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During powder sintering, it is widely accepted that the three unfavorable features, i.e., closed-pore hollow powder, satellite powder, and low excess free energy, can affect the densification behavior; however, their specific influences have previously never been determined. In this work, we report the efficient elimination of the three unfavorable features for atomized spherical titanium powder via discharge plasma modification and further clarify their influences on the densification behavior during spark plasma sintering. Our results show that the activation energy of power-law creep for the modified powder is two times lower than that of the atomized counterpart.

With the addition of Al element, the microstructure of high entropy alloy AlxCoCrCuFeNi (x = 0.5, 1.5 and 3.0) changes from single FCC to FCC + BCC and then to single BCC phase. Hardness and elastic modulus of different phases in the HEAs are measured utilizing nanoindentation method. It is found that with the increase of the Al element, the hardness rises more significantly in the BCC phase than that in the FCC phase. The reason is attributed to that the Al element has a stronger solid-solution strengthening effect in the BCC phase, due to the larger elastic modulus mismatch. The precise characterization of local mechanical properties of different phases in the HEAs provides us opportunity to design alloys with desired performance.

The ambient-temperature brittleness of bulk metallic glasses (BMGs) is a long-standing problem in materials engineering. Herein, we report a route to overcome this Achilles’ heel of BMGs via high-pressure die casting (HPDC) at a high filling rate and pressure to create bi-continuous interpenetrating-phase composites. Our results show that large tensile plasticity of 5.1% can be achieved in the Zr-based BMG/stainless steel interpenetrating-phase composite prepared by HPDC, which is superior to most of as-reported ex-situ secondary phase reinforced BMG composites. The excellent mechanical properties of the BMG composite mainly originate from excellent metallurgical bonding between matrix and reinforcement as well as high efficiency suppression of shear band propagation by three-dimensional metal skeleton. Our findings provide a promising approach for developing cost-effective BMG composites suitable for industrial applications.

For the electromagnetic transport (EMT) of liquid aluminum alloy during high pressure die casting (HPDC) by the plane induction electromagnetic pump (EMP), how to improve EMT efficiency and control EMT stationarity are key problems. Magnetic-flow coupling analysis was used to reveal effects of structural design and transport process parameters on EMT efficiency and stationarity. The output pump height of plane induction EMP was optimized by matching of iron core width W, coil width W′ and pump ditch width b, i.e., b values of bopt corresponding to 90% of the maximum output pump height, bopt/W = 1.27 and bopt/W′ = 1. Both EMT efficiency and stationarity are achieved under the optimum transport current 32 A. With the increase of the transport height from 350 mm to 500 mm, the EMT flow rate decreases from 4.28 kg/s to 3.59 kg/s, and the fillings of shot sleeve are always stationary. The transport tubes suffer a maximum positive pressure of 1.8 × 104 Pa and a minimum negative pressure of −1.42 × 104 Pa during EMT. For the liquid aluminum alloy soup occasions of 4.5 kg, 6.5 kg and 12.0 kg, the transport time could be shortened significantly from manipulator’s 16 s, 22 s and 38 s to EMT’s at most 2.195 s, 2.75 s and 4.28 s, respectively. The developed EMT process with plane induction EMP for HPDC is a process with low cost, high transport efficiency and stationarity.

Forming complex geometries using the casting process is a big challenge for bulk metallic glasses (BMGs), because of a lack of time of the window for shaping under the required high cooling rate. In this work, we open an approach named the &ldquo, entire process vacuum high pressure die casting&rdquo, (EPV-HPDC), which delivers the ability to fill die with molten metal in milliseconds, and create solidification under high pressure. Based on this process, various Zr-based BMGs were prepared by using industrial grade raw material. The results indicate that the EPV-HPDC process is feasible to produce a glassy structure for most Zr-based BMGs, with a size of 3 mm &times, 10 mm and with a high strength. In addition, it has been found that EPV-HPDC process allows complex industrial BMG parts, some of which are hard to be formed by any other metal processes, to be net shaped precisely. The BMG components prepared by the EVP-HPDC process possess the advantages of dimensional accuracy, efficiency, and cost compared with the ones formed by other methods. The EVP-HPDC process paves the way for the large-scale application of BMGs.

