Diffusion Bonding of Microduplex Stainless Steel and Ti Alloy with and without Interlayer: Interface Microstructure and Strength Properties

The interface microstructure and strength properties of solid state diffusion bonding of microduplex stainless steel (MDSS) to Ti alloy (TiA) with and without a Ni alloy (NiA) intermediate material were investigated at 1173 K (900 °C) for 0.9 to 5.4 ks in steps of 0.9 ks in vacuum. The effects of bonding time on the microstructure of the bonded joint have been analyzed by light optical microscopy and scanning electron microscopy in the backscattered mode. In the direct bonded joints of MDSS and TiA, the layer-wise σ phase and the λ + FeTi phase mixture were observed at the bond interface when the joint was processed for 2.7 ks and above holding times. However, when NiA was used as an intermediate material, the results indicated that TiNi₃, TiNi, and Ti₂Ni are formed at the NiA-TiA interface, and the irregular shaped particles of Fe₂₂Mo₂₀Ni₄₅Ti₁₃ have been observed within the TiNi₃ intermetallic layer. The stainless steel-NiA interface is free from intermetallics and the layer of austenitic phase was observed at the stainless steel side. A maximum tensile strength of ~520 MPa, shear strength of ~405 MPa, and impact toughness of ~18 J were obtained for the directly bonded joint when processed for 2.7 ks. However, when nickel base alloy was used as an intermediate material in the same materials, the bond tensile and shear strengths increase to ~640 and ~479 MPa, respectively, and the impact toughness to ~21 J when bonding was processed for 4.5 ks. Fracture surface observations in scanning electron microscopy using energy dispersive spectroscopy demonstrate that in MDSS-TiA joints, failure takes place through the FeTi + λ phase when bonding was processed for 2.7 ks; however, failure takes place through σ phase for the diffusion joints processed for 3.6 ks and above processing times. However, in MDSS-NiA-TiA joints, the fracture takes place through NiTi₂ layer at the NiA-TiA interface for all bonding times.     

Effect of Bonding Temperature on Interfacial Reaction and Mechanical Properties of Diffusion-Bonded Joint Between Ti-6Al-4V and 304 Stainless Steel Using Nickel as an Intermediate Material

An investigation was carried out on the solid-state diffusion bonding between Ti-6Al-4V (TiA) and 304 stainless steel (SS) using pure nickel (Ni) of 200-μm thickness as an intermediate material prepared in vacuum in the temperature range from 973 K to 1073 K (700 °C to 800 °C) in steps of 298 K (25 °C) using uniaxial compressive pressure of 3 MPa and 60 minutes as bonding time. Scanning electron microscopy images, in backscattered electron mode, had revealed existence of layerwise Ti-Ni-based intermetallics such as either Ni₃Ti or both Ni₃Ti and NiTi at titanium alloy-nickel (TiA/Ni) interface, whereas nickel-stainless steel (Ni/SS) diffusion zone was free from intermetallic phases for all joints processed. Chemical composition of the reaction layers was determined in atomic percentage by energy dispersive spectroscopy and confirmed by X-ray diffraction study. Room-temperature properties of the bonded joints were characterized using microhardness evaluation and tensile testing. The maximum hardness value of ~800 HV was observed at TiA/Ni interface for the bond processed at 1073 K (800 °C). The hardness value at Ni/SS interface for all the bonds was found to be ~330 HV. Maximum tensile strength of ~206 MPa along with ~2.9 pct ductility was obtained for the joint processed at 1023 K (750 °C). It was observed from the activation study that the diffusion rate at TiA/Ni interface is lesser than that at the Ni/SS interface. From microhardness profile, fractured surfaces and fracture path, it was demonstrated that failure of the joints was initiated and propagated apparently at the TiA/Ni interface near Ni₃Ti intermetallic phase.     

