Kuan JiangM. A. Sci. Candidate
Ottawa- Carleton Institute for Mechanical Engineering
Ottawa, Canada Fall 2012
Effects of Heat Treatment on Microstructure and Wear Resistance of Superalloys
Outline
Introduction
Experimental procedures
Results and discussion
Microstructure development
Hardness, wear volume loss
Worn surface analysis
Conclusion and future work
Acknowledgement
Introduction
Wear Failure of Materials
• Wear failure occurred frequently on mechanical components operating in high temperature, wear, corrosion, oxidation environment.
• The total economical loss caused by wear failure is as much as 7% of Gross National Product in many industrialized nations every year.
• Wear failures of some mechanical components served in severe environment can be catastrophic.
Introduction
Materials for High Temperature Environment
• Superalloys: Primary design for high temperature(540°C) applications. Typically examples: Stellite alloys, Tribaloy alloys.
• Stainless steels: Strong resistance for corrosion and high temperature attack.
Research Background
Coating Techniques
• Chemical vapor deposition (CVD), Physical vapor deposition (PVD), Slurry coating, etc.
Slurry Coating Process
Mixing Spraying Drying Sintering
Research Objectives
• Investigate the influence of sintering heat treatment on the microstructure and wear resistance of superalloys.
• Explore wear mechanism of superalloys at room temperature and elevated temperatures (250C, 450C).
Alloy Selection And Chemical Compositions
• Two cobalt-based superalloys (T-400C, Stellite 22) at cast state were selected.
Chemical composition (wt%, Co in balance) of the selected superalloys.
Alloy
Type
Process Co Cr Mo C Fe Ni Si Mn
T-400C Sand Cast Bal 14 26 0 0 0 2.6 0
Stellite22 Sand Cast Bal 27 11 0.25 3 2.75 1 1
Heat treatment Cycle
Micro Hardness Test
• Specimen with 6.5mm in diameter and 1.5-2mm in thickness• Well polished; methanol cleaned; air dried • Exposure temperatures: 25C, 250C, 450C, 600C• Indentation area: each individual phases and overall microstructure.
Hot-Stage Assembly
Pin-on-disc Wear Test
• Pin: ball (94% WC+6% Co)• Disc: sample disk• Exposure temperatures: 25C, 250C, 450C
Disc
PinDisk Sample
Wear tracks on a worn specimen surface.
Microstructure Development T-400C• Intermetallic Laves phase (Co3Mo2Si or CoMoSi) boundary became finer • Precipitation of some white phases
As-cast T-400C (1.00kx) Heat-treated T-400C (1.00kx)
Newly precipitated Laves phase
Primary intermetallic Laves phase
Co solid solution
EDS results of T-400C
Primary Laves phase• Si, Mo decreased
Solid solution• Si, Mo decreased
Element Weight% Atomic%
Si K 3.56 8.21
Cr K 12.14 15.07
Fe K 1.05 1.21
Co K 46.24 50.61
Mo L 37.02 24.90
Total 100.00 100.00
Element Weight% Atomic%
Si K 2.21 4.86
Cr K 16.16 19.16
Fe K 1.42 1.56
Co K 56.86 59.42
Mo L 23.35 15.00
Total 100.00 100.00
Element Weight% Atomic%
Si K 3.43 7.86
Cr K 12.66 15.64
Fe K 1.03 1.18
Co K 47.30 51.50
Mo L 35.59 23.82
Total 100.00 100.00
Element Weight% Atomic%
Si K 1.88 4.10
Cr K 17.10 20.10
Fe K 1.53 1.67
Co K 58.84 60.97
Mo L 20.65 13.15
Total 100.00 100.00
As-cast T-400C Laves phase Heat-treated T-400C Laves phase
As-cast T-400C Solid solution Heat-treated T-400C Solid solution
Laves phase Solid solution
Microstructure Development
Stellite 22• A finer eutectic boundary was found in heat-treated alloy• White area and black area became more distinct in multi-phase eutectic
As-cast Stellite 22 (2.00kx) Heat-treated Stellite 22 (2.00kx)
Primary sold solution
Cr7C3 carbide
Co3Mo and Co7Mo6
Primary dendritic Co solid solution
Secondary multi-phase eutectic
Results of Hardness Test
Results of Wear Test• Variation of wear volume with temperature in T-400C and Stellite 22
has a similar trend. • Each alloy exhibited different wear behavior at room temperature and
at elevated temperature
Wear volume loss of materials at different temperatures
Worn Surface Analysis T-400C • Plowing of the solid solution accompanied with fracture of the Laves phase
• Oxidation had occurred in the specimen surfaces
Worn surface of T-400C tested at room temperatureHeat-treatedAs-cast
Cavities
Oxide residuals
Worn Surface Analysis T-400C• Worn surface is very smooth, and also do not show any oxides.
