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Annealing behavior of molybdenum alloys containing 3 wt% rhenium
International Journal of Refractory Metals & Hard Materials 17 (1999) 381±384
Annealing behavior of molybdenum alloys containing 3 wt% rhenium Liu Sha
*
Department of Materials Science & Engineering, Central South University of Technology, Changsha, Hunan 410083, People's Republic of China Received 14 July 1997; accepted 16 February 1999
Abstract The annealing behavior of Mo±3%Re alloys fabricated by PM was investigated. It was observed that the relation between tensile strength and annealing temperature for the alloy wire specimens conformed to linear regression equations at 900±1400°C annealing temperatures. The Mo±3%Re alloy by dry±wet mixing method exhibited higher tensile strength and recrystallization temperature as compared with pure Mo and Mo±3%Re alloy fabricated by dry mixing method. The Mo±3%Re alloy wires after 1400°C annealing for 35 min still yielded higher tensile strength and hardness values. Ó 1999 Elsevier Science Ltd. All rights reserved. Keywords: Molybdenum; Rhenium; Annealing behavior
1. Introduction The previous studies have clearly demonstrated the solution-softening phenomenon in Mo±Re alloys [1,2]. Small additions of rhenium had the most eect on the level of strength at high temperatures, which is apparently connected with an increase in recrystallization temperature [3]. Even though Mo±Re alloys oered higher resistance to corrosion, workability and mechanical properties [4±6], the availability of these alloys is at best limited, partly because of the very high cost and scarcity of rhenium. It is signi®cant to study the low rhenium content alloys both from a performance viewpoint and a fabrication viewpoint. The study on fabrication of Mo alloys containing low Re content fabricated by PM creates the condition for investigation of its workability [7]. The annealing behavior of Mo±3%Re alloys fabricated by PM was investigated in this study. The annealing behavior of the wires was examined with optical micrography, scanning electron microscopy, microtensile tester and microhardness tester.
2. Experimental procedure Meterials used were sintered Mo±3%Re alloy 16 16 600 mm3 bars by the dry and dry±wet mixing *
Tel.: +86-731-883-7465. E-mail address: [email protected] (Liu Sha)
methods [7]. The chemical compositions of materials used are shown in Table 1. Some properties of the specimens are shown in Table 2. The alloy bars were swaged, annealed and drawn into 0.2 mm diameter wire. Samples were carefully annealed at 900±1400°C in a dry H2 atmosphere for 35 min. Scanning electron microscopy and optical micrograph were applied to observe the wire specimens. The tensile properties and hardness of the wire specimens were examined with microtensile tester and microhardness tester.
3. Results and discussion A comparison of optical micrographs of MD-1 and MDW-2 0.28 mm diameter wire specimens is given in Fig. 1. It is observed that the MDW-2 wire specimen exhibits the ®ner grain sizes than that of MD-1 both before and after drawing. The relation between tensile strength, elongation and annealing temperature for the wire specimens in 0.20 and 0.28 mm diameters are shown in Fig. 2. It appears that the tensile strength of the wire specimens decrease in straight line with the increase of annealing temperatures at 900±1400°C. The data tend to follow the linear regression equation relation between tensile strength and annealing temperature, expressed as in Table 3. Hypothesis testing shows that all absolute values of U are larger than ta=2 n ÿ 2, which illustrates that the
0263-4368/99/$ - see front matter Ó 1999 Elsevier Science Ltd. All rights reserved. PII: S 0 2 6 3 - 4 3 6 8 ( 9 9 ) 0 0 0 2 7 - X
382
L. Sha / International Journal of Refractory Metals & Hard Materials 17 (1999) 381±384
Table 1 Chemical composition of specimens Designation
MD-1 MDW-2 a
Element content (ppm) Fe
Al, Si
Mn, Mg, Co
Ni
Ti, V
Pb, Bi, Sn, Cd
Sb, Ca
W
Ka
Na
11 15
6 6
3 3
5 6
15 15
1 1
10 10
1000 1000
250 300
20 20
The usual potassium content of commercial Mo±Re alloys amounts to 6 10 ppm.