High-performance titanium alloys with an equiaxed composite microstructure were achieved by sintering and crystallizing amorphous powder. By introducing a second phase in a β-Ti matrix, series of optimized Ti–Nb–Fe–Co–Al and Ti–Nb–Cu–Ni–Al composites, which have a microstructure composed of ultrafine-grained and equiaxed CoTi2 or (Cu,Ni)Ti2 precipitated phases surrounded by a ductile β-Ti matrix, were fabricated by sintering and crystallizing mechanically alloyed amorphous powder. The as-fabricated composites exhibit ultra-high ultimate compressive strength of 2585 MPa and extremely large compressive plastic strain of around 40%, which are greater than the corresponding ones for most titanium alloys. In contrast, the alloy fabricated by sintering and crystallizing Ti–Zr–Cu–Ni–Al amorphous powder, which possesses significantly higher glass forming ability in comparison with the Ti–Nb–Fe–Co–Al and Ti–Nb–Cu–Ni–Al alloy systems, exhibits a complex microstructure with several intermetallic compounds and a typical brittle fracture feature. The deformation behavior and fracture mechanism indicate that the ultrahigh compressive strength and large plasticity of the as-fabricated equiaxed composites is induced by dislocations pinning effect of the CoTi2 or (Cu,Ni)Ti2 second phases and the interaction and multiplication of generated shear bands in the ductile β-Ti matrix, respectively. The results obtained provide basis guidelines for designing and fabricating titanium alloys with excellent mechanical properties by powder metallurgy.

Densification mechanism of Ti 40.6 Zr 9.4 Cu 37.5 Ni 9.4 Al 3.1 metallic glass (MG) powder with different heating rates during spark plasma sintering process was investigated using annealed crystalline counterpart powder as the object of reference. Results show that compared with single-stage densification process in the whole sintering process for the annealed crystalline counterpart powder, MG powder contains a two-stage densification process. Meanwhile, higher heating rate promotes obviously densification behavior for the both kinds of alloy powders. Further densification mechanism analysis based on Frenkel model indicates that the activation energy of the viscous flow for MG powder in the supercooled liquid region decreases with increasing heating rate, thus promoting densification behavior of the MG powder in the first stage. In contrast, for the annealed crystalline counterpart powder, the promoting densification behavior with increasing heating rate is attributed to the higher temperature gradient between the sample center and the edge. The variation in the viscosity of melt-solidified Ti 40.6 Zr 9.4 Cu 37.5 Ni 9.4 Al 3.1 bulk MG with temperature at different heating rates confirms the correctness of the obtained densification mechanism in our case. The results obtained can provide a new insight to understand the advantage of MG powder in fabrication of nano/ultrafine-grained titanium alloys with nearly full density.

Ultrafine grained Ti-based composites with equiaxed microstructure were fabricated by sintering and crystallizing from glassy powder precursors. The optimized composites exhibit ultimate strength of 2585 MPa and plasticity of exceeding 30%, occupying an unprecedented regime in the strength and ductility space of advanced titanium alloys. Dislocation pile-ups induced by precipitated phases and slip band propagation in the β-Ti matrix are the main reasons for the ultrahigh strength and plasticity respectively. The results provide an innovative route for fabricating titanium alloys with higher mechanical properties.

Nanocrystalline (NC) materials have fascinating physical and chemical properties, thereby they exhibit great prospects in academic and industrial fields. Highly efficient approaches for fabricating bulk NC materials have been pursued extensively over past decades. However, the instability of nanograin, which is sensitive to processing parameters (such as temperature and time), is always a challenging issue to be solved and remains to date. Herein, we report an ultrafast nanostructuring strategy, namely ultrasonic vibration consolidation (UVC). The strategy utilizes internal friction heat, generated from mutually rubbing between Ti-based metallic glass powders, to heat the glassy alloy rapidly through its supercooled liquid regime, and accelerated viscous flow bonds the powders together. Consequently, bulk NC-Ti alloy with grain size ranging from 10 to 70 nm and nearly full density is consolidated in 2 seconds. The novel consolidation approach proposed here offers a general and highly efficient pathway for manufacturing bulk nanomaterials.