• Loose/brittle silicates and small amount of hard/strong Cr-oxides were vulnerable under mechanical attack.
Worn surface of T-400C tested at 250°CHeat-treatedAs-cast
Worn Surface Analysis T-400C• Severe oxidation had occurred
• “Glaze” effects
Worn surface of T-400C tested at 450°CHeat-treatedAs-cast
Oxide residuals
Worn Surface Analysis Stellite 22• Some areas are smooth where the material was scraped away by the pin
under normal loading and some area were deformed with large plastic flow.
• Worn surface of heat-treated Stellite 22 is more smooth than that of as-cast one.
Worn surface of Stellite 22 tested at room temperatureHeat-treatedAs-cast
Plastic flow
Worn Surface Analysis Stellite 22• Less plastic deformation is found in specimen tested at 250°C
• Particle spallation had occurred on specimen surface.
Worn surface of Stellite 22 tested at 250°CHeat-treatedAs-cast
Particle spallation
Worn Surface Analysis Stellite 22• Surface oxidation is observed obviously in the as-cast specimen surface
• Oxide films decreased the frictional coefficient in as-cast specimen.
Worn surface of Stellite 22 tested at 450°CHeat-treatedAs-cast
Oxide films
Conclusions
• Annealing heat treatment promoted diffusion of alloying elements such as Si and Mo, thus contributed to the secondary precipitation of hard phases in T-400C and Stellite 22.
• The heat treatment increased the hardness and wear resistance of T-400C . As for Stellite 22, the hardness is increased while the tribological properties is degraded.
• T-400C and Stellite exhibited least wear resistance at elevated temperature at 250°C which may be attributed to the softening of material and formation of easily removed oxides.
Future work
• More superalloys will also be studied for the influence of heat treatment.
• Superalloys will be applied in a series of other heat treatment cycles to determine the effects of various heat treatment parameters such as heating temperature, holding time, cooling speed and cooling medium on these high temperature alloys.
• The heat treatment effects on superalloys with various other fabrication state (e.g. HIP) will be investigated.
• The effects of heat treatment on the corrosion behavior of superalloys will be studied.
Acknowledgement
I would like to thank people who made this work possible:
• Prof. Ming Liang, Dept. of Mechanical and Aerospace Engineering, University of Ottawa
• Prof. Rong Liu, Dept. of Mechanical and Aerospace Engineering, Carleton University
• Dr. Kuiying Chen, Institute for Aerospace Research, NRC
• Kennametal Stellite Inc.
Questions?
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Vickers Hardness Results
As-cast T-400C
TemperaturePrimary Laves
phase
Solid solution Overall
microstructure
25C 1068 (2.31%) 380 (3.51%) 574 (4.51%)
250C 1034 (3.46%) 342 (2.53%) 529 (3.04%)
450C 909 (2.29%) 329 (2.36%) 494 (3.87%)
600C 878 (2.41%) 324 (2.54%) 477 (4.68%)
Average hardness values (HV) for as-cast T-400C
Vickers Hardness Results
Heat-treated T-400C
TemperaturePrimary Laves
phase
Solid solution Overall
microstructure
25C 1048 (2.49%) 485 (1.37%) 587 (2.58%)
250C 980 (3.69%) 445 (3.47%) 546 (4.38%)
450C 908 (2.46%) 441 (2.38%) 505 (3.48%)
600C 889 (3.39%) 429 (2.43%) 495 (3.59%)
Average hardness values (HV) for heat-treated T-400C
Vickers Hardness Results
As-cast Stellite 22
TemperatureSolid solution Eutectic
mixture
Overall
microstructure
25C 314 (2.56%) 501 (1.65%) 420 (3.59%)
250C 255 (3.57%) 393 (2.54%) 342 (2.71%)
450C 242 (3.63%) 328 (2.18%) 326 (3.06%)
600C 246 (2.95%) 310 (2.38%) 305 (2.38%)
Average hardness values (HV) for as-cast Stellite 22.
Vickers Hardness Results Heat-treated Stellite 22
TemperatureSolid solution Eutectic
mixture
Overall
microstructure
25C 307 (2.47%) 646 (3.54%) 433 (2.75%)
250C 271 (3.42%) 542 (3.38%) 375 (3.49%)
450C 241 (3.69%) 418 (2.44%) 338 (2.53%)
600C 211 (2.34%) 360 (3.36%) 311 (3.45%)
Average hardness values (HV) for heat-treated Stellite 22.