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In this paper, the effect of heat treatment (760–1060 °C) on tribological behavior of selective laser melted Ti6Al4V alloy against Si3N4 counter-ball under different applied loads was investigated. Results show the wear rate of as-built Ti6Al4V alloy increased firstly and then gradually decreased with increasing the heat-treatment temperature, which obtained the lowest value when the heat treatment temperature was 1060 °C, exhibiting the best wear resistance. The higher applied load led to larger wear rate and lower coefficient of friction. The wear mechanism was strongly dependent on the microstructure transformation, micro-hardness and applied load, which was discussed in detail.

CoCrFeNi and CoCrFeNiAl0.3 high entropy alloys reinforced with in-situ oxide nanoparticles have been successfully fabricated by mechanical milling in combination with hot pressing and hot extrusion. The as-fabricated CoCrFeNi samples exhibited an ultrafine grained microstructure with in-situ Cr2O3 oxide nanoparticles formed during hot pressing and extrusion process and distributed both on grain boundaries and in grain interiors. Increasing extrusion temperature from 1000 to 1100 °C caused a significantly increase of grain size from 700 nm to 2.5 μm owing to recrystallization and growth of the recrystallized grains, as well as the coarsening of Cr2O3 nanoparticles with their mean size increasing from 57 to 140 nm. When adding Al elements, finer Al2O3 nanoparticles (mean size: 30 nm) formed in the CoCrFeNiAl0.3 high entropy alloy, leading to refinement of the grains (mean size: 504 nm) due to their pinning effect on grain boundary immigration. After T6 heat treatment, the CoCrFeNiAl0.3 high entropy alloy demonstrated improved mechanical properties with yield strength of 1335 MPa, ultimate tensile strength of 1346 MPa and an elongation to fracture of 7.9%. With quantitative analysis based on the current models, it was concluded that grain boundary strengthening and Orowan strengthening acted as the dominant strengthening mechanisms.

Additive manufacturing Ti6Al4V alloys have found their potential applications in artificial teeth and hip joints. In this work, the relationships between wear resistance, hardness and microstructure of Ti6Al4V alloys fabricated using various routes were investigated in artificial saliva. The results indicate that comparing with wrought and wrought + heat treated (HT) samples, the as-SLMed samples with hcp-α' martensite and few bcc-β phase exhibit higher hardness (∼410 HV) and better wear resistance. The as-SLMed samples, however, exhibit the worst wear resistance when wear direction is parallel to the molten pool line on XOZ-plane due to containing the softer fusion zone. Finally, the wear mechanism is discussed in detail, mainly including the abrasive and adhesive wear mechanism. The high hardness of matrix as well as the strong adhesion between the hardened layer, oxide layer and matrix are indispensable conditions for maintaining the optimum wear resistance.

This paper proposed a neuro-adaptive sliding mode fault-tolerant control (NASMFTC) method for the problem of actuator control gain loss fault in hypersonic vehicles. Described as the elevator yaw angle and the engine throttle setting valve fault. The controller combines the robust adaptive algorithm with the radial basis function (RBF) based neural network (NN) method for the hypersonic vehicle longitudinal motion model. The proposed fault-tolerant control method has the following advantages: 1. No need to estimate the value of the actuator fault; 2. The designed control algorithm is simple in structure and does not require a large amount of online calculation, can quickly deal with the occurrence of faults; 3. Can ensure that the system still has the ability to stably track in the case of constant or time-varying actuator faults. The final simulation experiment verifies the effectiveness of the proposed method.

In this study, the SiC/Al-Zn-Mg-Cu nanocomposites were fabricated using high energy ball milling combined with spark plasma sintering (SPS) and hot extrusion. The microstructure and mechanical properties were investigated by utilizing X-ray diffraction (XRD), scanning electron microscopy (SEM) and high resolution transition electron microscopy (HRTEM) analysis as well as tensile tests. The results showed that the as-extruded SiC/Al-Zn-Mg-Cu nanocomposite samples demonstrated a microstructure consisting of ultrafine α-Al grains, dispersed SiC nanoparticles and nano-scaled T phases probably formed by dynamic precipitation during extrusion. After T6 heat treatment, the coarsening of α-Al grains, dissolution of T phases and consequently the precipitation of fine η′ phases occurred, leading to a simultaneous increase of the strength and ductility. With increasing the content of SiC nanoparticles from 1 vol% to 3 vol%, the yield strength (YS) and ultimate tensile strength (UTS) increased from 456 and 528 MPa to 580 and 588 MPa (27.2% and 11.4% increase), respectively while the elongation to fracture decreased slightly from 11.8% to 10.2% (13.6% decrease). Various strengthening mechanism calculation results show that Orowan strengthening was mostly contributed to the improved strength of the T6 heat treated SiC/Al-Zn-Mg-Cu nanocomposites.

