This study investigates the new surface development on AA6061 and AA5086 alloys considering the wire-arc additive manufacturing technique as a direct energy deposition (DED) process of wire. Two different quantities of MWCNTs, i.e., 0.01 (low) and 0.02 (high) g, with a constant nickel (Ni) weight (0.2 g) were pre-placed in the created square patterns. ER4043 filler was used as a wire for additive deposition, and an arc was generated through a tungsten inert gas (TIG) welding source. Furthermore, hardness and pin-on-disk wear-testing methods were employed to measure the changes at the surfaces with the abovementioned inducements. This work was designed to illustrate the hardness and the offered wear resistance in terms of mass loss of the AA6061 and AA5086 aluminum alloys with the function of nano-inducements. Two sliding distance values of 500 m and 600 m were selected for the wear analysis of mass loss from tracks. A maximum increase in hardness for AA6061 and AA5086 alloys was observed in the experiments, with average values of 70.76 HRB and 74.86 HRB, respectively, at a high mass content of MWCNTs. Moreover, the tribological performance of the modified surfaces improved with the addition of MWCNTs with Ni particles in a broader sense; the modified surfaces performed exceptionally well for AA5086 compared to AA6061 with 0.02 and 0.01 g additions, respectively. The system reported a maximum of 38.46% improvement in mass loss for the AA5086 alloy with 0.02 g of MWCNTs. Moreover, the morphological analysis of the developed wear tracks and the mechanism involved was carried out using scanning electron microscope (SEM) images.

An investigation of flow behavior and the deformation mechanism for Ti-6Al-4V alloy during the superplastic deformation process is presented in this paper. Constant strain rate tensile tests were performed at 890–950 °C and strain rates of 10⁻², 10⁻³, and 10⁻⁴/s. Then, surface observation by Optical Microscope (OM), Scanning Electron Microscopy (SEM), and Electron Back-scattered Diffraction (EBSD) was applied to obtain the microstructure mechanism. With pole figure maps (PF) for α-phase, obvious texture gradually changed in the main deformation direction. For the titanium alloy, the evolution of texture in deformed samples was attributed to grain rotation (GR). Significant grain rearrangement occurred between grains after deformation. A complete grain rotation accommodated grain boundary sliding (GBS) deformation mechanism is proposed, which can explain texture evolution without grain deformation.

A physically-based constitutive model with internal state variables (ISVs) is established, it is used to describe the flow stress and microstructure evolution of Ti-6Al-4V alloy in the superplastic forming (SPF). The ISVs in the constitutive model includes the dislocation density, grain size, the volume fraction of dynamic recrystallization. The flow stress consists of σ_fd, σ_ta and σ_GB, which are related to forest dislocation, thermal activation and grain boundary sliding (GBS), respectively. The material constants of the constitutive model are determined by the genetic algorithm (GA) optimization. A modeling method path to optimize the flow stress model is established, which is on the basis of the errors between the predicted and experimental flow stresses. In the modified flow stress constitutive model, the grain rotation (GR) is applied as a hardening mechanism, and the void is treated as a softening mechanism. A new GR model is proposed to describe the flow stress which is related to the GR. The modified constitutive model can accurately predict the evolution of yield stress, grain size and flow stress in SPF. With the calculation results of multi-scales constitutive model, the mechanism of Ti-6Al-4V in SPF is discussed, and a new deformation map with dominant mechanisms for Ti-6Al-4V is obtained.