Effect of Bonding Time on Interfacial Reaction and Mechanical Properties of Diffusion-Bonded Joint Between Ti-6Al-4V and 304 Stainless Steel Using Nickel as an Intermediate Material

In the current study, solid-state diffusion bonding between Ti-6Al-4V (TiA) and 304 stainless steel (SS) using pure nickel (Ni) of 200-μm thickness as an intermediate material was carried out in vacuum. Uniaxial compressive pressure and temperature were kept at 4 MPa and 1023 K (750 °C), respectively, and the bonding time was varied from 30 to 120 minutes in steps of 15 minutes. Scanning electron microscopy images, in backscattered electron mode, revealed the layerwise Ti-Ni-based intermetallics like either Ni₃Ti or both Ni₃Ti and NiTi at titanium alloy-nickel (TiA/Ni) interface, whereas nickel-stainless steel (Ni/SS) interface was free from intermetallic phases for all the joints. Chemical composition of the reaction layers was determined by energy dispersive spectroscopy (SEM–EDS) and confirmed by X-ray diffraction study. Maximum tensile strength of ~382 MPa along with ~3.7 pct ductility was observed for the joints processed for 60 minutes. It was found that the extent of diffusion zone at Ni/SS interface was greater than that of TiA/Ni interface. From the microhardness profile, fractured surfaces, and fracture path, it was demonstrated that the failure of the joints was initiated and propagated apparently at TiA/Ni interface near Ni₃Ti intermetallic for bonding time less than 90 minutes, and through Ni for bonding time 90 minutes and greater.     

Interfacial Microstructure and Mechanical Strength of 93W/Ta Diffusion-Bonded Joints with Ni Interlayer

93W alloy and Ta metal were successfully diffusion bonded using a Ni interlayer. Ni₄W was found at the W-Ni interface, and Ni₃Ta and Ni₂Ta were formed at the Ni-Ta interface. The shear strength of the joints increases with increasing holding time, reaching a value of 202 MPa for a joint prepared using a 90-minute holding time at 1103 K (830 °C) and 20 MPa. The fracture of this joint occurred within the Ni/Ta interface.     

Evaluation of Microstructure and Mechanical Properties of Nano-Y2O3-Dispersed Ferritic Alloy Synthesized by Mechanical Alloying and Consolidated by High-Pressure Sintering

In this study, an attempt has been made to synthesize 1.0 wt pct nano-Y₂O₃-dispersed ferritic alloys with nominal compositions: 83.0 Fe-13.5 Cr-2.0 Al-0.5 Ti (alloy A), 79.0 Fe-17.5 Cr-2.0 Al-0.5 Ti (alloy B), 75.0 Fe-21.5 Cr-2.0 Al-0.5 Ti (alloy C), and 71.0 Fe-25.5 Cr-2.0 Al-0.5 Ti (alloy D) steels (all in wt pct) by solid-state mechanical alloying route and consolidation the milled powder by high-pressure sintering at 873 K, 1073 K, and 1273 K (600°C, 800°C, and 1000°C) using 8 GPa uniaxial pressure for 3 minutes. Subsequently, an extensive effort has been undertaken to characterize the microstructural and phase evolution by X-ray diffraction, scanning and transmission electron microscopy, and energy dispersive spectroscopy. Mechanical properties including hardness, compressive strength, Young’s modulus, and fracture toughness were determined using micro/nano-indentation unit and universal testing machine. The present ferritic alloys record extraordinary levels of compressive strength (from 1150 to 2550 MPa), Young’s modulus (from 200 to 240 GPa), indentation fracture toughness (from 3.6 to 15.4 MPa√m), and hardness (from13.5 to 18.5 GPa) and measure up to 1.5 through 2 times greater strength but with a lower density (~7.4 Mg/m³) than other oxide dispersion-strengthened ferritic steels (<1200 MPa) or tungsten-based alloys (<2200 MPa). Besides superior mechanical strength, the novelty of these alloys lies in the unique microstructure comprising uniform distribution of either nanometric (~10 nm) oxide (Y₂Ti₂O₇/Y₂TiO₅ or un-reacted Y₂O₃) or intermetallic (Fe₁₁TiY and Al_9.22Cr_2.78Y) particles' ferritic matrix useful for grain boundary pinning and creep resistance.     

