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Friction stir welding (FSW) was introduced to join laser powder bed fusion (LPBF) AlSi10Mg alloys in this study. Microstructure and texture evolution, microhardness distribution and tensile properties of the FSW joints were investigated. The evolution of grain size, grain boundary and misorientation angles distribution, dynamic recrystallization and crystallographic texture in various regions of the FSW joint concerning base metal (BM), thermo-mechanically affected zone (TMAZ), upper part of nugget zone (UPNZ) and low part of nugget zone (LPNZ) was characterized by using electron back-scattered diffraction (EBSD). The analysis reveals a strong texture evolution of shear components on the TMAZ, UPNZ and LPNZ as well as a fully recrystallized grain structure on the UPNZ and LPNZ. Additionally, a gradual evolution in Si-rich eutectic from continuous cellular networks in the BM to totally globularized particles in the UPNZ and LPNZ occurs in the FSW joint. The microhardness rapidly decreases to the TMAZ from the BM through heat affected zone (HAZ) reaching the lowest value of ∼65.0 HV at the TMAZ/NZ boundary. The FSW joint in LPBF AlSi10Mg alloys exhibits an ultimate tensile strength (UTS) of 247 MPa and an elongation-to-failure (EI) of 8.8%. The UTS of FSW joints is reduced compared to the BM, but the EI has been increased by 160%, implying an improvement in tensile ductility. [Display omitted] • Friction stir welding was introduced to weld laser powder bed fusion AlSi10Mg. • New shear textures of F, R-Goss and R-Cube components are developed in the FSW joint. • LAGBs are increased in the TMAZ, and a high fraction of HAGBs is developed in the NZ. • FSW of LPBF AlSi10Mg results in a gradual evolution of Si-rich phase morphology in the joint. • FSW of LPBF AlSi10Mg produces the highest UTS of 247.0 MPa and the maximum EI of 8.8%. [ABSTRACT FROM AUTHOR]

Environmental silicate debris such as sand, dust and volcanic ash is regarded as a major hazard for aviation safety. During the service process of gas turbines, these ingested silicate ashes can melt, impact and adhere to the thermal barrier coatings (TBCs) covered on the hot-section components, facilitating their structure and property instability. Here, we prepared a novel NdYbZr 2 O 7 coating which is expected to mitigate this issue. We comparatively study the infiltration behavior of natural volcanic ash and synthetic CMAS within it at 1250 ºC and 1300 ºC. In the case of volcanic ash, the lower CaO content improves the Nd3+ and Yb3+ solubility, suggesting more NdYbZr 2 O 7 coating has to be consumed to saturate the melt. The chemical reaction is delayed, and melt has more time to infiltrate. As a result, although volcanic ash has a relatively high viscosity, it exhibits a larger infiltration depth than CMAS. Apatite with a theoretical A 4 Ⅰ A 6 Ⅱ (Si O 4) 6 X 2 structure is the main corrosion product for either volcanic ash or CMAS. The calculated A Ⅰ : A Ⅱ ratios are 0.14 and 0.30 respectively, which indicates that precipitating per unit apatite needs to consume more NdYbZr 2 O 7 coating. In comparison with traditional YSZ coating, NdYbZr 2 O 7 coating exhibits a better anti-corrosion performance by rapidly precipitating crystalline grains (c -ZrO 2 and apatite) and further building dense reaction layer. • The Nd3+ and Yb3+ solubility in volcanic ash is higher than that of CMAS, negatively affecting the inhibition. • More NdYbZr 2 O 7 coating is consumed to precipitate per unit apatite in volcanic ash case. • NdYbZr 2 O 7 coating has an outstanding anti-corrosion performance in the presence of both volcanic ash and CMAS. [ABSTRACT FROM AUTHOR]

