1 Effect of Electric Field on the Self-propagating High-temperature Synthesis of Functionally Gradient Materials Meng Qingsen Quan wanglin Cheng dajun Shen yanli (Taiyuan University of Technology ， Taiyuan ， China ) Invitation for the 2 nd German-Sino Workshop on EPM, Oct.16-19, 2005

2 Self-propagating High-temperature Synthesis(SHS) SHS is a science-intensive process. Its comprehension requires erudition in thermodynamics, chemical kinetics, general and structural macrokinetics, materials science, and other allied fields of knowledge.

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4 Schema of SHS Fig.1. Schema of electric field activated synthesis reaction equipment

5 Preparation method of gradient reagent Gradient Reagent Pressure Machine (F) F

6 Schema of SHS.

7 Scheme of Experiment Tab.1. Components list of single-layer reactants stocks. testing number Fe% of 0.25(3Ni+Ti)+( ) (Ti+C) system testing number Fe% of 5Ti+3TiO 2 +3C+4Al A010%B010% A0210%B0210% A0320%B0320% A0430%B0430% A0540%B0540% A0650%B0650% A0760%

8 Design of Gradient Reagent Ti+C+2%Ni+0%Fe Ti+C+25%Ni+10%Fe Ti+C+25%Ni+20%Fe 5Ti+3TiO 2 +3C+4Al+20%Fe 5Ti+3TiO 2 +3C+4Al+0%Fe 5Ti+3TiO 2 +3C+4Al+10%Fe Fig.2. Schematic diagram of the reactants stock of TiC-Ni-x%Fe system. Fig.3. Schematic diagram of the reactants stock of TiC-Al 2 O 3 -x%Fe system.

9 Front edge zone of reaction Reagent Product Preheat zone Models of Combution Fig. 4. Combustion wave model of quenching Fig.5. Combustion reaction model of the gradient layers reactants Zone of partly reaction

10 Prepared FGM Fig. 6. TiC-Ni-x%Fe system FGM prepared by SHS. Fig.7. TiC-Al 2 O 3 -x%Fe system FGM prepared by SHS.

11 Testing and Analytic technique  Microscopic structure Analysing （ XJL- 024 、 SEM LEO520 ）  Hardness Testing （ M-400-Hi 、 HRBV ）  Phase composition Analysing （ Y-2000 ）

12 Microstructure Contrast between not imposed electric field and imposed electric field a 1mm c b Fig.8. Microstructures of TiC- Ni-x%Fe system compounds prepared before and after imposed electric field. not imposed electric field imposed electric field

13 Microstructure of FGM (TiC-Ni-x%Fe) First Layer Second layer Third Layer 200μm a First Layer Second layer 100μm 1mm Third Layer Second layer b Fig. 9. Microstructure of each gradient layer of TiC-Ni-x%Fe system Fig. 10. microstructure of gradient layers of TiC-Ni-x%Fe system

14 a TiC Metal and intermetallic compound c b d Fig. 11. Microstructure and energy spectrum analysis of the second layer.

15 Phase composition Analysing (TiC-Ni-x%Fe) a 2θ( o ) CPS First Layer b 2θ ( o ) CPS Second Layer

16 c CPS 2θ ( o ) Third Layer Fig. 12. Results of X-ray diffraction patterns of TiC- Ni-x%Fe system FGM. (a,b,c)

17 Hardness Testing (TiC-Ni-x%Fe) Tab.2. The micro hardness distribution of TiC-Ni-x%Fe system. First Layer(TiC-Ni- 0%Fe) Second Layer(TiC-Ni- 10%Fe) Third Layer(TiC- Ni-20%Fe) Testing Number Hardness(HV) Fig.13. The hardness distribution regularity of TiC-Ni-x%Fe system FGM Hardness /HRC Thickness of product /mm

18 Effect of electric field on SHS Fig.14. Profiles of temperature (T), conversion (η), and rate of heat release (φ) in the vicinity of an advancing reaction front with a thickness of δ w

19 Effect of electric field on SHS Fe / % v / mm·s -1 I/A×10 、 U/V·cm -1 t/s E / V·cm -1 v / mm·s -1 Fig. 15. Relationship between combustion wave velocity and Fe content Fig.17. Dependence of the wave velocity on E Fig. 16. Curve of current and voltage with time

20 Transmit Mechanism of Solid State Ion on Electric field

21 Conclusions  (1) The heat of self-propagation reaction and electric field induced is the driving force of mass transferring, which promoted the generating of the product of Ni 3 Ti and Fe 5 C 2.  (2) From Fig. 14., the imposed electric field makes the ions and free electrons of metal move in greater speed, which impels the temperature of the system increasing and improve the plenitude of reaction and the uniformity of products by accelerating the diffusion speed of electrons and ions.  (3) From Fig. 16., the field distribution on reactants and products makes high temperature in the front edge, which overcomes the thermodynamic limits of SHS and actuates the reaction to proceed, increases reaction speed.  (4)From Fig. 17., it is shown that the velocity of the combustion wave is linearly proportional to magnitude of electric field.

22 1) It is essential to understand the effect of the electric fields on the processes parameters such as density, combustion temperature, burning velocity, extent of conversion, composition, structure, properties of SHS products, etc. 2) Additional experimental and theoretical studies should be carried out about the effect of the electric fields on product of FGM. Requirement and Hope

23 Acknowledgement This project was financially supported by National Natural Science Fund of China ( ) Natural Science Fund of Shanxi Province ( )

24 Thanks for your Attention