Volume 09 - Metallography and Microstructures Part 11 pps

Fig. 79 Same as Fig. 78. The high oxygen content results in a region of coarser and more brittle oxygen-
stabilized α than observed in the bulk material. 100×

Fig. 80 Ti-6Al-4V α -β processed billet illustrating the macroscopic appe
arance of a high aluminum defect. See
also Fig. 81. 1.25×. (C. Scholl)

Fig. 81 Same as Fig. 80. There is a higher volume fraction of more elongated α
in the area of high aluminum
content. 50×. (C. Scholl)

Fig. 82 Ti-6Al-4V alloy. A replica electron fractograph. Cleavage facets typical of salt-water stress-
corrosion
cracking. Cleavage occurs in the α phase. 6500×

Fig. 83 Ti-6Al-4V β-
annealed fatigued plate specimen. Scanning electron micrograph at the polished and
etched/unetched fracture topography interface showing microstructure/fracture topography correlation.
Secondary cracks are a result of intense slip bands. Kroll's reagent. 2000×. (R. Boyer)

Fig. 84 Same as Fig. 83
. This scanning electron micrograph illustrates that the "furrows" or "troughs" down
which the striations propagate are defined by the lamellar α
plates. These furrows link up as the crack
progresses. Kroll's reagent. 2000×. (R. Boyer)


Fig. 85

Fig. 86

Ti-6Al-4V powder metallurgy compact, hot isostatically pressed at 925 °C (1700 °F), 103 MPa (15 ksi),
for 2 h. This fatigue specimen had an internal origin at point A, which initiated at an iron inclusion, as
determined in Fig. 86 by precision sectioning. The cleavage zone at point C in Fig. 85 is due to the
TiFe
2
zone seen at point C in Fig. 86. Below the TiFe
2
, the structure consists of transformed
Widmanstätten α. The section (Fig. 86) was taken at line B in Fig. 85. Fig. 85: scanning electron
micrograph. No etch. 80×. Fig. 86: optical micrograph. Kroll's reagent. 16×. (D. Eylon)


Fig. 87 Ti-6Al-2Sn-4Zr-6Mo, 100-mm (4-
in.) thick forged billet, annealed 2 h at 730 °C (1350 °F). The
microstructure consists of a matrix of transformed β (dark) cont
aining various sizes of a grains (light), which
are elongated in the direction of working. 2 mL HF, 8 mL HNO
3
, 90 mL H
2
O. 200×

Fig. 88 Ti-6Al-2Sn-4Zr-
6Mo, forged at 870 °C (1600 °F), solution treated 2 h at 870 °C (1600 °F), water
quenched, and aged 8 h at 595 °C (1100 °F), and air cooled. Elongated "primary" α
grains (light) in aged
transformed β matrix containing acicular α. See also Fig. 89, 90, 91, and 92. Kroll's reagent (ASTM 192). 500×


Fig. 89 Ti-6Al-2Sn-4Zr-

6Mo bar, forged at 870 °C (1600 °F), solution treated 1 h at 870 °C (1600 °F), water
quenched, and aged 8 h at 595 °C (1100 F). The structure is similar to that in Fig. 88
, except that, as the result
of water quenching, no acicular α is visible. 2 mL HF, 10 mL HNO
3
, 88 mL H
2
O. 250×

Fig. 90 Same as Fig. 88
, except solution treated at 915 °C (1675 °F) instead of at 870 °C (1600 °F), which
reduced the amount of "primary" α grains in the α + β matrix. See also Fig. 91 and 92
. Kroll's reagent (ASTM
192). 500×

Fig. 91 Same as Fig. 90
, except solution treated at 930 °C (1710 °F) instead of at 915 °C (1675 °F), which
reduced the amount of α grains and coarsened the acicular α in the matrix. See also Fig. 92
. Kroll's reagent
(ASTM 192). 500×

Fig. 92 Same as Fig. 90 and 91, but solution treated at 955 °C (1750 °F), which is above the β
transus. The
resulting structure is coarse, acicular α (light) and aged transformed β
(dark). Kroll's reagent (ASTM 192).
500×

Fig. 93 Ti-6Al-2Sn-AZr-6Mo forging, solution treated 2 h at 955 °C (1750 °F), above the β
transus, and
quenched in water, The structure consists entirely of α ' (martensite). Kroll's reagent (ASTM 192). 500×

Fig. 94 Ti-6Al-6V-2Sn as-extruded, 8 mm (
5
16
-in.) thick. The microstructure consists of transformed β

containing acicular α; light α is also evident at the prior-β grain boundaries. 2 mL HF, 8 mL HNO
3
, 90 mL H
2
O.
200×

Fig. 95 Ti-6Al-6V-2Sn billet, 100 mm (4 in.) thick, forged below the β
transus of 945 °C (1730 °F), annealed 2
h at 705 °C (1300 °F), and air cooled. Light α in transformed β matrix containing acicular α
. 2 mL HF, 8 mL
HNO
3
, 90 mL H
2
O. 200×

Fig. 96 Ti-6Al-6V-2Sn
hand forging, forged at 925 °C (1700 °F), solution treated for 2 h at 870 °C (1600 °F),
water quenched, aged 4 h at 595 °C (1100 °F), and air cooled. Structure: "primary" α
grains (light) in a matrix
of transformed β containing acicular α. Kroll's reagent (ASTM 192). 150×

Fig. 97 Ti-6Al-6V-2Sn forging, solution treated, quenched, and aged same as in Fig. 96

. The structure is the
same as in Fig. 96, except that alloy segregation has resulted in a dark "β
fleck" (center of micrograph) that
shows no light "primary" α. See also Fig. 98 and 102. Kroll's reagent (ASTM 192). 75×

