脉冲频率和热输入对电弧增材制造TC4形貌和组织的影响

Influence of Pulse Frequency and Heat Input on Macrostructureand Microstructure of TC4 Titanium Alloy by Arc Additive Manufacturing

摘要:

粗大β柱状晶导致的各项异性是电弧增材制造TC4合金面临的主要问题。为解决上述问题,本文采用不同的脉冲频率和热输入成形了多组试样,并结合有限元分析,重点研究了热输入和脉冲频率对成形TC4形貌和组织的影响。结果表明：随着脉冲频率增加,试样宽度先是快速减小,随后略有增加,β晶粒由柱状晶转变为等轴晶,并且得到细化,但α相没有显著变化；提高热输入有利于获得等轴晶,但会增加试样的宽度,还会导致α相变得粗大。试样的宽度由熔池的尺寸决定,主要与平均热输入和峰值阶段输入的热量相关。提高脉冲频率能破碎树枝晶,降低温度梯度,有利于增加形核率,提高热输入也能降低温度梯度,因此能够获得等轴晶。α相形貌主要与相变时的冷却速度相关,降低热输入能增加冷却速度, 细化α相。

Abstract:

The anisotropy caused by columnar β grains are the main challenges in arc additive manufacturing of Ti-6Al-4V. In order to handle these issues, multilayer walls are deposited with different pulse frequencies and heat inputs. Combined with finite element analysis, the influence of pulse frequency and heat input on macrostructure and microstructure of deposited Ti-6Al-4V compounds are investigated. Results indicate that with the increase of pulse frequency, the widths of deposited walls decrease rapidly at first, then increase slightly; columnar β grains transform into equiaxed β grains and the grains get finer, but α phases have no obvious variation. The increasing heat input is beneficial to obtaining equiaxed β grains, but the wall width will enlarge and α phases will be coarser. The width of the specimen is determined by the dimension of the molten pool, which is influenced by the average heat input and the input heat in peak time period. Improving pulse frequency can break the dendrites as well as reduce the temperature gradient, which is conducive to the nucleation. Besides, higher heat input can reduce the temperature gradient as well. Therefore, equiaxed β grains are formed with the increase of pulse frequency and heat input. The morphology of α phases are mainly associated with the cooling rate. Reducing heat input can increase cooling rate and refine α phases.