This work provides a comprehensive investigation of multi-walled carbon nanotubes (MWCNTs) inducement in weldment and their apparent effect on the microstructure, %elongation and ultimate fracture behavior of Al-Mg-Si alloy referring modified tungsten inert gas (TIG) welding joints. Serious experimental work is carried out at 1 wt%, 1.5 wt%, and 2 wt% of MWCNTs to provide a gradually increasing heterogeneous nucleation. The behavior of grain morphology showed the pure field of epitaxial growth without MWCNTs, and the forestry type morphology for 1 wt% MWCNTs at low welding currents (160 A), though there was a noticeable conversion into equiaxed (EQZ) grains filled with inter-dendritic particles at high welding currents (180 A and 200 A) for 1.5 wt% and 2 wt% of MWCNTs. Moreover, the formation of a cellular type network above the fusion line predominated initially at all parameters. Conversely, fine EQZ grains were formed as they moved upward into the welded zone (WZ) explicitly at a high heat input. A conceptual pictorial model is presented in the study which summarized the behavior of morphological changes at the utilized parameters. The welded joints have demonstrated an increasing trend of strength and %elongation in contrast to joints without added MWCNTs. Comparative results have shown an exceptional increment of 71 to 76% and 67 to 75% of elongation up to ultimate tensile strength (UTS), and a fracture point that was clinched for 1 wt% and 1.5 wt% MWCNTs at 180A. From macro to micro-examination of the fracture surfaces, pure ductile modes constituting elliptical cup and cone type isotropic flow was evident in all specimens. Detailed confirmation of the pull-out fracture mode of MWCNTs has highlighted in the scanning electron microscope (SEM) images that intimated a methodical contribution in load-transfer from matrix to the fiber under axial load. Overall, a concise en-route for MWCNTs inducement is well-appointed through tube fillers along with an activating facilitator (TiO₂) in contrast to stereotype fillers for improved behavior termed as modified TIG welding joint process in study.

The present paper is concerned with the dynamic recrystallization of the Ti-6Al-4V alloy. Electron Backscatter Diffraction (EBSD) observations are performed after high-temperatures tensile tests, with the temperature ranging from 700 to ~950 °C, and the strain rates varying between 10⁻⁴ and 10⁻²/s. Based on the analysis of flow behavior, the dominant mechanism is identified, and a mechanism map is proposed. In particular, the conditions of 890 °C and strain rates ranging from 10⁻³ to ~10⁻²/s serve as the delineating boundary of dynamic recovery (DRV) and dynamic recrystallization (DRX). For superplastic deformation, the dominant softening mechanism is DRV. Consequently, the occurrence of continuous dynamic recrystallization (CDRX) can naturally be ascribed to the process of grain refinement. Then, a multi-scales physical-based constitutive model of CDRX is developed, demonstrating a good agreement is obtained between the experimental and calculated grain sizes, so the above model could be used to describe the grain growth for superplastic deformation. In conclusion, DRV and DRX in the superplastic forming of Ti-6Al-4V are studied in this study, the condition boundaries of their occurrence are distinguished, and a constitutive equation-based CDRX recrystallization mechanism is given, which might be employed in the fracture mechanism research.

The activated slip system of Ti-6Al-4V alloy during the superplastic forming (SPF) was investigated by the in-grain misorientation axes analysis (IGMA), and the mechanisms of slip model activation have been discussed. Depending on the distribution of IGMA, one significant discovery from this study is that all the basal, prismatic, and pyramidal slip systems would be activated. Considering the effective slip models, Schmid factors, and the Euler angles together, it is suggested that the dominant slip systems not only desired the largest Schmid factors but strongly demand continuous Schmid factors among the adjacent grains. Meanwhile, the estimated critical resolved shear stress (CRSS) on basal and prismatic at the temperature of 920°C with the strain rate of 10⁻³/s is given. An original method of roughly estimating dominant slip models with Euler angles has been introduced, which predicts that grain rotation may change the slip model. Furthermore, Crystal Plasticity Finite Element Method (CPFEM) is employed to simulate the evolution of Euler angles, and the grain orientation presents the largest set of significant clusters around the (1 100) after deformation. Besides, the continuity of the Schmid factor assumption for the activated slip model has also been verified by CPFEM. In addition, the eigenvector corresponding to the eigenvalue λ₁=1 of Euler angle rotation matrix is calculated to be aligned with the grain rotation axis, which can be applied to describe the grain rotation.