Ni-Mo alloys of compositions ranging from pure Ni to Ni-40 at % Mo were rapidly solidified by Chill Block Melt Spinning in vacuum and were examined by optical metallography, X-ray diffraction and transmission electron microscopy. Rapid solidification resulted in an extension of molybdenum solubility in nickel from 28 to 37.5 at %. A number of different phases and microstructures were seen at different depths (solidification conditions) from the quenched surface of the melt spun ribbons

Glasgow, T. K.

Hemker, K. J.

Jayaraman, N.

Tewari, S. N.

English

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NASk'T'echn-Azal Memorandum 87100
4.	 4s 	 x,
Microstructures in Rapidly
Solidified Ni-Mo Alloys,
	
S,
(NISA-TH-87100 iiCRCSTRUCTUFEs IN FIPIDLY
SOLIDIFIED Ni-Ko ALLOYS (NASA) R p
EC 102 /MF A01
	 CSCL 11r
Unclas
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43/26 22229
N. Jayararnan
	
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University of Cincinnati
Cincinnati, Ohio
and
S.N. Tewari, K.J. Hemker, and T.K. Glasgow
Lewis Research Center
Cleveland, Ohio
6,
4 ,	 i
Prepared for the
International Conference on Rapidly Solidified Materials
sponsored by the American Society for Metals y
San Diego, California, February 3-5, 1985
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ABSTRACT	 NICKEL• MOLYBUENUM PHASE DIAGRAM
Ni-Mo alloys of com p ,)sitions ranging from
pure Ni to Ni-40 :.t % Mo were rapidly solidi-
fied by Chill Block Melt Spinning in vacuum
and were examined by optical metallography,
x-ray diffraction ana transmission electron
microscopy. Rapid solidifi-cation resulted
in ar extension of molybdenum solubility :n
nickel from 28 to 37.5 at	 A number of
different phases and micrustructur?s were
seen at different depths (solidification
conditions) from the quenched surface of the
melt spun ribbons.
RA?IDLY SOLIDIFIED ALLOYS exhibit
greatly refired microstructure, extended
solid solubility, and metastable phase forma-
tiotr. The microstrucrures produced in these
materials depend on alloy com;osition and
local solidification parameters. In this
paper the microstructural features observed
in binary nickel-molybdenum alloys after
Chill Block Melt Spinning are presented.
This study forrrs the basis for investigat—n
of other more complex Nickel-base alloy
systems.
The equilibrium phase diagram for the
Ni-Mo eutectic system (Ref. 1) is shown in
Fig. 1. Under equilibrium the maximum solid
solubility of Mo in Ni is 28.4 at %. B-phase
(NiMo) has an equilibrium composition range
from 51 to 53 at Y Mo. The goal of this
study was to determine the effect of rapid
solidification on the microstructures of
Ni-Mo alloys.
EXPERIMENTAL
The Ni-Mo ribbons used in this study
were cast on a 4340 steel wheel by the free
jet Chill Block Melt Spinning (CBMS) process
at the NASA-Lewis Research Center. This
tacility is described in Ref. 2. Ni-Mo
alloys of the compositions, Ni-0, 5, i7.5,
21, 27.5, 35, 37.5 and 40 at % Mo were used.
L
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J I 4J
I	 I	 I
^	 I	 I
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I	 I	 I	 1 .^.I
I	 I	 I	 I, '^,1 fI	 I	 1	 I	 1 1 •I
I	 I	 I	 I	 I	 I	 I	 aI	 I	 I	 I	 I	 I	 I
I	 I	 I	 I	 I	 I	 II	 I	 I	 i	 I	 I	 I
I	 I
I	 I	 I	 I	 I
0	 10	 20	 30	 40	 50
Mo (0/0)
Figure 1. - Nickel-Molybdenum phase a_sgram.
X's indicate cacting temperatures and
compositions.
All ribbons were examined by x-ray diffrac-
tion using Cu-Ka radiation on both sides
(wheel and free) of the ribbons. In this
paper the quenched side of the ribbon will be
referred to as the wheel side, and the side
away from the wheel will be referred to as
the free side. Cross sections of the samples
etched with Marble's Reagent were examined by
optical metallograph . Transmission electron
microscopy (TEM) was carried out for three
alloys, namely Ni-27.5 at % Mo (hypoeutectic),
Ni-35 at % Mo (eutectic) and 37.5 at % Mo
(hypereutectic). Three regions of the melt-
spun ribbons, namely wheel side, midsection
and the free side were examined. Of t'iese
three sections the wheel side represents the
fastest quench region. Samples were electro-
polished by a twin jet method using an etha-
nol (45 vol %), butyl ellusolve (45 vol %)
and perchloric acid (10 vol %) electrolyte
cooled to about 0 °C. For examination of
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JAYARAMAN
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near-wheel and near-free sides, these sur-
faces were protected by lacquer and the rib-
bon was thinned only from the other side.
RESULTS AND DISCUSSIONS
Ribbons cast for this search were
approximately 40 um thick, 2.5 mm wide and up
to 15 in in length. The castability of pure
nickel was so poor that no single layer rib-
bons of pure nickel were obtained. In gen-
