Effect of superplastic deformation on the bonding property of 00Cr25Ni7Mo3N duplex stainless steel

The superplastic deformation diffusion bonding of 00Cr25Ni7Mo3N duplex stainless steel was performed on a hot simulator. The microstructure of the bonding interface was characterized by scanning electron microscopy （SEM） and electron backscatter diffraction （EBSD）. The mechanical properties of the specimen were investigated by a shear strength test. The results indicated that the shear strength was improved with the increase of superplastic deformation reduction. When the deformation reduction was up to 50%, the shear strength of the specimen achieved 417 Mpa, approaching to that of the base metal. In addtion, the superplastic diffusion bonding technique was not very sensitive to surface roughness levels. When the surface roughness of the bonding specimen surpassed 0.416 pan （level G2）, the shear strength achieved at least 381 MPa.

CONSTITUTE EQUATIONS OF 40Cr STEEL UNDER SUPERPLASTIC COMPRESSIVE DEFORMATION

The microstructure of 40Cr steel sample and its surface is ultra-fined through salt-bath cyclic quenching and high frequency hardening, then the superplasticity is studied under isothermal superplastic compressive deformation condition. The experimental results indicate that the stress-strain curves are shown to take place obvious superplastic flow characteristic at the temperature of 750-770℃ and at the initial strain rate of (1.7-5.0)×10-4 s-1. Its strain rate sensitivity is 0.30-0.38, the steady superplastic flow stress is 60-70MPa, the superplastic flow activation energy is 198-217kJ/mol, and it is close to α-Fe grain boundary self-diffusion activation energy. The super-plastic compressive constitute equations of this steel are correspondingly set up. Due to the finer microstructure of high frequency hardening, it appears bigger strain rate sensitivity value, smaller the steady superplastic flow stress and the superplastic flow activation energy, so it has better superplastic deformation capability.

GRAIN SHAPE EFFECT IN SUPERPLASTIC DEFORMATION

The method controlling grain shape in TMT processing and the effect of grain shape on char- acteristic parameters in superplastic deformation were discussed.The accommodation velocity of grahl boundary sliding,which is the dominant mechanism in superplastic deformation,and the contribution of each mechanism to the total strain,as influenced by grain shape,were ana- lyzed.Grain shape has been shown to be an essential structural factor for superplasticity.Then an analysis was made about the effect of grain shape on the region transition strain rate so that a new concept,critical aspect for superplasticity,was worked out.These predictions were compared with the measured results in an Al-Zn-Mg alloy.

Simulation on Grain Boundary Sliding during Superplastic Deformation Using Molecular Dynamics Method

Grain growth and grain boundary sliding are the two main superplastic deformation mechanisms. In the paper, simulation work is focused on the sliding of a S3 (111) symmetric twist coincidence grain boundary, a S13 (110) asymmetric tilt coincidence grain boundary, and a S3 (110) symmetric tilt coincidence grain boundary in Al, and the energies of grain boundary for each of equilibrium configurations are computed. An embedded atom method (EAM) potential was used to simulate the atomic interactions in a bicrystal containing more than 2000 atoms. At 0 K, the relationships between total potential energy and time steps for S3 (111) symmetric twist coincidence grain boundary and S3 (110) symmetric tilt coincidence grain boundary during sliding at 2 m/s represent the periodic characteristic. However, the relationship between total potential energy and time steps for S13 (110) asymmetric tilt coincidence grain boundary represents the damp surge characteristic. It is found that grain boundary sliding for S3 (110) symmetric tilt coincidence grain boundary is coupled with apparent grain boundary migration.

FRACTAL DIMENSION OF SHAPE CHANGE OF CAVITIFS DURING SUPERPLASTIC DEFORMATION IN HIGH STRENGTH Al ALLOY

The fractal dimension changes of cavities have been determined during superplastic deformation of the high strength aluminiurn alloy 7475 with different strain,temperature, strain rate and grain size.The fractal dimension of cavities may increase with the increase of strain.It becomes higher as the alloy deformed under lower temperatures,greater strain rate and coarser grain size.The alloy would be approaching to rupture if the fractal dimension of cavities raised to a certain extent.

