Acta MetallurgicaPub Date : 1989-12-01Epub Date: 2003-06-11DOI: 10.1016/0001-6160(89)90204-6
K.P.D. Lagerlöf, T.E. Mitchell , A.H. Heuer
{"title":"Energetics of the break-up of dislocation dipoles into prismatic loops","authors":"K.P.D. Lagerlöf, T.E. Mitchell , A.H. Heuer","doi":"10.1016/0001-6160(89)90204-6","DOIUrl":"10.1016/0001-6160(89)90204-6","url":null,"abstract":"<div><p>The energetics of two different models leading to the formation of a row of prismatic loops from the fluctuation and subsequent break-up of dislocation dipoles or elongated dislocation loops have been evaluated as a function of fluctuation amplitude and wavelength. Break-up most likely occurs by spontaneous pinching off of small circular loops at the ends of closed-ended dipoles or elongated loops. The theoretical results agree well with experimental observations of the dislocation substructure in Ti<sup>4+</sup>-doped sapphire (α-Al<sub>2</sub>O<sub>3</sub>) deformed by basal slip.</p></div>","PeriodicalId":6969,"journal":{"name":"Acta Metallurgica","volume":"37 12","pages":"Pages 3315-3325"},"PeriodicalIF":0.0,"publicationDate":"1989-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0001-6160(89)90204-6","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81147638","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Acta MetallurgicaPub Date : 1989-12-01Epub Date: 2003-06-11DOI: 10.1016/0001-6160(89)90185-5
P.H. Leo , R.F. Sekerka
{"title":"The effect of elastic fields on the morphological stability of a precipitate grown from solid solution","authors":"P.H. Leo , R.F. Sekerka","doi":"10.1016/0001-6160(89)90185-5","DOIUrl":"10.1016/0001-6160(89)90185-5","url":null,"abstract":"<div><p>A system that consists of a misfit precipitate transforming from an infinite matrix is analyzed to determine the effect of elastic fields on a morphological stability analysis. Elastic fields enter the analysis through the boundary condition that sets the solute concentration at the interphase interface. Elastic fields influence the stability results when the shear modulus of the precipitate is different from that of the matrix; they act to stabilize the interface and favor spherical growth shapes if the shear modulus of the precipitate is greater than that of the matrix, and to destabilize the interface and favor non-spherical growth shapes in the alternative case. These elastic effects are especially pronounced at small supersaturations. For the case of a hard precipitate growing in a soft matrix, elastic fields can, at small supersaturations, absolutely stabilize the interface against any given perturbation wavelength. In the absence of capillarity, elastic fields spoil the shape preserving growth of an ellipsoidal precipitate, a solution found by Ham when both capillarity and elastic fields vanish. When a precipitate is undergoing unstable growth, elastic fields shift the value of the fastest growing harmonic such that stabilizing elastic fields favor long wavelength perturbations and relatively smooth growth shapes, while destabilizing elastic fields favor short wavelength perturbations and relatively rough growth shapes.</p></div>","PeriodicalId":6969,"journal":{"name":"Acta Metallurgica","volume":"37 12","pages":"Pages 3139-3149"},"PeriodicalIF":0.0,"publicationDate":"1989-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0001-6160(89)90185-5","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86571051","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Acta MetallurgicaPub Date : 1989-12-01Epub Date: 2003-06-11DOI: 10.1016/0001-6160(89)90199-5
Z.S. Basinski, S.J. Basinski
