查看更多>>摘要：P91 ferritic/martensitic and AISI 304L austenitic stainless steels were hot dip aluminized (HDA) in 99.9% pure aluminum in a pit type vertical furnace at three different temperatures i.e. 750, 800 and 850 degrees C for 1 to 10 min. Evolution of interface morphology, type and distribution of phases and growth kinetics of the reaction zones were studied using a variety of experimental techniques. Though similar intermetallic compounds formed in both steels, their distribution, morphology and growth kinetics were distinctly different. In P91 F/M steel, aluminized surface adjacent to the substrate had wide Fe2Al5 layer with serrated morphology containing high volume fraction of 2-3 mu m sized Cr rich intermetallic phases. Width of FeAl3 phase present adjacent to this layer did not show much variation with HDA conditions. Above FeAl3, on the surface, the pure Al top coat contained nonequilibrium phases. Compared to P91 steel, width of the aluminized layer in 304L SS was less (35 +/- 5 mu m vs 120 +/- 15 mu m at 800 degrees C-10 min) and the Fe2Al5 layer had a planar interface with the substrate. Optimum temperature-time combination to get thin, uniform, defect free surface aluminide layer in P91 F/M and 304L steels were found to be 750 degrees C-2 min and 800 degrees C-1 min respectively. Growth kinetics of surface aluminide layers in both steels were studied, kinetic parameters were determined and compared with information available in literature.
查看更多>>摘要：In this paper, bainitic railways were repaired designedly by laser cladding repairing method with AerMet100 steel powder as raw material. The microstructural evolution of repaired specimens was studied carefully, and the corresponding mechanical properties and wear resistance were compared to verify the feasibility of this method. Results show that the bainite microstructures formed in the AerMet100 repaired region exhibit a high microhardness of 515 HV due to high-alloyed solution strengthening and microstructure refinement. The thermal cycles during the repairing process lead to the microstructures in HAZ changing with the distance from the fusion line, and the bottom of HAZ consisting of tempered bainite becomes the microhardness valley. Tensile tests indicate that the overall mechanical properties of repaired specimens are comparable to the bainitic substrate. Compared to the bainitic matrix, wear tests present that the wear resistance of the AerMet100 repaired region is better with the mass loss decreasing by about 28%. The current experimental results suggest that laser cladding repairing with AerMet100 steels is suitable for high-performance repairing of high-strength bainitic steels.
查看更多>>摘要：Oxidants, such as oxygen, cannot easily approach the core Al due to the presence of dense alumina on the surface of aluminum particles, thereby resulting in high ignition temperature and long ignition duration. To overcome this challenge, we employed the solvent/non-solvent method using Viton A (a copolymer of 1,1-difluoroethylene and hexafluoropropylene) as a coating material to prepare the core-shell Al/Viton A composite particles. An orthogonal experiment was designed to identify the optimal preparation parameters by evaluating the peak pressure in a closed vessel. The sample with the largest peak pressure was compared with raw Al and Al/Viton A (prepared by the physical mixing method) using the combustion pressure and open combustion tests to evaluate the solvent/non-solvent method. The results from the orthogonal experiment revealed that the water bath temperature exhibited the greatest influence on the coating effects. The composite prepared under a water bath temperature of 55 degrees C and a stirring rate of 250 rpm, using 20 mL of acetone and a 5 mL/min dripping rate of the Viton A acetone solution, were uniformly coated by Viton A, and exhibited excellent combustion characteristics. In addition, the sample generated using the optimal preparation parameters burnt more vigorously and rapidly than raw Al and Al/Viton A. Finally, the reaction molecular dynamics simulation was employed to gain insight into the effect of Viton A on the combustion of Aluminum particles at the molecular level.
NSTL
Elsevier