Solidification of Highly Undercooled Hypereutectic Ni-Ni3B Alloy Melt

The solidification of undercooled Ni-4.5 wt pct B alloy melt was investigated by using the glass fluxing technique. The alloy melt was undercooled up to ΔT _p ~ 245 K (245 °C), where a mixture of α-Ni dendrite, Ni₃B dendrite, rod eutectic, and precipitates was obtained. If ΔT _p < 175 K ± 10 K (175 °C ± 10 °C), the solidification pathway was found as primary transformation and eutectic transformation (L → Ni₃B and L → Ni/Ni₃B); if ΔT _p ≥ 175 K ± 10 K (175 °C ± 10 °C), the pathway was found as metastable eutectic transformation, metastable phase decomposition, and residual liquid solidification (L → Ni/Ni₂₃B₆, Ni₂₃B₆ → Ni/Ni₃B, and L_r → Ni/Ni₃B). A high-speed video system was adopted to observe the solidification front of each transformation. It showed that for residual liquid solidification, the solidification front velocity is the same magnitude as that for eutectic transformation, but is an order of magnitude larger than for metastable eutectic transformation, which confirms the reaction as L_r → Ni/Ni₃B; it also showed that this velocity decreases with increasing ΔT _r, which can be explained by reduction of the residual liquid fraction and decrease of Ni₂₃B₆ decomposition rate.     

Infrared brazing Cu and Ti using a 95Ag-5Al braze alloy

Dynamic wetting angle measurements, microstructural evolution, reaction kinetics, and shear strength of infrared brazing Cu and Ti using a 95Ag-5Al braze alloy are evaluated. The specimen infrared brazed at 900 °C consists mainly of Cu₂Ti and Cu₄Ti. Both CuTi and Cu₄Ti₃ are observed at the interface between the braze and Ti substrate. Microstructures of Ti/95Ag-5Al/Cu joints infrared brazed at 830 °C and 850 °C are very different from that of the joint infrared brazed at 900 °C, because the dissolution of both substrates significantly decreased as the brazing temperature decreased. Specimens infrared brazed at 830 °C and 850 °C are primarily comprised of Ag-Cu eutectic and the Cu-rich phase. Two interfacial reaction layers, including Ti₂Cu and AlCu₂Ti, are found in the experiment. The shear strengths of infrared brazed specimens at 830 °C and 850 °C are between 160 and 198.5 MPa, and are fractured along the interfacial reaction layers, AlCu₂Ti and Ti₂Cu, between the braze alloy and Ti substrate. The use of the infrared brazing provides an effective way to inhibit the growth of intermetallics at the interface between the braze alloy and substrate.     

Experimental Studies on the Superplastic Forming of Square Shaped Components and Diffusion Bonding Characteristics of Ti–6Al–4V Alloy

Superplasticity is the ability of a polycrystalline material to exhibit, in a relatively isotropic manner, large elongations when deformed in tension. This property is exploited during superplastic forming in the fabrication of complex-shaped components which are otherwise technically difficult or economically costly to form by conventional methods. The ability of some titanium alloys to undergo superplastic deformation coupled with their diffusion bonding capability provides excellent opportunities to fabricate intricate parts resulting in significant cost and weight savings, particularly in the manufacture of aerospace structures. In the present work, experimental studies on the superplastic forming of square shaped components from titanium alloy Ti–6Al–4V sheets of 2 mm thickness that are commonly used in aerospace structural applications are reported. Superplastic forming of suitably sized blanks was carried out at temperatures of 1,148 K (875 °C), 1,173 K (900 °C) and 1,200 K (927 °C) using constant argon gas pressures of 1, 1.4 and 1.8 MPa. The formed components were characterized for their thickness distribution, mechanical and metallurgical properties. Diffusion bonding characteristics of the alloy sheet of 1 mm thickness were investigated for varying time durations at different temperatures and 4 MPa stress under an argon atmosphere and lap shear strength values of the joints are reported. Efforts were then made to carry out diffusion bonding concurrent with superplastic forming (SPF/DB). For these experiments, two sheets of 1 mm thickness each were superplastically formed into square components of size 80 mm square and 60 mm deep with an initial forming cycle followed by a diffusion bonding cycle by subjecting the component to a static pressure (higher than the forming pressure) for a specified period of time, which ensured good bonding between the two sheets. The components formed by the SPF/DB process were compared with those formed from the monolithic 2 mm sheet and the results are presented.     

