Tongmin Wang

A Promising New Class of High-Temperature Alloys: Eutectic High-Entropy Alloys

High-entropy alloys (HEAs) can have either high strength or high ductility, and a simultaneous achievement of both still constitutes a tough challenge. The inferior castability and compositional segregation of HEAs are also obstacles for their technological applications. To tackle these problems, here we proposed a novel strategy to design HEAs using the eutectic alloy concept, i.e. to achieve a microstructure composed of alternating soft fcc and hard bcc phases. As a manifestation of this concept, an AlCoCrFeNi2.1 (atomic portion) eutectic high-entropy alloy (EHEA) was designed. The as-cast EHEA possessed a fine lamellar fcc/B2 microstructure, and showed an unprecedented combination of high tensile ductility and high fracture strength at room temperature. The excellent mechanical properties could be kept up to 700°C. This new alloy design strategy can be readily adapted to large-scale industrial production of HEAs with simultaneous high fracture strength and high ductility.

A Criterion for Topological Close-Packed Phase Formation in High Entropy Alloys

The stability of topological close-packed (TCP) phases were found to be well related to the average value of the d-orbital energy level ( overline{Md} ) for most reported high entropy alloys (HEAs). Excluding some HEAs that contain high levels of the elements aluminum and vanadium, the results of this study indicated that the TCP phases form at ( overline{Md} ) > 1.09. This criterion, as a semi-empirical method, can play a key role in designing and preparing HEAs with high amounts of transitional elements.

A promising structure for fabricating high strength and high electrical conductivity copper alloys

To address the trade-off between strength and electrical conductivity, we propose a strategy: introducing precipitated particles into a structure composed of deformation twins. A Cu-0.3%Zr alloy was designed to verify our strategy. Zirconium was dissolved into a copper matrix by solution treatment prior to cryorolling and precipitated in the form of Cu5Zr from copper matrix via a subsequent aging treatment. The microstructure evolutions of the processed samples were investigated by transmission electron microscopy and X-ray diffraction analysis, and the mechanical and physical behaviours were evaluated through tensile and electrical conductivity tests. The results demonstrated that superior tensile strength (602.04u2009MPa) and electrical conductivity (81.4% IACS) was achieved. This strategy provides a new route for balancing the strength and electrical conductivity of copper alloys, which can be developed for large-scale industrial application.

Real-Time Observation on Evolution of Droplets Morphology Affected by Electric Current Pulse in Al-Bi Immiscible Alloy

The evolution of Bi-rich droplets morphology in a solidifying Al-Bi immiscible alloy was directly observed using a synchrotron microradiography technique. The electric current pulse (ECP) was applied to control the solidification process of Al-Bi immiscible alloy. It was found that the electromagnetic pinch force and Marangoni force induced by ECP and temperature gradient, respectively, can significantly affect the distribution of Bi-rich droplets. The electromagnetic pinch force drove the droplets from the center to side; meanwhile, the Marangoni force lifted the droplets from the bottom to the top. As a result, the droplets finally distributed with a manner of “inverted triangle.”

Study on continuous casting of cladding aluminium alloys with electromagnetic brake

Abstract The effects of electromagnetic brake (EMBR) on the flow of liquid melt during continuous casting of cladding aluminium alloys are investigated by numerical simulation and validated by experiments. The results show that the EMBR can effectively damp the strong impingement of the two streams of melt, decrease the jet length and reduce the recirculation zone in the centre of the mould. When the casting speed is 200 mm min−1, a 0·15 T direct current magnetic field can effectively constrain the mixing of different alloys in the molten pool. According to the parameters suggested by simulation, the cladding billet of Al–Si and Al–Mg alloys is successfully produced.

In situ study on growth behavior of Cu6Sn5 during solidification with an applied DC in RE-doped Sn–Cu solder alloys

The growth behavior of Cu6Sn5 intermetallic compounds in rare earth (RE)-doped Sn–Cu solder alloys with an applied direct current (DC) has been in situ investigated using synchrotron radiation imaging technology. The morphological evolutions of Cu6Sn5 with various shapes of I-like, Y-like and bird-like are directly observed. After doping RE, the number of I-like and bird-like Cu6Sn5 is decreased, but the number of Y-like Cu6Sn5 is increased. The morphologies of Cu6Sn5 are more uniform and the mean lengths of Cu6Sn5 of different shapes are reduced in RE-doped alloys compared with that in RE-free alloys, which is attributed to the adsorption effect of RE. The growth orientation of Y-like Cu6Sn5 is changed after La is doped. Additionally, with an applied DC, the nucleation rate of Cu6Sn5 is increased and the growth rate is markedly enhanced resulting in the refinement of Cu6Sn5. Furthermore, the mechanisms of refinement caused by RE and DC are specifically discussed.

Physical simulation of the effect of sample volume on ignition temperature in the thermal explosion synthesis of Ti+3Al→TiAl3

Abstract Semenovs theory of a spontaneous ignition was applied to study the sample geometrical dependence of ignition temperature ( T cr ) of thermal explosion synthesis in Ti–75at.%Al cylinder sample in various sizes. By linear-fitting of 2ln T cr +ln(1/ r +1/ h )∼−1/ RT cr plot, the apparent activation energy of ignition process is obtained 169±15 kJ/mol. The kinetic mechanism of the ignition process was also provided.

Effect of aluminium content of AlxCrFe1·5Ni0·5 multiprincipal alloys on microstructure and alloy hardness

Abstract AlxCrFe1·5Ni0·5 alloys (xu200a=u200a0·15, 0·2, 0·3, 0·4) were prepared by arc melting pure elements under argon atmosphere. All the AlxCrFe1·5Ni0·5 alloys present a single bcc solid solution crystal structure. Because of the common precipitation strengthening effect of lamellar precipitates and equiaxed particles, the hardness of the Al0·15CrFe1·5Ni0·5 alloy is quite high, reaching 443·2 HV. Microstructures of the AlxCrFe1·5Ni0·5 alloys (xu200a=u200a0·2, 0·3, 0·4) are very simple. The crystal boundary is quite straight. With the content of Al increasing from 0·2 to 0·4, the hardness of the alloy increases from 303·8 to 450·1 HV through the solution strengthening effect of the Al atom.

Study on Al/Mg compound materials by solid- liquid bonding method

Abstract Al/Mg compound materials were fabricated by a solid–liquid bonding method. The well bonded interface with a transition layer can be obtained. There were two kinds of interface structures in the ingot. The microstructures and bonding properties of Al/Mg interface were studied. The results showed that the brittle interface layer was composed mainly of intermetallic compound Al12Mg17 and Al3Mg2 at the top part and Al3Mg2 at the bottom part of ingot respectively. The reason why two kinds of interface structures existed was explained.

Grain refining performance of Al-B master alloys with different microstructures on Al-7Si alloy

The improved halide salt route has been employed to produce Al-3B master alloys with different microstructures. The micro-structural features of AlB2 particles exhibited different impacts on the grain refining response of Al-7Si alloy, evolving with the holding time after inoculation. Large blocky AlB2 particles suffer from an intense fading effect while strip-like particles are not effective enough at the 0.005 wt% B addition level. Among the various Al-3B master alloys, sample 1 containing fine, blocky AlB2 particles was revealed to be the most efficient in refining Al-7Si alloy. With inoculation of only 0.005%B of such alloy, the final grain size of Al-7Si alloy can reach 238 μm. Its grain refining efficiency was more or less retained for holding times up to 60 min.