Fig. 98 Ti-6Al-6V-2Sn forging, solution treated for 1
1
4
h at 870 °C (1600 °F), water quenched, and aged 4 h
at 575 °C (1070 °F). Structure: same as in Fig. 97
, but higher magnification shows a small amount of light,
acicular α in the dark "β fleck." See also Fig. 102. 2 mL HF, 8 mL HNO
3
, 90 mL H
2
O. 200×

Fig. 99 Ti-6Al-4V-2Sn alloy; fracture surface of a tension-
test bar showing a shiny area of alloy segregation
that caused low ductility. See also Fig. 100 and 101. Not polished, Kroll's reagent (ASTM 192). 10×

Fig. 100 Same as Fig. 99
, except a section normal to the fracture surface, polished down to a stringer of boride
compound (light needle) in the area of segregation. See also Fig. 101
. Polished, Kroll's reagent (ASTM 192).
400×

Fig. 101 Same as Fig. 99, except a replica transmission electro
n fractograph of the etched surface, which
shows the stringer of boride compound as parallel platelets. Not polished, Kroll's reagent (ASTM 192). 1500×

Fig. 102 Ti-6Al-6V-2Sn α + β forged billet illustrating macroscopic appearance of β
flecks that appear as dark
spots. See also Fig. 97 and 98. 8 mL HF, 10 mL HF, 82 mL H
2
O, then 18 g/L (2.4 oz/gal) of NH
4
HF
2
in H
2
O.
Less
than 1×. (C. Scholl)

Fig. 103 Ti-3Al-2.5V tube, vacuum annealed for 2 h at 760 °C (1400 °F). Structure is equiaxed grains of α

(light) and small, spheroidal grains of β (outlined). See also Fig. 104. 10 mL HF, 5 mL HNO
3
, 85 mL H
2
O. 500×

Fig. 104 Ti-3Al-
2.5V tube that was cold drawn, then stress relieved for 1 h at 425 °C (800 °F). Yield strength,
724 MPa (105 ksi); elongation, 15%. Elongated α grains; intergranular β. Kroll's reagent (ASTM 192). 500×

Fig. 105 Ti-11.5Mo-6Zr-4.5Sn sheet, 2 mm (0.080 in.) thick, solut
ion treated 2 h at 760 °C (1400 °F), and
water quenched. Elongated grains of β(light) containing some α (outlined or dark). See also Fig. 106.

Kroll's
reagent. 150×

Fig. 106 Same as Fig. 105
, except aged for 8 h at 565 °C (1050 °F) after the water quench following solution
treating. Most of the β shown in Fig. 105 has changed to dark α; some β
phase (light) has been retained.
Kroll's reagent. 150×

Fig. 107 Ti-5Al-2Sn-2Zr-4Cr-4Mo (Ti-17) β-
processed forging with heat treatment at 800 °C (1475 °F), 4 h,
water quench, + 620 °C (1150 °F). Consists of lamellar α structure in a β matrix with some grain-boundary α
.
95 mL H
2
O, 4 mL HNO
3
, 1 mL HF. 100×. (T. Redden)

Fig. 108 Same as Fig. 107, but a higher magnification better illustrating lamellar α structure in an aged β

matrix. Acicular secondary α due to aging not resolvable at this magnification. 95 mL H
2
O, 4 mL HNO
3
, 1 mL
HF. 500×. (T. Redden)

Fig. 109 Ti-3Al-8V-6Cr-4Zr-
4Mo rod, solution treated 15 min at 815 °C (1500 °F), air cooled, and aged 6 h at

565 °C (1050 °F). Precipitated α (dark) in β grains. 30 mL H
2
O
2
, 3 drops HF. 250×.

Fig. 110 Ti-3Al-8V-6Cr-4Zr-
4Mo rod, cold drawn, solution treated 30 min at 815 °C (1500 °F), and aged 6 h at
675 °C (1250 °F). Precipitated α (dark) in grains of β. Kroll's reagent (ASTM 192). 250×

Fig. 111 Ti-13V-11Cr-
3Al sheet, rolled starting at 790 °C (1450 °F), solution treated 10 min at 790 °C (1450
°F), air cooled. Equiaxed grains of metastable β. See also Fig. 112. 2 mL HF, 10 mL HNO
3
, 88 mL H
2
O. 250×.

Fig. 112 Same as Fig. 111, except aged for 48
h at 480 °C (900 °F) after solution treating and air cooling.
Structure: dark particles of precipitated α in β grains. 2 mL HF, 10 mL HNO
3
, 88 mL H
2
O. 250×.

Fig. 113 Ti-8.5Mo-0.5Si water quenched from 1000 °C (1830 °F), Thin-foil
transmission electron micrograph
illustrating heavily twinned athermal α '' martensite. 5000×. (J.C. Williams)

Fig. 114 Ti-10V-2Fe-3Al pancake forging, β forged about 50% + α -β
finish forged about 5%, with heat
treatment at 750 °C (1385 °F), 1 h, water quench, + 540 °C (1000 °F), 8 h. Lamellor α
with a small amount of
equiaxed α in an aged β matrix. 10 s with Kroll's reagent,
then 50 mL of 10% oxalic acid, 50 mL of 0.5% HF.
400×. (R. Boyer)

Fig. 115 Same as Fig. 114, but amount of α + β finish forging is 2%. Micrograph illustrates darkened aged β

surrounding a lighter etched β fleck. See also Fig. 116. Same etch as Fig. 114. 50×. (T. Long)

