1. 1 Subject: Composite Materials Science and Engineering Subject code: 0210080060 Prof C. H. XU School of Materials Science and Engineering Henan University of Science and Technology Chapter 2: Matrix: metals and alloys

2. 2 Matrix This chapter covers: Metal and Alloys Ferrous and nonferrous Mechanical Properties

3. 3 Ferrous Alloys: Iron (Fe) is the prime element. Widely use in industry Abundant quantity of iron-containing compounds on earth. Metallic iron and steel alloys can be produced economically. Ferrous alloys have wide range of mechanical and physical properties. Disadvantages: corrosion properties are not good relatively high density a relatively low electrical conductivity Classification: Steel and Cast irons Matrix: Metal and Alloys Ferrous

4. 4 Matrix: Metal and Alloys Ferrous - Steels Steels are iron-carbon alloys (C< 2.1%) that may contain other alloying elements; Plain carbon steels contain carbon and residual concentrations of impurities, such as silicon (Si), manganese (Mn), sulfur (S), phosphorous (P). Alloy steels have more alloying elements intentionally added. α-Fe (BCC) Fe 3 C (iron carbide)  -Fe (FCC) Martensite (α-Fe with high concentration C)

5. 5 Matrix: Metal and Alloys Ferrous - Cast Iron Cast iron: ferrous alloys with carbon 2.14 – 4.5wt % Low melting point 1150 -1300 0 C, forming by casting. Mechanical properties: brittle Four types of cast irons, according to their microstructures Grey Cast Iron White Cast Iron Malleable Cast Iron Nodular Cast Iron

6. 6 Matrix: Metal and Alloys Ferrous - Steels Corrosion or Oxidation Resistance Au, Pt … not oxidize Al, Cr, Si: formation of dense oxide scale Al 2 O 3, Cr 2 O 3, or SiO 2 (good oxidation resistance) Fe: formation of loose oxide scale (corrosion properties are not good).

7. 7 Stainless Steels (high alloy steels) they are highly resistant to corrosion, especially at ambient temperature. Main alloy element is chromium (>11wt%Cr). Nickel (Ni) and molybdenum (Mo) improves oxide scale connection. applications include gas turbines, high- temperature steam boilers, heat-treating furnaces, aircraft, and nuclear reactors. Matrix: Metal and Alloys ferrous - Stainless Steels

8. 8 Nonferrous alloys Copper and its alloys Aluminum and its alloys Magnesium and its alloys Titanium and its alloy Other alloys Matrix: Metal and Alloys nonferrous

9. 9 Aluminum Alloys Second most plentiful metal on earth high electrical and thermal conductivity, and resistance to corrosion. Aluminum and its alloys have low density (~2.7), one-third the density of steel (high specific strength) [Specific strength = strength/density] Main limitation is the low melting temperature (660 o C). Mechanical properties can be improved be cold- worked or alloying. Aluminum alloys can be up to 30 times stronger than pure Aluminum Applications; food/chemical handling, aircraft structures, bus wheels, fuel tanks

10. 10 Copper and Its Alloys Copper is soft and ductile, and is easy to machine. It is highly resistant to corrosion in various environments. Greater density than steel Specific strengths less than aluminum Excellent ductility, corrosion resistance, electrical and thermal conductivity The mechanical and corrosion-resistant properties can be improved by alloying. Matrix: Metal and Alloys nonferrous

11. 11 Brass: Copper-Zinc alloys < 40wt% Zn. The most common copper alloys are the brasses, which have substitutional zinc as the predominant alloying element. applications of brass alloys include costume jewelry, cartridge, automotive radiators, musical instruments, electronic packing, and coins. Bronzes are alloys of copper and several elements: tin (Sn), aluminum, silicon, and nickel. Beryllium (Be) coppers are stronger, have good electrical and corrosion property. Matrix: Metal and Alloys nonferrous

12. 12 Magnesium (Mg) Alloys Magnesium and its alloys have low density (1.74g/cm 3, lighter than Al) and are relatively soft. Specific strength comparable to Al Magnesium has an HCP structure, it and its alloys are difficult to deform at room temperature. Magnesium has low melting temperature (651 o C). Magnesium is susceptible to corrosion in marine environments. Fine magnesium power ignites easily. Application: automotive wheels, Matrix: Metal and Alloys nonferrous

