1. MICROSTRUCTURE AND PROPERTIES OF MECHANICAL ALLOYED AND EQUAL CHANNEL ANGULAR EXTRUDED TUNGSTEN CARBIDE Presented by Kannan Ramakrishnan LAMAR UNIVERSITY, BEAUMONT, TEXAS - USA

2. ACKNOWLEDGEMENT Dr. M. N. Srinivasan, Dr. V. Zaloom, Dr. J. Thomas, Dr. P. Corder, Dr. H. Chu and Xhemal Kaculi Dr. M. N. Srinivasan, Dr. V. Zaloom, Dr. J. Thomas, Dr. P. Corder, Dr. H. Chu and Xhemal Kaculi Advanced Technology Program (ATP) of the State of Texas. Advanced Technology Program (ATP) of the State of Texas. Dr. A. M. Clearfield and Ms. Zhike Wang of Texas A&M University (X-ray, SEM). Dr. A. M. Clearfield and Ms. Zhike Wang of Texas A&M University (X-ray, SEM). Dr. K. T. Hartwig, Mr. Robert Barber and Mr. A. Parasiris formerly of Texas A&M University (ECAE). Dr. K. T. Hartwig, Mr. Robert Barber and Mr. A. Parasiris formerly of Texas A&M University (ECAE).

3. OVERVIEW Introduction and Objective of study Introduction and Objective of study Literature Review Literature Review Mechanical Alloying Equal Channel Angular Extrusion Nanocrystalline Materials Modeling studies Experimental Procedure Experimental Procedure Results obtained Results obtained Conclusions and Suggestions for future research Conclusions and Suggestions for future research

4. OBJECTIVES OF STUDY The focus of this research is primarily: On the use of mechanical alloying (MA) to produce nanocrystalline WC-Co powder containing uniformly distributed cobalt (binder), and On the use of mechanical alloying (MA) to produce nanocrystalline WC-Co powder containing uniformly distributed cobalt (binder), and On the preservation of the fine scale structure and composition in the parts, produced from this powder aggregate using the equal channel angular extrusion process (ECAE). On the preservation of the fine scale structure and composition in the parts, produced from this powder aggregate using the equal channel angular extrusion process (ECAE).

5. OBJECTIVES (Contd.) The study also has the following objectives: To determine the influence of three important MA variables: milling time, speed, and powder to ball ratio, on the microhardness of WC-Co compacts (after MA, Annealing and ECAE). To determine the influence of three important MA variables: milling time, speed, and powder to ball ratio, on the microhardness of WC-Co compacts (after MA, Annealing and ECAE). To quantify the effects of milling time, speed and ball to powder ratio on the composition and grain size of the compacts. To quantify the effects of milling time, speed and ball to powder ratio on the composition and grain size of the compacts.

6. MECHANICAL ALLOYING (MA) MA is a high-energy ball milling process that uses the mechanical energy to produce composite powders with a controlled microstructure (nanocrystalline and amorphous). MA is a high-energy ball milling process that uses the mechanical energy to produce composite powders with a controlled microstructure (nanocrystalline and amorphous). Inter-dispersion of ingredients occurs by repeated solid state welding and fracture of free powder particles. Inter-dispersion of ingredients occurs by repeated solid state welding and fracture of free powder particles. Steady state processing is marked by constant saturation hardness and particle size distribution. Steady state processing is marked by constant saturation hardness and particle size distribution.

7. MECHANICAL ALLOYING (MA)

8. EQUAL CHANNEL ANGULAR EXTRUSION (ECAE) Severe plastic deformation is an effective method for forming nanocrystalline materials and ECAE is one such method. Severe plastic deformation is an effective method for forming nanocrystalline materials and ECAE is one such method. The uniqueness of this method comes from its ability to produce intense and uniform plastic deformation caused by simple shear of the material. The uniqueness of this method comes from its ability to produce intense and uniform plastic deformation caused by simple shear of the material.

9. EQUAL CHANNEL ANGULAR EXTRUSION (ECAE)

10. ECAE (Contd.)

12. TECHNOLOGICAL BENEFITS OF ECAE A high level of deformation can be reached in one pass. The level of deformation becomes large after multiple extrusion passes (heavy plastic strain). A high level of deformation can be reached in one pass. The level of deformation becomes large after multiple extrusion passes (heavy plastic strain). A variety of microstructures, substructures, and nanostructures, can be developed by modifying the shear plane and shear direction at each pass. A variety of microstructures, substructures, and nanostructures, can be developed by modifying the shear plane and shear direction at each pass. ECAE can be effectively used as a method to consolidate and preserve the nanostructured powders obtained from the MA process. ECAE can be effectively used as a method to consolidate and preserve the nanostructured powders obtained from the MA process.