Fig. 116 Same as Fig. 115, but at higher magnification to demonstrate the reduced amount of α in the β
fleck.
The α observed (light) is primary α; the α that forms upon aging is too fine to resolve. Same etch as Fig. 114
.
200×. (T. Long)

Fig. 117 A titanium-iron binary alloy, β solution treated, water quenched, and aged to form ω. The ω
is the
light precipitate in this thin-foil transmission electron micrograph. In alloys where the ω
has a high lattice
misfit, the ω is cuboidal to minimize elastic strain in the matrix. 320,000×. (J.C. Williams)


Fig. 118

Fig. 119
Ti-10V-2Fe-3Al deformed at 1150 °C (2100 °F). Fig. 118 demonstrates the as-deformed structure that
has been heavily etched. The specimen was recrystallized at 925 °C (1700 °F) for 1 h in a vacuum of 10

-
6
torr. Recrystallization in vacuum caused thermal etching of the recrystallized grains (Fig. 119 shows
recrystallized structure). The prior unrecrystallized structure can still be observed as ghost boundaries
remnant from the initial overetching. Fig. 118: 60 mL H
2
O, 40 mL HNO
3
, 10 mL HF for 30 min. Fig.
119: 60 mL H
2
O, 40 mL HNO
3
, 10 mL HF for 30 min + thermally etched at 925 °C (1700 °F) for 1 h in
vacuum (10
-6
torr). Magnification not known. (D. Eylon)



Fig. 120

Fig. 121

Fig. 122

Fig. 123
Ti-15V-3Cr-3Al-3Sn cold-rolled strip that has been annealed at 790 °C (1450 °F) for 10 min and aged
at various times to illustrate the progression of aging and what is termed "decorative aging," a
technique used to determine the extent of recrystallization. Equiaxed β grains are observed in Fig. 120,

which was not aged. Fig. 121 has been aged 2 h at 540 °C (1000 °F) and shows dark aciculor α that
forms upon aging. Grains in center are completely aged (uniform α precipitation throughout the
grains), which means they were not recrystallized (had more stored energy), resulting in rapid aging.
Fig. 122 and 123 carry the progression further with 4- and 8-h aging, respectively. An 8-h age results
in a fully aged structure. All etched with Kroll's reagent. All 200×. (P. Bania)


Fig. 124 Ti-40 at.% Nb, β solution heat treated at 900 °C (1650 °F), water quenched, then aged at 400 °C
(750 °F) for 24 h. The dark precipitate is β' (solute-lean β phase) in a solute-enriched β matrix. Thin-foil
transmission electron micrograph. 31,000×. (J.C. Williams)

Fig. 125 Ti-10V-2Fe-3Al, β solution treated, water quenched, and strained 5% at room temperature. This
Nomarski interference micrograph illustrates deformation-induced α'' martensite in a β matrix. No etch. 500×.
(J.E. Costa)

Uranium and Uranium Alloys: Metallographic Techniques and Microstructures
Kenneth H. Eckelmeyer, Division Supervisor, Sandia National Laboratories

Introduction
URANIUM is used in a variety of applications for its high density (19.1 g/cm
3
, 68% greater than lead) and/or its unique
nuclear properties. Uranium and its alloys exhibit typical metallic ductility, can be fabricated by most standard hot and
cold working techniques, and can be heat treated to hardnesses ranging from approximately 92 HRB to 55 HRC.
Metallography is a useful tool for quality assurance, failure analysis, and understanding the effects of processing on the
properties of uranium and its alloys.
Natural uranium consists of two primary isotopes: U
235
(0.7%) and U
238

(99.3%). Isotopic separation is carried out as one
of the steps in converting the ore to metal, resulting in two grades of metallic uranium. Enriched uranium, sometimes
termed "oralloy," contains more than 0.7% U
235
and is used primarily for its nuclear properties. Depleted uranium,
sometimes termed "tuballoy," DU, or D-38, contains only about 0.2% U
235
and is used primarily for its high density.
Although access to enriched uranium is controlled, depleted uranium is industrially available.
This article will consider the physical metallurgy and metallography of depleted uranium. The metallurgy of enriched
uranium is identical to that of depleted uranium, although additional measures are necessary during metallographic
preparation to maintain material accountability and to avoid health hazards. Detailed information on uranium alloy
metallurgy and microstructures is presented in subsequent sections of this article and in Ref 1, 2, 3, 4, 5, 6, 7, and 8.
Acknowledgement
The author wishes to thank the following individuals for their assistance: T.N. Simmons, Sandia National Laboratories;
A.G. Dobbins, Martin-Marietta; C.E. Polson, NLO, Inc.; A.L. Geary, Nuclear Metals, Inc.; and A.D. Romig, Jr., Sandia
National Laboratories.

References
1.

A.N. Holden, Physical Metallurgy of Uranium, Addison-Wesley, 1958
2.

W. Lehmann and R.F. Hills, Proposed Nomenclature for Phases in Uranium Alloys, J. Nucl. Mater.,
Vol 2,
1960, p 261
3.

W.D. Wilkinson, Uranium Metallurgy, Vol 1 and 2, Interscience, 1962

4.

J.J. Burke et al., Ed., Physical Metallurgy of Uranium Alloys, Brook Hill, 1976
5.

K.H. Eckelmeyer, Microstructural Control in Dilute Uranium Alloys, Microstruc. Sci., Vol 7, 1979, p 133
6.

Metallurgical Technology of Uranium and Uranium Alloys,
Vol 1, 2, and 3, American Society for Metals,
1982
7.

