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Aluminum–lithium alloy, being the lightest aluminum‐based alloy, holds significant potential for applications in the aerospace and military sectors. Currently, alloying treatment stands as a crucial method for enhancing the comprehensive performance of aluminum–lithium alloy. This article provides an overview of the production process of aluminum–lithium alloys, encompassing smelting and deformation processing characteristics. Additionally, it outlines the developmental history of the chemical composition for the primary grades of aluminum–lithium alloy, detailing the copper (Cu) and lithium (Li) content of the main alloying elements. And discusses the influence of various microalloying elements on the alloy's properties. Additionally, it summarizes the structure, properties, and precipitation morphology of the three primary strengthening phases formed by the alloying of aluminum–lithium alloys: T1 (Al2CuLi$\left(\text{Al}\right)_{2} \text{CuLi}$), θ′$\left(\theta\right)^{&aposx;}$ (Al2Cu$\left(\text{Al}\right)_{2} \text{Cu}$), and δ′$\left(\delta\right)^{&aposx;}$ (Al3Li$\left(\text{Al}\right)_{3} \text{Li}$). The analysis also examines the impact of anisotropy on the mechanical properties of the primary dispersion. Finally, the article addresses the challenges involved in alloying aluminum–lithium alloys and proposes key research directions for element composition design. [ABSTRACT FROM AUTHOR]

One of the most effective ways to increase the processing plasticity of advanced superalloys (heat-resistant nickel-based alloys) is the formation of an ultrafine-grained (UFG) microstructure in bulk semi-finished products. Such a microstructure is a necessary condition for the manifestation of the structural superplasticity effect in the technological processes of manufacturing products from such superalloys. One of the most promising methods for producing UFG microstructures is thermomechanical treatment (TMT) according to the multiple isothermal forging scheme. It has been shown that the EK79 superalloy after TMT, with a gradual decrease in the processing temperature from 0.88 to 0.62 Ts (where Ts is the strengthening phase dissolution temperature) leads to the transformation of the initial microduplex fine-grained microstructure into a mixed UFG microstructure. Such a mixed UFG microstructure consists of: 1) relatively coarse (inherited from the fine-grain microstructure) particles – γ'-phase with a size of 3.0±0.8 μm; 2) γ-grains, and incoherent γ'-phase particles with a size of 0.3–0.5 μm; 3) strengthening coherent intragranular γ'-phase particles with a size of 0.05–0.1 μm, released upon cooling from the TMT temperature to room temperature. During uniaxial compression tests, the EK79 superalloy with such microstructure, demonstrates low-temperature superplasticity in the temperature range of 800–1000 °C. It has been found that an increase in the deformation temperature up to 1000 °C, leads to the increase of γ-phase grains to micron size. The maintenance of superplastic properties in the presence of relatively coarse incoherent particles in the microstructure of the second phase (γ'-phase) is apparently related to the fact that the deformation is localised in the UFG component.

The Cu–Ti alloy has similar mechanical properties and electrical conductivity to the Cu–Be alloy. It also exhibits excellent high-temperature properties and stress relaxation resistance. Therefore, it has emerged as a promising material to replace the toxic Cu–Be alloy. With the technological advances, the new generation of connector materials put forward higher requirements for performance, such as strength over 1000 MPa and conductivity over 15%IACS. However, it is difficult to obtain Cu–Ti alloys with such high strength and conductivity. An effective way is to increase the aging temperature or prolong the holding time of the alloy. When the strength of the alloy is reduced, the increase in cost is inevitable. The refining of grains or the regulation of size and distribution of precipitates has proved more effective, which is also true for Cu–Ti alloys. Currently, the refined grain size is still 10–50 μm achieved through a series of common processing methods, including hot rolling, solid solution, and cold rolling. Therefore, the improvement of strength and conductivity is limited for the Cu–Ti alloy. This paper provides a preparation method for synchronously improving the strength and conductivity of the Cu–Ti alloy. The Cu–3Ti–0.1Mg–0.05B–0.05La alloy with an ultra-fine grain structure is obtained via the vacuum casting and cold billet opening. The secondary aging process is used to adjust the size and distribution of the second phase to obtain a Cu–Ti alloy strip with high strength and good conductivity. The results show that the Cu–3Ti–0.1Mg–0.05B–0.05La alloy displays the maximum microhardness of 356 HV and a conductivity of 14.5%IACS after aging at 400 ℃/2 h. The relationship between the second phase precipitation and properties of the Cu–3Ti–0.1Mg–0.05B–0.05La alloy was analyzed using TEM (Transmission electron microscope). The evolution of the second phase is the Ti-rich phase → the granular phase β′-Cu4Ti phase → the granular β′-Cu4Ti phase + lamellar β-Cu4Ti phase → the lamellar β-Cu4Ti phase. The granular β′-Cu4Ti phase is the most important strengthening phase; the lamellar β-Cu4Ti phase can decrease the strength of the alloy but increase the conductivity. The comprehensive properties of Cu–3Ti–0.1Mg–0.05B–0.05La alloy can be further optimized by the secondary aging process. The microhardness and electrical conductivity of the Cu–3Ti–0.1Mg–0.05B–0.05La alloy reach 341 HV and 20.5%IACS after the primary aging at 450 ℃/8 h + 50% cold rolling + secondary aging at 400 ℃/1 h.

