Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Summary of Material Science Chapter 1: Science of Materials Chapter 2: Properties of Materials Chapter 3: Material Testing Chapter 4: Alloys of Materials Chapter 5: Plain Carbon Steels Chapter 6: Heat Treatment Chapter 7: Cast Iron Chapter 8: Plastics/Polymers Chapter 9: Composite Materials Chapter 10: Ceramics Chapter 11: Semiconductors & Diodes Chapter 12: Biomaterials Chapter 13: Electrochemistry

Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Alloys of Materials Pure metal objects are used where good electrical conductivity, good thermal conductivity, good corrosion resistance or a combination of these properties are required. However, pure metals usually lack the strength required for structural materials. Therefore alloys are mainly used for structural materials since they are formulated to give superior mechanical properties.

Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Alloys of Materials Useful alloys can only be produced from component materials, which are soluble in each other in the molten state. That is, they must be completely miscible It would be useless to form an alloy with zinc and lead. The molten zinc would float to the top of the molten lead and upon cooling, they would form separate layers in the solid state.

Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Alloys of Materials Alloys are formed in three ways: 1.If alloying components in the molten solution have similar chemical properties, they will not react together but form a solid solution. 2.If the alloying component has different chemical properties they may attract each other and form chemical compounds. Fe 3 C 3.Or you get 1 and 2 occurring Upon cooling they will tend to separate out at the grain boundaries to form a heterogeneous mixture.

Alloying Elements for Steel: Aluminium (1%)-gives steels hard, wear-resistant skin by the process nitriding. Chromium (small amounts)-give hard carbides improves corrosion resistance and heat resistance (stainless steel). Cobalt improves the ability of tools steels to operate at high temperatures without softening. Copper (0.5%)- increase corrosion resistance Lead (0.2%)-improves machinability but reduces strength Alloying Elements

Alloying Elements for Steel: Nickel - improves corrosion resistance of steel. Silicon (0.3 %)- silicon improves the fluidity of casting steels without the reduction in mechanical properties Titanium (1%) -in stainless helps to reduce weld decay and temper brittleness. Tungsten-promotes the formation of very hard carbides Others mentioned in the notes Alloying Elements

Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering SOLID SOLUTIONS Most metals are completely and mutually soluble in the liquid state. There are two types of solid solution: 1.Substitutional solid solution 2.Interstitial solid solution Carbon atoms between iron atoms Iron atoms forming a face- centred cubic lattice

Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering PHASE Phase: A portion of a system which is of uniform composition and texture throughout, and which is separated from the other phases by clearly defined surfaces. Aluminum-Copper Alloy

PHASE When a liquid solution of two metals (binary alloy) solidifies one of the following will occur: 1.Soluble metals become insoluble in the solid state and separate out as grains in the pure state. Thus there will be two phases present. 2.Soluble metals remain soluble in the solid state resulting in a single-phase “solid solution” consisting of grains of the same composition. 3.The two metals may react together chemically to form an "intermetallic compound". Again a single phase consisting of many grains of the same composition. Liquid

Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering ALLOY TYPES Binary alloys can be classified into the following types: Simple eutectic type. The two components are soluble in each other in the liquid state, but completely insoluble in each other in the solid state. Solid solution type. The two components are completely soluble in each other both in the liquid state and in the solid state. Combination type. The two components are completely soluble in the liquid state, but are only partially soluble in the solid state. Thus the type of alloy combines some of the characteristics of both the previous types.

Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Eutectic Composition α ≠ 100% Pb β ≠ 100% Sn Soild α+β Liquid Solid α Solid β

Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Simple eutectic type

Dr. Joseph Stokes School of Mechanical & Manufacturing Engineering Combination Type

Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Solid Solution Type

Dr. Joseph Stokes School of Mechanical & Manufacturing Engineering Combination Type

Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering

HYPOEUTECTIC & HYPEREUTECTIC

COMPLEX PHASE DIAGRAMS: Cu-Zn