13. NANOCRYSTALLINE MATERIALS These are materials with grain size of the order of 1 – 100 nanometer (nm) or 10 Angstrom. There may be 3 – 5 atoms in a span of 1nm. These are materials with grain size of the order of 1 – 100 nanometer (nm) or 10 Angstrom. There may be 3 – 5 atoms in a span of 1nm. They have a significant fraction of the total atoms present at the grain boundaries, unlike their coarse-grained counterparts. They have a significant fraction of the total atoms present at the grain boundaries, unlike their coarse-grained counterparts. Since the grain boundaries occupy a significant volume in their material, their physical properties influence the overall material. Since the grain boundaries occupy a significant volume in their material, their physical properties influence the overall material.

14. MODELING OF ENERGY TRANSFER & POWER CONSUMPTION Main parameters to evaluate are: the kinetic energy involved per collision, the kinetic energy involved per collision, the impact velocity and impact frequency, the impact velocity and impact frequency, power involved in the milling process power involved in the milling process Energy and power analysis were carried out for various regions in the attritor.

15. GENERAL EQUATIONS The kinetic energy involved in each collision can be expressed by:  E = K a (1/2) m b V b 2 m b = mass of the ball V b = relative impact velocity K a = coefficient depending on the elasticity of the collision = 1 for perfect inelastic collision (balls covered with powder)

16. GENERAL EQUATIONS (Contd.) Power involved in the milling process for a single collision event is: P =  E V t  E = kinetic energy involved in each collision V t = collision frequency

17. MODELING RESULTS Location Speed (rpm) Kinetic Energy E (J) x 10 -3 Power Involved (J) x 10 -3 Limited Diffusion 2505000.006580.08060.01030.208 Impact and Mixing 2505000.01480.1330.00870.313 Bottom, near middle 2505000.00.00160.00.00044 Bottom, shear zone 2505000.006580.01480.00590.00157 Powder dead zone 2505000.00.00.00.0

18. EXPERIMENTAL PROCEDURE MA of 16 samples – 8 samples in each replicate. The composition was unaltered. MA of 16 samples – 8 samples in each replicate. The composition was unaltered. Sealed the 16 samples in SS billets, subjected the billets to annealing process and then extruded them using ECAE (two passes). Sealed the 16 samples in SS billets, subjected the billets to annealing process and then extruded them using ECAE (two passes). Two sets/replicate of WC-Co samples (each set comprising of 8 different experiments) were cut from the billets &then polished per ASTM E-3. Two sets/replicate of WC-Co samples (each set comprising of 8 different experiments) were cut from the billets &then polished per ASTM E-3. One of the sets was subjected to a detailed annealing procedure & polished again. One of the sets was subjected to a detailed annealing procedure & polished again.

19. ANNEALING PROCEDURE Powder samples obtained from MA process were annealed at 1200 0 C for one hour. Powder samples obtained from MA process were annealed at 1200 0 C for one hour. The extruded samples were annealed at 1400 0 C. The extruded samples were annealed at 1400 0 C. Argon atmosphere Argon atmosphere Heating rate: 5 0 C/min. Heating rate: 5 0 C/min. Dwelling time for 10 minutes at 150 0 C. Dwelling time for 10 minutes at 150 0 C. Dwelling time for one hour at 1400 0 C. Dwelling time for one hour at 1400 0 C. Cooling rate: 5 0 C/min to room temperature. Cooling rate: 5 0 C/min to room temperature.

20. EXPERIMENTAL PROCEDURE (Contd.) Vickers microhardness values were determined, per ASTM E-384, for both replicates of WC-Co extruded compacts. Vickers microhardness values were determined, per ASTM E-384, for both replicates of WC-Co extruded compacts. The microhardness values were then incorporated in the DOE equations to determine the influence (effects) of milling time, speed and ball to powder ratio, on the microhardness of WC-Co samples. The microhardness values were then incorporated in the DOE equations to determine the influence (effects) of milling time, speed and ball to powder ratio, on the microhardness of WC-Co samples. The compacts were subjected to X-ray diffraction for structure identification and particle size analysis. The compacts were subjected to X-ray diffraction for structure identification and particle size analysis.