Microstructure Evolution and Mechanical Behavior of Cold-Sprayed,Bulk Nanostructured Titanium

To provide insight into the microstructural evolution and mechanical behavior of bulk nanostructured Ti, we used cold gas dynamic spraying of Ti particles to synthesize thick coatings (e.g., >10 mm in thickness). Accordingly, the grain size, lattice parameter, lattice strain, residual stress, porosity, microhardness, tensile, and compressive behavior of the bulk Ti deposits before and after annealing were comparatively analyzed. Our results show that the microstructure of the as-sprayed bulk Ti was characterized by a grain size of ~60 nm, lattice expansion (~2 pct for \( a \) and ~3 pct for \( c \) ), lattice strain (~1.65 × 10^?5), and residual compressive stress (~53 MPa). Moreover, annealing of the as-deposited bulk Ti led to a significant decrease in lattice expansion, lattice strain, and residual stress, whereas porosity remained unchanged (~11 pct). The mechanisms of grain growth, as well as the evolution of particle interfaces during annealing, were also investigated. In terms of mechanical behavior, the as-deposited bulk Ti exhibited a very low modulus (52 GPa) with relatively high tensile and compressive strength values (180 and 850 MPa, respectively). Annealing in the temperature range of 1023 K to 1173 K (750 °C to 900 °C) led to a significant increase of tensile and compressive strength (to 380 MPa and more than 1200 MPa, respectively). Finally, annealing resulted in a slight increase of elastic modulus, which was rationalized on the basis of changes in pore geometry in the bulk Ti deposits.     

Infrared Brazing of Ti<Subscript>50</Subscript>Ni<Subscript>50</Subscript> Shape Memory Alloy and Inconel 600 Alloy with Two Ag-Cu-Ti Active Braze Alloys

Infrared brazing of Ti₅₀Ni₅₀ SMA and Inconel 600 alloy using Cusil-ABA and Ticusil filler metals has been investigated. The joints were dominated by Ag-Cu eutectic with proeutectic Cu in the Cusil-ABA brazed joint and with proeutectic Ag in the Ticusil one. A continuous curved belt composed of a Ni₃Ti layer and a (Cu _x Ni_1?x )₂Ti layer formed in the brazed Ti₅₀Ni₅₀/Ticusil/Inconel 600 joint. On the Ti₅₀Ni₅₀ SMA side, an intermetallic layer of (Cu _x Ni_1?x )₂Ti formed in all joints, with x values around 0.81 and 0.47. Layers of (Cu _x Ni_1?x )₂Ti, Ni₃Ti, and mixed Ni₃Ti and Ni₂Cr intermetallics were observed next to the Inconel 600 substrate in the brazed Ti₅₀Ni₅₀/Cusil-ABA/Inconel 600 joint. The maximum shear strengths of the joints using the Cusil-ABA filler metal and the Ticusil filler metal were 324 and 300 MPa, respectively. In the Cusil-ABA brazed joint, cracks with cleavage-dominated fracture propagated along the (Cu _x Ni_1?x )₂Ti interfacial layer next to the Ti₅₀Ni₅₀ SMA substrate. In the Ticusil brazed joint, ductile dimple fracture occurred in the Ag-rich matrix near the Inconel 600 alloy substrate. The absence of a detrimental Ti-Fe-(Cu) layer on the Inconel 600 substrate side can effectively improve the shear strength of the joint.     

Effect of Prior Oxidation on Tensile Properties of Bare and Al3Ti Diffusion Aluminide Coated Near α Titanium Alloy Titan 29A

The effect of prior oxidation, for various durations up to 2,000 h in air at 650 °C, on the room temperature tensile properties of uncoated and Al₃Ti diffusion aluminide coated near α Ti alloy, Titan 29A, has been evaluated. The tensile properties of the uncoated alloy deteriorated with oxidation. Oxidation for just 100 h caused 11–13 % decrease in yield strength (YS) and ultimate tensile strength (UTS) of the alloy. The uncoated alloy exhibited brittle fracture within the elastic regime at significantly lower stress after oxidation for 2,000 h. On the other hand, the strength of the coated alloy remained unaffected even after 2,000 h of oxidation and the YS and UTS was similar to that of the un-oxidized alloy. The ductility of the coated alloy, however, decreased with the increase in oxidation duration. Such differences in the tensile behavior of the uncoated and coated alloy can be ascribed to the beneficial effect of the Al₃Ti diffusion aluminide coating in preventing surface embrittlement in the alloy during oxidation.     

Effects of temperature and environment on the tensile and fatigue crack growth behavior of a Ni3AI-base alloy

The effects of temperature, frequency, and environment on the tensile and cyclic deformation behavior of a nickel aluminide alloy, Ni-9.0 wt pct Al-7.97 pct Cr-1.77 pct Zr (IC-221), have been determined. The tensile properties were obtained in vacuum at elevated temperatures and in air at room temperature. The alloy was not notch sensitive at room temperature or at 600 °C, unlike Cr-free Ni₃Al + B alloys. In general, crack growth rates of IC-221 increased with increasing temperature, decreasing frequency, exposure to air, or testing at higherR ratios. At 25 °C, crack growth rates were slightly higher than for a previously investigated Cr-free Ni₃Al alloy. However, at 600 °C, the crack growth rates for IC-221 were lower than for the Cr-free alloy. Substantial frequency effects were noted on crack growth of IC-221 at both 600 °C and 800 °C in both air and vacuum, especially at highK. The relative contributions of creep and environmental interactions to fatigue crack growth are discussed.     

