IRON-ALUMINIUM(Fe3Al) SUPERALLOY

Under the able guidance of Dr. Atikur Rehman

ROHIT KHANDELWAL- 603/11VIKAL MANWAL- 305/11JAGDEEP SINGH- 594/11RAJINDER SINGH – 614/11GAURAV KUMAR PANDEY- 513/11

CONTENTS

• ABSTRACT• INTRODUCTION• APPLICATION & PROPERTIES• MANUFACTURING PROCESS• HIGH TEMPERATURE OXIDATION• MORPHOLOGY• RESULTS• CONCLUSION• REFERENCES

ABSTRACT

Fe3Al superalloy were manufactured through Powder

Metallurgy process. Microstructure and cyclic high temperature oxidation behavior of IRON ALUMINIDES

have been investigated. Cyclic high temperature oxidation tests were conducted on samples at peak

temperatures of 900oC for up to 5 thermal cycles at the room temperatures. SEM was used to characterize the

morphology of the samples. The oxidation results confirmed an improved oxidation resistance of samples

as compared to normal alloys. The relevant oxidation mechanisms are discussed.

INTRODUCTIONFor more than 50 years, Iron-Aluminum intermetallic has received special interest because of their potentially high oxidation resistance at high temperature. They offer a good alternative for use in automotive parts, chemical processing, and gas turbine technologies since they possess a high melting point, high thermal conductivity, excellent oxidation resistance, low density, and low cost.Iron aluminides, based around the stoichiometric compositions of Fe3Al and Fe-Al,

offer excellent resistance to oxidation and sulphidation at high temperatures, with low material cost and density than austenitic and ferritic stainless steels . They contain enough aluminum to form a thin film of aluminum oxide (in oxidizing environments) that is often compact and protective. They possess relatively high specific strengths and suitable mechanical properties at elevated temperatures. They have, therefore, undergone extensive development, in the recent past, exclusively for high temperature applications. However, their potential use as structural materials at elevated temperatures has been hindered by limited ductility atroom temperature and sharp drop in strength above 600°C.

Iron aluminides are receiving special attention because they have a good yielding point between 600 and 800°C, and even up to 1000°C when they are alloyed with low expansion fibers such as alumina (Al203).[7] The charpy impact energy is satisfactory at room temperature, and, depending on the grain size, the FeAI(40 at.%) offers a yielding point between 250 and 600 MPa, which can be increased with additions of Hf or B.[8] Also, ingot iron aluminides have a lower density (5.6 g/cm3) compared that for stainless steels and some nickel-based alloys, and a relatively high melting point (1237°C). Their main disadvantage is their poor ductility at room temperature. In the last few years, some new processing routes have been tried to improve their ductility [9] together with the addition of fibers and some micro-alloying elements. The good oxidation resistance of these materials is based on their ability to develop a protective alumina layer (AI2O3) on their surface in many high- temperature environments. Because alloys based on FeS-AI and Fe-Al form Al2O3

during exposure to oxidizing gases, they typically display low oxidation rates when compared to iron-based and other alloys that do not form alumina in similar conditions. Recent studies on FeS-AI alloys containing 2 to 5 at.% and various minor additions of oxygen-active elements have shown that their long-term oxidation performance approximately matches that of FeCrAlY alloys and Ni-Al at 1000°C, but it is inferior at 1200 and 1300°C.

• A Super-alloy, or high-performance alloy, is an alloy that exhibits several key characteristics: excellent mechanical strength, resistance to thermal creep determination, good surface stability and resistance to corrosion or oxidation. The crystal structure is typically face centered cubic lattice. Examples of such alloys are Hastelloy, Inconel, Waspalloy, Rene Alloy, Haynes alloys, Inco-alloy, MP98T, TMS alloys, and CMSX single crystal alloys.

• Super Alloy development has relied heavily on both chemical and process innovations. Super Alloys develop high temperature strength through solid solution strengthening. An important strengthening mechanism is precipitation strengthening which forms secondary phase precipitates such as gamma prime and carbides. Oxidation or corrosion resistance is provided by elements such as Aluminium and Chromium.

• The primary application for such alloys is in turbine engines, both aerospace and marine.

