The increase of impact strength of ultrafine grained nickel after ultrasonic treatment

Samigullina, A. A.; Mulyukov, R. R.; Назаров, А. А.; Mukhametgalina, A. A.; Tsarenko, Yu. V.; Рубаник, В. В.

doi:10.22226/2410-3535-2014-1-52-54

Cited by 16 publications

(6 citation statements)

References 8 publications

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“…В работах [13,14] была иссле-дована зависимость механических свойств никеля, под-вергнутого равноканальному угловому прессованию, от амплитуды ультразвука. Было показано, что эта за-висимость является немонотонной, и существует опти-мальное значение амплитуды ультразвука, при котором и предел прочности, и удлинение до разрушения дости-гают максимума.…”

Section: Introductionunclassified

Effect of ultrasonic treatment on the structure and microhardness of ultrafine grained nickel processed by high pressure torsion

Mukhametgalina¹,

Samigullina²,

Sergeyev³

et al. 2017

LoM

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Effect of ultrasonic treatment (UST) on the microstructure and microhardness of ultrafine grained nickel processed by high pressure torsion (HPT) was studied. With this aim, samples after HPT were subjected to oscillating compression-tension stresses with amplitudes 15, 30, 45, 60 and 90 MPa in the zone of strain antinode of an ultrasonic instrument. The microstructure of initial and ultrasonically treated samples was studied by X-ray diffraction analysis, transmission electron microscopy and electron back-scatter diffraction (EBSD). Dependences of average dislocation density, internal strains and microhardness on the ultrasound amplitude were obtained. At lower amplitudes (15, 30 MPa) UST leads to some increase of microhardness, internal stresses and dislocation density. At amplitude 60 MPa a considerable reduction of all mentioned characteristics as compared to the initial state occurs, while with a further increase of the amplitude to 90 MPa they exhibit a back increase. An increase of the fraction of high-angle boundaries without a significant change in the average grain size also occurs after UST. The regularities observed are explained as follows. With an increase of ultrasound amplitude, generation and accumulation of dislocations in the grains occur first. Then the processes of their passing through grain boundaries and rearrangement are activated that results in an increase of misorientations of the grains, more effective screening of dislocation stress fields and stress relaxation. With further increase of the stress amplitude processes of generation and accumulation of dislocations prevails over the processes of their annihilation and rearrangement, so that the relaxation effect weakens and diminishes.

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Section: Introductionunclassified

Effect of ultrasonic treatment on the structure and microhardness of ultrafine grained nickel processed by high pressure torsion

Mukhametgalina¹,

Samigullina²,

Sergeyev³

et al. 2017

LoM

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“…Later studies of HPT-processed Ni have shown that the effect of UST is not monotonous: first an increase of the GB energy, rms strains, microhardness occurs with an increase of the UST amplitude, then all these characteristics decrease indicating on the GB relaxation [24,25]. Studies using ECAP-processed Ni revealed an uncommon effect of UST on mechanical properties: at stress amplitudes 50 ÷ 90 MPa it resulted in a simultaneous enhancement of both the elongation to failure and ultimate strength at room temperature tensile tests [22].…”

Section: Relaxation Of Nonequilibrium Grain Boundaries Induced By Cycmentioning

confidence: 99%

“…In [22] the following qualitative comparison between the effects of annealing and UST was proposed. The thermodynamic state of an as-prepared UFG metal can be considered as a point in the phase space.…”

Section: Relaxation Of Nonequilibrium Grain Boundaries Induced By Cycmentioning

confidence: 99%

Nonequilibrium grain boundaries in bulk nanostructured metals and their recovery under the influences of heating and cyclic deformation. Review

Назаров¹

2018

LoM

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Bulk nanostructured, or ultrafine-grained (UFG) metals and alloys produced by severe plastic deformation (SPD) methods have grain boundaries (GBs), which are in a specific, non-equilibrium state associated with extrinsic grain boundary dislocations (EGBDs) introduced into the boundaries during deformation. In the present review, the origin of this state is analyzed basing on the results of studies of large plastic deformations, according to which during straining the GBs accumulate mesodefects consisting of Rybin disclinations at triple junctions and tangential EGBD arrays and inherit them after removing the load. The main experimental evidences of the nonequilibrium character of GBs in as-prepared nanostructured materials are presented. Main ideas and results of the structural model of UFG metals based on the physics of dislocations and disclinations are overviewed. The latest works on molecular dynamics simulations carried out to explore the detailed atomic structure of disclinations and nonequilibrium GBs are considered and their results are compared to the predictions of the structural model. Mechanisms and kinetics of diffusion controlled recovery of nonequilirium GBs are described. An alternative mechanism of athermal relaxation of nonequilirium GB structure under the action of oscillating stresses has been most recently discovered and elucidated experimentally and by means of computer simulations. The main results of these studies are shortly reviewed too.

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“…UST of equal-channel angular pressing (ECAP) processed nickel also resulted in a simultaneous increase of ductility, strength and impact toughness [26,27].…”

Section: Introductionmentioning

confidence: 99%

Softening and hardening of ECAP nickel under ultrasonic treatment

Zhilyaev

Samigullina

Medvedeva

et al. 2017

Materials Science and Engineering: A

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Abstract.Commercially pure nickel was processed by equal channel angular pressing (ECAP) through route Bc for 12 passes to obtain an ultrafine grained (UFG) microstructure and further subjected to an ultrasonic treatment (UST) which introduced a maximum amplitude equivalent to anormal stresses of 100 MPa in a steady state regime. It was observed that the microstructure of UFG Ni can be differently altered depending on the position in the sample, i.e. on the amplitude of the ultrasonic wave. The microstructural analysis demonstrated a lower dislocation density (due to the activation of recovery) at the cross section of the specimen subjected to UST at an amplitude equal to 0.8 of the maximum one, plus enhanced hardening in the cross section at the maximum amplitude.

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The increase of impact strength of ultrafine grained nickel after ultrasonic treatment

Abstract: Impact strength tests of nickel samples exposed to equal-channel angular pressing (ECAP) were carried out. The influence of annealing and ultrasonic treatment with stress amplitudes of 20, 50 and 100 MPa on the impact fracture of ultrafine grained nickel processed by ECAP was shown.

Cited by 16 publications

References 8 publications

Effect of ultrasonic treatment on the structure and microhardness of ultrafine grained nickel processed by high pressure torsion

Effect of ultrasonic treatment on the structure and microhardness of ultrafine grained nickel processed by high pressure torsion

Nonequilibrium grain boundaries in bulk nanostructured metals and their recovery under the influences of heating and cyclic deformation. Review

Softening and hardening of ECAP nickel under ultrasonic treatment

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