Search

In this study, Ti-48Al-3Nb-1.5Ta powders were manufactured from cast bars by the supreme-speed plasma rotating electrode process (SS-PREP) and used to prepare hot isostatically pressed (HIPed) material at 1050–1260 °C with 150 MPa for 4 h. The phase, microstructure and mechanical performance were analyzed by XRD, SEM, electrical universal material testing machine and other methods. The results revealed that the phase constitution changed from γ phase to α2 phase and then to γ phase with the material changing from as-cast to powders and then to as-HIPed. Compared with the as-cast material, the grain size and element segregation were significantly reduced for both powders and as-HIPed. When the hot isostatic pressing (HIP) temperature was low, the genetic characteristics of the powder microstructure were evident. With the HIP temperature increasing, the homogeneity of the composition and microstructure increased, and the prior particle boundaries (PPBs) gradually disappeared. The elastic moduli of powder and as-HIPed were superior to those of as-cast, which increased with the HIP temperature increasing. The hardness of as-HIPed was lower than that of the powder. The compressive strength, compressive strain, bending strength, and tensile strength of as-HIPed were higher than those of as-cast. With an increase in the HIP temperature, the compressive strength decreased gradually, and the compressive strain first decreased and then increased. [ABSTRACT FROM AUTHOR]

In this study, Ti-48Al-3Nb-1.5Ta powders were manufactured from cast bars by the supreme-speed plasma rotating electrode process (SS-PREP) and used to prepare hot isostatically pressed (HIPed) material at 1050–1260 °C with 150 MPa for 4 h. The phase, microstructure and mechanical performance were analyzed by XRD, SEM, electrical universal material testing machine and other methods. The results revealed that the phase constitution changed from γ phase to α2 phase and then to γ phase with the material changing from as-cast to powders and then to as-HIPed. Compared with the as-cast material, the grain size and element segregation were significantly reduced for both powders and as-HIPed. When the hot isostatic pressing (HIP) temperature was low, the genetic characteristics of the powder microstructure were evident. With the HIP temperature increasing, the homogeneity of the composition and microstructure increased, and the prior particle boundaries (PPBs) gradually disappeared. The elastic moduli of powder and as-HIPed were superior to those of as-cast, which increased with the HIP temperature increasing. The hardness of as-HIPed was lower than that of the powder. The compressive strength, compressive strain, bending strength, and tensile strength of as-HIPed were higher than those of as-cast. With an increase in the HIP temperature, the compressive strength decreased gradually, and the compressive strain first decreased and then increased.

[Display omitted] • A novel high Zn Al alloy is processed via two-step thermo-mechanical treatments. • A dense distribution of η' precipitates is achieved due to the unique processing. • A superhigh ultimate tensile strength up to 789 MPa is attained. Precipitation strengthening is crucial for the high strength of Al-Zn-Mg-Cu (7xxx) alloys. In this study, we synthesized a novel high-Zn 7xxx Al alloy through a comprehensive two-step thermo-mechanical treatment that includes hot extrusion and hot rolling. This approach effectively mitigates casting defects caused by high Zn content and preserves a significant number of dislocations and low-angle grain boundaries. These deformation substructures, coupled with high Zn concentrations, promote the dense formation of η' nanoprecipitates. As a result, this alloy exhibits an exceptional combination of mechanical properties, with an ultimate tensile strength (UTS) of 789 MPa and a tensile elongation of 9.2 %. Our findings offer innovative insights into the design of ultra-strong and ductile Al alloys for advanced engineering applications. [ABSTRACT FROM AUTHOR]

• Mechanism responsible for the anomalously severe HCS of Al-Li alloys were investigated. • Strong strain localization resulting from Li-rich inclusions induces microcrack initiation. • Liquid refilling is impeded by Li-rich inclusions occupying the interdendritic channels. This work reports a new mechanism for the severe hot cracking susceptibility (HCS) of cast Al-Li alloys. In contrast to the narrow vulnerable solidification temperature range increasing cracking resistance, alloys with high Li content or solute content, which are supposed to show lower HCS, instead exhibit anomalously high HCS. Results reveal that this phenomenon arises from a variety of Li-rich inclusions distributed in the interdendritic paths, including Li 2 O, LiAlO 2 , Li 2 CO 3 and LiH. These particles can form spontaneously with O 2 , CO 2 and H 2 O during solidification, deteriorating the interfacial bonding capacity. Meanwhile, the occupation of refilling channels for residual liquid increases the potential risk of microcrack initiation. These unfavorable factors promote the rapid propagation of cracks from the casting surface inward, which eventually leads to catastrophic fractures. [ABSTRACT FROM AUTHOR]

Among the applications of aluminum-based alloys is that in the field of hydraulic installations and equipment. Some components of their structure, such as the rotors of the cooling pumps of motor vehicles, or the blades of propellers from the engines of fishing boats, or pleasure boats, and even the radiators of motor vehicles are subject to corrosion by the cavity created during operation. Among the aluminum alloys used in the manufacture of such components is the alloy 5083. These parts can be made by casting (rotors / pump housings and steam propeller) or laminated semi-finished products, such as blades for rotors / propellers with adjustable vanes. Cavitation operation inevitably leads to damage by erosion caused by cyclic stresses of micro-jets and shock waves generated by the implosion of cavitation bubbles. As a result, the paper presents the results regarding the degradation by vibration cavitation of alloy 5083, in the form of cast and rolled semi-finished product. The curves and parameters specific to the resistance of the alloy to cavity erosion, as well as the images of eroded surfaces, show, surprisingly, that the cast semi-finished product has a higher resistance than the laminated one, due to the mechanical properties and the type of microstructure. [ABSTRACT FROM AUTHOR]