eral ribbon length and castability increased
with increasing molybdenum content.
X-RAY DIFFRACTION - The Ni-fcc phase (y)
was identified in all compositions. The lat-
tice parameter of this phase increased with
increasing Mo content up to about 37.5 at %
Mo. The lattice parameter data for the
rapidly solidified ribbons are compared to
conventionally cast samples in Fig. 2. For
the conventionally cast material a linear
3.64
3.58	
— -A — —
♦ FCC ('')
a Conventionall y cost
3.52
0	 10 20 30 40 50 (Y,) Mo
Figure 2. - Lattice parameter of y as a
function of composition for conventionally
cast and rapidly solidified alloys.
increase in lattice parameter with the
increasing mo l ybdenum content is observed up
to about 27.5 at % Mo. The lattice parameter
remains constant beyond this molybdenu..i con-
tent, as would be expected from the Ni-Mo
phase diagram, Fig. 1.
The extended solid solubility of the
rapidly solidified ribbons up to about
37.5 at % Mo is illustrated by the extended
straight lire relationship between lattice
parameter and molybdenum content of the y
phase in this figure. The lattice parameter
data in this figure compare well with the
values reported for Ni-Mo alloys of the com-
position 0 to 20 at % Mo (Refs. 3 and 4).
This observation of extended solid solubility
by rapid solidification is further augmented
through TEM analysis. In addition to the
extended solid solubility of fcc Ni-phase
(y), indications of B-NiMo (orthorhombic)
were found near the wheel side of ribbons
from Ni-35 at % Mo and Ni-37.5 at % Mo
alloys. These observations were also found
to be consistent with the TEM analysis, as
will be shown in a latter section.
OPTICAL METALLOGRAPHY - Metallographic
analyses showed the following results:
Multiple layer pure Ni ribbons showed very
large grains. Alloys of 5 to 28 at % Mo,
those in the y solubility range (Fig. 3),
showed cellular/dendritic growth throughout
the thickness of the ribbon. The y grain
size was observed to decrease with increasing
molybdenum content. Three zones were
observed in alloys of higher Mo, >28 at %,
content. A featureless zone appeared closest
to the wheel (Figs. 3 (d) to (f)). Directly
adjacent and sepa r ated by a boundary was a
planar from growth zone. As the planar front
zone broke down, cellular/dendritic grains
formed. The amoun t_ of the featureless zone
increased with increasing Mo content.
TRANSMISSION ELECTRON MICROSCOPY - The
results of the TEM analysis of the three
alloys studied in detail are summarized in
Table I. Figures 4 to 9 snow the correspond-
ing typical microstructures. All three
alloys showed significant effects of rapid
quenching. One of the unique microstructural
features was that of supersaturated and
faulted Ni-fcc (y) Frains. This was the
only microstructure found in the hypoeutectic
alloy (27.5 at % Mo) in the near wheel
region. Here, as shown in Fig. 4, supersatu-
rated y-fcc grains were found to nucleate
along a line (presumably grinding marks on
the quenching wheel) and grow parallel to the
wheel surface (region A i^ Fig. 4). In addi-
tion, in several location,, Ni grains appear
to have nucleated at a point on the wheel
surface and grown radially, (region B in
Fig. 4) normal to the wheel surface resulting
in grain structures like flower petals. On
closer examination of the individual y
grains it was found that most of the grains
contained finely spaced linear features
(Fig. 5). These features are due to planar
faults, which could be considered as micro-
twinned platelets of about 15 A thickness.
Detailed diffraction analysis of these are
described elsewhere (Ref. 5). These taulted
y grains were also found in the eutectic
alloy (35 at % Mo) near the wheel-side and
in the hypereutectic alloy (37.5 at % Mo) in
the mid section. Figure 5 is typical of the
faulted y grails found in the alloys.
The eutectic and hypereutectic alloys
showed a fine NiMo microscrystalline region
near the wheel side of the ribbon (Fig. 6).
This is believed to have formed by crystal-
lization of an amorphous phase which
initially formed during quenchi.,g. The hyper-
eutectic alloy showed an amorphous region
surrounded by a-NiMo grains (Fig. 7).
In-situ heating of the amorphous regions in
the TEM produced a distribution of fine
microcrystallites similar to the ones shown
in Fig. 6.
eQ 3.70
JAYARAMAN
E
4
(f) 40%(c) 28%
(b ,' 17.5%
(a) 50
Wheel side
JAYARAMAN
3
ORIGINAL PAGE IS
OF POOR QUALITY
(e) 37%
^!	 fit. ^^,^' 
	 ^	
,•i
(d) 35%
Wheel side
Figure 3. - Thru thickness microstructures of ribbons `or Ni-5, 17.5, 28, 35, 37 and 40 at a Mo
alloys.
ia-it, 
Figure 5. - Typical fauited y-fcc Ni
grains in hypoeutectic (near-wheel side),
eutectic (near-wheel bide) and hypereutectic
(midsection) alloy ribbons.
1 Y
W.
Figure 4. - Bright field TEM micrograph
	