• A new method of non-contact ultrasonic-assisted laser metal deposition was used to perform laser deposition of Fe-based powder with 42CrMoA substrate. • The effects of ultrasonic amplitude (UA) and excitation distance (d) on the depth width of deposition layer, columnar crystal length, grain size and distribution, and mechanical properties were studied. • Due to the cavitation effect of ultrasonic, it effectively refines the grains and promotes the columnar to equiaxed transition (CET) of grains at the interface. Meanwhile, the cracks generated in the deposition layer can be effectively inhibited and the mechanical properties can be improved. • The application of ultrasonic-assisted can effectively improve the mechanical properties of the deposition layer, and the uniformity of mechanical properties is improved. In order to study the effects of ultrasonic parameters on the microstructure and mechanical properties of non-contact ultrasonic assisted laser deposition, Fe-based powder was deposited on 42CrMoA steels with different ultrasonic amplitudes (UA) and excitation distances (d). The results show that the ultrasonic-assisted laser metal deposition (LMD) of Fe-based powder increases depth and width of the deposition layers. Due to the cavitation effect of ultrasonic, it effectively refines the grains and promotes the columnar to equiaxed transition (CET) of grains at the interface. When d = 50 mm, the grain size greater than 8 μm accounts for only 3.1 %, but the ultrasonic vibrations haven't changed the phase type of the structures. With ultrasonic-assisted, the cracks generated in the deposition layer can be effectively inhibited and the mechanical properties can be improved. When d = 80 mm and UA = 30 μm, the average microhardness of the deposition layer reaches 772.9 HV, which is 95.8 HV higher than that without ultrasonic-assisted deposition. When UA = 40 μm, the tensile strength is 1237.9 MPa, which is increased by 26.8 % compared to without ultrasonic-assisted deposition. Compared to without ultrasonic-assisted, the friction coefficient of deposition layers is significantly decreased by 25.5 % with the application of UA = 30 μm. [ABSTRACT FROM AUTHOR]

Volcanic ash dispersed in the air adheres to thermal barrier coatings (TBCs) on the hot section components of gas turbines, posing a severe threat to aviation safety. Here, we report a novel strategy inspired by lotus leaf for mitigating the molten volcanic ash adhesion and corrosion. A hierarchical micro-nano structure composed of arrayed micro-conoids and numerous nanoparticles were constructed on the surface of NdYbZr 2 O 7 ceramic pellet by ultrafast laser direct writing technology, whose morphology could be changed by optimizing the processing parameters. The laser-ablated pellet exhibits larger contact angle of molten volcanic ash than the original one, revealing an enhanced resistance repelling volcanic ash. This phenomenon is primarily attributed to the air trapped in the micro-grooves, together with these nanoparticles. Note that the evolution of viscous force and capillary force with time accelerates the transition of molten volcanic ash from the Cassie state to the Wenzel state and reduces its contact angle. Also, this structure effectively inhibits the infiltration of molten volcanic ash by rapidly developing a reaction layer. These findings are an important step toward the design and development of next-generation silicate ash-repellent TBCs. [ABSTRACT FROM AUTHOR]

• A novel composite interlayer prepared with V multi-layers and a CrZrCu plate is introduced to join steel/Ti joint. • A sound steel/Ti joint is successfully obtained using the prepared composite interlayer. • The steel/Ti joint with 1.2 mm-thick V layer possesses the maximum UTS of 418 MPa and an EI of 15 %. • It can be found that Cu solid solution and V solid solution are generated in the FZ and FZ/V interface at TC4 alloy side. Vanadium (V) interlayers of 0.4 mm, 0.8 mm, and 1.2 mm thickness were firstly deposited on the TC4 alloy side using a laser metal deposition (LMD) process, which was then combined with a CuCrZr plate as a composite intermediate layer, for dissimilar laser welding of TC4 titanium alloys to 304 stainless steels (SS) successfully. The effects of different thicknesses of V interlayers on the weld shape, microstructure and mechanical properties of TC4/304SS joints were investigated. The results show that a sound TC4/304SS butt joint with full penetration is successfully obtained using the prepared composite interlayer. The TC4/304SS joint exhibits a maximum ultimate tensile strength (UTS) of 418 MPa and an elongation index (EI) of 15 % with a V layer thickness of 1.2 mm. With the V-layer thickness increasing, the size and content of the V-Cu solid solution in the fusion zone (FZ) on the TC4 alloy side are gradually increased without the formation of intermetallic compounds (IMCs) generated. [ABSTRACT FROM AUTHOR]

