Process Parameter Optimization and Microstructure and Property Investigation in Laser Cladding of Ti60 Alloy
Objective Ti60 is a near-α titanium alloy with good high-temperature performance that has been identified as an important candidate material for aero-engine compressor blades and integral blades.However,when high-temperature titanium alloys are fabricated using traditional processing technology,it has the disadvantages of difficult formation,low material utilization,and high cost.Laser cladding technology uses a laser with high energy density to melt the powder preset on the surface of the substrate,so as to obtain the expected performance of the cladding layer.There are many parameters of the laser cladding process that have significant influence on the forming quality.At the same time,complex thermal cycling in the laser cladding process leads to differences in the grain size,morphology,and size of the precipitated phase,which makes the differences in the mechanical properties of the laser cladding significant.Therefore,this paper mainly studies the effect of the process parameters on the forming quality of laser cladded Ti60 alloy,and the microstructure evolution and tensile properties of laser cladded Ti60 alloy are analyzed to lay a theoretical foundation for the application of laser cladded high-temperature titanium alloy components in the aerospace field.Methods The material selected in this experiment is Ti60 powder with a particle size of 50-150 μm,prepared using the plasma rotating electrode process(PREP).TC4 titanium alloy is used as the substrate,and the laser cladding system is used as the laser cladding experiment system.The section of the laser cladded sample along the thickness direction of the cladding layer is machined via electric discharge wire cutting into a flake sample with a thickness of 5 mm for the metallographic sample.The Kroll reagent is then used for etching,and finally,the microstructure is observed using a metallographic microscope and field emission scanning electron microscope(SEM).A field emission transmission electron microscope(TEM)is used to analyze the precipitated phase of the cladding specimen.A microhardness tester is used to test the Vickers hardness of the Ti60 cladded sample from top to bottom.The tensile experiment is performed on the high-temperature tensile test machine at room temperature,300 ℃,and 600 ℃,with a tensile speed of 1.0 mm/min.The tensile fracture is observed,and the fracture morphology and fracture mode are analyzed.Results and Discussions The influence of different factors on the size of the laser cladding layer is analyzed according to the shape and size of the cladding layer measured by the image scanner.When the width of the molten pool is large,the cladding efficiency can be effectively improved,the material utilization rate can be improved,and the cost can be reduced.The thickness of the cladding layer has a significant influence on deposition along the height of the cladding layer(Fig.5).The microstructure at the top region of the cladded sample is the thin layer of equiaxed grain,and its grain size gradually increases with increasing laser power.In the central region of the sample,the original β grains can be observed growing in the deposition direction along the epitaxial columnar pattern across multiple cladding layers.Moreover,the larger the laser power,the coarser the columnar grains and the microstructure inside the grains(Fig.6).The sample of the laser cladded Ti60 block is mainly composed of a netted basket of lath α and interlath β phases.There are white Ti5Si3 phases with different shapes on the slat α,and the content of the Ti5Si3 phase gradually decreases from the bottom to the top(Fig.9).At room temperature,the tensile strength and yield strength of the laser cladded Ti60 samples are 1128 MPa and 1035 MPa,respectively,and the elongation and section shrinkage are 8.8％and 14.4％,respectively.At 300 ℃,the tensile strength and yield strength are 932 MPa and 796 MPa,respectively,and at 600 ℃,the tensile strength and yield strength are 739 MPa and 627 MPa,respectively(Fig.12).Conclusions The microstructure at the bottom and top regions of the laser cladded Ti60 alloy sample is composed of β equiaxed grains,and the middle region is composed of β columnar crystals.Its size gradually increases with increasing laser power.The microstructure is mainly composed of lath α and interlath β phases,and there is a large amount of the white precipitated phase in the lath α phase.With an increase in laser power,the microstructure changes from a net basket structure to a Weisberg structure.The micro-hardness distribution of the bulk sample is uniform,and its hardness value fluctuates in the range 420-440 HV.The tensile strength of laser cladded Ti60 alloy at room temperature is 1128 MPa,and the elongation and section shrinkage after fracture are 8.8％and 14.4％,respectively.When the temperature is 300 ℃ and 600 ℃,the tensile strength is 932 MPa and 739 MPa,respectively.
laser techniqueTi60 high temperature titanium alloylaser claddingprocess parameter optimizationmicrostructuretensile property
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