Table 2 Some properties of specimens Designation
Density (g/cm3 )
Mean grain size (lm)a
Oxygen content (ppm)
MD-1 MDW-2
9.95 10.02
1.74 0.37
31 45
a
The grain size of the alloys was determined by Linear analysis.
Fig. 1. Optical micrographs (200´) of MD-1 (a) and MDW-2 (b) 0.28 mm diameter wire specimens.
relation between tensile strength and annealing temperature conforms to the linear regression equation at 900±1400°C. It is evident from Fig. 2 that the recrystallization temperature of MDW-2 wire specimen is higher than
Fig. 2. Tensile strength and elongation for 0.20 mm diameter (a) and 0.28 mm diameter (b) wire specimens. Annealing temperature measured in °C. , rb : MDW-2; j, rb : MD-1; M, d: MD-1; , d: MDW-2.
L. Sha / International Journal of Refractory Metals & Hard Materials 17 (1999) 381±384
383
Table 3 Linear regression equations Diameter (mm)
Designation
Linear regression equations
U
t0:025 [4]
0.20
MD-1 MDW-2
rb 2007 ÿ 0:868T rb 2351 ÿ 1:063T
12.55 5.76
2.78 2.78
0.28
MD-1 MDW-2
rb 1844 ÿ 0:761T rb 1979 ÿ 0:786T
7.14 11.23
2.78 2.78
Fig. 4. Relation between microhardness and annealing temperature for MDW-2 0.28 mm diameter wire specimen. Annealing temperature measured in °C. Fig. 3. SEM micrographs (1250´) of MDW-2 0.28 mm diameter wire specimen sections after 1000°C (a) and 1200°C (b) anneling.
that of MD-1 due to its curve of elongation lying in right side. Here it will also be noted that the elongations of the wire specimens increased signi®cantly at 1100± 1200°C owing to polygonization. It is observed from Fig. 3 that the change in grain sizes of the wire specimen section at 1200°C occurs while little or no change occurs at 1000°C. Because of the ®ner grain sizes (Hall±Petch eect). the MDW-2 wire after 1400°C annealing for 35 min still provided with higher tensile strength and hardness (as shown in Fig. 4) values, which also showed that the investigated material possessed higher recrystallization temperature probably owing to the high potassium content.
The microhardness of the MDW-2 wire specimen trend as function of annealing temperature is very similar to that of tensile behaviors, as indicated in Fig. 4. The tensile strength of MDW-2 0.65 mm diameter wire specimen is compared with pure Mo in Fig. 5. It is clear that the MDW-2 specimen oers higher tensile than that of pure Mo at 900±1400°C.
4. Conclusion The Mo±3% Re alloy bars with good workability could be fabricated to 0.20 mm diameter ®ne wire. The sintered Mo±3% Re alloy wire specimen produced by the dry±wet mixing method exhibit higher tensile strength and recrystallization temperature as compared
384
L. Sha / International Journal of Refractory Metals & Hard Materials 17 (1999) 381±384
with that of pure Mo and Mo±3%Re alloy fabricated by the dry mixing method. The Mo±3%Re alloy wires after 1400°C annealing for 35 min still oers higher hardness and tensile strength values.
References [1] Stephens JR, Witzke WR. J Less-Common Metals 1971;23:325±42. [2] Lundberg LB, Ohriner EK, Tuominen SM, Whelan EP, Shields Jr JA. Solution softening in Mo±Re alloy. In: Proceedings of the Symposium on Physical Metallurgy and Technology of Molybdenum and its Alloys. 1985:71±79. [3] Abramyan AV, Morgunova NN, Golovanenko SA, Kazakova NI. Mechanical properties of Mo±Re alloys at dierent test temperatures. [Trans., Metallovedenie i Termicheskaya Obrabotka Metallov, 1988;3:50±53]. [4] Igata N, Kohyama A. J Nucl Mater 1981;103 & 104:409±14. [5] Japanese Patent, 38540, 1983 [in Japanese]. [6] Lundburg LB. Los Alamos Scienti®c Laboratory Report LA-8685MS, 1981. [7] Sha L. Int J Refract Metals & Hard Materials 1997;15:219±22.
Fig. 5. Relation between tensile strength and annealing temperature for pure Mo and MDW-2 0.65 mm diameter wire specimen. Annealing temperature measured in °C.
