It has been a hot topic in the field of vehicle research to find a new anti-pollution and anti-drag means used for vehicle surface. In recent years, the traditional organic tin antifouling coatings are being eliminated. Titanium alloy has the advantages of low density, high strength, heat resistance and corrosion resistance, etc., and is widely used in the structure of vehicle shell and blade. Therefore, the realization of surface microtexture drag reduction on titanium alloy has a wide application prospect and important research significance. In this paper, the surface microtexture was obtained on the surface of TC4 titanium alloy by nano laser machine. The structure was characterized by optical microscopy and laser focusing observation. The experimental results show that the non-smooth surface with continuous structure can reduce the frictional resistance of fluid compared with smooth surface. In order to obtain the electrochemical parameters of surface texture under seawater condition, the corrosion and wear experiments of TC4 titanium alloy disk marked with surface microtexture were carried out by electrochemical friction testing machine. The results show that suitable surface microtexture can significantly reduce the friction coefficient, friction resistance and wear corrosion potential of titanium alloy materials, and improve the corrosion resistance and working life of the vehicle structure in the marine environment.
Thermal barrier coatings (TBC) utilize the adiabatic and corrosion resistance of ceramic coatings to effectively protect the alloy matrix of hot components in aero or land-based gas turbines engines. However, the constant pursuit of higher operating temperatures can lead to degradation, delamination, and premature failure of surface coatings. To meet the needs of future advanced TBC systems, new ceramic materials must be developed. This paper reviews recent advances in ceramic materials for advanced thermal barrier coatings, including YSZ (Yttria partially stabilized zirconia), A2B2O7–type compounds, rare earth tantalates, rare earth phosphates, high entropy rare earth ceramic materials, magnetite type hexa-aluminate oxides and self-healing materials with summarizing their properties and performance respectively, and the advantages and shortcomings of each material at the present stage of development. Finally, the development direction of thermal barrier coating materials is foreseen to provide guidance for the development of new barrier coatings.
As an effective metal surface modification technology, laser shock peening (LSP) has shown exciting application prospects in improving the fatigue properties and service life of additively manufactured (AMed) metals. Firstly, the development and classification of LSP technology and AM technology are briefly introduced. Then the research progress of LSP as a post-treatment method to improve the fatigue performance of AMed metals is overviewed, along with the mechanism of improving fatigue performance from the aspects of LSP induced changes in porosity, microstructure and residual stress near the AMed metal surface. Furthermore, the combinational technique that incorporates LSP during AM process to improve the fatigue performance of AMed metals is surveyed, and the reasons for the significant improvement of fatigue performance are analyzed in terms of the in-situ LSP induced surface residual compressive stress and its distribution depth. Finally, the summary and outlook on the research directions of LSP in improving fatigue performance of AMed metals are provided.
Laser shock peening (LSP) technology is a new surface modification technology that uses high power density and short pulse lasers to strengthen the surface of materials. It can generate gradient nanostructure and compressive residual stress on the material surface, improving the mechanical properties of materials. This paper introduces the development and research of laser shock penning and the application prospect of this technology is prospected. Subsequently, the principle of laser shock penning is analyzed, and the strengthening effect of the residual stress and gradient nanostructures induced by the laser shock penning on the material is analyzed. This paper reviews the influence of laser shock peening on the strength and ductility, fatigue resistance, wear resistance and stress corrosion cracking resistance of materials. Finally, the multiscale simulation research of laser shock peening is introduced from macroscopic, mesoscopic, micro-mesoscopic, microscopic and nanoscopic scales, and the differences in simulation methods at different scales are compared.
The Fe-based alloy/B4C composite coating prepared by electron beam recladding has the disadvantages of residual stress, uneven distribution of hard phase and high brittleness. In order to further improve the comprehensive properties of the composite coating, the effects of different quenching temperatures and low temperature tempering on the microstructure, hardness and wear resistance of the coating were studied. The results show that the morphology of the hard phases change from the parallel lamellar M2B phase to the rounded rod-like structure, and the surrounding entangled network M23(C, B)6 phase is dissociated and spheroidized into a granular structure after quenching at 950/1000/1050/1100 ℃ and tempering at 200 ℃. XRD analysis show that the residual stress of the recladding composite coating is effectively eliminated after heat treatment process, and the category of the phases remained unchanged. After heat treatment, the average microhardness of the coating shows a trend from increase to decrease with the increase of quenching temperature, and the hardness reaches the highest value of 970.9HV0.1 when quenched at 1050 ℃ and tempered at 200 ℃ . The wear weight loss of the composite coating quenched at 1050 ℃ and tempered at 200 ℃ reaches a minimum value of 0.10961 g, which is 18.7% lower than that of the composite coating without heat treatment. The wear morphology of the coating surface shows furrows, white spots and strip wear marks, and the wear mechanism is mainly abrasive wear.
