热处理对TC4-0.55Fe钛合金管材力学性能的影响

Effect of Heat Treatment on Mechanical Properties of TC4-0.55Fe Titanium Alloy Tube

摘要:

以斜轧穿孔（RP）TC4-0.55Fe钛合金无缝管为研究对象，通过固溶时效工艺调控微观组织，对其进行室温拉伸和 –20 ℃冲击性能测试，结合SEM、XRD、TEM等分析组织演变对力学性能的影响。结果表明，RP试样的变形魏氏组织在两相区固溶时效（STA910）后，α_C尺寸和α_L平均晶粒厚度显著增大，组织取向性和均匀性也显著增强。RP试样的抗拉强度、屈服强度和断后伸长率分别为904±1.23 MPa、793±2.62 MPa和(14.2±0.72)%，在–20 ℃冲击功与冲击韧性值分别达到66.2±1.62 J和82.7±1.03 J/cm²。两相区固溶时效后，STA910试样的抗拉强度、屈服强度和断后伸长率分别升高到984±8.92 MPa、904±9.93 MPa和(16.2±0.93)%，–20 ℃冲击功和冲击韧性略有下降，但仍然保持在52.8±1.77 J和64.9±1.78 J/cm²。STA910试样通过固溶时效析出α_S和ω相增加了α/β界面，增大位错滑移和运动阻力的同时改善了合金元素的偏析现象，达到了晶界强化和固溶强化的双重效果，从而同时提高了合金的强度和塑性。另一方面，所有状态的TC4-0.55Fe合金均表现出优异的冲击韧性，合金的断裂方式以韧性断裂和穿晶断裂为主，α相晶粒尺寸的粗化和β相稳定性的下降及β_t中α_S和ω相析出的综合影响导致合金冲击性能的下降。

Abstract:

The cross piercing (RP) TC4-0.55 Fe titanium alloy seamless tube was taken as the research object. The microstructure was controlled by solid solution and aging treatments. The tensile properties at room temperature and impact properties at –20 ℃ were tested. The effects of microstructure evolution on mechanical properties were analyzed by scanning electron microscope, X-ray diffractometer, and transmission electron microscope. The results show that the size of α_C and the average grain thickness of α_L increase significantly, and the orientation and uniformity of the microstructure are also significantly enhanced. The tensile strength, yield strength, and elongation of RP samples are 904±1.23 MPa, 793±2.62 MPa and (14.2±0.72)%, respectively. The impact energy and impact toughness at –20 ℃ are 66.2±1.62 J and 82.7±1.03 J/cm², respectively. After solution and aging in the two-phase region, the tensile strength, yield strength, and elongation of STA910 sample increase to 984±8.92 MPa, 904±9.93 MPa and (16.2±0.93)%, respectively. The impact energy and impact toughness at –20 ℃ decrease slightly, but still maintain at 52.8±1.77 J and 64.9±1.78 J/cm², respectively. The α/β interface is increased by the precipitation of α_S and ω phases in the STA910 sample, which increases the dislocation slip and motion resistance and improves the segregation of alloying elements. The dual effects of grain boundary strengthening and solid solution strengthening are achieved, thus improving the strength and plasticity of the alloy. On the other hand, all TC4-0.55Fe alloys show excellent impact toughness. The fracture modes of the alloys are mainly ductile fracture and transgranular fracture. The coarsening of α phase grain size, the decrease in β phase stability, and the precipitation of α_S and ω phases in β_t lead to the decrease in impact properties of the alloys.