Thema: Erfahrungen mit Thermocalc und Dictra auf dem Gebiet der Bondcoat phasenbestimmung und Diffusion

Transcription

1 Thema: Erfahrungen mit Thermocalc und Dictra auf dem Gebiet der Bondcoat phasenbestimmung und Diffusion Prof. Dr. D. R. G. Achar Institut für Werkstoffe und verfahren der Energietechnik Thermocalc Anwendertreffen und Schulung Juni 2003 Access Materials & Processes, Aachen Germany

2 CONTENTS BACKGROUND MODELLING MCrAlY - Coating Alloys PHASE EQUILIBRIA COMPARE WITH EXPERIMENTAL DATA MODELLING INTER DIFFUSION MCrAlY Ni-BASE MATERIAL EXPERIMENTAL OBSERVATIONS - DISCUSSION CONCLUSIONS

3 BACKGROUND GAS TURBINE BLADES - DEMANDS - HIGH OPERATING TEMPERATURES - PROBLEMS - PHASE CHANGES - SUBSTRATE MATERIAL - BOND COAT - TBC S INTERDIFFUSION - SUBSTRATE / BOND COAT LIFE PREDICTION - LIMITED EXPERIMENTAL DATA MODELLING + EXPERIMENTAL VERIFICATION

4 Isothermal Section of theternary Phase diagram Ni-Cr-Al 950 C 950 C Al possible MCrAlY compositions Cr Ni

5 Microstructure across the interface between a Ni-based Superalloy substrate and MCrAlY bond coat after exposure at 1000 o C for 1000 hrs. Bond Coat Diffusion Band Substrate alloy

6 MATERIALS SELECTED FOR MODELLING PHASE EQUILIBRIA STUDIES THREE GROUPS OF MCrAlY COATING ALLOYS OF INDUSTRIAL IMPORTANCE GROUP I - Ni 20Cr (3 to 12%)Al GROUP II - Ni 20Cr 20Co (3 to 12%)Al GROUP III - Ni 20Cr 20Co 9Al (0 to 5%)Re

7 EXPERIMENTAL WORK PHASE EQUILIBRIA STUDIES HEAT TREATMENT C, C & C - ARGON ATMOSPHERE HOURS - WATER QUENCHING Re CONTAINING COATING ALLOYS - HOMOGENISATION AT C - ARGON ATMOSPHERE FURNACE COOLING

8 Thermocalc Phase Equilibria Calculation Results Effect of Al content on calculated phase equilibria in ternary Ni-17Cr-xAl coating alloys at C. 1,0 Content of Phases / npm 0,8 0,6 0,4 0,2 0,0 γ γ α β Al concentration / Wt-%

9 Effect of Al on microstructural changes in ternary Ni- 17Cr-x Al coating alloy at C. g / g N - i Y 6%Al N - i Y g / g g a 9%Al a 12%Al g b

10 Simulated phase changes in the Ni-20Cr-12Al coating alloy with and without Cobalt as a function of temperature 1,0 1,0 Content of Phases / npm 0,8 0,6 0,4 γ γ α β 0% Co Content of Phases / npm 0,8 0,6 0,4 γ β σ 20% Co 0,2 0,2 0, Temperature / o C 0, Temperature / o C

11 Microstructure of the ternary Ni-20Cr-12Al coating alloy with and without Cobalt at different temperatures 950 C 0% Co 950 C 20% Co a b γ β g σ 1000 C g 0% Co 1000 C β 20% Co Ni - Y γ a b g

12 Effect of Re content on calculated phase equilibria in quaternary Ni-20Cr-xCo-9Al at 950 o C Content of Phases / npm 1,0 0,8 0,6 0,4 0,2 10% Co γ γ α β Content of Phases / npm 1,0 0,8 0,6 0,4 0,2 20% Co γ β σ 0, Re concentration / Wt-% 0, Re concentration / Wt-%

13 Effect of Re content on Microstructure of the quaternary Ni-20Cr-10Co-9Al coating alloy a) 0% Re and b) 3% Re b g a) Ni - Y g b) b Ni - Y

14 Effect of Re content on Microstructure of the quaternary Ni-20Cr-20Co-9Al coating alloy a) 0% Re and b) 3% Re g b a) Ni - Y g b b)

