Effect of yttrium oxide volume fraction and particle size on elevated temperature strength of a dispersic strengthened s
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diate t e m p e r a t u r e strength is usually low. Successful combination of dispersion strengthening for elevated t e m p e r a t u r e strength and ~' precipitation hardening for intermediate t e m p e r a t u r e strength has been obtained in a dispersion strengthened corrosion r e s i s tant nickel-base superalloy, designated IN-853. This alloy is made by mechanical alloying;** a high energy, dry milling technique through which c o m p o s i t e p a r t i cles may be produced containing a fine and h o m o g e n e ous dispersion of Y203 in a precipitation hardenable, oxidation resistant, nickel-base superalloy matrix. This paper d e s c r i b e s the effect of varying the volume fraction and particle size of the dispersion, Y2Os, on the intermediate and elevated t e m p e r a t u r e rupture strengths of this m a t e r i a l .
EXPERIMENTAL PROCEDURE The YzOs dtspers0id was p r e p a r e d by calcination of yttrium oxalate. The average particle size, which is closely controlled by calcination t e m p e r a t u r e was m e a s u r e d by X - r a y line broadening in a manner s i m ilar to that described by Ferguson. 12 Average Y20 s particle sizes were also m e a s u r e d by t r a n s m i s s i o n electron m i c r o s c o p y of s e v e r a l b a r s of extruded, heat treated superalloy. Compariso n of particle Sizes m e a sured by the two methods is made in Table I. The standard deviation (or) given for each electron microscope deterfnination reflects p r i m a r i l y the distribution function of oxide particle sizes within the specimen rather
Table I. Comparisonof Y203 Particle SizesMeasuredby X-Ray Line Broadeningand by TransmissionElectron Microscopy
X-Ray Line Broadening
Electron Microscopy
Average
Average*
o
A
nm
A
nm
A
nm
151
15.1 27.9 57.8
188.7 252.6 509.4
18.9 25.3 50.9
60.2 83.7 151.9
(i.0 8.4 15.2
279 578
*Average of 150 particle size measurements.
"VOLUME 5, MARCH 1 9 7 4 - 6 1 5
than the uncertainty of the measurement. There is a tendency for the electron microscopy average to be somewhat below the X - r a y line broadening average at l a r g e r average particle sizes. This is probably due to selective loss during foil preparation of larger Y~Os particles comparable in diameter to the foil thickness. Otherwise the agreement between the two methods is good. The values obtained by the more convenient Xray line broadening method were used for the bulk of the work described in this paper. The range of average Y, Os particle sizes investigated was from 151~ (15.1 nm) to 578.~ (57.8 nm) and Y~Os volume fractions varied from 0.70 pct to 4.55 pct. The alloys contained about 0.5 pct oxygen in excess of that present as Y20s and about 0.18 pct carbon plus nitrogen. In order to determine the effects of the hard phases resulting from these elements, one powder batch was made with no Y,O 3 added. Raw materials used to produce the alloys for this study are listed in Table II. The nominal composition was 20 C r - l . 2 Al-2.4 Ti-0.07 Zr-0.007 B-Bal Ni and Y~Os. The mechanically alloyed
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