CERTAIN PHASE EQUILIBRIA IN THE SYSTEM TITANIUM-COBALT Dissertation Presented in Partial, fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of the Ohio State University By Prank Lewis Orrell, Jr., B.S., M.S. in Met. Eng. The Ohio State University 1953 Approved hy; Adviser Dedicated, to my wife, Helen K. Orrell A Q S 8 2 1 . iii ACKN QWLBD&MEHT S The author acknowledges the assistance of Professor M.G-. Fontana, his adviser, in the prosecution of this investiga­ tion. He also wishes to express his appreciation to other members of the Department of Metallurgy Faculty at The Ohio State Univer­ sity, Professors Deraorest, Lord, Speiser and Spretnak, for many helpfnl suggestions. Gratitude is expressed to the follotting individuals and organizations for contributions which materially aided this program: Dr. S.F. Urban of the Titanium Alloy Manufacturing Division of The National Lead Company for quantities of sponge titanium and for the vacuum fusion analyses; Mr. J.B. Johnson of the Wright Air Development Center for a generous supply of iodide titanium; Mr* J. Kurtz of the Kulite Tungsten Company for a liberal quantity of cobalt metal; to Professor J.E. Shank of the Engineering Experiment Station of The Ohio State University and to the members of the Station's Analytical Division for the chemical analysis of many of the alleys studied; to Mr. P. Whibley of the Tube Laboratory at The Ohio State Univei*sity for construct­ ing the necessary apparatus and for sealing specimens in capsules. Appreciation is freely expressed for the assistance of the persons, too numerous to list individually, who so willingly gave of their time for discussion or loaned equipment to aid this program. Special mention must be made of the innumerable kind­ nesses performed by Dr. F.H. Seek of The Engineering Experiment Station and by the author's colleagues in the Department of Metal lurgy at The Ohio State University, The author is grateful to The Titanium Alloy Division of The Mational Lead Company who sponsored the G-ra&uate fellow­ ship under which this work was conducted. V TAB 15! OF COHTEETS Page Introduction----------------------------------------------------- 1 Scope of the Investigation------------------------------ 2 Summary and Conclusions — ------------------------------------- 3 Literature Survey ------------------------------- 5 Preparation of Alloys ----------------------------------------- 12 Choice of Technique --------------------------------------- 12 Initial Arc Furnace Designs ------------------------- 13 Final Arc Furnace Design ---------------------- 1.6 Operation of the Furnace ---------------------------------- 19 Melting Stock --------------------------------------------- 22 Homogenization and Equilibration — 23 Sealing ----- .23 Furnaces -------------------------------------------------- 26 Heat Treat Schedules and Quenching--- -------------------- 29 Examination and Analysis of Alloys --------------------------- 32 Metallographic Technique ------------------------- 32 X-Ray Diffraction --------------------------------------- 3h Chemical Analysis ---------------------------------------- 35 Hardness Determinations -------------------------------.— 36 Resistivity Measurements ------------------------------ 3 6 Results and Discussion ----------------------------------------- 39 Preparation of Alloys -------------------- r- 39 Homogenization and Equilibration----------- *------------ hi Determination of Beta/(alpha + Beta) Solvus ------------ h3 Determination of Beta/(Bets, -f-.TigCo) So l v u s ------------ h5 Determination of Beta-Ti2 Co Eutectic Temperature---■— h5 Determination of Ti2 Co—TiCo Peritectie Temperature --- h6 Verification of Eutectoid Decomposition — ---------------- h6 Determination of the Crystal Structure of the Various Phases ----------------------------- — - ------ h9 The Phase Diagram ----------------------------- ?---------- 53 Hardness Determinations --- 5h Appendix ------------------------------------------------------- 5 6 Tables I — Chemical Analysis of Melting Stock ------------ 57 II - Chemical Analysis of Alloys -------------------- 58 III - Microstructures of As-Cast Alloys --------------- 59 IV - Micro structures of Homogenized Al l o y s ---------- 60 V — Microstructures of Alloys Equilibrated for Beta/(Alpha + Beta) Solvus -------------- 6 l VI — Microstructures of Specimens for Determina­ tion of Beta/Beta + Ti2 Co) S o l v u s ------— 62 VII - Determination of Beta-Ti2 Co Eutectic Hori­ zontal ---------- ■----- 63 VIII - Determination of T±2Co -TiCo Peritectie Temp. 6h IX - X-Ray Diffraction Data for Specimen I8C163S--- 65 X - X-Ray Diffraction Data for Specimen 19 G1 6 3 1 7 0 D 66 vi TABLE OF CQHTEIJTS (Continued) Page Tables (Continued) XI - X-Ray Diffraction Data for TigCoCSpecimen I38C154A) ------------------------------------ 67 XII - X-Ray Diffraction Data for Specimen I52C172A 68 XIII - X-Ray Diffraction Results for Specimen I68C177A 6^ XIV - Intorplanar Spacings of TICog from the L i t e r a t u r e ---------------------- 70 Figures 1 . Arc Melting Furnace ------------ 71 2. Schematic Diagram of Arc-Melting Furnace -------- 72 3. Accessories for Arc-Melting Furnace ------------- 74 4. Arrangement of Apparatus for Sealing Specimens — 76 5. High Temperature Resistance Furnace .