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Hole machining of nickel-based alloys has a wide application space in aerospace manufacturing industry, but the high cutting force, high cutting temperature, large plastic deformation, cold work hardening and severe tool wear during the cutting process of nickel-based alloys make them typical difficult-to-machine materials. Therefore, when drilling nickel-based alloys, the selection of cutting parameters is very important. Reasonable cutting parameters will help to control the chip shape and facilitate chip removal. In this paper, the cutting force, cutting temperature, and tool life of high-speed steels in drilling Nickel-based superalloy Inconel 718 was investigated through orthogonal cutting experiments. Then the empirical method of multi-factor line regression was used to establish the empirical models of drilling torque, thrust force, cutting temperature, and tool life of the drills with emulsion as the cutting fluid, and to verify the validity of the established model, and the significance of the regression method is tested to verify the effectiveness of the model. The tool wear morphology and wear mechanisms were examined by scanning electron microscope (SEM) and energy spectrum analysis (EDS). The results revealed that the major drill wear modes incorporate flank wear, peripheral wear, micro-chipping and chipping, and the tool failure mechanisms were comprehensively synergistic interactions among abrasive wear, adhesive wear, and oxidation wear. In addition, the cutting parameters of high-speed steels in drilling Nickel-based superalloy were optimized based on the response surface methodology of equivalent tool life-efficiency, and then the reasonable cutting parameters under the condition of using cutting fluid were recommended. [ABSTRACT FROM AUTHOR]

Rock bolts are widely used in the main structure of the DC transit system and play the role of the main body reinforcement and support. Because of the extensive stray current in the subway system, the corrosion risk of rock bolts is greatly increased. Therefore, the rock bolt was experimentally studied by simulating the input stray current and monitoring the polarization potential in this paper. After the stray current corrosion (SCC) process was finished, a tensile and breaking experiment of the corroded specimens was conducted for the mechanical properties. As an important parameter to indirectly characterize the corrosion strength of the stray current, the polarization potential was analyzed. Two types of rock bolts were compared for their mechanical properties and corrosion parameters. The result shows that the rock bolt with stranded steel wire as the rod has better corrosion resistance than the HRB500 rebar. Hence, the bonded stranded steel wire is more resistant to the stray current corrosion than the HRB500 rebar, which is adaptive for rock bolts in the direct current (DC) transit system. [ABSTRACT FROM AUTHOR]