FM 1-506 Fundamentals of Aircraft Power Plants ... - Survival Books

WWW.SURVIVALEBOOKS.COMFM 1-506Thermal shock resistance—the ability of a metalto withstand extreme changes in temperature inshort periods of time.Hardness—the ability of a metal to resistabrasion penetration cutting action or permanentdistortion. Hardness may be increasedby working the metal or by heat treatment.Alloying—the combining of metals in their moltenstate to create desirable qualities or reduceor eliminate undesirable qualities.Common metal working terms include the following:Casting—a process whereby molten metalsolidifies in a mold.Forging—a process of plastic deformationunder pressure that may be slowly or quicklyappliedElectrochemical machining (ECM)—controlledhigh-speed deplating using a shaped tool(cathode), an electricity-conducting solutionand the workpiece (anode).Machining—any process where metal is formedby cuttin,- hot or cold rolling pinching, punching,grinding, or by laser beams.Extrusion—pushing through a die to formvarious cross-sectional shapes.Welding—a process of fusing two pieces ofmetal together by locally melting part of thematerial by arc welders, plasmas, lasers, orelectron beams.Pressing—a process of blending, pressing,sintering (fusing the power particles togetherthrough heat), and coining metals out of prealloyedpowders.Protective finish and surface treatment—includesplating by electrical and chemicalprocesses ceramic coatings, or painting. Surfacetreatments for increased wear may take theform of nitriding, cyaniding, carburizing, diffusioncoating and flame plating.Shot peening—a plastic flow or stretching of ametal’s surface by a rain of round metallic shotthrown at high velocity. Shot peening alsoserves to work-harden metals, especiallyaluminum alloy.Heat treatment—a series of operations involvingthe controlled heating and cooling of metalsin the solid state. Its purposes is to change amechanical property or combination of propertiesso that the metal will be more useful,serviceable, and safe for a specific purpose. Itincludes normalizing annealing stress relievingtemperingand hardening.Inspection (strictly speaking not a part of themetalworking process but integrally associatedwith it) – includes magnetic particle and dyepenetrant inspection, X-ray inspection dimensionaland visual inspection, and inspection bydevices using sound, light, and air.Heat Ranges of MetalsThe operating conditions inside a gas turbine enginevary considerably, and metals differ in their ability tosatisfactorily meet these conditions.Aluminum Alloys. Aluminum and its alloys areused in temperature ranges up to 500ºF. With low densityand good strength-to-weight ratios, aluminum forgingsand castings are used extensively for centrifugal compressorwheels and housings, air inlet sections, accessorysections, and for the accessories themselves.Magnesium Alloys. Magnesium is the world’slightest structural metal. Aluminum is 15 times heavier,titanium 25 times heavier, steel 4 times heavier, andcopper and nickel alloys are 5 times heavier. Magnesiumis combined with small amounts of certain other metals,including aluminum, manganese, zinc, zirconium,thorium, and others, to obtain the strong lightweightalloys needed for structural purposes.Titanium Alloys. Titanium and its alloys are usedfor axial-flow compressor wheels, blades, and otherforged components in many large, high-performanceengines. Titanium combines high strength with low densityand is suitable for applications up to 100ºF.Steel Alloys. This group includes high-chromium,molybdenum, high-nickel, and iron-base alloys in additionto low-alloy steels. Because of the relatively lowmaterial cost, ease of fabrication, and good mechanicalproperties, low-alloy steels are commonly used for bothrotating and static engine components such as compressorrotor blades, wheels, spacers, stator vanes and structuralmembers. Low-alloy steels can be heat-treated andcan withstand temperatures up to 100°F. High nickelchromiumiron-base alloys can be used up to 1250ºF.Nickel-Base Alloys. Nickel-base alloys are some ofthe best metals for use between 1200ºF and 1800ºF. Mostcontain little or no iron. They develop high-temperaturestrength by age hardening and are chacterized by longtimecreep-rupture strength as well as high ultimate andyield strength combined with good ductility. Many ofthese materials, originally developed for turbine bucket3-25