Tham khảo tài liệu 'kỹ thuật máy bay chiến đấu episode 2 part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | STRUCTURES AND LOADS 361 embrittling titanium is hydrogen followed by oxygen and nitrogen. After forming titanium must be treated for embrittlement by chemical pickling or through heat treatment in a controlled environment. Titanium is very expensive costing about five to ten times as much as aluminum. Much of the titanium comes from the Soviet Union. To handle the aerodynamic heating of Mach 3 flight the structure of the SR-71 is about 93 titanium. The XB-70 uses a substantial amount of titanium in the forebody area. Titanium is extensively used in jet-engine components and is also used in lower-speed aircraft for such high-stress airframe components as landing-gear beams and spindles for all-moving tails. Because it does not cause galvanic corrosion with graphite-epoxy titanium is sometimes used as the substructure to graphite-epoxy skins. Reference 57 gives a more detailed discussion of titanium and its alloys. Magnesium Magnesium has a good strength-to-weight ratio tolerates high temperatures and is easily formed especially by casting forging and machining. It has been used for engine mounts wheels control hinges brackets stiffeners fuel tanks and even wings. However magnesium is very prone to corrosion and must have a protective finish. Furthermore it is flammable Mil Specs advise against the use of magnesium except to gain significant weight savings. Also magnesium should not be used in areas which are difficult to inspect or where the protective finish would be eroded by rain leading edges or engine exhaust. High-Temperature Nickel Alloys Inconel Rene 41 and Hastelloy are high-temperature nickel-based alloys suitable for hypersonic aircraft and re-entry vehicles. Inconel was used extensively in the X-15 and Rene 41 was to have been used in the X-20 Dynasoar. Hastelloy is used primarily in engine parts. These alloys are substantially heavier than aluminum or titanium and are difficult to form. For these reasons the Space Shuttle uses an aluminum structure .
