Jet Engine Materials A quick overview of the materials requirements, the materials being used, and the materials being developed
Motivation for Materials Development • Higher Operating Temperatures • Higher Rotational Speeds • Lower Weight Engine Components • Longer Operating Lifetime • Decreased Failure Occurrence • This all adds up to: • Better Performance • Lower Life Cycle Costs
Materials Requirements • thousands of operating hours at temperatures up to 1,100°C (2000 °F) • high thermal stresses caused by rapid temperature changes and large temperature gradients • high mechanical stresses due to high rotational speeds and large aerodynamic forces • low- and high-frequency vibrational loading • oxidation • corrosion • time- , temperature- and stress-dependent effects such as creep, stress rupture, and high- and low-cycle fatigue.
Regions of the Engine • Cold Sections • Inlet/Fan • Compressor • Casing • Hot Sections • Combustor • Turbine/Outlet
Cold Section Materials Requirements • High Strength (static, fatigue) • High Stiffness • Low Weight • Materials: • Titanium Alloys • Aluminum Alloys • Polymer Composites • Titanium intermetallics and composites
Fiber Reinforced Polymer Composite Properties - Graphite/Kevlar • Very high strength-weight ratios • Very high stiffness-weight ratio (graphite) • Versatility of design and manufacture • Specific 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 components • Fan disks/blade • Compressor disks/blades • Typical Alloy:Ti-6Al-4V
Titanium Properties • High strength & stiffness to weight ratios > 150 ksi, E = 18 Msi • Specific 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 defects • Accident occurred JUL-19-89 at SIOUX CITY, IAAircraft: 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 titanium • Conventional 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 Ti • Max temp for advanced alloys: ~ 350 °C (600 °F) • Lower weight & rotating part inertia
Titanium Aluminide Ti3Al • An intermetallic alloy of Ti and Al • Extends the temperature range of Ti from 1100 °F to 1200-1300 °F • Suffers from embrittlement due to exposure to atmosphere at high temperature - needs to be coated.
Titanium Composites (MMC) • Titanium matrix with SiC fibers • Decreases weight while increases strength and creep strength TYPICAL Ti/SiC COMPOSITE 100X
Hot Section Materials Requirements • High Strength(static, fatigue, creep-rupture) • High temperatureresistance 850 °C - 1100 °C (1600 °F - 2000 °F) • Corrosion/oxidation resistance • Low 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 Tm • Aluminum ~1.4 Tm • Titanium ~0.7 Tm • Conclusion: We need something other than conventional materials!
High Temperatures - 1100 °C (2000 °F)What Materials Can Be Used? • Unconventional metal alloys - or superalloys • Ceramics
Superalloys • Nickel (or Cobalt) based materials • Can be used in load bearing applications up to 0.8Tm - this fraction is higher than for any other class of engineering alloys! • High strength /stiffness • Specific gravity ~8.8 (relatively heavy) • Over 50% weight of current engines
Typical Compositions of Superalloys CHEMICAL COMPOSITION, WEIGHT PERCENT Chromium yields corrosionresistance
Microstructure of a Superalloy • Superalloys are dispersion hardened • Ni3Al and Ni3Tiin a Ni matrix • Particles resistdislocation motion andresist growth at hightemperatures
Creep - Rupture • Strain 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 grains • Can increase creep-rupture strength by eliminating transverse grain boundaries
Controlled grain structure in turbine blades: Directionally solidified (DS) Single Crystal (SX) Equi-axed
Performance of superalloy parts enhanced with thermal barrier coatings • Thin coating - plasma sprayed • MCrALY coating materials • Increased corrosion/oxidation resistance • Can reduce superalloy surface temperature by up to 40 °C (~100 °F)
Non-metallics - Ceramics • Cobalt • Nickel • Chromium • Tungsten • Tantalum CERAMIC • Silicon • Nitrogen • Carbon SUPERALLOY
Ceramics - Advantages • Higher Temperatures • Lower Cost • Availability of Raw Materials • Lighter Weight • Materials: • Al2O3, Si3N4, SiC, MgO
Superalloys Ceramics Ceramics - Challenges DUCTILITY IMPACT TOUGHNESS CRITICAL FLAW SIZE
Ceramic Composites • Ceramic Fiber Reinforced Ceramic Matrix • Improve toughness • Improve defecttolerance • Fiber pre-form impregnated with powder and then hot-pressed to fuse matrix
Carbon-Carbon composite • Carbon fibers in a carbon matrix • Has 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 materials TURBINE ROTOR INLET TEMP, F
Materials for F109 engine F109 FAN MODULE MATERIALS
F109 HP COMPRESSOR MATERIALS INCO 625 (side plates) INCO 718 (vanes) 201-T6 Aluminum HAST X 17-4 PH Ti 6-4 INCO 718 Ti 6-2-4-2
F109 COMBUSTOR/MIDFRAME MATERIALS HS 188 + TBC INCO 718 300 SS HS 188 INCO 718 INCO 718 INCO 600 HS 188 HAST S HAST X
F109 HP TURBINE MATERIALS MAR-M 247 INCO 738 MAR-M 247 DS MAR-M 247 DS MAR-M 247 DS HAST X HAST S INCO 738 HAST X INCO 718 WASP B
F109 LP TURBINE MATERIALS HAST X BACK WITH HAST X 0.032 CELL. HONEYCOMB INCONEL 625 HAST X BACK WITH HAST X 0.032 CELL. HONEYCOMB INCONEL 625 HASTELLOY X EQUIAXED MAR-M 247 COATED WITH RT-21 EQUIAXED MAR-M 247 EQUIAXED MAR-M 247 COATED WITH RT-21 HAST X BACK WITH HAST X0.032 CELL. HONEYCOMB HAST X BACK WITH HAST X 0.032 CELL. HONEYCOMB WASPALOY WASPALOY WASPALOY WASPALOY WASPALOY