高强韧TC4-0.55Fe钛合金低温冲击韧性及断裂机理研究

Low-Temperature Impact Toughness and Fracture Mechanisms of a High-Strength, High-Toughness TC4-0.55Fe Titanium Alloy

摘要:

钛合金凭其优异的耐蚀性和低温力学性能,是极地资源开发,北极航路运输等极端工况应用重大装备的理想结构材料。为了进一步提高钛合金的低温韧性,研究钛合金低温断裂失效机理,本文采用Fe微合金化方法制备了TC4-0.55Fe钛合金,系统研究了其在20~-196 °C范围内的冲击性能及断裂机制。结果表明：TC4-0.55Fe钛合金在常温下的低温韧性达到66.75J/cm₂^{。随着温度减低至}-20℃,低温韧性没有发生任何改变。当温度继续下降至-70℃时,低温韧性开始降低,达到46.75J/cm₂^,当温度降至-196 °C时,冲击韧性仍保留有25.1 J/cm2,较TC4钛合金提升23.8%。扫描断口分析显示,-196 °C仍未达到该合金的韧-脆转变温度。通过EBSD表征发现,各温度下裂纹附近均有显著数量的孪生行为,且温度越低,孪晶密度越高。分析表明：TC4-0.55Fe合金优异的冲击韧性主要归因于细晶强化、β基体中弥散分布的细小针状αs相,以及低温下孪晶密度显著增加的协同作用,三者共同诱导裂纹扩展路径偏转,显著提升抗断裂能力。

Abstract:

Because of their exceptional corrosion resistance and superior low-temperature mechanical properties, titanium alloys are ideal structural materials for critical equipment operating under extreme conditions, such as Arctic resource exploitation and polar shipping routes. To further enhance low-temperature toughness and clarify the fracture–failure mechanisms of titanium alloys, a TC4-0.55Fe alloy was produced by micro-alloying with Fe, and its impact performance and fracture behavior were systematically investigated over the temperature range 20?°C toS?196?°C. The alloy exhibits a room-temperature Charpy impact toughness of 66.75?J?cm?2, which remains unchanged down to ?20?°C. When the temperature is lowered to ?70?°C, the toughness decreases to 46.75?J?cm?2, and at ?196?°C it still retains 25.1?J?cm?2—representing a 23.8?% improvement over conventional TC4. Scanning electron fractography confirms that ?196?°C is still above the alloy’s ductile–brittle transition temperature. EBSD characterization reveals abundant deformation twinning in the vicinity of the crack at all test temperatures, with twin density increasing markedly as temperature decreases. The outstanding impact toughness of the TC4-0.55Fe alloy is attributed to the synergistic effects of grain refinement, the dispersion of fine acicular α_s precipitates within the β matrix, and the pronounced rise in twin density at low temperature; together they promote crack-path deflection and significantly enhance resistance to fracture.