The development of thermal spraying nanostructured thermal barrier coatings is briefly reviewed. Several main challenges for thermal spraying nanostructured thermal barrier coatings in high temperature and long-term service performance are listed. The research status of these challenges in recent years is discussed. Finally, several research and development directions urgently awaiting attention and breakthroughs are pointed out.
Metal additive manufacturing has broad application prospects in the civil aviation. By comparing three typical metal additive manufacturing technologies, this paper summarizes the research of metal additive manufacturing in the DFAM, materials and process. The progress of typical applications is introduced according to the technical classification. Based on the special requirements for airworthiness certification in civil aviation, this paper analyzes several challenges such as immature design methods, low processing efficiency, limited quality monitoring methods, and lack of uniform airworthiness certification requirements, and looks forward to the future development trend.
This paper introduced the principle and application of warm laser shock peening, aiming at the existing problems in engineering application, and summarized the research status and academic achievements of domestic and foreign. From residual stress failure and tissue instability under high-temperature and alternating load, the mechanism of residual stress release induced by laser shock peening was analyzed. The auxiliary heat source based on laser shock peening is analyzed (WLSP), which can promote dynamic strain aging and dynamic precipitation in the process of laser impact reinforcement (LSP), and the dispersion distribution reinforcement phase is precipitated around the dense dislocation, and the strengthening phase is further nailed and positioned. Fault forms air mass. The stability of high temperature tissue and creep resistance of the material are significantly improved. At last, the future development of warm laser shock peening was looked forward.
8Cr4Mo4V steel is mainly used to the aero-engine bearings manufacture. The service environment is complex and the working conditions are harsh. In order to meet the requirements of fatigue performance and surface state, some parts of the bearings need sand blasting treatment. In this paper, the surface of 8Cr4Mo4V steel was sand-blasted under various conditions. The residual stress on the surface of 8Cr4Mo4V steel was measured by X-ray residual stress tester after sand blasting under various conditions. The surface morphology was observed by SEM, and the variation of dimension and surface roughness were measured after sand blasting. The results show that the residual compressive stress on the surface of 8Cr4Mo4V steel is generated by sand blasting, and the maximum residual compressive stress can reach –1576MPa. The value of residual compressive stress is proportional to the pressure and time of sand blasting, and inversely proportional to the particle size of sand. After sand blasting treatment, a compact layer was formed on the surface of 8Cr4Mo4V steel. The thickness of the compact layer was mainly affected by sand blasting pressure and increased with the sand blasting pressure raising. Sand blasting has a stripping effect on the surface layer of 8Cr4Mo4V steel. The amount of surface layer stripped increases with the increase of sand blasting pressure and time, and the decrease of sand particle size. The main factor is the sand particle size which affects the surface roughness of 8Cr4Mo4V steel after sand blasting. When the sand particle size is small, the roughness value is the lowest after sand blasting.
In this study, the adhesion properties of titanium alloy after three different surface treatments, i.e., acid wash, sulfuric acid anodizing and micro-arc oxidation, were investigated by tensile shear tests based on plateplate specimens. The control sample (without any surface treatment) exhibits a shear strength of 30.1MPa and features an adhesion failure. The acid wash sample shows a shear strength of 45.3MPa, half adhesion failure and half cohesive failure. The anodized sample possesses the optimal shear strength of 61.6MPa, and shows cohesive failure. But the microarc oxidation sample only has a shear strength of 9MPa and fails in intermediate tear of the oxide film layer. The results indicate that both acid wash and sulfuric acid anodizing can improve the adhesion properties, whereas micro-arc oxidation treatment cannot. In the case of anodizing in sulfuric acid, abundant micro rough structures are formed and generating higher bonding area, which leads to improved adsorption force of the surface. The bonding performance is optimal when the anodizing voltage was 25V.
In order to extend the fatigue life of 7075 aluminum alloy joints, the stress distribution around the hole processed by cold expansion was simulated by ABAQUS. The finite element model of ultrasonic peening was established according to the kinetics analysis of ultrasonic shot peening process. In order to get the stress distribution around hole processed by cold expansion combined with ultrasonic shot peening, the ultrasonic shot peening process around the entrance surface of cold expanded joint hole was numerically simulated. Finally, the very high cycle fatigue test was carried out to validate the numerical calculation. The results show that the compound strengthening process can improve the stress distribution of the joint, inhibit the crack initiation and propagation, so it can improve the fatigue strength of the joints significantly.
