退火处理对粉末冶金Ti2AlNb合金电子束焊接接头显微组织和拉伸性能的影响

Influence of Annealing on Microstructure and Tensile Properties of Electron Beam Weldment of Powder Metallurgy Ti2AlNb Alloy

摘要:

研究了焊态和退火处理态粉末冶金Ti2AlNb合金电子束焊接接头的显微组织与拉伸性能。结果表明，焊态下熔合区为单一B2相，由粗大的柱状晶和等轴晶组成。经800 ℃~900 ℃焊后退火处理后，熔合区B2相内析出板条O相，形成O+B2相两相结构，随着退火温度升高，熔合区内O相尺寸增加，O相体积分数变化不大。焊接接头中熔合区显微硬度高于母材，焊后退火处理后，熔合区显微硬度升高，随着退火温度升高，熔合区显微硬度逐渐降低。焊态下，焊接接头表现出较高的室温拉伸强度和塑性，但在650 ℃高温拉伸时，焊接接头试样在未达屈服点时即在熔合区发生脆性断裂。经焊后退火处理，焊接接头室温拉伸强度和塑性未略有降低，高温拉伸强度和塑性均显著改善，高温拉伸强度和塑性随退火温度升高而逐渐增加。

Abstract:

Annealing treatments in the temperature range of 800℃ to 900℃ was applied to the electron beam weldments of powder metallurgy Ti2AlNb alloys to investigate its influence on microstructure and tensile properties at room temperature and 650℃. The results show that there are coarse columnar and equiaxed B2 grains in the fusion zone (FZ) in the as-welded weldments. Transformation from B2 phase to O+B2 phase occurs in the FZ during the post-weld annealing treatments. The morphology of the O phase is characterized as the basket-weave structure and the size of the O phase plate increases with the increase of the annealing temperature. The microhardness in the FZ of the as-welded weldments are higher than that in the base metal (BM). After the annealing treatments, the microhardness in the FZ increases significantly, which gradually decreases with the increase of annealing temperature. At room temperature, all tensile speciems are fractured in the FZ. The tensile strength of the as-welded weldments is close to that of the BM and local large plastic deformation occurs in the FZ. However, the strength and ductility of the weldments decrease slightly after the post-weld annealing treatment. At 650℃, most of the tensile speciems are fractured in the FZ. The as-welded weldments are failured in the FZ, which are characterized as brittle intergranular fracture. After the annealing treatments, there is an apparent improvment of strength and ductility in the FZ of the weldments. With the annealing temperature increasing up to 900 ℃, the failured locations are shifted from the FZ to the BM.