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The microstructure evolution, cyclic oxidation, and hot corrosion behavior of the unheated-treated (As-built) and solution + double aging (SDA)-treated Inconel 718 alloys fabricated through laser-induction hybrid cladding (LIHC) were investigated. It was found that the as-built Inconel 718 alloy exhibits a columnar dendritic with intergranular Laves phase. After SDA-treated, γ'', γ′, δ and carbide phases precipitated, the Laves phase became fine and dispersed. After cyclic oxidation, the Cr2O3 scales were formed on both as-built and SDA-treated LIHC-produced Inconel 718 alloy, which could provide good cyclic oxidation resistance for the Inconel 718 alloy. However, the as-built and SDA-treated LIHC-produced Inconel 718 alloy suffered severe hot corrosion in 95 wt% Na2SO4 + 5 wt% NaCl mixed salt solution and many corrosion products were generated, including Cr2O3, NiCr2O4, NaNbO3, Na2CrO4, NiFe2O4, Fe3O4, and NiO. Nevertheless, the SDA-treated sample showed better cyclic oxidation and hot corrosion resistance than the as-built sample, owing to the more compact Cr2O3 scale.

A series of (Ti42.5Zr42.5Nb10Ta5)100-xMox (x = 0, 3, 5 and 7 at.%) refractory high-entropy alloys (RHEAs) were prepared, and the influence of Mo content on microstructure and mechanical properties of the RHEAs were systematically studied. All the RHEAs consist of a single body-centered cubic (BCC) phase. As the Mo content increases from 0 at.% to 7 at.%, the yield strength of RHEAs increases from 670 MPa to 975 MPa at room temperature. The high strength of the BCC RHEAs mainly depends on solid-solution strengthening caused by the Mo addition. The RHEAs with low Mo content (0–5 at.%) can possess high tensile plasticity of ∼20 %, while it reflects brittle after the 7 at.% Mo addition. The high tensile plasticity of the RHEAs was attributed to the combined effects of lattice rotation to promote and refine crystalline strengthening. The RHEAs with 5 at.% Mo addition have high specific yield strength (∼32 MPa g−1cm3) and excellent fracture strains (＞60 %) at 1173 K. Moreover, the incipient plasticity of the RHEAs was analyzed by nanoindentation. It is shown that the maximum shear stress (τmax) of the RHEAs from 1.80–2.34 GPa to 2.67–4.83 GPa. The activation volumes (v∗) of the RHEAs from 0.7 Ω to 1.1 Ω. The nanomechanical properties of the RHEAs are related to the Mo content. The purpose of this work is to design RHEAs with excellent mechanical properties and to offer a theoretical foundation to assist new RHEA design.

Graphite/Cu composite is widely used in pantograph slide plates. To further understand its lubrication behaviors, the tribological properties of graphite/Cu composites with different graphite content were studied using ball-on-disk wear tests. The results reveal that the composites contain only graphite and Cu phases. The tribological results show that the friction coefficient and wear rate of 7 wt.% graphite/Cu composite were decreased 7.7% and 12.7%, respectively, compared with 5 wt.% graphite/Cu. However, both friction coefficient and wear rate increased with the graphite content exceeding 7 wt.%. The excellent tribological properties of the composites were mainly attributed to the synergistic action of the oxidative trib o-layer and graphite lubricant film, which is composed of graphite, Cu, CuO, and Fe2O3. The wear mechanism of the graphite/Cu composites was mainly abrasive wear, accompanied by adhesion and oxidation wear.

The microstructure of machined superficial layer significantly affects the mechanical properties and service life of mechanical components. Herein, to obtain a machined surface with excellent properties, a comprehensive application of theoretical calculations and test analysis research methods was conducted to investigate the influence mechanism of machining on performance and quality of machined superficial layer of high-strength alloy steel during machining, and reveal the intrinsic correlation between microstructure evolution, quality and performance of machined superficial layer. The results indicate that the machining can achieve gradient microstructure on the machined surface, which can improve the performance of machined surface greatly. From the surface to the inside region, the layers are respectively the recrystallized layer where compact nano-sized equiaxed grains are located, the rheological layer with clusters of high-density sub-grain structures, and the distorted layer with residual distorted grains. The maximum strain of superficial layer in the machined state is 2.81 times that of the original state. The grains are evidently refined and the grain size is reduced by 49.03%. The dislocation density is enhanced by 100.69%, while the number of small-angle grain boundaries (SAGB) and other substructures increase sharply, being 5.26 times that in the original state. By performance testing, the machining substantially enhances the hardness of the superficial layer of high-strength alloy steel with certain rise in toughness simultaneously, which is exactly the result of the combined effect of fine-grain strengthening and dislocation strengthening caused by the machining process above.