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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]

• 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]

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]

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]

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]