A STUDY OF THE FLOW AND FRACTURE OF SINGLE CRYSTALS OF IRON BINARY ALLOYS

190 Pages·06.819 MB·English

by  BRITTAIN, JOHN O

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*