Solid Solution

Presented by Dr. R. D. Palhade, Professor, Department of Mechanical Engineering, SSGMCE, Shegaon Pin-444203

1/21/2017 Introduction to Solid Solution by- 1 RDP Introduction to Solid Solution

 Solid solution is simply a solution in solid-state  solid-state solution of one or more solutes in a solvent.  Thus solidified alloy, results in one kind of crystal in which both metals are present, but they cannot be detected by the microscope, although the properties of the crystal are profoundly by the microscope.  Example- brass is a solid solution of copper and zinc, a typical compositions is copper 64% and Zinc 36%. – Cu atoms are solvent and Zn atoms are solute atoms.  Homogeneous distribution of two or more constituents so form single phase i.e. solid solution.  In solid solution binary alloy system, the two metals (e. g. Cu & Ni) are completely soluble in both the liquid & solid states.

1/21/2017 Introduction to Solid Solution by- 2 RDP  A solid solution is the result of metals dissolving in each others.  Solid solution are conductor, but not as pure metals.  Such a mixture is considered a solution rather than a compound when the crystal structure of the solvent remains unchanged by addition of the solutes, and when the mixture remains in a single homogeneous phase.  The solute may incorporate into the solvent crystal lattice substitutionally, by replacing a solvent particle in the lattice, or interstitially, by fitting into the space between solvent particles.  Both of these types of solid solution affect the properties of the material by distorting the crystal lattice and disrupting the physical and electrical homogeneity of the solvent material.  Some mixtures will readily form solid solutions over a range of concentrations, while other mixtures will not form solid solutions at all. 1/21/2017 Introduction to Solid Solution by- 3 RDP  The propensity for any two substances to form a solid solution is a complicated matter involving the chemical, crystallographic, and quantum properties of the substances in question.  Hume-Rothery (1899-1968) was a metallurgist who studied the alloying of metals. His research was conducted at Oxford University where in 1958, he was appointed to the first chair in metallurgy.

1/21/2017 Introduction to Solid Solution by- 4 RDP Crystal lattice for alloys

1. Adding alloying elements to pure metal alters the dimensions of lattice structure of metal, & may also change the type of lattice. 2. The position of allying element (solute) in the space-lattice of the alloy and the alterations made in size & type of the unit cell are of great importance in determining the properties of the alloy and its reaction to heat treatment & other processing methods. It may form the following solutions: 1. Substitutional solid solution 2. Interstitial solid solution 3. Intermetallic compound 4. Simple mechanical mixture

1/21/2017 Introduction to Solid Solution by- 5 RDP 1/21/2017 Introduction to Solid Solution by- 6 RDP 1/21/2017 Introduction to Solid Solution by- 7 RDP Hume-Rothery rules The Hume-Rothery rules are a set of basic rules describing the conditions under which an element could dissolve in a metal, forming a solid solution. There are two sets of rules, one which refers to substitutional solid solutions, and another which refers to interstitial solid solutions. Hume-Rothery rules for substitutional solid solutions, the are: 1. The atomic radii of the solute and solvent atoms must differ by no more than 15%: If a solute differs in its atomic size by more than about 15% from the host, then it is likely to have a low solubility in that metal. The size factor is said to be unfavorable. 2. The crystal structures of solute and solvent must match. 3. Maximum solubility occurs when the solvent and solute have the same valency. Metals with lower valency will tend to dissolve metals with higher valency. 4. The solute and solvent should have similar electronegativity. If the electronegativity difference is too great, the metals will tend to form intermetallic compounds instead of solid solutions. 1/21/2017 Introduction to Solid Solution by- 8 RDP 1/21/2017 Introduction to Solid Solution by- 9 RDP 1/21/2017 Introduction to Solid Solution by- 10 RDP Importance of Solid Solution o Solid solutions have important commercial and industrial applications, as such mixtures often have superior properties to pure materials. o Many metal alloys are solid solutions. o Even small amounts of solute can affect the electrical and physical properties of the solvent.

1/21/2017 Introduction to Solid Solution by- 11 RDP • The phase diagram in Fig. 1 displays an alloy of two metals which forms a solid solution at all relative concentrations of the two species. • In this case, the pure phase of each element is of the same crystal structure, and the similar properties of the two elements allow for unbiased substitution through the full range of relative concentrations.

1/21/2017 Introduction to Solid Solution by- 12 RDP 3. Intermetallic compound

 In many binary alloy system, when the chemical affinity of metals is great, their mutual solubility becomes limited and indermediate phases are formed (rather than solid solution)  It is also possible for the solute atoms to join with solvent atoms & forming an intermetallic compound.  Intermetallic compound are similar to ordinary chemical compound.  Intermetallic compound structure is more complicated than ordinary structure Thus intermetallic compound - lower conductivity - lower ductility, plasticity, - But higher strength & hardness

1/21/2017 Introduction to Solid Solution by- 13 RDP 1/21/2017 Introduction to Solid Solution by- 14 RDP 4. Simple Mechanical Mixture

 Mechanical mixture are formed when the components of an alloy have no solubility in each other and no tendency to combine with each other.  Under these circumstances each metal of the alloy freezes independently of the other and does not allow the other in its crystal lattice.  The final solid consists of discrete regions of the pure components as a mechanical mixture rather than as a solid solution or compound.  In some instances the elements of the alloy are insoluble in each others, resulting in a simple mechanical mixture

1/21/2017 Introduction to Solid Solution by- 15 RDP 1/21/2017 Introduction to Solid Solution by- 16 RDP