13. 13 Titanium Pure metals have relatively low density (~4.5), a high melting point (1668 0 C). High strength-to-weight ratio Good mechanical properties to ~550°C Major limitation is the chemical reactivity with other materials at high temperatures. But the corrosion resistance at normal temperatures is unusually high Alloys are extremely strong, and highly ductile and easily forged. Applications include airplane structures, space vehicles, and in the petroleum and chemical industries. Matrix: Metal and Alloys nonferrous

14. 14 Beryllium (Be) Alloys Light metal (1.848 g/cm 3 ), lighter than Al High modulus of elasticity (42 x 10 6 psi), (stiffer than steel) High specific strengths Very expensive Toxic to some individuals, BeO is a carcinogenic material for some people. Oxidation at elevated temps. Matrix: Metal and Alloys nonferrous

15. 15 Matrix: Metal and Alloys nonferrous

16. 16 Mechanical Properties of Metal & alloy Tensile test A standard tensile specimen (ASTM E8 standard, USA) Tension Test

17. 17 Mechanical Properties of Metal & alloy Tensile test Load or force F; (unit: newton N) Elongation  l;  l = l i – l 0 Where l i is instantaneous length, l 0 is original length before load (unit: m) Engineering stress σ; where A 0 is the original cross- section area before load (unit: MPa, 1MPa = 10 6 N/m 2 ) Engineering strain: ε (unitless) Tensile load and elongation

18. 18 Mechanical Properties of Metal & alloy Tensile Testing Force – elongation curve Engineering Stress - Strain curve (1) elastic deformation (2) yielding strength (3) plastic deformation (4) Tensile strength (5) necking (6) failure strain stress 2 1 4 35 6 Engineering stress-stain behavior

19. 19 Mechanical Properties of Metal & alloy Tensile test - Elastic Behavior Elastic deformation is recoverable. In most materials, elastic deformation is linear. σ=Eε (Hooke’s Law) Where E is modulus of elasticity or Young modulus (unit: GPa; 1GPa = 10 9 N/m 2 ) In some materials, elastic deformation is non-linear Slope = modulus of elasticity Load Unload Strain ε Stress σ

20. 20 Mechanical Properties of Metal & alloy Tensile test - Poisson’s ratio Axial Z: positive strain (elongation) Axial X or Y: negative strains (contractions) Poisson’s ratio : Most metals exhibit values between 0.25 and 0.35 Strains at different direction during a load at Z direction

21. 21 Mechanical Properties of Metal & alloy Tensile test – Yield stress Plastic deformation: Irreversible Yielding: plastic deformation begins Yielding strength: σ y = 0.002 strain offset or = Low yield point. σyσy Stress-strain behavior for a metal: showing elastic plastic deformation and σ y = σ 0.002 Stress-strain behavior for some metals: showing yield point phenomenon σ y = σ low yield point

22. 22 Mechanical Properties of Metal & alloy Tensile test – tensile strength Tensile strength σ TS maximum stress on engineering stress- strain curve Strain < point ofσ TS uniform plastic deformation Strain > point ofσ TS : necking deformation Fracture strain stress 2 1 4 35 6 Engineering stress-stain behavior

23. 23 Mechanical Properties of Metal & alloy Tensile test - Ductility Ductility is a measure of the degree of plastic deformation at fracture expressed as percent elongation also expressed as percent area reduction l f and A f are length and area at fracture

24. 24 Mechanical Properties of Metal & alloy Tensile test Information: Elastic deformation Elastic modulus Plastic deformation Yield strength Elastic recovery during plastic deformation Tensile strength Non-uniform plastic deformation Fracture Ductility: Strain after fracture

25. 25 Mechanical Properties of Metal & alloy Tensile Testing - Toughness Toughness: the combination of strength and ductility. Toughness measurement: total area under a stress- strain curve. Physical means: the ability to absorb energy before fracture. Stress-strain curves

26. 26 Mechanical Properties of Metal & alloy Tensile test

27. 27 Mechanical Properties of Metal & alloy Hardness Hardness: material ’ s resistance to localized plastic deformation Simple and inexpensive Nondestructive Both tensile strength and hardness are indicators of a metal ’ s resistance to plastic deformation  TS (MPa) = 3.45HB  TS (psi) = 500HB

28. 28 Further Reading Reference Book: Introduction to Materials ( 材料概论 ) pages 35- 74 Other reference: lecture note 2