Substructure And Mechanical Properties Of Refractory Metals
Report Number: WADD TR 61-181 Part II
Author(s): Lement, B.S., Weismann, S., Owen, W. S., Hirsch, P. B., Thomas, D.A.
Corporate Author(s): Manufacturing Laboratories, Inc.
Laboratory: Directorate of Materials and Processes
Date of Publication: 1962-10
Pages: 293
Contract: AF 33(616)-6838
DoD Project: 7351 - Metallic Materials
DoD Task: 735101
Identifier: AD0290691
Abstract:
Considerable progress has been made by the five research participants in elucidating the relation of substructure to the mechanical properties of tungsten, molybdenum, tantalum and columbium. ManLabs has show that during recovery of heavily deformed tungsten wire there is an initial increase in hardness accompanied by increased delineation of etch-pit subboundaries, which may be associated with segregation of interstitials to dislocations. Micro-twinning, which is indicated by a decrease in the effective particle size as determined by x-ray line shape analysis may also contribute to the initial hardening. The sharp drop in room temperature ductility on annealing above about 1100°C was correlated with the rise of the transition temperature (Td) above room with annealing temperature, it appears that the rise of temperature. Since the crack propagation energy as calculated by the Cotrell-Petch equation does not change appreciably with annealing temperature, it appears that the rise of Td is mainly due to the increase in width of the fibrous grains. Microstructural observations and x-ray diffraction particle size determinations were also made of substructure in molybdenum, tantalum, and columbium. M.I.T has shown by transmission electron microscopy of thin films that competing processes of polygonization and strain induced fiber boundary migration occur on annealing 30-mil tungsten wire up to 1400°C. The texture of tungsten sheet was found to sharpen on recovery-annealing which is attributable to subgrain growth. Determination of textural and microstructural changes during drawing of columbium wire has provided further confirmation of the proposed mechanism of formation of ribbon-like grains in b.c.c. metals which involves restricted slip at high deformations. Measurements made on iron-3.19% silicon indicate that most of the changes in mehanical properties occur during recovery rather than the recrystallization stage.Rutgers has shown by transmission electron microscopy of thin films of plastically deformed tantalum that the following substructural phenomena occur: a) dislocation pinning by superjogs, b) isolated dislocation loops left behind as debris of moving dislocations, and c) dislocation entanglement to form cells. The tangles appear to be formed by the interactions of dislocations moving on different slip systems. Quantitative strain analyses of tantalum single crystals were carried out using the x-ray back reflection divergent beam method. The maximum principal strain was found to change from positive to negative values as deformation in compression is carrie out below and above the upper yield point respectively. This indicates that extensive slip occurs on many systems and results in increased complexity of dislocation tangles. In the case of molybdenum single crystals, the low ductility relative to tantalum is partly attributed to restriction of slip to a limited number of active planes.Liverpool has shown that a variety of dsilocation densities and arrangements can be formed in tantalum by annealing. In a narrow annealing range above the recrystallization temperature, <111>/<100> dislocation network subboundaries are formed; at high te,peratures a low density of random dislocations is observed. The aging of tantulum containing oxygen, nitrogen and carbon can be divided into three stages: a) Snoek-ordering of interstitials in the strain field of the dislocation resulting in an increase in the difficulty of slip propagation, b) long-range diffusion of interstitials to dislocations giving weak locking, and c) strong temperature-independent locking of dislocations. The binding eergy, as determined by quenching experiments, is about 0.53 e.v. OIf the total interstitial content is low (less than about 50 ppm), the locking parameter increases as the dislocation density is decreased by annealing at higher temperatures; for higher contents, the dislocations are apparently saturated at all annealing temperatures and ky is unaffected. The stress for slip propagation (δi) can be altered by changes in substruture and interstitial content but the effect is small. All the yield data can be explained satisfactorily by a modified Cottrell-Petch theory in which it is assumed that the necessary local stress concentration is achieved near the tip of a slip band blocked at a grain boundary. Transmission elctron-microgaphic evidence of the latter process has been obtaine. The condition that iunstable plastic flow (necking) occurs before the heterogeneous Luders strain is complete has been derived in terms of the strain-hardening exponent (n) and the yield parameters (ky and δi). The effects of metallurgical variables such as grain size, substructure and strain-aging on the plastic-instability transition temperature for impure tantalum have been assessed quantitatively. Down to the last 77°K, no cleavage fracture has been found in polycrystalline tantalum; however, {100} cleavage occurs in suitably oriented single crystals at 195°K.Cambridge has found that the activation energy for the annealing-out of dislocation lops in columbium and tantalum, as observed by transmission electron microscopy of thin films, corresponds to 3.0 ± 0.5 e.v. This relatively low value suggests that the recovery process may invlove pipe-diffusion instead of volume-diffusion as generally assumed for the process of dislocation climb.
