At present, no consensus has been reached on the generation mechanism of anisotropy in materials fabricated by laser powder bed fusion (LPBF), and most attention has been focused on crystallographic texture. In this paper, an analysis and test were carried out on the hardness, defect distribution, residual stress distribution, and microstructure of WE43 magnesium alloy fabricated by LPBF. The results indicate that LPBF WE43 exhibits obvious anisotropy—the hardness HV of X–Z surface (129.9 HV on average) and that of Y–Z surface (130.7 HV on average) are about 33.5% higher than that of X–Y surface (97.6 HV on average), and the endurable load is smaller in the stacking direction Z compared to the X and Y directions. The factors contributing more to the anisotropy are listed as follows in sequence. Firstly, the defect area of the X–Y projection surface is about 13.2% larger than that of the other two surfaces, so this surface shows greatly reduced mechanical properties due to the exponential relationship between the material strength and the number of defects. Secondly, for laser scanning in each layer/time, the residual stress accumulation in the Z direction is higher than that in the X and Y directions, which may directly reduce the mechanical properties of the material. Finally, more fine grains are distributed in X–Z and Y–Z surfaces when comparing them with those in an X–Y surface, and this fine-grain strengthening mechanism also contributes to the anisotropy. After T5 aging heat treatment (250 °C/16 h), a stronger crystallographic texture is formed in the direction, with the orientation density index increasing from 10.92 to 21.38, and the anisotropy disappearing. This is mainly caused by the enhancement effect of the texture in the direction on the mechanical properties in the Z direction cancelling out the weakening effect of the defects in the X–Y surface in the Z direction.

The effect of an alternating electromagnetic field on the microstructure and properties of the Ti-Al coating on the titanium alloy surface is studied. The Ti-Al coating is prepared on the surface of titanium alloy by using an alternative electromagnetic field assisted by high temperature thermal diffusion. The preparation method is simple and easy to operate. The microstructure and element distribution of the coating under different magnetic field intensities are analyzed. The mechanism of improving the comprehensive properties of coatings by alternative electromagnetic fields with different intensities is discussed. The test results show that the outer surface of TA15 titanium alloy diffused at 850 degrees C without magnetic field is not smooth, the quality is poor, and internal structure cracks appear. No obvious cracks are found in the coating microstructure of 850 degrees C diffused by a magnetic field with 10 A current intensity, but there are still some holes. A large number of holes and cracks appear in the coating microstructure with 850 degrees C diffusion under the magnetic field with 15 A current intensity; mostly longitudinal cracks are perpendicular to the interface and penetrating through the interface, which may be caused by the thermal effect of the magnetic field. The coating diffused under the magnetic field of 20 A current intensity has good overall quality, good bonding with the substrate, relatively flat interface, dense, uniform, and fine structure, and no obvious cracks and holes are found. The main phases are TiAl, Ti3Al and elemental Al, and Ti3Al has obvious texture, with an average equivalent diameter of 3.2 mu m. TiAl has no obvious texture and has an average equivalent diameter of 2.2 mu m. The electromagnetic stirring effect makes the strengthening phase in the coating more evenly distributed and reduces component segregation. With the increase of magnetic field intensity, the stress concentration and cracking sensitivity decrease and the migration distance of Ti atoms from the matrix to the coating direction increases. The interfacial hardness of the coating extends outward at first and then decreases, and the maximum hardness reaches 468.2 HV0.2. The cracking sensitivity of the coating is reduced by the magnetic field, and the microstructure and properties of the coating are improved.

Ti–Al composite coating was prepared on the surface of a titanium alloy by the laser cladding technology and coaxial powder feeding under argon protection. The cladding material was AlSi10Mg aluminum alloy powder. The intermediate sample was thermally diffused at high temperature for 6 h and then placed in a certain intensity of the alternating electromagnetic field until completely cooled. The alloy substrate and coating solidified under the action of the alternating electromagnetic field, and the surface coating of a high strength titanium alloy was obtained. The morphology and microstructure of the composite coating were analyzed by SEM, XRD, and energy dispersive spectroscopy (EDS), and the hardness of the coating was measured. The results showed that the high temperature thermal diffusion promoted the interatomic diffusion; repaired some defects, such as cracks and pores; and eliminated the elemental metals that did not participate in the reaction, and the surface hardness of the coating joint reached the maximum. The electromagnetic stirring makes the titanium alloy coating and substrate bond well, the joint is relatively straight, the number of cracks and pores is obviously reduced, and the comprehensive performance of the coating is improved.

