The Pennsylvania S tate College The Graduate School D ivision of M etallurgy A Study of th e Plow and Fracture of Single C rystals of Iron Binary Alloys A th esis lay John 0. B rittain Submitted in p a rtia l fu lfillm en t of the requirem ents fo r the degree of Doctor of Philosophy August, 19^1 Approved? k, August 19^1 irfrtTV' M etallurgy ABSTRACT The nickel equivalents of chromium and molybdenum, as determined in single crystals of binary iron alloys, indicates that small additions of nickel, chromium and molybdenum have sim ilar relativ e strength ening effects in polycrystalline and single crystals of iron. The presence of the y ield point phenomenon in decarburized iron single crystals has been established. The in ten sity of the y ield point has been shown to be a function of the carbon content, furtherm ore, the y ield point elongation in single crystals of iron is of the same order of magnitude as poly cry stallin e iron w ith an equivalent carbon content* 36074-i A C KN C5WLEDGMENTS The author is indebted to the International Nickel Company for supporting this investigation. The assistance and guidance of Brs. J. w. Fredrickson, H. J. Read and J. R. Low, J r ., tmder whose direction th is theses was conducted is gratefully acknowledged. The assistance of Rrs. ■ci. W. Lindsay and H. M. Davis is also acknow­ ledged. Acknowledgment is also due Mr. A, Walsh for his participa­ tion in the experimental work, the Bethlehem S teel Company for the chemical analyses and the United States S teel Company fa r the gas and carbon analyses. TABLE QF CONTENTS ABSTRACT.............................................................................................................Page i ACKNOWLEDGMENTS............................................................................................... ii TABLE OF CONTENTS.......................................................................................... i i i LIST OF TABLES............................................................................................... ir LIST OF FIGURES............................................................................................... v I INTRODUCTION ................................................. .......................................... 1 II PURPOSE OF THE INVESTIGATION.................................................................... 2 III SURVEY OF THE LITERATURE........................................................................... 3 A. Production of Single C rystals of I r o n ....................... 3 B. Deformation of Body-0entered Cubic Single Crystals 9 C. The Yield Point Phenomenon in Single Crystals of Iron ............................................................................................... 13 D. The Fracture of Single C rystals . . . . . . . . . 19 IV MATERIAL AND TESTING TECHNIQUES............................................................. 23 A. Production and Fabrication of A llo y s............................ 23 B. Production of Single C rystals............................................... 25 C. O rientation of the Single C ry sta ls................................. 28 D. C rystal Perfection.................................... 29 E. Tensile Tests of Single C rystals . . . . . . . . . 30 V IRESENTATION AND ANALYSES OF DATA ON THE EFFECT OF SINGLE ATOMS ON THE YIELD STRESS OF SINGLE CRYSTALS QF IRON BINARY ALLOYS .......................................................................... 3U VI PRESENTATION AND ANALYSES OF DATA ON THE YIELD POINT BEHAVIOR QF SINGLE CRYSTAIS OF IRON BINARY ALLOYS . . . . 1*0 VII PRESENTATION AND ANALYSES OF DATA ON THE FRACTURE OF SINGLE CRYSTALS OF IRON BINARY ALLOYS......................................... 52 A. Ductile Failures ................................................................ 53 B. Cleavage F a ilu r e s .......................... 53 V III SUMMARY AND CONCLUSIONS ....................................................................... 