Swapan Kumar Karak. Department of Metallurgical and Materials Engineering NIT Rourkela, , India

Transcription

1 NMD-ATM Development of Nano-Y 2 O 3 Dispersed Ferritic Alloys for Nuclear Reactors S. K. Karak, J. Dutta Majumdar, W. Lojkowski and I. Manna by Swapan Kumar Karak Department of Metallurgical and Materials Engineering NIT Rourkela, , India

2 Introduction to Nuclear Materials Important Properties:expectedexpected Higher operating temperatures Higher neutron flux exposure Highly corrosive environment Longer life time (> 60 years) Factors for Selection: Stability under radiation Swelling / growth Tensile properties at high Temperature Fracture toughness Corrosion behavior Common Alloys used F-M steels Zircaloy Austenitic stainless steels Ni based super alloys Low Cr steels Limitations High temperature instability Corrosion and radiation resistance insuficient Swelling

3 ODS steels: The Change in the Scenario Excellent creep properties (750 0 C) Addition of grain refiners removes anisotropy Big advancements in mechanical alloying and heat treatment Strengthening by dispersion hardening Strength depends upon the oxide size, shape, distribution and bonding Interaction with dislocations Mechanism of Strengthening Kimura et al. SMINS, 07,Germany, June4-6,2007

4 Application of ODS Ferritic Steel: Clad tubes of fast breeder reactor Structural materials for advanced breeding blanket replacing EUROFER and replacing reduced activation ferritic-martensitic steel (RAFM) in fusion reactor Backbone materials for gas cooled divertor in fusion reactors Clad tubes Advanced breeding blanket Divertor

5 Aim and Objectives of the work Optimization of the chemical composition of nano-oxide oxide dispersion strengthened ferritic alloy in order to produce it without anisotropy. Standardization of various operating parameters like milling time, sintering temperature, atmosphere and holding time. To study the distribution and the shape of the Yttria (Y 2 O 3 ) dispersoid on the ferritic matrix. To study the effect of elements like Cr and nano-yttria on the microstructure and mechanical properties of ferritic alloys.

6 Powder Processing Mechanical Alloying FRISTSCH planetary ball mill Room temperature milling SS vials and 10 mm balls 300 rpm, 10:1 (ball to powder weight) Wet milling with 50 ml toluene Fe, Cr, Al, Ti, Y powder (~ µm) Mechanism of MA Alloy Ti (wt %) Al (wt %) Cr (wt %) Fe (wt%) Y 2 O 3 (wt%) A B C D Composition (initial) of the powder blends for mechanical alloying /milling

7 X-Ray Diffraction analysis of Powders in different Milling time Alloy A Alloy B EDS patterns of alloy A XRD patterns from the elemental powder blends of alloy A,B subjected to mechanical alloying for 0 h ( manually blended before mechanical alloying) to 40 h Variation of crystallite size and plastic strain during milling of alloys for 0 h ( manually blended before mechanical alloying) to 40 h

8 Powder Characterization (110) (211) TEM image of Alloy A at 40 h milled powder (a) Bright field and (b) the corresponding SAD pattern (200) TEM images at 40h milling powder (110) (211) (200)

9 High Pressure Consolidation Ceramic crucible WC Coated Die HPS Parameters: Diameter, d = 7 mm Pressure, P = 8 GPa Temperature, T = 600 o C,800 o C,1000 o C Time, t = 3 min Transient heating + high pressing

10 Hot Isostatic Pressure (HIP) Working Chamber 1step 100MPa 2 step 25MPa 3 step Sample after hipping oil receptacle oil N Ar compressor HIP Parameters: Diameter, d = 10 mm, Length l = 30mm Pressure, P = 1.5 GPa Temperature, T = 600 o C,800 o C,1000 o C Time, t = 30 min Atmospheres argon gas

11 Pulse Plasma Sintering (PPS) Chamber 600x600x600 mm Vacuum10-6 mbar Hydraulic press: Pressure 50 kn Strokeofpress200mm Samples HIP Parameters: Diameter, d = 15 mm, Height, h = 12mm Pressure, P = 50 kn Temperature, T = 600 o C,800 o C,1000 o C Time, t = 5 min

12 Hydrostatic Extrusion (HE) Sample Sample Dimension: Diameter- 12 mm, Length - 50 mm Schematic Diagram of Working Chamber

13 Phase Evolution in Consolidated Products (a) (b) (c) (d) XRD patterns from the elemental powder blends of alloy A, B, C and D consolidated at different temperatures Bright field and Dark field TEM image of Alloy A sintered at 600 o C

14 Phase Evolution in Consolidated Products 50 nm Bright field TEM image of Alloy A sintered 1000 o C

15 Assessment of Physical and Mechanical Properties Variation of density and porosity as function of sintering temperature used for different alloys Variation of hardness and Young s Modulus as function of sintering temperature used for different alloys

16 Assessment of Mechanical Properties Plots showing for the alloy A prepared by high pressing at different temperatures : (a) the variation of engineering stress with displacement and (b) cumulative acoustic emission events against the compressive stress Plots showing for the alloy D prepared by hot iso-static pressing at different temperatures : (a) the variation of engineering stress with displacement and (b) cumulative acoustic emission events against the compressive stress

