| Laser Additive Manufacturing(LAM)is a new type of manufacturing technology that uses a high-energy laser beam to melt metal powder layer by layer and directly generate metal parts from a three-dimensional CAD model.Compared to the conventional manufacturing technologies,LAM possesses several advantages,namely a high material utilization ratio,a lower time-to-market,no limit on component size and geometries,low manufacturing cost and a near-net-shape production without needing expensive molds,etc.,which has attracted widespread attention.However,most of the titanium alloys currently used for laser additive manufacturing are traditional alloy systems,which do not take into account the unique ultra-high temperature,strong convection,small molten pool and ultra-high temperature gradient in the laser additive manufacturing process,and the extremely fast non-equilibrium solidification conditions,resulting in very few alloy materials that can be used in industrial application.Therefore,to develop a new titanium alloy system which is suitable for laser additive manufacturing is significantly important.As a material used for laser additive manufacturing,it is necessary to achieve effective control of its full shape from molten state to solidification.This requires the alloy materials to have good liquid fluidity,low crack sensitivity,small segregation of components,and wide processing window.One of the priority principles is to be close to the direct melting point.Recent studies showed that Ti-Zr congruent alloy has high structural stability and uniformity,good formability and excellent corrosion resistance,and its plastic strain is up to 56%,but has lower strength and hardness.Therefore,how to effectively improve the mechanical properties of the congruent alloy while maintaining the inherent performance advantages is the key to determining whether the alloy system can be used as a laser additive manufacturing material.Therefore,this paper proposes to design Ti-Zr-V-Nb alloys with binary Ti-Zr congruent alloy as the basic alloy,V and Nb as alloying elements,and the Ti-Zr-V-Nb alloys are designed using the"cluster plus glue atom"model.In order to use the good liquid flow and low micro-segregation of Ti-Zr congruent alloy to improve the formability of the alloy,and use the stability of V and Nb to?-Ti phase and the different atomic radius with Ti to improve the structural stability and mechanical properties of the alloys.According to the mixing enthalpy between the alloying element and the matrix titanium,combined with the effect of the alloying element,the position of the alloying element in the cluster structure model is determined,and a series of Ti-Zr-V-Nb alloys with constant V content and different Nb contents is designed,and the alloys are fabricated on the TA2plates by laser additive manufacturing.The microstructure,hardness,mechanical properties,wear resistance,corrosion resistance and forming properties of the as-fabricated alloys have been systematically studied.The results show that all as-deposited alloys consist of near-equiaxed?grains with multiple orientations,but the lattice constant of the phase enlarges and grain size reduces with the increase of Nb content.As a result,hardness and strength gradually increase,which in turn improves anti-abrasive wear capacity,causing an enhanced wear resistance.Ductility shows a completely opposite trend to strength since enhanced solid solution strengthening causes a decrease in plastic flow.Corrosion resistance is an increasing function of Nb content due to increased Nb2O5 formed in the passive film.A good combination of fluidity and spreadability of melt makes the alloy with 2.35 at.%Nb have the lowest surface roughness.The optimized alloy with 2.35 at.%Nb exhibits outstanding advantages in hardness,strength,wear and corrosion resistance,but it has slight decreases in ductility and forming property compared with Ti60.94Zr39.06 congruent alloy,being a promising candidate used for laser additive manufacturing. |
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