The deformation mechanisms of superplasticity

Hayden, Howard C.; Floreen, S.; Goodell, Paul Douglas.

doi:10.1007/bf02647657

Cited by 139 publications

(40 citation statements)

References 13 publications

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“…This value is comparable with the activation energy for GBD of Fe, Cr and Ni in Fe-Cr-Ni stainless steels. In contrast, the activation energies for superplastic deformation in similar alloys were reported earlier by others 47,48 to be comparable with the activation energy for lattice diffusion when no prior straining was employed. (3) In a few studies, where investigations were made over a wider range of temperatures, two values of activation energy for superplastic deformation were reported.…”

Section: Diffusionsupporting

confidence: 54%

Interfacial phenomena and microstructural evolution during superplastic deformation

Kashyap

2001

Surface & Interface Analysis

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Certain polycrystalline materials of fine equiaxed grains of size <10 µm exhibit tensile ductility of several hundred to a few thousand per cent, called superplasticity, at intermediate strain rates and high temperatures. Experimental and theoretical results on mechanisms for superplastic deformation and concurrent microstructural evolution are reviewed to understand the role of grain boundary phenomena towards enhancement of grain growth and cavitation, etc. Grain boundary sliding (GBS) dominates superplastic flow, the extent of which varies between the grain and interphase boundaries in twophase alloys. Accommodation to GBS is provided by diffusional and dislocation mechanisms, which are manifested in the form of grain boundary migration (GBM), grain rotation and grain switching events. Although GBS helps in retaining the initial equiaxed grain shape of superplastic materials, the accommodation processes accelerate grain growth. In the lack of other accommodation processes the cavities are formed, being more pronounced at the boundaries of maximum sliding. The ppm-level impurities present in superplastic materials do not influence the sliding and flow characteristics under typical superplastic conditions but they do promote cavitation and limit the ductility. The presence of precipitate or hard particles in quasi-single-phase superplastic materials inhibits GBM but provides sites for cavitation. Such materials exhibit more dislocation activities than anticipated for accommodation of GBS. The nature of microstructural changes noted during superplastic deformation supports the operation of cooperative GBS, in addition to a large variety of combinations between sliding and accommodation processes.

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Section: Diffusionsupporting

confidence: 54%

Interfacial phenomena and microstructural evolution during superplastic deformation

Kashyap

2001

Surface & Interface Analysis

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“…T = 563 K for eutectoid and 603 K for the eutectic), the vo]ume diffusion coefficient for the eutcctoid al]oy (Dvo])T=563 K = 6• 10 -l~ cm2/s, whi]e for the eutectic alloy (Dvol)r=60 ~ K = 7 • 10-i~ cm2/s. Ir is elear that the presently calculated va]ues of diffusivity ranging from 2 X 10-~ to 6 X 10-i~ cm2/s, for both alloys agreed well with the previously reported values [26]. It might thus be concluded that volume diffusion forros a]so one of the dominating creep processes in temperaturc regions around that of apparent strain tate peaks.…”

Section: Role Of Diffusionsupporting

confidence: 79%

Effect of transformation on the steady creep characteristics of Zn−Al alloys

1981

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Apparent steady state creep of eutectoid and eutectic Zn--A1 alloys was studied under different cortstant stresses ranging from 0--20 MPa near the eutectoid transformation temperatures.The strain tate sensitivity parameter m amounted to 0.50• at the apparent maximum strain tate peaks. The energy activating the apparent steady state creep, determined in the vicinity of these peaks, amounted to (1.0i0.07) • 10-22 KJ/atom characterizing dislocation climb along the grain boundaries, thus causing boundary sliding and migration of the dissolved grains into new grains of an (Al)2 phase.Microstructural analysis confirmed that the afore-mentioned mechanism took place during apparent steady state transformation creep.

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“…Like other alpha titanium alloys, Ti-5Al-2.5Sn alloy cannot be age hardened, and hence it is highly weldable. Superplastic forming (SPF) has been developed to simplify complicated assembly structures, allowing the manufacturing of complex shaped structural component [2][3][4]. It also offers dramatic cost and weight savings over other conventional manufacturing processes [5].…”

Section: Introductionmentioning

confidence: 99%