Superplasticity in Aluminium Brass(HAl 66-6-3-2)

1.IntroductionSuperplasticity is not merely a specialphenomenon for certain specific alley,but isone of the intrinsic properties of metallicmaterials[1].When the internal and externalconditions are suitable,superplasticity ofmetal materials will be presented.

SUPERPLASTICAL DEFORMATION AND FRACTURE MECHANISM 0F A SiC_p/2024Al COMPOSITE

Soperplastic tensions on an IM SiCp/2024Al composite were conducted. The microstrvcture and fmcture sudece of the composite under the optimum saperplastic deformation condition were examined. The eoperimental results show that as the increase of strain during superpldstic deformation, grains fundarnentally remained equiaxed structure, and dislocation density increases gradually and its structure changes hem intererossed into nets each other to tangled and cellular structure,and the amount of liquid phase at the intedeces or gruin boundaries increases gradually. Mcrostructure examination revealed that failure took place by damage accumulation of the pmpressive decohesion of the SiC particle-matrix until a critical volume fruction was reached.

Deformation behavior of fine-grained 5083 Al alloy at elevated temperature

The microstructure evolution of the fine-grained 5083 Al alloy was investigated in annealing temperature range of 150−300℃.Then the effects of the different annealed microstructures on high-temperature deformation behavior were further studied.The results indicate that the initial recrystallization temperature is about 200℃.By tensile tests at 380−570℃and in strain rate range of 4.17×10^(−4)−1.0×10^(−2) s^(−1),the optimum superplastic parameters are obtained as follows:the annealed temperature 250℃,the tensile temperature 550℃and the strain rate 4.17×10^(−4) s^(−1).With the aid of scanning electronic microscopy(SEM),the fractography of the alloy after the superplastic deformation was analyzed.The results reveal that intergranular cavities with fine size and homogeneous distribution are beneficial to superplastic deformation.

SLIP SYSTEMS AND DISLOCATION DISTRIBUTION IN α-PHASE OF SUPERPLASTICALLY DEFORMED Ti-6AI-4V ALLOY

The activated slip systems in the α-phase of the superplastically deformed Ti-6Al-4V alloy were analyzed by systematic operation method with TEM.The results show that the dominately activated slip systems in the α-phase are{01(?)0}〈2(?)0〉and{01(?)}2(?)0〉, The{0001}〈2(?)0〉system as well as the c+a dislocalions of b=[1/3]〈11(?)3〉will be acti- vated when the deformation temperature is lowered.Large amounts of TEM observations in- dicate that the dislocations in the α-phase were mainly activated near the triple grain bounda- ry junctions,α/α grain boundaries and α/β interlaces.

On the superplastic deformation mechanisms of near-αTNW700 titanium alloy

The new near-αTNW700 titanium alloy is a potential candidate material for high performance ultrasonic/hypersonic aircrafts,which is designed for short-term service at 700℃.This study systematically investigated the superplastic deformation microstructure evolution and mechanism of TNW700 alloy at different strain rates and true strains at 925℃.Results show that TNW700 alloy exhibits excellent superplastic behavior in a constant strain rate range of 0.0005-0.005 s^(-1) with elongation above 400%.The peak stress decreases with decreasing strain rate,which is related to the increase ofβ-phase volume fraction caused by the increase of thermal exposure time.In addition,significant strain hardening is observed in early-middle stage of superplastic deformation,and flow softening is followed in middle-late stage.To rationalize these complex flow behaviors,electron backscatter diffraction(EBSD)and high resolution transmission electron microscopy(HRTEM)were used to characterize the microstructure.Strain hardening is correlated to the synergistic effect ofβgrain growth,dislocation accumulation,silicide precipitate,and solid solution strengthening ofαphase.Continuous dynamic recrystallization(CDRX)induced the fragmentation of primaryαgrains in middle-late stage of superplastic deformation,and the refinement ofαgrains,the increase ofβphase volume fraction and dynamic dislocation recovery are main causes of high strain softening.In addition,EBSD and TEM observations confirmed texture randomization,fine equiaxed primaryαgrains and intragranular dislocation movement,indicating that grain boundary sliding(GBS)accommodated by dislocation sliding/climb is the dominant superplastic deformation mechanism of TNW700 alloy.