To obtain better comprehensive properties of cast Al-Cu-Mg alloys, the secondary aging (T6I6) process (including initial aging, interrupted aging and re-aging stages) was optimized by an orthogonal method. The microstructures of the optimized Al-Cu-Mg alloy were observed by means of scanning electron microscopy and transmission electron microscopy, and the properties were investigated by hardness measurements, tensile tests, exfoliation corrosion tests, and intergranular corrosion tests. Results show that the S phase and θ' phase simultaneously exist in the T6I6 treated alloy. Appropriately increasing the temperature of the interrupted aging in the T6I6 process can improve the mechanical properties and corrosion resistance of Al-Cu-Mg alloy. The optimal comprehensive properties (tensile strength of 443.6 MPa, hardness of 161.6 HV) of the alloy are obtained by initial aging at 180 °C for 2 h, interrupted aging at 90 °C for 30 min, and re-aging at 170 °C for 4 h. [ABSTRACT FROM AUTHOR]

The synergistic effects of 0-0.3 wt.% Sc addition and retrogression and re-aging (RRA) on microstructure and mechanical properties were evaluated in Al-8.0Zn-2Mg-2Cu-0.15Zr alloy. The minor Sc addition can effectively refine the grains of the tested alloy. When the Sc content increased from 0 to 0.2 wt.%, the grain size decreased from 200-250 to 30 μm. As the Sc content increased from 0.2 to 0.3 wt.%, the grain size was still 30 μm, almost without change. The grain refining is due to the formation of Al3(Sc, Zr), which has a better coherent relationship with the matrix than Al3Zr. The RRA treatment results in a slight decrease in the tensile strength (Rm) and significant improvement in the total elongation (A) of the tested alloy. The sample's Rm before and after the RRA decreased slightly from 517 to 510 MPa when the Sc is 0.3 wt.%; the A increased significantly from 6.0 to 12.0%. The tested alloy prepared by adding 0.1-0.3 wt.% Sc has a higher tensile strength and toughness than those alloys without Sc due to the formation of Al3(Sc, Zr). After the RRA treatment, both the formation of η (MgZn2) and the release of internal stress decrease the strength and increase the total elongation of the tested alloy relative to values before the RRA treatment. [ABSTRACT FROM AUTHOR]

The effects of different Si and Cr contents on the microstructure and mechanical properties of new type aluminum alloy with low silicon content were studied by means of hardness test, tensile test and metallographic preparation, SEM, EDS and DSC. The results showed that when the Si content increased gradually, the hardness and tensile strength increased first and then decreased. When the Si content was 3.5%, the hardness and tensile strength reached the maximum. The microstructure observation showed that when the Si content was 3.5%, the microstructure was the most fine and dense, and the secondary dendrite arm spacing (SDAS) of the alloy had the minimum value. When the content of Cr element increased gradually, the tensile strength and elongation showed a trend of increasing gradually, and the maximum value was obtained at 0.5%. When Si was 3.5% and Cr was 0.5%, the best mechanical properties were obtained. At this time, the microstructure of the alloy was fine, dense and uniform, and Mg2Si strengthening phase was precipitated during heat treatment. Cr element has the functions of solid solution, fine crystal and dispersion strengthening. Therefore, the tensile strength, yield strength and elongation of the new aluminum alloy were 350.7 MPa, 303.0 MPa and 8.56%, which has obvious advantages over the traditional cast Al-Si alloy. [ABSTRACT FROM AUTHOR]

The structural stabilities and thermal properties of η′ and η phase at high temperature and pressure were investigated via first principles calculations combined with quasi-harmonic Debye approximation (QHA). The calculated results illustrate η′ possess high formation enthalpy with lower structural stability at high temperature, which may transits to equilibrium phase η at temperature range of 510–520 K. The calculated thermodynamic properties indicate η exhibits better thermal stability than η′ at high temperature. The thermoelastic properties of η′ and η were estimated based on the temperature-dependent elastic constants Cij(T), and it is revealed the elastic moduli of η′ are larger than that of η though both two phases become deformable with elevated temperature. Moreover, the evaluated thermoelastic anisotropies suggest η′ and η are essentially elastic isotropic on {0001} plane, while η′ exhibit serious mechanical anisotropy and angular bonding characters on both {10-10} and {01–10} planes at high temperature.

