1. Delta Phase Transformation in Inconel 625 T.E.A.M. Ryan Lewis, Megan McCabe, Jennifer Rowe, Regan Rumph, Bryce Simmons, Jessica Williams California Polytechnic State University, San Luis Obispo Materials Engineering Department

2. History of Inconel 625 Ni-Cr-Mo-Nb-Fe and trace elements High temperature aerospace applications

3. Kinetics Theory

4. Thermally Activated Martensitic Transformation Isothermal Thermally Activated Phase Transformation

5. Experimental Procedure: Heat Treatments ▫Samples were cut to be ½ inch thick from ⅜ rod ▫Heat Treatment time-temperature combinations ▫Standard Operating and safety procedures were followed

6. Experimental Procedure: Hardness ▫Used rounded surface of sample by using the V- shaped anvil.

7. Experimental Procedure: Metallography ▫Standard Metallographic Procedures were used ▫Electrolytic etching was done with 4v and 30 seconds in 10% oxalic acid

8. Experimental Procedure: SEM/EDS SEM ▫The Scanning Electron Microscope (SEM) in conjunction with Energy Dispersive X-ray Spectroscopy (EDS) was used to analyze the samples. ▫Samples were prepped with conductive copper tape to produce a conductive path. ▫The back scatter detector was place over the aperture.

9. Results: XRF X-Ray Fluorescence was preformed to ensure our stock bar was IN-625

10. Results: Hardness Temperatures Time (min) 750°C800°C850°C900°C 0A-B-D-F- 10A-BC-E-G 20A-BC-E-G 30A-BC-E-G 40A-BC-E-G 50A-BC-E-G 60A--C-E-G Interval Plots of Hardness versus time at 750°C, 800°C, 850°C, 900°C. Tukey Pairwise comparisons of the times at each temperature.

11. Results: Hardness General trend: decrease in hardness with increase temperature

12. Results: SEM/EDS Precipitates found to be high in Nb, Ni, and Cr

13. Discussion: TTT Diagram Empirical Time- Temperature- Transformation Diagram  Red Values – not significantly different  Black Values – significantly different value  Bold Values – first significantly different value

14. Discussion: Hardness Hardness decreased with increasing time in the furnace ▫Our sample 8.6 HRC higher than annealed Inconel 625  Additional strengthening ▫XRF data indicates a lack of Ta, W, Rh ▫Our rod of Inconel could have contained γ´´

15. Discussion: SEM

16. Conclusions Decrease in hardness of the as-received alloy. ▫Difference in hardness for 750/800°C and 850/900°C Secondary phase found in the heat treated samples ▫Rich in niobium ▫Significant amounts of chromium and nickel

17. Complications Recommendations The phases we were looking for were nanoscale – SEM is limited. TEM/SAD to see nanoscale structures. The post processing of the alloy was unknown Conflicting aging parameters in the literature. Hardness differential between Inconel 625 and epoxy is large. Solutionize the rod before heat treatments. More time/temperature combinations. Increase the time scale relative to the temperature scale. Use Bakelite

18. Recommendations for Future Study Solutionize the rod before heat treatments. TEM in conjunction with SAD to see nanoscale structures. Electrical conductivity to determine percentages of intermetallics. More time/temperature combinations. Increase the time scale relative to the temperature scale.

19. The End