Low Temperature Superplasticity Research Articles

Low-temperature superplasticity of commercial sheets of the titanium alloy Ti-6Al-4V

Superplastic behaviors of sheets out of commercial Ti6Al4V titanium alloy thickness by 1.0mm and 1.5mm were investigated at relatively low temperatures in the field of 650°C - 800°C and at strain rates ranging from 7x10-5s-1 up to 4x10-2s-1. The obtained results show that sheets exhibit excellent low temperature superplasticity

Pressure welding of nickel-based 58Ni-Cr-Mo-B-Al-Cu alloy under low-temperature superplasticity conditions

Both the ultrafine-grained (UFG) structure with a grain size (d) less than 1 mm and nanocrystalline (NC) structure (d £ 100 нм) can be processed in nickel-based alloy 58Ni-Cr-Mo-B-Al-Cu using methods severe plastic deformation, in particular, multistep isothermal forging within the temperature range of g+δ - region on Bridgman anvils at strains е=5,5.

Microstructural evolution and superplastic behavior in friction stir processed Mg–Li–Al–Zn alloy

A Mg–Li–Al–Zn alloy was friction stir processed (FSP) under water, and the microstructures and superplastic behavior in the FSP alloy were investigated. The FSP Mg–Li–Al–Zn alloy consisted of a mixed microstructure with fine, equiaxed, and recrystallized α (hcp) and β (bcc) grains surrounded by high-angle grain boundaries, and the average grain size of the α and β grains was ~1.6 and ~6.8 μm, respectively. The fine α grains played a critical role in providing thermal stability for the β grains. The FSP Mg–Li–Al–Zn alloy exhibited low-temperature superplasticity with a ductility of 330 % at 100 °C and high strain rate superplasticity with ductility of ≥400 % at 225–300 °C. Microstructural examination and superplastic data analysis revealed that the dominant deformation mechanism for the FSPed Mg–Li–Al–Zn alloy is grain boundary sliding, which is controlled by the grain boundary diffusion in the β phase.

Microstructure and high temperature deformation of an ultra-fine grained ECAP AA7075 aluminium alloy

AbstractAn AA 7075 aluminium alloy with an ultra-fine grained structure was prepared through equal channel angular pressing (ECAP) at pressing temperatures TECAP of 120, 170, and 220 °C. A decrease in TECAP from 220 to 120 °C was found to lead to a more pronounced refinement of the microstructure and to worse stability of the microstructure – the onset of grain coarsening was displaced to lower temperatures. The material pressed with the highest TECAP exhibited superplastic behaviour at temperatures close to 400 °C and grain boundary sliding was identified as the dominant operating deformation mechanism. The materials prepared with both of the lower TECAP exhibited only enhanced ductility of about 200 %, however this behaviour was observed at temperatures as low as 200 °C. It was found that this “low temperature superplasticity” resulted from a combined operation of grain boundary sliding at selected grain boundaries and glide of lattice dislocations.

К вопросу о порообразовании в титановом сплаве ВТ6 при деформации в условиях низкотемпературной сверхпластичности

Uniaxial tension and superplastic forming experiments are performed with ultra fine grained titanium VT6 alloy under conditions of low temperature superplasticity at temperatures 600 and 650оС. The initial mean grain size in ultra fine grained titanium VT6 alloy was 0,2 mm. Pores were not display at the steady superplastic state up to 600% of sample extension. It is revealed accelerated a and b-phase grain growth stimulated by superplastic deformation.<br /> Ключевые слова: Низкотемпературная сверхпластичность, поры, сверхпластическая формовка, титановый сплав ВТ6.<br /> <br />

Low Temperature Superplasticity of Ti-6Al-4V Processed by Warm Multidirectional Forging

Multidirectional forging has been developed to produce an ultrafine-grain (UFG) microstructure in the two-phase titanium alloy Ti-6Al-4V. A microstructure with a grain size of 135 nm was attained, enabling low-temperature superplasticity (LTSP) at 550°C. A total elongation of 1000% and strain-rate-sensitivity coefficient m=0.47 were obtained at the optimal strain rate of 2×10-4 s-1. Important features of the microstructure and superplastic behavior of the alloy are summarized in the present work. It is shown that microstructure evolution during low-temperature deformation plays a key role in superplastic flow behavior.