Nickel-based superalloys have been widely used in manufacturing turbine blades, vanes, and discs of aircrafts and power generators that serve in challenging environment. In order to meet the requirements for rapid manufacturing of these large-scale and high-performance components, the extreme high-speed laser metal deposition (EHLMD) technology have attracted great attention in recent years. The EHLMD technology can significantly improve the efficiency compared with conventional laser metal deposition (LMD). Meanwhile, the solidification condition and the resultant microstructures and mechanical properties can also be dramatically changed. In this study, a high chromium superalloy (K648) has been additively manufacturing by using EHLMD for the first time. The key process parameters and the resulted microstructure and mechanical properties are investigated. The results have shown that the most important factors affecting the height, width, and depth of the single-track deposit of EHLMD K648 superalloy are powder feeding rate, laser power, and scanning speed, respectively. The height and the width of the deposits are the largest when the laser power, scanning speed, and the powder feeding rate are 1400 W, 25 m/min, and 30 g/min. There exist some incomplete fusions in the interlayer region and some pores in the interior region of the multi-track-multi-layer deposits. Columnar grains grow in the build direction within each layer, while equiaxed grains tend to form in the interlayer region. The average value of microhardness of EHLMD K648 superalloy is about 298.1 HV. The ultimate strength of EHLMD K648 superalloy is slightly lower than that of the forging GH648 superalloy but higher than that of the conventional LMD K648 superalloy.

Ti–6Al–4V alloys are utilized in various industrial applications. Here, the effect of heat treatment on the microstructural evolution and mechanical properties of the Ti–6Al–4V alloys, which were fabricated by selective laser melting (SLM), was investigated. The as-fabricated-1133 K sample possessed a significantly higher ductility than that of the as-fabricated sample. This was attributed to the precipitation of the micro/nanoscale β and athermal ω phases that was accompanied by the equiaxial transformation of the β columnar grains.

The effects of chromium and vanadium additions on the microstructure, hardness and wear resistance of high-vanadium alloy steel (containing 5–10 wt-% V and 2–10 wt-% Cr) were studied by means of optical microscopy, scanning electron microscope (SEM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS), Vickers hardness and Rockwell-hardness tester & M-200 ring block wear tester. Researching results showed that the solidification structure of high-vanadium wear-resistant alloy steel was mainly consisted α-Fe (martensite), vanadium carbide (VC), M3C and M7C3. Vanadium is mainly distributed over VC, and certain amount of vanadium exists in the matrix and M7C3 type eutectic carbide. Chromium is mainly distributed over the M7C3, and the matrix also contains a small quantity of chromium. It is found that the content of VC increases with the increase of vanadium content when carbon and chromium contents are constant. The change of micro- and macro-hardness was not obvious with the increase of vanadium ...

The Fe-B-Al alloy containing 0 to 10.0 wt.-% Al was melted in a vacuum induction furnace. Effects of the aluminum addition on the microstructure and properties of Fe-B-Al alloys were studied by means of optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), hardness testing and MMG-500 type pin-on-disk high temperature vacuum wear testing. The results showed that the as-casted microstructure of the aluminum-free Fe-B alloy consisted of α-Fe, Fe2(B,C), and Fe23(B,C)6 type borocarbides. However, the as-casted microstructure of the Fe-B-Al alloy consists of a Fe3Al type intermetallic compound when the aluminum content is more than 6.0 wt.-%. Compared with the aluminum-free Fe-B alloy, parts of the borocarbide networks are broken, and the fracture tendency became more obvious with the increase of the aluminum content. Boron is mainly distributed over the borocarbide. Aluminum is mainly distributed over the matrix and Fe3Al type intermetallic compound. Compared with the aluminum-free Fe-B alloy, the addition of a small amount of aluminum reduces slightly the hardness. The hardness gradually increased with the further increasing of the aluminum content. The hardness reached 48.1 HRC when aluminum content was 10.0 wt.-%. The high temperature wear resistance of Fe-B-Al alloy gradually increased with the increase of the aluminum content. When the aluminum content reached 10.0 wt.-%, the high temperature wear resistance of the alloy was the best.

In this paper, the high-temperature oxidation behaviors at 900 °C of the conventional laser metal deposition (LMD) and extreme high-speed laser metal deposition (EHLMD) high chromium K648 superalloys were comprehensive studied. The experimental results reveal that the oxidation resistance of the LMD K648 superalloy is better than the EHLMD K648 superalloy. The oxidation films of LMD and EHLMD K648 superalloy consists of continuous Cr2O3 film and an internal wedge-shaped Al2O3. The oxidation process is mainly controlled by the outward diffusion of oxide-forming elements and the inward penetration of oxygen.