The effect of mechanical properties on wear resistance of Si3N4 - SiC composite materials with different portions of SiC strengthening phase was investigated. Properties of monolithic silicon nitride were compared to ceramic composites consisting of Si3N4 matrix with 10 and 20 vol.% SiC. The SiC strengthening phase had a positive effect on the hardness of Si3N4 - SiC ceramic composite materials. Wear resistance of tested ceramic materials was mainly influenced by their fracture toughness. The highest wear resistance value was achieved for material with the highest fracture toughness. Worn surfaces of all experimental ceramic materials were damaged by both microcutting and microcracking mechanism. Microcracking was the predominant wear mechanism mainly at ceramic composites. The wear resistance of SiC-Si3N4 ceramic composites can be described by the model W ~ HV/KIC.

In this paper, 7050-T6 high-strength aluminum alloy with 3-mm-thickness is taken as the research object, and it is welded by CMT Advanced 4000R NC welding system. The microstructure, mechanical properties, evolution of joint phase and fatigue properties are studied, and the tensile and fatigue fracture are observed and analyzed. It is found that the fusion zone is dominated by columnar crystal structure and typical epitaxial solidification; the structure of weld zone is mainly equiaxed crystal and dendrite. After 360 h of natural aging, the hardness distribution of the joint is not uniform, and the hardness of the weld zone is the smallest. The hardness of the overaging softening zone is 10 HV lower than that of the solid solution zone, and a softening zone with a width of about 5 mm appears in the joint. The HAZ softens obviously, and the fracture surface shows typical dimple fracture morphology. The results show that the conditional fatigue limits of the specimens are 166.4 and 109.3 MPa respectively under the condition of setting Nf = 107 fatigue cycle. The fatigue initiation area of the joint is mainly welding porosity, and the fatigue striation spacing of the extension area is different. In the process of crack propagation, the striation tends to bypass the second phase particles; The instantaneous fracture area consists of dimples of different sizes. The thermal simulation test of the weld is carried out through the moving Gaussian heat source model in ANSYS software. In addition to the plate-like Mg2Si phase observed in the weld, FeAl3 and (FeMn)Al6 impurity phases are also found, only a weak diffraction peak of MgZn2 phase is found in the solid solution zone. The microstructure evolution of HAZ is analyzed by HRTEM images. It is found that there are tiny GP zone precipitates in the solution zone. [ABSTRACT FROM AUTHOR]

The time-temperature-property (TTP) curves of 7050 aluminum alloy die forgings were determined by an interrupted quenching method. The second phase dissolving and precipitation mechanism and the strengthening mechanism were studied by TEM and JMA equation.The results show that the nose temperature and incubation period of TTP curves are 337℃ and 0.7s, with the quenching sensitivity range 270-400℃. Low level of the quenching sensitivity to sort the result followed by high temperature, low temperature, medium temperature; Al3Zr particles are the primary nuclear sites of supersaturated solid solution, whose main precipitate phases are η particles during early isothermal process, with the increase of temperature, the grain boundary becomes narrower; after the holding time is prolonged, needle dispersion S phases are the main precipitates of the alloy in the low temperature range; in the medium and high temperature range, a large number of η particles precipitate and aggregate, accompanied by the decrease of volume fraction of S phases, meanwhile the grain boundary becomes coarser and continuous; with the temperature rising, the size of η particles increases while the amount decreases; the rank of strength levels of precipitation is GP zones and η' phases, needle-like S phases, clubbed η phases.

• W-Y 2 O 3 composites were manufactured by mechanical alloying and powder sintering. • The content of the Y 2 O 3 strengthening phase was 5 and 10 wt% • During milling, a W-based solid solution was formed. • After sintering, new phases appeared in addition to the W-based solid solution. • The sinters' microhardness increases with the increasing content of Y 2 O 3. The aim of this work was to manufacture tungsten composites from different initial powder mixtures by mechanical alloying followed by sintering. Two initial powder mixtures, W + 5 wt% of Y 2 O 3 and W + 10 wt% of Y 2 O 3 , and pure W for comparison were mechanically alloyed for 50 h in a Fritsch Pulverisette P5 planetary ball mill under an argon atmosphere. The final products were consolidated by pulse plasma sintering at 1640 °C under a pressure of 20 MPa. The powders and consolidated pellets were examined by the XRD method. The obtained results show that during milling, the tungsten based solid solution formed. After consolidation, the XRD examination revealed that in addition to the tungsten-based solid solution and yttria, new carbide phases (Fe 3 C, WC, W 2 C and Fe 3 W 3 C) appeared. The graphite present in the carbides originated from the die used in the sintering process. SEM observations of the surfaces of the sinters revealed that the microstructure is not homogeneous and consists of areas rich in one or two elements, such as W, C, Fe or the Y 2 O 3 phase. The microhardness of the pellets increases with the increasing content of the Y 2 O 3 strengthening phase, whereas the values of the relative density decrease. [ABSTRACT FROM AUTHOR]