J.G. Speer, "A Study of Solid-
State Phase Transformations in Uranium Alloys," Ph.D. thesis, Oxford
University, 1983
8.

K.H. Eckelmeyer, A.D. Romig, and L.J.
Weirick, The Effect of Quench Rate on the Microstructure,
Mechanical Properties, and Corrosion Behavior of U-6 Wt. Pet. Nb, Met. Trans. A, Vol 15, 1984, p 1319
Principles of Uranium Alloy Metallurgy
Uranium ore is processed by mineral beneficiation and chemical procedures to produce enriched or depleted uranium
tetrafluoride (UF
4
). The UF
4
is then reduced with magnesium or calcium at elevated temperature, resulting in metallic
uranium ingots that are known as "derbies." These derbies are vacuum induction remelted and cast into the shapes
required for engineering components or for subsequent mechanical working. Crucibles and molds are usually made of

graphite; a zirconia or yttria wash prevents or minimizes carbon pickup by the metal.
Solid elemental uranium exhibits three polymorphic forms: γ phase (body-centered cubic) above 771 °C (1420 °F), β
phase (tetragonal) between 665 and 771 °C (1230 and 1420 °F), and α phase (orthorhombic) below 665 °C (1230 °F).
Hot working (rolling, forging, extruding) is readily accomplished in the γ(800 to 840 °C, or 1470 to 1545 °F) or high α
(600 to 640 °C, or 1110 to 1185 °F) temperature ranges, and cold or warm working (rolling, swaging) can be done from
room temperature to about 400 °C (750 °F). Because of its relatively low ductility, deformation in the β-phase is not
desirable. Recrystallization of cold-worked material can be performed in the high α region (500 to 640 °C, or 930 to 1185
°F). The material can be machined by most normal cutting and grinding techniques, but special tools and cutting
conditions as well as safety precautions are recommended.
Uranium is frequently alloyed to improve its corrosion resistance and/or to modify its mechanical properties. These alloys
are produced by vacuum induction or vacuum arc melting and, like unalloyed uranium, can be fabricated hot, warm, or
cold. As shown in Fig. 1, the high-temperature γ phase can dissolve substantial amounts of several alloying elements, but
these elements are less soluble in the intermediate- and low-temperature β and α phases. Uranium alloys are generally
heat treated at approximately 800 °C (1470 °F) to get all the alloying additions into solid solution in the γ phase, then
cooled at various rates to room temperature. Slow cooling permits the γ phase to decompose to two-phase structures
morphologically similar to pearlite in steels. Rapid quenching suppresses these diffusional decomposition modes,
resulting in various metastable phases.

Fig. 1 Polymorphism and solubilities of alloying element
s in uranium. Note that alloying elements are
substantially less soluble in lower temperature phases.
The microstructures and hardnesses produced by quenching are summarized in Fig. 2. Very dilute alloys (see Fig. 17 in
the section "Atlas of Microstructures for Uranium and Uranium Alloys" in this article) exhibit supersaturated α phase with
an irregular grain morphology similar to that of unalloyed uranium. Slightly more concentrated alloys exhibit acicular
martensitic microstructures (Fig. 21). Both of these microconstituents are orthorhombic variants of α-uranium. Their
hardness and yield strength increase with increasing alloy content due to solid-solution effects.

Fig. 2 Effects of alloy concentration on structure and properties of quenched alloys

Further increases in alloy content cause a transition to a thermoelastic, or banded, martensite (Fig. 29 and 38). The

hardness and yield strength of the thermoelastic martensites decrease with increasing alloy content, apparently due to
increasing mobilities of the boundaries of the many fine twins produced during the transformation. Midway in the
thermoelastic martensite composition range, the crystal structure changes to monoclinic, as one lattice angle departs
gradually from 90°. This change in crystal structure has little apparent effect on mechanical behavior. These martensitic
variants of α -uranium are frequently termed α '
a
, α '
b
and α ''
b
; the subscripts a and b denote the acicular and banded
morphologies, respectively, and the prime and double prime superscripts denote the orthorhombic and monoclinic crystal
structures, respectively.
Additional increases in alloy content produce a transition to γ°, an ordered tetragonal variant of elevated-temperature γ-
uranium (Fig. 40). Further alloy additions cause retention of the cubic γ phase. These variants of the γ phase can be
distinguished by x-ray diffraction, but not by metallography.
The phases produced by quenching are metastable and supersaturated; therefore, they are amenable to subsequent heat
treatment. As substitutional solid solutions, they are relatively soft (92 HRB to 35 HRC) and ductile (15 to 32% tensile
elongation). Subsequent heat treatment increases their hardness and strength. Age hardening occurs at temperatures below
approximately 450 °C (840 °F) due to fine-scale microstructural changes observable only by transmission electron
microscopy or other very high resolution techniques. Overaging occurs at higher temperatures or longer times by
decomposition of the metastable structures. This decomposition, which commonly takes place by cellular or
discontinuous precipitation, is revealed by optical metallography (Fig. 24, 30, and 39).
Although heat treatment is the primary method for controlling mechanical properties, ductility is also strongly influenced
by the presence of impurities. Carbon, oxygen, and nitrogen are picked up in the melting process from the crucibles and
molds (in the case of carbon), from contamination of the surfaces of the materials being melted, or from the furnace
atmosphere. These elements cause inclusions to form in the metal. Metal fluorides can also be carried over from the metal
reduction process. Other tramp elements, such as silicon and iron, can form intermetallic compound inclusions with
uranium. These impurities deleteriously affect ductility when present above various threshold levels.
Perhaps the most insidious impurity, however, is hydrogen, which can be introduced during melting or subsequent

