Lamellar structures of Ti–46Al–0·5W–0·5Si (at-) alloy solidifying through the primary α phase were successfully aligned parallel to the growth direction using a self-seeding technology in a Bridgman type directional solidification furnace. At the growth rate of 20 μm s−1 and temperature gradient of 12·1 K mm−1, the α phase grows along the [Formula: see text] direction. Therefore, the parallel lamellar structures, whose lamellar orientation is [Formula: see text] direction, can grow continuously until the end of solidification under these solidification parameters. The original lamellar structures of the unmelted region parallel to the growth direction and suitable solidification parameters are necessary for TiAl alloys solidifying through the primary α phase to control the lamellar orientation. The self-seeding technology gets rid of the cutting and fixing of seeds and simplifies the processing of controlling the lamellar orientation of TiAl alloys. It can promote the engineering applications of the lamellar orientation control of TiAl alloys.
Fe52Cr15Mo26C3B1Y3 amorphous particle-reinforced pure aluminum (Al) matrix composite was prepared by powder metallurgy. The ferrum (Fe)-based amorphous particles prepared by atomization method have good amorphous structure, and the circular reinforcement particles are evenly distributed in the Al matrix. The composite has high strength, hardness, and excellent corrosion resistance. The hardness of the composite increases gradually with the increase in the content of the reinforcement, from 46 Vickers hardness (HV) of pure Al to 220.5 HV, with remarkable effect. The tensile strength of the composite increases first and then decreases with the increase in the content of the reinforcement. When the content of reinforcement is 15%, the maximum tensile strength is 234 MPa, which is 154% higher than that of pure Al. The fracture mode of the composite is the mixture of plastic fracture and brittle fracture. The corrosion resistance of pure Al is significantly improved by the addition of reinforcements, which shows that the composite has a smaller corrosion current density and a more positive corrosion potential than that of pure Al.
As a new tunnel presupport construction technology, the freeze-sealing pipe roof method (FSPR) has been successfully applied to the Gongbei Tunnel Project for the first time in China. To overcome the practical difficulties of this new method in the freezing construction process, such as welding difficulties of the profiled freezing tube, refrigerant leakage, and long construction period, based on the principle of an equal cooling capacity, an improved design of freezing tube was proposed. By designing three different pipe configurations and using scaled model tests and numerical simulation, the feasibility of the improvement and the difference in the freezing temperature field were studied. The research results show that the improved design with double circular freezing tubes exhibited a lower temperature and a higher cooling rate during the test, and the time required to meet the freezing design requirements was significantly shortened. Finally, a composite structure of “pipe roof and frozen soil curtain” with a better carrying capacity and water sealing performance was formed. It was recommended to strengthen the temperature monitoring at the pipe wall in the preliminary stage of the freezing construction to ensure the water sealing effect between the pipes. In the later stage, attention should be paid to monitoring the thickness of the frozen curtain and reducing excessive frost heave through technical means such as cooling capacity control. The improvement and configurations proposed in this research could effectively replace profiled freezing tubes in the original project, better adapt to horizontal freezing projects of similar curved tunnels, achieve the freezing goal faster, and provide a reference for the promotion of the FSPR.
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