| Laser Direct Deposition Modeling (LDMD) technology has broad application prospects on manufacturing high-performance parts with complex shapes. However, the parts prepared by LDMD still have various problems, such as cracks defects, which hinder its practical application, therefore, to improve the toughness of rapid prototyping materials, metal matrix composite can be reinforced by in situ particles precipitated during LDMD process which combines multi-element components design, the formation of in situ reinforced particles by laser-induce, and the optimization of LDMD, moreover it has both scientific significance and application value to do this investigation.In this experiment, components of deposited alloy powder ingredients were prepared based on high-entropy alloy design ideas the theory of forming in situ reinforce particles, and the percentage optimization of alloy component have been applied to improve toughness and strength of materials prepared by LDMD. Specifically, FL-Dlight02-3000W semiconductor laser equipment was used to fabricate three kinds of alloy coating on 45# steel, including FeCrCoNiTiAl0.5 deposition layers, gradient deposition layers adding C and B elements, and deposited layers optimizing proportion of alloy elements Al, Ti, Co, Ni, respectively. Finally OM, EDS, SEM, XRD, and TEM, micro-hardness tester, wear test machine and other characterize and analysis equipments were used to investigate the microstructure, composition, phase, crack elimination mechanism and wear behavior of the cladding coatings. The results show that:The optimal process parameters for this test are shown as follows:laser power is 1400W; defocus amount is 312mm, spot size is 7.18mm×4.30mm, scanning speed is 300mm/min, and overlapping ratio of 10%. The obtained deposition layers displayed homogeneous microstructure with little cracks, holes and other defects. The crystal structure of FeCrCoNiTiA10.5 deposition layer is simple BCC solid solution, and more importantly, its micro-structures mainly full of different size equiaxed grains, at the same time, Ti-rich phase were precipitated in both grain boundary and interior; and the micro-hardness can be reach to about 650HV.After added B and C elements in FeCrCoNiTiA10.5 powder, lots of TiC precipitates appear in the gradient deposit layer, and their morphologies show as irregular quadrilateral and flower shape. Moreover, the crystal structure was transferred from the original BCC solid solution to FCC. Additionally, the microstructure, crystal structure and the amount of cracking of the laser deposited layers would be changed with different Al element content in the alloy. Ain-situ TiC particle reinforced metal matrix composite with thickness of 3mm and no cracks were successful prepared using the optimized formula of Fe-Cr-Co-Ni-Ti-Al-B-C-Si-Y2O3 composite alloy powders, its average hardness is 500HV. The size of the in situ TiC particle is about in from nanometer to micrometer range, a large number of nano size particles produced in-situ in metal matrix composite is an important factor for laser direct deposited material with a higher strength and toughness. |
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