| Near-α-type high-temperature titanium alloys not only have the thermal strength ofα-type titanium alloys,but also have the high plasticity of β-type titanium alloys,and have many advantages such as corrosion resistance,weldability,and low density,etc.It is widely used in aerospace and other fields,mainly as cold-end structural parts of engines.With the rapid development of technology,higher requirements are put forward for parts,such as complex structure,integrated forming,topological weight reduction,etc.,the traditional subtractive manufacturing process can no longer meet the above requirements,at the same time,the traditional process also has the disadvantages of long production cycle,high cost,and low material utilization rate.As one of the most potential additive manufacturing technologies,laser selective melting technology provides the possibility for the integration of complex parts and weight reduction.Therefore,it is of great significance to study the selective laser melting process of high-temperature titanium alloys.In this paper,the high-temperature titanium alloy powder used at 600 °C is used as the raw material,and the laser selective melting technology is used as the processing method to study the influence of laser power and scanning speed on the internal defects of the sample,and analyze the formation mechanism of different types of defects;study the microstructure change and tensile property change of the samples in different systems under the three states of formation,solid solution state and solid solution aging state,and clarify the relationship between process parameters,structure and performance.The research results show that when the laser power changes from low to high and the scanning speed changes from high to low,the defects change from unfused irregular holes to regular spherical holes.Irregular holes are caused by the phenomenon of spheroidization due to the low energy inside the molten pool and the inability of the powder to completely melt;the regular spherical holes are caused by the high energy inside the molten pool,which leads to the gasification of the molten metal and the entrainment of argon in the molten pool,which cannot escape in time.On this basis,the best process parameters were selected by comparing the formed structure and tensile properties: laser power 200 W,scanning speed 1250 mm/s,at this time,the tensile strength is 1353 MPa,the yield strength is 1218 MPa,the elongation is 9.5%,and the reduction of area is 32%.Formed internal organization is acicular martensite.Through solution treatment and solution aging treatment,the acicular martensite in the formed form is transformed into α phase and β phase,and a basket structure is obtained.As the solid solution temperature increases,the α phase in the structure gradually coarsens and transforms into a β phase,and the β phase gradually transforms into an α phase and a βtransformation structure during the subsequent cooling process;as the solution temperature increases,the tensile strength and yield strength of the samples gradually decrease,while the elongation increases.After solution aging treatment,the internal structure of the sample is more uniform,and there are precipitated phases that hinder the movement of dislocations,after aging,the strength of the sample increased obviously,but the plasticity decreased.Finally,it is considered that when the solution aging system is945 ℃/2 h,AC+720 ℃/8 h,AC,the comprehensive performance of the sample at room temperature and high temperature is the best Its tensile strength at room temperature is1138 MPa,yield strength is 1043 MPa,elongation is 15%,and cross-sectional expansion rate is 26%;Its tensile strength at 600 °C is 715 MPa,yield strength is 566 MPa,elongation is 16%,and cross-section shrinkage is 41%. |
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