This study investigated the impact of the equal channel angular pressing (ECAP) combined with heat treatments on the microstructure and mechanical properties of AlSi10Mg alloys fabricated via selective laser melting (SLM) and gravity casting. Special attention was directed towards determining the effect of post-fabrication heat treatments on the microstructural evolution of AlSi10Mg alloy fabricated using two different routes. Three initial alloy conditions were considered prior to ECAP deformation: (1) as-cast in solution treated (T4) condition, (2) SLM in T4 condition, (3) SLM subjected to low-temperature annealing. Light microscopy, transmission electron microscopy, X-ray diffraction line broadening analysis, and electron backscattered diffraction analysis were used to characterize the microstructures before and after ECAP. The results indicated that SLM followed by low-temperature annealing led to superior mechanical properties, relative to the two other conditions. Microscopic analyses revealed that the partial-cellular structure contributed to strong work hardening. This behavior enhanced the material's strength because of the enhanced accumulation of geometrically necessary dislocations during ECAP deformation. [ABSTRACT FROM AUTHOR]

The chilled cast iron tappet comprises three gradient microstructures, including chill, mottle, and gray iron. In this work, the effect of Tellurium (Te) on the chilled iron tappet's microstructure and properties is studied. The addition of Te to gray cast alloy enhances its mechanical and thermal properties, which can be used in new designing of materials for heavy automotive applications. The gray cast iron alloy with 0.01 to 0.05 wt.% of Te was prepared in order to examine the effect of Te wt.% on the chill depth, microstructure, wear, and hardness. The scanning electron micrographs are used to distinguish and analyze the chill zone, mottle, and gray zone in the tappet, and the hardness was studied by Vickers hardness test, and wear behavior by a pin on disc method was measured. The present study showed that the addition of Te strongly influenced the formation of chill and efficiently enhanced the tappet's mechanical properties along with the favorable effect to eliminate the mottled zone and separate the chill zone and gray zone with a clear boundary. [ABSTRACT FROM AUTHOR]

• The NiCoCr alloys were prepared by mechanical vibration solidification. • The microstructure of as-cast NiCoCr alloys is significantly refined. • The yield stress increases at room temperature without loss of elongation. The NiCoCr multi principal element alloy (MPEA) show excellent ductility at cryogenic temperatures and corrosion-resistance properties under the condition that it prepared by thermal–mechanical processing. However, the coarse as-cast grains negatively impact mechanical properties significantly and grain refinement is necessary for forming complex castings. Most grain refining methods need extra alloying elements, which may result in loss of ductility by brittle second phases. In this work, a significant microstructure refinement of the as-cast NiCoCr MPEA was achieved by pollution-free vacuum mechanical vibration, with the average grain size refined from the initial value of 620 μm to 140 μm. As a result, the room-temperature yield strength was increased by 54 % (from 255 MPa to 392 MPa) without loss of elongation compared to the as-cast condition without vibration. [ABSTRACT FROM AUTHOR]

[Display omitted] • Unmodified eutectic Si particles have diverse multi-faceted morphologies. • The transformation of eutectic Si particles has a morphological dependence. • The molecular dynamics simulation of solution treatment was carried out. The morphological features of unmodified eutectic Si microstructure before and after solution treatment were revealed by the deep etching technique with a hypoeutectic Al-Si casting alloy as the study material. Before the solution treatment, the unmodified eutectic Si particles showed multi-faceted morphological features such as sheet-like, parallel hexahedral, truncated pyramidal, triangular platelet-like, octahedral, etc. After the six-hour solution treatment, the eutectic Si particles exhibit non-faceted morphological features such as spheroidal, cylindrical, and edge rounding. In addition, the edge rounding transformation of the octahedral Si particle during the holding process of solution treatment is visualised in combination with the molecular dynamics simulation. [ABSTRACT FROM AUTHOR]

• Functionally graded unidirectionally solidified (FGDS) Al-33Cu eutectic alloy was produced. • The mean interlamellar spacing and the volume fraction of eutectic Al 2 Cu were controlled in centrifugal casting. • The hardness of FGDS Al-33Cu eutectic alloy gradually decreased from 183 HB to 155 HB in 75 mm section length. To produce a functionally graded and directionally solidified (FGDS) structure, an Al-33Cu eutectic alloy has been centrifugally cast into a bar-shaped steel mold using a vacuum centrifugal casting system. Uni-dimensional cooling was performed to obtain directional solidification. Microstructural characterizations were carried out on the longitudinally sectioned cast bar along the solidification direction. Results showed that the Al 2 Cu eutectic lamellar spacing varied between 0.32 µm and 1 µm from the outer region to the inner region of the cast bars along a 75 mm distance. Centrifugal casting has resulted in microsegregation of copper concentration in a range between 55.8 % and 53.9 % from the outer region to the inner region, respectively. Similarly, the volume fraction of the Al 2 Cu eutectic has also varied between 45.3 % and 53.7 %. This leads to a significant variation in the hardness of the FGDS Al-33Cu eutectic alloy from 183 HB to 155 HB from the outer region towards the inner region. [ABSTRACT FROM AUTHOR]

