Superplasticity and anelasticity in fine-grained Sn-Pb alloys
<p>Mechanisms which may play a role in superplastic deformation (grain strain mechanisms, grain boundary sliding (GBS) mechanisms) are reviewed. Two well-known lattice dislocation mechanisms are re-evaluated for grain boundary dislocations (GBDs). The manner in which the deformation mechanism...
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| Format: | Thesis |
| Language: | English |
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1979
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| _version_ | 1817931922807980032 |
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| author | Schneibel, J Joachim H. Schneibel |
| author2 | Hazzledine, P |
| author_facet | Hazzledine, P Schneibel, J Joachim H. Schneibel |
| author_sort | Schneibel, J |
| collection | OXFORD |
| description | <p>Mechanisms which may play a role in superplastic deformation (grain strain mechanisms, grain boundary sliding (GBS) mechanisms) are reviewed. Two well-known lattice dislocation mechanisms are re-evaluated for grain boundary dislocations (GBDs). The manner in which the deformation mechanisms interact, or are inhibited or obscured, is discussed.</p> <p>Mechanisms of anelastic deformation are outlined, with particular reference to fine-grained materials. Expressions for anelastic recovery caused either by grain boundary (GB) tension or by the relaxation of GBD pile-ups are derived. The plastic properties of Sn-38.1w/o Pb and Sn-2w/o Pb are measured. They are similar in both alloys. No threshold stress for plastic deformation is detected, for stresses and strain rates as low as 0.IMPa and 10<sup>-10</sup>s<sup>-1</sup> respectively. The presence of GB diffusion creep (Coble creep) is established experimentally in Sn-2w/o Pb with grain sizes ≥ 50μm. Coble creep is inhibited for small grain sizes (~10μm). The inhibition is explained by GBS caused by GBDs. In disagreement with the measurements, high threshold stresses are predicted for Sn-38.1w/o Pb. This implies that GBD line tensions are lower than those of lattice dislocations.</p> <p>The anelastic properties of Sn-2w/o Pb and Sn-38.1w/o Pb are determined from the elastic after-effect (anelastic recovery after unloading). They are remarkable: anelastic contractions larger than 0.2% and relaxation strengths (= ratio of anelastically recovered to elastically recovered strain) in excess of 100 are found. The anelastic strains are approximately proportional to the stress and the inverse grain size. A wide range of relaxation times (~ 6 decades) is observed.</p> <p>A mechanism based on the relaxation of GBD pile-ups is in qualitative agreement with the measured anelasticity. The high measured relaxation strengths, however, imply that the interaction between GBDs is much weaker (~ 2 orders of magnitude) than that between lattice dislocations. This could be due to a relatively low self-energy of GBDs and would be in qualitative agreement with the low GBD line tensions suggested above.</p> <p>The influence of anelasticity on transients (e.g. stress relaxation, dip test) is investigated using a rheological model with three Voigt elements (anelasticity) and a nonlinear dashpot (plasticity). Using independently determined plastic and anelastic parameters the 4-th order differential equa tion corresponding to the model is solved numerically for several examples. Measured transients are much more accurately predicted with the present model than with models neglecting anelasticity.</p> |
| first_indexed | 2024-03-06T18:47:52Z |
| format | Thesis |
| id | oxford-uuid:0f2594f3-63e6-488d-bdd1-76c1351ff3d6 |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-12-09T03:29:43Z |
| publishDate | 1979 |
| record_format | dspace |
| spelling | oxford-uuid:0f2594f3-63e6-488d-bdd1-76c1351ff3d62024-12-01T12:26:51ZSuperplasticity and anelasticity in fine-grained Sn-Pb alloysThesishttp://purl.org/coar/resource_type/c_db06uuid:0f2594f3-63e6-488d-bdd1-76c1351ff3d6SuperplasticityLead-tin alloysEnglishPolonsky Theses Digitisation Project1979Schneibel, JJoachim H. SchneibelHazzledine, PHazzledine, P<p>Mechanisms which may play a role in superplastic deformation (grain strain mechanisms, grain boundary sliding (GBS) mechanisms) are reviewed. Two well-known lattice dislocation mechanisms are re-evaluated for grain boundary dislocations (GBDs). The manner in which the deformation mechanisms interact, or are inhibited or obscured, is discussed.</p> <p>Mechanisms of anelastic deformation are outlined, with particular reference to fine-grained materials. Expressions for anelastic recovery caused either by grain boundary (GB) tension or by the relaxation of GBD pile-ups are derived. The plastic properties of Sn-38.1w/o Pb and Sn-2w/o Pb are measured. They are similar in both alloys. No threshold stress for plastic deformation is detected, for stresses and strain rates as low as 0.IMPa and 10<sup>-10</sup>s<sup>-1</sup> respectively. The presence of GB diffusion creep (Coble creep) is established experimentally in Sn-2w/o Pb with grain sizes ≥ 50μm. Coble creep is inhibited for small grain sizes (~10μm). The inhibition is explained by GBS caused by GBDs. In disagreement with the measurements, high threshold stresses are predicted for Sn-38.1w/o Pb. This implies that GBD line tensions are lower than those of lattice dislocations.</p> <p>The anelastic properties of Sn-2w/o Pb and Sn-38.1w/o Pb are determined from the elastic after-effect (anelastic recovery after unloading). They are remarkable: anelastic contractions larger than 0.2% and relaxation strengths (= ratio of anelastically recovered to elastically recovered strain) in excess of 100 are found. The anelastic strains are approximately proportional to the stress and the inverse grain size. A wide range of relaxation times (~ 6 decades) is observed.</p> <p>A mechanism based on the relaxation of GBD pile-ups is in qualitative agreement with the measured anelasticity. The high measured relaxation strengths, however, imply that the interaction between GBDs is much weaker (~ 2 orders of magnitude) than that between lattice dislocations. This could be due to a relatively low self-energy of GBDs and would be in qualitative agreement with the low GBD line tensions suggested above.</p> <p>The influence of anelasticity on transients (e.g. stress relaxation, dip test) is investigated using a rheological model with three Voigt elements (anelasticity) and a nonlinear dashpot (plasticity). Using independently determined plastic and anelastic parameters the 4-th order differential equa tion corresponding to the model is solved numerically for several examples. Measured transients are much more accurately predicted with the present model than with models neglecting anelasticity.</p> |
| spellingShingle | Superplasticity Lead-tin alloys Schneibel, J Joachim H. Schneibel Superplasticity and anelasticity in fine-grained Sn-Pb alloys |
| title | Superplasticity and anelasticity in fine-grained Sn-Pb alloys |
| title_full | Superplasticity and anelasticity in fine-grained Sn-Pb alloys |
| title_fullStr | Superplasticity and anelasticity in fine-grained Sn-Pb alloys |
| title_full_unstemmed | Superplasticity and anelasticity in fine-grained Sn-Pb alloys |
| title_short | Superplasticity and anelasticity in fine-grained Sn-Pb alloys |
| title_sort | superplasticity and anelasticity in fine grained sn pb alloys |
| topic | Superplasticity Lead-tin alloys |
| work_keys_str_mv | AT schneibelj superplasticityandanelasticityinfinegrainedsnpballoys AT joachimhschneibel superplasticityandanelasticityinfinegrainedsnpballoys |