cm247lc
TRANSCRIPT
EFFECT OF PROLONGED THERMAL EXPOSURE ON THE MICROSTRUCTURE OF INVESTMENT CAST NICKEL BASE SUPERALLOY - CM247LC
By
M.JayarajL.MathiyazhaganG.MuralidharanT.Sivanesan
Final Year - Metallurgy
OBJECTIVENickel base super alloys are extensively used in gas turbines for aero engine applications, which demand good mechanical properties and long life at elevated temperatures. During service,CM247LC alloy will be operated at a temperature of around 900°C in jet fuel starter (JFS) as stator and rotor. So, the work was aimed at studying micro structural stability at operating temperature
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 M 6 C 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.
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 1.6Mg - 80 ppm
Mo 0.4 0.6N - 10 ppm
Ni Bal BalO - 10 ppm
P - 0.005Pb - 2 ppmSe - 1 ppmTa 3.1 3.3Te - 0.3Ti 0.6 0.9Tl - 0.3W 9.3 9.7Zr 0.007 0.02
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.
Vacuum Heat Treatment Furnace
CRAFTSMAN Air Heat Treatment Furnace
Tensile sample &Integral
Standard heat-treatment cycle for solution treatment & double ageing
INVESTMENT CAST CM247LC
SOLUTION TREATMENT & DOUBLE AGEING
EXPOSURE-1100 HOURS AT 900°C
EXPOSURE-2
125 HOURS AT 900°C
EXPOSURE-3150 HOURS AT 900°C
EXPOSURE-4175 HOURS AT 900°C
EXPOSURE-5200 HOURS AT 900°C
POWER SAW CUTTING
ISOMET CUTTING
MOUNTING
SEM ANALYSIS
VICKERS’ HARDNESSEXPOSURE-5225 HOURS AT 900°C
EXPERIMENTAL WORK-FLOW CHART
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
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 - 30mlGlacial acetic acid - 30mlMethyl alcohol - For post cleaning purpose
•observed under magnifications 50x, 100x, 200x, 500x and microstructures were recorded.
RESULTS AND DISCUSSIONS
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 prime was found to be coarse and irregular at eutectic regions
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
SEM micrographs showing the γ׳size (0.7136µm) and cuboidel Morphology of STA exposed sample
at 10000X
SEM micrographs showing the γ׳size (0.8905µm) and Morphology of 100 h exposed sample
at 10000X
SEM micrographs showing the γ׳size (0.8805µm) and Morphology of 125 h exposed sample
at 10000X
SEM micrographs showing the γ׳size (1.0419µm) and Morphology of 150 h exposed sample
at 10000X
SEM micrographs showing the γ׳size (0.9370µm) and Morphology of 175 h exposed sample
at 10000X
SEM micrographs showing the γ׳size (0.8982µm) and Morphology of 200 h exposed sample
at 10000X
SEM micrographs showing the γ׳size (0.9561µm) and Morphology of 225 h exposed sample
at 10000X
SEM micrographs showing the size and Morphology of Grain boundary carbides at 2000X
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 γ’ sizes as calculated from the micrographs
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 E1 E2 E3 E4 E5 E6
Exposure time, hours
γ’
SIZ
E(µ
m)
γ’ SIZE(µm)
GAMMA PRIME SIZE
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 size of γ’ and at the same time decrease in hardness
VICKERS HARDNESS (VHN)
280290300310320330340350360370
STA E1 E2 E3 E4 E5 E6
Thermal Exposure,Hours
Har
dn
ess,
VH
N
VICKERSHARDNESS(VHN)
CONDITIONEXPOSURE
HOURS
VICKERS HARDNESS
(VHN)
STA - 360
E1 100 332
E2 125 328
E3 150 318
E4 175 316
E5 200 312
E6 225 314
VICKER’S HARDNESS RESULT
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.
• Hardness is decreasing with increasing in exposure time.
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Publishers 1977.13. Heat Treater’s Guide Practice And Procedure for Non Ferrous Alloys 199914. Worked Examples in Quantitative Metallography : R.L. Higginson and C.M Sellars 200315. Metallography Etching ,2nd Edition : Günter,Petzow16. Metallography principles and practice: George F. Vander Voort 2007.
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