Annealing behavior of molybdenum alloys containing 3 wt% rhenium Liu Sha
*
Department of Materials Science & Engineering, Central South University of Technology, Changsha, Hunan 410083, People's Republic of China Received 14 July 1997; accepted 16 February 1999
Abstract The annealing behavior of Mo±3%Re alloys fabricated by PM was investigated. It was observed that the relation between tensile strength and annealing temperature for the alloy wire specimens conformed to linear regression equations at 900±1400°C annealing temperatures. The Mo±3%Re alloy by dry±wet mixing method exhibited higher tensile strength and recrystallization temperature as compared with pure Mo and Mo±3%Re alloy fabricated by dry mixing method. The Mo±3%Re alloy wires after 1400°C annealing for 35 min still yielded higher tensile strength and hardness values. Ó 1999 Elsevier Science Ltd. All rights reserved. Keywords: Molybdenum; Rhenium; Annealing behavior
1. Introduction The previous studies have clearly demonstrated the solution-softening phenomenon in Mo±Re alloys [1,2]. Small additions of rhenium had the most eect on the level of strength at high temperatures, which is apparently connected with an increase in recrystallization temperature [3]. Even though Mo±Re alloys oered higher resistance to corrosion, workability and mechanical properties [4±6], the availability of these alloys is at best limited, partly because of the very high cost and scarcity of rhenium. It is signi®cant to study the low rhenium content alloys both from a performance viewpoint and a fabrication viewpoint. The study on fabrication of Mo alloys containing low Re content fabricated by PM creates the condition for investigation of its workability [7]. The annealing behavior of Mo±3%Re alloys fabricated by PM was investigated in this study. The annealing behavior of the wires was examined with optical micrography, scanning electron microscopy, microtensile tester and microhardness tester.
2. Experimental procedure Meterials used were sintered Mo±3%Re alloy 16 16 600 mm3 bars by the dry and dry±wet mixing *
Tel.: +86-731-883-7465. E-mail address: [email protected] (Liu Sha)
methods [7]. The chemical compositions of materials used are shown in Table 1. Some properties of the specimens are shown in Table 2. The alloy bars were swaged, annealed and drawn into 0.2 mm diameter wire. Samples were carefully annealed at 900±1400°C in a dry H2 atmosphere for 35 min. Scanning electron microscopy and optical micrograph were applied to observe the wire specimens. The tensile properties and hardness of the wire specimens were examined with microtensile tester and microhardness tester.
3. Results and discussion A comparison of optical micrographs of MD-1 and MDW-2 0.28 mm diameter wire specimens is given in Fig. 1. It is observed that the MDW-2 wire specimen exhibits the ®ner grain sizes than that of MD-1 both before and after drawing. The relation between tensile strength, elongation and annealing temperature for the wire specimens in 0.20 and 0.28 mm diameters are shown in Fig. 2. It appears that the tensile strength of the wire specimens decrease in straight line with the increase of annealing temperatures at 900±1400°C. The data tend to follow the linear regression equation relation between tensile strength and annealing temperature, expressed as in Table 3. Hypothesis testing shows that all absolute values of U are larger than ta=2 n ÿ 2, which illustrates that the
0263-4368/99/$ - see front matter Ó 1999 Elsevier Science Ltd. All rights reserved. PII: S 0 2 6 3 - 4 3 6 8 ( 9 9 ) 0 0 0 2 7 - X
382
L. Sha / International Journal of Refractory Metals & Hard Materials 17 (1999) 381±384
Table 1 Chemical composition of specimens Designation
MD-1 MDW-2 a
Element content (ppm) Fe
Al, Si
Mn, Mg, Co
Ni
Ti, V
Pb, Bi, Sn, Cd
Sb, Ca
W
Ka
Na
11 15
6 6
3 3
5 6
15 15
1 1
10 10
1000 1000
250 300
20 20
The usual potassium content of commercial Mo±Re alloys amounts to 6 10 ppm.
Table 2 Some properties of specimens Designation
Density (g/cm3 )
Mean grain size (lm)a
Oxygen content (ppm)
MD-1 MDW-2
9.95 10.02
1.74 0.37
31 45
a
The grain size of the alloys was determined by Linear analysis.
