MSE 258:Physical Metallurgy of Non-Ferrous Metals

Dr. Emmanuel Kwesi Arthur

Department of Materials Engineering,

Kwame Nkrumah University of Science and Technology, Kumasi

2019

Lecture Ten

Nickel and Nickel Alloys

Discovered in 1751. Like Magnesium it is a major alloying element that imparts strength, toughness, and corrosion resistance. It is also highly magnetic.

Nickel is produced by preliminary sedimentary and thermal processes followed by electrolysis. Undersea mining is not yet economical

Common alloys of Nickel:Nichrome (Nickel Chromium Iron)Invar and Kovar (Nickel Iron)Hastelloy (Nickel Chromium)Monel (Nickel Copper)Inconel (Nickel Chromium)

High melting point, 1453ºC Density, 8.9 g/cm3 Adherent oxide film Resists alkalis Ductile Alloys readily - as solute and solvent Magnetic at room temperature Deposited by electroplating Catalytic

Nickel has a unique combination of properties

Uses:High temperature applications, food handling, chemical processing, coins, marine applications.

The Nickel Advantage - Nickel in Stainless Steels

Versatility Reliability Corrosion resistance Hygienic High quality of 18/8 and 18/10 grades Formability Weldability Availability Many finishes Non-magnetic Lasting value and high intrinsic value as scrap Recyclability

The Nickel Advantage - Nickel as an alloying element

Tough low alloy steels High strength maraging steels Ductile and wear-resistant cast irons Stainless steels Corrosion resistant, high nickel alloys Superalloys for gas turbines Copper-nickel alloys for marine applicationsMagnetic and controlled expansion alloys Shape memory alloysNickel metal hydrides for hydrogen storage

The Nickel Advantage - Nickel plating

An early application of nickel Electrolytic and chemical deposition Provides lustre, uniformity and corrosion protection Substrate for decorative coatings Engineering coatings e.g. for wear resistance Electroforming

The Nickel Advantage - Catalysts

Make chemical reactions faster and more efficient Based on finely divided nickel and nickel compounds

(high surface area)Man-made fibres, fertilisers, fats, detergents, oil

refining

Aerospace flow bodies

Turbine blades

Nickel - the versatile metal

>60% used in stainless steel high-nickel corrosion- and heat-resisting alloys other alloys - strength, corrosion resistance, special

physical and magnetic properties plating - decorative and engineering uses batteries chemicals catalysts

Nickel-titanium superelastic alloys

Self-expanding stents Glasses frames Earthquake protection in bridges

Superalloys

• Also known as heat resistant alloys or high temperature alloys

• Used in high temperature applications and have good resistant properties to:• Mechanical and thermal fatigue, thermal shock, creep, and erosion at

elevated temperatures

• Iron based superalloys, Cobalt based superalloys and Nickel based superalloys are all common.

• Examples: jet engines, gas turbines, and reciprocating engines• Max temp.- 1000°C (1800°F)• Max temp. (non load)- 1200°C (2200°F)

• Identified by trade names or by a

special numbering system

Nickel and Cobalt Alloys Nickel and Cobalt alloys are used for corrosion protection and for high-

temperature resistance, taking advantage of their high melting points and high strengths.

Nickel is FCC and has good formability. Cu-Ni is the classic example of complete solid solubility. Monel is the name given to commercial alloys with Ni-Cu ratios of roughly 2:1 by weight.

These alloys are good examples of solution hardening in which the alloys are strengthened by the restriction of plastic deformation due to solid-solution formation.

Cobalt is FCC above 417 oC and HCP below this temperature.

Cobalt is used because of its exceptional wear resistance, and because of its resistance to body fluids, as a biomedical material for prosthetic devices such as hip and knee socket replacement.

Typical alloys and their uses are listed in the following table.

Superalloys: a broad class of materials with specially high strength at elevated temperatures

Turbine blade design for active cooling by a gas shown in a) and the increase in the high-temperature capability of Ni superalloys as a result of improved manufacturing methods from producing a polycrystalline material to a single crystal material.