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Precipitation of germanium from aluminium
174
SHORTCOMMUNICATIONS
J. G. Morris and H. K. Howard
Department of Metallurgical Engineering, University of Kentucky, Lexington (U.S.A.) REFERENCES 1 J. G. MORRIS, R. L. SKAGGS, H. K. HOWARD AND J. T. TIDWELL, Mater. Sci. Eng., 4 (1969) 198.
Precipitation of germanium from aluminium Aluminium and germanium form a simple eutectic system. No metastable intermediate phases are known. There are only a few investigations on the precipitation behaviour of aluminium-germanium alloys 1-4. According to Sorokin et al. 3'4 germanium precipitates as small triangular plates with {111 }germaniumparallel to {111 }matrix as habit plane. Our investigations with an aluminium-l.3 at. germanium alloy indicated that germanium is
Fig. 1. Triangular plates in AI-Ge aged for 500 h at 150° C. (Note the large irregularly shaped or spherical particles precipitated at the grain boundary.) ( × 40000).
2 A. NADAI AND M. J. MANJOINE, Trans. ASME, 63 (1941) A-77. 3 U. S. LINDHOLM AND L. M. YEAKLEY, High Strain Rate Testing: tension and compression, Southwest Res. Inst. Report #3134.6. 4 D. L. HOLT, S. G. BABCOCK, S. J. GREEN AND C. J. MAIDEN, Am. Soc. Metals Trans. Quart., 60 (1967) 152.
Received October 24, 1969 Mater. Sci. Eng., 5 (1969/70) 172-174
precipitated with three different shapes and orientation relationships depending on the aging conditions; formation of G.P.-zones was not observed: (1) Triangular plates (Fig. 1): After aging the homogenized samples at about 150°C or at still lower temperatures most particles are small triangular plates in agreement with the quoted Russian works 3'4. Electron diffraction patterns show the occurrence of double reflections and of strong spikes around the germanium reflections in (111) directions. A precipitation free region along the grain boundaries was observed. Particles in the environment of this region are clearly larger than those in the interior of the grains. (2) Rod-shaped particles (Fig. 2): Aging at about 250° C leads to precipitation of rods which lie along the (100) matrix directions; the orientation relationship of these particles is given in Table 1. It is characterized by a good agreement between the atomic spacing in matrix and particles along the axis of the rods. In contrast with the results which B6hm 1 has found by electrical resistivity measurements the precipitation behaviour above 200°C depends on the time of an intermediate period of aging at room temperature. A decrease of this intermediate aging leads to a retardation of the decrease of electrical resistivity during aging at 250°C (see Fig. 4) and--as could be shown by transmission electron micros c o p y - t o a decrease of the density of nucleation sites as well as to a change in the shape of the precipitated particles. (3) Large rectangular plates (Fig. 3): Aging of specimens which were directly quenched to an aging temperature of 250°C or which were aged just below the solubility line lead predominantly to formation of very large plates on the {100}-planes of the aluminium lattice. The orientation relationship is given in Table 1. Inside of these particles a large number of twin lamellae are found. The corresponding diffraction patterns show strong spikes and twin reflections. Mater. Sci. Eng., 5 (1969/70) 174-176
175
SHORT COMMUNICATIONS TABLE 1" SHAPE
AND ORIENTATION RELATIONSHIP OF GERMANIUM PRECIPITATES IN ALUMINIUM-GERMANIUM
Shape
Habit plane
Orientation relationship
Triangular plates
{ 111 }matrix bounded by (llO)mat~ix
(111)g. . . . . i~m [1101
( 111)malri. [llO 1
rods along
(111)8. . . . . ium
(001)matrix
0oo) .... ~x
[o~2]
[0201 (211), ..... [0221 (011), . . . . . [1]-1]
Rod-shaped particles
identical with :
Rectangular plates
{100} . . . . i x bounded by (011)matrix
(111)g. . . . . [2201
ium
ium
ium
(001)matrix [0203 (O01)matrix
[020]
(001)m,,tri:, [220]
The results of the different isothermal aging treatments can be combined in a diagram (Fig. 4). Emphasis may be put on the break in the curve for the undeformed crystal at about 160° C: below this temperature small triangular plates are precipitated (see Fig. 1), above this temperature the rate of precipitation is decreased depending on the intermediate
aging at room temperature, and rod-shaped particles are precipitated (see Fig. 2). The precipitation behaviour of this alloy can be understood based on the following reasons: the considerably larger atomic volume of the precipitated germanium, its covalent bond as compared with the metallic aluminium matrix and especially
Fig. 2. (100)-plane. Rod-shaped particles : Al~3e, 100 min 250 ° C. (Note the moir6 along the rods due to the good matching between the atomic spacing in matrix and particles in this direction.) ( × 80 000).
