D.-Q. Yi’s research while affiliated with Central South University and other places

The effect of cold rolling and annealing on the microstructure and properties of an Fe–13Cr–4.5Al–2.2Mo–1.1Nb alloy was investigated. The results showed that the recrystallization rate increased with increasing annealing temperature and rolling reduction. Recrystallization kinetics was constructed based on Johnson–Mehl–Avrami–Kolmogorov equation. The apparent activation energies of recrystallization were 161.385, 144.770, and 95.362 kJ/mol for the samples with 30%, 50%, and 70% cold-rolling reduction, respectively. With the cold-rolling reduction increasing, the texture γ fiber partly changed to 〈100〉//ND. After annealing, γ fiber of the alloy with 30% thickness reduction retained, the subgrains disappeared through merging, and the proportion of coincident site lattice grain boundaries increased and became more continuous. 30% cold-rolling reduction alloy annealed at 730 °C for 120 min not only possessed relatively high yield strength (YS) of ~ 730 MPa and ultimate tensile strength (UTS) of ~ 880 MPa, but also exhibited elongation of ~ 16% at room temperature. After annealing at 730 °C for 120 min, 70% cold-rolled alloy has finer and more uniform grain, with higher elongation of ~ 22%, YS of ~ 615 MPa and UTS of ~ 774 MPa. The mechanism of mechanical properties difference was explained according to Schmid factor analysis. These results provided an effective way for tuning strength and ductility of FeCrAl alloy.

The activity and solubility of alloying elements in Mo were investigated by using Miedema's model and its related physical parameters, and these results were compared with the results predicted by the first-principle calculations and other's empirical approach. These results show that the activity of alloying elements in Mo increases with the increasing temperature and alloying concentration. Under the same concentrations, the activities of main group elements Ge, Al and Si in Mo are small, and the activities of transition elements Ti, Hf, Nb, Zr, and Re are relatively large, which the latter should be chosen as the main alloying elements of Mo-based alloys. The solubility results also point out that the solubility of alloying element in Mo is influenced by atomic size factor, electron density factor, and electronegativity factor. And the solution heat of alloying elements in Mo is a comprehensive reflection of the last two factors. Furthermore, Miedema-Alonso plot was established by using the solution heat of alloying elements in Mo and atomic size parameters as the horizontal and vertical coordinates, respectively. It is found that the alloying element, which its atomic difference from Mo is smaller than 15% and its solution heat in Mo lies in the rang from -20 to 20 kJ/mol always has large respectively solubility limit in Mo.

Ni-based self-lubricating composites containing a fixed amount of hexagonal boron nitride (h-BN) (5 wt%) and different amounts of graphene (0–1.5 wt%) were prepared by ultrasonic dispersion, high-energy ball milling, and spark plasma sintering. The effects of the graphene content on the physical, mechanical, and wear properties of the Ni/h-BN composites were evaluated. These properties were first enhanced with increasing graphene content, reaching optimal behavior for a graphene content of 1 wt%, and then degraded with further graphene addition. Compared to the pure Ni/h-BN composite, the relative density, hardness, and bending strength of the composite with 1 wt% graphene increased by 2.7%, 7.4%, and 6.3%, respectively, while the friction coefficient decreased by 56% to 0.31, and a reduction in wear rate by a factor of 5–15 was observed. The mechanism for improving the wear properties of the composite with added graphene was due to the formation of a graphene lubricating film on the worn surface, which increased the load bearing capacity of the surface and enhanced lubrication during wear.

The activity and solubility of Si in Mo solid solution were studied by the first-principles calculations and quasi-harmonic approximation. The lattice constants, bulk modulus, and formation enthalpies of Mo-Si intermetallics were investigated, and the thermodynamic properties of Mo were also calculated. The Si activity coefficient γSi is approximately 10−16 at 100 K, while it increases by about 15 orders of magnitude over the investigated temperature range (100–2000 K). It is clear that Si activity coefficient in Mo solid solution increased rapidly with the increasing temperature, which should be ascribed to the Si–Mo interaction being evidently stronger than Mo–Mo interaction. According to the calculated thermodynamic properties, the solubility curve of Si in Mo solid solution was also predicted. The solubility limit of Si in Mo solid solution is ∼5.5 at.%, which agrees well with the other experiment and assessed results.