The effect of mechanical properties on wear resistance of Si3N4 - SiC composite materials with different portions of SiC strengthening phase was investigated. Properties of monolithic silicon nitride were compared to ceramic composites consisting of Si3N4 matrix with 10 and 20 vol.% SiC. The SiC strengthening phase had a positive effect on the hardness of Si3N4 - SiC ceramic composite materials. Wear resistance of tested ceramic materials was mainly influenced by their fracture toughness. The highest wear resistance value was achieved for material with the highest fracture toughness. Worn surfaces of all experimental ceramic materials were damaged by both micro-cutting and microcracking mechanism. Microcracking was the predominant wear mechanism mainly at ceramic composites. The wear resistance of SiC-Si3N4 ceramic composites can be described by the model W ~ HV/KIC [ABSTRACT FROM AUTHOR]

The authors have analyzed the necessity to improve the composition of existing critical structural materials for the purpose of developing metal matrix materials, which combine a highly plastic metal base and high-melting, high-strength, high-modulus fillers. Dispersed yttrium oxide (Y2O3) particles are preferred for iron matrix alloys, because of their stability at pyrometallurgical process temperatures and inertness to alloy components. The manufacturing of new materials by addition of dispersed particles into a liquid melt during casting using a centrifugal casting machine to obtain a hollow (pipe) billet is considered. The potential for improving the mechanical and operational properties of metal matrix materials in comparison with the monomaterial is demonstrated. This paper describes the thermodynamic modeling of high-temperature processes in the yttrium oxide–metal matrix (melt) system. The modeling has been carried out using the FactSage software package. A composition corresponding to 12Cr18Ni10Ti (12Kh18N10T) steel was used to model the matrix material. The calculations have been based on the ratio of 1 g of yttrium oxide additive per 100 g of matrix metal melt. It can be concluded based on the modeling results that the added dispersed yttrium oxide powder does not interact with alloy components, does not dissociate, and does not undergo allotropic transformations. The experiments on production of centrifugal castings using yttrium oxide as a strengthening phase with the aim of increasing radiation resistance have been proved to be expedient. The developmental focus of the most effective technology for creating metallic materials based on iron matrix dispersed-hardened with yttrium oxide has been established. [ABSTRACT FROM AUTHOR]

NiCrAlY coatings were fabricated by atmospheric plasma spraying. The influence of the heat treatment on the corrosion–wear behavior of the coatings in artificial seawater was investigated. The microstructure of the coatings became denser and more homogeneous after the heat treatment. After heat treatment at 1100 °C, the coating had the fewest pores and cracks and the oxide dispersive strengthening phase of Y2O3 was clearly increased to form a layer approximately 10 nm thick and uniformly distributed in the matrix. The heat treatment effectively improved the microhardness and corrosion–wear properties of the coatings. This coating had the highest microhardness of 371.1 HV, the lowest friction coefficient, and a wear rate of 0.24 and 1.01 × 10−6 mm3/Nm and the lowest corrosion rate after heat treatment at 1100 °C, giving it excellent corrosion–wear properties. [ABSTRACT FROM AUTHOR]

Magnesium alloys are highly sought after as environment-friendly engineering materials for the 21st century. Mg-RE (rare earth) alloys, especially Mg-Gd-(Y)-Zn alloys, have attracted significant interest in the past two decades due to their potential high performances over conventional or commercial magnesium alloys. Recent research has revealed that the LPSO、 β series and γ series phases are the main strengthening phases in Mg-Gd-(Y)-Zn alloys. This article aims to provide a review of recent progress on the transformation of these main strengthening phases in the as-cast Mg-Gd-(Y)-Zn alloys, especially the co-existence of multiple strengthening mechanisms. Further, substantial research recommendations for the future development of high-performance and even ultra-high-strength casting Mg-RE alloys are proposed in terms of casting procedure, heat treatment process, alloying elements, and strength-plasticity trade-off. [ABSTRACT FROM AUTHOR]

