SUPER ALLOYSPREPARED BY:

Syed Nooruddin (D-12-MT-347)Ali Asad Zaheer(D-12-MT-355)Khurram Khan(D-12-MT-349)Faisal Shabir (D-12-MT-384)

Manzoor Ahmed (D-12-MT-385)Department of Metallurgy & Materials

Dawood University Of Engineering & Tech.(Karachi)

Contents

Introduction

Development

Composition

Types

Processing & Properties

Applications

References

IntroductionWhat is Superalloy?

A superalloy is a metallic alloy which can be used at high temperatures, often in excess of 0.7 Tm ( absolute

melting temperature)

Superalloy is an alloy that exhibits excellent mechanical strength and creep resistance at high temperatures.

Alloying additions for solution strengthening is by addition of lower amount of W, Mo, Ta, Nb & for Precipitation hardening by addition of of g and g’ formers like Ti, Al & Nb.

 Examples of such alloys are Hastelloy, Inconel, Waspaloy, Rene alloys, Haynes alloys, Incoloy, MP98T, TMS alloys, and CMSX single crystal alloys.

Development of Super Alloys

Superalloys develop high temperature strength through Solid solution strengthening(SSS).

SSS is a type of alloying that can be used to improve the strength of the metals. It is the hardening mechanism process.

The technique works by adding atoms of one element (alloying element) to the crystalline lattice of another element (the base metal).

Composition of some Super alloys

Types of Super Alloys

Ni – Based Superalloy.

Co – Based Superalloy.

Fe-Ni – Based Superalloy.

Iron based Super Alloys:(a) 9-38 % nickel(b) 15-22 % chromium(c) 32-67 % ironCommon type of Iron based alloy is Incoloy series. Iron based Super alloys are characterised by high temperature as well

as room temperature strength.

Apart from this, it will have good resistance to creep , oxidation, corrosion and wear.

Oxidation resistance increases with chromium content.

Cobalt based Super alloys:

(a) Up to 35% nickel(b) 19-30 % chromium(c) 30-65 % cobaltCobalt based alloys can retain their strength at high temperature but they are not as strong as nickel based alloys.

Nickel based alloys:

(a) 38-76% nickel(b) Up to 27 % chromium(c) Up to 20 % cobalt.Some of the common type of nickel based alloysare Nimonic, Hastelloy and Inconel.These are the most common types of Superalloy which are widely used in turbine blades

Major phases in Nickel Superalloys

Gamma (g)

Gamma Prime (g')

Carbides

Topologically Close-Packed Phases

Gamma (g)The continuous matrix (called gamma) is an face-centered-cubic (FCC) nickel-based austenitic phase that usually contains a high percentage of solid-solution elements such as Co, Cr, Mo, and W.

SEM micrograph of minor microstructural constituents of the alloy in the g matrix.

Gamma Prime (g') The primary strengthening phase in nickel-based superalloys is

Ni3(Al,Ti), and is called gamma prime (g '). It is a coherently precipitating phase (i.e., the crystal planes of the precipitate are in registry with the gamma matrix) with an ordered FCC crystal structure.

Carbides

Carbon, added at levels of 0.05-0.2%, combines with reactive elements such as titanium, tantalum, and hafnium to form carbides (e.g., TiC, TaC, or HfC). During heat treatment and service, these begin to decompose and form lower carbides such as M23C6 and M6C, which tend to form on the grain boundaries. These common carbides all have an fcc crystal structure.

The general opinion is that in superalloys with grain boundaries, carbides are beneficial by increasing rupture strength

at high tempeature.

Topologically Close-Packed PhasesThese are generally undesirable, brittle phases that can form during heat treatment or service.

TCPs (Sigma, Mu, Laves, etc.) usually form as plates (which appear as needles on a single-plane microstructure).

TCPs are potentially damaging for two reasons: they tie up g and g ' strengthening elements in a non-useful form, thus reducing creep strength, and they can act as crack initiators because of their brittle nature.

True stress–true strain flow curves for the Ni-based superalloy under different strain rates and temperatures: (a) 1050 °C, (b) 1100 °C, (c) 1140 °C, and (d) 1180 °C.

Properties of Superalloys

Excellent mechanical strength and wear resistance at high temperature.

Resistance to corrosion and oxidation at very high temperature.

Good surface stability.

High Impact toughness

APPLICATIONS

Nickel-based super alloys are widely used in load-bearing structures to the highest homologous temperature

0.9 Tm, or 90% of their melting point.

Aerospace Turbine blades and jet/rocket engines

Marine industry Submarines

Nuclear reactors Heat exchanger tubing Industrial gas turbines

A jet engine (Rolls-Royce Trent 800)

Intermediate pressure compressor (IPC),

High pressure compressor (HPC),

High pressure turbine (HPT),

Intermediate pressure turbine (IPT),

Low pressure turbine (LPT),

and the pressure and temperature profiles along the engine.

Gas Turbine for Marine Propulsion

Pressurized water reactor vessel head

Gas Turbine at thermal power plant

Rocket Motor Engine

Turbine Blades (Jet Engine)

Nickel-based superalloy, about 65% of gamma-prime precipitates in a polycrystalline gamma matrix.

References

http://www.msm.cam.ac.uk/phase-trans/2003/Superalloys/superalloys.html.  http://www.patentstorm.us/patents/5366695.html Manufacturing process for engineering materials by Kalpakjian Material science and Engg by William Callister F. Zupani, T. Bonˇcina, G. Lojen, B. Markoli, S. Spai, Structure of the continuously

cast Ni-based superalloy GMR 235, Journal of Materials Processing Technology 186 (2007) 200–206

Dayong Cai, Liangyin Xiong, Wenchang Liu, Guidong Sun, Mei Yao, Development of processing maps for a Ni-based superalloy, Materials Characterization 58 (2007) 941–946

F. Zupanic, T. B oncina, A. Krizman, B. Markoli, S. Spaic, Microstructural constituents of the Ni-based superalloyGMR 235 in the as-cast condition, Scripta Materialia 46 (2002) 667–672