tailieunhanh - Titanium Part 12

Tham khảo tài liệu 'titanium part 12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 322 7 Beta Alloys The high strength p titanium alloys Ti-17 and Ti-6246 are used in the compressor part of aero-engines replacing the Ti-6Al-4V alloy because of their higher basic strength. A good example is the large Ti-17 fan disk shown in Fig. which is used in the GE-90 aero-engine. The fan disk shown in that figure has an outside diameter of about 800 mm and is manufactured from three separate forgings which are welded together using solid state inertia welding see Sect. . The three pieces are p forged and conventionally heat treated . they received the two-stage heat treatment shown in Fig. steps IVa and IVb . Since the p grains in the fan disk forgings will be pancake shaped typical for p processed material see Sect. with the thin dimension parallel to the axial direction of the disk. The major applied stresses acting on the fan disk will be parallel to the pancake plane of the p grains only the properties described in Sect. as properties in L test direction of p processed material see also Table will be important. As described already in Sect. the LCF strength . a combination of fatigue crack nucleation resistance and microcrack propagation resistance is the important design criteria for compressor disks. Both of these properties are good in L testing direction Table considering the anisotropy of the pancake shaped p grains. It should be pointed out however that those properties would be even better for the bi-modal microstructure and that the major drawback of the bi-modal microstructure the low fracture toughness see Fig. is not important for compressor disks because the fracture toughness has an insignificant effect on life time and no effect on inspection intervals see discussion in Sect. . As also pointed out already in Sect. for fatigue life calculations of disks based on fatigue crack propagation data it is important to use the microcrack propagation data because macrocrack propagation data .