Fusion welding of cast high-temperature nickel alloys with high content of strengthening disperse phases is problematic. Even more serious problem is welding of intermetallic-based materials. Therefore, different methods of brazing are widely used for such materials joining. TLP-bonding (Transient Liquid Phase Bonding) is a term which has the most often application abroad. Considering that brazing filler materials have lower melting temperature than base metal the concentration of depressants (reducing brazing filler metal melting temperature) in brazed weld shall be reduced to the minimum in order to increase working temperature of brazed joints in brazing process. The depressants of high-temperature brazing filler metals are divided on several groups. Interaction of Ni3Al-based alloy with brazing filler metals containing boron, zirconium and hafnium was investigated in the work. SBM-3 brazing filler metal of Ni-Cr-Co-Al-Ti-Ta-Re-W-Mo-Hf-B system was developed based on research results. [ABSTRACT FROM AUTHOR]

Fusion welding of cast high-temperature nickel alloys with high content of strengthening disperse phases is problematic. Even more serious problem is welding of intermetallic-based materials. Therefore, different methods of brazing are widely used for such materials joining. TLP-bonding (Transient Liquid Phase Bonding) is a term which has the most often application abroad. Considering that brazing filler materials have lower melting temperature than base metal, the concentration of depressants (reducing brazing filler metal melting temperature) in a brazed weld shall be reduced to the minimum in order to increase working temperature of brazed joints in brazing process. The depressants of high-temperature brazing filler metals are divided on several groups. Interaction of Ni3Al-based alloy with brazing filler metals containing silicon, boron, zirconium and hafnium was investigated in the work. SBM-3 brazing filler metal of Ni-Cr-Co-Al-Ti-Ta-Re-W-Mo-Hf-B system was developed based on investigations results. [ABSTRACT FROM AUTHOR]

It is established that intercrystallite corrosion of cutting-ceramic inserts arises when the chromium content in the peripheral zone of the grains is depleted by the deposition of chromium carbides at the grain boundaries, in the presence of stress due to the fast cooling of the inserts from high temperatures. This is especially apparent when 12Kh18N10Т, 40Kh13, 14Kh17N2, and other steels that are hard to machine are worked by a tool equipped with inserts of VOK-60M modified cutting ceramic. Research shows that the intercrystallite corrosion of cutting-ceramic inserts may be attributed to the stress arising in the surface layers of the grains as a result of carbide or nitride deposition. Heating cutting-ceramic inserts at 650–800°С lowers this stress and restores their resistance to intercrystallite corrosion. Research also shows that chromomanganese cutting-ceramic inserts are less susceptible to intercrystallite corrosion than are chromium–manganese–nickel inserts, while chromium–manganese–nickel cutting-ceramic inserts are less susceptible than are chromonickel inserts. The benefits of chromium–manganese–nickel cutting-ceramic inserts are especially pronounced with relatively brief machining of 12Kh18N10Т, 40Kh13, 14Kh17N2, and other such steels, in rigorous conditions, with a temperature of 600–650°С in the workpiece–tool contact zone. A new theory of the intercrystallite corrosion of VOK-60M modified cutting ceramic is based on the role of the kinetic factor at the relatively low tempering temperatures associated with the deposition of metastable carbide, although this does not lead to maximum change in free energy of the system but only to a relative change. In the cutting ceramic, this carbide may be chromium carbide (Cr, Тi)23C6, which is greatly enriched with titanium. With increase in tempering temperature, the deposited carbide tends toward the stable composition Cr23С6. Prolonged holding at the tempering temperature also tends to favor thermodynamic equilibrium. In other word, the chromium carbide is gradually enriched to reach the stable composition Cr23С6. This process is more rapid at higher temperatures. Obviously, the variation in composition of the carbide deposited at the grain boundaries in VOK-60M cutting ceramic with change in temperature and holding time will affect the kinetics of electrochemical solution of the system consisting of the carbide in contact with a solid solution. Research shows that vacuum sintering and annealing markedly improve the thermal stability. For the cutting ceramic, this is explained not only by the removal of fusible impurities but also by the larger quantity of aluminum and other alloying elements that remain in the strengthening phase, rather than being bound in oxides. Sintering in vacuum ensures greater plasticity of cutting ceramic based on nickel and cobalt in cutting 12Kh18N10Т and 14Kh17N2 steel at high speeds, with high temperatures in the machining zone. In addition, on sintering in vacuum furnaces, the content of small nonmetallic inclusions in the basic structure is 5–7 times less than in regular cutting ceramic. That significantly improves the deformability of the ceramic inserts. [ABSTRACT FROM AUTHOR]

