Study On Microstructure And Properties Of Dual Wires Arc Additive Manufacturing Titanium Aluminum Alloys

Titanium and titanium aluminum alloys have the advantages of high temperature resistance and low density,it can be used to manufacture aircraft engine low-pressure turbine blades and other components.However,the plasticity of titanium aluminum alloy is extremely poor due to the exists of brittle phase,thus it is difficult to carry out subsequent machining.Additive manufacturing is a kind of near-net forming manufacturing technology,which can directly manufacture parts and components but decrease the subsequent machining problems.At present,the main method of Ti-Al alloy additive manufacturing is powder additive manufacturing while few researches on arc additive manufacturing technology in Ti-Al additive manufacturing.This is due to the brittleness of titanium aluminum alloy which makes it difficult to fabricate welding wire.Therefore,this paper adopts the method of dual wires arc additive manufacturing to make titanium aluminum alloy.Moreover,the technology of in situ alloying arc additive manufacturing was proposed based on this.In situ alloying arc additive manufacturing technology is used to increase the properties of the alloy by adding trace alloying elements into the deposited alloys.XRD,OM,SEM,TEM,high temperature oxidation test and micro mechanical tensile test were used to investigate the microstructure and properties of the deposited alloys.The necessity of inert gas protection in twin-wire arc additive manufacturing was firstly proved by taking Ti-15Al as the research object.After that,Ti-30Al,Ti-40Al,Ti-48Al(at.%)alloy was successfully manufactured by controlling the relative wire feeding speed.The continuous control of the composition and structure of the deposited alloy was realized.The micromechanical test results show that the Ti-15Al stacking sample has the best performance,with a tensile strength of about 685MPa and a elongation of about 3%.The mechanical properties of Ti-30Al,Ti-40Al and Ti-48Al alloys are poor due to the existence of microscopic cracks in the deposited samples.The reason of micro crack is that the microstructure of sample contains?₂phases.On the above basis,Ti-48Al-2Cr-2Nb(at.%)alloy and Ti-6Al-x Nb(x=0,4,7,10wt.%)alloy were deposited by in situ alloying arc additive manufacturing.The mechanical properties of Ti-48Al-2Cr-2Nb alloy were slightly improved compared with Ti-48Al alloy.In addition,as Ti-48Al-2Cr-2Nb alloy is a high temperature alloy,the high-temperature oxidation resistance of the alloy was tested.Meanwhile,Ti-15Al,Ti-30Al,Ti-40Al and Ti-48Al were compared as test subjects.The results showed that the oxidation resistance of the alloy increases with the increase of aluminum content.At the same time,the addition of trace chromium and niobium further enhanced the oxidation resistance of the alloy.After the 800°C-100h high-temperature test,the alloy gained 1.95mg/cm2 in weight and the oxide thickness was about 12?m.For Ti-6Al-x Nb alloy,the mechanical properties of the alloy were gradually enhanced with the increase of niobium content.When the niobium content was 7wt.%,the alloy had the best performance.Among them,the tensile strength of the transverse tensile specimen was 910MPa and the elongation was 7.26%,while the tensile strength of the longitudinal tensile specimen was 875MPa and the elongation was 6.21%.When the niobium content was 10wt.%,undissolved niobium foil was observed in the stacking sample.At the same time,the friction and wear properties of Ti-6Al and Ti-6Al-7Nb were tested.