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The current work investigates the possibility of fabricating additive manufacturing products in solid-state form, from AA2011-T6 of 40 mm diameter rods as a feedstock, using an additive friction stir deposition (A-FSD) technique. The use of large diameter feedstocks, especially high-strength aluminum alloys (2XXX series), is a challenge, as it necessitates high power and the critical selection of the optimal A-FSD parameters, such as feed rate and spindle rotation speed. The study included applying a wide range of spindle rotation speeds, ranging from 400 to 1200 rpm, at three levels of feeding rates of 1, 3, and 5 mm/min. The AA2011-T6 friction stir deposited parts (FSDPs) were visually evaluated. This was followed by an examination of macrostructures through the thickness of the fabricated specimens. The characterization of microstructures was also carried out using optical microscopy and a scanning electron microscope equipped with advanced EDS analysis. Furthermore, the mechanical properties in terms of hardness and compressive strength of the AA2011-T6 base material (BM) and deposited materials were evaluated. Sound, additively manufactured products were successfully fabricated from 40 mm diameter AA2011-T6 feedstocks using the suggested deposition variables of 600 and 800 rpm spindle speeds and feeding rates of 1, 3, and 5 mm/min. The results indicated that the spindle speed and feeding rate govern the quality of the FSDPs. Furthermore, the axial load during the A-FSD process increased with increasing these parameters. In comparison to the AA2011-T6 BM, the additively deposited materials showed a refined grain structure and uniform dispersion of the fragment precipitates in their continuous multi-layers. The reduction ratio in grain size attains 71.56%, 76%, and 81.31% for the FSDPs processed at 800 rpm spindle speed and feeding rates of 1, 3 and 5 mm/min, respectively, compared to the grain size of BM. The Al2Cu and Al7Cu2Fe intermetallics are detected in the AA2011-T6 BM, and their deposited parts are in different shapes of spherical, almost spherical, irregular, and rod-like shapes. The compressive strength and hardness of the deposited parts increased with increasing spindle speed and feeding speeds. At a spindle speed of 800 rpm and a 5 mm/min feeding rate, the higher hardness and compressive strength gained were 85% and 93%, respectively, from that of the AA2011-T6 feedstock.

The current work reports the manufacturing and electrochemical characterization of Ti–5%Al–5%Cu, Ti–5%Al–10%Cu, and Ti–5%Al–20%Cu alloys, which were fabricated using mechanical alloying technique. The corrosion of these alloys after varied immersion periods of time in 3.5% NaCl solution was studied using electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, and potentiostatic current time measurements. The phase analyses of the alloys were investigated using X-ray diffraction. Scanning electron microscopy (SEM) was employed to observe the surface morphology of the corroded surfaces whereas the composition of the corrosion products formed on the alloys surfaces was examined using energy dispersive X-ray spectroscopy (EDX). The uniform corrosion of these alloys was found to greatly decrease with the increase of Cu content from 5 wt% to 20 wt%, this occurrence is due to decreasing the values of corrosion current (jCorr) together with corrosion rate (RCorr) and increasing the corrosion resistance (RP). Prolonging the immersion time up to 48 h was found to further increase the values of RP and decrease the values of jCorr and RCorr. Both the electrochemical and the spectroscopic investigations indicated that the increase of Cu content and prolonging the immersion time have significantly decreased all corrosion parameters and increase the corrosion resistance of the alloys in NaCl solution. Keywords: Ti-base alloys, Corrosion, Mechanical alloying, Electrochemical techniques

The effects of oxidation and alumina addition on the physical and mechanical properties of Ti/Al2O3 composites were studied. The variation in alumina addition used in this study was 0, 10, 20 and 30 wt%. The mixture of Ti and Al2O3 was prepared by semi-powder metallurgy method and then pressed and followed by sintering in air atmosphere at 1000 °C for 2 h. The present results show that the density of the sintered Ti/Al2O3 decreased with increasing alumina amount and oxidation. XRD and EDX analysis indicates that the sample free of alumina produced the oxides in the form of TiO2 on the surface of the composite. With alumina addition, the AlTiO2 oxide appears besides TiO2. This occurrence confirms that the oxidation of Ti increases with increasing the amounts of alumina. The intermetallic phase Ti3Al has appeared in the Ti/Al2O3 composites, which might be due to reduction in alumina by Ti. The oxidation of Ti/Al2O3 composites decreases the hardness and compressive yield strength and hardness values. The decrease in mechanical properties becomes more obvious with increasing the alumina amount which enhanced the formation of oxidation scales after sintering.