Currently, critical components and assemblies made of traditional materials do not always meet the increased requirements of designers and service conditions. One solution to this problem is the development and application of dispersion-strengthened metal matrix composites. According to the informational–analytical review, a new fabrication technology of aluminum-based dispersion-strengthened composite material is presented. The peculiarities of this technology are described and sample macro- and microstructures, as well as mechanical characteristics of as-cast samples, are presented. The synthesis of strengthening particles immediately in the melt makes it possible to fabricate composites in one stage and provide thermodynamic stability, dense contact, and good adhesion between the matrix and strengthening phase. The particle sizes of the solid phase are in a range from 3 μm to 2 mm. The structural-and-phase state of the produced material is studied using optical metallography and X-ray diffraction analysis (a DRON-2 diffractometer). The microstructure is studied using a Keyence VHX-1000 microscope. The sample hardness is determined using a TKS-1M device, microhardness is determined using PMT-3 and HMV Shimadzu devices, ultimate strength is determined using ZD 10/90 and UME-10TM universal tensile testers, and impact strength is determined using an MK-30a pendulum impact tester. It is found that the variation in size and content of the strengthening phase makes it possible to vary mechanical properties of cast metal in a wide range. The application of the proposed technology will substantially decrease temporal and economical costs. A decrease in the fabrication cost of the dispersion-strengthened composite material is expected according to the results of the evaluative calculation. [ABSTRACT FROM AUTHOR]

Abstract—The intermetallic Ti3Al based alloys with the strengthening boride phases were obtained by the powder metallurgy methods; their composition, structure, and properties were studied. The optimum conditions for thermal treatment allowing obtaining the composite materials of the specified composition with the inclusions of the MAX phase were determined. [ABSTRACT FROM AUTHOR]

The tensile strength stability of aging hardened Mg-10Y-1.5Sm (mass fraction, %) alloy was investigated by microstructure analysis and tensile tests. The results show that the microstructure of Mg-10Y-1.5Sm alloy consists of α -Mg matrix and Mg 24 Y 5 phase and the formation of Sm-containing phase is not observed. With the increase of temperature from 20 to 300 o C, the tensile strength exceeds 200 MPa and has no obvious change. It is insensitive to temperature and the variation range is less than 10 MPa. The strength stability is superior to that of heat resistant magnesium alloy WE54 developed most successfully. It is mainly attributed to the hardness stability of strengthening phase Mg 24 Y 5 enhanced by dissolved Sm. [ABSTRACT FROM AUTHOR]

GH4169 Ni-based superalloy was prepared by wire arc additive manufacturing (WAAM) in this study. Similar to the microstructure of other additive manufactured superalloys, the additively manufactured GH4169 alloy suffered from a high-volume fraction of Laves phase, which is detrimental to the alloy's mechanical properties. To solve this problem, two different post heat-treatment approaches were selected to improve the tensile properties at both room and elevated temperatures, which are the one with solution treatment temperature at 950 °C and the modified one with solution treatment at 1150 °C, respectively. Detailed phase analysis during different heat treatment processes was conducted using both scanning and transmission electron microscopes. Comparative tensile tests were also conducted at both room temperature and 650 °C to analyze the role of the different microstructures on the deformation responses of the prepared samples. By increasing the solution treatment temperature from 950° to 1150°C, the volume fraction of Nb-rich Laves phase dramatically decreased, and the previously Laves-phase-trapped Nb contributed to the formation of the strengthening γ″ phase. As a result, the tensile strength of this modified treated alloy is significantly improved at both room and elevated temperatures. Additionally, due to lower volume fraction of the Laves phase, the elongation of the modified treated alloy at room temperature is improved by ∼35%. These findings provided new insights into the post-heat treatment approaches of the WAAM Ni-based superalloy. • Wire arc additive manufactured GH4169 Ni-based superalloy and post-heat treatment. • Post-treatment induced microstructure evolution from μm to nm by electron microscopes. • Discussion of the treatment-microstructure-mechanical property relationship of GH4169. • Industrial heat treatment cannot avoid the effects from the detrimental Laves phase. • Modified heat treatment improves both room and high temperature tensile properties. [ABSTRACT FROM AUTHOR]

To clarify the effect of the characteristics of strengthening phase on the material transfer behavior of silver base contact materials, the good electrical and thermal-conductive TiB 2 ceramic and insulating and poor thermal-conductive SnO 2 ceramic were selected as the strengthening phases, and the Ag-4wt.%TiB 2 and Ag-4wt.%SnO 2 contact materials were prepared with different sized TiB 2 and SnO 2 powders by powder metallurgy. The electrical contact tests were performed on an electrical contact material testing system at a voltage of 12 V DC and a current ranging from 5 A to 24 A. The results show that the material transfer mode is from cathode to anode at small currents for the Ag-4wt.%TiB 2 contact material. However, it changes reversely at large currents. For the Ag-4wt.%TiB 2 contact materials prepared with 500 nm and 60 nm TiB 2 powders, the critical current at which the material transfer mode changes are 16 A and 24 A, respectively. Nevertheless, the material transfer mode for the Ag-4wt.%SnO 2 contact material is always from cathode to anode at 5-24 A. Furthermore, fine strengthening particles are beneficial for less mass loss and relative transfer mass for both Ag base contact materials. The Ag-4wt.%TiB 2 contact material presents a lower relative transfer mass than Ag-4wt.%SnO 2 contact material. [ABSTRACT FROM AUTHOR]

