Subject: Composite Materials Science and Engineering Subject code: 0210080060

1. Subject: Composite MaterialsScience and EngineeringSubject 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. Matrix This chapter covers: • Metal and Alloys • Ferrous and nonferrous • Mechanical Properties

3. Matrix: Metal and AlloysFerrous • 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

4. Matrix: Metal and AlloysFerrous - 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) • Fe3C (iron carbide) • -Fe (FCC) Martensite (α-Fe with high concentration C)

5. Matrix: Metal and AlloysFerrous - Cast Iron • Cast iron: ferrous alloys with carbon 2.14 – 4.5wt % • Low melting point 1150 -13000C, 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. Matrix: Metal and AlloysFerrous - Steels • Corrosion or Oxidation Resistance • Au, Pt … not oxidize • Al, Cr, Si: formation of dense oxide scale Al2O3, Cr2O3, or SiO2 (good oxidation resistance) • Fe: formation of loose oxide scale (corrosion properties are not good).

7. Matrix: Metal and Alloysferrous - Stainless Steels • 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) improvesoxide scale connection. • applications include gas turbines, high-temperature steam boilers, heat-treating furnaces, aircraft, and nuclear reactors.

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

9. Matrix: Metal and Alloys nonferrous 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 (660oC). • 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. Matrix: Metal and Alloys nonferrous 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.

11. Matrix: Metal and Alloys nonferrous • 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.

12. Matrix: Metal and Alloys nonferrous Magnesium (Mg) Alloys • Magnesium and its alloys have low density (1.74g/cm3, 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 (651oC). • Magnesium is susceptible to corrosion in marine environments. • Fine magnesium power ignites easily. • Application: automotive wheels,

13. Matrix: Metal and Alloys nonferrous Titanium • Pure metals have relatively low density (~4.5), a high melting point (16680C). • 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.

14. Matrix: Metal and Alloys nonferrous Beryllium (Be) Alloys • Light metal (1.848 g/cm3), lighter than Al • High modulus of elasticity (42 x 106psi), (stiffer than steel) • High specific strengths • Very expensive • Toxic to some individuals, BeO is a carcinogenic material for some people. • Oxidation at elevated temps.

15. Matrix: Metal and Alloys nonferrous

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

17. Mechanical Properties of Metal & alloy Tensile test • Load or force F; (unit: newton N) • Elongation l; l = li – l0 Where li is instantaneous length, l0 is original length before load (unit: m) • Engineering stressσ; where A0 is the original cross-section area before load (unit: MPa, 1MPa = 106 N/m2) • Engineering strain:ε (unitless) Tensile load and elongation

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

19. Stress σ Unload Slope = modulus of elasticity Load Strain ε Mechanical Properties of Metal & alloyTensile 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 = 109 N/m2) • In some materials, elastic deformation is non-linear

20. Mechanical Properties of Metal & alloyTensile 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. Mechanical Properties of Metal & alloy Tensile test– Yield stress • Plastic deformation: Irreversible • Yielding: plastic deformation begins • Yielding strength:σy = 0.002 strain offset or = Low yield point. Stress-strain behavior for a metal: showing elastic plastic deformation and σy = σ0.002 Stress-strain behavior for some metals: showing yield point phenomenon σy = σlow yield point σy

22. 4 3 5 2 6 stress 1 Engineering stress-stain behavior strain Mechanical Properties of Metal & alloy Tensile test– tensile strength • Tensile strength σTS • maximum stress on engineering stress-strain curve • Strain < point ofσTS uniform plastic deformation • Strain > point ofσTS: necking deformation • Fracture

23. Mechanical Properties of Metal & alloyTensile test - Ductility • Ductility is a measure of the degree of plastic deformation at fracture • expressed as percent elongation • also expressed as percent area reduction • lf and Af are length and area at fracture

24. Mechanical Properties of Metal & alloyTensile 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. Mechanical Properties of Metal & alloyTensile 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. Mechanical Properties of Metal & alloyTensile test

27. Mechanical Properties of Metal & alloyHardness • 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. Further Reading Reference Book: Introduction to Materials (材料概论) pages 35-74 Other reference: lecture note 2