The work aims to investigate the effect of Cr content of the coating on the microstructure and corrosion resistance of Fe60-xMn20Ni10Co10Crx (x=10, 12.5, 15, 20, 25, 30) high-entropy alloy coatings prepared by laser cladding technique on the Q345 steel substrate. The microstructure of the high-entropy alloy coating was analyzed by X-ray diffractometry and scanning electron microscopy. Meanwhile the microhardness and corrosion of the coating were characterized respectively by microhardness tester and electrochemical workstation. The results show that Cr10 coating consists only of BCC phase, and other coatings consist of BCC and FCC phases. With the increase of Cr content, the content of FCC phase first increases and then decreases. The microstructure changes from large equiaxed crystal to fine dendrites, and then changes to larger columnar crystals. At the same time, the hardness of the coatings also increased first and then decreased, reaching a maximum value (~500HV) when the Cr atomic fraction was 20%. Corrosion resistance tests in 3.5% NaCl solution showed that the Cr10 coating had the lowest corrosion current density and Cr12.5 had the highest corrosion potential. Therefore, laser cladding high-entropy alloy coating Cr20 has good comprehensive mechanics and corrosion resistance.
In order to enhance the nitriding efficiency, 42CrMo steel was selected as the testing material. Plasma oxynitriding using different air flow in the same pulsed plasma nitriding system for 42CrMo steel was investigated innovatively, and compared with conventional plasma nitriding processing. The cross-sectional microstructures, phases, corrosion resistance were determined by optical microscopy, X-ray diffraction, microhardness tester and electrochemical workstations. The results show that plasma oxynitriding owns much higher efficiency compared with plasma nitriding, thus makes thicker compound layer under the same other conditions. Meanwhile, higher porosity of nitrided layer is obtained. Furthermore, corrosion resistance can be significantly improved due to chemically stable formation and compact Fe3O4 oxide in the compound layer during plasma oxynitriding process, and air flow of 0.3L/min offers the optimum performance for 42CrMo steel due to highest ratio of Fe3O4 to Fe2O3. This research can provide a reference for improving the surface modification process of 42CrMo.
The effects of geometric shape, resisted shrinkage and free shrinkage, sample size on the linear shrinkage ratio of two high Nb-TiAl alloy investment castings were investigated by orthogonal test. The results show that the average linear shrinkage ratio of Ti–45Al–8Nb is 2.12%–3.28%, and the average linear shrinkage ratio of Ti–48Al–7.5Nb is 2.55%–3.39%, and the linear shrinkage ratio of the latter is larger. The linear shrinkage ratio of the resisted shrinkage specimen in the unblocked direction is 44.8%–47.7% higher than that of the free shrinkage specimen. The geometry and size have little effect on the linear shrinkage ratio, and resistance to solidification shrinkage has a greater impact on linear shrinkage ratio. As the sample size increases, the linear shrinkage increases by 100%, but the linear shrinkage ratio gradually decreases to 20%.
In this paper, the framed mould used in autoclave processing for composite structure forming was optimized considering thermos-elastic stress field. By adopting the finite element (FE) method, the deformation of the framed mould was obtained under thermo-mechanical loading. Through comparing the deformation of the mould surface in X, Y, Z direction from an engineering point of view, it is concluded that in the design of the framed mould one should focus on reducing the deformation in X & Y direction. A thermos-elastic structural topology optimization method was developed to minimize the thermal deformation of the mould surface, leading to the optimal configuration with periodic hollow units. FE analysis of the reconstructed model shows that compared with the original design, the thermal deformation and weight of the optimized result are reduced by 15.92% and 21.32%, respectively, thus demonstrating the validity of the proposed method.
Some cutting experiments were carried out to investigate the influences of different cooling and lubrication methods on the milling process of titanium alloy with carbide tools. These experiments were conducted under the conditions of flood cutting (WET), dry cutting (DRY), minimum quantity lubrication (MQL), cooling air cutting (CA) and minimum quantity lubrication with cooling air (MQL–CA). The influences of different lubrication methods were evaluated by the following standards which included the shape and the color of chips, cutting forces, surface roughness and tool wear. The results showed that MQL obtained the lowest cutting force along with the best surface quality and the best surface quality stability but only a medium tool wear among all the ways; CA cutting gathered higher cutting force with only a slight tool wear up to 0.008mm. The surface quality & surface quality stability of working piece were also the worst by this way. As far as MQL–CA cutting, all the key elements listed above were in the middle level. To summary, MQL was more suitable for finish machining. CA was better for rough machining and the three ways of cooling and lubrication were superior to the traditional flood cutting or dry cutting, and could be popularized and applied in the production of titanium alloy milling.
The reasonable supporting structure plays an important role in ensuring the forming quality of the parts in the selective laser melting process. The Thin-walled support is the most widely used type of the supporting structure. By analyzing the process elements of thin-walled support structure and describing the automatic generation process of thinwalled grid support structure based on STL model, the algorithm of automatic generation of thin-walled support structure of separate area is proposed and the corresponding software functions are developed. The feasibility of the implementation method is verified by generating the thin-walled partition support structures for parts.