The additive manufactured (AM) parts of aluminum alloys have been widely used in defense, aerospace, automotive and other industries. There is a growing demand for joining or repairing of the AM parts of aluminum alloys using welding technology. However, the problems of high porosity and joint softening are occurred when welding of aluminum alloy AM parts, which have become technical bottlenecks that need to be solved urgently. Laser welding of AlSi10Mg alloys fabricated by selective laser melting (SLM) with an addition of Er and Zr in the filler metal was carried out. The effect of Er and Zr addition on the porosity, microstructures and mechanical properties of the welded joints was investigated, and the contribute of Er and Zr addition to the yield strength (YS) of the welded joints was calculated. Compared that joints without Er and Zr addition, the average ultimate tensile strength (UTS) and YS of the welded joints with Er and Zr addition have been increased by 10.5% and 23.5%, respectively. The improved mechanical poverty of the welded joints is due to the refined α-Al grains and Si-rich cellular networks, and the reduced hydrogen pores occurred in the weld metal (WM) with the addition of Er and Zr. The YS calculation of the weld joints indicates the most important contribution to the YS is the enhancement effect of the Si-rich networks with Er and Zr. [Display omitted] • Filler metal with Er and Zr addition was introduced in laser welding of SLM AlSi10Mg alloys. • Er and Zr addition in Filler metal effectively reduces hydrogen pores generated in the WM. • Er and Zr addition in Filler metal greatly increases the UTS and YS of the welded joints. • Enhancing Si-rich network effect with Er and Zr addition is the most important contribution to the enhancement of YS. [ABSTRACT FROM AUTHOR]

In order to improve and consolidate the properties of boron (B)-modified molybdenum disilicide (MoSi 2) powders applied in selective laser melting and make them attractive candidate for selective laser melting, in this study, induction plasma spheroidization (IPS) was conducted to spheroidize Mo–62Si–5B (at.%) powders. Mo–62Si–5B powders prepared by mechanical crushing exhibited polygonal morphology and consisted of MoSi 2 and MoB 2 phases. Subsequently, spherical B-modified MoSi 2 powders with the size in the range of 45–100 μm were obtained via IPS. The effect of plasma power on the spheroidization rate, flowability, and oxygen content of the powders was investigated, which improved obviously with the increase of the plasma power. Powders spheroidized at the largest plasma power of 40 kW exhibited the highest spheroidization rate (89%) and the best flowability (25 s/50 g). Furthermore, morphological evolution and microstructural evolution of particles were systematically explored based on melting and solidification processes of powders. With the increase in heat absorption, the morphology of particles gets gradually converted from polygonal to spherical. The microstructure of spherical particles transforms from original hypoeutectic structure to cellular eutectic structure with the decrease in the powder size. [ABSTRACT FROM AUTHOR]

Abstract: A series of Fe–xCr cored wires (x =15, 20, 25, 30, 35 and 40% in weight) were used to produce protective coatings for components used in high-temperature environments by wire-arc spraying. The microstructure, morphology and high-temperature oxidation behavior of the Fe–xCr coatings were investigated. The Fe–xCr coatings presented a homogeneous structure with thin oxide inclusions and low porosity. Thermogravimetric analysis was used to evaluate the high-temperature oxidation behavior of the coatings at a temperature of 650°C under cyclic oxidation conditions. The results showed that all the Fe–xCr coatings exhibited significantly lower weight gain than the uncoated substrate. As Cr content of the coatings increased, the thickness of oxide scales decreased and oxidation resistance improved. [Copyright &y& Elsevier]

Abstract: Al-4.7Mg-0.7Mn-0.3Er alloy plates were welded by laser beam welding (LBW) and tungsten inert gas (TIG). Mechanical properties and microstructures of both welded joints were analyzed. The results showed that the tensile strength of LBW joint was 315MPa, which was approximately 10% higher than that of TIG welded joint. This was attributed to the fine grains, dispersed primary Al3Er phase and low Mg evaporation in LBW weld. Equiaxed grains with average size of 30μm were obtained in the fusion zone, which were much smaller than that of 90μm in the fusion zone of TIG joint, due to the low heat input during LBW process. Moreover, finer primary Al3Er particles were uniformly distributed in the LBW joints, which resulted in a substantial increase of nucleation rate in LBW welds. In addition, it was also found that Mg concentrations in the fusion zones, in both TIG and LBW joints, were lower than that of the base one tested by EPMA. The burning loss rates of Mg in TIG and LBW joints were 36% and 22%, respectively. [Copyright &y& Elsevier]

