On a phase diagram the intersection of the eutectic temperature and the

On a phase diagram the intersection of the eutectic

This preview shows page 63 - 65 out of 79 pages.

On a phase diagram the intersection of the eutectic temperature and the eutectic composition gives the eutectic point . [1] Not all binary alloys have a eutectic point; for example, in the silver-gold system the melt temperature ( liquidus ) and freeze temperature ( solidus ) both increase monotonically as the mix changes from pure silver to pure gold. [2] Eutectic alloys have two or more materials and have a eutectic composition. When a non-eutectic alloy solidifies, its components solidify at different temperatures, exhibiting a plastic melting range. A eutectic alloy solidifies at a single, sharp temperature. The phase transformations that occur while solidifying for a given alloy can be understood by drawing a vertical line from the liquid phase to the solid phase on a phase diagram. Some uses include: o eutectic alloys for soldering , composed of tin (Sn), lead (Pb) and sometimes silver (Ag) or gold (Au). o casting alloys, such as aluminium - silicon and cast iron (at the composition for an austenite - cementite eutectic in the iron - carbon system) one method used by the semiconductor industry to bond silicon chips to gold-plated substrates is to induce a silicon-gold eutectic through the application of ultrasonic energy to the chip.
Image of page 63
~ Page 64 of 79 ~ o brazing , where diffusion can remove alloying elements from the joint, so that eutectic melting is only possible early in the brazing process. o non-toxic mercury replacements, such as galinstan . o experimental glassy metals , with extremely high strength and corrosion resistance. o eutectic alloys of sodium and potassium ( NaK ) that are liquid at room temperature and used as coolant in experimental fast neutron nuclear reactors . 3. COMBINATION The components of the alloy are completely soluble in the liquid state, but are only partially soluble in each other in the solid state or in other words the components may show limited solubility in each other on solidifying. This type of alloy combines the characteristics of both the Solid Solution and Eutectic. 4. INTERMETALLIC COMPOUNDS Whilst some metal alloy systems exhibit total or partial solubility and others are insoluble in the solid state, a number of metals combine together to form an intermediate phase or intermediate compounds. Intermetallic compounds are complex metallic alloys with large unit cell. These are classes of substances composed of definite proportions of two or more elemental metals, rather than continuously variable proportions (as in solid solutions). In addition to the normal valences of their components, the relative sizes of the atoms and the ratio of the total number of valence electrons to the total number of atoms have important effects on the composition of intermetallic compounds. The crystal structures and the properties of intermetallic compounds often differ markedly from those of their constituents.
Image of page 64
Image of page 65

You've reached the end of your free preview.

Want to read all 79 pages?

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern

Stuck? We have tutors online 24/7 who can help you get unstuck.
A+ icon
Ask Expert Tutors You can ask You can ask You can ask (will expire )
Answers in as fast as 15 minutes
A+ icon
Ask Expert Tutors