In this study, manufacturing of Ti–5Al and Ti–5Al–5Cu alloys were accomplished employing mechanical alloying technique. The corrosion resistance in 3.5 wt% NaCl solution of Ti–5Al and Ti–5Al–5Cu alloys was investigated using cyclic polarization (CPP), electrochemical impedance spectroscopy (EIS) and chronoamperometric current–time measurements. The corroded surfaces of Ti–5Al and Ti–5Al–5Cu were examined by the use of a scanning electron microscopy and energy dispersive X-ray spectroscopy. It is found that Ti–5Al suffers both uniform and pitting corrosion, particularly with prolonging the time of exposure period in the chloride solution. While, the addition of Cu, Ti–5Al–5Cu alloy, increases the intensity of uniform corrosion and decreases the probability of pitting attack. Prolonging the immersion time to 48 h before measurement decreases the corrosion of Ti–5Al alloy, while increases the corrosion of Ti–5Al–5Cu.

Polyester-based composites filled with various contents of alumina (Al2O3) (i.e., 0, 1, 5, and 10 vol%) have been fabricated in this study. Physical and mechanical properties of the composites have also been analysed. The analysis results showed that the experimental density of the polyester/alumina composites was smaller than the theoretical density, which could be attributed to the formation of voids during preparation of the composites. Meanwhile, the tensile strength, stiffness, and hardness of the composites increased with increasing alumina content, while the strain-at-break of the composites decreased. It was observed that the composites containing 5 vol% of alumina had the best tensile strength, stiffness, and hardness. The uniform distribution and dispersion of alumina particles were likely responsible for the improvement of the mechanical properties. In other hand, small decrease in tensile strength, stiffness, and hardness of composite was found in the composites with 10 vol% of alumina. The formation of agglomerates and voids was believed to be the main factor for the decrease of the both properties.

The oxidation and hardness of thermally exposed titanium (Ti) prepared using inductive sintering-assisted powder metallurgy was evaluated through cyclic tests in air at 700&ndash, 900 C for 100 h (5 cycles). In general, the oxidation kinetics of the Ti samples followed the parabolic law and their oxidation rates increased with increasing oxidation temperatures. The rutile form of titanium dioxide (TiO2) was detected by X-ray diffraction in the oxide scales after oxidation at 700 C and 900 C. Furthermore, the TiO2 grain size and thickness were significantly influenced by an increase in the oxidation temperature. Lastly, the formation of rutile as a single-phase on the surface of oxidized Ti enhanced the hardness of the oxide scales, whereas the substrate had lower hardness values than the oxide scales due to diffusion of Ti atoms at the surface to form the TiO2 oxide scales.

Morphological analysis of the nanocomposites showed that multi-wall carbon nanotubes were uniformly distributed in polypropylene. Nanoindentation creep and nano-impact tests were carried out. Several equations/models were used to analyze creep data. From creep test, hardness of the nanocomposites increased by 18 and 36% for C150P and C70P, respectively, compared to polypropylene, whereas elasticity also increased by 20 and 34%. From nano-impact test, hardness of the nanocomposites was also higher than that of neat polypropylene. However, hardness (dynamic/impact) values were slightly higher than the (quasi-static) hardness resulted from creep test. In addition, degree of crystallinity of nanocomposites also increased by 12.6 and 14.3%.