17 Fractographic Analysis FESEM images of the fracture surfaces generated during compression tests carried out on the alloy A consolidated by high pressure sintering at 1000 oc (a) low and (b) high magnification FESEM images of the fracture surfaces generated during compression tests carried out on the alloy A consolidated by pulse plasma sintering at 1000 oc (a) low and (b) high magnification FESEM images of the fracture surfaces generated during compression tests carried out on the alloy D consolidated by hot-isostatic pressing at 1000 oc (a) low and (b) high magnification FESEM images of the fracture surfaces generated during compression tests carried out on the alloy A and alloy B consolidated by hydrostatic extrusion at 1000 oc

18 Assessment of Mechanical Properties High Pressure Sintering at 1000 ο C Pulse Plasma Sintering at 1000 ο C Hot isostatic Pressing at 1000 ο C Alloy Hardness (GPa) Young s Modulus (GPa) Yield Stress (MPa) Maximum Compres sive Stress (MPa) Hardness (GPa) Young s Modulus (GPa) Yield Stress (MPa) Maximum Compres sive Stress (MPa) Hardness (GPa) Young s Modulus (GPa) Yield Stress (MPa) Maximum Compres sive (MPa) A B C D Stress

19 Summary and Conclusions Mechanical alloying is a potential route for synthesis of nano-size Y 2 O 3 dispersed Fe-Cr Cr-Al-Ti alloy powders with wide variation composition (13.5 to 25.5 Cr wt. %). XRD analysis of the milled product show that in each alloy produces a single phase body centre cubic (BCC) solid solution indicating that Cr, Al and Ti completely dissolve in Fe in course of high-energy ball milling for h XRD analysis show the degree of size reduction of powders is the function of the Cr content of the alloys, which confirms by crystallite size reduction from alloy A to D. The microstructures of 40 h milled product have shown mixtures of nanocrystalline BCC-Fe-Cr grains with presence of nm Y 2 Ti 2 O 7 / Y 2 TiO 5 or unreacted Y 2 O 3 particles uniformly dispersed in the nanocrystalline matrix. Phase evolution of consolidated product showed by XRD analysis is that the presence of BCC-Fe(Cr) phase along with intermetallic phases like Fe 11 TiY and Al Cr Y and mixed oxide phase Y 2 Ti 2 O 7 / Y 2 TiO 5 and confirms by TEM analysis. Substantial grain coarsening occurs in all the alloys consolidated at 1000 o C as compared to that at 600 o C or at 800 o C due to greater extent of volume diffusion of Cr in α-fe at this higher temperature Bulk physical properties (density and porosity) and mechanical properties (compressive strength, hardness, Young s modulus) for the present alloys are the function of sintering temperatures. Bulk mechanical properties of present ferritic alloys consolidated hot isostatic pressing route by record extremely high levels of compressive strength ( MPa), Young s modulus ( GPa), indentation fracture toughness ( MPa m) and hardness ( GPa), albeit low ductility and brittle failure. The same set of ferritic alloys consolidated by high pressure sintering are found high levels of compressive strength ( MPa), Young s modulus ( GPa), indentation fracture toughness (3.6 to 15.4 MPa m) and hardness ( GPa), with brittle faliure The present ferritic alloys consolidated by pulse plasma sintering record extremely high ranges of compressive strength ( MPa), yield strength ( MPa), Young s modulus ( GPa) and hardness ( GPa), with improvement of ductility. It found that the present ferritic alloys record significantly high of compressive strength ( MPa) and yield strength ( MPa) with a true strain ( %) in transverse direction and compressive strength ( MPa) and yield strength ( MPa) with a true strain ( %) in longitudinal direction, Young s modulus ( GPa) and hardness ( GPa) in hydrostatic extrusion route.

20 Publication Studies on Wear Behavior of Nano-Y 2 O 3 Dispersed Ferritic Steel Developed by Mechanical Alloying and Hot Isostatic Pressing by S. K. Karak, C.S.Vishnu, Z. Witczak, W. Lojkowski,J.Dutta Majumdar and I. Manna in WEAR, 270(2010)5-11. Development of Ultra High Strength Nano-Y 2 O 3 Dispersed Ferritic Steel by Mechanical Alloying and Hot Isostatic Pressing by S. K. Karak, T. Chudoba, Z. Witczak, W. Lojkowski, and I. Manna in Material Science Engineering A, 528 (2011) Mechanical Properties of Nano-Y 2 O 3 Dispersed Ferritic Steel Developed by Mechanical Alloying and Pulse Plasma Sintering by S. K. Karak, J.Dutta Majumdar, T. Chudoba, Z. Witczak, W. Lojkowski, L. Ciupinski, K. J. Kurzydłowski and I. Manna in Philosophical Magazine, 92 (2012) Evaluation of Mechanical Properties of Nano-Y 2 O 3 Dispersed Ferritic Steel Developed by Mechanical Alloying and High Pressure Sintering by S. K. Karak, J.Dutta Majumdar, T. Chudoba, Z. Witczak, W. Lojkowski, L. Ciupinski, K. J. Kurzydłowski and I. Manna in Metallurgical and Materials Transaction A in Press (2012). Papers communicated.. Microstructure and Mechanical properties of nano-y 2 O 3 dispersed ferritic alloys by mechanical alloying and hydrostatic extrusion by S. K. Karak, J.Dutta Majumdar, T. Chudoba, Z. Witczak, W. Lojkowski, and I. Manna in Material Science Engineering A Isothermal oxidation kinetics of nano Y 2 O 3 dispersed high Cr ferritic steel prepared by mechanical alloying and hot isostatic pressure sintering by S. K. Karak, A.Meherwal, J. Dutta Majumdar and I. Manna in Metallurgical and Materials Transaction A

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