B.SREE KRISHNA

116107013

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SUPERALLOY

Superalloy is an alloy that exhibits

excellent mechanical strength and creep

resistance at high temperatures.

Superalloys are metallic materials for

service at high temperatures ,

particularly in hot zones of gas turbine ,

jet engines etc..

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Development of Superalloys

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

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

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Properties

High temperature creep resistance

(1050°C to 1200°C)

Fatigue life

Corrosion resistance

Good surface stability

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Classification

Superalloys are often classified into generations and until today there were five generations

The sixth generation is in the form of project at National Institute of Material Science in Japan (NIMS)

First generation superalloys are characterstic with a relatively huge amount of chromium in comparision with other generations

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The second and third generation

contains about 3 wt % and 6 wt % of

rhenium respectively

Rhenium is a very expensive addition

but leads to an improvement in creep

strength and fatigue resistance

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Composition of some Super

alloys

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As an example of fourth generation of

superalloys TMS-138 can be

characterised.

It was developed in NIMS with the

addition of Mo for increasing the lattice

misfit .

The excellent creep behaviour at high

temperatures (about 1373K) is attributed

with the recent generation of superalloys

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The representation of the fifth

generation of the superalloys is for

example TMS-169 alloy developed at

NIMS in collaboration with Ishikawajima-

Harima Heavy insdustries co.,Ltd (IHI) in

japan in 2006

TMS-169 is an advanced superalloy

containing 5 wt % Ru and 4.6 wt % Cr

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TMS 169 with superior high temperature

creep and oxidation resistance by

incorporating further Ru and Cr content

over the composition of fourth

generation alloys

With Ru additions it will enhance the

phase stability

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Super alloys are classified into three

based on the predominant metal present

in the alloy. They are

Nickel based Super alloy

Iron based Super alloy

Cobalt based Super alloy

With Al,W,Ti as additional elements

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Nickel based Super alloy

Nickel based Super alloys can be either Solid solution strengthening or Precipitation hardening.

Solid solution strengthened alloys such as Hastelloy are used only in applications which require very modest strength

Most Ni based alloy contain 10-20% Cr, up to 8% Al and Ti, 5-10% Co, and small amounts of B , Zr and C

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Iron based Super alloy

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

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Cobalt based Super alloy

Cobalt based Super alloys have their

origin in the stellite alloys.

Cobalt alloys have higher melting points

than nickel alloys.This gives them the

ability to absorb stress to a higher

temperature

Cobalt alloys show superior thermal

fatigue resistance and weldability over

the nickel alloys

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Applications

Aircraft gas turbines: disks,

combustion chambers, bolts, casings,

shafts, exhaust systems, cases, blades,

vanes, burner cans, afterburners, thrust

reversers

Steam turbine power plants: bolts,

blades, stack gas re-heaters

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Reciprocating engines: turbochargers,

exhaust valves, hot plugs, valve seat

inserts

Metal processing: hot-work tools and

dies, casting dies

Space vehicles: aerodynamically

heated skins, rocket engine parts

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MTT TURBINE SUPERBIKE Y2K

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Engine of Y2K Superbike

High temperature steel

During the 1950s, utility boilers

operating above 1000°F at pressures

above 1500 psi were experiencing

premature failures.

These failures were initially attributed to

an extremely fine grain size occasioned

by a low temperature solution heat

treatment

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Reheat treatment at higher temperature to produce coarse grain structure reduce the incidence of failure

Results of a subsequent research found out that carbon content plays a major role in this along with final solution heat treatment and not the grain size.

A new designation was introduced which incorporated specific heat treatments and control of carbon.

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Importance

High temperature steels are specially

alloyed steels and are designed for

High strength

Impact toughness

Wear resistance

The main categories of this steels are

High-speed steels(HSS)

Hot-work steels

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High speed steels

It was first developed in the early 1900s,

and are the most highly alloyed steels

which can maintain their hardness and

strength at elevated operating

temperatures

There are two basic types of high-speed

steels

Molybdenum type

Tungsten type

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Hot-work steels

These are designated for use at

elevated temperatures and have high

toughness and high resistance to wear

and cracking.

The alloying elements are generally

tungsten ,molybdenum , chromium and

vanadium

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Applications

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Kawasaki H1 – Engine exhaust

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Valves used in combustion chamber

References

http://www.msm.cam.ac.uk/phase-

trans/2003/Superalloys/superalloys.html.

http://www.patentstorm.us/patents/5366

695.html

Manufacturing process for engineering

materials by Kalpakjian

Material science and Engg by William

callister

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