A new casting method for processing copper alloy bonding wires was proposed. The microstructure evolution process of melt-extracted copper alloy wires was analyzed. The causes of the formation of non-uniform microstructures were analyzed. [Display omitted] Copper alloy wires are regarded as essential for bonding in semiconductor packaging. However, the existing single-crystal copper wires are susceptible to oxidize, resulting in connection failure. And the current production process of multi-pass cold-drawing is complicated. In this study, nickel-aluminum-bronze (NAB) alloy wires by the melt-extracted method were investigated to avoid the problems mentioned above. The results showed that the microstructure of the copper alloy wire differs depending on the region. The nano-Ni 3 Al phase precipitates on the lath martensitic β' phase in the concave area, while the interior of the copper alloy wires contains a large number of reflection-twin of the β' phase. As the melt-extracted process continues, the cooling speed increases until the formation of the stable lamellar α w + β' structure. These results will shed new light on the formation mechanism of copper alloy bonding wires. [ABSTRACT FROM AUTHOR]

Borides have been found to play a significant role in determining the mechanical properties of cast TiAl alloys. In order to investigate the influence of cooling rate on the morphology and structure of borides, SEM and HRTEM techniques were utilized to analyze borides in Ti-43Al-4 Nb-1Mo-0.5B (at%) cast plates with varying thicknesses. A higher cooling rate was observed to result in the formation of elongated, curvy borides with high aspect ratios, increased planar faults, and complex structures consisting of a combination of B2 phase and various boride phases. Conversely, a slower cooling rate yielded shorter bar-shaped borides with fewer planar faults. This variation in boride morphology can be attributed to the differing thicknesses of the solute-rich layer, where the eutectic reaction occurs, at the solidification front during fast and slow cooling processes. The B f -TiB with a habit plane of (010) was identified as the dominant phase at all cooling rates. Borides in the [100] and [001] directions demonstrated a faster growth rate compared to those in the [010] direction. Additionally, HRTEM results indicated the presence of TiB 2 while Ti 3 B 4 was absent. This can be explained by the limited phase region of Ti 3 B 4 in both the binary Ti-B and ternary Ti-Al-B phase diagrams, which is the smallest among all phases. These findings enhance the understanding of how cooling rate influences the morphology and structure of borides in TiAl alloys, thus providing insights for optimizing alloy design and manufacturing processes. [Display omitted] • Borides varied from long curvy to short bar with decreasing cooling rate. • Borides in TNM-0.5B alloy mainly consist of Bf-TiB and B2. • Change of the solute-rich layer thickness causes variation of boride morphologies. • Existence of TiB2 confirms the peritectic reaction between varied boride phase. [ABSTRACT FROM AUTHOR]

• A casting eutectic high entropy alloy Ni 30 Co 30 Cr 10 Fe 10 Al 18 W 2 was designed and prepared. • The alloy consists of soft FCC and hard B2 eutectic phases with the semi-coherent interface. • The alloy possesses a tensile strength of 1266.5 MPa and an elongation of 20.3% in the as-cast condition. Mechanical properties of casting alloys are generally limited. To make casting alloys applicable for a high level of service environments, a novel casting eutectic high entropy alloy (EHEA) with excellent mechanical properties is proposed. The hierarchical microstructures are with fine regular lamellar eutectic and coarse irregular eutectic. The eutectics consist of face-centered cubic (FCC) and ordered body-centered cubic (B2) phases with the semi-coherent interface. In the as-cast state, it shows a tensile strength of 1266.5 MPa and elongation of 20.3%. The unusual as-cast properties make it possible to manufacture high performance products by direct casting. [ABSTRACT FROM AUTHOR]

Whether selective laser melting (SLM) printed AlMgScZrMn alloy possesses more excellent performances than other processing routes was unknown. In the study, the microstructures and mechanical properties of AlMgScZrMn alloys fabricated by selective laser melting (SLM), spark plasma sintering (SPS) and cast were comparatively investigated. SLM printed sample shows columnar and equiaxed duplex grains with average grain size about 7 μm, which is coarser than SPS consolidated sample with finest equiaxed grain (4 μm) but smaller than casting sample with coarse equiaxed grain (25 μm). SLM printed sample shows the highest tensile strength (394 ± 5 MPa) and elongation (10.5 ± 1.2%) than SPS sample (231 ± 3 MPa, 0.59 ± 0.21%) and cast sample (188 ± 2.3 MPa, 3.7 ± 0.58%), although SPS sample has the finest equiaxed grains. For SPS sample, previous particle boundary (PPB) with oxide inclusion significantly deteriorates ductility. For cast sample, the coarse equiaxed grain with intergranular eutectic leads to inferior strength. In addition, the average dimension of Al 3 (Sc,Zr) particle in SLM sample is about 1–10 nm, which is much finer than SPS sample (0.5–0.8 μm) and cast sample (1–2 μm). The present study will provide a basis for the future industrial applications of the AlMgScZrMn alloy. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Basalt fibres have shown reinforcement potential for metal composite development. • Al matrix-basalt fibre interaction form α-Fe intermetallics at the interface. • This chemical interaction influences the morphology of these intermetallics. • Overall improvement in composite performance over the reference alloy is observed. Abstract A novel aluminium-basalt metal matrix composite has been produced by employing a combination of stir mixing and ultrasonication processing techniques. A study of the matrix-fibre interface has revealed the formation of Al-Si-Ca and Al-Fe-Si-Mn intermetallic compounds (IMC) with both phases displaying a polyhedral morphology. The new composite exhibited a tensile strength of 189 MPa, resulting in a 13% improvement over the monolithic Al alloy. A 22% increase in yield strength and a 33% increase in wear resistance were also achieved, although the flexural and elastic moduli remained unchanged. It is proposed that these IMCs assist in load transfer from the matrix to the fibres. [ABSTRACT FROM AUTHOR]