Provenance: Lockheed Martin Missiles & Fire Control
Author(s): Lement, B.S., Weismann, S., Owen, W. S., Hirsch, P. B., Thomas, D.A.
Corporate Author(s): Manufacturing Laboratories, Inc.
Laboratory: Directorate of Materials and Processes
Date of Publication: 1962-10
Pages: 293
Contract: AF 33(616)-6838
DoD Project: 7351 - Metallic Materials
DoD Task: 735101
Identifier: AD0290691
Abstract:
Considerable progress has been made by the five research participants in elucidating the relation of substructure to the mechanical properties of tungsten, molybdenum, tantalum and columbium. ManLabs has show that during recovery of heavily deformed tungsten wire there is an initial increase in hardness accompanied by increased delineation of etch-pit subboundaries, which may be associated with segregation of interstitials to dislocations. Micro-twinning, which is indicated by a decrease in the effective particle size as determined by x-ray line shape analysis may also contribute to the initial hardening. The sharp drop in room temperature ductility on annealing above about 1100°C was correlated with the rise of the transition temperature (Td) above room with annealing temperature, it appears that the rise of temperature. Since the crack propagation energy as calculated by the Cotrell-Petch equation does not change appreciably with annealing temperature, it appears that the rise of Td is mainly due to the increase in width of the fibrous grains. Microstructural observations and x-ray diffraction particle size determinations were also made of substructure in molybdenum, tantalum, and columbium. M.I.T has shown by transmission electron microscopy of thin films that competing processes of polygonization and strain induced fiber boundary migration occur on annealing 30-mil tungsten wire up to 1400°C. The texture of tungsten sheet was found to sharpen on recovery-annealing which is attributable to subgrain growth. Determination of textural and microstructural changes during drawing of columbium wire has provided further confirmation of the proposed mechanism of formation of ribbon-like grains in b.c.c. metals which involves restricted slip at high deformations. Measurements made on iron-3.19% silicon indicate that most of the changes in mehanical properties occur during recovery rather than the recrystallization stage.Rutgers has shown by transmission electron microscopy of thin films of plastically deformed tantalum that the following substructural phenomena occur: a) dislocation pinning by superjogs, b) isolated dislocation loops left behind as debris of moving dislocations, and c) dislocation entanglement to form cells. The tangles appear to be formed by the interactions of dislocations moving on different slip systems. Quantitative strain analyses of tantalum single crystals were carried out using the x-ray back reflection divergent beam method. The maximum principal strain was found to change from positive to negative values as deformation in compression is carrie out below and above the upper yield point respectively. This indicates that extensive slip occurs on many systems and results in increased complexity of dislocation tangles. In the case of molybdenum single crystals, the low ductility relative to tantalum is partly attributed to restriction of slip to a limited number of active planes.Liverpool has shown that a variety of dsilocation densities and arrangements can be formed in tantalum by annealing. In a narrow annealing range above the recrystallization temperature, <111>/<100> dislocation network subboundaries are formed; at high te,peratures a low density of random dislocations is observed. The aging of tantulum containing oxygen, nitrogen and carbon can be divided into three stages: a) Snoek-ordering of interstitials in the strain field of the dislocation resulting in an increase in the difficulty of slip propagation, b) long-range diffusion of interstitials to dislocations giving weak locking, and c) strong temperature-independent locking of dislocations. The binding eergy, as determined by quenching experiments, is about 0.53 e.v. OIf the total interstitial content is low (less than about 50 ppm), the locking parameter increases as the dislocation density is decreased by annealing at higher temperatures; for higher contents, the dislocations are apparently saturated at all annealing temperatures and ky is unaffected. The stress for slip propagation (δi) can be altered by changes in substruture and interstitial content but the effect is small. All the yield data can be explained satisfactorily by a modified Cottrell-Petch theory in which it is assumed that the necessary local stress concentration is achieved near the tip of a slip band blocked at a grain boundary. Transmission elctron-microgaphic evidence of the latter process has been obtaine. The condition that iunstable plastic flow (necking) occurs before the heterogeneous Luders strain is complete has been derived in terms of the strain-hardening exponent (n) and the yield parameters (ky and δi). The effects of metallurgical variables such as grain size, substructure and strain-aging on the plastic-instability transition temperature for impure tantalum have been assessed quantitatively. Down to the last 77°K, no cleavage fracture has been found in polycrystalline tantalum; however, {100} cleavage occurs in suitably oriented single crystals at 195°K.Cambridge has found that the activation energy for the annealing-out of dislocation lops in columbium and tantalum, as observed by transmission electron microscopy of thin films, corresponds to 3.0 ± 0.5 e.v. This relatively low value suggests that the recovery process may invlove pipe-diffusion instead of volume-diffusion as generally assumed for the process of dislocation climb.
Provenance: Lockheed Martin Missiles & Fire Control