo0.08Cr0.03 250 380 550 180 230 330 Ni2.83Fe0.04 Cr0.08W0.03Mo0.02 Al0.43Ti0.28W0.08Mo0.03Cr0.10 230 340 450 30 60 80 Ni2.76Co0.09Fe0.01Cr0.06Mo0.02 Al0.79W0.08Mo0.11Cr0.03 260 340 580 20 40 50 the diffusion mobility in the crystal lattice. The probability of an atom transfer to an adjacent node of the crystal lattice also increases. The smaller the amplitudes of the atomic vibrations the greater the high-temperature strength of the Y phase. A decrease in amplitudes results in an increase in the value of the activation energy AU in Eq. 6.13 and the creep rate decreases. In the first phase practically pure NÌ3AI Table 6.5 the atomic displacements of the lighter atoms of aluminum nodes A appreciably exceed the displacement of the nickel atoms nodes B at all tested temperatures uA úịị. The replacement of approximately one sixth of the aluminum atoms with titanium atoms decreases the amplitudes of the heat vibrations in the aluminum sublattice so that now uA . The effect of titanium dissolution in the sublattice A on decreasing amplitudes becomes more evident if the temperature rises. The effect of adding molybdenum and tungsten to the y phase is even greater. One can see from Table 6.5 that the values U2A are 10-16 times less at 1023K in phases containing both these elements. The vibration amplitudes decrease less in the sublattice B. The decrease of uA is not proportional to the growth of the mean atomic mass because of Mo and W dissolution but exceeds it essentially. Actually the effective mass of atoms A in the investigated strengthening phases increases only by 64-78 in comparison with the effective mass of aluminum atoms. The mass of
