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									      JOURNAL DE PHYSIQUE
      Colloque C8, supplgment au n012, Tome 48, d6cembx-e 1987


               A. WOLFENDEN, C.K.           FRISBY, K.J. HERITAGE, S.S.               VINSON* and
               R.C. KNIGHT*
               Mechanical Engineering Department, Texas A & M U n i v e r s i t y ,
               College S t a t i o n , TX 77843, U . S . A .
               *LTV Missiles and E l e c t r o n i c s Group, Missiles D i v i s i o n , PO Box
               650003, D a l l a s , TX 75265, U . S . A .


      The PUCOT (piezoelectric ultrasonic composite oscillator technique) has been used at
      frequencies near 100 kHz to measure internal friction and dynamic Young's modulus of
      various metal matrix composites (MMCs) and advanced alloys. The materials in the
      study were: Al/SiC MMCs with up to 20 volume % Sic and powder metallurgy (PM)
      A1-Fe-X alloys denoted as 452 and B014L. The testing was performed at various
      temperatures ranging from room temperature to over 300°C. The strain arnplhtude
      dependence of internal friction was investigated over the strain range 10- to
      The modulus data were fitted to a linear equation of the type: E = E 0 - MT, where
      E (GPa) is the dynamic modulus at temperature T (OC), E 0 is the modulus at O°C and
      M is the slope dE/dT in GPa/OC. The values of M for the materials studied varied in
      the range 0.03 to 0.10 $ a ' , while values of M/E(O) (= -(l/E)(dE/dT))    fell in the
      interval (4 to 9 x 10- OC-
                      )                    .
                                      The effects of a flash anneal (540°C for 5 minutes)
      on the dynamic modulus (measured at room temperature) for the PM (Powder Metallurgy)
      Aluminum specimens was also investigated. The PUCOT is described, and the damping
      and dynamic modulus data are discussed.

           Aluminum matrix composites and powder metallurgy materials are major research
      areas in the aerospace industry. This field is particularly interested in materials
      that have a large Young's modulus to density ratio (specific modulus).
           Powder metallurgy (PM) aluminums and metal matrix composites (MMCs) have been
      supplied by LTV Aerospace & Defense Co. for testing. Several manufacturing
      processes have been varied, such as: type of matrix aluminum, rolling direction of
      PM alloy and volume fraction of Sic. These materials must withstand elevated
      service temperatures without an appreciable loss in mechanical properties. All of
      these variables must be considered so that an optimum material can be chosen for a
      specific application. This paper reports the results of an investigation using the
      PUCOT (piezoelectric ultrasonic composite oscillator technique) to determine
      internal friction and dynamic Young's modulus at temperatures up to slightly above
                                            EXPERIMENTAL PROCEDURES
           The PUCOT (1-4) was used to determine internal friction and dynamic Young's
      modulus at room temperature and at elevated temperatures. Since the PUCOT technique
      is not well-known, a brief description of the apparatus and its operation is given
      here. A schematic of the PUCOT is shown in Figure 1. The technique incorporates
      two identical alpha-quartz piezoelectric crystals (driver and gage), a spacer rod
      (used at elevated temperatures), and a test specimen. The two crystals are joined
      together followed by the addition of the quartz spacer rod using Loctite glue.

Article published online by EDP Sciences and available at
C8-378                         JOURNAL DE PHYSIQUE

Since the specimen is to sustain high temperature, it is cemented to the end of the
spacer rod using ceramic cement. At ambient temperatures, the spacer rod is omitted
and the test specimen is glued directly to the crystals as seen in the three
component system of Figure 1 In this arrangement, the piezoelectric crystals
excite longitudinal ultrasonic stress waves in the test specimen of appropriate
resonant length. The resonant system is driven by a closed-loop oscillator that
maintains a constant maximum strain amplitude in the test specimen. During the
experiment the resonant period, the drive voltage, gage voltage and temperature
(above ambient temperature) are measured. Other recorded values are the density,
mass and length of the test specimen along with the mass and period of the
piezoelectric crystals and spacer rod. The thermal expansion coefficient is used
for corrections in length and density at elevated temperatures. Since the quartz
rod is tuned to resonate at a particular temperature, measurements of damping and
modulus are made at specific, selected temperatures only, in our case 20, 100, 175,
200 and 316OC (depending on the alloy). The data analysis was completed on a
Commodore 64 computer equipped with appropriate programs.
Metal Matrix Composites:
     Three categories of cast A 357Al/SiC composites were investigated. Aluminum
A 357 is a castable aluminum alloy with a Young's modulus of approximately 71 GPa
depending on heat treatment. The MMCs had various volume percent of silicon carbide
whiskers (10 v/o, 15 v/o, 20 v/o). Each group consisted of several test specimens.
The cast specimens measured 5 mm x 5 mm x 40 mm.
Powder Metallurgy Alumi~ums:

     Alloys 452 and B014L are advanced powder metallurgy aluminum alloys that are
produced using rapid solidification processing techniques. The alloys are produced
by Allied-Signal Corporation, the composition of the individual alloys being
tailored to produce desired properties. Alloy 452 is a high stiffness composition
that exhibits exceptional elevated temperature properties. Alloy B014L is designed
to exhibit slightly lower stiffness and strength properties, but high fracture
toughness and high corrosion resistance characteristics. The novel (and
proprietary) alloy compositions give rise to thermally stable, fine dispersoids that
improve properties over those of conventional aluminums.
                               RESULTS AND DISCUSSION
A 357Al/SiC:
     For these specimens modulus was measured at all temperatures and damping was
found at 100 and 200°C. The av ra e values of damping and modulus for the 10 v/o
specimens at41000C were x loag atd 82.5 GPa, respectively. The damping ranged
from 4 x 10- to 6 x 10- and the modulus ranged from 81.2 to 83.4 GPa. The
temperature dependence of the modulus was fitted to a linear equation of the form:
E = 88.4 - 0.05T (GPa, OC); the correlation coefficient averaged 0.99 for the 10 v/o
     The 15 r/o specimens t 100°C showed an average damping of 8.8 x
                           )                                               (ranging
from 4 x 10- to 1.5 x 10- and an average modulus of 87.1 GPa (ranging from 85.2 to
89.7 GPa). The linear equation for the temperature dependence of modulus was E =
87.2 - 0.09T and the correlation coefficient averaged 0.96.
     Fina ly, for the 20 v/o spe~imensthe avesage damping and modulus at 100°C were
1.4 x l- (ranging from 8 x 10- to 1.8 x 10- ) and 89.9 GPa (ranging from 89.6 to
90.3 GPa), respectively. The linear equation for the temperature dependence of
modulus was E = 95.9 - 0.05T and the correlation coefficient averaged 0.97 for the
20 v/o specimens.
PM Al:
     Two types of PM aluminum specimens were provided: PM 452 and PM B014L. Each
type was further divided into two orientations, perpendicular and parallel. The
parallel orientation refers to the specimen being cut parallel to the rolling
direction, while the perpendicular orientation refers to a perpendicular cut. The
damping and modulus values were found at room temperature (20°C) and at an elevated
temperature of 300°C. These same properties were also found after a flash anneal of
540°C for 5 minutes.
     The PM 452 specimens had an average damping value of      at ro m temperature
for both orientations. The values ranged from 8 x       to 1.4 x 10-3 . The dynamic
modulus ranged from 91.3 GPa to 95.6 GPa with an average of 94.4 GPa.
     The amping values at room temperature for the PM B0145 specimens ranged from
1.1 x l- to 1.9 x
       o'                with an average value of 1.4 x 10-.   The modulus averaged
86.7 GPa and did not deviate a significant amount from this value.
     The damping and dynamic modulus were again found at room temperature after the
exposure of the specimens to ax elevated tem erature of 540°C for five m'nutes. The
damping ranged between 5 x 10- to 1.7 x l - with an average of 9 x 10f for the PM
452 specimens. The modulus for these specimens averaged 95.4 Pa. The damping
valyes of the PM B014L specimens fell between 6 x 10- and       (average = 8 x
10- ), while the modulus ranged between 85.0 GPa and 86.6 GPa (av5rage = 85.6 GPa).
At 316°C 5he average values of damping and modulus were 4.7 x 10- and 82.4 GPa, and
4.9 x 10- and 73.0 GPa for the 452 and B014L materials, respectively.
     The source of internal friction in MMCs is an intriguing topic. An examination
of the data for Al/SiC in Table 1 reveals that3 at 100°C the damping increases by a
factor of three (from 4.7 x      to 1.43 x 10- , average values) as the volume
percentage of Sic increases from 10 to 20%. At 200°C, however, 3 partial reve se
trend is jndicated: the internal friction ranges from 2.2 x 10- to 7.7 x l- to
1.2 x 10- as the volume percentage of Sic goes from 10 to 15 to 20%. A possible
interpretation of these results is suggested by the TEM observations of Fisher and
Arsenault (5) of high concentrations of dislocations near the Al/SiC interfaces.
The authors proposed that thermal stresses at the interfaces were induced on cooling
the MMC and these stresses generated large numbers of dislocations. Thus, in our
specimens we postulate that for the test temperature of 100°C such high dislocation
concentrations may exist, leading to higher damping levels as the percentagae of Sic
is increased, while at 200°C, where significant annealing out of dislocations in the
Al/SiC ought to occur, the damping level due to the dislocations near the Al/SiC
interfaces should decrease. In support of this postulate, we may note that for the
PM A1 alloys, which have been formulated to contain thermally stable, fine
dispersoids (to prevent significant annealing out of dislocations at higher
temperatures), the internal friction increases by a factaor of 4.5 (for PM 452) or
3.3 (for PM B014L) as the test temperature increases from 29 to 316°C. In other
words, the PM A1 alloys behave in a conventional manner (Q- increases as
temperature increases), whereas the MMCs do not, due to the unusually high
dislocation concentrations near the Al/SiC interface. Thus, it apears that a
significant contribution to internal friction over a certain temperature range in
MMCs may arise from the high concentration of dislocations near the fiberhatrix
     Many conclusions can be drawn from the data obtained. First of all, the
modulus and damping values of the PM aluminum specimens are not significantly
dependent on the rolling direction. The properties of the specimens remained fairly
constant at a given temperature. As expected, the damping increased by a factor of
about five and the modulus decreased by about 12 GPa with the increase in
temperature of approximately 300°C. The flash anneal had little effect on the
damping or the modulus. A longer exposure time would probably have resulted in more
significant changes in the material properties.
     It was noted from the average modulus values found for the Al/SiC composites
for each volume percent category that the 20 volume percent material has the highest
stiffness properties at all temperatures.
     For all the mat rial tested the values of M/E(O) (=-(l/E)(dE/dT))  fell in the
range (4 to 9) x l- ' - . This agrees with the range noted by Friedel (6) for
                  o'   CI
many elements.
     It seems likely that significant internal friction over a certain temperature
range in MMCs may arise from the high concentrations of dislocations near the
fiber/matrix interfaces.
C8-380                                 J O U R N A L D E PHYSIQUE