Fig. 1. Optical micrographs (200´) of MD-1 (a) and MDW-2 (b) 0.28 mm diameter wire specimens.
relation between tensile strength and annealing temperature conforms to the linear regression equation at 900±1400°C. It is evident from Fig. 2 that the recrystallization temperature of MDW-2 wire specimen is higher than
Fig. 2. Tensile strength and elongation for 0.20 mm diameter (a) and 0.28 mm diameter (b) wire specimens. Annealing temperature measured in °C. , rb : MDW-2; j, rb : MD-1; M, d: MD-1; , d: MDW-2.
L. Sha / International Journal of Refractory Metals & Hard Materials 17 (1999) 381±384
383
Table 3 Linear regression equations Diameter (mm)
Designation
Linear regression equations
U
t0:025 [4]
0.20
MD-1 MDW-2
rb 2007 ÿ 0:868T rb 2351 ÿ 1:063T
12.55 5.76
2.78 2.78
0.28
MD-1 MDW-2
rb 1844 ÿ 0:761T rb 1979 ÿ 0:786T
7.14 11.23
2.78 2.78
Fig. 4. Relation between microhardness and annealing temperature for MDW-2 0.28 mm diameter wire specimen. Annealing temperature measured in °C. Fig. 3. SEM micrographs (1250´) of MDW-2 0.28 mm diameter wire specimen sections after 1000°C (a) and 1200°C (b) anneling.
that of MD-1 due to its curve of elongation lying in right side. Here it will also be noted that the elongations of the wire specimens increased signi®cantly at 1100± 1200°C owing to polygonization. It is observed from Fig. 3 that the change in grain sizes of the wire specimen section at 1200°C occurs while little or no change occurs at 1000°C. Because of the ®ner grain sizes (Hall±Petch eect). the MDW-2 wire after 1400°C annealing for 35 min still provided with higher tensile strength and hardness (as shown in Fig. 4) values, which also showed that the investigated material possessed higher recrystallization temperature probably owing to the high potassium content.
The microhardness of the MDW-2 wire specimen trend as function of annealing temperature is very similar to that of tensile behaviors, as indicated in Fig. 4. The tensile strength of MDW-2 0.65 mm diameter wire specimen is compared with pure Mo in Fig. 5. It is clear that the MDW-2 specimen oers higher tensile than that of pure Mo at 900±1400°C.
4. Conclusion The Mo±3% Re alloy bars with good workability could be fabricated to 0.20 mm diameter ®ne wire. The sintered Mo±3% Re alloy wire specimen produced by the dry±wet mixing method exhibit higher tensile strength and recrystallization temperature as compared
384
L. Sha / International Journal of Refractory Metals & Hard Materials 17 (1999) 381±384
with that of pure Mo and Mo±3%Re alloy fabricated by the dry mixing method. The Mo±3%Re alloy wires after 1400°C annealing for 35 min still oers higher hardness and tensile strength values.
References [1] Stephens JR, Witzke WR. J Less-Common Metals 1971;23:325±42. [2] Lundberg LB, Ohriner EK, Tuominen SM, Whelan EP, Shields Jr JA. Solution softening in Mo±Re alloy. In: Proceedings of the Symposium on Physical Metallurgy and Technology of Molybdenum and its Alloys. 1985:71±79. [3] Abramyan AV, Morgunova NN, Golovanenko SA, Kazakova NI. Mechanical properties of Mo±Re alloys at dierent test temperatures. [Trans., Metallovedenie i Termicheskaya Obrabotka Metallov, 1988;3:50±53]. [4] Igata N, Kohyama A. J Nucl Mater 1981;103 & 104:409±14. [5] Japanese Patent, 38540, 1983 [in Japanese]. [6] Lundburg LB. Los Alamos Scienti®c Laboratory Report LA-8685MS, 1981. [7] Sha L. Int J Refract Metals & Hard Materials 1997;15:219±22.
Fig. 5. Relation between tensile strength and annealing temperature for pure Mo and MDW-2 0.65 mm diameter wire specimen. Annealing temperature measured in °C.