56 BIBLIOGRAPHY : : : : : : ............................................ 59 iv LIST OF TABLES Table 1. COMPOSITION OF IRON BINARY ALLOYS.......................................Page 6U Table 2. MELTING PRACTICE 65 Table 3. FABRICATION PROCEDURE................................................ 66 Tablek . ANNEALING TREATMENT TO OBTAIN THE OPTIMUM CRAIN SIZE FOR THE PRODUCTION OF SINGLE CRYSTALS . . . 67 Table 5. DETAILS OF THE FABRICATION OF SINGLE CRYSTALS . . 68 Table 6 . VALUES OF THE ORIENTATION FACTOR ON BASIS QF MULTIPLE SLIP IN BODY-CENTERED-CUBIC LATTICE . . 70 Table 7. RESOLVED SHEAR STRESS FOR MULTIPLE SLIP IN SINGLE CRYSTALS OF IRON BINARY ALLOYS........... 72 Table 8. NICKEL EQUIVALENTS OF SINGLE CRYSTALS AND POLYCRYSTALLINE IRON BINARY ALLOYS.................. 7U Table 9. MODE OF FALLURE AND CLEAV/ STRESS OF SINGLE CRYSTALS OF IRCN BINARY ALLOYS .................................... 75 Table 10. CLEAVAGE PLANE OF SINGLE CRYSTALS OF IRON BINARY ALLOYS 76 V LIST OF FIGURES Fig* 1. GRAIN STRUCTURE OF VACUUM-MELTED INGOTS REVEALED BY HEAT ETCHING EFFECT......................................................................Page 77 Fig. 2. BA C K-REFLECTI ON LAUE PATTERN OF CRYSTAL 11-10 . . . 77 Fig. 3 . BACK-REFLECT I ON LAUE PATTERN OF CRYSTAL 27-6 . . . 78 Fig. 1;. BA C K-R EFLECTI ON LAUE BITTERN OF CRYSTAL 15-lU . . . 78 Fig. 5. EA3K-REFLECTI0N LAUE BAT "FEN OF CRYSTAL A-22-A . . . 79 Fig. 6. STEREOGRAPHIC PROJECTION OF TENSILE AXIS OF SINGLE-CRYSTAL SPECIMENS................................................... 80 Fig. 7. VARIATION OF YIELD STRESS WITH THE ORIENTATION OF CRYSTALS OF IRON-BINARY ALLOYS...................................... 81 Fig. 8. THE VARIATION OF THE YIELD STRESS WITH ATOMIC PER CENT ADDED SOLUTE................................................ 82 Fig. 9. EFFECT OF SOLUTE ELEMENTS IN INCREASING THE YIELD STRESS ( (Tq.IxS) OF EON-ALLOY SINGLE CRYSTALS . 83 Fig. 10. TRUE STRESS-TRUE STRAIN CURVES FOR SINGLE & 10A CRYSTALS OF CARBONYL IR O N ......................................................... 8U,8£ Fig. 11. TRUE STRESS-TRUE STRAIN CURVES FCR SINGLE CRYSTALS OF VACUUM-MELTED IRON......................................................... 86 Fig. 12. TRUE STRESS-TRUE STRAIN CURVES FCR SINGLE CRYSTALS OF ARMCO IR O N ................................................ 87 Fig. 13. TRUE STRESS-TRUE STRAIN CURV 3 FCR SINGLE CRYSTALS QF IRON WITH 9.26 ATOMIC PER CENT NICKEL........................ 88 Fig. 1U. TRUE STRESS-TRUE STRAIN CURVES FOR SINGLE CRYSTALS OF IRON v'ilTH 0.78 ATOMIC PER CENT NICKEL........................ 89 Fig. 15. TRUE STRESS-TRUE STRAIN CURVES FOR SINGLE CRYSTALS Sc l£A OF IRON WITH 0.26 ATOMIC PER GENT CHROMIUM 90, 91 Fig. 16. TRUE STRESS-TRUE STRAIN CURVES FOR SINGLE CRYSTALS 4 16A OF IRON WITH 0.83 ATOMIC PER CENT CHROMIUM..........................92, 93 v i. Fig. 17. TRUE STRESS-TRUE STRAIN CURVES FOR SINGLE CRYSTALS & 17A OF IRON WITH 1.67 ATOMIC PER CENT CHROMIUM........................Page 9h,9$ Fig. 18. TRUE STRESS-TRUE STRAIN CURVES FOR SINGLE CRYSTALS OF IRON WITH 0.18 ATOMIC PER CENT COBALT.................... 96 Fig. 19. TRUE STRESS-TRUE STRAIN CURVES FOR SINGLE CRYSTALS OF IRON WITH 0.67 ATOMIC PER CENT COBALT.................... 97 Fig. 20. TRUE STRESS-TRUE STRAIN CURVES FOR SINGLE CRYSTALS OF IRON WITH 2 *92 ATCM C PHI CENT COBALT........... 98 Fig. 21: TRUE STRESS-TRUE STRAIN CURVES FCR SINGLE CRYSTALS OF IRON WITH 0.23 ATOMIC PER CENT MOLYBDENUM . . . 