Fe79.3Mo4.5P8.1C6.75B1.35 amorphous alloy composite powder from respective element powders of Fe, Mo, C, B, and Fe–P intermediate compound, was synthesized by mechanical alloying. Microstructure evolution analysis indicates that the synthesized amorphous alloy composite powder after a milling time of 70 h encompasses predominately amorphous matrix embedded by nanocrystalline α-Fe with a grain size of about 5.5 nm. However, unlike other Fe-based amorphous alloys, the synthesized amorphous alloy composite powder exhibits no obvious supercooled liquid region with only crystallization temperature. The corresponding crystallization onset temperature and exothermic enthalpy measured from DSC curves are about 762 K and 15.86 J/g, respectively. The results obtained provide good candidate materials for fabricating bulk metallic glass composites and related bulk nanocrystalline materials.

High-strength Ti66Nb13Cu8Ni6.8Al6.2 composites with intermetallic matrix reinforced by nanocrystalline WC particles were fabricated via spark plasma sintering and crystallization of amorphous phase. Microstructure analysis indicates that the bulk composites contain isolated nanocrystalline WC particles surrounded by crystallized intermetallic matrix, including ductile bcc β-Ti regions surrounded by a mixed-phase region of (Cu, Ni)-Ti2, TiC, and remaining amorphous phase. With increasing sintering temperature the crystallized intermetallic matrix transforms from nanocrystalline to an ultrafine-grained structure. The composite with ultrafine-grained intermetallic matrix reinforced by 4.5 vol.% WC exhibits high yield and fracture strengths of 2194 and 2277 MPa, respectively. The variation of fracture strength for the fabricated composites can be explained based on the volume fraction of the crystallized ductile β-Ti phase and the scale of the crystallized phase regions.

The multidimensional finned surface can greatly improve the capability of separation, extraction, absorption and heat transfer, so it is wildly applied to modern environmental protection, petrochemical industry, medical industry, and micro-electronics cooling, etc. By ploughing-extrusion process, this paper obtained a novel micro-groove array structure composed of micro-grooves, primary fins and compound fins, which have macro-structure, meta-structure, and micro-structure. The depth of micro groove is about 200 μm, and the height of the primary fin is about 80 μm. The height of the compound fins is larger than 100 μm, and the space of two compound fins is about 400 μm. In this process, the metal undergoes plastic deformation and turns into primary fins. Owing to the friction stress between the extrusion surfaces and the metal surpass the break limit of the metal, some regions of the primary fin undergo ductile fracture and turn into denticular compound fins. The whole process can be divided into four steps, i.e. splitting, extruding, frictional tearing and fin forming. The four stages are continuous and happen at the same time. The novel finned micro-groove array structure can be manufactured in a single procedure.

It is well known that semi-solid forming could only obtain coarse-grained microstructure in a few alloy systems with a low melting point, such as aluminum and magnesium alloys. This work presents that semi-solid forming could also produce novel bimodal microstructure composed of nanostructured matrix and micro-sized (CoFe)Ti2 twins in a titanium alloy, Ti62Nb12.2Fe13.6Co6.4Al5.8. The semi-solid sintering induced by eutectic transformation to form a bimodal microstructure in Ti62Nb12.2Fe13.6Co6.4Al5.8 alloy is a fundamentally different approach from other known methods. The fabricated alloy exhibits high yield strength of 1790 MPa and plastic strain of 15.5%. The novel idea provides a new insight into obtaining nano-grain or bimodal microstructure in alloy systems with high melting point by semi-solid forming and into fabricating high-performance metallic alloys in structural applications.