The impact toughness of a few selected precipitation hardening aluminium alloys that have potential for vehicle armour applications is reported for the first time. It is observed that although the impact toughness is considerably higher in the solution heat-treated condition, it degrades with artificial ageing. The formation of weak grain boundaries in the artificially aged tempers is the major cause of poor impact toughness in these alloys. The impact toughness of commercially purity aluminium is reported for the first time within the context of the present work.

The effect of Sc addition to AA2195 (NoSc) alloy by 0.025 wt A_1^* and A_2^* ideal shear texture components and an increase in the intensity of the C components (100 < 011 >), resulting from the easier dynamic recovery and recrystallization that occurs with the presence of larger precipitates. As a result, the highest microhardness was achieved in the LoSc alloy due to the formation of a nanocrystalline microstructure along with a homogeneous distribution of nanoscaled precipitates. This fine distribution of precipitates in LoSc alloy retained the smallest crystallite size and highest dislocation density at the disk periphery around a strain of 30. These enhanced properties in LoSc were attributed to the nearly homogeneous formation of fine precipitates ranging between 15 and 25 nm within the grains and < 100 nm at the grain boundaries during HPT processing.

The hot workability of third generation AA2195 (Al-Li-Cu-Ag-Mg-Zr) alloy with different Sc (0.15-0.25 wt%) and Nb (0.15-0.25 wt%) additions in the homogenized condition was investigated using processing maps approach. The additions of Sc and Nb were found to be beneficial in refining the as-cast grain size of AA2195 and changing the morphology from less dendritic grain structure to a globular or equiaxed form. Hot compression tests carried out in the temperature, T, range of 300-450 degrees C and strain rate, (epsilon)over dot, of 10(-3) - 10 s(-1) were utilized to generate processing maps at a true strain, epsilon = 0.5. The flow curves of the alloys exhibit a typical dynamic recovery (DRV) characteristics and Arrhenius type constitutive equations successfully predicted flow stress of the alloys. The results obtained from the processing maps and complementary microstructural analysis of the deformed specimens revealed that 0.15 wt% additions of Sc and Nb (separately or in combination) are optimum to improve its workability. However, increasing Sc and Nb contents to 0.25 wt% relatively expanded flow instability regions. With the aid of the processing maps, deformed specimens microstructural analysis, activation energy and Zener-Hollomon parameter, Domain D-3 occurring at higher temperatures and strain rates were identified as the "safe" regimes for hot working of AA2195 with optimum Sc and Nb contents (0.15 wt% added separately or in combination). Limited pancake type grain morphology with higher fractions of dynamically recrystallized (DRX) grains was observed in Domain D-3. The microstructural manifestation in the flow instability regions was flow localization (at higher strain rates), cavities formation at the grain boundaries & precipitates, particles breakage and wedge cracking at the triple junctions at lower strain rates.

In the present work, attempts have been made to control the yield strength anisotropy in an Al–Cu-Li alloy by implementing a novel processing route combining multi-axial forging (MAF) and rolling with an aim to weaken the texture. It has been observed that continuous destabilization of deformation texture during MAF results in weakening of texture. Further weakening of texture could be achieved upon post MAF cold cross rolling, which has been attributed to (i) the geometry induced shear in the roll gap, and (ii) the change in strain path during rolling. Such a weak texture is in contrast to strong Brass-type texture, generally observed in these alloys. Further annealing in the solution treatment regime led to even more weakening of texture. Uniaxial tensile tests along different directions of the as-processed sheets confirmed the weak dependency of yield strength on orientation of tensile axis.

In the present study, the evolution of microstructure, crystallographic texture and their influence on mechanical properties of the Al–Li alloy, AA2195 has been studied. A novel hybrid processing route involving warm multi-axial forging (MAF) and subsequent warm rolling was employed. Different rolling procedures were followed to obtain optimal microstructure and properties. The processing conditions significantly influenced the course of evolution of microstructure and texture. A variation in tensile properties as a function of angle from RD for the differently processed samples was noticed. The tensile properties were closer to isotropic case for the samples deformed using a combination of MAF with cross rolling. By controlling grain size and texture through optimal processing, it was possible to achieve isotropic tensile properties in the AA2195 alloy. The processing conditions have also led to enhancement in strength, which has been attributed to grain boundary strengthening, precipitation strengthening and dislocation strengthening.