{"title":"Copper single crystal PSB morphology between 4.2 and 350 K","authors":"Z.S. Basinski, S.J. Basinski","doi":"10.1016/0001-6160(89)90199-5","DOIUrl":"10.1016/0001-6160(89)90199-5","url":null,"abstract":"<div><p>For fatigue at temperatures from 4.2 to 350 K, crystals in saturation comprise PSB and matrix regions, however, details of PSB morphology are temperature-dependent. There are three main types of profile. Type I: at very low temperatrures, mildly bulged PSBs comprising smooth extrusions. Type II: from ≈15 to ≈250 K, triangular bulges reaching > 10 μm in height. Type III: above 300 K, non-bulged PSBs comprising both intrusions and extrusions. Transition regions with PSBs of mixed character are found between the distinct types. Room temperature is near the end of a transition region, PSB morphology therefore depends on fatigue conditions. PSB profile development is independent of fatigue environment; crack propagation is environment dependent. There is no correlation betwen PSB morphology and point defect mobility.</p></div>","PeriodicalId":6969,"journal":{"name":"Acta Metallurgica","volume":"37 12","pages":"Pages 3263-3273"},"PeriodicalIF":0.0,"publicationDate":"1989-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0001-6160(89)90199-5","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85887134","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Acta MetallurgicaPub Date : 1989-12-01Epub Date: 2003-06-11DOI: 10.1016/0001-6160(89)90196-X
P. Fratzl , J.L. Lebowitz
{"title":"Universality of scaled structure functions in quenched systems undergoing phase separation","authors":"P. Fratzl , J.L. Lebowitz","doi":"10.1016/0001-6160(89)90196-X","DOIUrl":"10.1016/0001-6160(89)90196-X","url":null,"abstract":"<div><p>We present a novel heuristic “universal” formula for the scaled structure function following a quench into the miscibility gap which gives very good fits to a variety of experimental observations. The single adjustable parameter γ needed to fit data for alloys, binary fluids, polymer mixtures and computer simulation curves depends essentially only on the fraction of the volume of the minority phase. Minimizing the ratio of “surface area to volume” of the minority phase predicts a rough morphology of the system—its local character changes from spherical isolated droplets to interconnected plate-like objects as the minority fraction increases. By relating γ to this microstructure we obtain the value of γ correctly to within 10%.</p></div>","PeriodicalId":6969,"journal":{"name":"Acta Metallurgica","volume":"37 12","pages":"Pages 3245-3248"},"PeriodicalIF":0.0,"publicationDate":"1989-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0001-6160(89)90196-X","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88583467","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Acta MetallurgicaPub Date : 1989-12-01Epub Date: 2003-06-11DOI: 10.1016/0001-6160(89)90193-4
D. Kuhlmann-Wilsdorf
{"title":"Dynamic effects in the mesh length theory of workhardening","authors":"D. Kuhlmann-Wilsdorf","doi":"10.1016/0001-6160(89)90193-4","DOIUrl":"10.1016/0001-6160(89)90193-4","url":null,"abstract":"<div><p>According to the mesh length theory of workhardening, low-temperature strain rate effects in materials exhibiting a dislocation cell structure are due to the simultaneous operation of a number <em>X</em> of super-critically bowing links in the average, typically roughly equiaxed, cell of diameter <em>L</em>. The corresponding length of mobile dislocations per cell is then <em>LX</em>. Defining <span><math><mtext>g = </mtext><mtext>L</mtext><mtext>l</mtext><mtext>̄</mtext></math></span>, with <span><math><mtext>l</mtext><mtext>̄</mtext></math></span> the average link length in the cell walls, dislocation cell breakdown is expected for <em>X</em><sub><em>max</em></sub> ≈ 0.3 <em>g</em><sup>2</sup>, on the criterion that at the most 50% of all cell wall dislocations may be simultaneously destabilized and therefore at most 10% of all possible dislocation sources may be activated simultaneously since each destabilizes four adjoining links besides itself. When <em>X</em> = <em>X</em><sub><em>max</em></sub>, the mobile dislocation density within the cells is about 30% of that in the walls, but significant interactions and thus extra hardening is expected only if the dislocation density in the cell interiors is about sixteen times the cell wall dislocation density. Therefore the mobile dislocations can add little, if anything, to the permanent strain hardening. However, on account of the decrease of average source length with increasing <em>X</em> a transient increase of flow stress and workhardening coefficient arises which typically amounts to a few percent per ten-fold increase of strain rate. Mobile dislocations remaining in the cell interiors decrease the elastic modulus and can give rise to anelastic creep as well as to recovery effects. Numerical estimates are in good agreement with observations.