Figure b. - Typical microcrystalline B-NiMo
showing y-Ni (fcc) grains in hypoeutectic	 regions seen in eutectic (near wheel side)
alloy in the rear wheel side region of the 	 and hypereutectic (near wheel side) alloy
ribbon.	 ribbons.
14%
Mai 9.b Y
Figure ). - Amorphous phase (region A)
surrounded by a-NiMo grains in the
hypereutectic alloy ribbon (near wheel side).
JAYARAMAN
4
S 4W
Another unique microstructure is the
faulted f3-NiMo grains found in the mid-
sections of hypereutectic (37.5 at x Mo)
:ibboas. The :atilt contrast is seen both in
the bright field and dark field images shown
in Fig. 8.
•	 w'
.4
ORIGINAL PAGE IS
Of POOR QUALITY
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t	 R b
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Figure 8. - Bright field (a) and dark field
(b) TEM micrographs of B-NiMo grains
(faulted ?) seen ir, hypereutectic (mid-
section) alloy ribbons.
k	 1U40
Figure 9. - Typical cellular/dendritic micro-
structures found in hypoeutectic (midsection
and near free surface); eutectic (midsection
and near free surface) and hypereutectic
(midsection and near free surface). (a)
shows a typical cellular structure without
any intercellular eutectic and (b) shows a
typical dendritic structure with inter-
dendritic eutectic.
CONCLUSIONS
Dendritic y cells were found in the
midsection and free surface region of all
three alloys. The typical cellular appear-
ance as shown in Fig. 9 was the same for all
three alloys. The fraction of the inter-
dendritiL eutectic found in the y dendrites
was greater in the near free surface regions
than other part of the ribbon. It also
increased wi,h the increasing molybdenum
content of the alloy.
The following conclusions were made from
this study of rapidly solidified Ni-Mo alloy
ribbons:
(1) Molybdenum solid solubility in fcc
Ni (y) was extended from about 28 to
37.5 at % Mo by rapid soiidification.	 It
resulted in the formation of y grains
with planar-faults.
(2) Alloys with molybdenum content at
and above the eutectic composition
035 at % Mo) showed an amorphous phase as
JAVARAMAN
5
a result of rapid solidification. Some of
this amorphous region crystallized into very
fine microcrystallites.
(3) The hypereutectic composition alloy
formed very large, faulted, orthorhombic
B-NiMo grains, even at moderate cooling rates
(mid sections of ribbons).
(4) In the slow cooled regions all the
alloys showed the cellular/dendritic growth
of y phase with y/fl interdendritic
eutectic.
ACKNOWLEDGMENT
Appreciation is expressed to R.W. Jech,
T.J. Moore and N.W. Orth for preparing the
melt-spun ribbons. Special thanks are due to
Dr. Hugh R. Gray for his keen interest and
continuous encouragement.
REFERENCES
1. Metals handbook, Vol. 8, p. 319,
American Society for Metals, Metals
Park, OH, 1973.
2. R.W. Jech, T.J. Moore, T.K. Glasgow,
and N.W. Orth:	 J. Met., 1984, Vol. 36,
No. 4 pp. 41-45.
3. W.B. Pearson: Handbook of Lattice
Spacings and Structures of Metals and
Alloys, p. 753, Pergamon Press,
New York, 1958.
4. C.N. Brooks, J.E. Spruiell, and E.E.
Stansbury: Int. Met. Rev., 1984, Vol
29, pp. 210-248.
5. N. Jayaraman, and S.N. Tewari: NASA
Lewis Research Center, Cle •ieland, OH,
unpublirned research, 1985_
0
. Z1;
TABLE I. - SUMMARY OF PHASES AND MICROSTRUCTURES IN RAPIDLY
SOLIDIFIED RIBBONS OF Ni-Mo ALLOYS.
Position of	 Alloy
ribbon
Ni-!7.5 at X Mo,	 Ni-35 at % Mo,	 Ni-37.5 at % Mo
hypoeutectic	 eutectic	 hypereutectic
I
Near wheel	 Supersaturated
faulteJ y grains
(Figs. 4 and 5)
(1) Faulted y
grains (Fig. 5)
(2) Microcrystalline
B, NiMo (Fig. 6)
(1) Amorphous phase
(Fig. 7)
(2) Microcrvs:alline
2, NiMo (tig. 6)
(3) Fine 2, NiMo
grains (Fig. 7)
(1) Faulted y
grains (Fig. 5)
(2) Large f, NiMo
grains (Fig. 8)
(3) y	 cells
(Fig. 9(a))
y dendrites with
interdendritic
eutectic (Fig. 9(b))
Midsection	 y cells/dendrites	 y cells/dendrites
(Fig. 9(a))
	