Abstract: Butt joints of 3.0mm thick sheets of an Al–Li based alloy have been produced using Nd:YAG laser welding without filler metals. The hardness distribution and microstructure of the alloy and welded joints were investigated. The changes in the grain shapes, grain orientations, microtexture, and precipitates of the fusion zone were analyzed using optical microscope, electron back scattered diffraction (EBSD) and transmission electron microscopy (TEM). The results show that Nd:YAG laser welding leads to a change of the microhardness, grain shape, grain orientations, and a disappearance of the microtexture and precipitates. A narrow band of EQZ along the fusion boundary and a predominantly equiaxed dendritic structure are developed in the fusion zone. The formation of the predominately equiaxed dendritic grains is due to a heterogeneous nucleation mechanism aided by equilibrium A13Zr phases as well as the growth of pre-existing nuclei created by dendrite fragmentation, or by grain detachment resulted from Nd:YAG laser welding processes. In addition, Nd:YAG laser welding produces lower Vickers hardness than that of the base metal due to the decrease in the in quantity of δ′ precipitates in the fusion zone. [Copyright &y& Elsevier]

Abstract: Samples of Al–Mg–Mn–Zr–Er alloys have been welded using the method of TIG welding. Microstructures characterization was performed by optical microscopy (OM), energy dispersive X-ray (EDX) and transmission electron microscopy (TEM), respectively. In addition, tensile and hardness test was conducted. The relationship between mechanical properties and microstructure of welded joints is evaluated. Results indicate that the ultimate tensile strength of the joints is 72% of that of the base metal. The base metal consists of a typical rolled structure, and the fusion zone (FZ) is mainly made up of dendrite grains. A characteristic equiaxed zone (EQZ) is obtained at the fusion boundary between the base metal and fusion zone. Fine dispersion of coherent Al3Er precipitates was found in the base metal, however, the quantity of these particles dropped significantly in the fusion zone. The hardness test results indicate that the microhardness in the fusion zone is lower than that of the base metal, due to the as-cast structure in this region. Based on the present work, it is concluded that TIG welding is the suitable welding procedure for joining this new type Er-containing aluminum alloy. [Copyright &y& Elsevier]

In this work, the creep behaviors of the graphitic and graphite-TiB 2 composite as cathode materials have been investigated at high temperature aluminum electrolysis for discussing the role of TiB 2 particles in creep resistance and mechanical properties connected with the microstructural evolution involving electrolyte penetration and cracking. The graphite-TiB 2 composite has superior creep resistance over the graphitic sample. The corresponding creep strain can be as low as ~0.2% after the high temperature electrolysis. The addition of TiB 2 particles greatly densifies the prepared composite with low porosity, resulting in the reduction of penetrating channels. The well-wetted TiB 2 particles by liquid Al generate a protective dense Al layer on the surface of composite, greatly blocking the electrolyte penetration. In turn, liquid Al may slowly penetrate into the composite via the cracks formed channels. The fracture strength of the graphite-TiB 2 composite increases from 41.6 MPa to 48.9 MPa after creep test at high temperature loading. Such improved properties should be attributed to the combined mechanism with reduced micro-cracks, decreased penetrating channels and the reinforcement due to addition of TiB 2 particles. [ABSTRACT FROM AUTHOR]