Fig. 3. (100)-plane. A1-Ge directly quenched to 250 ° C and aged for 2 h at this temperature. ( × 9000).
Mater. Sci. Eng., 5 (1969/70) 174-176
176
SHORTCOMMUNICATIONS
1.0
Homogeneous solid Solution
1.5 F•nU
L~
350
'°
"N
~ 2.0
300
A
250 ° 200°
~o~
"150 °
E 2.5
E AI 1.3 at.*/oGe homogenized at 500"C
3.C
1
10 Time
-100"
100 m
1000 10
10000 min 1()0 1000 h
Fig. 4. Precipitation diagram obtained from electrical resistivity measurements; each point indicates the precipitation from 50 of the excess germanium : undeformed crystal, after homogenisation; - - x - - × 80 h at room temperature before aging, A A 6 rain at room temperature, A directly quenched to the aging temperature, - - • ...... • 90~o deformed by rolling.
the very high interaction energy vacancy germanium atom. The binding energy between vacancy and germanium atom (0.33 eV 5) is considerably larger than the corresponding value for most other aluminium alloys and larger than the binding energy vacancy-vacancy. Germanium atoms and vacancies stay in random distribution during rates of cooling at which in other alloys precipitation of vacancies occurs. In spite of the high density of vacancies in quenched aluminium-germanium samples no dislocation loops formed by precipitation of excess vacancies are observed. It can be assumed that small vacancy-germanium clusters are formed which act as nucleation sites for the germanium precipitates. Their size and stability will strongly depend on the heat treatment before aging. Above 160° C these clusters start to dissolve and therefore the density of nucleation sites decreases considerably. Grain boundaries are suitable nucleation sites for germanium precipitation in addition to vacancygermanium clusters (see Fig. 1). Precipitation at dislocations is not observed. The strong acceleration of precipitation by plastic deformation (see
Fig. 4) can be explained by an additional formation of vacancies and grain boundaries. An explanation for the three morphologies can be based on the decreasing number of excess vacancies with increasing aging temperature. The transition to the different shapes and orientation relationships may result from the following principles: In case of low temperature and high excess vacancies, accommodation of the interface is easier and the orientation relationship of {111}~e parallel to {lll}A1 is preferred. At higher temperatures and low vacancy density an orientation relationship with good matching at the interface and therefore minimized number of vacancies required for accommodation, or with a habit plane with minimized strain energy of the interface are preferred. The details of these mechanisms are under investigation and will be discussed more fully in a future work. The author would like to thank Professor E. Hornbogen for valuable discussions. Uwe K6ster*
Institut 3~r Metallphysik, Universitdt G6ttingen (Germany) REFERENCES 1 H. BOnM, Z. Metallk., 51 (1960) 409. 2 M. I. ZAKHAROVAAND YU. A. TUMAN'YAN, Soviet Phys.Crystal., 9 (1964) 414. 3 L. M . SOROKIN AND A. A. SITNIKOVA, Soviet Phys.-Solid State, 9 (1968) 1525. 4 k M. SOROKINAND G. N. MOSlNA, Soviet Phys.-Solid State, 10 (1968) 127. 5 R. R. HASIGUTI, J. Phys. Soc. Japan, 20 (1965) 625.
Received October 9, 1969 * Present address: Institut f'tir Werkstoffe, Ruhr-Universit~it Bochum, Germany. Mater. Sci. Eng., 5 (1969/70) 174-176
Solid solution hardening of silver single crystals by cadmium Solid solution hardening of Ag-Cd alloy crystals was investigated with particular emphasis on the solute concentration dependence of the plateau stress.
