CM247LC

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EFFECT OF PROLONGED THERMAL EXPOSURE

ON THE

ON THE MICROSTRUCTURE OF INVESTMENT

MICROSTRUCTURE OF INVESTMENT

CAST NICKEL BASE SUPERALLOY - CM247LC

By

M.Jayaraj

L.Mathiyazhagan

G.Muralidharan

T.Sivanesan

Final Year - Metallurgy

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OBJECTIVE

Nickel base super alloys are extensively used in gas turbines Nickel base super alloys are extensively used in gas turbines forfor aero engine applications, which demand good

aero engine applications, which demand good mechanicalmechanical properties and

properties and long life at elevated temperatures. Duringlong life at elevated temperatures. During service,CM247LC alloy will be operated at a

service,CM247LC alloy will be operated at a temperature of temperature of around 900°C in jet fuel starter (JFS) as stator and rotor. So, the around 900°C in jet fuel starter (JFS) as stator and rotor. So, the work was aimed

work was aimed at studying micro structural stability atat studying micro structural stability at operating temperature

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INTRODUCTION

•CM-247 LC is a low Carbon, modified chemistry of Mar –M-247 alloy, specially designed for turbine blade and vane applications.

•The primary alloying modification are the reduction of ‘C’ by

approximately one-half to improve carbide microstructure, stability and alloy ductility, plus the tailoring of the Zr and Ti contents to improve DS grain boundary cracking resistance without sacrificing strength.

•W and Mo levels in the alloy are slightly reduced to compensate for the lower C and Ti concentrations, thereby minimizing the formation of

deleterious secondary M₆C platelets, µ phase and /or alpha W platelets

•The lower Ti content in CM-247LC compare to Mar-M247 is to

significantly reduce the size of γ-γ’ eutectic nodules as well as to lower the

volume fractions of eutectic form approximately 4 volume % in Mar-M247 to 3 volume % in CM-247LC directionally solidified (DS) components.

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CHEMICAL COMPOSITION OF ALLOY CM-247LC ( wt% )

Element Min. Max.

C 0.075 0.085 Si - 0.03 Mn - 0.01 S - 10 ppm Ag - 5 ppm Al 5.4 5.7 B 0.01 0.02 Bi - 0.3 Nb - 0.01 Co 9 9.5 Cr 8 8.5 Cu - 0.005 Fe - 0.15 Ga - 15 ppm

Element Min Max

Sn - 15 ppm Sb - 50 ppm As - 50 ppm Zn - 50 ppm Hg - 50 ppm U - 50 ppm Th - 50 ppm Cd - 50 ppm Ge - 0.1 V - 50 ppm Au - 50 ppm In - 50 ppm Na - 50 ppm K - 50 ppm

Element Min Max

Hf 1.4 1.6 Mg - 80 ppm Mo 0.4 0.6 N - 10 ppm Ni Bal Bal O - 10 ppm P - 0.005 Pb - 2 ppm Se - 1 ppm Ta 3.1 3.3 Te - 0.3 Ti 0.6 0.9 Tl - 0.3 W 9.3 9.7 Zr 0.007 0.02

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EXPERIMENTAL WORK

•

Samples of 10mm diameter and 15mm long were taken from the disc of cut-up rotor casting.

•

The samples were subjected to a standard solution heat

treatment in a vacuum heat treatment furnace of Degussa make.

•

Double aging followed by thermal exposure was carried out in

CRAFT’SMAN air heat treatment furnace with Silicon carbide (SiC) as heating element.

•

Six samples were subjected to thermal exposure at 900°C for the following hours (100,125,150,175,200 and 225) later these

samples are studied under optical and scanning electron microscope (SEM).Then samples were subjected to Vickers hardness test.

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Vacuum Heat Treatment Furnace CRAFTSMAN Air Heat Treatment Furnace Tensile sample &Integral

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Standard heat-treatment cycle for solution treatment &

double ageing

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INVESTMENT CAST CM247LC

SOLUTION TREATMENT & DOUBLE AGEING EXPOSURE-1 100 HOURS AT 900°C EXPOSURE-2 125 HOURS AT 900°C EXPOSURE-3 150 HOURS AT 900°C EXPOSURE-4 175 HOURS AT 900°C EXPOSURE-5 200 HOURS AT 900°C

POWER SAW CUTTING

ISOMET CUTTING MOUNTING SEM ANALYSIS VICKERS’ HARDNESS EXPOSURE-5 225 HOURS AT 900°C

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SAMPLE PREPARATION

Seven samples from two equi-axed rods of CM247LC alloy

casting disc were taken and cut into seven pieces using ISOMET for Metallography

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OPTICAL MICROSCOPY

•

All the seven samples (6 exposed & 1 unexposed) were mounted by using SIMPLIMET 3000 Machine. After mounting, the samples were metallographically grinded starting from a variety of emery paper grades like 150,320,400,600,800 and 1000, followed by diamond disc polishing with various grades like 9µ, 3µ, 1µ and 0.5µ

•

Etchant of following chemical composition: Hydrochloric acid - 45ml

Nitric acid - 30ml

Glacial acetic acid - 30ml

Methyl alcohol - For post cleaning purpose

•

observed under magnifications 50x, 100x, 200x, 500x and microstructures were recorded.