Low-Temperature Superplasticity in an Al–Mg–Mn Alloy Subjected to ECAP and Subsequent Isothermal Rolling

An ultra-fine grained structure with an average size of ~ 1 μm was produced in a commercial Al–5.4%Mg–0.5%Mn–0.1%Zr–0.12%Si–0.014%Fe alloy by hot equal-channel angular pressing (ECAP) followed by isothermal rolling (IR). It was found that in the strain rate interval from 5.6×10-4 to 2.8×10-2 s-1 the alloy exhibits a low-temperature superplasticity with elongation-to-failure exceeding 400% and the strain rate sensitivity coefficient of ~0.3. The highest elongation-to-failure of ~ 620% appeared at a temperature of ~ 275°C and an initial strain rate of ~ 5.6×10-3 s-1. The relationship between superplastic properties and microstructural evolution of the examined alloy is discussed.

Low Temperature Superplasticity of Hydrostatically Extruded Mg-Al-Zn Alloys

In this work, the superplastic behavior of AZ31, AZ61 and AZ80 magnesium alloys was investigated. The alloys were hydrostatically extruded at only 150 °C to get fine grained microstructures (−2, 10−3 and 10−4 s−1. It was found that all alloys exhibited superplasticity at 200 °C, 175 °C and 225 °C for AZ31, AZ61 and AZ80 alloys, respectively. Low temperature dynamic recrystallisation played an important role for generating a finer and homogeneous microstructure during testing which enhances the deformation behavior of the alloys at these temperatures.

Superplastic behavior of reciprocating extruded Mg-6Zn-1Y-0.6Ce-0.6Zr from rapidly solidified ribbons

RRE-Mg66 alloy with a composition of Mg-6.0%Zn-1.0%Y-0.6%Ce-0.6Zr was prepared by combinatorial processes of rapid solidification, reciprocating extrusion and extrusion. Microstructure was evaluated on SEM and TEM. The average grain size of the alloy is 0.7 μm, the size of the second phase at grain boundary is 0.15 μm, and the size of the intragranular precipitates in round shape is less than 20 nm. Superplastic behavior of the material was investigated in a temperature range of 150 to 250 °C and initial strain rate range of 3.3×10−4 to 3.3×10−2 s−1 in air. The highest elongation of 270% was obtained at 250 °C and 3.3× 10−3 s−1. High-strain-rate superplasticity and low-temperature superplasticity were achieved. The superplasticity results from intragranular sliding (IGS) at temperatures from 170 to < 200 °C and grain boundaries sliding (GBS) at 250 °C. At 200 °C a combination of IGS and GBS contributes to the superplastic flow.

Low-temperature superplasticity of forged Ti–43Al–4Nb–2Mo–0.5B alloy

The forged Ti–43Al–4Nb–2Mo–0.5B (at.%) alloy exhibits remarkable low-temperature superplasticity between 900 and 950°C in strain rate range 1.0×10−4 – 4.0×10−4s−1. A maximum elongation of 405% was obtained at 950°C with strain rate sensitivity index (m) 0.52. This excellent superplasticity is ascribed to fine-grained microstructure containing soft β phase. Dynamic recrystallization and lamellar (α2/γ) structure decomposition during tensile straining contribute to superplastic deformation. Microstructure evolution and cavity development were studied by means of SEM, TEM, EBSD and XRD techniques. It was found that dynamic recrystallization and lamellar (α2/γ) structure decomposition took place prior to cavity formation. The formation of cavity stringers and their transverse coalescence resulted in the failure of superplastic deformation.

