ASTM E963-95
(Practice)Standard Practice for Electrolytic Extraction of Phases from Ni and Ni-Fe Base Superalloys Using a Hydrochloric-Methanol Electrolyte
Standard Practice for Electrolytic Extraction of Phases from Ni and Ni-Fe Base Superalloys Using a Hydrochloric-Methanol Electrolyte
SCOPE
1.1 This practice covers a procedure for the isolation of carbides, borides, TCP (topologically close-packed), and GCP (geometrically close-packed) phases (Note 1) in nickel and nickel-iron base gamma prime strengthened alloys. Contamination of the extracted residue by coarse matrix (gamma) or gamma prime particles, or both, reflects the condition of the alloy rather than the techniques mentioned in this procedure.
1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. (See 3.3.2.1 and 4.1.1.)
Note 1--Ni3 Ti (eta phase) has been found to be soluble in the electrolyte for some alloys.
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Designation: E 963 – 95
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Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
Standard Practice for
Electrolytic Extraction of Phases from Ni and Ni-Fe Base
Superalloys Using a Hydrochloric-Methanol Electrolyte
This standard is issued under the fixed designation E 963; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope quantitatively analyzed by X-ray diffraction or microanalysis.
3.2 Careful control of parameters is necessary for reproduc-
1.1 This practice covers a procedure for the isolation of
ible quantitative results. Within a given laboratory, such results
carbides, borides, TCP (topologically close-packed), and GCP
can be obtained routinely; however, caution must be exercised
(geometrically close-packed) phases (Note 1) in nickel and
when comparing quantitative results from different laborato-
nickel-iron base gamma prime strengthened alloys. Contami-
ries.
nation of the extracted residue by coarse matrix (gamma) or
3.3 Comparable qualitative results can be obtained routinely
gamma prime particles, or both, reflects the condition of the
among different laboratories using this procedure.
alloy rather than the techniques mentioned in this procedure.
1.2 This standard does not purport to address all of the
4. Apparatus
safety concerns, if any, associated with its use. It is the
4.1 Cell or Container for Electrolyte—A glass vessel of
responsibility of the user of this standard to establish appro-
about 400-mL capacity is recommended. For the sample size
priate safety and health practices and determine the applica-
and current density recommended later in this procedure,
bility of regulatory limitations prior to use. (See 3.3.2.1 and
electrolysis can proceed up to about 4 h, and up to about4gof
4.1.1.)
alloy can be dissolved in 250 mL of electrolyte without
NOTE 1—Ni Ti (eta phase) has been found to be soluble in the
exceeding a metallic ion concentration of 16 g/L. Above this
electrolyte for some alloys.
concentration, cathode plating has been observed to be more
likely to occur. A mechanism for cooling the electrolyte is
2. Terminology
recommended. For example, an ice water bath or water-
2.1 Definitions:
jacketed cell may be used to keep the electrolyte between 0°
2.1.1 extraction cell—laboratory apparatus consisting of a
and 30°C.
beaker to contain the electrolyte, a dc power supply, a noble
4.2 Cathode—Material must be inert during electrolysis.
metal sheet or screen cathode and a noble metal wire basket or
Tantalum and platinum sheet or mesh are known to meet this
wire to affix to the sample (anode).
requirement. Use of a single wire is to be avoided, since
2.1.2 geometrically close-packed (GCP) phases—
cathode surface area should be larger than that of sample.
precipitated phases found in nickel-base alloys that have the
Distance between sample and cathode should be as great as
form A B, where B is a smaller atom than A. In superalloys,
possible, within the size of cell chosen. For example, a sample
these are the common FCC Ni (Al, Ti) or occasionally found
with a surface area of 15 cm should have no side closer than
HCP Ni Ti.
1.2 cm to the cathode. If the cell is cylindrical, as for the case
2.1.3 topologically close-packed (TCP) phases—
of a beaker or the upper part of a separatory funnel, the cathode
precipitated phases in nickel-base alloys, characterized as
could be curved to fit the inner cell wall to facilitate correct
composed of close-packed layers of atoms forming in basket
sample-cathode distance. The sample would then be centered
weave nets aligned with the octahedral planes of the FCC g
within the cell at the same height as the cathode. The cathode
matrix. These generally detrimental phases appear as thin
need not make a complete ring around the sample nor be more
plates, often nucleating on grain-boundary carbides. TCP
than 5 cm high.
phases commonly found in nickel alloys are s, μ , and Laves.