The thermal oxidation behavior of Fex(CoCrMnNi)100-x high-entropy alloys (x = 20 and 40 at.%) and medium-entropy alloy (x = 60 at.%) at temperatures ranging from 900 °C to 1100 °C under air atmosphere was investigated. The oxidation kinetics of the alloys followed the parabolic law, indicated by the increase of oxidation rate constants with increasing Fe content and temperature. The addition of Fe content lowered the configurational entropy and activation energy of the alloys, supporting the acceleration of metal atoms diffusion. Furthermore, the oxide scales formed on the surface were strongly dependent on the alloy composition. In general, a Cr2O3 inner layer, spinels (NiCr2O4 and CoMn2O4) as intermediate layers, and the outer layers of Fe3O4 and Mn3O4 were formed after oxidation at 900 °C in all alloys. On the other hand, severe internal oxidation and pores were observed in the alloy containing 60 at.% of Fe after oxidation at 1100 °C. In addition, the pores were formed due to the Kirkendall effect, acting as diffusion path and reaction place which may facilitate the oxidation process.

The combined effects of thermo-mechanical treatment and equal channel angular pressing (ECAP) on the strength and microstructure of Cu-3.75Ag were studied. The strength of Cu-3.75Ag at 1% strain after eight passes of ECAP with two intermediate heat treatments reached 758 MPa and 849 MPa in route A and route Bc respectively. The hardness increased upon heat-treatment in route Bc, in contrast to the drop of the hardness in route A, suggesting that the hardening caused by re-precipitation is more active due to more effective dissolution of second-phase particles in route Bc. The flow stress increased more rapidly with intermediate heat treatments and reached 842 MPa after 8 passes, greater than that (791 MPa) without intermeadiate heat treatment in route Bc. The more rapid increase of strength/hardness and the attainment of higher hardness/strength after intermediate heat treatment are likely to be attributed to the formation of more stable wall structure and rearrangement of solute atoms/precipitates. The spacing between precipitates in Cu-3.75Ag ECAPed for 4 pass in route Bc was measured to be approximately 12.5 nm, which is close to the calculated activated length (12.8 nm). The most probable rate controlling mechanism of Cu-3.75 Ag is suggested to be the interaction between dislocations and precipitates.

The influence of post ageing treatment on creep behaviour of aluminide coating prepared by low-activity high-temperature on a Ni-based single crystal superalloy was investigated. The results showed that the aluminide coating reduced the creep behaviour of Ni-based single crystal superalloy. The decrease in creep behaviour may be due to the change in microstructures after aluminizing treatment. However, the post ageing treatment at low temperature has successfully improved the creep behaviour of aluminized Ni-based single crystal superalloy. The increase in creep behaviour of aluminized Ni-based single crystal superalloy after post ageing treatment was due to the formation of fine spherical carbides which are distributed in the substrate of Ni-based single crystal superalloy. These fine spherical carbides are able to hinder the dislocation movement and suppress the amount of topologically close-packed phase.

Influence of primary and secondary orientations on the creep behavior of aluminized single crystal Ni-based superalloy was investigated at a high temperature with various tensile stress directions and side-surface orientations. The specimens were aluminized by pack aluminizing treatment at 1000 °C for 5 h under argon flow. The creep rupture tests were performed at 900 °C/392 MPa for thick specimens and at 900 °C/300 MPa for the thin specimens. The aluminizing treatment reduced the creep strength of the superalloy because of the crack initiation in hardened diffusion layers. Furthermore, it was found that the creep strength of thin aluminized specimens was affected by the crystallographic orientations, not only in the tensile direction, but also in the thickness direction. This is due to the difference in the crystallographic geometry of {111} planes, which is associated with the magnitude of 〈112〉 direction shear stress on the planes and the effective cross-section change by the crack propagation.

The effect of thermal exposure on the creep properties of an aluminized Ni-based single crystal superalloy in different surface orientations has been studied in the present study. The specimens were coated by a pack aluminizing process conducted at 1000 °C for 5 h under an argon atmosphere. Long-term exposure was performed at 1100 °C for 500 h prior to the creep test. The creep properties were found to deteriorate after the long-term exposure as a result of the coarsening of γ′ precipitates accompanied by the formation of a secondary reaction zone which is known to degrade the strength of aluminide coating on a Ni-based single crystal superalloy. The formation of a topologically close-packed phase is one of the degradation factors that are responsible for the reduction of the creep strength of the aluminide coating on a Ni-base single crystal superalloy both with and without long-term exposure. The anisotropic creep properties between the two side-surfaces are due to the different arrangements of { 1 1 1 } 〈 1 0 1 〉 slip systems.

