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To develop an ultra-high-temperature resistant coating for a reusable thermal protection system, the preparation of a tantalum-based MoSi2-Mo coating by a new two-step process of multi-arc ion plating and halide activated pack cementation is presented. The coating has a dense structure and is well compatible with the tantalum substrate, which can be thermally shocked from room temperature to 1750 °C for 360 cycles without failure. The mechanism of the coating’s excellent resistance to high-temperature thermal shocks is that a strong-binding gradient interface and a dense SiO2 oxide scale with good oxygen resistance are formed by the high-temperature self-diffusion of Si.

Tantalum (Ta) alloys are important ultra-high-temperature structural materials owing to their excellent high-temperature mechanical properties and processability. However, they exhibit poor high-temperature oxidation resistance. In this study, a dense MoSi2 ceramic coating was prepared on a Ta substrate using an innovative multi-arc ion plating process and halide activated pack cementation in order to improve its ultra-high-temperature oxidation resistance. This ceramic coating exhibited a low roughness space arithmetic (287.1 ± 26.3 nm) and a dense structure. The relationship between the thickness of the coating and the duration of pack-cementation at 1250 ℃ was parabolic. The coating had a service life of more than 12 h at 1750 ℃, and showed excellent high-temperature oxidation resistance because of the uniform and dense structure of the coating and the rapid formation of a dense SiO2 layer with low O2 permeability during high-temperature oxidation.

To protect refractory metal against oxidation at ultra-high temperatures, a MoSi2-TaSi2 ceramic coating was prepared on a pure tantalum (Ta) substrate using a novel three-step process, which included dip-coating with a molybdenum slurry, vacuum sintering, and halide-activated pack cementation (HAPC). The original coating had a MoSi2-TaSi2 double-layer structure from the surface to the substrate. After oxidation at 1700°C for 8 h in air, the coating exhibited a complex multi-layer structure composed of SiO2-Mo5Si3-MoSi2-(Mo,Ta)5Si3-TaSi2-Ta5Si3 from the outer layer to the inner layer, due to the high-temperature phase transition and diffusion of Si and O. The coating effectively protected the Ta substrate at 1700°C for 12 h without failure, thereby demonstrating great improvement to its service life in an ultra-high-temperature aerobic environment. The protective effect was attributed to the integrity of the ceramic coating and the formation of a dense, uniform SiO2 film that effectively lowered the inward oxygen diffusion rate.

A new YSZ (yttria stabilized zirconia) modified silicide coating was prepared on Mo-based alloy through a two-step process, including spraying of Si-Mo-YSZ slurry followed by reaction sintering. Microstructure and oxidation behavior of the coatings with different YSZ content (0, 5, 10 and 15%) were studied. The coating consists of a MoSi2-ZrSi2-SiO2 outer layer and a MoSi2 inner layer. The 10% YSZ modified coating possessed the best oxidation protection at ultra-high temperatures and, for the coating, the mass gain was 0.96 mg/cm2 after being exposed at 1725 °C in air for 22 h, whereas the uncoated Mo-based alloy completely ablated for 0.35 h. The excellent oxidation resistance of the silicide coating was attributed to the compact and self-healing SiO2 protective scale, which contained the dispersed ZrO2 and ZrSiO4. Keywords: Molybdenum-based alloy, Silicide coating, Oxidation, YSZ, MoSi2, Ultra-high temperature

The cobalt coating with an average thickness of 15–20 nm was uniformly plated on the surface of ultra-fine WC powders by electroless plating in the present work. The effects of electroless plating condition parameters on the deposition rate were studied. It was found that the deposition rate increased with the increase of CoSO4·7H2O content, pH value, complexing agent concentration, and bath temperature, while decreased with the increase of reducing agent (NaH2PO2·H2O) concentration. Furthermore, the cobalt deposition rate empirical equation and activation energy were determined. The results show that the activation energy (Ea) for the electroless cobalt on WC substrates is approximately 54.65 kJ/mol.

A new type MoSi 2 /(Mo, Ti)Si 2 dual-phase composite coating for oxidation protection was designed and prepared on molybdenum alloy by a method of fused slurry. High temperature oxidation resistance of the coating has been investigated by isothermal oxidation test. Microstructure evolution and phase transformation of the as-prepared and oxidized coating were characterized. The results show that the composite coating is composed of primary C11 b MoSi 2 and C40 (Mo, Ti)Si 2 phases. The substitution of molybdenum with titanium in MoSi 2 gave (Mo,Ti)Si 2 of the C40 structure, resulting the formation of a C11 b MoSi 2 /C40 (Mo, Ti)Si 2 dual-phase composite coating. The composite coating could provide long term oxidation resistant protection for Mo alloy at high temperature, attributing to the good protection of a Si-Ti-O compound glass formation during oxidation.