4.3 Anode—The sample must be suspended in the electro-
lyte by a material that is inert during electrolysis. Anode
3. Significance and Use
3.1 This practice can be used to extract carbides, borides,
TCP and GCP phases, which can then be qualitatively or
Donachie, M. J. Jr., and Kriege, O. H., “Phase Extraction and Analysis in
Superalloys—Summary of Investigations by ASTM Committee E-4 Task Group I,”
This practice is under the jurisdiction of ASTM Committee E-4 on Metallog-
raphy and is the direct responsibility of Subcommittee E04.11 on X-Ray and Journal of Materials, Vol 7, 1972, pp. 269–278.
Electron Metallography. Donachie, M. J. Jr., “Phase Extraction and Analysis in Superalloys—Second
Current edition approved Jan. 15, 1995. Published March 1995. Originally Summary of Investigations by ASTM Subcommittee E04.91,” Journal of Testing
published as E 963 – 83. Last previous edition E963 – 83 (1989). and Evaluation, Vol 6, No. 3, 1978, pp. 189–195.
E 963
FIG. 1 Schematic Diagram of Extraction Cell
connection material should be cleaned to prevent any contami- which is commonly used for phase analysis of the residue.
nating material from falling into the cell. Good electrical Otherwise, filter diameter is not critical. Filters should be
contact should be maintained between the sample wire and the handled with blunt tweezers.
permanent anode wire from the dc power supply. Two methods 4.6 Centrifuge—Centrifuging for residue collection can be
are found to be successful. Either method is subject to performed as an alternate to microfiltration.
disconnection of the sample due to shrinkage, which puts a 4.7 Balance—If quantitative analysis is desired, a balance
limit on the electrolysis time: sensitive to 0.0001 g is required.
4.3.1 Suspend the sample by platinum or platinum-rhodium
5. Reagents
thermocouple wire (20 gauge) wrapped around it to form a
5.1 Electrolyte—Add and mix 1 part of 12 N hydrochloric
basket. To avoid a shielding problem, the ratio of sample area
acid (sp gr 1.19) to 9 parts of absolute methyl alcohol by
covered by the wire to the exposed sample area should be
volume to make a 10 % HCl-methanol solution. For alloys
small.
containing W, Nb, Ta, or Hf, add one part by weight tartaric or
4.3.1.1 Mechanically attach or spot weld the platinum or
citric acid to 100 parts by volume HCl-methanol to make an
platinum-rhodium thermocouple wire to the sample.
approximately 1 % tartaric or citric acid solution. All reagents
4.3.2 If the weld is not immersed, non-inert wire may be
should be of at least ACS reagent grade quality.
substituted; for example, chromel, nichrome, 300 series stain-
5.1.1 Caution—Add hydrochloric acid to absolute methyl
less steel, etc. Stop-off lacquer should be used below the
alcohol slowly and with constant stirring; otherwise sufficient
meniscus to maintain constant electrolyte level. This also
heat is generated to cause a hazardous condition. Mixing must
eliminates formation of insoluble deposits immediately above
be done in an exhaust hood, because the fumes are toxic.
the meniscus and prevents arcing.
5.2 Sample and Residue Rinse—Absolute methyl alcohol is
4.3.2.1 Caution—Care must be taken to prevent arcing
to be used.
between anode and cathode which could ignite the methanol.
4.4 Power Supply—A variable dc power supply capable of
6. Procedure
providing 0 to 5 V is needed to obtain currents from 0 to 1.2 A
6.1 Sample Size and Geometry—A cube, cylinder, or rect-
depending on total surface area of the sample. For example, a
angular prism is preferred. Ideally, constant density should be
sample with total surface area of 15 cm , electrolyzed at a
maintained during electrolysis. Flattened samples, especially
current density of 0.1 A/cm , requires:
thin sheet, will experience considerable shrinkage due to edge
2 2
15 cm 3 0.1 A/cm 5 1.2 A (1)
effects and current density increase as the electrolysis pro-
4.4.1 Current and voltage fluctuation should be no more ceeds. A cube approximately 1.6 cm on a side will have a total
than 65%. A 65 % current fluctuation represents a current surface area of approximately 15 cm . Smaller samples have
density fluctuation of about 65 % which, for samples under 15 larger increases in current density during constant current
cm total surface area, is less than or equal to one-half the electrolysis due to shrinkage. Larger samples may require more
current density shift due to sample shrinkage over 4 h. than 250 mL of electrolyte and a power supply capable of
Potentiostatic control is not necessary, but may be helpful for delivering more than 1.2 A. Samples requiring higher total
determining optimum current density when setting up proce- current may cause a cathode plating problem due to the higher
dures for a new alloy. voltage required, and may make a
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