ME 350 – Ch 6, 7 – Metals & Ceramics

1. ME 350 – Ch 6, 7 – Metals & Ceramics Ch6 - Metals: • Alloys • Binary Phase Diagrams • Metal Types and Designations Ch 7 - Ceramics: • Types • Characteristics

2. Alloys An alloy = a mixture or compound of two or more elements, at least one of which is metallic • Two main categories: • Solid solutions - An alloy in which one element is in another to form a single‑phase structure • Intermediate phases - When the amount of the dissolving element in the alloy exceeds the limit of the base metal, a second phase forms in the alloy • A = any homogeneous mass of material, in which the grains all have the same crystal lattice structure

3. Two Forms of Solid Solutions • solid solution - atoms of solvent element are replaced in its unit cell by dissolved element • solid solution - atoms of dissolving element fit into vacant spaces between base metal atoms in the lattice structure • In both forms, the alloy structure is generally than either of the component elements

4. Two Forms of Solid Solutions

5. Types of Intermediate Phases • Metallic compounds – consist of a metal and nonmetal, such as Fe3C ( ) • Intermetallic compounds ‑ two metals that form a compound, such as Mg2Pb • In some alloy compositions, the intermediate phase is mixed with the primary solid solution to form a two‑phase structure • Some two‑phase alloys are important because they can be heat treated for much higher strength than

6. Phase Diagrams A graphical means of representing the phases of a metal alloy system as a function of composition and temperature • A phase diagram for two elements (at atmospheric pressure) is called a

7. Inverse Lever Rule - Example Solid phase composition: Liquid phase composition: Liquid 2000 1500 1000 α + Liquid Temperature °C Solid phase proportion: Liquid phase proportion: α 0 10 20 30 40 50 60 70 80 90 % A

8. Nickel-Copper Binary Phase Diagram: • A melt is formed with 35% Ni and 65% Cu, it is slowly cooled from 1300°C to ~1270°C: • initial solid is Ni, initial liquid is Ni • middle solid is Ni middle liquid is Ni • at end solid is Ni

9. Inverse Lever Rule – Example 2 Solid phase composition: Liquid phase composition: 2000 1500 1000 Temperature °C Solid phase proportion: Liquid phase proportion: 0 10 20 30 40 50 60 70 80 90 % A

10. Iron-Carbon Phase Diagram γ = α = Fe3C =

11. Solubility Limits of Carbon in Iron • Ferrite phase can dissolve only about carbon at 723C (1333F) • Austenite can dissolve up to about carbon at 1130C (2066F) • The difference in solubility between alpha and gamma provides opportunities for strengthening by heat treatment

12. Steel and Cast Iron Defined = an iron‑carbon alloy containing from 0.02% to 2.1% carbon = an iron‑carbon alloy containing from 2.1% to about 4.3% carbon • Steels and cast irons can also contain other alloying elements besides carbon

13. Eutectic and Eutectoid Compositions composition of Fe-C system = 4.3% C • Phase changes from solid ( + Fe3C) to liquidat 1130C (2066F) composition of Fe-C system = 0.77% C • Phase changes from  to  above 723C (1333F) • Below 0.77% C, called steels • From 0.77 to 2.1% C, called steels

14. Carbon Content in Steel

15. AISI-SAE Designation Scheme Specified by a 4‑digit number system: 10XX, where 10 indicates plain carbon steel, and XX indicates carbon % in hundredths of percentage points • For example, 1020 steel contains C • Developed by American Iron and Steel Institute (AISI) and Society of Automotive Engineers (SAE), so designation often expressed as AISI 1020 or SAE 1020

16. AISI-SAE Designation Scheme AISI‑SAE designation uses a 4‑digit number system: YYXX, where YY indicates alloying elements, and XX indicates carbon % in hundredths of % points • Examples: 13XX - Manganese steel 20XX - Nickel steel 31XX - Nickel‑chrome steel 40XX - Molybdenum steel 41XX - steel

17. Stainless Steel (SS) Highly alloyed steels designed for corrosion resistance • Principal alloying element is , usually greater than 15% • forms a thin impervious oxide film that protects surface from corrosion • Nickel (Ni) is another alloying ingredient in certain SS to increase • Carbon is used to strengthen and harden SS, but high C content reduces corrosion protection since chromium carbide forms to reduce available free Cr

18. Designation Scheme for Stainless Steels • Three‑digit AISI numbering scheme • First digit indicates general type, and last two digits give specific grade within type • Examples: Type 302 – Austenitic SS • 18% Cr, 8% Ni, 2% Mn, 0.15% C Type 430 – Ferritic SS • 17% Cr, 0% Ni, 1% Mn, 0.12% C Type 440 – Martensitic SS • 17% Cr, 0% Ni, 1% Mn, 0.65% C

19. Cast Irons Iron alloys containing from carbon and from 1% to 3% silicon • Most important is • Other types include ductile iron, white cast iron, malleable iron, and various alloy cast irons • Ductile and malleable irons possess chemistries similar to the gray and white cast irons, respectively, but result from special processing treatments

20. Cast Iron Chemistries – C & Si

21. Designations of Aluminum Alloys Alloy group Wrought codeCast code Aluminum  99.0% purity 1XXX 1XX.X Copper alloy 2XXX 2XX.X Manganese alloy 3XXX Silicon alloy 4XXX 4XX.X Zinc alloy 7XXX 7XX.X Tin alloy 8XX.X

22. Magnesium and Its Alloys • alloys of the structural metals • Available in both wrought and cast forms • Relatively easy to machine • In all processing of magnesium, small particles of the metal (such as small metal cutting chips) oxidize rapidly, and care must be taken to avoid hazards