processing. (Salt baths for heating metal prior to working are notorious sources of hydrogen.) In some alloys, the presence
of less than 1 ppm (by weight) hydrogen causes a 50% decrease in the reduction in area associated with tensile fracture.
Hydrogen is commonly removed by vacuum heat treatment at 800 to 900 °C (1470 to 1650 °F).
Sample Preparation
Methods for preparation of metallographic samples of uranium have been thoroughly reviewed in Ref 1 and 9. This
section draws heavily on these references and emphasizes current, successful techniques. Methods for preparation of thin
foils for transmission electron microscopy are also described in the literature (Ref 6, 10), but will not be reviewed in this
article.
Health and Safety Considerations. Handling and metallographic preparation of depleted uranium is similar to that
of most metals, although its mild radioactivity, chemical toxicity, and pyrophoricity require additional precautions.
Although extreme measures such as shielded glove box handling are not required, a common-sense approach based on a
realistic understanding of the hazards involved is essential. This section briefly outlines the principal hazards and
necessary precautions associated with the metallographic preparation of depleted uranium. More complete information on
the health and safety aspects of working with uranium can be found in Ref 11, 12, and 13. Organizations performing
uranium metallography should have their procedures as well as the engineering designs of their cutting and grinding areas
approved regularly by an occupational health and safety organization for compliance with the referenced guidelines and
state regulations. Personnel and work areas should also be tested and inspected periodically.
The primary radiological hazards associated with depleted uranium are beta and alpha emission. The beta-ray dose rate at
the surface of a uranium slug is 0.23 rad/h. This dose rate decreases dramatically with increasing distance from the
source, due to absorption in the air and geometric effects. In addition, for specimens mounted in Bakelite or epoxy,
virtually none of the beta radiation passes through the mount. Alpha radiation is also emitted, but is almost totally
absorbed in 10 mm (0.4 in.) of air or in the 0.07-mm (0.003-in.) thick protective layer of skin and, therefore, presents no
external health hazard. The gamma-radiation dose rate measured at a typical working distance of 400 mm (16 in.) from an
unmounted 55-g sample is 1 × 10
-6
R/h, or about one tenth of the natural gamma background rate. (1 R, or roentgen,
equals 2.58 × 10
-4
coulomb per kilogram.) As a result, normal metallographic handling of depleted uranium virtually
never causes exposures approaching the federal and state external exposure limits of 3 rem (roentgen equivalent man) per

quarter/5 rem per year for whole body exposure or 25 rem per quarter/75 rem per year for extremity (e.g., finger)
exposures. Undesirable exposure could result, however, from storing samples in clothes pockets or repeatedly wearing lab
coats extensively soiled with fine debris from uranium cutting or grinding operations.
While alpha radiation poses essentially no external health hazard, it does require caution during sectioning and grinding to
ensure that finely divided uranium particles do not become airborne, where they could be inhaled and result in alpha
irradiation of delicate lung tissue. Methods for ensuring that airborne uranium concentrations remain below the
Occupational Safety and Health Administration standard of 0.25 mg/m
3
of air are discussed later in this section.
Depleted uranium is about as chemically toxic as other heavy metals, such as lead. Although this does not dictate a need
for extreme measures in handling, appropriate housekeeping and personal hygiene practices will minimize the possibility
of ingesting uranium, which could damage the kidneys. For example, disposable gloves should be worn during cutting
and grinding; hands should be washed thoroughly before eating; smoking, eating or drinking should not be permitted in
areas where cutting and grinding are performed; and tabletops and floors should be wet wiped or mopped daily. These
measures are particularly important in areas where hot-worked parts are being handled, because the powdery oxide scale
accentuates contamination of laboratory furniture and personnel.
Because finely divided uranium is also pyrophoric, sparks are frequently generated during cutting. The ignition
temperature for 270-mesh (about 50-μm) powder is only 20 °C (68 °F). Therefore, liberal amounts of cutting fluid should
be used in cutting and grinding, and cleaning should be done regularly to avoid accumulation of finely divided waste in
saws, cutoff wheels, or grinders. Extinguishers for metal fires should also be available.
Sectioning. Samples for metallographic preparation can be cut with a power saw or an abrasive cutoff wheel (see the
article "Sectioning" in this Volume for additional information on these methods). Liberal amounts of nonflammable
cutting fluid will minimize the generation of airborne material and the danger of fire. In addition, high-speed cutoff
wheels that produce finely divided uranium particles should be enclosed and their interiors vented with negative pressure
filtered units to prevent airborne material from escaping into the room, where it could be directly inhaled or perhaps
eventually ingested after settling on laboratory surfaces. Wearing disposable gloves during cutting as well as washing
samples and hands after sectioning will further reduce laboratory contamination and health hazards. Finely divided metal
residue should be removed regularly to minimize the danger of fire. Metal scraps, cutting residue, used cutting fluid, worn
grinding papers, and so forth should be stored and discarded appropriately.
Excessive heat during sectioning can alter the hardness and microstructures of many uranium alloys. Cutting-induced