</p></div>","PeriodicalId":6969,"journal":{"name":"Acta Metallurgica","volume":"37 12","pages":"Pages 3217-3223"},"PeriodicalIF":0.0,"publicationDate":"1989-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0001-6160(89)90193-4","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78558862","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Acta MetallurgicaPub Date : 1989-12-01Epub Date: 2003-06-11DOI: 10.1016/0001-6160(89)90202-2
D.M. Stump, B. Budiansky
{"title":"Finite cracks in transformation-toughened ceramics","authors":"D.M. Stump, B. Budiansky","doi":"10.1016/0001-6160(89)90202-2","DOIUrl":"10.1016/0001-6160(89)90202-2","url":null,"abstract":"<div><p>The dependence of the tensile fracture stress on crack length in dilatationally phase-transforming ceramics is studied by modeling the evolution of the transformed regions around the tips of finite cracks during crack growth. The presence of the transformation is found to reduce the stress required for crack-growth <em>initiation</em>. However, the peak, or “ultimate”, tensile stress is found to occur during subsequent crack growth, and the <em>transformation-strengthening</em>, that is, the increase of tensile strength due to phase transformation, is found as a function of initial crack size.</p></div>","PeriodicalId":6969,"journal":{"name":"Acta Metallurgica","volume":"37 12","pages":"Pages 3297-3304"},"PeriodicalIF":0.0,"publicationDate":"1989-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0001-6160(89)90202-2","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73892777","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Acta MetallurgicaPub Date : 1989-12-01Epub Date: 2003-06-11DOI: 10.1016/0001-6160(89)90208-3
F. Stobiecki
{"title":"Reactive diffusion in amorphous Fe-B and Co-Zr multilayer films","authors":"F. Stobiecki","doi":"10.1016/0001-6160(89)90208-3","DOIUrl":"10.1016/0001-6160(89)90208-3","url":null,"abstract":"<div><p>The diffusion in <span><math><mtext>Fe</mtext><msub><mi></mi><mn>1−x</mn></msub><mtext>B</mtext><msub><mi></mi><mn>x</mn></msub><mtext>Fe</mtext><msub><mi></mi><mn>1−y</mn></msub><mtext>B</mtext><msub><mi></mi><mn>y</mn></msub></math></span> and <span><math><mtext>Co</mtext><msub><mi></mi><mn>1−x</mn></msub><mtext>Zr</mtext><msub><mi></mi><mn>x</mn></msub><mtext>Co</mtext><msub><mi></mi><mn>1−y</mn></msub><mtext>Zr</mtext><msub><mi></mi><mn>y</mn></msub></math></span> amorphous bi- and multilayers was investigated. The dependence of the diffusion coefficient on concentration was observed. This effect was explained taking into account the concentration dependence of mixing enthalpy correlated with chemical short range order in amorphous state.</p></div>","PeriodicalId":6969,"journal":{"name":"Acta Metallurgica","volume":"37 12","pages":"Pages 3361-3366"},"PeriodicalIF":0.0,"publicationDate":"1989-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0001-6160(89)90208-3","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79179864","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Acta MetallurgicaPub Date : 1989-12-01Epub Date: 2003-06-11DOI: 10.1016/0001-6160(89)90214-9
T. Takasugi, S. Watanabe, O. Izumi, N.K. Fat-Halla
