DEVELOPMENT OF NOVEL HIGH TEMPERATURE ALUMINUM ALLOYS by Joseph Jankowski A thesis submitted to the Faculty and the Board of Trustees of the Colorado School of Mines in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Metallurgical and Materials Engineering). Golden, Colorado Date _____________ Signed: _______________________ Joseph Jankowski Signed: _______________________ Dr. Michael Kaufman Thesis Advisor Signed: _______________________ Dr. Amy Clarke Thesis Advisor Golden, Colorado Date _____________ Signed: _______________________ Dr. Angus Rockett Professor and Head George S. Ansell Department of Metallurgical and Materials Engineering ii ABSTRACT High temperature aluminum alloys can possess a desirable combination of specific strength, corrosion resistance, electrical and thermal conductivity, and creep resistance at temperatures in excess of 300 C. However, the selection of commercial high temperature aluminum alloys is quite limited due to material cost and/or challenges in solidification ° processing of the highest performance alloys. In the present work, the high temperature aluminum alloy 8009 (Al-4.4Fe-0.6V-1.8Si, at.%) was modified to create alloys containing face-centered cubic Al (FCC-Al) and the -phase intermetallic, and remove the deleterious h-phase intermetallic. The crystal structures of the α competing h and -phase intermetallics in 8009 and related alloys were characterized using powder diffraction. The differences in atomic structure of the two phases were used to predict α alloy modifications that promote the -phase and mitigate h-phase formation. Atomistic and thermodynamic modeling were used αto determine novel FCC-Al + -phase alloy compositions. Various compositions of Al-(Co-Fe-Mn-Cr-V-Mo)-Si FCC-Al + -phaseα alloys were experimentally investigated to verify the modeling results. The alloy Al-4.4Fe-0.2V-0.4Mo-2.3Si α (at.%) was identified as a promising dispersoid-strengthened FCC-Al + -phase alloy and the Al- Fe-Mn-Cr-Si alloy system was chosen as a model system for studying theα FCC-Al + -phase eutectic solidification behavior and assessing its mechanical properties. α The solidification behavior of Al-Fe-Mn-Cr-Si alloys was investigated using chill casting and autogenous welding. Microstructure-processing maps were generated from these experiments. Mechanical properties were assessed using microhardness, compression, and in situ tensile testing. Al-Fe-Mn-Cr-Si FCC-Al + -phase eutectic alloys were found to have mechanical properties that meet or exceed those of most existing, conventionally-processed high α temperature Al alloys at temperatures up to 370 C. Additionally, these alloys can be processed under conditions similar to conventional processing routes like strip casting and die casting, as ° well as additive manufacturing. Because of their enhanced microstructural stability relative to most commercial high-temperature Al alloys, FCC-Al + -phase eutectic alloys are a promising new class of aluminum alloys α iii TABLE OF CONTENTS ABSTRACT ................................................................................................................................... iii LIST OF FIGURES ..................................................................................................................... viii LIST OF TABLES ........................................................................................................................ xii ACKNOWLEDGEMENTS ......................................................................................................... xiv CHAPTER 1 INTRODUCTION .............................................................................................1 1.1 Outline................................................................................................................1 1.2 References ..........................................................................................................3 CHAPTER 2 BACKGROUND ...............................................................................................4 2.1 High Temperature Aluminum Alloys ................................................................4 2.2 State-of-the-Art in High-Temperature Structural Aluminum Alloys ................5 2.3 Current Areas of Research .................................................................................8 2.4 Structure Determination from Powder Diffraction ..........................................11 2.5 Electronic Structure of Metals .........................................................................13 2.6 Eutectic Solidification ......................................................................................15 2.7 Research Questions ..........................................................................................16 2.8 References ........................................................................................................17 CHAPTER 3 DETERMINATION OF THE CRYSTAL STRUCTURE OF h- Al40(Fe,V)9Si IN CHILL CASTINGS OF 8009 USING CHARGE FLIPPING WITH HISTOGRAM MATCHING FROM POWDER DIFFRACTION DATA ...................................................................................20 3.1 Introduction ......................................................................................................20 3.2 Methods............................................................................................................22 3.2.1 Material Preparation.......................................................................22 3.2.2 Experimental (Synchrotron) ...........................................................22 3.2.3 Experimental (Neutron) .................................................................23 3.2.4 Experimental (Electron Probe Microanalysis, EPMA) ..................23 3.2.5 Structure Determination .................................................................23 3.2.6 Rietveld Refinement ......................................................................24 3.3 Results ..............................................................................................................24 3.3.1 Structure Determination .................................................................24 3.3.2 Refinement .....................................................................................27 iv 3.3.3 Structure Confirmation ..................................................................32 3.4 Discussion ........................................................................................................33 3.5 References ........................................................................................................36 CHAPTER 4 EXPERIMENTAL AND COMPUTATIONAL RE-EVALUATION OF SILICON ORDERING IN α-Al12Mn3Si2 ..................................................38 4.1 Introduction ......................................................................................................38 4.2 Methods............................................................................................................39 4.3 Results and Discussion ....................................................................................40 4.4 Conclusions ......................................................................................................47 4.5 References ........................................................................................................47 CHAPTER 5 SYNTHESIS AND CHARACTERIZATION OF METASTABLE AlGe .....................................................................................50 5.1 Introduction ......................................................................................................50 5.2 Experimental Procedures .................................................................................51 5.3 Results and Discussion ....................................................................................52 5.4 Conclusions ......................................................................................................57 5.5 References ........................................................................................................57 CHAPTER 6 DETERMINATION OF THE INTERMETALLIC α-PHASE CRYSTAL STRUCTURE IN ALUMINUM ALLOYS SOLIDIFIED AT RAPID COOLING RATES.......................................................................59 6.1 Abstract ............................................................................................................59 6.2 Introduction ......................................................................................................59 6.3 Methods............................................................................................................61 6.4 Results ..............................................................................................................62 6.5 Discussion ........................................................................................................68 6.6 Conclusions ......................................................................................................72 6.7 Acknowledgements ..........................................................................................72 6.8 References ........................................................................................................72 CHAPTER 7 ASSESSING PHASE STABILITY IN METALLIC COMPOUNDS TO DEVELOP NOVEL HIGH TEMPERATURE ALUMINUM ALLOYS THAT CONTAIN THE INTERMETALLIC α-PHASE ................74 7.1 Introduction ......................................................................................................74