Highlights • Hot isostatic pressing has the potential to heal millimeter-scale cavity defect. • Diffusion is the dominant mechanism during cavity healing process. • Cavity healing can be considered as a process from incomplete to complete wetting. • Both the temperature and pressure are essential during the healing process. Abstract Hot isostatic pressing (HIP) is considered as an effective means in healing micro-defects inside the superalloy. However, can HIP effectively heal macro defect? Here we design a sealed cavity inside the superalloy to simulate the millimeter-sized cavity defect and focus on its healing behavior by HIP. Results show that HIP has the potential to heal the millimeter-scale cavity and the main mechanism is diffusion based on the features of diffusion zone and honeycomb structure during healing process. This exploratory work helps to better understand and broaden the applications of HIP and make the manufacturing sustainable. [ABSTRACT FROM AUTHOR]

Abstract This study was undertaken to investigate the influence of Er addition on microstructure and mechanical properties of as-cast Mg-10Li-5Zn alloy. With addition of Er, the grain size of as-cast alloys is greatly reduced, meanwhile, Mg-Zn-Er phase forms and increases gradually and Mg-Li-Zn phase decreases. The Mg-Zn-Er phase is mainly W-phase. The size of W-phase becomes larger with the increase of Er content from 0.5 wt% till 3.5 wt% and W-phase is mainly distributed from in the grain interiors to along the grain boundaries as well. The size, quantity and distribution of W-phase is an important factor that influences the mechanical properties of Mg-10Li-5Zn- x Er alloys. Overmuch coarse W-phase in the grain boundaries is detrimental to strength. The Mg-10Li-5Zn-0.5Er alloy exhibits an optimum combination of tensile properties with the ultimate tensile strength, yield strength and elongation of 198 MPa, 223 MPa and 14.7%. The optimal Er addition in as-cast Mg-10Li-5Zn alloy is ~0.5 wt%. [ABSTRACT FROM AUTHOR]

AZ91 magnesium as a lightest structural material, of the alloying additions to magnesium to date, composite Ca, Y and Sm have not been studied. Herein, the effects of Ca and RE(Y, SM) on the microstructure and mechanical properties of as-cast AZ91 magnesium alloy were studied. The results showed that the addition of 1 wt% Ca into AZ91 magnesium alloy could effectively refine the grains, and change the second phase distribution as well. Based on that, the addition of Y and Sm can change the second phase distribution of as-cast AZ91-1Ca alloy. When the content of Y and Sm increased to 0.67 wt% and 0.33 wt% respectively, Al _2 Y,Al _2 Sm and Al _2 (Y _x , Sm _1-x ) composite phases are introduced to refine the alloy grains, also change the size and distribution of the second phase (Mg _17 Al _12 ,Al _2 Ca). Furthermore the mechanical properties of AZ91 magnesium Alloy can be improved by Ca and RE (Y, Sm), among which the comprehensive mechanical properties of AZ91-1Ca-0.67Y-0.33Sm alloy has the best presentation, Consequently, the yield strength and tensile strength reached the highest, which are 126 MPa and 198 MPa respectively due to the ensuring elongation. The fracture mode of magnesium alloy can be changed by composite addition of Ca and RE (Y, Sm).

• Precipitation microstructures and mechanical properties of Al-2Li-2Cu-0.5 Mg-0.15Sc-0.1Zr-0.1Ti alloy aged at 175 °C are investigated. • The precipitates of alloy aged at 175 °C mainly consisted of T 1 , δ′, core–shell phase, S′ and cubic phase. • The cubic phase was transformed from Al 6 Cu 5 Li 2 to Al 6 Cu 5 Mg 2 with the aging time increasing from 8 h to 64 h. The microstructure evolution corresponding to the mechanical properties of cast Al-2Li-2Cu-0.5Mg-0.15Sc-0.1Zr-0.1Ti alloy aged at 175 °C was investigated, especially in the identification and variation of the cubic phase. The yield strength and ultimate strength of the peak-aged alloy reach 449 MPa and 502 MPa, respectively. From the transmission electron microscopy characterization, it was found that the precipitates primarily consisted of the cubic phase, T 1 (Al 2 CuLi), S′(Al 2 CuMg), core–shell particles and δ′(Al 3 Li) phases. Longer exposure to temperature changed the composition from Al 6 Cu 5 Li 2 to Al 6 Cu 5 Mg 2 , and these two phases are in competition with the T 1 and S′ phases. [ABSTRACT FROM AUTHOR]

