三重热处理对热变形后TC4-DT合金微观组织的影响

Effect of triple heat treatment on microstructure of TC4-DT titanium alloy after thermal deformation

TC4-DT钛合金经高温恒应变速率变形后,进行三重热处理,具体工艺为：（920~960℃）×1 h水冷（WQ）＋（880~920）℃×1h WQ＋820℃×1.5 h空冷（AC）,观察热处理后的微观组织。结果表明：TC4-DT钛合金950℃变形后,第一重热处理温度越高,初生等轴α相含量越少,在温度为920℃时由等轴α相、针状α＇相及β基体组成,960℃时等轴α相完全消失;第二重热处理中,初生α相有减少的趋势,温度越高,减少越快。第二重热处理温度对次生条状α相含量及最终形态也有影响,当二重热温度为920℃时得到的条状α组织更为粗大;经过第三重热处理,条状α相的间距均匀,在条状一次次生α相之间分布有更加细小的二次次生α相。因而采用不同条件的多重热处理制度可以调节材料的微观组织,包括次生α的长度、宽度及次生α片层的数量等,从而可以优化TC4-DT钛合金的微观组织。TC4-DT钛合金950℃高温变形后,经960℃×1 h WQ＋880℃×1 h WQ＋820℃×1.5 h AC热处理,得到细小均匀的网篮组织;经940℃×1 h WQ＋920℃×1 h WQ＋820℃×1.5 h AC热处理,得到双态组织。

The effect of triple heat treatment on microstructure of TC4-DT titanium alloy after thermal deformation at high temperature was studied. The results show that, primary equiaxed α phase in TC4-DT titanium alloy decreases with increase of the first heat treatment temperature after thermal deformed at 950 ℃. The microstructure of alloy composes of equiaxial α-phase, acicular a prime and β matrix when the temperature is 920 ℃ ,and the equiaxial a phase totally disappears with acicular α prime and β matrix left when the temperature reached 960 ℃ ;while the primary α-phase decreases during the second heat treatment： the higher the temperature, the faster the reduction. The temperature of the second heat treatment also has a great influence on the content and the final form of secondary strips of a phase. The α banded structure will becomes thicker and bigger when the temperature of second heat treatment is 920 ℃. After the third heat treatment, there are more tiny next secondary a phase distribute between the strip primary secondary of α phase with the space of stripe α phase becomes well-distributed. Thus the use of multiple heat treatment can be adjusted microstructure of the materials in different conditions, including the length, width and the number of secondary α sheets, which can optimize the microstrueture of TC4-DT titanium alloy. The thin and uniform basket-weave microstructure can be obtained via the method 960 ℃ × 1 h WQ ＋ 880 ℃ × 1 h WQ ＋ 820 ℃ × 1.5 h AC thermal treatment after 950 ℃ high temperature deformation of TC4-DT alloy. The duplex structure results from 940 ℃ × 1 h WQ ＋920 ℃ × I h WQ ＋ 820 ℃ × 1.5 h AC heat treatment.