Ductile fracture of mechanically alloyed iron-yttria alloys
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I.
INTRODUCTION
M E C H A N I C A L alloying (MA) has been used e x t e n sively in the past 2 decades as a process to produce a wide range o f oxide-dispersion strengthening (ODS) alloys, usually based on Ni, Fe, or A1.~11 A principal technological goal o f most o f the alloys processed by MA is high-temperature strength, and as a result, the associated creep response o f several ODS alloys has been studied in detail. Furthermore, while ODS has been examined in systems where internal oxidation and particle formation are likely to create a good interfacial bond with the matrix, [z~ the fracture resistance o f the particle-matrix interface formed during MA is not known, especially with regard to its susceptibility to void formation during deformation. Conventional w i s d o m suggests that increasing dispersoid content will result in a decrease o f tensile ductility. In fact, commercial MA alloys usually contain l o w volume fractions o f oxide particles, typically about 1 to 2 vol pct. However, certain properties, such as oxidation resistance, may benefit from much h i g h e r levels o f dispersoid content.t3] The purpose o f this research is to systematically examine the influence o f dispersoid content on the tensile fracture behavior o f MA-processed alloys containing a range o f dispersoid contents. The study is based on a m o d e l system o f Fe containing Y203 particles at levels ranging from 0 to 10 vol pct. Selected data for an Fe-A1203 system will also be presented. II.
EXPERIMENTAL P R O C E D U R E
The study is based primarily on four alloys processed by MA: (1) Fe-IY203, (2) Fe-2YzO3, (3) Fe-4Y203, and (4) F e - 1 0 Y 2 0 3 (in all cases, the l e v e l o f Y 2 0 3 is denoted in volume percent). Data for an Fe-2A1203 alloy will also be presented. The starting materials were atomized iron J.B. KOSCO, formerly Graduate Research Assistant, Department of Materials Science and Engineering, Pennsylvania State University, is Development Engineer, Hoeganaes Cow. , Riverton, NJ 08077. D.A. KOSS, Chairman, is with the Department of Materials Science and Engineering, Pennsylvania State University, UniversityPark, P A 16802. Manuscript submitted January 2 2 , 1992. METALLURGICAL TRANSACTIONS A
powder (~90 ~m) and Y203 powder (
(
e
~
4
y
Fe/2%Y203
.
2
g 0
"
0.00
•
F...
,
1.
,
,
0 20
,
.
,
0.40
0.60
STRAIN Fe/10%Y203
000 0,00
,
- -
-
,
020
,
0.40
-
,
-
0.60
Fig. 6 - - T h e dependence of the areal d e n s i t y of v o i d s o n specimen strain. T h e void nucleation strains eN are denoted by arrows and correspond to strains at which the area density of v o i d s is less than 3 x 102 v o i d s / m m2.
STRAIN Fig. 5 - - T h e dependence of the area fraction of v o i d s o n specimen strain. The void nucleation strains es are denoted b y arrows and correspond to strains at which the area fraction of v o i d s i s less than 0 . l pct.
decreases roughly the same amount (A ~N ~ O. 1) but decreases from eN ~ 0.13 to ~ 0.02 over the same 2 t o 10 vol pct r a n g e of particle conten
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