To develop an ultra-high temperature resistant coating for niobium alloy, a new type of 10%ZrB2 + 5%YSZ-modified Si-Mo-18%W coating with a boride diffusion barrier was prepared by a novel three-step method. The coating with NbB2-Nb3B2 diffusion barrier can effectively protect Nb521 alloy at 1850 °C for more than 8 h, while the life of coating without diffusion barrier was only 3.5 h. The excellent performance of the coating was attributed to the present of diffusion barrier and formation of self-healing SiO2-B2O3-ZrSiO4-ZrO2 oxide scale. The diffusion barrier can effectively hinder mutual diffusion of coating and substrate, and reduce inward consumption of silicon element.

A high-temperature oxidation-protective Si-Mo coating on a molybdenum alloy substrate was prepared by slurry sintering method. The structure, composition, phase distribution, and oxidation behavior of the coating were studied. The results show that the coating has a double-layer microstructure with an outer MoSi 2 layer and an inner Mo 5 Si 3 layer. After oxidation, the coating is composed of a SiO 2 outer layer, a MoSi 2 middle layer, and a Mo 5 Si 3 inner layer. The mechanism of the phase distribution and the oxidation kinetic equation were also studied. The oxidation rate K p determined over 12 h at 1650 °C, was found to be 0.061 mg 2 cm − 4 h − 1 . The excellent oxidation protective ability of the coating at ultra-high temperatures is attributable to the formation of self-healing SiO 2 on the coating surface after the oxidation of MoSi 2 .

The stress-aging method is proposed to improve the dimensional stability of Al-Cu-Mg (2024 aluminum) alloy. Both the reduction of residual stress and the acceleration of precipitates are investigated during the stress-aging process. It is observed that some S′ particles precipitate in the alloy during stress-aging. With the external stress increase to 100 MPa, the residual stress and thermal strain (ɛ c ) decrease, while the micro-yield strength increases significantly. This is attributed to that the dislocations are effectively pinned by the uniformly distributed precipitates and the stored elastic energy diminishes remarkably, which leads to a considerable improvement of the dimensional stability of 2024 aluminum alloy. However, when further increases the external stress to 150 MPa, due to the coarsened precipitates, the residual stress and thermal strain increase, while the micro-yield strength decreases slightly.

Due to the excellent structural and functional properties, such as low density, high fracture toughness and fatigue strength, Al-Cu-Mg (2024 aluminum) alloy has become an attractive light weight material for inertial instruments and aerospace applications. However, it has relatively low dimensional stability. The aim of this investigation is to enhance the dimensional stability of 2024 aluminum alloy via two-stage aging method, and identify the precipitation behavior and the underlying stabilizing mechanisms of 2024 aluminum alloy. When the second aging time was 24 h, the uniformly distributed precipitates could effectively pin the dislocations and impede their movement. This leaded to a significant improvement of the micro-yield strength and the thermal strain in the 2024 aluminum alloy, and thus the dimensional stability of the alloy increased.

Due to excellent chemical stability, high rigidity, superior corrosion and wear resistance, aluminum oxynitride (AlON) has been considered as one of most promising candidate ceramic materials in high-performance structural, advanced abrasives and refractory fields. However, it usually exhibited relatively low flexural strength and poor fracture toughness. The study is aimed to develop silicon carbide (SiC) and zirconium nitride (ZrN) nano-particulate reinforced AlON composites with improved mechanical properties and fracture resistance via a hot-press sintering process. It was found that the addition of ZrO 2 nanoparticles would be transformed into ZrN during sintering. Due to the pinning effect of SiC and ZrN nano-particles positioned at grain boundaries of micro-sized AlON particles, the presence of SiC and ZrN nano-particles resulted in the reduction of both porosity and grain size, and a change of fracture mode from intergranular cracking in AlON to intragranular cracking in composites. With presence of 8 wt% SiC and 5.2 wt% ZrN nano-particles, the relative density, microhardness, Young’s modulus, flexural strength and fracture toughness increased. Different toughening mechanisms including crack bridging, crack branching and crack deflection were observed, thus effectively increasing the crack propagation resistance and leading to a considerable improvement in flexural strength and fracture toughness.

The thermodynamic stability and mechanical properties of titanium carbonitrides TiC x N1−x (0 ⩽ x ⩽ 1) are investigated by a combination of the universal cluster expansion method and the first-principles calculations. By considering the ordering of the N/C distributions on the anion sublattice sites of TiC x N1−x , a binary diagram of the heat of formation is constructed, and seven kinds of ground-state structures are predicted in the whole range of 0 ⩽ x ⩽ 1. These predicted ground-state TiC x N1−x structures are further proved to be dynamically and mechanically stable by examining their phonon dispersion spectra and elastic constants. Further studies indicate that the mechanical and thermodynamic properties of the ternary TiC x N1−x structures are generally better than those of the binary TiC or TiN, while the differences within the ternary systems are insignificant. The possible origin of the enhancement of the mechanical and thermodynamic properties of the predicted ground-state TiC x N1−x are discussed together with the electronic structures.

