This presentation covers the design criteria, different types of alloys, composites used in the aerospace industry over the decades , the problems that need to be overcome especially at the high temperature and stress and description of the future aerospace materials are discussed.

1. SEMINAR
(COURSE CODE:MTN 700)
Presented by
Harshan
E.No:19545003
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2. Introduction
Understanding Aerospace Materials
• Physical properties (e.g. density)
• Mechanical properties (e.g. stiffness, strength and toughness)
• Chemical properties (e.g. corrosion and oxidation)
• Thermal properties (e.g. thermal conductivity)
• Electrical properties (e.g. electrical conductivity)
• Materials technology aims to transform materials into useful structures or components
e.g: Converting soft Aluminium into a high strength metal alloy for use in an aircraft wing
e.g: Making a ceramic composite with high thermal insulation properties needed for the heat shields of
spacecraft.
The properties needed by the material are depended on the type of the component
• Ability to carry stress without deforming excessively or breaking
• Resist corrosion or oxidation
• Operate at high temperature without softening
• Provide high structural performance at low weight or low cost
• ability to carry stress without deforming excessively or breaking;
• resist corrosion or oxidation;
• operate at high temperature without softening;
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3. The main groups of materials used in aerospace structures
• Aluminium alloys
• Titanium alloys
• Steels
• Composites
• Nickel-based alloys
Table 1. Grading of Aerospace Materials on Key Design Factors
Source: Introduction to Aerospace Materials by Adrian P Mouritz
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4. Fig. 1. Structural Materials and their Weight Percentage used in the Airframes of Civilian and Military Aircrafts
Source: Introduction to Aerospace Materials by Adrian P Mouritz
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6. Fig. 2. Usage of Different Materials in the Series of Boeing Aircraft
• The density of Al is nearly one-third that of steel whereas the 7075-T6 alloy has a yield strength which reaches
upto 515 MPa.
• Further Mg-based alloys have good stiffness. These properties of Mg-based alloys helps in weight reduction
and increase in payload.
• The usage of composite materials is primarily due to fatigue, corrosion resistance and high amount of specific
strength. In the composite materials, ceramic matrix composites can bear upto 1350°C.
• Nickel based alloys are better than stainless steels at high temperatures greater than 650°C.
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7. Design Criteria of Aircraft Materials
Factors:
• Loading
• Ability to maintain
• Manufacture.
Airframe materials
• Wings should have high tensile and compressive strengths
• In Fuselage 2024 Aluminium based alloy has been used because of intermediate yield strength (320 MPa) and
fair fracture toughness (36 MPa m0.5).
• Carbon fiber reinforced polymer usage has been increased because of high temperature withstand capability
(upto 350°C), high strength (4825 MPa) and elastic modulus upto 240 GPa.
Materials for engine
• The materials which are to be considered for engine applications should have less weight and enhancement in
the mechanical properties to withstand high temperatures and corrosive conditions
• Aluminium based alloys, Ti-based alloys and Polymer composites are the preferable materials for the cold
section parts
• Hot section such as turbines has a working temperatures of 1350-1500°C
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8. Recent Progress in Materials for Aerospace Applications
Aluminium Based Alloys
• Aluminium is used because it is light in weight, lesser cost and easy to manufacture
2000 series Aluminium-Copper Based Alloys
• These are alloyed with copper and can undergo heat treatment to give a strength of steel.
• Alloys that have been used include 2024-T3 and 2324-T39 both in the form of rolled plate
• 2xxx means Al-Cu-Mg alloys
7000 series Aluminium-Zinc Based Alloys
• The highest strength is shown by 7075-T6 alloy which has yield strength of 510 MPa.
• 7xxx means Al-Zn-Mg-Cu alloys.
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9. Magnesium Based Alloys
• The attraction of Mg-based alloys are low density, ability to recycle, castability and having in abundance
• The disadvantages of Mg based alloys for the Aircraft applications are their poor corrosion resistance
Titanium Based Alloys
• The main attraction of Ti-based alloys are good corrosion resistance, good performance at elevated temperatures
and high specific strength
Alpha Titanium Alloys
• Generally Alpha Ti alloys has better properties such as corrosion resistance, creep resistance and low density.
Beta Titanium Alloys
• Beta Ti alloys have good fatigue and tensile strength
Alpha-Beta Titanium Alloys
• The Alpha-beta alloy is primarily used Ti-based alloy because it consists of excellent combinations of fracture
toughness, strength and ductility.