15 XRD patterns of quaternary Ni-20Cr-xCo-9Al-3Re coating alloy γ γ β α / / b) Cps / / Ni-20Cr-20Co-9Al-3Re Ni-20Cr-10Co-9Al-3Re q

16 INTER DIFFUSION STUDIES - DICTRA DIFFUSION DATA BASE DIFFUSION IN DISPERSED PHASES MODEL MATRIX PHASE DIFFUSION DISPERSED PHASE/S - POINT SINK / SOURCES OF SOLUTE CALCULATE PHASE FRACTIONS AND COMPOSITIONS AT EACH NODE LOCAL EQUILIBRIUM DIFFUSION COUPLE: 2mm Substrate alloy and 0.3mm Bond Coat at C for 3000hrs.

17 Chemical composition (in mass %) of materials used in diffusion simulation ALLOY Ni Co Cr Al Ti Ta Mo W Re Hf CMSX-4 Substrate PWA 286 Coating Bal Bal DIFFUSION EXPERIMENTAL WORK: 20mm Bars of CMSX 4 Plasma Coated with 0.3mm PWA286 Bond coats exposed to 1000 o C for 1000hrs. in an argon atomosphere.

18 Interface between Ni-Base Alloy (CMSX 4) and NiCoCrAlY (PWA 286) coating after 1000 h exposure at 1000 C - a) SEM-picture, b) calculated phases NiCoCrAlY coating g b γ-phase g Ni-base alloy Mole fraction γ'-phase β-phase a) Distance in micrometer b)

19 Interface between Ni-Base Alloy (CMSX 4) and NiCoCrAlY (PWA 286) coating after 1000 h exposure at 1000 C - measured and calculated element concentrations. 4,E Concentration (mass.-% 4,E+09 3,E ,E ,E+09 2,E ,E+09 calculated measured Cr Co Al 5,E+08 0 Ni-base alloy NiCoCrAlY coating 0,E Distance (micrometer)

20 Major Thermocalc Calculations Carried out: 1. Modelling of phase changes in Ni-a%Cr-b%Co-c%Al-d%Re alloy systems in the temperature range between o C. 2. Phase formations and activity calculations between o C in - Mn base alloy - Ni-Fe-Mo alloy - Centrifugal cast FeNiCrC alloy - FeCrAl alloy Major Dictra Diffusion simulations carried out: 1. Interdiffusion studies involving major Ni-base Turbine materials with different MCrAlY bond coats in the temperature between o C for exposure time up to 3000hrs. 2. Effect of carbon in the carbide formations across diffusion interface between turbine materials and different bond coat materials. 3. Diffusion in dissimilar steels welding.

21 Comparison of Carbide Formation Across Diffusion Interface Between Bond Coat A with 15% Co (left) and Alloy 738 (modified) (right) for Different Exposure periods at 1000 o C - interface at 200µm Content of Carbide / npm 0,10 0,08 0,06 0,04 0,02 Bond Coat A 738 Turbine Material m23c6-1hr m23c6-10hr m23c6-100hr m23c6-200hr 0, Distance / µm 0,10 Comparison of Carbide Formation Across Diffusion Interface Between Bond Coat B (left) and Alloy 738 (modified) (right) for Different Exposure periods at 1000 o C - interface at 200µm Content of Carbide / npm 0,08 0,06 0,04 0,02 0,00 Bond Coat B m23c6-1hr m23c6-10hr m23c6-100hr m23c6-200hr D istance / µm 738 Turbine Material

22 Concluding Remarks: Thermocalc calculations have predicted phase equilibria in commercial MCrAlY coating alloys with reasonable accuracy. Some deviations have been observed for high Al and Co coating alloys at 1000 o C. When alloy compositions lie on the multiphase boundaries, calculations have shown fluctuations in the phase compositions.

23 Interdiffusions between Ni-base superalloys and MCrAlY bond coats have been modelled with a high degree of accuracy with Dictra, provided the composition of the alloys are effectively reduced to consist of a maximum of eight elements. Dictra has shown integration failure problem in systems involving more than eight elements. Integration failure problems have also been observed in situations involving more than four spheroidal phases in the region.

24 THANK YOU