temperature increases can be minimized with low cutting rates and large amounts of cutting fluid. The care required to
avoid heating depends on the material being prepared and on the type of measurements planned. The most temperature-
sensitive materials are as-quenched alloys (particularly those containing substantial amounts of alloying elements), such
as U-6Nb. In these alloys, changes in hardness and fine microstructural features (sometimes resolvable by transmission
electron microscopy and similar techniques, but not by light microscopy) can occur from short-time exposures to
temperatures as low as 150 °C (300 °F), and gross microstructural changes (resolvable by light microscopy) can occur
below 400 °C (750 °F). As-quenched alloys that contain lesser amounts of alloying elements, such as U-0.75Ti, are more
stable, exhibiting fine and gross microstructural changes at approximately 350 °C (660 °F) and 500 °C (930 °F),
respectively. Age-hardened materials are stable up to the temperature at which they had been heat treated, while annealed
two-phase materials and unalloyed uranium are stable to greater than 600 °C (1110 °F).
Cutting-induced deformation can also result in microstructural artifacts. Sensitivity to deformation generally increases
with decreasing hardness and is most acute in unalloyed uranium and as-quenched alloys near the α '' to γ° transition,
such as U-6Nb. Sectioning deformation is best minimized with low cutting rates; when suspected, it can often be removed
by careful grinding to below the depth of deformation damage.
Mounting. Uranium can be mounted in any of the common metallographic mounting materials, such as Bakelite,
phenolic, and epoxy (see the article "Mounting of Specimens" in this Volume for additional information on these
materials). Frequently, the metal reacts with epoxy mixtures, resulting in minimal gas evolution during curing. This
produces small bubbles in the mount that, during subsequent polishing, can trap abrasives and contaminate polishing
cloths. Coating of specimens (nickel plating, spraying with epoxy paint, etc.) prior to mounting can prevent bubble
formation. Nickel plating also can be used to avoid edge rounding during polishing when a fracture profile is to be
examined, for example. However, because uranium surfaces oxidize rapidly when exposed to air, the nickel plating may
not adhere. This can be overcome by sputter depositing a thin layer of a conductive material, such as a gold-palladium
alloy, onto the oxidized surface prior to nickel plating. Sputtering can usually be performed in a scanning electron
microscopy laboratory, because nonconductive materials must be coated prior to examination by scanning electron
microscopy.
Grinding. Uranium samples can be ground by various standard metallographic procedures. Fixed abrasive silicon
carbide papers flushed with water work well, as does 600-grit aluminum oxide powder in a kerosene vehicle on a cast iron
lapping wheel. A uniform 600-grit finish is adequate for subsequent polishing.
Sufficient material should be removed in each grinding step to eliminate the deformed material produced by the previous
coarser grit. The depth of deformation damage increases with decreasing metal hardness; damage is most severe in soft

materials, such as unalloyed uranium and as-quenched U-6Nb. Deformation-induced artifacts in unalloyed uranium are
shown in Fig. 10 in the section "Atlas of Microstructures for Uranium and Uranium Alloys" in this article.
The health and safety precautions listed in the previous discussion of uranium sample sectioning also apply to grinding.
Dry grinding should always be avoided to minimize the possibility of producing hazardous airborne particulates and to
prevent the possibility of excessive specimen heating.
Polishing. Uranium can be polished by standard mechanical and electrolytic techniques, as described in the articles
"Mechanical Grinding, Abrasion, and Polishing" and "Electrolytic Polishing" in this Volume. Rough polishing is best
done on a low-nap cloth, such as nylon. Diamond abrasive with a commercial petroleum-base vehicle works best, but
silicon carbide and aluminum oxide (Al
2
O
3
) abrasives with water vehicles are also satisfactory. As a standard technique
for rough polishing, the author's laboratory uses 30-μm diamond paste followed by 6-μm diamond paste on a nylon lap
with a petroleum-base vehicle.
Final polishing can be accomplished mechanically or electrolytically. Mechanical polishing is most frequently used when
the samples are to be etched and viewed using bright-field illumination. This is normally the case with multiphase
specimens. Chemical differences between the phases cause them to respond differently to etchants, thus producing
differential surface relief effects that make the various microstructural features discernible with bright-field illumination.
Final mechanical polishing is best done on a high-nap cloth with 0.3-μm α -Al
2
O
3
abrasive and a deionized water vehicle.
In some cases, this can be followed by a similar step using 0.05-μm γ-Al
2
O
3
. These final polishing steps can be carried
out on rotating wheels or vibratory polishers. In the author's laboratory, final mechanical polishing is performed by

vibratory polishing for 6 to 12 h using a thin paste of 0.3-μm Al
2
O
3
in deionized water.
The high chemical reactivity of uranium sometimes results in pitting during these final polishing steps, particularly when
long-term vibratory polishing is employed. Often caused by chemical interactions with materials in the polishing system,
pitting usually can be overcome by thorough cleaning of the polishing system and use of new polishing cloths and slurry.
It can also occur due to galvanic reactions inherent in the sample. This is particularly common with nickel-plated uranium
samples and is best avoided by final polishing for a short time on a rotating wheel, although this often compromises the
quality of the final polish.
Electrolytic final polishing is frequently used to remove the last vestiges of surface deformation in preparation for
polarized light examination. Electrolytic polishing and polarized light examination are usually applied to unalloyed
uranium and single-phase alloys, where the primary distinctions between adjacent microstructural features are differences
in crystallographic orientation. Electrolytic polishing solutions and the conditions for their use are given in Table 1.
Orthophosphoric acid (ortho-H
3
PO
4
) and water (No. 1 in Table 1) works well with many alloys.
Table 1 Electropolishing solutions for uranium and uranium alloys
Solution Comments
1

1 part ortho-H
3
PO
4
acid
1 part H

2
O
30 V open circuit, stainless steel cathode
2

1 part ortho-H
3
PO
4
acid
1 part ethylene glycol
1-2 parts ethyl alcohol
10-30 A/cm
2
(65 to 195 A/in.
2
), must be kept cold and free of water

