| Titanium alloys are widely used in aerospace,medical and military fields.Among them,high strength titanium alloys are widely used in aircraft landing gear,flaps,and hydraulic system and so on.However,high strength titanium alloys have low material utilization,long processing cycle and machining difficulties in traditional processing.Since the 1990s,the additive manufacturing,which has been emergence and continuous development,has provided an effective way to solve this problem.Plasma arc and wire additive manufacturing(PAAM)has vast potential in future industrial applications because of its advantages of high utilization rate of raw materials,low cost and short production cycle.In this paper,the RT-1400 alloy,which is high-strength titanium alloy,is taken as the research object,and the samples were prepared by plasma arc and wire additive manufacturing.The effect of process parameters,overlap rate and scanning strategy on the formability of the sample were studied by quadratic regression orthogonal experiment to determine the appropriate process parameters,overlap rate and scanning strategy.The heat treatment of the deposited state was carried out by solid solution and aging.The effects of different solid solution temperatures and different aging temperatures on the microstructure and mechanical properties of the alloy were clarified.The main conclusions are as follows:The quadratic regression orthogonal model is established to obtain that different process parameters have different effects on formability.The walking rate has the greatest influence on the melting width,but the interaction between the power and the walking rate has the least influence.For the melting height,the wire feeding speed has the greatest influence,but the walking speed has the least influence.For the aspect ratio,the interaction between power and wire feeding rate is the largest,and the influence of walking rate is the smallest.When the lap width is 5.3 mm,the lap effect of the deposition sample is good.The forming performance of the sample is improved by using parallel bead lap and frame constraint.There are obvious anisotropy of mechanical properties with the X and Z directions in the deposited samples.The ultimate tensile strength(UTS)in the X direction is 1194 MPa,and the elongation(EL)is 1.5%.The tensile strength(UTS)in the Z direction is 1154 MPa,and the elongation(EL)is 6.6%.There is noαphase precipitated in the upper part of the sample,andαphase precipitated in the middle and lower part.The cluster structures appear.Two kinds ofαphase,which are micron and nanoαphase,occurred in the middle part.The tensile strength of the alloy decreases with the increase of solution temperature,and the elongation increases in the range of 700～780°C and decreases in the range of 780～850°C.It was found that the original nanoscaleαphase completely disappeared after solution treatment,while the micron-sized crab-likeαphase changed into a regular short rod-likeαphase.At solution temperature of 780°C,the aspect ratio of short rod-likeαphase is small and densely distributed,which make the plasticity best.However,the proportion ofαphase and the interface decreases,which make the plasticity decreases with the solution temperature of 780～850°C.The strength increases and the plasticity decreases of the alloy after aging treatment.The precipitation of secondaryαphase with acicular like has a great influence on the strength.At the aging temperature of 500°C,because of the width ofα_p is the smallest and the aspect ratio is the largest,the tensile strength is the largest(UTS=1243MPa),meanwhile,the plasticity is the lowest(EL=1.2%).At the aging temperature of 600°C,the secondaryαphase with acicular like is not obviously precipitated,so theα_p plasticity is the best(EL=6%). |
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