The variation of tensile properties of A356alloy at 20 °C~−60 °C has been investigated. the distribution of dislocation slip bands near the fracture surface was studied by scanning electron microscopy SEM. Dislocation distribution was observed by transmission electron microscope TEM. The elastic stress field near the Mg 2 Si phase at low temperature was analyzed by ANSYS. When the temperature is decreased from 20 °C to −60 °C, the tensile strength and yield strength of A356 alloy increase and the elongation decreases. Under the effect of cold shrink, the elastic stress produced by the alloy matrix hinders the movement of the dislocation. In low temperature environment, the edge dislocation whose excess half atom facing toward Mg 2 Si experiences a repulsing force. On the contrary it experiences a gravitational force. [ABSTRACT FROM AUTHOR]

Adding strengthening phase is an important way to improve the arc erosion and anti-welding performance of Ag-based electrical contact materials. Ag-CNTs composites with different contents of CNTs were prepared by electroless silver plating, high-energy milling and powder metallurgy. The effect of CNTs addition on strengthening mechanism and arc erosion behavior of Ag-CNTs were investigated. The results show that agglomerating degree of the CNTs increases with the increase of content. CNTs distribute mainly at the grain boundaries and partially in the grains along the processing direction. The processing can disintegrate CNTs clusters which is beneficial for the dispersion of CNTs. With the increase of CNTs content, strength of the composite first increases then decreases while the elongation and electrical resistivity decreases.. The maximum yield strength (245 MPa) and tensile strength (296 MPa) was achieved when the CNTs content was 8 vol%. The electrical breakdown tests show that the addition of CNTs can obviously stabilize the arc and reducing welding. Materials transfer from the anode to the cathode and the transfer mass first decreases then increases with the CNTs content increasing. The Ag-CNTs composite with 8 vol% CNTs added presents the desired properties of stable arc and no obvious craters or pips on the eroded surface. Excessively high CNTs content will lead to the decreasing of strength and serious arc erosion. [Display omitted] • Ag-CNTs composites with CNTs highly dispersed were fabricated. • CNTs content influence dispersion of CNTs and mechanical property of the composite • Strengthening mechanism of CNTs is the load transfer mechanism mainly. • Addition of CNTs with a certain content improves arc erosion and welding resistance. [ABSTRACT FROM AUTHOR]

Features of the effect of alloying elements on linear thermal expansion coefficient of wrought heat-resistant alloys based on the Ni–Fe system are studied. Short-term and long-term strength at 600°C is simulated and parameters are used successfully as equivalent alloy chemical composition, calculated by a system of unpolarized ionic radii equations. A new deformable weldable alloy based on Ni–Fe–Co is developed with working temperature up to 650°C, with $ \upsigma_u^{20 } $ = 1400 MPa, $ \upsigma_u^{600 } $ = 1200 MPa, and $ \upsigma_{100}^{600 } $ = 950 MPa, with low linear thermal expansion coefficient (α = 11.8 · 10 –6 K –1 in the temperature range 20–600°C). The alloy is structurally stable, efficient in forming and welding, and with respect to set of properties it is better than standard alloys of similar designation. New alloy structure, phase composition, and properties are described. [ABSTRACT FROM AUTHOR]

Abstract: This study attempted to investigate the high temperature tensile deformation behaviour of new Al-1%Mg-1.1%Si-0.8%CoNi heat resistant aluminium alloy. New aluminium alloy strengthened by Co-Ni based phase was manufactured by using powder ball milling and continuous casting, based on the alloy design & preliminary test. High temperature tensile tests were conducted at various temperatures from 25°C to 450°C. OM, SEM, EPMA, XRD, FIB and HR-TEM equipments were used to analyse microstructure, phases, and fracture surface. Microstructure of the new alloy mainly consisted of Al matrix and Co-Ni based phases (1∼8μm). The Co-Ni based phase was analyzed and confirmed as (Ni, Co)3Al having incoherent interface with matrix. In high temperature tensile results, the new aluminium alloy didn’t show significant decrease (19.6%) of strength with increasing temperature (450°C), suggesting totally different behaviour with conventional A319 alloy (87.0% decrease of T.S.). Fractography observation results of new alloy represented the ductile fracture mode with dimples. Voids were mainly initiated at Co-Ni based strengthening phases. It was apparently observed that the strengthening effect of the (Ni, Co)3Al could be still maintained at high temperature of 450°C. The deformation mechanism of this alloy was also discussed. [Copyright &y& Elsevier]