An investigation on oxidation behavior of coated Ni-based single crystal superalloy in different surface orientations has been carried out at 1100 °C. It has been found that the {100} surface shows a better oxidation resistance than the {110} one, which is attributed that the {110} surface had a slightly higher oxidation rate when compared to the {100} surface. The experimental results also indicated that the anisotropic oxidation behavior took place even with a very small difference in the oxidation rates that was found between the two surfaces. The differences of the topologically close packed phase amount and its penetration depth between the two surfaces, including the ratio of α-Al 2 O 3 after 500 h oxidation, were responsible for the oxidation anisotropy.

The influences of ruthenium and surface orientation on creep behavior of aluminized Ni-base single crystal superalloys were investigated by comparing two different types of NKH superalloys. The aluminized coated specimens were then subjected to creep rupture tests at a temperature of 900 °C and a stress of 392 MPa. The coating treatment resulted in a significant decrease in creep rupture lives for both superalloys. The diffusion zones between the coating and substrate led to changes in microstructure, which diminished the creep behavior of the aluminized superalloys. Because of the interdiffusion of Ru, Al and Ni, the solubility of some of the refractory elements, such as W, Re. Mo, Co and Cr decreased in the diffusion zone; the precipitation of topologically close-packed (TCP) phases was thus inevitable. In the present study, the addition of Ru increased the degree of Re and Cr supersaturation in the γ matrix. Consequently, the addition of Ru indirectly promoted the precipitation of TCP phases in aluminized Ni-base single crystal superalloys. Furthermore, the growth of TCP precipitates was greatly influenced by the specific surface orientations of the Ni-base single crystal superalloys. In conclusion, the {110} specimens showed shorter creep rupture life than the {100} specimens, this was due to the difference in the crystallographic geometry of {111}〈101〉 slip system and TCP precipitates between the two side-surface orientations of the specimens.

The influence of heat treatment on creep behavior of aluminide coating on a Ni-base single crystal superalloy with different surface orientations was examined. The specimens were coated by pack aluminizing treatment at 1000 °C for 5 h under argon environment. The coated specimens were then tested by the tensile creep test at a temperature of 900 °C and a stress of 320 MPa. To determine the effect of aluminide coating, the bare specimens were also tested. The aluminizing treatment decreased the creep strength of Ni-base single crystal superalloy. The solution heat treatment procedures had a great impact on the creep behavior of Ni-base single crystal superalloy. The combination of solution treatment and subsequent double aging treatment was effective to improve the creep strength of Ni-base single crystal superalloy because of more regular the shape of γ′ precipitates and more homogeneous distribution of γ′ precipitates. In addition, the {1 0 0} specimens showed a better creep lives than those {1 1 0} specimens both in aluminized specimens and bare specimens. The anisotropic creep behavior was primarily induced by the different arrangement of {1 1 1} 〈1 0 1〉 slip systems between the two surface orientations of the specimens. The difference in creep rupture lives between {1 0 0} and {1 1 0} side-surface specimens was more pronounced in the specimens STA than in the specimens A because of homogenization of the γ/γ′ microstructure promoted the deformation by {1 1 1} 〈1 0 1〉 slip system which leads to anisotropy of creep behavior. Moreover, the change in microstructures was also considered as one of factors for the decrease of creep life. Besides, the formation of TCP phase, the depth of TCP phase penetration and the gradient of hardness values in the coating to the substrate regions would be additional factors to clarify the anisotropic creep behavior in aluminized Ni-base single crystal superalloy.

Oxidation behavior of an aluminized Ni-based single crystal superalloy CM186LC was performed between 900 °C and 1100 °C in air. The oxidation kinetics approximately followed a parabolic oxidation law at 900 °C and 1100 °C. The mass gains were significantly increased owing to the formation of θ-Al2O3 during initial oxidation stage. After 100 h oxidation, the mass gain rates were then decreased due to the transformation from θ-Al2O3 to α-Al2O3. The microstructures after 500 h oxidation at all temperatures generally consisted of scale, coating layer, interdiffusion zone (IDZ), substrate diffusion zone (SDZ) accompanied with the topologically close-packed (TCP) and substrate.

