Effect of double annealing on microstructure and mechanical properties of near-α titanium alloys
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摘要: Ti6321 合金作为我国自主研制的近 α 型钛合金，凭借高强度、高韧性及优异耐海水腐蚀性能成为海洋工程关键结构材料。然而常规热处理下其强度与塑性难以兼顾，限制了在深海极端环境中的应用。以舰船用 Ti6321 钛合金为研究对象，通过设计退火（970、980、990、
1000 ℃保温 2 h 空冷）与双重退火（980 ℃保温 2 h 空冷后，再经 550 ℃或 600 ℃保温 2 h 空冷）工艺，结合光学显微镜（OM）观察及力学性能测试，系统探究了退火工艺对合金组织及力学性能的影响规律。结果表明：退火时，Ti6321 合金呈现 α+β 两相区组织演变特征，980 ℃时强韧性匹配最优；双重退火通过在 β 转变组织晶内及晶界析出次生 α 相实现组织细化，其中 980 ℃+550 ℃处理可显著提升强度和韧性。研究为海洋工程用Ti6321合金热处理工艺优化提供了理论依据。Abstract: Ti6321 alloy, a near-α titanium alloy independently developed in China, has become a key structural material for marine engineering because of its high strength, high toughness and outstanding seawater-corrosion resistance. Nevertheless, under conventional heat treatment its strength and ductility are difficult to balance, restricting its use in deep-sea extreme environments. In this work, ship-grade Ti6321 alloy was subjected to single annealing (970, 980, 990, 1000 ℃ for 2 h, air cooled) and duplex annealing (980 ℃ for 2 h, air cooled, then 550 ℃ or 600 ℃ for 2 h, air cooled). The effects of these annealing routes on microstructure and mechanical properties were systematically investigated by optical microscopy (OM), scanning electron microscopy (SEM) and mechanical testing. The results revealed that single annealing produced the typical α+β two-phase microstructural evolution, with the best strength–toughness combination obtained at 980 ℃. Duplex annealing refined the microstructure by precipitating secondary α phases within and along the boundaries of the β-transformed structure, annealing treatment at 980 ℃ + 550 ℃ markedly increased both strength and toughness. This study provides a theoretical basis for optimizing the heat treatment process of Ti6321 alloy for marine engineering applications.-
Key words:
- titanium alloy /
- double annealing /
- dual-phase microstructure /
- mechanical properties
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图 3 样品各个方向初始组织形貌
(a)轴向AD; (b)径向RD; (c)切向TD
Figure 3. Initial microstructure of the sample in different directions
图 4 970～
1000 ℃不同温度退火后不同方向组织形貌Figure 4. Microstructures after annealing at different temperatures (970-
1000 ℃)(a)(d)(g)(j) RD; (b)(e)(h)(k) AD; (c)(f)(i)(l) TD
图 5 970～
1000 ℃不同温度退火相组成Figure 5. Phase composition at different annealing temperatures (970-
1000 ℃)
图 6 970～
1000 ℃不同温度退火力学性能(a)抗拉强度;(b)屈服强度;(c)冲击功
Figure 6. Mechanical properties after different annealing temperatures (970-
1000 ℃)
图 7 980 ℃单次退火和不同双重退火条件下各方向组织形貌
Figure 7. Microstructural morphology in various orientations under single annealing at 980 °C and different double annealing conditions
(a)(d)(g): RD; (b)(e)(h): AD; (c)(f)(i): TD
图 8 980 ℃单次退火和不同双重退火条件下不同方向组织SEM图
Figure 8. SEM images of microstructures in different orientations under single annealing at 980 °C and various double annealing conditions
(a)(d)(g): RD; (b)(e)(h): AD; (c)(f)(i): TD
图 10 单次退火和不同双重退火温度力学性能
(a)抗拉强度; (b)屈服强度; (c)冲击功
Figure 10. Mechanical properties of single annealing and different double annealing temperatures
图 11 双重退火组织演变机理
Figure 11. Mechanism diagram of dual annealing microstructure evolution
表 1 Ti6321合金成分
Table 1. The composition of Ti6321 alloy
Al Nb Zr Mo Fe Si Ti 6.22 3.15 2.17 1.20 0.03 <0.03 balance 
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