The quality and durability of metallic materials is of considerable importance in many branches of industry, in particular, in metallurgy, engineering, and construction. This article gives the results of studying the effect of strengthening solid particles on structural heterogeneity, hardness, chemical composition and wear resistance of billets, prepared by centrifugal casting. [ABSTRACT FROM AUTHOR]

Fe-based/B 4 C composite coatings without and with 1–5 wt% Ni (Ni-free and Ni-added, respectively) were fabricated on the surface of ASTM 1045 steel via vacuum cladding. The effects of Ni addition on the microstructure, hardness and reciprocating wear of Fe-based/B 4 C composite coatings were investigated by optical microscopy (OM), electron probe microanalysis (EPMA) equipped with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), hardness tester and reciprocating wear tester. The results showed that all coating composed of α-Fe, γ-Fe, (Fe, Ni) solid solution, M 23 (C, B) 6 , and M 2 B phases, which indicated that Ni addition into the coating had little impact on the composition of the M 2 B-type borides and M 23 (C, B) 6 -type carboborides in the coating. However, with the increase of Ni addition, the hardenability of the coating matrix was improved, and toughness phase of martensite was formed. Meanwhile, the morphology of strengthening phases gradually changed from chrysanthemum-like to intermittent net-like. When Ni addition was 3 wt%, the irregular block and net-like strengthening phases were uniformly distributed in the coating matrix of martensite, which made the microhardness of the coating relatively stable and the average hardness was 920 HV. Under different applied loads, non-significant variations in the coefficient of friction were observed. The wear volume of the coating with 3 wt% Ni addition was the minimum, which was only 2 × 10−3 mm3 under the applied load of 30 N, showing the best sliding wear performance. The wear morphology and elements distribution analysis suggested that the main wear mechanism of dry sliding wear of the coatings with different Ni addition were oxidative, adhesive and abrasive wear. • Good metallurgical bonding is formed and composite coating is relatively compact. • Ni addition causes the coating matrix to change from pearlite to martensite. • Ni addition can improve the wear resistance of the composite coating. • M 2 B and M 23 (C, B) 6 are used as wear-resistant skeleton to improve wear resistance. [ABSTRACT FROM AUTHOR]

As a light-weight and high-strength structural material, aluminum alloy has become an irreplaceable metal material in the aerospace field. In this paper, 25 mm thick Al-Cu alloy (2A12) was welded by electron beam. The welded joints softened leading to the hardness and tensile strength of the joint decreased. In view of the decrease of mechanical properties, the microstructure in different areas of the welded joint was analyzed. At the same time, the formation mechanism of rosaceous microstructures and eutectic structures was revealed. The influence of impurity elements on the joint was analyzed. In addition, the reason of joint strengthening effect weakening was explained combining with welding temperature field and the precipitation model of competition. • A competitive precipitation model of strengthening phases of aluminum-copper alloy welded joint was proposed. • Whether impurity elements can contaminate the weld joints in vacuum electron beam welding was clear. • The mechanism of segregation of element and formation of eutectic structure in the fusion zone was analyzed. [ABSTRACT FROM AUTHOR]

The effects of successive deposition using continuous heat from a plasma arc on a multi-layer Inconel 718 deposit was investigated using a wire-arc additive manufacturing (WAAM) process with cold metal transfer (CMT). Deposits consisting of 10 layers were manufactured, where interpass time was the only process parameter varied. The shape of the deposits was determined by the interpass time, while microstructural characteristics (growth of dendrite, segregation of chemical component, formation of various phases, etc.) developed due to successive deposition. An aging effect was observed, which caused precipitation of the γ″ and γ′ strengthening phases and the δ phase. The highest hardness value was measured in the middle section of each deposit due to precipitation of the strengthening phases. The cooling rate was calculated using the thermal profile of the deposition process and was found to be slower using the CMT-based WAAM process than that of other additive manufacturing (AM) processes that use laser or electron beams. The results presented here also demonstrated that in-situ heat treatment during deposition is possible using this CMT-based WAAM approach. • An aging effect was identified in CMT-based WAAM process. Strengthening phases such as γ″ and γ' were formed, which contributed to a microhardness of 250 to 306 HV. • In the CMT-based WAMM process of Inconel 718, the Laves, MC-type carbide, γ″, γ′ and δ phase precipitates were identified by SEM, SEM-EDS and EBSD. • This study showed that a cooling rate of the CMT process was slower than that of the AM process which use laser or electron beams. The strengthening phases such as the γ″ and γ′ were generated faster by using the CMT-based WAMM method rather than the use laser or electron beams as heat sources of AM. This result suggests the possibility of performing in-situ heat treatments simultaneously with deposition. [ABSTRACT FROM AUTHOR]