Microstructure Evolution and Mechanical Properties of FeCoCrNiCuTi0.8 High-Entropy Alloy Prepared by Directional Solidification.

A CoCrCuFeNiTi0.8 high-entropy alloy was prepared using directional solidification techniques at different withdrawal rates (50 µm/s, 100 µm/s, 500 µm/s). The results showed that the microstructure was dendritic at all withdrawal rates. As the withdrawal rate increased, the dendrite orientation become uniform. Additionally, the accumulation of Cr and Ti elements at the solid/liquid interface caused the formation of dendrites. Through the measurement of the primary dendrite spacing (λ1) and the secondary dendrite spacing (λ2), it was concluded that the dendrite structure was obviously refined with the increase in the withdrawal rate to 500 µm/s. The maximum compressive strength reached 1449.8 MPa, and the maximum hardness was 520 HV. Moreover, the plastic strain of the alloy without directional solidification was 2.11%, while the plastic strain of directional solidification was 12.57% at 500 µm/s. It has been proved that directional solidification technology can effectively improve the mechanical properties of the CoCrCuFeNiTi0.8 high-entropy alloy.

The Effect of Copper Content on the Mechanical and Tribological Properties of Hypo-, Hyper- and Eutectoid Ti-Cu Alloys.

Titanium alloys are widely used in aerospace, chemical, biomedical and other important fields due to outstanding properties. The mechanical behavior of Ti alloys depends on microstructural characteristics and type of alloying elements. The purpose of this study was to investigate the effects of different Cu contents (2.5 wt.%, 7 wt.% and 14 wt.%) on mechanical and frictional properties of titanium alloys. The properties of titanium alloy were characterized by tensile test, electron microscope, X-ray diffraction, differential scanning calorimetry, reciprocating friction and wear test. The results show that the intermediate phase that forms the eutectoid structure with α-Ti was identified as FCC Ti2Cu, and no primary ß phase was formed. With the increase of Cu content, the Ti2Cu phase precipitation in the alloy increases. Ti2Cu particles with needle structure increase the dislocation pinning effect on grain boundary and improve the strength and hardness of titanium alloy. Thus, Ti-14Cu shows the lowest elongation, the best friction and wear resistance, which is caused by the existence of Ti2Cu phases. It has been proved that the mechanical and frictional properties of Ti-Cu alloys can be adjusted by changing the Cu content, so as to better meet its application in the medical field.

Electronic structure studies on single crystalline Nd2PdSi3, an exotic Nd-based intermetallic: evidence for Nd 4f hybridization.

In the series R2PdSi3, Nd2PdSi3 is an anomalous compound in the sense that it exhibits ferromagnetic order unlike other members in this family. The magnetic ordering temperature is also unusually high compared to the expected value for a Nd-based system, assuming 4f localization. Here, we have studied the electronic structure of single crystalline Nd2PdSi3 employing high resolution photoemission spectroscopy and ab initio band structure calculations. Theoretical results obtained for the effective on-site Coulomb energy of 6 eV corroborate well with the experimental valence band spectra. While there is significant Pd 4d-Nd 4f hybridization, the states near the Fermi level are found to be dominated by hybridized Nd 4f-Si 3p states, which is possibly responsible for the ferromagnetism in Nd compound. Nd 3d core level spectrum exhibits multiple features manifesting strong final state effects due to electron correlation, charge transfer and collective excitations. These results serve as one of the rare demonstrations of hybridization of Nd 4f states with the conduction electrons possibly responsible for the exoticity of this compound.

Investigation of Microstructure Evolution and Phase Selection of Peritectic Cuce Alloy During High-Temperature Gradient Directional Solidification.

In this work, a CuCe alloy was prepared using a directional solidification method at a series of withdrawal rates of 100, 25, 10, 8, and 5 µm/s. We found that the primary phase microstructure transforms from cellular crystals to cellular peritectic coupled growth and eventually, changes into dendrites as the withdrawal rate increases. The phase constituents in the directionally solidified samples were confirmed to be Cu2Ce, CuCe, and CuCe + Ce eutectics. The primary dendrite spacing was significantly refined with an increasing withdrawal rate, resulting in higher compressive strength and strain. Moreover, the cellular peritectic coupled growth at 10 µm/s further strengthened the alloy, with its compressive property reaching the maximum value of 266 MPa. Directional solidification was proven to be an impactful method to enhance the mechanical properties and produce well-aligned in situ composites in peritectic systems.

Mechanical and Corrosion Resistance Enhancement of Closed-Cell Aluminum Foams through Nano-Electrodeposited Composite Coatings.

This work aims to improve the properties of aluminum foams including the mechanical properties and corrosion resistance by electrodepositing a SiC/TiN nanoparticles reinforced Ni-Mo coating on the substrate. The coatings were electrodeposited at different voltages, and the morphologies of the coating were detected by SEM (scanning electron microscope) to determine the most suitable voltage. We used XRD (x-ray diffraction) and TEM (transmission electron microscope) to analyze the structure of the coatings. The aluminum foams and the substrates on which the coatings were electrodeposited at a voltage of 6.0 V for different electrodeposition times were compressed on an MTS (an Electro-mechanical Universal Testing Machine) to detect the mechanical properties. The corrosion resistance before and after the electrodeposition experiment was also examined. The results showed that the coating effectively improved the mechanical properties. When the electrodeposition time was changed from 10 min to 40 min, the Wv of the aluminum foams increased from 0.852 J to 2.520 J and the σs increased from 1.06 MPa to 2.99 MPa. The corrosion resistance of the aluminum foams was significantly improved after being coated with the Ni-Mo-SiC-TiN nanocomposite coating. The self-corrosion potential, pitting potential, and potential for primary passivation were positively shifted by 294 mV, 99 mV, and 301 mV, respectively. The effect of nanoparticles on the corrosion resistance of the coatings is significant.