3

1 part 118 g CrO
3
in 100 mL H
2
O

3-4 parts glacial acetic acid
40 V open circuit
4

85 parts ortho-H
3
PO
4
acid
13 parts H
2
O
2 parts H
2
SO
4

0.4 A/cm
2
(2.5 A/in.
2
), stainless steel cathode
5

1-2 parts ortho-H
3
PO
4
acid
2 parts H
2
SO
4

2 parts H
2
O
0.5 A/cm
2
(3 A/in.
2
), agitate solution
6

1 part HClO
4
(perchloric acid)
(a)

20 parts glacial acetic acid
60 V, 0.6-0.8 A/cm
2
(4-5 A/in.
2
), vigorous stirring

(a)

Solutions containing substantial amounts of HClO
4
are potentially explosive, especially in contact with oxidizable materials, such as organics.
This solution should be prepared by slowly adding HClO
4
to acetic acid while stirring. Use of more concentrated solutions is also reported in

the literature, but is not recommended because of safety considerations.

An alternative for obtaining deformation-free surfaces for polarized light microscopy is attack polishing, in which
chemically active solutions are used as vehicles in final polishing. In addition to producing a deformation-free surface,
these solutions often cause a thin epitaxial oxide layer to form on the surface, enhancing the contrast obtained during
polarized light examination. Specific solutions for attack polishing are given in Table 4, along with other methods of
preparing previously polished samples for polarized light examination.

References cited in this section
1. A.N. Holden, Physical Metallurgy of Uranium, Addison-Wesley, 1958
6. Metallurgical Technology of Uranium and Uranium Alloys,
Vol 1, 2, and 3, American Society for Metals,
1982
9. R.F. Dickerson, Metallography of Uranium, Trans. ASM, Vol 52, 1960, p 748
10.

A.D. Romig, Jr. an
d W.R. Sorenson, Uranium Alloys: Sample Preparation for Transmission Electron
Microscopy, J. Microsc., Vol 132, 1983, p 203
11.

Radiological Health Handbook,
U.S. Department of Health, Education, and Welfare, Public Health Service,
Food and Drug Administration, Bureau of Radiological Health, Rockville, MD, 1970
12.

"Occupational Health Guideline for Uranium and Insoluble Compounds," U.S. Department of Health and
Human Services, Washington, DC, 1978
13.

"Hygienic Guide Series Uranium," American Industrial Hygiene Association, Detroit
Macroetching and Macroexamination
Macroetching and macroexamination are sometimes used to characterize the grain structures, segregation patterns, and
metal flow geometries produced by solidification and mechanical working processes. Macroetching procedures are listed
in Table 2. Contrast between regions of different chemical composition may be enhanced by heating the part to the -
phase field, quenching, and slightly averaging; because decomposition of the martensite generally begins at lower
temperatures in alloy-rich regions, the regions in which alloying elements are concentrated will preferentially overage and
etch much darker. Flow lines in forged or extruded parts are often difficult to delineate unless segregation in the original
ingot provides bands of varying alloy content. It is sometimes useful to produce deliberately banded vacuum arc melted
uranium alloy ingots for studying metal flow during subsequent forming operations.

Table 2 Macroetching procedures for uranium and uranium alloys
Procedure Comments
1

Immerse 30 s to 1 min in HCl
Rinse in cold water
Rinse in HNO
3
1 to 5 s
(a)

Rinse in cold water
Macroetches unalloyed uranium
2

Immerse 30 min in:
1 part acetic acid
1 part HNO
3

(a)

Macroetches unalloyed uranium
3

Electrolytically etch at 0.05 A/cm
2
(0.3 A/in.
2
) in:
1 part trichloracetic acid
1 part H
2
O
Remove black film in 50% HNO
3
(a)

Macroetches unalloyed uranium
4

Electrolytically etch at 0.05 A/cm
2
(0.3 A/in.
2
) in:
5 g citric acid
5 mL H
2
SO

4

450 mL H
2
O
Macroetches unalloyed uranium
5

Heat tint at 200 to 400 °C (390 to 750 °F) for 3 to 5
min
Reveals chemical segregation in alloys. Surface must be clean and free of
oxide prior to heat tinting.
6

Water quench from 800 °C (1470 °F)
Age to just past peak hardness (temperature varies
depending on alloy)
Electroetch with H
3
PO
4
or oxalic acid (see Table 5)
Reveals chemical segregation in alloys
7

Heat sample to 450 °C (840 °F)
Cool
Electroetch to 0.01 A/cm
2
(0.06 A/in.

2
) in:
1 part 55 g CrO
3
in 50 mL H
2
O
1 part saturated solution of Na
2
CrO
4
(sodium
chromate) in H
2
O
Reveals chemical segregation and flow lines in uranium-niobium alloys

(a)

Solutions containing HNO
3
are not recommended for use with uranium-niobium alloys due to the formation of an explosive surface layer.

Macroexamination and photography are carried out with low-magnification optical devices and techniques identical to
those used with other alloy systems. Typical macrographs are shown in Fig. 3 and 4 in the section "Atlas of
Microstructures for Uranium and Uranium Alloys" in this article.

Microetching and Microexamination
Inclusions in uranium and uranium alloys are usually visible without etching. Metallographic techniques for inclusion
identification include heat tinting, copper plating from a copper cyanide solution, and chemical etching in nitric acid.

