Jet Engine MaterialsA quick overview of the materials requirements, the materials being used, and the materials being developed

Motivation for Materials DevelopmentHigher Operating TemperaturesHigher Rotational SpeedsLower Weight Engine ComponentsLonger Operating LifetimeDecreased Failure OccurrenceThis all adds up to:Better PerformanceLower Life Cycle Costs

Materials Requirementsthousands of operating hours at temperatures up to 1,100C (2000 F)high thermal stresses caused by rapid temperature changes and large temperature gradientshigh mechanical stresses due to high rotational speeds and large aerodynamic forceslow- and high-frequency vibrational loadingoxidationcorrosiontime- , temperature- and stress-dependent effects such as creep, stress rupture, and high- and low-cycle fatigue.

Regions of the EngineCold SectionsInlet/FanCompressorCasingHot SectionsCombustorTurbine/Outlet

Cold Section Materials RequirementsHigh Strength (static, fatigue)High StiffnessLow WeightMaterials:Titanium AlloysAluminum AlloysPolymer CompositesTitanium intermetallics and composites

Applications of Polymer Composites

Fiber Reinforced Polymer Composite Properties - Graphite/KevlarVery high strength-weight ratiosVery high stiffness-weight ratio (graphite)Versatility of design and manufactureSpecific gravity: ~1.6 (compared to 4.5 for titanium & 2.8 for aluminum)Can only be used at low temperatures < 300 C (600 F)

Titanium alloys used for critical cold section componentsFan disks/bladeCompressor disks/bladesTypical Alloy: Ti-6Al-4V

Titanium PropertiesHigh strength & stiffness to weight ratios > 150 ksi, E = 18 MsiSpecific gravity of 4.5 ( 58 % that of steel)Titanium alloys can be used up to temperatures of ~ 590 C (1100 F)Good oxidation/corrosion resistance (also used in medical implants)High strength alloys hard to work - therefore many engine components are cast

Metallurgy of disks critical to achieve desired properties and to eliminate defectsAccident occurred JUL-19-89 at SIOUX CITY, IA Aircraft: MCDONNELL DOUGLAS DC-10-10, Injuries: 111 Fatal, 47 Serious, 125 Minor, 13 Uninjured.A FATIGUE CRACK ORIGINATING FROM A PREVIOUSLY UNDECTECTED METALLURGICAL DEFECT LOCATED IN A CRITICAL AREA OF THE STAGE 1 FAN DISK THAT WAS MANUFACTURED BY GENERAL ELECTRIC AIRCRAFT ENGINES. THE SUBSEQUENT CATASTROPHIC DISINTEGRATION OF THE DISK RESULTED IN THE LIBERATION OF DEBRIS IN A PATTERN OF DISTRIBUTION AND WITH ENERGY LEVELS THAT EXCEEDED THE LEVEL OF PROTECTION PROVIDED BY DESIGN FEATURES OF THE HYDRAULIC SYSTEMS THAT OPERATED THE DC-10'S FLIGHT CONTROLS.

Aluminum alloys can reduce weight over titaniumConventional alloys have lower strength/weight ratios than Ti but more advanced alloys approach that of Ti.Specific gravity: 2.8 ( 62 % that of Ti)Lower cost than TiMax temp for advanced alloys: ~ 350 C (600 F)Lower weight & rotating part inertia

Titanium Aluminide Ti3AlAn intermetallic alloy of Ti and AlExtends the temperature range of Ti from 1100 F to 1200-1300 FSuffers from embrittlement due to exposure to atmosphere at high temperature - needs to be coated.

Titanium Composites (MMC)Titanium matrix with SiC fibersDecreases weight while increases strength and creep strengthTYPICAL Ti/SiC COMPOSITE100X

Hot Section Materials RequirementsHigh Strength (static, fatigue, creep-rupture)High temperature resistance 850 C - 1100 C (1600 F - 2000 F)Corrosion/oxidation resistanceLow Weight

High Temperatures - 1100 C (2000 F)Creep becomes at factor for conventional metals when the operating temperature reaches approximately 0.4 Tm (absolute melting temp.) Conventional engineering metals at 1100 C:Steel ~0.9 TmAluminum~1.4 TmTitanium ~0.7 TmConclusion: We need something other than conventional materials!