This study explores using high-energy pulsed laser to improve the surface property and corrosion behavior of Ti-6Al-4V, aiming to develop a more eco-friendly and efficient approach. The study comprises conventional cast samples, advanced 3D-printed samples, and their respective laser-treated counterparts, all tested in a 3.5 wt% NaCl solution. The findings showed that sample 3 (as-3D-printed) had a more stable passivation film than sample 1 (as-cast). The laser-treated surface of sample 2 (laser-treated cast) greatly enhances film stability and resistance. Moreover, sample 4 (laser-treated 3D-printed) exhibited significantly better corrosion performance compared to sample 3 (as-3D-printed) due to the increased thickness of the passivation film in the laser-treated samples, resulting in higher film corrosion resistance. The results reveal that laser remelting treatment can eliminate macroscopic defects, reduce grain size, increase grain boundary density, and generate denser and more stable passivation films on the surface of Ti-6Al-4V, leading to reduced corrosion currents during dynamic potential polarization. Furthermore, laser remelting treatment has the capability to transform and refine the α phase into a finer lamellar and needle-like structure, thereby increasing the density of passivation nucleation sites during the corrosion process, resulting in the formation of a high-density passivation layer, and ultimately improving the corrosion resistance. By gaining a better understanding of the underlying mechanisms involved in high-energy pulsed treatment, this work provides valuable insights that can be used to optimize the treatment process and improve the overall surface properties of Ti-6Al-4V alloys. [Display omitted] • The microstructure of cast and 3D-printed Ti-6Al-4V differs, impacting passivation film thickness and resistance. • Laser remelting treatment significantly improves corrosion resistance of cast and 3D-printed parts. • Laser treatment increases the density of grain boundaries on surface, improving passivation layer stability. [ABSTRACT FROM AUTHOR]

High temperature tensile properties of Inconel 713C without and with Yttrium microaddition have been investigated. Yttrium addition affected the solidification structure with promotion of equiaxed grain formation in the center of mold. Ultimate tensile strength increased from approximately 892 to 1006 MPa while the elongation increased from approximately 13% to 21% by 0.05 mass% Yttrium addition. 0.05 mass% Yttrium addition in Inconel 713C alloy showed optimum high temperature tensile property. [ABSTRACT FROM AUTHOR]

The microstructure and aging precipitates of a new cast Mg-Y-Sm-Zn-Zr alloy were investigated. The results showed that eutectic phase forming in solidification process was proved to be (Mg,Zn) 3 (Y,Sm). The alloy exhibited high hardness (maximum value of 148 HV), which is higher in comparison with other high rare-earth Mg alloy. The aging precipitate β′ is thermally stable at 200 °C for the crystal structure of β′ kept unchanged in the whole aging process. [ABSTRACT FROM AUTHOR]

A quarternary Co-free Ni 35 Al 21.67 Cr 21.67 Fe 21.67 high entropy alloy was designed and prepared by arc melting. The Ni 35 Al 21.67 Cr 21.67 Fe 21.67 high entropy alloy (HEA) possesses disordered BCC phase and ordered BCC phase (B2). A “sunflower-like” microstructure was found in Ni 35 Al 21.67 Cr 21.67 Fe 21.67 high entropy alloy. B2 phase forms the continuous matrix with the disordered BCC spherical particles (200 nm–300 nm) in ‘core’ region. In ‘petal’ region, striped B2 phases are inlaid in disordered BCC matrix. Moreover, the result of mechanical property test suggests that alloy presents outstanding compressive strength and excellent ductility with the microstructure of B2/BCC phase. The alloy showed an excellent comprehensive properties at room temperature (yield strength σ 0.2  = 1471 MPa, compressive strength σ b  = 3541 MPa and compression rate ε = 40%) , which was superior to some traditional metallic materials. High strength was mainly attributed to high volume fraction of hard B2 phase matrix and B2 precipitations strengthening. Dislocations motion in disordered BCC matrix provided ductility for the alloy. The Ni 35 Al 21.67 Cr 21.67 Fe 21.67 HEA has promising use in future structural applications. [ABSTRACT FROM AUTHOR]

Chilled cast iron tappet has a tendency microstructure of white, mottled and gray iron. The exact composition and other casting parameters, like pouring temperature, inoculation and coating, need to be determined for achieving the desired thickness of the chilled layer. Chilled cast iron finds applications in areas where improved hardness and wear resistance are required. Mottled cast iron has very poor machinability and high brittleness due to the presence of secondary cementite. These constitute the limitations for its use. The influence of inoculation, pouring temperature, coating thickness and chill plate on chilled depth was investigated. Taguchi design-of-experiments (DOE) are used for generating an optimal set of casting parameters to obtain a satisfactory chilled depth. Analysis of the effects of all the parameters on chilled depth has been carried out through a microstructure study. [ABSTRACT FROM PUBLISHER]

In order to comprehensively understand the forming mechanism of abnormal phases solidified in a nickel-base cast superalloy with additives of tungsten and molybdenum, the coupling effects of W and Mo on the microstructure and stress-rupture properties were investigated in this paper. The results indicated that the precipitation of primary α-(W, Mo) phase depended tremendously on the amount of W and Mo addition. When the total amount of W and Mo was greater than 5.79 at%, α-(W, Mo) phase became easily precipitated in the alloy. With increasing of Mo/W ratio, the dendrite-like α-(W, Mo) phases were apt to convert into small bars or blocky-like phases at the vicinities of γ′/γ eutectic. The morphological changes of α-(W, Mo) phase can be interpreted as the non-equilibrium solidification of W and Mo in the alloy. Since the large sized α-(W, Mo) phase has detrimental effects on stress-rupture properties in as-cast conditions, secondary cracks may mainly initiate at and then propagate along the interfaces of brittle phases and soft matrix. During exposing at 1100 ℃ for 1000 h, the α-(W, Mo) phases transformed gradually into bigger and harder M 6 C carbide, which results in decreasing of stress-rupture properties of the alloy. Finally, the alloy with an addition of 14W-1Mo(wt%) maintained the longest stress lives at high temperatures and therefore it revealed the best microstructure stability after 1100 ℃/1000 h thermal exposure. [ABSTRACT FROM AUTHOR]

