WORCESTER POLYTECHNIC INSTITUTE – METAL PROCESSING INSTITUTE The Controlled Diffusion Solidification Process Fundamentals and Principles Kimon Symeonidis Worcester, 2008 Contents Acknowledgments ...........................................................................................6 Summary.......................................................................................................7 1. Introduction..............................................................................................8 1.1 Identification and significance of the process ..........................................8 1.2 Problem Overview ...............................................................................8 1.3 Affected Industries..............................................................................9 1.4 Limitations and constraints of current Al alloys...................................... 10 1.5 Potential of wrought Al alloys in the aircraft industry.............................. 10 2. Diffusion Solidification .............................................................................. 12 2.1 Introduction ..................................................................................... 12 2.2 Process Advantages .......................................................................... 12 2.3 Metallurgy of CDS ............................................................................. 14 3. Theory ................................................................................................... 16 3.1 Introduction ..................................................................................... 16 3.2 Mixing ............................................................................................. 16 3.2.1 Mixing of two liquids.......................................................................... 16 3.2.2 Mixing of two liquid melts................................................................... 17 3.2.3 Mixing paths .................................................................................... 17 3.3 Thermal and Mass transport phenomena .............................................. 18 3.4 Nucleation ....................................................................................... 18 3.4.1 Classical nucleation theory ................................................................. 18 3.4.1.1 Homogeneous nucleation ............................................................. 18 3.4.1.2 Heterogeneous nucleation ............................................................ 20 3.4.2 Nucleation Rate ................................................................................ 23 3.4.3 Nucleation Rate in the CDS ................................................................ 23 3.5 Microstructure stability ...................................................................... 28 3.5.1 Globular Stability Under Stirring.......................................................... 28 3.5.2 Mullins Sekerka stability criterion ........................................................ 29 3.5.3 Undercooling Factors ......................................................................... 33 3.5.4 Nucleation rate and stability ............................................................... 37 3.5.5 Model of globular growth.................................................................... 39 3.5.5.1 Effect of solute fields overlap........................................................ 39 3.5.5.2 Globular stability analysis............................................................. 42 4. Experimental .......................................................................................... 47 4.1 Mixing of two liquid metal melts.......................................................... 47 4.1.1 Mixing paths ................................................................................. 48 4.1.2 Respective microstructures of the three mixing paths ......................... 49 4.2 Assessment of Process Variables Sensitivity.......................................... 51 4.2.1 Introduction .................................................................................. 51 4.2.2 Experimental procedure .................................................................. 51 4.2.3 Sample Preparation for Microstructure Evaluation:.............................. 51 4.2.4 Process variable: al superheat ......................................................... 52 4.2.5 Data analysis – discussion............................................................... 56 4.3 Process variable: Cooling rate............................................................. 57 4.3.1 Introduction .................................................................................. 57 4.3.2 Experimental procedure .................................................................. 57 4.3.3 Experimental data.......................................................................... 57 4.3.4 Data analysis-discussion ................................................................. 57 4.4 Process variable: grain refiner ............................................................ 59 4.4.1 Introduction .................................................................................. 59 4.4.2 Experimental procedure .................................................................. 59 4.4.3 Experimental data.......................................................................... 59 4.4.4 Data analysis-discussion ................................................................. 59 4.5 Hot Tearing Tendency of alloys cast via CDS......................................... 61 4.5.1 Introduction .................................................................................. 61 4.5.2 Ring Mold Test............................................................................... 61 4.5.3 Experimental Procedure .................................................................. 61 4.5.4 Experimental Results - Discussion .................................................... 62 4.5.5 Microstructure ............................................................................... 64 Conclusions ............................................................................................ 65 5. Conclusions ............................................................................................ 66 6. Future work ............................................................................................ 67 7. Published Work ....................................................................................... 68 7.1 Study of undercooling mechanism in the Al-Cu alloy system cast via Controlled Diffusion Solidification (CDS) Process............................................. 68 7.2 Controlled Diffusion Solidification ........................................................ 68 7.3 Controlled Diffusion Solidification: Application to metal casting................ 68 Controlled Diffusion Solidification.......................................................................... 80 INTRODUCTION ......................................................................................... 80 BACKGROUND ........................................................................................... 81 SENSITIVITY OF PROCESSING VARIABLES...................................................... 85 Effect of Superheat......................................................................................... 85 Effect of Cooling Rate ..................................................................................... 85 Effect of Grain Refiner Addition ......................................................................... 86 EFFECT OF EXPERIMENTAL VARIABLES - CONCLUSIONS ................................... 87 APPLICATION OF CDS FOR COMMERCIAL ALLOYS .......................................... 87 CASTING OF 2014 ALLOY USING CDS ........................................................... 88 CASTING OF 4145 ALLOY USING CDS ........................................................... 90 CASTING OF 5056 ALLOY USING CDS ........................................................... 91 CASTING OF 7050 ALLOY USING CDS ........................................................... 92 (a) (b)........................................................................................... 93 SUMMARY................................................................................................. 93 REFERENCES............................................................................................. 94 Appendix ..................................................................................................... 96 Numerical simulation algorithm in MATLAB .................................................... 96 Bibliography ............................................................................................... 101 Acknowledgments First of all, I would like to sincerely thank Prof. Diran Apelian, supervising my work throughout these years. He has not only guided me in the professional field, but also encouraged me and gave me valuable support. Thank you for letting me participate in decisions regarding the direction of my PhD work, which enabled me to work in fields that interested me the most. My deep gratitude goes to Prof. Makhlouf M. Makhlouf for his guidance and the numerous insightful conversations on a variety of topics. His input has been invaluable to this work and is gratefully acknowledged. It has been a great opportunity and experience to present my work to the MPI’s conferences. The