{"title":"Plastic flow of Ni3(Si,Ti) Single crystals","authors":"T. Takasugi, S. Watanabe, O. Izumi, N.K. Fat-Halla","doi":"10.1016/0001-6160(89)90214-9","DOIUrl":"10.1016/0001-6160(89)90214-9","url":null,"abstract":"<div><p>The flow stress of L1<sub>2</sub>-type Ni<sub>3</sub>(Si, Ti) by the compression test was measured as a function of temperature, strain rate, orientation and alloy composition. The critical resolved shear stress (CRSS) increased from 77 K, reached a peak, and then decreased rapidly with increasing temperature. The single crystals with orientations close to [011] and [1&#x0304;11] showed the operations of octahedral slips (111) [1&#x0304;01] below the peak temperature and of cube slips (001) [1&#x0304;10] above the peak temperature, whereas those with orientation close to [001] showed the operations of octahedral slips {111} over the entire temperatures. The CRSS depended on the orientation and alloy composition below the peak temperature but on the orientation and the strain rate above the peak temperature. The peak temperature was dependent on the orientation but almost independent of the strain rate and alloy composition. It is suggested that the deformation mechanisms for Ni<sub>3</sub>(Si, Ti) single crystals are quite similar to those for other Ni-based L1<sub>2</sub> single crystals such as Ni<sub>3</sub>Al, Ni<sub>3</sub>Ga and Ni<sub>3</sub>Ge; at low temperatures the dislocation movement of the superpartials dissociated on (111) plane with APB became sessile by micro cross slip to (001) plane. At high temperatures, two deformation modes were operative, depending on the orientation. The deformation of the single crystals with orientations far from [001] is due to the Peierls-Nabarro mechanism of (001) [1&#x0304;10] slip, whereas the deformation of the single crystals with orientations close to [001] is due to the intrusion of the “diffusive” process of (111) [1&#x0304;01] slip.</p></div>","PeriodicalId":6969,"journal":{"name":"Acta Metallurgica","volume":"37 12","pages":"Pages 3425-3436"},"PeriodicalIF":0.0,"publicationDate":"1989-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0001-6160(89)90214-9","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90462461","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Acta MetallurgicaPub Date : 1989-12-01Epub Date: 2003-06-11DOI: 10.1016/0001-6160(89)90194-6
G. Eggeler
{"title":"The effect of long-term creep on particle coarsening in tempered martensite ferritic steels","authors":"G. Eggeler","doi":"10.1016/0001-6160(89)90194-6","DOIUrl":"10.1016/0001-6160(89)90194-6","url":null,"abstract":"<div><p>The high creep strength of tempered martensite ferritic steels results from the presence of a dislocation network of subgrain boundaries (SGBs) which is stabilized by carbides. In these microstructures creep accelerated particle coarsening is observed at creep rates of the order of 10<sup>−10</sup> s<sup>−1</sup> (long-term creep). The microstructural explanations presented in this study, are based on the close contact between particles and SGBs: </p><ul><li><span>1.</span><span><p>(i) the difference in the thermodynamic potential on SGBs perpendicular and parallel to the stress axis results in short range pipe diffusion fluxes over distances of the order of the mean subgrain size (0.5 μm) which are not enforced during stress free ageing;</p></span></li><li><span>2.</span><span><p>(ii) at high temperatures, recovery processes can result in a decrease of the dislocation density within SGBs, which results in a decrease of pipe diffusion along SGBs. In the presence of a stress higher dislocation densities in SGBs (higher pipe diffusion fluxes) can be maintained than without stress (ageing);</p></span></li><li><span>3.</span><span><p>(iii) during primary creep carbides interrupt “knitting” reactions between “free” dislocations and SGBs. As a result carbides “come in contact” with additional pipe diffusion paths (pinned dislocations). At low stresses the “pinned” dislocations stay in contact with the “pinning” carbides throughout the creep life. These “additional” matrix/carbide pipe diffusion paths do not form during ageing (absence of primary creep). All three effects can contribute to “creep accelerated particle coarsening” in tempered martensite ferritic steels.</p></span></li></ul></div>","PeriodicalId":6969,"journal":{"name":"Acta Metallurgica","volume":"37 12","pages":"Pages 3225-3234"},"PeriodicalIF":0.0,"publicationDate":"1989-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0001-6160(89)90194-6","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84818920","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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