Spécimen     Temp.    Q"1       Modulus    Temp.        Q"1      Modulus     Temp.       Q"1        Modulus
                           -3                               -3                                 3
             <°C)    (xlO )      (GPa)     (°C)        (xlO )      (GPa)     <°C) ( x H F )          (GPa)

SIC A357
10%#1        20       —          87.1      100          —          —         200        —             —
102#2        20       —          87.5      100          0.4        81.2      200        1.5          77.7
10£#3        20       —          88.8      100          0.6        83.4      200        3.1          78.2
102#4        20       —          87.5      100          0.4        82.9      200        2.0          78.5

15X#1        100      0.7        87.4      175                               200        0.7          88.6
152#2        100      1.0        89.7      175          1.0        89.5      200        0.7          84.8
15X#3        100      0.4        86.9      175          1.3        85.0      200        —            —
15£#4        100      0.8        86.2      175          1.3        83.6      200        —            —
152#5        100      1.5        85.2      175          1.5        87.2      200        0.9          84.0

20Z#1       20                   95.6      100                               200
202#2       20        —          95.8      100          1.7        89.6      200        1.3          86.8
20X#3       20        —          95.0      100          1.8        90.3      200        0.8          86.2
20X14       20        —          95.1      100          0.8        89.7      200        1.5          85.7


Spécimen    Temp.    Q"1        Modulus      Q"1*       Modulus*    Temp.    Q"1         Modulus
                           -3                     -3                               -3
             (°C)    (xlO )      (GPa)     (xlO )        (GPa)      (°C)     (xlO )         (GPa)

PM 452

#1   PAR      20     0.9        95.1        1.7          94.2          316   2.9            85.8
#2   PAR      20     1.4        95.6        0.6          95.6          316   7.7            78.8
#1   PER      20     0.8        91.3        0.5          96.7          316   4.4            85.0
#2   PER      20     1.0        95.6        0.6          95.0          316   3.6            80.0

PM B014L

#1   PAR     20      1.1        86.7        0.7          85.0          316   4.7            71.6
#2   PAR     20      1.1        86.7        0.6          85.0          316   3.5            74.4
#1   PER     20      1.8        86.7        1.0          86.6          316   7.5            73.0
#2   PER     20      1.9        86.6        1.0          85.8          316   3.9            72.9

PAR:       Parallel to rplling direction
PER:       Perpendicular to rolling direction

*After flash anneal at 540°C for 5 minutes.

1.   J. Marx, Rev. Sci. Instr.   22,   503-509 ( 1 9 5 1 ) .

2.   W.H. Robinson and A. Edgar, Trans. Sonics and Ultrasonics, IEEE,                 E,98-105

3.   J.L. Tallon and A . Uolfenden, J. Phys. and Chem. of Solids, 40, 831-837 ( 1 9 7 9 ) .
4.   M.R. Harmouche and A. Wolfenden, J. of Testing and Evaluation,                 13,424-428

5.   R.J. Arsenault and R.M. Fisher, Scripta Met.              17,67-71   (1983).

6.   J. Friedel, "Dislocations", Pergammon Press, New York, 1964, Appendix B,


                               THREE COMPONENT                      FOUR COMPONENT
                                    SYSTEM                              SYSTEM


                                                                          1 fli
                                                        SPACER ROD         I   I,
                                                                           I   1,

                                                               SPECIMEN             F""A"E

     Figure 1 :    Schematic drawing of the PUCOT. Left hand side: apparatus for
                   measurements at room temperature; right hand side: for measurements at
                   elevated temperatures.

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