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OPTICAL MICROSCOPE

•

The Metallography samples revealed the various

microstructural features such as grain size, grain boundary

carbides and γ-γ’ eutectic at grain boundary when observed at 200x. γ’ was discernable at higher magnifications. Gamma

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SCANNING ELECTRON MICROSCOPY (SEM)

•

studied under SEM for calculating γ’ sizes, Morphology

oberved and recorded at 10000X .

•

Secondary gamma prime precipitates were observed to be fairly uniform and cuboidal in shape and showed in STA

sample. The tertiary gamma prime was observed in the gamma corridor between secondary gamma prime precipitates in the E1 – E6 samples.

•

The morphology of discrete grain boundary carbides and the composition of these carbides has been revealed mainly as TaC

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SEM micrographs showing the γ size (0.7136µm) and cuboidel Morphology of STA exposed sample

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SEM micrographs showing the γ size (0.8905µm) and Morphology of 100 h exposed sample

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SEM micrographs showing the size and

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γ’ SIZE

•

Average γ’ sizes of the samples STA and E1 to E6 were measured at 10000x.

•

The sides were measured in relation to the micron marker on the micrograph and the values were averaged. The values of

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CONDITION γ’ SIZE(µm) STA 0.7136 E1 0.8905 E2 0.8827 E3 1.0419 E4 0.9370 E5 0.8982 E6 0.9561 γ’ SIZE(µm) 0 0.2 0.4 0.6 0.8 1 1.2 STA E 1 E2 E3 E4 E5 E6

Exposure time, hours

γ ’ S I Z E ( µ m ) γ’ SIZE(µm)

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VICKER’S HARDNESS TESTING

•

From the graph hardness values starts to decrease from STA sample and again slightly increases at E6 (225hours).

•

The data of γ’ size and hardness show opposite trends though

in a very gradual manner. The exposure time appears to affect

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VICKERS HARDNESS (VHN) 280 290 300 310 320 330 340 350 360 370 STA E1 E2 E3 E4 E5 E6 Therma l Exposure,Hours H a r d n e s s , V H N VICKERS HARDNESS (VHN) CONDITION EXPOSURE HOURS VICKERS HARDNESS (VHN) STA - 360 E1 100 332 E2 125 328 E3 150 318 E4 175 316 E5 200 312 E6 225 314

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CONCLUSIONS

•

γ’ size variations was studied with respect to exposure time. There is overall increase in γ’ size with exposure time from

0.71 at 100h to 0.95 at 225h.however Max of 1.04 at 150h.

•

γ’ shape was also observed with respect to exposure time. There is overall change in γ’ shape with respect to exposure

time. cuboidal morphology was observed at low exposure

time. While at higher exposure time rounded, blocky and less cuboidal morphology of γ’ was observed.

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REFERENCES

1. SUPERALLOYS II: Chester T. Sims and William C. Hagel.

2. The SUPERALLOYS Fundamentals and Applications: Roger C. Reed.

3. SUPERALLOYS A Technical Guide: Mattew J. Donachie and Stephen Donachie. 4. SUPERALLOYS I: Chester T. Sims and William C. Hagel.

5. Superalloys a Technical Guide: F. Bradley ASM internationals, 1987.

6. CMSX SINGLE CRYSTAL, CM DS & INTEGRAL WEEL ALLOYS PROPERTIES AND PERFORMANCE: K.Harris, G.L.Erickson and R.E.Schwer Cannon-Muskegon Corp. 7. Superalloys – Processing : Proceedings of the international conference

Sept.18-2,1972,MCIC Report, and Sept 1972.

8. Superalloys 1984 : Proceedings of fifth international symposium on superalloys TMS.AIME. 9. Superalloys 1988 : Proceedings of fifth international symposium on superalloys TMS.AIME. 10. Superalloys 1992 : Proceedings of fifth international symposium on superalloys TMS.AIME. 11. Heat treatment structure and properties of non-ferrous alloys, ASM C.R. BROOKS.

12. Microstructure of Superalloy : Madeleine Durand-Chrame Gordon Breach Science Publishers 1977.

13. HeatTreater’sGuide Practice And Procedure for Non Ferrous Alloys 1999

14. Worked Examples in Quantitative Metallography : R.L. Higginson and C.M Sellars 2003 15. Metallography Etching ,2nd_{Edition : Günter,Petzow}

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