In this work, laser shock peening (LSP) induced spalling on aero-engine blades was studied. Multitimes LSP–induced spalling behavior was investigated using variable-thickness blade specimens (11° leaf surface angle), which were designed according to a real aircraft engine TC17 titanium alloy compressor blade. Further, the influence of specimen thickness and spot shape on the initiation site of spalling was explored using different thickness plate specimens. Results show that concave deformation was generated on the peened surface and macroscopic distortion was observed on the variable-thickness TC17 titanium alloy blade specimens after peening with 25 J, 4 mm square spot. Spalling and local peeling was not detected until peened 6 times and 8 times, respectively. Furthermore, analysis of the plate specimen that LSP–induced spalling is positively correlated with specimen thickness. The thicker the specimen is, the higher peening-times threshold for initiating spalling. Besides, spalling is not significantly related to the shape of the laser spot. Both circular and square spots can induce spalling, which is more easily generated in the softening region where Cr and Sn are enriched. LSP-induced spalling is not only related to the transmission characteristics of the shock waves but may also be related to material factors such as element segregation, and enrichment.
In order to explore the evolution law of molten pool flow and morphology of 42CrMo steel for crankshaft during laser remelting treatment, a two-dimensional simulation model with high fitting to the original morphology was established, and the surface of the sample was simulated and analyzed by finite element method under different laser powers, and the variation law of surface roughness and microhardness was compared and analyzed by experiments. The results show that the molten pool flow model can well predict the surface molten pool flow and surface micro-fluctuation of 42CrMo steel. The flow velocity in the molten pool increases first and then decreases. By adjusting the laser power, the surface remelting can be realized and the surface smoothness of the sample can be improved. After laser remelting treatment, the surface hardness of 42CrMo steel is significantly improved, which meets the requirements of crankshaft working conditions. The prediction results of surface roughness and weld pool depth by simulation model are basically consistent with the experimental results.
Shot peening affects the fatigue crack growth performance of the material by changing the surface integrity of the material such as surface roughness, microhardness and residual stress. In this paper, two different shot peening coverage rates (100% and 300%) were used to strengthen the surface of 7B50–T7751 aluminium alloy, and the surface integrity of the strengthened specimens was characterized by roughness tester, scanning electron microscope (SEM) and X-ray diffraction (XRD). Fatigue crack growth tests were carried out on shot peened specimens and fatigue fractures were analysed to investigate the effect of different shot peening coverage rates on the rate of fatigue crack growth. The test esults show that shot peening reduces the crack growth rate of the specimen and increases the fatigue crack growth life of the specimen. In the range of 100%–300% shot peening coverage, fatigue specimens with 300% coverage showed relatively good fatigue crack growth performance, mainly due to the shot peening introducing a beneficial layer of compressive residual stress in the surface layer of the specimen and increasing the hardness of the surface layer of the specimen.
Aiming at the requirement of high-precision calibration of light plane for double-line structured light skin seam measurement system, a calibration method of two-line structured light plane based on planar target is proposed. First, take the datum point on the target plane as input, construct the target plane pose solution model, and obtain its plane equation in the camera coordinate system. Then, according to the line surface model of the camera, the depth of the fitting control points is reconstructed. Finally, the eigenvalue method is used to fit the denoised fitting control point set to complete the calibration of double-line structured light plane. Experiments show that this method can simultaneously complete the calibration of two light planes in the measurement system. After calibration, the repeated measurement accuracy of seam gap is better than 0.050 mm, and the repeated measurement accuracy of seam flush is better than 0.030 mm.
The outer wing wall of civil aircraft is usually constructed with T-truss structure. The long girder connection structure at the root of the wing is a vital force transmission structure. The long truss structure at the root of the wing is mainly connected with the corresponding corner box. In this paper, the evolution rule, mechanical properties, and defects of titanium alloy long girder angle box of civil aircraft were studied by using laser stereotyping technology. The internal microstructure of the furnace sample is small rod-shaped α phase, there is no anisotropy in performance, and is net basket structure. The tensile strength of the test block in the X、Y and Z directions is higher than 889 MPa, and the degree and dispersion of its deviation from the average tensile strength in three directions of X、Y and Z are not exceeded over 5%, indicating good overall performance; The tensile fracture of the sample belongs to ductile fracture, and the tensile fracture is composed of three parts: fiber zone, radiation zone, and shear lip zone. Fatigue fracture is plastic fracture, and in fatigue fracture, secondary cracks are continuous and dense. The size and forming quality of the processed sample meet industry usage requirements.
In order to investigate the influence of cutting parameters on machined surface temperature and subsurface damages, a CFRP orthogonal cutting experiment was conducted at various fiber cutting angles with different rake angles, flank angles and cutting depths, and cutting temperature was also measured. Results show the increasing of rake angle and flank angle can decrease the cutting force and surface temperature by decreasing the compressive force and contact area between flank face and machined wall separately. The most serious subsurface damages occur when against fiber cutting, which are induced by fiber bending fracture, resulting in obvious serrated surface at θ =150°. The fiber bending angle and irregular fracture are decreased with rake angle and flank angle increasing. Moreover, the obvious increase trends of cutting force, machined surface temperature and subsurface damage are confirmed as cutting depth increased.
In the manufacturing process of aviation composite parts, autoclave is the key equipment, which needs to accept composite preforms from other lay-up sections, and then pack into autoclave according the equipment area, resources, number of parts, process parameters, process constraints and tooling equipment and so on. In order to improve the production scheduling efficiency of autoclave, considering the characteristics of multi variety, small batch and multi factor constrains of composite parts, a method for production plan of autoclave based on multifactor constrain in composite forming manufacturing is proposed, which is successfully applied to a composite parts manufacturing enterprise. Through the actual production data verification, the scheduling method based on multifactor constrains can not only realize the guidance of production, but also improve the scheduling efficiency.