The correlation between the thermal transport properties and microstructural evolution of amorphous alloys is crucial for their application in thermal insulation. Herein, Fe 48 Cr 15 Mo 14 C 15 B 6 Y 2 amorphous alloy with low thermal conductivity of 7.74 W/mK was investigated to reveal this relationship. Isochronal annealing experiment demonstrates a limited increase in thermal conductivity at temperatures below the crystallization temperature (T x1 = 620.7 °C), despite the occurrence of structural relaxation or partial crystallization, which is ascribed to the conflicting variations of electron and phonon contributions with increasing temperature. At annealing temperature above T x1 , the two contributors start to cooperate, leading to abrupt enhancement of thermal conductivity. On the other hand, isothermal annealing experiments reveal that at temperatures below T x1 , the thermal conductivity is independent of annealing time. Although full crystallization can be induced slowly by annealing at 600 °C, the thermal conductivity keeps nearly constant at 8.35 W/mK, which is attributed to additional scattering by a newly introduced phase interface. Moreover, grain growth upon prolonged annealing at 850 °C results in a slow increase in thermal conductivity, which asymptotically saturates at 12.44 W/mK. The obtained results demonstrate the potential of the Fe-based amorphous alloy as thermal insulator and form a basis for future works aiming to shed further light on the evolution of amorphous alloy and the sluggish effect of transformation kinetics. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Rare-earth zirconates (RE 2 Zr 2 O 7) are potential thermal barrier coatings (TBCs) candidates exhibiting excellent thermal insulation property to protect underlying superalloy substrate. These coating materials, however, are subjected to degradation caused by molten silicon-containing sand dust and volcanic ash whose main compositions are CaO-MgO-AlO 1.5 -SiO 2 (brief to CMAS) at higher operating temperatures (> 1200ºC). Here, we have studied the thermochemical interactions between three RE 2 Zr 2 O 7 (Sm 2 Zr 2 O 7 , Gd 2 Zr 2 O 7 and Yb 2 Zr 2 O 7) and CMAS with three different compositions (referred to as CMAS-1, CMAS-2 and CMAS-3, respectively) at 1300ºC/30 min. Both the diversities of the REO 1.5 identity and CMAS composition result in the precipitation of apatite with varying stoichiometry. For an equivalent CMAS case, there is a linear correlation between the apatite content and the RE cation radius. In CMAS-1, the Ca:RE ratio of apatite observed in the Sm 2 Zr 2 O 7 case is ∼0.31, larger than that of Gd 2 Zr 2 O 7 (∼0.30) and Yb 2 Zr 2 O 7 (∼0. 2 0). Additionally, the RE3+ solubility in equilibrium with apatite decreases with the increased CaO content from CMAS-3 to CMAS-1 for a given RE 2 Zr 2 O 7 material, facilitating the apatite precipitation within a short time. For example, in Sm 2 Zr 2 O 7 case the Sm3+ solubility decrease from ∼3.18 at % to ∼0.70 at % as the CaO content increases from 19 mol % (in CMAS-3) to 33 mol % (in CMAS-1). Also, the composition of residual CMAS melt changes as the interaction proceed, which can impact its flow property and infiltration propensity. These finds may advance the design of current and next-generation TBCs material and development of effective strategies to mitigate the CMAS-induced coating failure. • Special attention is payed to the phase equilibrium at the early-stage of interaction between RE2Zr2O7 and CMAS melt. • For an equivalent CMAS the apatite content increases linearly with the increase in RE3+ radius from Yb3+ to Gd3+ to Sm3+. • The RE3+ solubility in equilibrium with apatite decreases with the CaO content of initial CMAS for a given RE2Zr2O7 material. • The increased CaO:SiO2 ratio in residual CMAS melt induced by the interaction may facilitate the CMAS infiltration. [ABSTRACT FROM AUTHOR]

Abstract In this study, an Al 0.6 TiCrFeCoNi high entropy alloy coating was produced by high-velocity-oxygen-fuel spraying. The microstructure and phase composition of the coating were investigated, moreover the hardness and the fracture toughness of the coating were determined. The wear behavior of the coating at different temperatures was evaluated using a pin-on-disc test. The results show that the coating was very dense and consisted of lamellae. Two BCC phases with similar lattice parameters were detected in the as-sprayed coating. The wear of the coating against an Al 2 O 3 counter body was mainly caused by abrasion at all temperatures. The role of fatigue wear increased with increasing test temperature. In addition, tribo-reaction played an important role at the test temperature of T = 500 °C, which led to the lowest friction coefficient of the coating under the given test conditions. Highlights • The wear behavior of Al 0.6 TiCrFeCoNi HVOF coating was investigated at room temperature, T=300°C and T=500°C in detail. • The wear behavior of the coating changed significantly with the increasing test temperatures. • The wear behavior of the coating changed significantly with the increasing test temperatures. • The wear mechanism changed with temperatures, tribo-reaction played an important role at test temperature of T=500°C. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, wrought magnesium alloy AZ31B sheets were brazed by means of high-frequency induction heating device using a novel Al-based filler metal in argon gas shield condition. The interfacial microstructure, phase constitution and fracture morphology of the brazed joint were studied. The experimental results show that α-Mg solid solution and β-Mg17Al12 phase were formed in brazing region. Moreover, the homogeneous Mg32(Al, Zn)49 phase in the original Al-based filler metal disappeared entirely after the brazing process due to the fierce alloying between the molten filler metal and the base metal during brazing. Test results show that the shear strength of the brazed joint is 45MPa. The fracture morphology of the brazed joint exhibits intergranular fracture mode and the crack originates from the hard β-Mg17Al12 phase. [Copyright &y& Elsevier]