(Fig. 9(a))
Free surface	 y dendrites with	 y dendrites with
interdendritic	 interdendritic
eutectic (Fig. 9(b))	 eutectic
(Fig. 9(b))
f
JAYARAMAN
6
B Pertornung Organization Report No
E-2694
10 Wow% unit No
11 Contract or Gram Nc
I Report No	 2 Government Accession No 	 3 Recipients Catalog No
NASA TM-87100
a Title and Subtitle
Microstructures in Rapidly Solidified Ni-Mo Alloys
7 Authorlsi
	 - - -	 -- -	 -	 —	 --
N. Jayaraman, S.N. Tewari, K.J. Hemker, and
T.K. Glasgow
9 Performing Organization Name and Add ess
National Aeronautics and Space Administration
Lewis Research Center
Cleveland, Ohic 44135
12 Sponsoring Agency Name anj Adereas
National Aeronautics and Space Administration
Washington, G.C.	 20546
5 Repo rt Date
505-33-62
6 Performing Organization Code
13 Type o f Report and Pe r iod Coverer
Technical Memorandum
14 Sponsoring Agency Code
15 SuDDtementa y Notes
N. Jayaratnan, University of Cincinnati, Dept. of Metallu rgical Engineering, Cincinnati, Ohio
45221-0012, S.N. Tetsari, NK-MSA Research Associate, on leave from Defense Metallurgical Research
Laboratory, Hydorabad, India; K.J. Hefter and T.K. Glasgoti, NASA Lewis Research Center. Prepared for
the International Conference on Rapidly Solidified Materials, sponsored by the American Society for
Metals, San Diego, California, February 3-5, 1995.
16 Abstract
Ni-Mo alloys of compositions ranging from pure Ni to Ni-40 at % Mo were rapidly
solidified by Chill Block Melt Spinning in vacuum and were examined by optical
metallography, x-ray diffraction and transmission electron microscopy. Rapid
solidification resulted in an extension of molybdenum solubility in nickel from
28 to 37.5 at %. A number of different phases and rr'crostructures were seen at
different depths (solidification conditions) from the quenched surface of the
melt spun ribbons.
17 Key Words )Suggested by Authvnsl)
	
18 Distribution Statement
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Melt spinning	 STAR Category 26
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Microstructures in rapidly solidified Ni-Mo alloys

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