23. Copper Alloys • Strength and hardness of copper is relatively low; to improve strength, copper is frequently alloyed • - alloy of copper and tin (typical  90% Cu, 10% Sn), widely used today and in ancient times (i.e., ) • - alloy of copper and zinc (typical  65% Cu, 35% Zn). • Highest strength alloy is beryllium‑copper (only about 2% Be), which can be heat treated to high strengths and used for springs

24. Titanium • Coefficient of thermal expansion is relatively low among metals • Stiffer and stronger than Al • Retains good strength at elevated temperatures • Pure Ti is reactive, which presents problems in processing, especially in molten state • At room temperature Ti forms a thin adherent oxide coating (TiO2) that provides excellent corrosion resistance

25. Zinc and Its Alloys • Low melting point makes it attractive as a casting metal, especially die casting • Also provides corrosion protection when coated onto steel or iron • The term steel refers to steel coated with zinc • Widely used as alloy with copper ()

26. Refractory Metals • Metals capable of enduring high temperatures - maintaining high strength and hardness at elevated temperatures • Most important refractory metals: • Other refractory metals: • Columbium • Tantalum

27. Superalloys High‑performance alloys designed to meet demanding requirements for strength and resistance to surface degradation at high service temperatures • Many superalloys contain substantial amounts of , rather than consisting of one base metal plus alloying elements • Operating temperatures often around 1100C (2000F) • Applications: gas turbines ‑ jet and rocket engines, steam turbines, and nuclear power plants (all are systems in which operating efficiency increases with higher temperatures)

28. Three Groups of Superalloys • Iron‑based alloys ‑ in some cases iron is less than 50% of total composition • Alloyed with Ni, Cr, Co • Nickel‑based alloys ‑ better high temperature strength than alloy steels • Alloyed with Cr, Co, Fe, Mo, Ti • Cobalt‑based alloys ‑  40% Co and  20% chromium • Alloyed with Ni, Mo, and W • In virtually all superalloys, including iron based, strengthening is by precipitation hardening

29. How to Enhance Mechanical Properties • – adding additional elements to increase the strength of metals • - strain hardening during deformation to increase strength (also reduces ductility) • Strengthening of the metal occurs as a byproduct of the forming operation • - heating and cooling cycles performed on a metal to beneficially change its mechanical properties • Operate by altering the microstructure of the metal, which in turn determines properties

30. Ch7 - Three Basic Categories of Ceramics • ceramics ‑ clay products such as pottery, bricks, common abrasives, and cement • ceramics ‑ more recently developed ceramics based on oxides, carbides, etc., with better mechanical or physical properties than traditional ceramics • ‑ based primarily on silica and distinguished by their noncrystalline structure

31. Strength Properties of Ceramics • Ceramics are substantially stronger in than in or in bending • Ceramics fail by much more readily than metals • grain size generally increases strength

32. Oxide Ceramics Most important oxide ceramic is • also has good hot hardness, low thermal conductivity, and good corrosion resistance

33. Carbide Ceramics Silicon carbide (), tungsten carbide (), titanium carbide (), tantalum carbide (), and chromium carbide () • WC, TiC, and TaC are valued for their hardness and in applications requiring these properties (e.g., cutting tools) • WC, TiC, and TaC must be combined with a metallic binder such as or in order to fabricate a useful solid product

34. Nitrides Important nitride ceramics are silicon nitride (Si3N4), boron nitride (BN), and titanium nitride (TiN) • Properties: usually electrically insulating, TiN being an exception • Applications: • Silicon nitride: components for gas turbines, rocket engines, and melting crucibles • Boron nitride and titanium nitride: cutting tool materials and coatings

35. Glass Ceramics • is the main component in glass products, usually comprising 50% to 75% of total chemistry • It naturally transforms into a glassy state () upon cooling from the liquid, whereas most ceramics crystallize upon solidification • Glass-ceramics are a class of ceramic material that contain % crystalline phase with very small grain size (0.1 - 1μm) and are usually . • They can contain sodium oxide (Na2O), calcium oxide (CaO), aluminum oxide (Al2O3), magnesium oxide (MgO), potassium oxide (K2O), lead oxide (PbO), and boron oxide (B2O3)

36. Advantages of Glass‑Ceramics • Efficiency of processing in the glassy state • Close dimensional control over final shape • Good mechanical and physical properties • High strength (stronger than glass) • Absence of porosity; low thermal expansion • High resistance to thermal shock • Applications: • Cooking ware • Heat exchangers • Missile radomes

37. Graphite Form of carbon with a high content of crystalline carbon in the form of layers • Bonding between atoms in layers is covalent and strong, but parallel layers are bonded to each other by weak van der Waals forces • Structure makes graphite anisotropic; properties vary significantly with direction • As a powder it is a lubricant, but in traditional solid form it is a refractory • As a fiber, it is a high strength structural material (e.g., fiber reinforced plastics)

38. Diamond Carbon is a cubic crystalline structure with covalent bonding between atoms – very high hardness • Applications: cutting tools and grinding wheels; also used in dressing tools to sharpen grinding wheels • Synthetic diamonds fabricated by heating graphite to around 3000C (5400F) under very high pressures

39. Boron Semi-metallic element in same periodic group as aluminum • Properties: , semiconducting properties, and very high modulus of elasticity) in fiber form • Applications: B2O3 in certain glasses, as a nitride (cBN) for cutting tools, and in nearly pure form as a fiber in polymer matrix composites

40. Guide to Processing Ceramics • Processing of ceramics can be divided into two basic categories: • Molten ceramics - major category of molten ceramics is glassworking (solidification processes) • Particulate ceramics - traditional and new ceramics (particulate processing)