The oxidation behavior of B-bearing high-speed steel was studied at 923[Formula: see text]K. The results showed that the as-cast microstructure of 1.0 wt.%B high-speed steel was composed of pearlite + ferrite + M7(C, B)3+ M2(B, C). When the boron content increased, the microstructure gradually changed into martensite + retained austenite + netlike M2(B, C) + M[Formula: see text](C, B)6+ M7(C, B)3. The cyclic oxidation of B-bearing high-speed steel at K followed parabolic rule. The unit area mass gain of 1 wt.%B high-speed steel was 4.2 g/m2after 923 K/250 h oxidation, and the unit area mass gain of 3 wt.%B high-speed steel was only 3.5 g/m2. The oxidation of boron element formed B2O3, which was mainly enriched at the interface of the oxide film/matrix. B2O3flowed in the oxide film at high temperature and was easy to fill the defect. B2O3was easy to form B2O3-SiO2borosilicate with SiO2. The more boron content was, the more favorable it was to form B2O3-SiO2borosilicate oxide layer rich in B2O3and the more favorable it was to spread in the oxide film, so that the oxidation resistance of B-bearing high-speed steel could be remarkably improved.

In this work, we employed first-principles calculations to investigate the stability, electronic structures, mechanical and thermodynamic properties of FexAlyCz compounds which were first observed in Fe-Cr-B-Al-C alloy. The results reveal that the FexAlyCz compounds are thermodynamically stable, and the addition of C element improves the stability of FexAlyCz compounds. These FexAlyCz compounds display disparate anisotropy according to different calculated 3D curved surfaces of Young's modulus and anisotropic index. The Fe3AlC compound has the biggest shear modulus, bulk modulus and Young's modulus with the values of 141.2 GPa, 212.6 GPa and 346.8 GPa, respectively, which indicates that the Fe3AlC compound has the largest rigidity, lateral deformation resistance and good solid compressibility under static pressure. The ratio of G/B shows that FeAl and Fe3AlC are brittle phases, while the Fe3Al and FeAl3 phases appear to be ductile. The calculated electronic structure reveals that the bonding characteristics of the FexAlyCz compounds are the mixture of both metallic and covalent bonds, which also exhibits anti-bond effects. The Fe3AlC compound has the biggest Debye temperature of 702.2 K. Meanwhile, the hardness of Fe3AlC is 19.4 GPa which is three times of the Fe3Al compound. The results obtained in this study provide a theoretical basis for the applications of Fe3AlC compound in Fe-Cr-B-Al-C alloys.

The effect of temperature on the oxidation resistance of a novel wear-resistant Fe-10Cr-1.5B-6Al-0.3C-0.8Mn-0.6Si alloy is investigated. The mass growth rate shows that this alloy exhibits superior oxidation resistance at 900 °C. As the oxidation temperature increases from 900 °C to 1100 °C, the structure of the observed oxide scales transforms from a porous bilayer to a flat monolayer, while the oxidation rate increases sharply. The selective oxidation of Al suppresses the outward diffusion of Cr and Mn to form MnCr2O4 oxides in the monolayer oxide scale, thereby decreasing the oxidation resistance at 1100 °C.

Additive manufacturing Ti6Al4V alloys have found their potential applications in artificial teeth and hip joints. In this work, the relationships between wear resistance, hardness and microstructure of Ti6Al4V alloys fabricated using various routes were investigated in artificial saliva. The results indicate that comparing with wrought and wrought + heat treated (HT) samples, the as-SLMed samples with hcp-α′ martensite and few bcc-β phase exhibit higher hardness (∼410 HV) and better wear resistance. The as-SLMed samples, however, exhibit the worst wear resistance when wear direction is parallel to the molten pool line on XOZ-plane due to containing the softer fusion zone. Finally, the wear mechanism is discussed in detail, mainly including the abrasive and adhesive wear mechanism. The high hardness of matrix as well as the strong adhesion between the hardened layer, oxide layer and matrix are indispensable conditions for maintaining the optimum wear resistance.

A high chromium (Cr) superalloy, K648, has been additively fabricated by using laser metal deposition (LMD) for the first time, and the microstructure and mechanical properties of the deposits are investigated. The results show that the main phases of the K648 superalloy are γ-Ni, γ′, α-Cr and M23C6. The microstructure from the bottom to the middle region is mainly composed of epitaxially grown columnar dendrites, and the microstructure in the top region is mainly equiaxed grains. Element segregation exists in the LMD K648 superalloy. The average microhardness of the LMD K648 superalloy is about 220.5HV. The tensile strengths of LMD K648 superalloy show obvious anisotropic characteristics and the maximum ultimate tensile strength is about 833 MPa.