Why Super-Alloys ??Superior

Mechanical

Strength

Excellent

Creep Resistance

Good Surface Stability

Corrosion Resistant

Oxidation Resistant

Manufacturing Processes

• Powder selection• Powder mixing• Compaction• Sintering

Powder selection Iron Powder and aluminum powder of 20µm were selected 30gms of each metal.• Powder was weighed using a digital weighing machine

according to the stoichiometric coefficient and composition.

S.no Iron Composition

Aluminum composition

Weight of iron(For 5gm sample)

Weight of aluminum

1. 0.55 0.45 3.583 1.416

2. 0.50 0.50 3.371 1.628

3. 0.45 0.55 3.143 1.856

Powder Mixing• Mixing of powder was done in a porcelain dish with

a mortar and pestle.• Mixing was done thoroughly for 150 minutes with

slow addition of methanol.• Mixed powder was taken out from the mortar.

Powder Compaction

• Powder was compacted in the mounting machine.• Cold compaction of powder was done at room

temperature and at 1.5atm.• A binding agent Tri-ethylene Di-amine was used for

proper compaction.

Sintering• Sintering was done for the compaction and

formation of a solid mass of material by heat without melting it to the point of liquefaction.

• Sintering was done at 1173K for three hours in a muffle furnace.

• After Three hours the furnace was shut down and samples was left to cool in the furnace itself.

Metallography • Surface grinding was employed to produce a smooth finish on flat surface.• Grinding was done on those samples which were not oxidized.• Grinding was done on emery paper with increasing fineness number.• Polishing is the most important step in preparing a specimen for microstructural

analysis.• Polishing was done with iron oxide.• Etching can help reveal hidden flaws or defects in a part or component before

submitting the sample to traditional destructive or nondestructive examination, metallography, microscopy, or other analytical technique.

• Etching – nital (98% alcohol and 2% nitric acid)

High Temperature oxidation• To Study the oxidation behavior of Fe-Al super alloy samples were heated at high temperature. • Three Samples with Different Compositions were

subjected to 1273K for 2 hours in a electric furnace.• Samples were cooled in air for half hour and then

weighed.• Samples were subjected to a total of 5 heating-

cooling cycles.• The gain in weight is observed with respect to total

exposure time.

Observations

Cycle Initial weight(gm)

Final weight(gm)

Weight Gain(mg)

Cumulative weight

Surface area(cm2)

Weight/area(mg/cm2)

1 6.060 6.120 60 60 14.18 4.2292

2 6.120 6.129 9 69 14.18 4.8660

3 6.129 6.132 3 72 14.18 5.0775

4 6.132 6.135 3 75 14.18 5.2891

5 6.135 6.136 1 76 14.18 5.3596

FOR SAMPLE A

Graph of Sample A

For sample B

Cycle Initial weight(gm)

Final weight(gm)

Weight Gain(mg)

Cumulative weight

Surface area(cm2)

Weight/area(mg/cm2)

1 6.403 6.480 77 77 14.37 5.3583

2 6.480 6.521 41 118 14.37 8.4899

3 6.521 6.546 25 143 14.37 9.9512

4 6.546 6.565 19 162 14.37 11.2734

5 6.565 6.567 2 164 14.37 11.4126

Graph for Sample B

0

1

2

3

4

5

6

7

8

9

10

11

12

0 2 4 6 8 10

0

5.3583

8.4899

9.9512

11.273411.4126 M

g/C

m2

FOR SAMPLE C

Cycle Initial weight(gm)

Final weight(gm)

Weight Gain(mg)

Cumulative weight

Surface area(cm2)

Weight/area(mg/cm2)

1 6.765 6.905 140 140 15.700 8.9171

2 6.905 6.993 88 228 15.700 14.5222

3 6.993 7.040 47 275 15.700 17.5159

4 7.040 7.057 17 292 15.700 18.5987

5 7.057 7.059 2 294 15.700 18.7261

GRAPH OF SAMPLE C

0

2

4

6

8

10

12

14

16

18

20

0 2 4 6 8 10

0

8.9171

14.5222

17.5159

18.598718.7261 M

g/C

m2

MORPHOLOGY OF SAMPLESSAMPLE A

SAMPLE B

SAMPLE C