The sample geometry by way of its influence on stress distribution is expected to control the superelastic and fatigue behavior of Nitinol. A variety of sample geometries are reported in literature for studying the fatigue behavior of Nitinol and it is unclear which geometry is the most suitable. To establish this, we conducted finite element simulations on the different geometries employing the ANSYS software package. Guided by the simulation predictions, samples bearing two different geometries, g_1 and g_5, were fabricated from Nitinol sheetswhich were apriori heat treated at 300 degrees C. The heat treated Nitinol was characterized by optical microscopy and differential scanning calorimetry to reveal the grain structure and transformation temperatures. Tensile samples of this material were subjected to cyclic uniaxial tensile tests where the maximum stress was increased gradually from 600 to 800 MPa in steps of 100 MPa every 10 cycles. The residual strain at the end of every 10th cycle was noted and found to be higher for g_1 compared to g_5. X-ray diffraction investigations on the cycled samples indicated a higher residual martensite phase in g_1 compared to g_5. The higher residual martensite is considered to be the cause of the poorer fatigue life of samples bearing geometry g_1 compared to that of g_5. Scanning electron microscope studies validated the fatigue measurements as the g_1 fractographs demonstrated higher void fraction vis-a-vis g_5.

Hot deformation behavior of equiatomic FCC CoCuFeMnNi complex concentrated alloy has been investigated via isothermal compression tests on Gleeble-3800 thermo-mechanical simulator in the temperature (T) range of 1073-1273 K and strain rate (epsilon)over dot range of 1-10(-3) s(-1). This has been aided with detailed microstructural analysis using SEM, EBSD and TEM to decipher the deformation micro-mechanisms during hot compression tests. The processing maps have been constructed by superimposition of the instability map with efficiency map and the optimum thermo-mechanical processing conditions were found to be T = 1173 K, (epsilon)over dot = 10(-3) s(-1) and T = 1273 K, (epsilon)over dot = 10(-2) s(-1). Microstructural investigation using SEM and EBSD reveal phase separation between Cu-rich and Cu-lean regions wherein Cu-rich FCC phase at the grain boundaries undergoes discontinuous dynamic recrystallization (DDRX) while the Cu-lean phase undergoes dynamic recovery (DRV). The average activation volume in the range of 44-250 b(3) suggest that cross slip is the rate controlling mechanism during the deformation and activation energy of 394 kJ/mol, that is almost twice than that for diffusion in copper, indicate contribution from both mechanical and thermal component to the overall activation energy. It is evident that the diffusion assisted copper segregation aids in obtaining higher efficiency of deformation and easy processability due to a unique microstructure comprising of Cu-lean grains surrounded by soft Cu-rich grains near grain boundaries which undergo DDRX. Numerical simulations using finite element method are able to correctly predict hot deformation behavior, establishing the processing-microstructure-property paradigm in CoCuFeMnNi complex concentrated alloy.

In this study, one of the severe plastic deformation (SPD) techniques, Equal Channel Angular Pressing (ECAP) has been successfully applied to the Al-Cu-Li alloy AA2195 at 250 degrees C and the development of microstructure, texture and mechanical properties has been studied. A systematic analysis has been carried out by using EBSD and TEM to understand the microstructural features, and the nature of different precipitates presence in the alloy AA2195. Microstructural features indicate considerable grain refinement leading to an average grain size of 2.8 +/- 0.7 mu m after 4 ECAP passes. Continuous dynamic recrystallization (CDRX) has been identified as the mechanism that leads to the formation of fine grain structure in the alloy AA2195 during the warm ECAP process. TEM results confirm the distribution of strengthening precipitates delta'(Al3Li),beta(Al3Zr) and T-1(Al2CuLi) in the alloy. The overall texture has become weak after ECAP processing and has been simulated using Visco-plastic self-consistent simulation (VPSC). The evaluation of mechanical properties indicates a substantial increment in hardness, strength properties with a minor reduction of ductility after 4 passes. Low mechanical property anisotropy is expected in the processed AA2195 alloy due to its weak texture. (C) 2019 Elsevier B.V. All rights reserved.

In the present study, influence of Scandium (Sc) content (0.025 and 0.25 wt%) on microstructure, texture and mechanical properties of a thermo-mechanically processed AA2195 alloy has been investigated. Addition of Sc to AA2195 alloy results in grain refinement and enhanced precipitation kinetics. TEM analysis revealed the presence of Al-3(Sc,Zr) dispersoids in the Sc containing AA2195 alloys. Solution treatment and peak aging of the Sc containing alloys revealed partially recrystallized microstructure. Texture of Sc containing alloys displayed weaker Brass component compared to the Sc free material. A clear improvement in hardness and strength was observed which could be attributed to grain refinement as well as the presence of fine Al-3(Sc,Zr) dispersoids. Ductility decreased slightly on Sc addition and there was an associated change in fracture mode as a result of Sc addition. (C) 2017 Elsevier B.V. All rights reserved.