Development of a Nb-free TiAl-based intermetallics with a low-temperature superplasticity

In this work, the possibility for developing TiAl-based intermetallics without Nb element was explored. Fe and Mo were alloyed with TiAl intermetallics. By using Scanning Electron Microscopy (SEM), transmission electron microscopy (TEM), electron back scattered diffraction (EBSD) and mechanical tests, the microstructural evolution and deform behavior of a Ti-45Al-3Fe-2Mo intermetallics were investigated. The results indicate that the TiAl-Fe-Mo intermetallics show a (B2 + α2 + γ) three-phase microstructures. The microstructures are significantly refined to about 14 μm by additions of Fe and Mo. The TiAl-based intermetallics show a high ductility at 750 °C and a superplastic behavior at 790 °C. The dynamic recrystallization of β(B2) grains is the main acting mechanism for the superplastic behavior of TiAl-based intermetallics at low-temperatures.

Low temperature quasi-superplasticity of ZK60 alloy prepared by reciprocating extrusion

Fine-grained ZK60 alloy was prepared by 2-pass reciprocating extrusion, and the low temperature superplasticity was conducted in a temperature range from 443 to 523 K and an initial strain rate ranging from 3.3×10−4 to 3.3×10−2 s−1. The results show that the alloy has an equiaxed grain structure with an average grain size of about 5.0 μm, and the sizes of broken secondary particles and precipitates are no more than 175 and 50 nm, respectively. The alloy exhibits quasi-superplasticity with a maximum elongation of 270% at 523 K and an initial strain rate of 3.3×10−4 s−1. The strain rate sensitivity m is less than 0.2 at 443 and 473 K, and it is 0.42 at 523 K. The apparent activation energies at temperature below 473 K and at 523 K are less than 63.2 and 110.6 kJ/mol, respectively. At temperature below 473 K, mainly intragranular sliding contributes to superplastic flow. At 523 K, grain boundary sliding is the dominant deformation mechanism, and dislocation creep controlled by grain boundary diffusion is considered to be the main accommodation mechanism.

Сварка давлением объемных образцов из наноструктурного титанового сплава Ti-6Al-4V в состоянии низкотемпературной сверхпластичности

Сварка давлением объемных образцов из наноструктурного титанового сплава Ti-6Al-4V в состоянии низкотемпературной сверхпластичности

Сварка давлением титанового сплава ВТ6 в условиях низкотемпературной сверхпластичности

Проведены результаты экспериментов по сварке давлением титанового сплава ВТ6 в условиях низкотемпературной сверхпластичности. Показано, что чем ниже температура, тем выше должно быть значение давления относительно напряжения течения при этой температуре. При этом качество твердофазного соединения титанового сплава ВТ6 существенно зависит от степени деформации.

Texture Studies of Superplastically Deformed Electrodeposited Nanocrystalline Ni and Ni-P Alloy

Nanocrystalline Ni and Ni-P alloy with grain size down to 6 nm were processed by pulsed electrodeposition. The as-deposited materials, possessing a strong fiber texture, were tested in tension at different temperatures and strain rates. Both materials exhibited low temperature superplasticity but with significant differences in mechanical characteristics. In comparison with nano-Ni, the nano Ni-P alloy exhibited significant strain hardening in flow behavior and lower superplastic elongations at relatively low strain rates, although the grain size was finer at test temperatures with limited grain growth in nano Ni-P alloy. Texture study as a function of strain and strain rate by bulk X-ray Schultz reflection and electron back scattered diffraction (EBSD) revealed development of cube components {001} and {013} with negligible deformation texture components (Cu or brass type) and limited fraction of low angle grain boundaries (&lt; 10 %) in superplastically deformed samples. The reasons for the formation of cube components and their influence on flow behavior of electrodeposited materials were critically analyzed. Additional microstructural investigation by transmission electron microscopy revealed dislocations movement constrained by intragranular particles, leading to strain hardening and cavitation in the nano Ni-P alloy.

