Effects Of Re And C On The Microstructure And Properties Of Ta-W Based Refractory Alloy

Ta-W-based refractory alloys are used at significantly higher temperatures than other refractory alloys such as Nb-Mo and Ta-Nb,and are widely used in hot-end components such as rocket engines and hypervelocity vehicles.However,similar to other refractory alloys,the Ta-W-based alloy softens severely at high temperatures,so it is important to study and develop the theory and method of strengthening this alloy at high temperatures,which has scientific significance and engineering value.Two refractory alloys,Ta_1.9W_0.2 and NbTaW_0.4（in molar ratio）,were chosen as the matrix alloys.Ta_1.9W_0.2alloy is Ta-10W（wt.%）refractory superalloy which has been put into use.The desired alloys with homogeneous composition and dense structure were prepared by vacuum arc melting.This study investigated the effects of Re,C,and Re+C additions on the microstructure and properties of Ta_1.9W_0.2 and NbTaW_0.4 refractory alloys.The reinforcing mechanisms of Re and C on the matrix alloy were discussed.The results showed that:（1）Firstly,the effects of Re on the microstructure and mechanical properties of Ta_1.9W_0.2and NbTaW_0.4 alloys was investigated.A small amount of Re had no effect on the phases of the alloy,only exhibiting a weak grain refinement effect.However,at 1450℃,the yield strength of Re_0.1Ta_1.9W_0.2 was 2.25 times that of Ta_1.9W_0.2,and the yield strength of Re_0.1NbTaW_0.4 was 1.69 times that of NbTaW_0.4.Re significantly improved the high-temperature strength of the alloy while not affecting the room temperature ductility.The analysis concluded that Re had a strong solid solution strengthening effect and significantly increased the alloy’s solidus and recrystallization temperatures,thereby improving the alloy’s high-temperature mechanical properties.（2）The effect of C on the microstructure and mechanical properties of Ta_1.9W_0.2 and NbTaW_0.4 alloys was investigated.C significantly altered the microstructure of the alloys.The microstructure of Ta_1.9W_0.2C_0.25 and NbTaW_0.4C_0.25 alloys was a hypoeutectic structure,consisting of a fine BCC matrix and a large amount of BCC+Ta₂C eutectic structures at the grain boundaries,with dispersed secondary Ta₂C precipitates in the matrix.The addition of C greatly improved the room temperature and high-temperature strength of the alloys.At1450℃,the yield strength of Ta_1.9W_0.2C_0.25 was 2.02 times higher than that of Ta_1.9W_0.2 alloy,and the yield strength of NbTaW_0.4C_0.25 was 4.17 times higher than that of NbTaW_0.4 alloy.In addition,the addition of C did not significantly reduce the room temperature ductility of the alloys.The fracture strains of Ta_1.9W_0.2C_0.25 and NbTaW_0.4C_0.25 at room temperature were15.1%and 12.4%,respectively,significantly higher than those of other refractory alloys with similar strength levels.This is because Ta₂C is a ductile carbide,which can deform plastically at room temperature and coordinate with the matrix,effectively strengthening the matrix without significantly reducing ductility.（3）After adding both Re and C to Ta_1.9W_0.2 alloy,there was no significant difference in the microstructure compared to Ta_1.9W_0.2C_0.25 alloy.After adding both Re and C to NbTaW_0.4alloy,the primary carbide in the alloy transformed into a finer block-like hypoeutectic structure,and the secondary precipitated phases in the matrix become finer in size and smaller in number.The addition of both Re and C significantly improved the room temperature and high-temperature strength of the alloys.At 1450℃,the yield strength of Re_0.1Ta_1.9W_0.2C_0.25 was 4.12 times higher than that of Ta_1.9W_0.2 alloy,and the yield strength of Re_0.1NbTaW_0.4C_0.25 was 3.33 times higher than that of NbTaW_0.4 alloy.The fracture strains of Re_0.1Ta_1.9W_0.2C_0.25 and Re_0.1NbTaW_0.4C_0.25 at room temperature were 14.4%and 9.1%,respectively.Furthermore,the high-temperature strength of Re_0.1NbTaW_0.4C_0.25 was not as good as that of NbTaW_0.4C_0.25 alloy.Reducing the content of Re in the alloy could significantly improve the inhibitory effect of Re on carbides.This study provides a reference for the design and preparation of high-strength Ta-W-based refractory alloys and offers insights into the strengthening of other ultrahigh-temperature metallic materials.