Al–Cu–Li–Mg–Ag–Zr alloy AA2195, in the form of 4mm thick sheets, was heat treated to T87 temper with the pre-aging cold work provided by a combination of 5% cold rolling followed by 2% stretching. The tensile properties of the material were evaluated at ambient and cryogenic temperatures (i.e. −196°C and −253°C). Transmission electron microscopy of the heat treated (i.e. T87 treated) material revealed that the major strengthening precipitate is indeed the T1 (Al2CuLi) phase nucleated on the {111}Al planes. In addition, θ′ [metastable Al2Cu (θ)] precipitates on {100}Al planes, and “plate like features” lying on {111}Al planes were further observed. The one atom layer thick “plate like features” have the same crystal structure as that of the matrix Al. The possibility of such “plate like features” being either the early stages of the Ω phase (i.e. a chemically modified coherent form of θ-Al2Cu phase) in the constituent Al–Cu–Mg–Ag system or the evolutionary stages of the T1 phase itself is discussed.

Constant stress amplitude fatigue life of an austenitic Ni (55.88wt.%)–Ti shape memory alloy (SMA) within the stress amplitude range of 180–450MPa was evaluated. The stress–strain hysteresis loops were monitored throughout the fatigue loading. They reveal that with the increasing number of fatigue cycles, the critical stress required for the stress-induced martensitic transformation, width of the hysteresis loop, recoverable and frictional energies of each cycle, all decrease while accumulated plastic strain increases. Post-mortem characterization of the fatigued specimens by employing differential scanning calorimetry (DSC), X-ray diffraction (XRD), and fractography were carried out, in order to understand the fatigue micromechanisms. Results indicate that the progressive accumulation of stress-induced martensite in the alloy is the source for the fatigue failure. Implications of these observations are discussed within the context of fatigue performance of SMAs and other materials that undergo stress-induced transformations.

Progressive accumulation of stress-induced martensite during cyclic loading of NiTi shape memory alloys results in both structural and functional fatigue. We present experimental data demonstrating that periodic annealing of the fatigued samples above the austenite finish temperature ('healing') retransforms the residual martensite back into the parent phase, and therefore enhances the fatigue life (stress-controlled testing, structural fatigue) or partly reverses the changes in the pseudo-elastic hysteresis (strain-controlled testing, functional fatigue).

Increased strength to weight ratio of aluminium–lithium alloys has attracted material scientists to develop these for aerospace applications. But commercial scale production of these alloys has always been slow in view of difficulties encountered during addition of lithium and in ensuring homogeneous billet composition. A new technique of Li addition has been adapted, which gives maximum recovery of Li in the billet. Using this technique, aluminium–lithium alloys of two different grades for aerospace application were cast. Billets were hot forged and rolled to the thickness range of 3–4mm and heat-treated for different temper conditions. Mechanical properties were evaluated in T6 (solution treated and artificial aged), T8 (solution treated, cold worked and artificial aged) and T4 (solution treated and natural aged) temper conditions. Both alloys exhibit a strong natural aging response. Reversion for short periods at 180°C results in decrease of strength. With artificial reaging strength reaches above the T4 temper condition level. Characterization was carried out using optical microscope (OM) and scanning electron microscope (SEM). Experimental investigation shows that addition of lithium at high melt temperature gives lower recovery of Li, and use of impure aluminium adversely affects the mechanical properties of the alloy in all temper conditions.

Analytical investigation of homogenization of aluminum alloy (AA2219) was carried out for different grain sizes. Homogenization parameters were calculated using diffusion laws. Probable low melting eutectic formation in Al-Cu alloys was also considered. A two step homogenization cycle was found as optimum for the AA2219 Al alloy with respect to different grain sizes.On a effectué une investigation analytique de l’homogénéisation de l’alliage d’aluminium (AA2219) pour différentes tailles de grain. On a calculé les paramètres d’homogénéisation en utilisant les lois de la diffusion et l’on a considéré la formation probable d’un eutectique à faible point de fusion des alliages d’Al-Cu. On a trouvé un cycle optimal d’homégénéisation à deux étapes pour l’alliage d’Al AA2219 par rapport aux différentes tailles de grain.

An analytical evaluation of homogenization of aluminum alloy AA2219 with different grain sizes is performed. The homogenization parameters are computed with the use of diffusion laws and under the assumption that a low-melting eutectic can form in alloys of the Al - Cu system. With allowance for the difference in the grain sizes a two-stage homogenization regime is shown to be optimum for alloy AA2219.