21. 2 3 FACTORIAL DESIGN OF EXPERIMENTS

22. MICROHARDNESS OF WC-CO COMPACTS

23. EFFECTS OF MILLING VARIABLES (After Annealing)

24. SCHERRER’S EQUATION D = K / (  cos  ) D = Crystallite size in Angstrom units (normal to diffracting planes). K = 0.89 = Scherrer constant (crystallite shape constant) = X-ray wavelength (1.5418 Angstrom) used in the experiment = X-ray wavelength (1.5418 Angstrom) used in the experiment  = Observed diffraction peak breadth at half- maximum intensity (full-width-half- maximum) measured in radians  = Bragg angle

25. X-Ray Diffraction Pattern

26. AVERAGE MICROHARDNESS VALUES AND GRAIN SIZE VALUES

27. EFFECTS OF MILLING VARIABLES AFTER ANNEALING

28. PLOT OF AVERAGE MICROHARDNESS VS. GRAIN SIZE

29. Analysis of Variance (ANOVA) of Microhardness Values after Annealing Source of Variation Sum of Square Degrees of Freedom Mean Squares F = Mean Sq./Mean Sq. of E Time (A) Speed (B) B/P Ratio (C) AB AC BC ABC Error (E) Total 23914 5441 645 2040 3993 66667 25648 16872 68211 1 8 15 95654 21762 2579 8161 15972 266669 102592 21091 4.54** 1.03 0.12 0.39 0.76 12.64* 4.86** * Significant at 95% and 99% confidence levels. **Significant at only 90% confidence level.

30. CONCLUSIONS The highest average microhardness value (after annealing) was achieved with 40 hours, 150 rpm, and 30:1 combination, for both the replicates (Sample No. 6). The highest average microhardness value (after annealing) was achieved with 40 hours, 150 rpm, and 30:1 combination, for both the replicates (Sample No. 6). The lowest average microhardness value (after annealing) was achieved with 10 hours, 550 rpm, and 30:1 combination, for both the replicates (Sample No. 7). The lowest average microhardness value (after annealing) was achieved with 10 hours, 550 rpm, and 30:1 combination, for both the replicates (Sample No. 7). Sample No. 7 went from being the best sample before annealing to being the worst sample after annealing in both the replicates. Sample No. 7 went from being the best sample before annealing to being the worst sample after annealing in both the replicates.

31. CONCLUSIONS (Contd.) Milling time is the only factor that significantly and positively affects the process in both replicates (after annealing). Milling time is the only factor that significantly and positively affects the process in both replicates (after annealing). The combination of all three (higher values) primary factors has a high negative effect on the process. (Sample 8-both the replicates) The combination of all three (higher values) primary factors has a high negative effect on the process. (Sample 8-both the replicates) Replicates 1 and 2 displayed almost similar trend in the results. Sample Nos. 6, 5, 3 and 8, have the same respective combination of milling factors in both the replicates (after annealing). Replicates 1 and 2 displayed almost similar trend in the results. Sample Nos. 6, 5, 3 and 8, have the same respective combination of milling factors in both the replicates (after annealing).

32. CONCLUSIONS (Contd.) The grain size values (nm) obtained establish the fact that nanostructured compacts can be successfully produced by employing MA and ECAE processes. The grain size values (nm) obtained establish the fact that nanostructured compacts can be successfully produced by employing MA and ECAE processes. It should be noted that the grain size values obtained were under constant ECAE conditions for just two replicates. It should be noted that the grain size values obtained were under constant ECAE conditions for just two replicates. This work would contribute to the development of technology to produce superior quality WC-Co parts required by the oil tool industry. This work would contribute to the development of technology to produce superior quality WC-Co parts required by the oil tool industry.

33. SUGGESTIONS FOR FUTURE RESEARCH Perform more than two replicates to determine statistically if there is a substantial difference in the variance of the data related to both average microhardness and grain size values. Perform more than two replicates to determine statistically if there is a substantial difference in the variance of the data related to both average microhardness and grain size values. Obtain X-ray diffraction results for milled powder at various stages during the experiments and then analyze to see if there is any substantial grain growth after ECAE. Obtain X-ray diffraction results for milled powder at various stages during the experiments and then analyze to see if there is any substantial grain growth after ECAE.

34. SUGGESTIONS FOR FUTURE RESEARCH (Contd.) Implement a computer model or mathematical model to simulate the MA and ECAE processes (to optimize the variables involved). Implement a computer model or mathematical model to simulate the MA and ECAE processes (to optimize the variables involved). Conduct experiments by varying ECAE conditions. For ex. No. of passes, extrusion temperature, route of pass (A, B, C), and direction of cutting the samples (along, transverse, etc.). Conduct experiments by varying ECAE conditions. For ex. No. of passes, extrusion temperature, route of pass (A, B, C), and direction of cutting the samples (along, transverse, etc.).