These methods are detailed in Table 3, along with descriptions of the typical morphologies of inclusions and intermetallic
compounds associated with impurities in uranium. Typical micrographs are also shown in Fig. 11, 12, 13, and 14 in the
section "Atlas of Microstructures for Uranium and Uranium Alloys" in this article. These indirect metallographic methods
were widely used prior to the proliferation of electron beam microanalytical techniques in the 1960s and '70s, and they
continue to be useful for rapid analysis of heat-to-heat variations in microcleanliness, etc. More definitive inclusion
identification can now be done on as-polished samples with electron probe microanalysis and/or scanning Auger
microscopy.
Table 3 Metallographic identification of inclusions and intermetallic compounds in uranium and uranium
alloys
Appearance Inclusion/compound

Morphology Sample
condition
Bright field Polarized
light
As-polished White/gray . . .
Heat tinted Orange/red . . .
Copper plated 1-2 min Discontinuous
deposit
. . .
UC Small and angular or large and dendritic
HNO
3
etched Black Black
As-polished Gray Dark gray
Copper plated 3-10 s Continuous deposit

. . .
UN Angular, dendritic, or Chinese script
HNO

3
etched Gray Dark gray
As-polished Gray Dark gray
Heat tinted Yellow . . .
Copper plated 20 s Continuous deposit

. . .
U(C,N) Angular, dendritic, or Chinese script
HNO
3
etched Dark gray Dark gray
As-polished Light gray Dark gray
Heat tinted Dark gray . . .
UO or U(O,C,N) Spherical, rimmed with second phase, or
irregular globules
Copper plated 1-2 min No deposit . . .
UO
2
Globular or partly elongated As-polished Dark gray Red, rust
Heat tinted Dark gray . . .

Copper plated 1-2 min No deposit . . .
As-polished Tan, light brown Gray
Heat tinted Silver halo . . .
UH
3
Needles or stringers
HNO
3
etched No attack . . .

U
3
Si
2
Globular, frequently rimmed with U
3
Si Attack polished with dilute
HF-HNO
3

Gray . . .
U
3
Si Globular, or rim around globular U
3
Si
2
Attack polished with dilute
HF-HNO
3

Brown . . .
MgF
2
and CaF
2
Glassy, globular or partly elongated
stringers
As-polished Black White
UF

3
Globular, elongated As-polished Black Violet
Electropolished Gray . . .
Copper plated 1 min Continuous deposit

. . .
U
6
Fe Decorates γ grain boundaries
HNO
3
etched Gray . . .
Nb
2
C Sharp, angular As-polished White . . .
NbC Sharp, angular As-polished Light gray . . .

The microstructures of unalloyed uranium and single-phase uranium alloys are most frequently characterized with
polarized light microscopy. Although such features as grain and twin boundaries are often difficult to delineate by etching
and bright-field examination, the optical anisotropy of the orthorhombic crystal structure of uranium allows adjacent
regions of differing crystallographic orientation to be defined by polarized light microscopy. Development of good
polarized light contrast requires metallographic surfaces that are free from polishing deformation; therefore, final
polishing is usually done by electropolishing or chemical-attack polishing. Some metallographers perform polarized light
microscopy on as-polished samples, but most employ various treatments to form a thin epitaxial oxide film on the
polished surface prior to metallographic examination. This thin oxide frequently increases polarized light contrast. Heat
tinting, incorporation of chemically active vehicles during final mechanical polishing, and electrolytic anodization are
some of the ways epitaxial oxide films can be formed. These preparation treatments for polarized light microscopy are
summarized in Table 4. Examples of the microstructures revealed by these techniques are shown in Fig. 5, 6, 7, 8, 9, 10,
15, 17, 23, 29, 31, 32, 34, and 38 in the section "Atlas of Microstructures for Uranium and Uranium Alloys" in this
article.

Table 4 Final preparation of uranium samples for polarized light microexamination
Solution Comments
Attack polishing methods
1

5 wt% CrO
3
in H
2
O Use as vehicle during final polishing.
2

1 part HF
1 part HNO
3

2 parts H
2
O
A few drops on final polishing wheel. Caution: Hydrofluoric acid solutions cause severe burns if allowed to contact
skin.
Anodizing solutions (electrolytic)
(a)

3

1 part NH
4
OH

30 parts ethylene glycol
60 V open circuit potential, 30 s to 2 min. Solution must be kept free of water.
4

1 part NH
4
OH
4 parts ethanol

Chemical
(a)

5

10% AgNO
3
(silver nitrate)
in H
2
O
Immerse sample in boiling solution.
6

10% FeCl
3
in H
2
O Immerse sample in boiling solution.
Atmospheric oxidation
(a)

7

Air Allow sample to oxidize in air at 25 to 300 °C (75 to 570 °F). Temperature and time vary strongly
with alloy composition.

(a)

Sample must have deformation-free polished surface prior to treatment; electropolishing is suggested as a means of producing this surface.

Uranium alloys with more than one phase are frequently etched and examined by bright-field microscopy. Etching is most
often done electrolytically, although some chemical etchants are also used. Preparation treatments for bright-field
microscopy are listed in Table 5, and examples of microstructures revealed by this method are shown in Fig. 18, 19, 20,
21, 22, 24, 25, 26, 27, 28, 30, 33, 35, 36, 37, 39, and 40.
Table 5 Final preparation of uranium samples for bright-field microexamination
Solution Comments
Electrolytic etches
1 1 part ortho-H
3
PO
4
acid
1 part H
2
O
1-5 V open circuit
(a)
, stainless steel cathode
2 5-10% oxalic acid in H
2

O 1-5 V open circuit
(a)
, stainless steel cathode
3 1 part 118 g CrO
3
in 100 mL H
2
O
3 parts glacial acetic acid
5-20 V open circuit
(a)
, stainless steel cathode
4 1 part ortho-H
3
PO
4
acid
2 parts H
2
SO
4

2 parts H
2
O
1-10 V open circuit
(a)
, stainless steel cathode