Microstructure and Tensile Strength of the Bonded Interfaces and Parent Materials in W/ODS Steel Joints Fabricated by Direct SSDB

In the present work, Tungsten (W)/oxide dispersion strengthened (ODS) steel joints were fabricated by the direct solid state diffusion bonding (SSDB) technology with a multistage cooling process, and the microstructure and tensile strength of the bonded interfaces and parent materials were experimentally investigated. The results show that W and ODS steel can be successfully bonded at the temperature ranging from 900 °C to 1050 °C, without severe macroscopic deformation or obvious microscopic defects. Reaction layers generated at the bonded interfaces are evolutive with the bonding temperature, result in different fracture locations of the bonded joints. In the joint bonded at 950 °C, a higher interfacial strength of ~ 234.2 MPa is achieved, due to the formation of nano-scale intermetallic compound FeW. Microstructure of W remains stable after all the SSDB processes, while the lath structure of ODS steel is completely broken and transformed into the equiaxed grains, which should be responsible for the deterioration of strength. When the bonding temperature is higher than 950 °C, the pinning effect of precipitates M₂₃C₆ and nano-oxide particles on the movement of dislocations is observed.

     

Nanostructure and Mechanical Properties of Bulk Al86Ni6Y6Ce2 Alloy Produced by Hot Consolidation of Amorphous Melt-Spun Flakes

Amorphous Al₈₆Ni₆Y₆Ce₂ (at. pct) flakes produced by melt spinning were consolidated using hot pressing at different conditions. The influence of pressing conditions on the crystallization behavior, thermal stability, and mechanical properties of the alloy has been studied through differential scanning calorimetry, scanning electron microscopy, X-ray diffraction, microhardness, and compression test. The results show rapid solidification combined with the hot consolidation produce a highly dense sample (3.41 ± 0.2 g cm^?3) with the ideal interflake bonding, good thermal stability, good microhardness (381 ± 12 HV), and remarkably high strength (910 ± 7 MPa) combined with 20 pct fracture strain were obtained at T = 748 K (475 °C) and P = 1.2 GPa in a lightweight Al-based material. The high mechanical properties mainly result from structural refinement during the controlled consolidation method.     

Interfacial microstructure and mechanical properties of diffusion-bonded joints of titanium TC4 (Ti-6Al-4V) and Kovar (Fe-29Ni-17Co) alloys

Diffusion bonding is a near net shape forming process that can join dissimilar materials through atomic diffusion under a high pressure at a high temperature.Titanium alloy TC4(Ti-6 Al-4 V)and 4 J29 Kovar alloy(Fe-29 Ni-17 Co)were diffusely bonded by a vacuum hot-press sintering process in the temperature range of 700-850°C and bonding time of 120 min,under a pressure of 34.66 MPa.Interfacial microstructures and intermetallic compounds of the diffusion-bonded joints were characterized by optical microscopy,scanning electron microscopy,X-ray diffraction(XRD)and energy dispersive spectroscopy(EDS).The elemental diffusion across the interface was revealed by electron probe microanalysis.Mechanical properties of joints were investigated by micro Vickers hardness and tensile strength.Results of EDS and XRD indicated that(Fe,Co,Ni)-Ti,TiNi,Ti_2Ni,TiNi_2,Fe_2 Ti,Ti_(17) Mn_3 and Al_6 Ti_(19) were formed at the interface.When the bonding temperature was raised from 700 to 850°C,the voids of interface were reduced and intermetallic layers were widened.Maximum tensile strength of joints at 53.5 MPa was recorded by the sintering process at 850°C for 120 min.Fracture surface of the joint indicated brittle nature,and failure took place through interface of intermetallic compounds.Based on the mechanical properties and microstructure of the diffusion-bonded joints,diffusion mechanisms between Ti-6 Al-4 Vtitanium and Fe-29 Ni-17 Co Kovar alloys were analyzed in terms of elemental diffusion,nucleation and growth of grains,plastic deformation and formation of intermetallic compounds near the interface.     