Evolution of Microstructure and Texture during Hot Deformation of a Commercially Processed Supral100

The microstructure and texture in a commercially processed AI-6 wt% Cu-0.4 wt% Zr （Suprall00） aluminium alloy have been investigated after annealing and hot tensile straining at 450℃, using a field emission gun scanning electron microscope （SEM） and electron backscatter diffraction （EBSD）. The microstructure of commercially processed alloy had a relatively large fraction of high angle grain boundaries （HAGBs） which were aligned parallel to the rolling direction, and a strong texture. Annealing at 450℃ led to an increase in the fraction of HAGBs and to an increase in HAGB spacing and these changes were progressively enhanced by subsequent tensile deformation. The increasing fraction of HAGBs was due to the annihilation of low angle grain boundaries （LAGBs）. A sharpening of texture during annealing was attributed to preferential textural growth, and the reduction of texture at higher tensile strains led to the development of superplastic behaviour. The present work supports the view that the evolution of the fine grain microstructure during the high temperature straining of SuprallO0 is primarily due to the accumulation of a large area of grain boundary during the initial thermomechanical processing, and does not involve any unusual restoration processes.

Superplastic behavior of an ultrafine-grained Mg-13Zn-1.55Y alloy with a high volume fraction of icosahedral phases prepared by high-ratio differential speed rolling

An ultrafine-grained（UFG） Mg-13Zn-1.55 Y alloy（ZW132） with a high volume fraction（7.4%） of icosahedral phase（I-phase, Mg;Zn;Y） particles was prepared by applying high-ratio differential speed rolling（HRDSR） on the cast microstructure following homogenization. The alloy exhibited excellent superplasticity at low temperatures(tensile elongations of 455% and 1021% 473 K-10;s;and 523 K-10;s;,respectively). Compared with UFG Mg-9.25Zn-1.66 Y alloy（ZW92） with a lower volume fraction of I-phase particles（4.1%）, which was prepared using the same processing routes, the UFG ZW132 alloy exhibited a higher thermal stability of grain size. Rapid grain coarsening, however, occurred at temperatures beyond523 K, leading to a loss of superplasticity. The high-temperature deformation behavior of the HRDSRprocessed ZW132 alloy could be well described assuming that the mechanisms of grain boundary sliding and dislocation climb creep competed with each other and considering that the grain-size was largely increased by accelerated grain growth at the temperatures beyond 523 K.

Superplastic behavior of a powder metallurgy superalloy during isothermal compression

In this work,the flow behaviors and microstructure evolution of a powder metallurgy nickel-based superalloy during superplastic compression is investigated.Based on the strain rate sensitivity m determined by flow data,superplastic region is estimated at relatively low temperature and strain rate domains,specifically around 1000℃/10^-3s^-1.Thereafter,the cylinder specimens are isothermally compressed at 1000℃/10^-3s^-1 and 1025℃/10^-3s^-1 with different strains,to exam the superplasticity and related mechanisms.The experimental results indicate that the accumulated dislocations are mainly annihilated by dynamic recovery and dynamic recrystallization(DRX),and the grain boundary sliding(GBS)contributes to the total strain during superplastic compression as well.In addition,the cavities and cracks at triple junctions or interfaces between matrix and second phase particle have not been detected,which is different from superplastic tensile deformation.

Influence of the Accumulative Roll Bonding Process Severity on the Microstructure and Superplastic Behaviour of 7075 Al Alloy

The 7075 Al alloy was processed by accumulative roll bonding （ARB） at 350 ℃ using 2：1, 3：1 and 4：1 thickness reductions per pass （Rp） up to 8, 6 and 3 passes, respectively. Microstructural examinations of the processed samples revealed that ARB leads to a microstructure composed of equiaxed crystallites with a mean size generally lower than 500 nm. It was found that, due to both the stored energy through- out the processing and the particle pinning effect, the alloy is affected by discontinuous recrystallisation during the inter-pass heating stages, the precise microstructural evolution being dependent on Rp. Me- chanical testing of the ARBed samples revealed that the main active deformation mechanism in the ARBed samples in the temperature range from 250 to 350 ℃ at intermediate and high strain rates is grain bound- ary sliding, the superplastic properties being determined by both the microstructure after ARB and its thermal stability.