99 Fig. 22. VARIATION OF YIELD POINT ELONGATION OF SINGLE CRYSTALS OF BINARY IRON ALLOYS WITH CARBON CONTENT 100 1 I. INTRODUCTION Although the crystallography of the flcsr and cleavage processes has been w ell established for Iron, the stresses required to in itia te flow and cleavage fracture are relativ ely unknown. *he complexity of the deformation mechanism and the d ifficu lties asso­ ciated with the production of single crystals of iron have retarded investigations of th is nature. The effect of alloying elements on the stress to in itia te flow in iron crystals has received very little considera­ tion, although the yielding of alloy crystals of many metals has been studied An investigation of the temperature dependency of the yield stress of crystals of iron alloys, together with the cleavage stress of such cry stals, should be a firm basis on which to build a quantitative theory of transition tem peratures. The prediction of an upper and lower yield point in iron crystals by the dislocation theory has resulted in several recent investigations of the yield point phenomenon in iron cry stals. The question of the existence of the yield point phenomenon in decarbur- ized, virgin iron single crystals has not been resolved prior to th is investigation. II. PURPOSE OF THE INVESTIGATION This investigation was undertaken to study the effect of solute atoms on the yielding and fracture behavior of single crystals of iron binary alloys* Although a number of investigators have studied the mechanical behavior of polycrystalline iron binary alloys, only a few observa­ tions have been reported for single crystals of iron. Thus, while the strengthening effect of various solute elements in decarburized iron is fairly w ell knovm, there is a complete lack of data on the effect of solute elements on the yield stress of iron cry stals, ^'he influence of solute elements upon the strain-aging and yield characteristics of low carbon steel has also been investigated, but very little is known of the yielding behavior in iron-alloy cry stals. The recent works on the yielding of iron crystals have failed to demonstrate clearly the existence of a yield point in decarburized cry stals. Iron crystals which have been carburized, n itrid ed , or strain-aged, have been shown to yield inhomogeneously* The existence of the normal stress is fairly w ell established for hexagonal close-packed cry stals, but not far cubic m etals, ^he frac­ ture process in cubic crystals has not been investigated extensively and is not w ell understood. It is generally believed that cubic crystals obey the normal stress law for cleavage failu re, but th is has not been reported for the effect of solute atoms on the nonm*l stress law. Sim ilarly, there is no available infcrm etion on the effect of prior stra in , strain rate, or temperature on the cleavage strength of body-centered cubic iron. III. SURVEY QF THE LITERATURE A. Production of Single Crystals of Iron The production of large single crystals of iron has been ac­ complished by means of the strain-anneal technique. This technique is based on the theory that a stra in nucleus acts as a center of recrystal­ lizatio n on annealing. The single crystal is grown by primary re- crystallisation* By controlling the number of strain nuclei, the an­ nealing temperature and the purity of the iron, i t is possible to fab­ ricate large single cry stals. However, the frequency of success in growing large single crystals of iron is much lower than w ith other com­ mon m etals• The d ifficu lties associated w ith the technique are due to the large number of inter-related variables in the strain-anneal technique• The early work of Chappell(l) and Ruder(2) indicated th at ab­ normally large grains resulted from the annealing of iron and silicon fe rrite which had been deformed a sm all amount. However, the firs t single crystals of iron produced by the strain-anneal technique appear to have been made by Edwards and P feil(3) in 1923* They studied the effect of four factors on the production of large iron crystals • the in i­ tia l grain size as obtained by various decarburiaation treatm ents, strain gradients by means of s trip and tapered specimens, temperature gradi­ ents, and the rate of heating to the annealing temperature* Their results indicated th at the grain size resulting from a wet hydrogen treatm ent of U8 hours a t 95>0°C. followed by slow cooling to 100°C. was the optimum grain size far the production of large single crystals*