连续冷却条件下Ti-1300合金的组织演变与连续转变图

Microstructural Evolution and Continuous Cooling Transformation Diagram in Ti-1300 Alloy under Continuous Cooling Condition

摘要:

通过OM、SEM、TEM和EBSD研究了Ti-1300合金在连续冷却条件下组织演变规律和亚稳β相的分解形式,并采用高精度膨胀法建立了合金的连续冷却转变动力曲线。结果表明：当连续冷却速度比较缓慢时,Ti-1300合金发生β → α + β转变,并获得集束状的显微组织；而当冷却速度0.3 °C/s ＜v＜ 1.5 °C/s时,Ti-1300合金发生β → α + β + β_m,并获得细针状的α + β组织和残余的β_m相；当冷却速度大于3 °C/s时,Ti-1300合金基本获得全部β相,所以把3 °C/s认为是合金的临界冷却转变速度。在缓慢冷却过程中,Mo当量梯度是合金中α相生长主要动力。随着冷却速度的增加,Ti-1300合金的显微硬度先增加后降低,在冷却速度为0.3 °C/s时,显微硬度达到最大值。

Abstract:

Microstructural evolution of Ti-1300 alloys was investigated using an optical microscopy, scanning electron microscopy, transmission electron microscopy and electron backscatter diffraction during continuous cooling. Then, a continuous cooling transformation diagram was established using dilatometric method, and the different kinds of β phase decomposition modes in the alloy under continuous cooling were investigated in detail. Moreover, the β → α + β phase transformation and colony structures are observed for low cooling rates. When the cooling rate is from 0.3 °C/s to 1.5 °C/s, the β → α + β + β_m phase transformation and needle-like structures are observed in the alloy. However, when the cooling rate exceeds 3 °C/s, the alloy is only composed of a single metastable β phase. Thus, a rate of 3 °C/s is considered as critical cooling rate of the alloy under continuous cooling condition. The concentration gradient of molybdenum equivalent is considered as a driving force of α phase growth in the alloy.The microhardness of the alloy initially increases and then decreases with increasing of the cooling rate. When the cooling rate is 0.3 °C/s, the microhardness of the alloy reaches its maximum.