We examined the creep behavior of aluminized Ni-based single crystal superalloy TMS-75 with {100} and {110} side-surfaces. The specimens were aluminized by pack aluminizing treatment at 1000 °C for 5 h under argon flow. The creep rupture tests were performed at 900 °C under a stress of 392 MPa. The stress orientation of all of the specimens was within 4° of 〈001〉. It was evident that the {100} specimens exhibited higher creep rupture lives compared to the {110} specimens, indicating that anisotropy of the secondary orientation—which is normal in the primary orientation—occurred. The anisotropic creep behavior of the aluminized specimens was induced primarily by the different arrangements of {111} 〈101〉 slip systems between the two side-surface orientations. The gradient of hardness values in the coating-to-substrate regions and depth of TCP penetration were additional degradation factors.

An aluminized Ni-based single-crystal superalloy was examined to investigate the anisotropic creep properties at intermediate and high temperatures. It was found that the specimens with a (1 0 0) side surface showed longer creep rupture life than the specimens with a (1 0 0) side surface. This means that anisotropy of the secondary orientation, which is normal to the primary orientation, occurred. The anisotropic creep behavior of the aluminized specimen was induced by a different arrangement of {1 1 1}〈1 0 1〉 slip systems between the two side-surface specimens.

The effects of different sintering temperatures, namely 400, 500 and 600 °C, on the mechanical properties of four aluminum–graphite alloys were reported. Different percentages of exfoliated graphite nanoplatelets particles (xGnP) were added to pure aluminum by using the powder metallurgy technique to produce Al-0 wt.%xGnP, Al-1 wt.%xGnP, Al-3 wt.%xGnP, and Al-5 wt.%xGnP. The density, fracture surface, compression, and hardness measurements were carried out to report the mechanical properties of the different aluminum–xGnP alloys. Combined data indicated that the Vickers hardness and compressive strength increase, on the other hand, the density decreases with increasing the graphite content in the Al alloys.

Aluminum composites with different amounts of exfoliated graphite nanoplatelets particles were fabricated by powder metallurgy method. The mixture powders were consolidated at 520 MPa for 5 min and followed by pressureless sintering at 600 °C for 6 h. The mechanical properties of composites were evaluated by compression and hardness tests. The corrosion behavior in 3.5% NaCl solution was investigated using potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) measurements. The mechanical testing results showed that the maximum strength and Vickers hardness increase as a function of exfoliated graphite nanoplatelets content. Corrosion data indicated that the presence of exfoliated graphite nanoplatelets and the increase of its concentration raise the corrosion rate and reduce the polarization resistance of Al. SEM/EDX investigations revealed that the presence of exfoliated graphite nanoplatelets activates the corrosion of Al due to the occurrence of galvanic corrosion. SEM/EDX investigations confirmed the electrochemical measurements showing that the increase of exfoliated graphite nanoplatelets content increases the corrosion of Al.

The effect of chemical compositions and secondary crystallographic orientation dependence on the formation of diffusion layer and creep behavior were investigated. Three alloys of different generations: PWA 1480 (1 st generation), CMSX-4 (2 nd generation) and TMS-75 (3 rd generation), were studied. After aluminized coating process, creep rupture test were performed at 900 °C and 392 MPa. The creep rupture properties of the alloys with and without the aluminized coating treatment were compared. The coating treatment resulted in a significant decrease in rupture lives for three alloys. No reductions in rupture elongation were observed. Creep strength was significantly degraded with aluminide coating due to the diffusion layers formed under coating layer. Creep fractures of the coated materials were essentially controlled by the crack nuclei in the coated layer. It was also found that the specimens with (100) side-surface showed longer creep rupture life than the specimens with (110) sidesurface, which means the results were anisotropic with respect to the secondary orientation which is normal to the primary orientation. The anisotropic creep behavior was caused by the different arrangement of {111} slip systems between the two side-surface specimens. The results obtained in this study suggest the importance of secondary orientation normal to the component surface on designing the single-crystalline turbine blades.