Effect Of Yb Addition On Microstructure And High Temperature Properties Of TiAl Alloy

TiAl alloy has the advantages of high specific strength,low density,high specific modulus of elasticity at high temperature,good creep resistance,oxidation resistance and corrosion resistance,etc.It is expected to replace nickel-based alloys as a lightweight high-temperature structural material at 600～900℃ for aerospace,weaponry,automotive and other fields with promising applications.However,its poor mechanical properties and insufficient high-temperature oxidation resistance have greatly restricted the development and wide application of TiAl alloys.Therefore,it is important to improve the mechanical properties and high temperature oxidation resistance of TiAl alloys for the development of TiAl alloys.In this paper,Ti-45Al alloy was prepared by discharge plasma sintering,and different contents of rare earths Yb₂O₃and YbB₆were added to study the effects of different rare earths on the organization and properties of titanium-aluminum alloy.The fracture mechanism of titanium-aluminum alloy was investigated by compressive stress-strain curves and compressive fracture morphology.Frictional wear experiments were conducted to determine the friction coefficient and frictional wear surface morphology,and to analyze the wear mechanism.The composition,structure and morphology of the oxidation film of titanium-aluminum alloy were studied by the oxidation weight gain method.And its antioxidation mechanism was elucidated.The experimental results showed that:The two rare earths,Yb₂O₃/YbB₆,and the various addition contents of each have a substantial impact on the microstructure,mechanical characteristics,and high-temperature oxidation resistance of titanium-aluminum alloy.When rare earths are introduced to the alloy in the form of Yb₂O₃,among them,Ti-45Al-0.7Yb₂O₃alloy has the best overall performance.The grain refinement effect is the best（3.39μm）,which is 43.3%higher than that of Ti-45Al alloy（5.98μm）.And the microhardness reaches 458HV_0.1,which is 22.5%higher than that of Ti-45Al alloy(374HV_0.1),and the compressive strength is 2314MPa,which is 38.4%higher than that of Ti-45Al alloy（1671MPa）.Frictional wear experiments show that the alloy(1.73mm²·N^-1)has a low wear rate,which is 29.67%lower than that of Ti-45Al alloy(2.47mm²·N^-1),and the frictional wear resistance is also effectively improved.The oxidation mass gain is only 10.9g after 100h high temperature oxidation at 800℃,which is 25.1%lower compared to Ti-45Al alloy（14.6g）.The rare earth oxide Yb₂O₃in the alloy with Yb₂O₃is mainly distributed diffusely along the grain boundaries in the form of dots,with its content increasing,there is a tendency to gather into blocks,which is detrimental to its performance;When rare earths were added to the alloy in the form of YbB₆,among them,Ti-45Al-0.3YbB₆alloy had the best overall performance.The best grain refinement（2.23μm）was achieved,which improved 62.7%compared to Ti-45Al alloy（5.98μm）.The microhardness is 431 HV_0.1,which is 15.2%higher than that of Ti-45Al alloy,and the compressive strength is 2580 MPa,which is 54.4%higher than that of Ti-45Al alloy.Frictional wear experiments show that the alloy has a low wear rate(1.60mm²·N^-1),which is34.96%lower than that of Ti-45Al alloy,and the antifrictional wear performance is effectively improved.The oxidation weight gain is only 6.4g after 100h high temperature oxidation at 800℃,which is 56.0%lower compared to Ti-45Al alloy.Hard particles TiB and rare earth oxides Yb₂O₃generated due to in-situ reaction occur in the addition of YbB₆alloy.During the spark plasma sintering process,Yb in YbB₆absorbs oxygen from the alloy to generate Yb₂O₃,which purifies the matrix and has the effect of oxide dispersion strengthening.At the same time,the second phase TiB is generated,which has a very good effect of fine grain strengthening.