METAL COUPON TESTING IN AN AXIAL ROTATING DETONATION ENGINE FOR WEAR CHARACTERIZATION A Thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Materials Science and Engineering by GARY S. NORTH B. S., Colorado School of Mines, 2017 2020 Wright State University WRIGHT STATE UNIVERSITY GRADUATE SCHOOL April 15, 2020 I HEREBY RECOMMEND THAT THE THESIS PREPARED UNDER MY SUPERVISION BY Gary S. North ENTITLED Metal Coupon Testing in an Axial Rotating Detonation Engine for Wear Characterization BE ACCEPTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF Master of Science in Materials Science and Engineering. _____________________________ H. Daniel Young, Ph.D. Thesis Director _____________________________ Raghavan Srinivasan, Ph.D., P.E. Professor and Interim Chair, Department of Mechanical and Materials Engineering Committee on Final Examination: ________________________________ H. Daniel Young, Ph.D. ________________________________ Raghavan Srinivasan, Ph.D., P.E. ________________________________ Christopher Stevens, Ph.D. ________________________________ Barry Milligan, Ph.D. Interim Dean of the Graduate School ABSTRACT North, Gary S. M.S.M.S.E., Department of Mechanical and Materials Engineering, Wright State University, 2020. Metal Coupon Testing in an Axial Rotating Detonation Engine for Wear Characterization. Rotating Detonation Engines (RDE) are being explored as a possible way to get better fuel efficiency for turbine engines than is otherwise possible. The walls of the RDE are subjected to cyclic thermal and mechanical shock loading at rates of approximately 3 KHz, with gas temperatures as high as 2976 K. This project performed testing with Inconel 625 and 304 stainless steel coupons in an RDE outer body to attempt to measure material ablation rates. Significant microstructural changes were observed to include grain growth in both alloys, carbide formation and grain boundary melting in Inconel, and formation of delta ferrite in the stainless steel. The testing performed in this study was unable to generate a wear rate for either material. The Inconel coupons exhibited threshold behavior, with no measurable material loss below a critical temperature, and near instantaneous melting and failure above that temperature. The 304 survived the most aggressive test conditions the facility could produce without measurable ablation. Longer duration testing is required in order to determine a damage rate for these materials under a detonative environment. iii TABLE OF CONTENTS 1 INTRODUCTION ........................................................................................................ 1 1.1 RDE Coupon Testing ................................................................................................ 3 1.2 Research Objectives and Methodology ..................................................................... 5 2 LITERATURE REVIEW ............................................................................................. 6 2.1 Detonation vs Deflagration ....................................................................................... 7 2.2 Detonation Engines ................................................................................................. 10 2.3 High Temperature Material Research ..................................................................... 13 2.3.1 Metals ............................................................................................................... 13 2.3.2 Ceramic Matrix Composites ............................................................................. 17 2.3.3 Other RDE Experiments ................................................................................... 19 2.3.4 Ablation Studies ............................................................................................... 22 2.4 Inconel 625 .............................................................................................................. 24 2.4.1 Basic Properties ................................................................................................ 25 2.4.2 High Temperature Properties............................................................................ 26 2.5 Stainless Steel Alloy 304......................................................................................... 27 3 EXPERIMENTAL METHODS ................................................................................. 29 iv 3.1 Facility ..................................................................................................................... 29 3.1.1 Detonation Engine Research Facility ............................................................... 30 3.1.2 RDE Test Stand ................................................................................................ 31 3.1.3 Water Cooled RDE ........................................................................................... 33 3.2 Coupons ................................................................................................................... 39 3.2.1 Coupon Adapter ................................................................................................ 39 3.2.2 Coupon Designs ................................................................................................ 41 3.3 Testing ..................................................................................................................... 44 3.3.1 Test Procedure .................................................................................................. 44 3.3.2 Test Matrix ....................................................................................................... 46 3.4 Measurement and Analysis Techniques .................................................................. 47 3.4.1 Thermocouples ................................................................................................. 47 3.4.2 Optical Examination ......................................................................................... 48 3.4.2 SEM .................................................................................................................. 50 3.5 Assumptions ............................................................................................................ 51 4 RESULTS AND DISCUSSION ................................................................................. 51 4.1 Temperature Data .................................................................................................... 52 4.2 Optical Examination ................................................................................................ 59 4.2.1 Surface Examination ......................................................................................... 62 4.2.2 Cross Section .................................................................................................... 73 v 4.3 Scanning Electron Microscopy ............................................................................... 79 4.3.1 Surface .............................................................................................................. 80 4.3.2 Cross Section .................................................................................................... 90 5 CONCLUSIONS ........................................................................................................ 94 REFERENCES ................................................................................................................. 97 vi LIST OF FIGURES Figure 1: Schematic of Rotating Detonation Engine modified from [1] ............................ 4 Figure 2: Detonation Cell Size [4] ...................................................................................... 8 Figure 3: Left: Plot showing relationship between detonation cell size and stoichiometry for hydrogen-air mixtures. Right: Plot showing relationship between cell size and temperature for hydrogen-air mixtures [4].......................................................................................................... 9 Figure 4: Temperature vs Entropy Plot Comparing the Humphrey and Brayton Cycles [6] ....................................................................................................................................................... 10 Figure 5: Computational Fluid Dynamic Representation of an RDE [7] ......................... 12 Figure 6: Typical alloy uses in turbine engines [10] ......................................................... 14 Figure 7: Strength to Weight Ratios of Different Material Classes [11] .......................... 18 Figure 8: SEM Images Showing Stress Cracking of CMC Test Coupons after RDE Exposure [13] ................................................................................................................................ 21 Figure 9: Entire CMC outer body showing damage track after AFRL testing [14] ......... 22 Figure 10: True Stress Strain Curves for Inconel 625 at Different Temperatures [23] .... 27 Figure 11: Layout of the test facility (DERF) [3] ............................................................. 30 Figure 12. Photograph showing pre-detonator (highlighted in blue box) assembly installed on the rig. ........................................................................................................................ 32 Figure 13: CAD Model of 3/4 pie RDE outer body.......................................................... 34 Figure 14. RDE Cooling Water Plumbing with specific lines labeled. The center body water is fed