Two novel Mg-Sn based wrought alloys are developed with good mechanical properties, which are Mg-2Sn-2.5Zn-2Al (TZA222) alloy and Mg-4Sn-2.5Zn-2Al (TZA422) alloy. The as-cast alloys with high elongations to failure over 10% and low tensile strengths just over 70 MPa are suitable for hot deformation processing. After hot rolling at 350 °C of 60% total reduction, the strengths of the alloys are significantly improved, meanwhile, their elongations to failure still remain at high level. The as-hot-rolled TZA422 alloy has better mechanical properties, of which the yield strength, ultimate tensile strength and elongation to failure are 196.9 MPa, 285.5 MPa and 20.7%, respectively. It has nano-sized Mg 2 Sn particles dispersed within fine grains with an average size of 10 µm, while the main second phase is coarse Mg 5 Zn 2 Al 2 in the as-cast TZA422 alloy. Both the as-hot-rolled TZA422 and TZA222 alloys have good combinations of strength and ductility, which are comparable to other as-hot-rolled Mg alloys with high performances. [ABSTRACT FROM AUTHOR]

Microstructural morphology of CoCrMo alloy by control of the cooling rate during the solidification was investigated. Samples were obtained using both an induction furnace for slow cooling rate and electric arc furnace for fast cooling rate. Microstructural characterizations were performed with metallographic techniques. It was found that the difference between the formation temperature of hard secondary phases of M23C6-type carbides determine the reduction of carbide size by increasing the cooling rate.

An NbC-Fe composite powder was synthesized from an Nb2O5/Fe/C mixture by electrochemical reduction and subsequent carbonization in molten CaCl2-NaCl. The composite has a core-shell structure, in which NbC acts as the cores distributing in the Fe matrix. A strong bonding between NbC and Fe is benefit from the core-shell structure. The sintering and electrochemical reduction processes were investigated to probe the mechanism for the reactions. The results show that NbC particles about several nanometers were embraced by the Fe shell to form a composite about 100 nm in size. This featured structure can feasibly improve the wettability and sinterability of NbC as well as the uniform distribution of the carbide in the cast steel. By adding the composite into steel in the casting process, the grain size of the casted steel was markedly deceased from 1 mm to 500 μm on average, favoring the hardening of the casted steel. [ABSTRACT FROM AUTHOR]

A novel casting TiAl alloy with fine homogeneous microstructure and excellent performances is obtained assisted by the ultrasonic melt treatment. The coarse columnar crystal is modified into non-dendritic structure and the large grain is refined from 3098 μm to 88 μm; the micro-segregation, micro-porosities and precipitates are eliminated as well. After ultrasonic melt treatment for 90 s, the highest compressive strength is improved up to 1705 MPa, about 12% higher than the “quasi-oriented” TiAl alloy. [ABSTRACT FROM AUTHOR]

• A new AlCrFeMnNi 2 HEA with a unique sunflower-like eutectic structure was designed. • The HEA has excellent comprehensive mechanical properties. • Coherent interface and bimodal distribution of B2 phase lead to good properties. Although most BCC-based high-entropy alloys have high strength and excellent high temperature mechanical properties, their low plasticity greatly limit their application. It is a new challenge to develop new BCC-based high-entropy alloys with excellent combination of high strength and plasticity. In this study, we prepare a new BCC/B2 AlCrFeMnNi 2 high-entropy alloy with a unique sunflower-like eutectic microstructure. This alloy has a high yield strength of 1206 MPa, a high fracture strength of 3437 MPa and large compressive plastic strain of 37.5%. The excellent compressive mechanical properties are superior to many other BCC/B2 high-entropy alloys. These properties can be attributed to its unique microstructure consisting of coherent interface between BCC and B2 phase and the bimodal distribution of the B2 precipitates. Our results can provide a meaningful reference for improving the plasticity of BCC-based high entropy alloys. [ABSTRACT FROM AUTHOR]

• A low cost and high performance TMCs was prepared by a simple casting method. • Cr 3 C 2 tents to react with Ti matrix in situ to form TiC with different morphologies. • TiC strengthening and Cr solid solution strengthening play a dominate role. A low-cost, high performance TiC reinforced titanium matrix composite was successfully fabricated using an in situ reaction casting method. The results showed that the morphology and distribution of TiC in the microstructure were the more important factors affecting the properties of composites. And due to the second phase strengthening of the TiC and the Cr element solid solution strengthening for titanium matrix, it provides exceptionally high strength and toughness (1034.5 MPa ultimate tensile strength and 9.0 % elongation) for titanium structural components and increases extremely high hardness (50.4HRC) for titanium wear-resistant components. This study provides additional options for the application of low-cost titanium components. [ABSTRACT FROM AUTHOR]