The Effect of Minor Addition of Ni on the Microstructural Evolution and Mechanical Properties of Suction Cast Al-0.14 at. pct Sc Binary Alloy

Aluminum scandium binary alloys represent a promising precipitation-hardening alloy system. However, the hardness of the binary alloys decreases with the rapid coarsening of Al₃Sc precipitate during high-temperature aging. In the current study, we report a new approach to compensate for the loss of mechanical properties by combining rapid solidification with very small ternary addition of transition metal Ni. This addition yields dispersion, and at a critical concentration improves the mechanical properties. We explore additions of a maximum of 0.06 at. pct of Nickel to a binary Al-0.14 at. pct Sc alloy, which yield nickel-rich dispersions. We report two kinds of biphasic dispersions containing AlNi₂Sc/Al₉Ni₂ and α-Al/Al₉Ni₂ phase combinations. The maximum improvement in mechanical properties occurs with the addition of 0.045 at. pct Ni with a yield strength of 239 ± 7 MPa for an aging treatment at 583 K (310 °C) for 15 hours.     

Microstructure and Mechanical Properties of Mg-7Al-2Sn Alloy Processed by Super Vacuum Die-Casting

The microstructural evolution of Mg-7Al-2Sn (AT72) alloy processed by super vacuum die-casting and heat treated at various conditions was studied. The results showed that the dendritic microstructure in the as-cast AT72 alloy consisted of α-Mg, Mg₂Sn, and Mg₁₇Al₁₂ phases. After solution treatment at temperatures ranging from 663 K to 703 K (390 °C to 430 °C), the Mg₁₇Al₁₂ phase dissolved into the Mg matrix entirely, while the Mg₂Sn phase partially dissolved into matrix. An average grain size of about 40 μm in the alloy could be achieved after solution treatment at 683 K (410 °C) for 16 hours. A large amount of lath-shaped precipitates of Mg₂Sn and Mg₁₇Al₁₂ was observed in the aged AT72 alloy. The results of tensile property evaluation at room temperature showed that the ductility of the solution-treated alloy was dramatically improved, in comparison with the as-cast alloy. In the peak aged condition, the tensile strength of the alloy was increased, which was attributed to the deposition of fine Mg₁₇Al₁₂ and Mg₂Sn precipitates during the aging treatment.     

Stability of Ni3(Al,Ti) Gamma Prime Precipitates in a Nickel-Based Superalloy Inconel X-750 Under Heavy Ion Irradiation

Phase stability of Ni₃(Al, Ti) precipitates in Inconel X-750 under cascade damage was studied using heavy ion irradiation with transmission electron microscope (TEM) in situ observations. From 333 K to 673 K (60 °C to 400 °C), ordered Ni₃(Al, Ti) precipitates became completely disordered at low irradiation dose of 0.06 displacement per atom (dpa). At higher dose, a trend of precipitate dissolution occurring under disordered state was observed, which is due to the ballistic mixing effect by irradiation. However, at temperatures greater than 773 K (500 °C), the precipitates stayed ordered up to 5.4 dpa, supporting the view that irradiation-induced disordering/dissolution and thermal recovery reach a balance between 673 K and 773 K (400 °C and 500 °C). Effects of Ti/Al ratio and irradiation dose rate are also discussed.     

Evaluating the Superplastic Flow of a Magnesium AZ31 Alloy Processed by Equal-Channel Angular Pressing

Experiments show that the magnesium AZ31 (Mg-3 pct Al-1 pct Zn) alloy exhibits excellent superplastic properties at 623 K (350 °C) after processing by equal-channel angular pressing using a die with a channel angle of 135 deg and a range of decreasing processing temperatures from 473 K to 413 K (200 °C to 140 °C). A maximum elongation to failure of ~1200 pct was achieved in this alloy at a tensile strain rate of 1.0 × 10^?4 s^?1. Microstructural inspection showed evidence for cavity formation and grain growth during tensile testing with the grain growth leading to significant strain hardening. An examination of the experimental data shows that grain boundary sliding is dominant during superplastic flow. Furthermore, a comprehensive review of the present results and extensive published data for the AZ31 alloy shows the exponent of the inverse grain size is given by p ≈ 2 which is consistent with grain boundary sliding as the rate-controlling flow mechanism.