Microstructure And Properties Of Ti-Mo Base Alloys By Laser Additive Manufacturing

Additive manufacturing technology is a technology manufacturing parts by accumulating materials layer by layer based on CAD-designed data.Laser additive manufacturing is one of the technologies therein developing rapidly with good prospect and great influence.It is mainly used in the production of complex metal structural parts.Manufacturing titanium alloy by laser additive manufacturing technology is one of the key research objects in the field of metal additive manufacturing.At present,alloys extensively used in additive manufacturing have good melt flowability and solid-liquid structural compatibility,showing the relatively narrow solid-liquid phase region on the binary phase diagram.Ti-Mo alloy has many excellent properties and broad application prospects,but the solid-liquid phase region broadens with the increase of Mo content.At present,less research has been done in the field of laser additive manufacturing Ti-Mo alloys.In this paper,the laser process of the binary Ti-Mo alloy by laser additive manufacturing was investigated.According to the phase transition and deformation mechanism of binary TiMo alloy,five kinds of binary Ti-Mo alloys with different contents of Mo were selected for the experiment.According to the change of simulated solid-liquid phase region and mixing enthalpy between elements,five alloying elements were added to Ti-15 Mo,including 2~6 wt% of Al,Fe,Nb,Cr and V.The forming plate of the alloy was prepared on pure titanium plate by laser additive manufacturing technology,and microstructures of alloys were analyzed by x-ray diffraction,optical microscope and scanning electron microscope.The laser confocal microscope and Vickers hardness tester were used to measure and analyze the roughness and hardness of the surface,respectively.The experimental results show that macro morphology of solidified surface can be improved by changing process parameters in manufacturing process of laser cladding.Best process parameters(laser power 2000 W,scanning speed 5 mm/s,defocus distance 235 mm)suitable for laser additive manufacturing Ti-Mo alloys were obtained.The roughness of binary Ti-Mo alloys produced by laser cladding decreased with increasing of Mo content,while aspect ratio and contact angle increased with increasing Mo content.? phase content decreased with increasing of Mo content,while ? phase content increased.Microstructures of binary Ti-Mo alloy produced by laser cladding consisted of equiaxed grains on surface and columnar grains in interior.With increasing of Mo content,equiaxed grains changed to dendritic grains and segregation intensified gradually.Plate-like ? phase precipitated in coarse ? phase grains.Vickers hardness decreased with increasing of Mo content.When adding different alloy elements more than 4 wt%,surface roughness of all components increased.Adding 2 wt% Al,Cr and V reduced surface roughness.When Nb was added,contact angle decreased.When other alloy elements were added,contact angle decreased first and then increased.After adding Al and Nb,aspect ratio decreased with the increasing of content.After adding other elements,aspect ratio first decreased and then increased.Comparing with Ti-15 Mo,aspect ratio showed a decreasing trend.The content of ? phase decreased after Al was added.After adding other elements,content of ? phase increased.The content of ? phase decreased with increasing of Al content.After adding of Al,defects in cladding layer were reduced.After adding more than 4 wt% Cr,cracks in cladding layer increased.After adding Al,Fe and Nb,surface structures were cellular grains.Adding other elements,surface structures still were equiaxed grains.With increasing of stable ? phase element content,volume and quantity of ? phase in the surface layer decreased.Vickers hardness increased slightly after adding Al and Nb.After adding other elements,Vickers hardness decreased.