• Al-YOF/TiB 2 composites are fabricated by molten-salt-assisted stirring casting. • Modification with fluorine makes Y 2 O 3 particles entering Al melt. • Fine equiaxed YOF particles evenly distributed in the Al matrix. • YOF provides a good dispersion strengthening effect. • YOF can be a well-chosen of reinforcement for AMCs. The poor wettability between oxides and Al melt and presence of alumina film on Al melt surface seriously limits the fabrication of Al matrix composites (AMCs) reinforced by oxides via casting method. The wettability of oxides can be improved by modification with fluorine, and the oxyfluoride is more feasible to incorporate into Al melt, but the strength of the oxides may decrease after modification. Therefore, it is necessary to assess the strengthening effect of oxyfluoride by comparison with classical reinforcement. In this work, AMCs reinforced with yttrium oxyfluoride (YOF) and TiB 2 were successfully fabricated by molten-salt-assisted stirring casting. YOF particles exhibit a better distribution in Al matrix than TiB 2 particles, and the YOF particles show better bonding strength with Al matrix than TiB 2 due to reactive wetting. Al-YOF composite shows higher hardness, tensile strength, and ductility than Al-TiB 2 composite. The values of microhardness, yield strength (σ 0.2) and ultimate tensile strength (σ b) of Al-YOF composite are 27.2 HV, 55 MPa and 81 MPa, which are 25.9 %, 62 % and 53 % higher than that of pure Al. [ABSTRACT FROM AUTHOR]

• A novel method combining vacuum purification and mechanical stirring was proposed. • The purification mechanism in A356 alloy melts was discussed under vacuum-stirring. • Tensile strength and ductility of A356 alloys was enhanced by vacuum-stirring. Vacuum purification technology that is dependent on the static pressure between liquid and gas is an effective method to acquire high-quality alloy melts. However, during purification, there is a low degassing efficiency. Here, a novel method combining vacuum purification with mechanical stirring was proposed to purify aluminum alloy melts. The results showed that compared with the vacuum purification, the hydrogen content decreased from 0.12 to 0.08 ml/100 g; the yield strength, tensile strength and elongation increased by 51.3 %, 33.4 % and 114.8 %, respectively, in the A356 alloy subjected to the vacuum-stirring purification. Furthermore, the purification mechanism related to bubbles was discussed in melts under vacuum-stirring. [ABSTRACT FROM AUTHOR]

Scanning electron microscopy (SEM), transmission electron microscopy (TEM), small-angle X-ray scatter (SAXS) and atom probe tomography (APT) were combined to characterize the change of δ phase microstructure under the effect of in-situ iron-rich nanoparticles. In-situ nanoparticle wall model was proposed to elucidate the effect of high density of iron-rich nanoparticles on inhibiting tin segregation which causes δ phase formation. This work sheds light on a potential pathway for fabricating bulk homogenous materials during casting process. [ABSTRACT FROM AUTHOR]

A lamellar Mg 10 GdZn phase was observed near the secondary eutectic β-phase ((Mg,Zn) 3 Gd) in an as-cast Mg–Gd–Zn alloy. It shows that the Mg 10 GdZn phase exhibits a 18R-type long period stacking ordered (LPSO) structure, while the lamellae within the α-Mg matrix exhibits a 14H-type LPSO structure. Moreover, it reveals that the hardness and elastic modulus of Mg 10 GdZn phase are much higher than those of the α-Mg by nano-mechanical measurements. [ABSTRACT FROM AUTHOR]

In this paper, the ultrasonic vibration treatment was applied to the TiAl alloy melt during the solidification aiming at modifying the coarse microstructure and improving the mechanical properties. Effects of ultrasonic vibration on the microstructure and mechanical properties of TiAl are elaborately studied. The results show that the grain size was refined from 545 μm to 96 μm, the yield strength was improved from 419 MPa to 854 MPa, and the coarse dendrite structure was modified into fine non-dendrite grains after ultrasonic vibration. Given the high melt viscosity and narrow liquid–solid temperature range, the predominant refinement mechanism of ultrasonic vibration for TiAl is the cavitation-enhanced nucleation due to the nucleus activation and/or heightened supercooling. [ABSTRACT FROM AUTHOR]

The microstructure and mechanical properties of Mg-6Sn and Mg-6Zn are investigated and compared in cast/heat treated, rolled and extruded conditions. Compared to the heat treated alloys, the grain size of both alloys decreases while the volume fraction of precipitates increases by rolling and extrusion in Mg-6Sn alloy at 350 ºC due to dynamic recrystallization and dynamic precipitation of intermetallic phases. Zinc has a stronger grain refining effect than tin in the heat treated alloys while the opposite effect is found in the rolled and extruded alloys. For the heat treated alloys the Mg-6Sn the strength reached 158.7 MPa with elongation 5.2% while Mg-6Zn exhibited a higher strength of 183.7 MPa and 8.4% elongation. In rolled condition the strength of Mg-6Sn reached 224 MPa with 1.6% elongation while Mg-6Zn exhibited a lower strength of 124 MPa and a lower ductility of 0.5% elongation due to susceptibility to hot shortness. Extrusion of Mg-6Sn alloy resulted in the maximum attained strength of 281 MPa and an elongation of 6.1% while Mg-6Zn cracked during extrusion due to hot shortness. The results obtained are discussed with respect to microstructure evolution in both alloys. [ABSTRACT FROM AUTHOR]