High Temperatures - 1100 C (2000 F)What Materials Can Be Used?Unconventional metal alloys - or superalloys Ceramics

SuperalloysNickel (or Cobalt) based materialsCan be used in load bearing applications up to 0.8Tm - this fraction is higher than for any other class of engineering alloys!High strength /stiffnessSpecific gravity ~8.8 (relatively heavy)Over 50% weight of current engines

Typical Compositions of SuperalloysCHEMICAL COMPOSITION, WEIGHT PERCENTChromium yields corrosion resistance

Microstructure of a SuperalloySuperalloys are dispersion hardenedNi3Al and Ni3Ti in a Ni matrixParticles resist dislocation motion and resist growth at high temperatures

Creep - RuptureStrain increases over time under a static load - usually only at elevated temperatures (atoms more mobile at higher temperatures)The higher energy states of the atoms at grain boundaries causes grain boundaries - particularly ones transverse to load axis - to creep at a rate faster than within grainsCan increase creep-rupture strength by eliminating transverse grain boundaries

Controlled grain structure in turbine blades:Equi-axedDirectionally solidified (DS)Single Crystal (SX)

Performance of superalloy parts enhanced with thermal barrier coatingsThin coating - plasma sprayedMCrALY coating materialsIncreased corrosion/oxidation resistanceCan reduce superalloy surface temperature by up to 40 C (~100 F)

Non-metallics - CeramicsCobaltNickelChromiumTungstenTantalumSiliconNitrogenCarbonSUPERALLOYCERAMIC

Ceramics - AdvantagesHigher TemperaturesLower CostAvailability of Raw MaterialsLighter WeightMaterials:Al2O3, Si3N4, SiC, MgO

Ceramics - ChallengesDUCTILITYTOUGHNESSIMPACTCRITICAL FLAW SIZE

Ceramic CompositesCeramic Fiber Reinforced Ceramic MatrixImprove toughnessImprove defect toleranceFiber pre-form impregnated with powder and then hot- pressed to fuse matrix

Carbon-Carbon compositeCarbon fibers in a carbon matrixHas the potential for the highest temperature capability > 2000 C (~4000 F)Must be protected from oxidation (e.g. SiC)Currently used for nose-cone for space shuttle which has reentry temperatures of 1650 C (3000 F)

Trends in turbine materialsTURBINE ROTOR INLETTEMP, F

Materials for F109 engineF109 FAN MODULE MATERIALS

F109 HP COMPRESSOR MATERIALSTi 6-4INCO 718Ti 6-2-4-2INCO 625 (side plates)INCO 718 (vanes)201-T6 Aluminum17-4 PHHAST X

F109 COMBUSTOR/MIDFRAME MATERIALSINCO 600HAST XHAST SINCO 718INCO 718INCO 718HS 188+ TBCHS 188300 SSHS 188

WASP BINCO 718HAST XHAST XMAR-M 247DSHAST SMAR-M 247DSINCO 738MAR-M 247DSMAR-M 247INCO 738F109 HP TURBINE MATERIALS

WASPALOYWASPALOYWASPALOYWASPALOYWASPALOYHAST X BACK WITH HAST X0.032 CELL. HONEYCOMBEQUIAXED MAR-M 247COATED WITH RT-21EQUIAXED MAR-M 247HASTELLOY XHAST X BACK WITH HAST X0.032 CELL. HONEYCOMBINCONEL 625 HAST X BACK WITHHAST X0.032 CELL.HONEYCOMBEQUIAXED MAR-M 247 COATED WITH RT-21INCONEL 625 HAST X BACK WITH HAST X0.032 CELL. HONEYCOMBF109 LP TURBINE MATERIALS