放电等离子烧结Ti-47.5Al-6.8Nb-0.2W-xY合金高温压缩蠕变行为及机理研究

High-Temperature Compression Creep Behaviour and Mechanism of Ti-47.5Al-6.8Nb-0.2W-xY Alloy by Spark Plasma Sintering

摘要:

采用高能球磨（high-energy ball milling，HEM）和放电等离子烧结（spark plasma sintering，SPS）工艺制备Ti-47.5Al-6.8Nb-0.2W-xY（x=0，0.1，0.2，at%）合金，通过SEM、EBSD、TEM等研究Y微合金化对Ti-47.5Al-6.8 Nb-0.2W合金高温压缩蠕变性能的影响，分别在800~850 ℃进行蠕变试验，应力为250 MPa，时间为50 h。结果表明：Ti-47.5Al-6.8Nb-0.2W-xY合金均由等轴γ晶粒、γ晶界的块状α₂和B2相、α₂/γ片层团组成。添加的Y主要以Al₂Y颗粒的形式在晶界处形成链状结构，Y能细化晶粒并增大α₂/γ片层团，Y含量由0增至0.2at%时，晶粒尺寸从12.1 μm减小至7.8 μm，细化效果最为显著。在蠕变后合金中γ晶粒轻微扁平化，片层发生弯曲和退化现象，片层团内部出现大量细小的再结晶晶粒及球状B2相，蠕变温度升高促进动态再结晶形成。Y的加入显著提高合金的压缩蠕变性能，在800 ℃下，0.2Y合金的最大蠕变应变为8.96%，稳态蠕变速率为4.01×10^–7 s^–1，与无Y合金相比分别降低了32.83%和38.31%。合金力学性能的改善是由于Al₂Y颗粒的第二相强化、片层细化和B2相的减少。

Abstract:

Ti-47.5Al-6.8Nb-0.2W-xY (x=0,0.1,0.2, at%) alloys were prepared by high-energy ball milling and spark plasma sintering processes, and the effects of Y microalloying on the high-temperature compression creep properties of Ti-47.5Al-6.8 Nb-0.2W alloys were investigated by SEM, EBSD and TEM. Creep experiments were carried out at 800–850 ℃, with a stress of 250 MPa and a time of 50 h. The results show that the Ti-47.5Al-6.8Nb-0.2W-xY alloys are all composed of equiaxial γ grains, the bulk α₂ and B2 phases at γ grain boundaries, and α₂/γ lamellar colonies. The added Y mainly exists in the form of Al₂Y particles at the grain boundaries to form a chain structure and Y can refine the grains and increase the α₂/γ lamellar colonies. When the Y content is increased from 0 to 0.2at%, the grain size is reduced from 12.1 μm to 7.8 μm, exhibiting the most significant refining effect. After creep, γ grains in the alloy are slightly flattened, accompanied by lamellar bending and degradation phenomena, and a large number of fine recrystallized grains and spherical B2 phase appear within the lamellar clusters. Creep temperature increase can promote the formation of dynamic recrystallisation. The addition of Y significantly improves the compressive creep properties of the alloy. At 800 ℃, the maximum creep strain of the 0.2Y alloy is 8.96%, and the steady creep rate is 4.01×10^–7 s^–1, reduced by 32.83% and 38.31% compared with those of the alloy without Y, respectively. The improvement in the mechanical properties of the alloys is attributed to the precipitation strengthening of the second phase Al₂Y particles, lamellar refinement, and reduction of the B2 phase.