-------- 77 6 . Circuit Diagram for High-Tenrperature Furnace 79 7. Equipment for Resistivity Measurements — 8 0 8 * Electrical Circuit for Resistivity Measurements - 82 9* Micro structure , As-Cast 2$Co A l l o y ---------------- 84 1 0 . Micro structure , As—Cast 5^Co Alloy -— --- 84 1 1 . Micro structure , As-Cast 9$Co A l l o y ----------- 84 12. Micro structure, As-Cast 22^0 o A l l o y -------------- 84 1 3 . Micros trueture , As-Cast Z6%Co A l l o y ------------ -— 84 14*. Microstrueture, As-Cast 28^Co Alloy ------------- 84 15• Microstructure, As—Cast 32$Co Alloy -------------— 8 6 16. Micro structure, As—Cast 34^Co A l l o y -------------- 8 6 1 7 . Micro structure, As-Cast 3 S$Go A l l o y -------------- 8 6 18. Micro structure, As-Cast 3 8 $Co A l l o y -------------- 8 6 19* Micro structure , As-Cast 46%C o A l l o y ------------- — 8 6 20. Micro structure „ As—Cast 5 2$ Co A l l o y -------------- 8 6 2 1 . Microstructure, As-Cast 55/^Co Alloy ------------- 8 8 2 2 . Microstructure, As—Cast 68^0o Alloy — *----------- 8 8 23* Micro structure, Homogenized 2$&Go A l l o y ----- 90 24. Microstructure, Homogenized 5 t^Co Alloy — ---------- 90 25* Micro structure, Homogenized 9^Co A l l o y ----------- 90 2 6 . Microstructure, Homogenized l8 ^Go Alloy — -------- 90 27* Microstructure, Homogenized 24$Co Alloy ---------- 90 28. Microstructure, Homogenized 2 6 $Go A l l o y ---------- 90 29. Micro structure, Homogenized 2 8 $Co A l l o y ---------- 92 30. Microstructure, Homogenized 30^Co Alloy ---------- 92 31* Micro structure, Homogenized 32$Co Al l o y ---------- 92 32. Microstructure, Homogenized 38$Co Alloy --------- 92 33. Microstructure, Homogenized 46$Co Alloy ---------- 9 2 34. Microstructure, Homogenized 55^0o Alloy ---- 92 35* Micro structure, Homogenized 6Q%Co A l l o y ---------- 94 3 6 . Microstructure, 6%Co Alloy Equilibrated 3 6 0 hours at 7 C0 °G. 9 6 37* Microstructure, 8$Co Alloy Equilibrated 360 hours at 700°C. ----------------- 96 vii TABLE OF CONTENTS (Continued) Figures (Continued) 38. Micro structure , 12^Co Alloy Equilibrated 360 hours at 700°C. — ----------------— ------- 96 39* Microstructure, 8^Co Alloy Equilibrated 510 hours at 650°C. --------------------------- 98 40. M icr os true ture, 9$Co Alloy Equilibrated 2l6 hours at 675°C. 98 4-1. Mi cros true ture , 9^Co Alloy Equilibrated 216 hours at 675°C . 98 *f2. Micro structure, l8^Co Alloy Heated Above Eutectic Temperature --------------------------- 100 if3 . Microstructure, if6j&Co Alloy Heated Above Beritectic Temperature ----------- 100 4A. Microstrueture 8$Co Alloy Equiliterated 56if hours at 675°C. 102 if-5* Mi cros true ture, 9^Co Alloy Equiliterated 216 hours at 700°C. 102 if6. Microstrueture, lO^Co Alloy Equiliterated 56if hours at 675°C - 102 4-7* Ti—Co Equiliterium Diagram -------------------------- 103 48. Comparison of the Effectiveness of Various Solute Elements on the Lowering of the Beta—to—Alpha Transformation Temperature of Titanium ----------------- — ----- *----------- 104 49* Hardness vs. Composition for Binary Ti-Co A l l o y s -------------------------------------105 Literature Cited ----------------------------------------------------- 106 Autobiography ----------------- 112 1 GKRTAIU PHASE aQUIUIBBA IK THE SYSTEM TITAETUM - COBALT Introd.Ti.ct ion The advent of commercial production of titanium metal in 1 9 ^S was accompanied by the most optimistic predictions as to its future place among engineering materials. Such appellations as "wonder metal", "miracle metal" and "Cinderella metal" were un— blushingly applied. Since that time, as would be expected, the superficial exh.uberan.ee has abated but the intensity of effort de­ voted to metal and alloy development has continued undiminished. The situation with regard to the development of titanium is also unique in that there has been a concomitant, although not equal, effort devoted to the study of titanium equilibrium systems. Know­ ledge of the various phase equilibria is a prerequisite for the rapid and efficient development of alloys and for wise engineering application and economical industrial use of these alloys. Although investigations of titanium equilibrium systems are being conducted in a great many laboratories,