No abstract

Laser additive manufacturing for high performance large aerospace structural components of difficult to process metallic materials like titanium alloys based on layer-wise rapid solidification powder deposition has many advantages over traditional forging, casting and powder-metallurgy processes. However, applications of the revolutionary near-net-shaping technology have been limited to small components for the past decades. In this presentation, R&D progresses on processing, microstructure control and mechanical properties optimization and of laser deposition near-net-shaping of large metallic structures such as titanium airframes and super-high strength steels landing-gears having mechanical properties equivalent and/or better than forged counterparts have been reported. The challenging issues such as the metallurgical kinetics, evolution behaviors of internal stresses, control of rapid solidification microstructures and internal defects during laser melting deposition were reviewed.

Coping with the characteristic of flow shop scheduling problem with uncertain due date, fuzzy arithmetic on fuzzy numbers is applied to describe the problem, and then a new hybrid algorithm model which integrate particle swarm optimization into the evolutionary mechanism of the knowledge evolution algorithm is presented to solve the problem. By the evolutionary mechanism of knowledge evolution algorithm, we can exploit the global search ability. By the operating characteristic of PSO, we can enhance the local search ability. The algorithm is tested with MATLAB simulation. The result, compared with Genetic algorithm and modified particle swarm optimization, shows the feasibility and effectiveness of the proposed algorithm.

A new process was provided for decomposition of ilmenite by ammonium hydroxide under hydrothermal process. The significant effects of reaction temperature, NH4OH concentration, NH4OH-to-ilmenite mass ratios on titanium extraction were studied. The temperature showed significant influence on titanium extraction. The experimental data of the extraction rates under the relevant operating variables were well interpreted with the shrinking core model under chemically controlled process.

Recently, laser melting deposition (LMD) undergoes rapid development since its fabricating advantages make it particularly suitable for the fabrication of titanium aerospace components. The dry sliding wear behavior of forged, uncoated and laser nitrided LMD TC18 titanium alloy sliding against the forged TA15 alloy were investigated. Then, reasons of their wear behavior were further studied. The specimens were tested on the M-200 tester, worn surface morphology and wear debris were carefully analyzed by means of SEM and EDS. The results show that in the case of forged and LMD TC18 titanium alloy sliding against TA15 alloy, wear mechanism are abrasive wear and adhesive wear. Because of the lubricious nature of TiO2 oxides produced during sliding which reduces the wear and consequently wear loss, the wear resistance of forged TC18 titanium alloy is superior to that of LMD TC18 titanium alloy. After using laser nitriding treatment on LMD TC18 alloy, the formation of a protective layer composed of dendritic TiN attributes to significant wear resistance improvement.