L5_Aalloying need_solid solution types_rules_MMS
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The document discusses alloys and their properties. It defines an alloy as a mixture of two or more elements having metallic properties. Alloys are made to enhance properties like hardness, lower melting point, increase tensile strength, improve corrosion resistance, modify color, and provide better castability compared to pure metals. Solid solutions are important alloy systems where solute atoms dissolve into the solvent metal lattice. There are two types of solid solutions - substitutional and interstitial. Hume-Rothery rules govern the solid solubility between elements based on factors like atomic size, chemical affinity, relative valency, and crystal structure.
L5_Aalloying need_solid solution types_rules_MMS
- 1. A1MET201 Metallurgy and Material Science Jagadeesh N B.Tech, M. Tech (NIT -W) Materials Faculty of Materials and Manufacturing Sciences MVGR College of Engineering-Autonomous Vizianagaram-535005 njagadeesh@mvgrce.edu.in
- 2. Jagadeesh N, B. Tech, M. Tech (NIT W), Assistant Professor 2
- 3. What is an alloy? Alloy is a mixture of two or more elements having metallic properties. The element present in the largest portion is a metal and others can be metals or non-metals The element which is present in the largest amount is called as the base metal or parent metal or solvent Other alloying elements are called as solute
- 4. Necessity of Alloying Pure metals possess few important physical and metallic properties, such as melting point, boiling point, density, specific gravity, high malleability, ductility, and heat and electrical conductivity. These properties can be modified and enhanced by alloying it with some other metal or nonmetal, according to the need Alloys are made to:
- 5. Enhance the hardness of a metal An alloy is harder than its components. Pure metals are generally soft. The hardness of a metal can be enhanced by alloying it with another metal or nonmetal. EX: Bronze (Cu+ 11% tin) is harder than copper, making it useful for tools and weapons
- 6. Lower the melting point Pure metals have a high melting point. The melting point lowers when pure metals are alloyed with other metals or nonmetals. This makes the metals easily fusible. This property is utilized to make useful alloys called solders. EX: Tin, lead and their alloys, due to their low melting temperatures and wide availability, are the most commonly used solder materials
- 7. Enhance tensile strength Alloy formation increases the tensile strength of the parent metal Enhance corrosion resistance Alloys are more resistant to corrosion than pure metals. Metals in pure form are chemically reactive and can be easily corroded by the surrounding atmospheric gases and moisture. Alloying a metal increases the inertness of the metal, which, in turn, increases corrosion resistance. EX: Stainless Steel (alloy of Fe and Cr) is more corrosion resistant than Iron
- 8. Modify color The color of pure metal can be modified by alloying it with other metals or nonmetals containing suitable color pigments Provide better cast ability One of the most essential requirements of getting good castings is the expansion of the metal on solidification. Pure molten metals undergo contraction on solidification. Metals need to be alloyed to obtain good castings because alloys expand
- 9. Can you name Different alloys….
- 10. Classification of alloy systems
- 11. Solid Solution
- 12. Solid Solution It is an alloy in which the solute atoms are distributed in the solvent and has the same structure as that of the solvent Solid solutions have different compositions with similar structures and are like liquid solutions as sugar in water
- 13. Solid Solution Solid solutions are of two types Substitutional Solid Solution Interstitial Solid Solution
- 14. Substitutional Solid Solution Substitutional solid solution means the atoms of solute are substituted at the atomic sites of solvent Observed generally when the atomic sizes of solute and solvent are of same order
- 15. Substitutional Solid Solution Depending on the distribution of Solute atoms in solvent these are classified into two types Regular or ordered (Ex: Au-Cu Solid solution below 400°C) Random or Disordered (Ex: α-Brass)
- 16. Interstitial Solid Solution The solute atoms occupy the interstitial sites of solvent atoms Generally observed when atomic sizes of solute are very small as compared to the atomic sizes of solvent atoms C, B, O, H, N can form interstitial solid solution with Iron
- 17. HUME-ROTHERY’S RULES OF SOLID SOLUBILITY In the formation of solid solutions, the solubility limit of solute in the solvent is governed by certain factors. These factors are known as Hume-Rothery’s rules of Solid Solubility
- 18. If the atomic sizes of solute and solvent differ by less than 15%, it is said to have a favorable size factor for solid solution formation . If the atomic size difference exceeds 15%, solid solubility is limited RRule 1: Atomic Size Factor
- 19. The greater the chemical affinity of two metals , the more restricted is their solubility and greater is the tendency of formation of a compound In general, wider the separation of elements in the periodic table, greater is their chemical affinity Rule 2: Chemical Affinity Factor
- 20. A metal of higher valency can dissolve only a small amount of a lower valance metal. The lower valance metal may have good solubility for the higher valency metal Rule 3: Relative Valency factor
- 21. metals with same crystal structure will have greater solubility. Differences in crystal structure limits the solid solubility * For continuous solubility, atomic size difference should preferably be less than 8% with other factors favorable Rule 4: Crystal Structure Factor