• Novel C-doped TiB 2 particles are introduced into an Al-Si-Mg alloy. • The average grain size of α-Al can be reduced by 70% via C-doped TiB 2 particles. • The C-doped TiB 2 particles enhance the strength-ductility synergy of A357 alloy. We report novel C-doped TiB 2 particles introduced into an Al-Si-Mg alloy. The impact of C-doped TiB 2 particles on the α-Al grain and associated mechanical properties were systematically investigated. These particles were introduced via a master alloy (Al-TBC master alloy, or Al-TBC for short). The results show that the C-doped TiB 2 particles have a dramatical nucleation capability for the α-Al grain, thus eliminating the grain refinement problem of Si "poisoning" in the A357 alloy (one typical category in Al-Si-Mg alloy). As a result, the average grain size of α-Al can be refined to 140 μm from 490 μm by adding 0.5 wt% Al-TBC. The C-doped TiB 2 particles can also enhance the strength-ductility synergy of A357 alloy at room temperature. At 0.5 wt% Al-TBC, the ultimate tensile strength, yield strength, and elongation of T6-treated A357 alloy are 370.1 ± 1.2 MPa, 302.5 ± 7.5 MPa, 12.38 ± 1.2 %, respectively. This work provides a novel prospect for resolving the problem of Si "poisoning" in grain refinement and strength-ductility trade-off in hypoeutectic Al-Si alloys via C-doped TiB 2 particles. [ABSTRACT FROM AUTHOR]

Microstructure and thermal properties of Mg-(3 mass% or 5 mass%) Sn-2 mass% Ca alloys as casts and extrusions have been investigated with different ram speeds and extrusion temperatures. Mg-(3 mass% or 5 mass%) Sn-2 mass% Ca alloys are composed of $$\upalpha $$ -Mg, MgSnCa, and $$\hbox {Mg}_{2}\hbox {Ca}$$ phases. By adding Sn content from 3 mass% to 5 mass%, the MgSnCa phase is increased and the $$\hbox {Mg}_{2}\hbox {Ca}$$ phase is decreased. During hot extrusion, the average grain sizes are increased with increasing ram speed and temperature. The ultimate tensile strength ( UTS) and elongation for the Mg-5Sn-2Ca alloy at $$2.3\, \hbox {mm}{\cdot }\hbox {s}^{-1}$$ are 227.73 MPa and 18.43 %, respectively. With increasing extrusion ram speed, the UTS and elongation for the Mg-5Sn-2Ca alloy are remarkably decreased to 215.95 MPa, 206.33 MPa, and 14.74 %, 6.88 %, respectively. The thermal conductivity for the Mg-3Sn-2Ca alloy is dramatically improved, compared to commercialized Mg alloys such as AZ31 and AZ91 due to formation of MgSnCa and $$\hbox {Mg}_{2}\hbox {Ca}$$ phases. [ABSTRACT FROM AUTHOR]

Fe-B-C wear-resistant alloy, as a new type of iron-based wear-resistant materials, has drawn extensive attention of the researchers in materials at home and abroad. The boron concentration plays an important role in the microstructure and mechanical properties of Fe-B-C wear-resistant alloy. In this paper, the solidification microstructure, volume fraction of eutectic, macro and micro hardness of Fe-B-C alloy are researched. The samples are measured by optical microscopy (OM), scanning electron microscopy (SEM), Rockwell-hardness tester, Vickers-hardness tester. Image processing software such as image-pro and photoshop are used. The content of boron in experiment alloys are 1.0%, 1.5%, 2.0%, 2.5% and 3.0% respectively. As a result, the solidification microstructure of as-cast Fe-B-C mainly consists of metallic matrix and eutectic structure. The eutectic phase is continuous netlike distribution along the grain boundary. As boron concentration increases, the volume fraction of borocarbide increases in the matrix, and the size is larger. The hardness of Fe-B-C also has a tendency to rise with the increase of boron concentration. [ABSTRACT FROM AUTHOR]

The wide popularities of grain refiner and modifier in aluminum alloy industry enable us to achieve improved properties and performances. Here, using aluminothermic reaction between nano-oxide particles (ZnO, ~20 nm in size) and aluminum alloy (A356), the microstructure refining effect on aluminum alloy is investigated. By the incorporation of nanoparticles with semi-solid melt treatment, the coarse primary aluminum dendritic microstructures are transformed to more fine and equiaxed structure showing improved mechanical properties. Converting mechanisms are interpreted in terms of the nucleation site increment, as well as the grain growth restriction, by decomposition and dissolution of the nano-oxide particles in aluminum alloy melt. [ABSTRACT FROM AUTHOR]

• Biodegradable HR Zn-1Mg-xZr alloys are fabricated via alloying and hot-rolling. • HR Zn-1Mg-0.05Zr alloy shows YS of 218.0 MPa, UTS of 263.2 MPa, and EL of 12.1% • Hot-rolling enhances the YS, UTS, and EL due to the dynamic recrystallization. • HR Zn-1Mg-0.05Zr alloy possesses a degradation rate of 71 μm/y in Hanks' solution. Zn-1Mg-xZr alloys were prepared via alloying with different Zr contents and hot-rolling, and their microstructures, mechanical properties, and corrosion behaviors were assessed systematically. The results indicated that the mechanical strength of as-cast and hot-rolled (HR) samples initially increased and subsequently decreased with increasing Zr addition. HR samples showed a substantial increase in yield strength (YS), ultimate tensile strength (UTS) and elongation (EL) compared with their as-cast counterparts. HR Zn-1Mg-0.05Zr alloy showed higher mechanical property matching (218.0 MPa for YS, 263.2 MPa for UTS, 12.1% for EL) and an appropriate corrosion rate of 455 μm/y in Hanks' solution among the Zn-1Mg-xZr alloys for biomedical applications. [ABSTRACT FROM AUTHOR]