Thermal diffusion process (TD) is an important surface modification technique to prepare carbide coating on steel, which can effectively improve the hardness and wear resistance, as well as prolong the service life of the substrate. However, cracking problems are often encountered in the TD processing of high-speed steel. In this work, TD process was used to prepare vanadium carbide coating on M35 high speed steel. The results indicated that the coarse crack after TD treatment was quenching crack. The mechanism of such failure were attributed to the diffusion of elements (mainly C and V) and the volume expansion caused by martensitic transformation during the TD process. Bainite isothermal quenching and three times tempering process were selected as the way of solving this cracking failure. The microstructure and properties of the coating prepared by the improvement process were studied. The coating was composed of fine equiaxial crystals containing V6C5 and VC. The hardness of the coated sample could achieve 2644 HV, which increased greatly compared with uncoated M35 matrix (750 HV), and the friction/wear performance of the samples treated by TD process increase by 82.8%.

MoSi2-NbSi2 coating and Ce-modified MoSi2-NbSi2 coating were prepared on Nb-alloy through a new two-step process, including molybdenum slurry spraying and halide-activated pack cementation. The bare alloy was pulverized after oxidation at 1600 °C for 15 min. The both two coated samples have the effective protection for 24.7 h and 28.5 h with the weight gain rate of 3.578 and 2.947 mg2 cm−4 h−1, respectively. Ce-modified samples show better performance due to Ce has the ability of grain refinement. The reasons for the excellent performance are the good matching between MoSi2 outer layer and NbSi2 inner layer and the continuous SiO2 oxide scale.

A double-layer MoSi2 thick coating was prepared on Titanium-Zirconium-Molybdenum (TZM) alloy through a new two-step method, including molybdenum slurry vacuum sintering and halide-activated pack cementation. The coating was formed by a porous MoSi2 outer layer and a dense MoSi2 inner layer. The ball-milled fine Mo powder can effectively improve the coating density and the high temperature oxidation resistance. The oxidation protection time of the coatings prepared by coarse and fine Mo powders were 1 h and 6 h at 1700 °C, respectively. After oxidation, the coating exhibited multilayer structure consisted of SiO2 oxide layer, porous MoSi2 layer, dense MoSi2 layer and Mo5Si3 layer from the outer to the inner. With oxidation proceeding, the Mo5Si3 layer thickened, while the MoSi2 layer thinned and eventually transformed into Mo5Si3 completely, leading to coating failure because of the depletion of silicon.

The microstructure and mechanical properties of columnar-grained copper under casting and drawing conditions were investigated in the present work. It was found that the as-casted copper mainly consisted of continuous columnar grains with orientation preference along and exhibited excellent plastic deformation ability. Moreover, the texture of columnar-grained copper transferred from to during the drawing process. A typical microstructural morphology as multangular-cup feature of as-casted copper as well as drawn copper was observed on the fracture surfaces. With increasing the drawn strain, the texture evolution and the grains broken occurred, leading to a significant increase in the work hardening rate and tensile strength.

Aluminum doped zinc oxide (AZO) polycrystalline thin films were prepared by sol–gel dip-coating process on optical glass substrates. Zinc acetate solutions of 0.5 M in isopropanol stabilized by diethanolamine and doped with a concentrated solution of aluminum nitrate in ethanol were used. The content of aluminum in the sol was varied from 1 to 3 at.%. Crystalline ZnO thin films were obtained following an annealing process at temperatures between 300 °C and 500 °C for 1 h. The coatings have been characterized by X-ray diffraction, UV–Visible spectrophotometry, scanning electron microscopy, and electrical resistance measurement. The ZnO:Al thin films are transparent (∼ 90%) in near ultraviolet and visible regions. With the annealing temperature increasing from 300 °C to 500 °C, the film was oriented more preferentially along the (0 0 2) direction, the grain size of the film increased, the transmittance also became higher and the electrical resistivity decreased. The X-ray diffraction analysis revealed single-phase ZnO hexagonal wurtzite structure. The best conductors were obtained for the AZO films containing 1 at.% of Al, annealed at 500 °C, 780 nm film thickness.

The MoSi2 coating on C103 niobium based alloy was prepared by pack cementation method. The formative mechanism, morphology and structure of coating were investigated. The silicide coating was formed by reactive diffusion obeying parabolic rule during pack cementation process. It is found that the composite structural coating is composed of three inferior layers as follows. The main layer is composed of MoSi2, the two phases' transitional layer consists of NbSi2 and a few Nb5Si3 and the diffuse layer is composed of Nb5Si3. The dense amorphous glass layer formed on the surface at high temperature oxidation circumstance can effectively prevent the diffusion of oxygen into coating.

We investigate the exchange bias effect in La0.67Sr0.33MnO3/G-SrMnO3/ La0.67Sr0.33MnO3 (LSMO/SMO/LSMO) sandwiches, where the spacer is a G-type antiferromagnet. Because of the cycloid bulk spins in the SMO modulated by the top LSMO layer, the sandwich structure exhibits an oscillatory exchange bias behavior as a function of the SMO thickness. This unprecedented phenomenon vanishes in LSMO/SMO bilayers, where the exchange bias saturates as the SMO thickness increases, giving rise to the antiferromagnetic anisotropy constant of SMO, 1.0 –2.0 × 105 erg cm−3. The results provide a broad opportunity to tailor antiferromagnetic moments by interfacial design for antiferromagnet spintronics.