Fabrication Of Mo-Si-B Alloy By Laser Additive Manufacturing And Its Properties

Mo-Si-B alloy has the potential to replace nickel-base superalloy as a new generation of high-temperature structural materials because of its high melting point,good high-temperature stability,excellent high-temperature strength and high-temperature mechanical properties.However,the Mo-Si-B alloy has poor high temperature oxidation resistance,and there are some shortcomings including long forming time and inability to form complex shape parts for traditional preparation methods such as arc melting and powder metallurgy,which limit its application.As a near-net shape technology,laser additive manufacturing has the advantages of short forming time and fine alloy microstructure.It is expected to replace some traditional preparation processes and become a new technology for preparing Mo-Si-B alloy parts in the future.In this paper,Mo-12Si-8B alloy was prepared by laser additive manufacturing technology,and the effects of laser process parameters on the forming quality and tissue formation pattern of the alloy were investigated to obtain optimized laser process parameters.Subsequently,the properties of Mo-12Si-8B alloy prepared by laser additive manufacturing were compared with those of conventional methods.Finally,Ti was added to improve the high temperature oxidation resistance of Mo-12Si-8B alloy and to reduce the density of the alloy,and the effect of Ti content on the properties of Mo-12Si-8B-x Ti alloy was investigated.The following main conclusions were obtained.（1）A single-pass alloy clad layer with essentially no internal defects such as cracks can be obtained by the laser processing parameters with a spot diameter of 2.65 mm,a laser power of 850 W and a scanning speed of 5 mm/s.The microstructure within the clad layer consists mainly of flat grains at the bottom,cellular and columnar grains at the bond,and dendrites at the top.A fine grains zone due to laser remelting occurs between the multi-layer lap regions.（2）The microstructure of the laser additive manufactured Mo-12Si-8B alloy is finer than the alloy prepared by conventional arc melting and spark plasma sintering due to the faster cooling rate of the preparation process,and its average microhardness value can reach 978HV and compressive strength is 2738 MPa.After oxidation at 1100°C for 8 h,the mass loss is only 57%of the alloy prepared by the conventional method.After the addition of Ti to Mo-12Si-8B,the phase consists ofα-Mo phase,Mo₅Si B₂phase and Mo₃Si phase,and Ti is mainly solidly soluble in Mo₅Si B₂phase and Mo₃Si phase.The density of Mo-12Si-8B-x Ti alloy decreases significantly with the increase of Ti content,and at the same time,its microhardness and compressive strength are also increased.The density of Mo-12Si-8B-15Ti reaches the lowest value of 8.63 g/cm³when the Ti content is 15at.%,while the average microhardness is 1132 HV and compressive strength is 2984 MPa.Mo-12Si-8B-15Ti can quickly form a complete and dense oxide protective film which is Ti O₂and borosilicate glass on the surface,thus the oxidation resistance can significantly improve,its oxidation weight loss at 1100℃is only 28.2%of Mo-12Si-8B.