Experimental Pure silver crystals with 5 different additions of Cd were melted in a medium-frequency inductionfurnace in a pure argon atmosphere and swaged into rods of 3.5 mm diameter. Single crystals were grown by the Bridgman method in pure graphite molds with 4 mm diameter Mater. Sci. Eno. , 5 (1969/70) 176-178
SHORTCOMMUNICATIONS
J. G. Morris and H. K. Howard
Department of Metallurgical Engineering, University of Kentucky, Lexington (U.S.A.) REFERENCES 1 J. G. MORRIS, R. L. SKAGGS, H. K. HOWARD AND J. T. TIDWELL, Mater. Sci. Eng., 4 (1969) 198.
Precipitation of germanium from aluminium Aluminium and germanium form a simple eutectic system. No metastable intermediate phases are known. There are only a few investigations on the precipitation behaviour of aluminium-germanium alloys 1-4. According to Sorokin et al. 3'4 germanium precipitates as small triangular plates with {111 }germaniumparallel to {111 }matrix as habit plane. Our investigations with an aluminium-l.3 at. germanium alloy indicated that germanium is
Fig. 1. Triangular plates in AI-Ge aged for 500 h at 150° C. (Note the large irregularly shaped or spherical particles precipitated at the grain boundary.) ( × 40000).
2 A. NADAI AND M. J. MANJOINE, Trans. ASME, 63 (1941) A-77. 3 U. S. LINDHOLM AND L. M. YEAKLEY, High Strain Rate Testing: tension and compression, Southwest Res. Inst. Report #3134.6. 4 D. L. HOLT, S. G. BABCOCK, S. J. GREEN AND C. J. MAIDEN, Am. Soc. Metals Trans. Quart., 60 (1967) 152.
Received October 24, 1969 Mater. Sci. Eng., 5 (1969/70) 172-174
precipitated with three different shapes and orientation relationships depending on the aging conditions; formation of G.P.-zones was not observed: (1) Triangular plates (Fig. 1): After aging the homogenized samples at about 150°C or at still lower temperatures most particles are small triangular plates in agreement with the quoted Russian works 3'4. Electron diffraction patterns show the occurrence of double reflections and of strong spikes around the germanium reflections in (111) directions. A precipitation free region along the grain boundaries was observed. Particles in the environment of this region are clearly larger than those in the interior of the grains. (2) Rod-shaped particles (Fig. 2): Aging at about 250° C leads to precipitation of rods which lie along the (100) matrix directions; the orientation relationship of these particles is given in Table 1. It is characterized by a good agreement between the atomic spacing in matrix and particles along the axis of the rods. In contrast with the results which B6hm 1 has found by electrical resistivity measurements the precipitation behaviour above 200°C depends on the time of an intermediate period of aging at room temperature. A decrease of this intermediate aging leads to a retardation of the decrease of electrical resistivity during aging at 250°C (see Fig. 4) and--as could be shown by transmission electron micros c o p y - t o a decrease of the density of nucleation sites as well as to a change in the shape of the precipitated particles. (3) Large rectangular plates (Fig. 3): Aging of specimens which were directly quenched to an aging temperature of 250°C or which were aged just below the solubility line lead predominantly to formation of very large plates on the {100}-planes of the aluminium lattice. The orientation relationship is given in Table 1. Inside of these particles a large number of twin lamellae are found. The corresponding diffraction patterns show strong spikes and twin reflections. Mater. Sci. Eng., 5 (1969/70) 174-176
175
SHORT COMMUNICATIONS TABLE 1" SHAPE
AND ORIENTATION RELATIONSHIP OF GERMANIUM PRECIPITATES IN ALUMINIUM-GERMANIUM
Shape
Habit plane
Orientation relationship
Triangular plates
{ 111 }matrix bounded by (llO)mat~ix
(111)g. . . . . i~m [1101
( 111)malri. [llO 1
rods along
(111)8. . . . . ium
(001)matrix
0oo) .... ~x
[o~2]
[0201 (211), ..... [0221 (011), . . . . . [1]-1]
Rod-shaped particles
identical with :
Rectangular plates
{100} . . . . i x bounded by (011)matrix
(111)g. . . . . [2201
ium
ium
ium
(001)matrix [0203 (O01)matrix
[020]
(001)m,,tri:, [220]
The results of the different isothermal aging treatments can be combined in a diagram (Fig. 4). Emphasis may be put on the break in the curve for the undeformed crystal at about 160° C: below this temperature small triangular plates are precipitated (see Fig. 1), above this temperature the rate of precipitation is decreased depending on the intermediate
aging at room temperature, and rod-shaped particles are precipitated (see Fig. 2). The precipitation behaviour of this alloy can be understood based on the following reasons: the considerably larger atomic volume of the precipitated germanium, its covalent bond as compared with the metallic aluminium matrix and especially
Fig. 2. (100)-plane. Rod-shaped particles : Al~3e, 100 min 250 ° C. (Note the moir6 along the rods due to the good matching between the atomic spacing in matrix and particles in this direction.) ( × 80 000).