Steam cooler is one of the most important mechanical equipment in thermal power generation system and nuclear power generation system. The steam cooler bears a huge temperature gradient load when the working conditions are switched. In order to analyze the thermal stress of steam cooler tube sheet with high temperature load under harsh working conditions, the thermal-structural coupling analysis model of steam cooler tube sheet is constructed with finite element method. The results show that the stress concentration exists at the position connection between heat exchanger tube and cylinder. The maximum stress is located at the outermost heat exchanger tube with the peak stress of 320MPa. The heat exchanger tube layout alone cause higher stress. This situation should be avoided in the design of heat exchanger tube sheet. Furthermore, the strength and safety of the steam cooler tube sheet are evaluated with the stress linearization method. The steam cooler tube sheet design meets the safety requirements of structural strength under high temperature load.

The effect of hot isostatic pressing (HIP) on the microstructure and properties of hot dip aluminum coating cooled in a magnetic field was investigated in this study. In order to improve the microstructure and properties of magnetic dip aluminum coating, hot isostatic pressing technology was used for post-treatment. Initially, a traditional aluminum-impregnated coating was prepared on the surface of titanium alloy TA15, an alternating electromagnetic field was applied during the forming and solidification process of the coating. Finally, the coating was treated with hot isostatic pressing technology. Analyzed three different coatings of the microstructure and element distribution, and tested the microhardness of the coatings at various positions. The test results revealed that the TA15 titanium alloy hot-dip aluminum coatings obtained through the three different processes exhibited a gradient structure. Compared with the traditional hot-dipped aluminum air-cooled coating, when an appropriate intensity of alternating electromagnetic field was applied during the coating solidification process, the outer coating structure was enhanced, the number of holes was reduced, the microstructure density increased, and the number of cracks significantly decreased. The defects of the 800 °C hot isostatic magnetic cold and hot dip aluminum coating were repaired under high temperature and pressure, resulting in a uniform and fine microstructure. The comprehensive properties of the magnetic cold and hot dip aluminum coating on the surface of the titanium alloy were effectively enhanced through hot isostatic pressing.

To enhance the surface properties of titanium alloys and meet the design requirements for high efficiency and stability, this study employs hot isostatic pressing (HIP) technology to post-process the hot-dip aluminum coating on titanium alloy surfaces. The research investigates the impact of HIP on the microstructure and performance of the hot-dip aluminum coating. Initially, a hot-dip aluminum coating was prepared on the TA15 titanium alloy surface, and the causes of defects were analyzed. Subsequently, the coating underwent post-processing, involving remelting and repair under high temperature and pressure conditions. Microhardness tests were conducted on the interface area near the coating under various processing conditions, and the morphology, microstructure, and elemental distribution of the coating were analyzed. The mechanism by which HIP eliminates defects in the hot-dip aluminum coating and enhances its performance was also explored. Experimental results indicate that samples without post-processing exhibit a microstructure characterized by through-going cracks, a loose transition layer with poor density and porosity, as well as numerous shrinkage pores and cavities. After HIP treatment at 600 °C, the outer coating and transition layer become more porous, with increased defect formation, primarily in the form of pores and cracks. Some portions of the transition layer and original bonding layer transform into a thicker bonding layer. Following HIP treatment at 800 °C, cracks and pores are significantly reduced, the atomic ratio of Ti to Al in the bonding layer approaches 1.17, forming a more stable intermetallic compound, along with the emergence of a new phase, AlV₃. Defects such as pores and cavities are repaired, leading to improved surface hardness across all regions of the coating. Consequently, the microstructure and performance of the titanium alloy surface hot-dip aluminum coating are effectively enhanced.