ME 350 – Lecture 10 – Chapter 6

1. ME 350 – Lecture 10 – Chapter 6 Ch6 - Engineering Materials • Alloys and Phase Diagrams • Ferrous Metals • Non-ferrous Metals • Superalloys

2. Inverse Lever Rule - Example Liquid 2000 1500 1000 α + Liquid Temperature °C α 0 10 20 30 40 50 60 70 80 90 % A

3. 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

4. Inverse Lever Rule – Example 2 2000 1500 1000 Temperature °C 0 10 20 30 40 50 60 70 80 90 % A

5. Iron-Carbon Phase Diagram γ = α = Fe3C = • Austenite can dissolve carbon up to about • Ferrite phase can dissolve carbon up to about • The difference in solubility between alpha and gamma provides opportunities for strengthening by heat treatment

6. Steel and Cast Iron Defined Iron‑carbon alloy containing from 0.02% to 2.1% carbon: Iron‑carbon alloy containing from 2.1% to about 4.3% carbon: • Both contain other alloying elements besides carbon (Ni, Cr, Mo, Mg, Si, etc.)

7. Carbon Content in Steel

8. Stainless Steel (SS) Highly alloyed steels designed for corrosion resistance • Principal alloying element, usually in concentrations 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

9. 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 ‑copper (only about 2% Be), which can be heat treated to high strengths and used for springs

10. 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 that refers to steel coated with zinc: • Widely used as alloy with copper:

11. Refractory Metals • Metals capable of enduring high temperatures - maintaining high strength and hardness at elevated temperatures • Important refractory metals: • Tantalum • Sometimes referred to as a refractory metal: • Titanium

12. 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)

13. 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

14. 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