The surface stability and equilibrium morphology of MoO3 were investigated by the first principles calculations. The thermodynamic energies of the stoichiometric surfaces of MoO3 are in the order (0 1 0) < (1 0 1) < (0 0 1) < (1 0 0). It is found that the (0 1 0) surface has a lowest surface energy, which agrees well with the previous calculations. The energies of the non-stoichiometric surfaces were evaluated as functions of temperature and oxygen partial pressure. The results show that the energies of Mo-terminated surfaces decrease with temperatures, and increase with oxygen partial pressures, while the energies of O-terminated surfaces show the opposite rule. The equilibrium morphology of MoO3 was predicted by using the Gibbs-Wulff model, and then was compared with the other's experiments and theoretical results.

Industrial application of superhydrophobic surfaces is often hindered by complicated process and sophisticated machines. A facile wet etching method (sandblast, HCl and sandblast/HCl) with vapor deposition of PFDS (1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane) was applied to fabricate superhydrophobic surface of heat-resistant steel used for vane. The coating component, surface morphology and surface roughness parameters of sample were observed by attenuated total reflectance Fourier transform infrared spectroscopy, scanning electron microscopy and atomic force microscopy. Static water contact angle (WCA) of samples with and without PFDS coating was measured by contact angle goniometer. The results showed that WCA values of polished, sandblast, HCl and sandblast/HCl-etched samples are 98°, 97°, 100° and 101°, respectively, and increase to 112°, 148°, 151° and 154° after vapor deposition of PFDS. The sandblast/HCl-etched sample with PFDS coating shows higher superhydrophobicity because of very large surface roughness and lotus protrusion-like structure. The superhydrophobicity of this fabricated surface has no obvious change after 38 cycles of the film adhesion test, indicating excellent durability.

Three types of FGH4169 alloy with carbon mass fraction of 0.026%, 0.045% and 0.078% were prepared by hot-isostatic pressing (As-HIP) and heat treatment. The effects of carbon content on the original particle boundary (PPB) and mechanical properties of FGH4169 alloy were investigated. The results show that, with the carbon content increases from 0.026% to 0.078%, the precipitated carbide of FGH4169 alloy increases, and when the carbon content exceeds 0.078%, the PPB formed. The carbides in FGH4169 alloy are mainly MC type carbides rich in Ti and Nb, and the carbon content has no obvious effect on the type and morphology of carbides in FGH4169 alloy; Within a certain range of the C content, as the C content increases, the amount of γ″ phase precipitated in the FGH4169 alloy matrix decreases, and the carbides tend to aggregate at the PPB, resulting in the strength and plasticity gradually decreasing under room temperature and 650 ℃. © 2018, Editorial Office of Materials Science and Engineering of Powder Metallurgy. All right reserved.

The primary silicon phase in the hypereutectic Al-Si alloy was refined by phosphorus modification, and various kinds of particles existing in the industrial melt were studied. The results show that there are heterogeneous particles(AlP and SiO 2 )and complex heterogeneous particles[AlP/SiO 2 and AlP/ (AI 2 O 3 +SiO 2 )] in the melt, which provides the solid phase substrate for the nucleation of the primary silicon phase.In the casting process, the variety of roles by heterogeneous nucleation needs to be taken into account. © 2018, Chinese Mechanical Engineering Society. All right reserved.

The microstructures and mechanical properties of powder metallurgy Inconel 718 alloy were investigated in the temperatures range between 25 and − 253 °C. Tensile strength increased with the decrease in temperature, while the ductility first increased and then decreased. There was no significant change in impact toughness. When the temperature was − 253 °C, a zigzag stress–strain curve was observed for the alloy, owing to the interaction of dislocation glide and twinning, which effectively maintained the relatively good ductility.

The mechanical properties of oxide dispersion-strengthened copper are largely dictated by its internal interfaces, i.e. the oxide interfaces and the grain boundaries (GBs). Here we present a systematic first-principles study for evaluating the potential impact of Ag alloying on adhesion of Cu/α-Al2O3 interfaces and Cu grain boundaries as well. The results suggest that, in contrast to the strong segregation of S that is always detrimental, Ag only slightly segregates to the Al2O3 interfaces, strengthens the weak stoichiometric interface, and slightly weakens the strong Al-rich interface. Ag cannot pin S inside the matrix. The co-segregation of Ag with S modestly negates the detrimental influence of S on adhesion, but can hardly occur. Ag segregation to most of the GBs is found also to be weak, and reduces the adhesion slightly. The only one exception is on the Σ9 GB. Based on the gained insights, we suggest that Ag alloying has only limited benefits but can still be encouraged.