• Ti-6Al-4V is the most widely used when compared with other alloys in this group
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10. Composite Materials
• Composite materials usage has increased to such an extent that Boeing 787 aircrafts constitutes 50% and Airbus
A380 constitutes more than 25%.
• The attractiveness of the composite materials is due to higher elevated temperature resistance, corrosion
resistance and higher specific strength when compared with most metals.
Fig. 3. The % of Total Structural Weight and Use of Composites in Various Aircraft Models
Source: Progress in Aerospace Sciences, 2018 - Elsevier
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11. Fig. 4. Percentage of materials usage in Boeing 777 Fig. 5. Material usage in last 10 years( Boeing 777 vs 787)
Source: ResearchGate Source: ResearchGate 11

12. Ceramic matrix composite material
• Stability at elevated temperatures (1400°C), high hardness( for Al2O3 based composite it is 23 GPa) and
excellent corrosion resistance
• Ceramic matrix composites are used in exhaust nozzle which is a high temperature section.
• For aircraft brakes where the temperatures could reach upto 1200°C, the suitable material to be used is carbon
fiber reinforced silicon carbide.
• CMCs experiences poor fracture toughness
Metal matrix composite materials
• These have low thermal expansion coefficients, low fracture toughness, higher yield strength and suitable
amount of wear resistance.
Polymer Matrix Composites
• Thermoplastics and thermosets
• The key features of PMCs are lightweight and specific strength
• Thermoplastic and thermoset PMCs are used in the aircraft structural application such as landing-gear doors and
flaps
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13. Steels
• Although steel is used in many parts for the aircraft applications, it experienced a severe decline in recent years
due to poor corrosion resistance when compared with composites and new alloys
• Ultra-high strength steel found to be more attractive which has a yield strength above 1375 MPa.
Table 2. The Compositions, Applications and Yield Strengths of Ultra-High Strengths Low Alloy Steels
Source: Introduction to Aerospace Materials by Adrian P Mouritz
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14. Nickel based Superalloy
• Recently advanced Ni-based superalloys have high strength at elevated temperatures.
• The tensile strength of wrought Ni-Cr-W superalloy at 800°C can reach a maximum of 550 MPa.
• Because of their good strength at elevated temperature, parts such as turbine section and combustor are made
with these alloys which has a 1100-1250°C as their temperature of operation.
• Oxidation resistance and hot corrosion resistance increases in these alloys with the addition of chromium.
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15. Challenges Faced in the Progress of Recently Advanced Materials
Fretting wear
• This is caused by minor amplitude of oscillation between any two contact bodies . It occurs in engine parts as
well as structural components.
• Methods to prevent fretting wear: Use of lubricants, new design.
Corrosion
• Types of corrosion such as galvanic corrosion, crevice and pitting corrosion.
• Coatings are used to prevent this. To inhibit the corrosion chromium can be used.
Fatigue
• Common occurrence among all metal airframes due to the repeated flight cycles
Creep
• Occurs in the high temperature regions
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16. Future Aerospace Materials
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17. Stealth Materials
• Radar absorbing materials and structures are designed to absorb radar waves and minimize or eliminate
reflection
• Since these radar waves are not returned , RAM and RAS provide a reduced signature for detection
• One such example for RAM is Iron ball paint.
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18. Future Platforms
• High temperature
• Superior mechanical properties
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19. Takeaways
• From early 1920s Al-based alloys were using because of their good mechanical behaviour.
• The criteria of materials for engines should have good corrosion resistance at elevated temperatures and less
density. In the compressor section of an aircraft, temperature upto 600°C are recorded where Ti-based alloys
can be used.
• For the turbine section Ni-based super alloys are used where temperatures upto 1500°C takes place.
• The usage of composite materials has been increasing.
• The advantage of magnesium over the other metals is its lesser density
• In the future several properties such as corrosion, fretting wear will remain as a challenges for the
development of next generation materials.
• Stealth technology has an immense scope
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20. References
• T. Dursun, C. Soutis, Recent developments in advanced aircraft aluminium alloys, Mater. Des. 56 (2014) 862–
871
• A. Warren, Developments and challenges for aluminum–A boeing perspective, in:Materials Forum, Citeseer,
2004
• https://link.springer.com/chapter/10.1007/978-981-10-2134-3_24
• https://www.sciencedirect.com/science/article/pii/S026130691400764X
• https://www.globalspec.com/learnmore/materials_chemicals_adhesives/electrical_optical_specialty_materials/r
adar_absorbing_materials_structures_ram_ras
• https://cr4.globalspec.com/thread/69537/Jet-Fighters-Escaping-Radar
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21. Thank you
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