Intermediate temperature deformation behaviour of fine grained AZ61 alloy processed by hydrostatic extrusion

Abstract In this work, the intermediate temperature deformation behaviour of alloy AZ61 processed by hydrostatic extrusion has been examined. By means of this thermomechanical process it is possible to refine the microstructure to generate an average grain size of about 5 μm directly from the as-cast microstructure in one single step when extruded at only 150 °C and an extrusion rate of 8 m/min. The evolution of microstructure and texture after tensile testing at 175, 200 and 225 °C in air at three different strain rates of 10 −2 , 10 −3 and 10 −4 s −1 were investigated. It was found that the alloy exhibited low temperature superplasticity at 175 °C (0.33 T m , where T m is the melting point on the absolute scale). The maximum elongation recorded was 540% for AZ61 tested at 225 °C and 1.5 × 10 −3 s −1 . The intermediate temperature deformation behaviour and deformation mechanisms involved were discussed in terms of microstructure and texture development.

Microstructure and Properties of Nanostructured Alloy 718

Nickel-iron Alloy 718 is widely used for fabricating parts by superplastic deformation. Refinement of grains down to a nanostructure (NS) size improves the alloy’s processing properties. Thermomechanical treatment has been carried out to form a NS state in bulk alloy by multiple isothermal forging (MIF) at gradually decreasing temperatures. Investigation of superplastic properties and processing behavior of Alloy 718 has been performed. The alloy with a grain size of 80 nm displays superplasticity (SP) at a temperature which is lower than for a conventional fine grained alloy by about 350°C. The values of the relative elongation  and the strain rate sensitivity coefficient m are 350% and 0.37, respectively. The experimental data on the influence of grain size on solid-state weldability in the range of SP have been obtained. The application of the effect of low temperature SP yields lower temperatures of superplastic forming (SPF) and pressure welding (PW) as compared with conventional SP of fine-grained material. The experiment of the combined process of SPF and PW by counter-forming of two polished sheets, demonstrates its low temperature processing feasibility using NS specimens. The SPF processing of NS sheets in a cylindrical die has been investigated. It has revealed that macro-deformation is uniform in cross and longitudinal sections. Mechanical properties of Alloy 718 in NS condition and after strengthening heat treatment have been discussed.

Low-temperature superplasticity of Al 2O 3(p)/Ni–Co nanocomposites

Nanocomposites of Al 2O 3/Ni–Co prepared using Al 2O 3 of various particle sizes were fabricated by pulse current electrodeposition. Their superplastic tensile deformation was investigated at strain rates of 8.33 × 10 −4 s −1 and 1.67 × 10 −3 s −1 and temperatures of 723–823 K. The Al 2O 3 particle sizes and the deformation temperature had significant influence on the elongation of the deposited materials. The optimal superplastic condition and the maximum elongation were determined. A low temperature superplasticity with elongation of 632% was achieved at a strain rate of 1.67 × 10 −3 s −1 and 823 K. Scanning electron microscopy and transmission electron microscopy were used to examine the microstructures of the deposited and deformed samples. The grains grew to a micrometer dimensions and were elongated along the tensile direction after superplastic deformation. Superplasticity in electrodeposited nanocomposites is related to the presence of S at grain boundaries and to deformation twinning.

Low-temperature superplasticity of extruded Mg–Sn–Al–Zn alloy

The tensile properties of extruded Mg–Sn–Al–Zn alloy at elevated temperature were investigated. Low-temperature superplasticity was found in the alloy, which exhibited tensile elongations of 410–950% at strain rates in the range 1 × 10−3–1 × 10−4 s−1 at 473 K. The superplastic deformation behavior was attributed to the fine-grained microstructure, which contained thermally stable Mg2Sn precipitates.

Сверхпластичность и твердофазное соединение наноструктурированных материалов. Часть II. Физическая модель формирования твердофазного соединения в титановом сплаве в условиях низкотемпературной сверхпластичности

The manuscript presents a chronological review of studies dealing with the influence of the effect of superplasticity (SP) on improved solid state weldability of crystalline materials. The manuscript considers a model of solid state joining under conditions of low temperature superplasticity for nanostructured titanium alloy VT6. The data of physical modeling of the process of solid state joining under low temperature SP conditions provide scientific basis for substantiation of practical implementation of nanostructured materials at aircraft and air engine enterprises for developing advanced resource-saving technologies for producing hollow components by pressure welding. <br />