Fig. 3. (100)-plane. A1-Ge directly quenched to 250 ° C and aged for 2 h at this temperature. ( × 9000).
Mater. Sci. Eng., 5 (1969/70) 174-176
176
SHORTCOMMUNICATIONS
1.0
Homogeneous solid Solution
1.5 F•nU
L~
350
'°
"N
~ 2.0
300
A
250 ° 200°
~o~
"150 °
E 2.5
E AI 1.3 at.*/oGe homogenized at 500"C
3.C
1
10 Time
-100"
100 m
1000 10
10000 min 1()0 1000 h
Fig. 4. Precipitation diagram obtained from electrical resistivity measurements; each point indicates the precipitation from 50 of the excess germanium : undeformed crystal, after homogenisation; - - x - - × 80 h at room temperature before aging, A A 6 rain at room temperature, A directly quenched to the aging temperature, - - • ...... • 90~o deformed by rolling.
the very high interaction energy vacancy germanium atom. The binding energy between vacancy and germanium atom (0.33 eV 5) is considerably larger than the corresponding value for most other aluminium alloys and larger than the binding energy vacancy-vacancy. Germanium atoms and vacancies stay in random distribution during rates of cooling at which in other alloys precipitation of vacancies occurs. In spite of the high density of vacancies in quenched aluminium-germanium samples no dislocation loops formed by precipitation of excess vacancies are observed. It can be assumed that small vacancy-germanium clusters are formed which act as nucleation sites for the germanium precipitates. Their size and stability will strongly depend on the heat treatment before aging. Above 160° C these clusters start to dissolve and therefore the density of nucleation sites decreases considerably. Grain boundaries are suitable nucleation sites for germanium precipitation in addition to vacancygermanium clusters (see Fig. 1). Precipitation at dislocations is not observed. The strong acceleration of precipitation by plastic deformation (see
Fig. 4) can be explained by an additional formation of vacancies and grain boundaries. An explanation for the three morphologies can be based on the decreasing number of excess vacancies with increasing aging temperature. The transition to the different shapes and orientation relationships may result from the following principles: In case of low temperature and high excess vacancies, accommodation of the interface is easier and the orientation relationship of {111}~e parallel to {lll}A1 is preferred. At higher temperatures and low vacancy density an orientation relationship with good matching at the interface and therefore minimized number of vacancies required for accommodation, or with a habit plane with minimized strain energy of the interface are preferred. The details of these mechanisms are under investigation and will be discussed more fully in a future work. The author would like to thank Professor E. Hornbogen for valuable discussions. Uwe K6ster*
Institut 3~r Metallphysik, Universitdt G6ttingen (Germany) REFERENCES 1 H. BOnM, Z. Metallk., 51 (1960) 409. 2 M. I. ZAKHAROVAAND YU. A. TUMAN'YAN, Soviet Phys.Crystal., 9 (1964) 414. 3 L. M . SOROKIN AND A. A. SITNIKOVA, Soviet Phys.-Solid State, 9 (1968) 1525. 4 k M. SOROKINAND G. N. MOSlNA, Soviet Phys.-Solid State, 10 (1968) 127. 5 R. R. HASIGUTI, J. Phys. Soc. Japan, 20 (1965) 625.
Received October 9, 1969 * Present address: Institut f'tir Werkstoffe, Ruhr-Universit~it Bochum, Germany. Mater. Sci. Eng., 5 (1969/70) 174-176
Solid solution hardening of silver single crystals by cadmium Solid solution hardening of Ag-Cd alloy crystals was investigated with particular emphasis on the solute concentration dependence of the plateau stress.
Experimental Pure silver crystals with 5 different additions of Cd were melted in a medium-frequency inductionfurnace in a pure argon atmosphere and swaged into rods of 3.5 mm diameter. Single crystals were grown by the Bridgman method in pure graphite molds with 4 mm diameter Mater. Sci. Eno. , 5 (1969/70) 176-178