Electrochemical dissolution and passivation of laser additive manufactured Ti6Al4V controlled by elements segregation and phases distribution

元素偏析和相分布控制的激光增材制造Ti6Al4V合金的电化学溶解与钝化

The electrochemical dissolution and passivation of laser additive manufactured Ti6Al4V were investigated through Tafel polarization,potentiostatic polarization and AC impedance measurements.The results show that the solution treatment−aging(STA)process aggravates the element micro-segregation compared to the annealing process,leading to varied Al and V contents of the phases from different samples.It is proven that either Al-rich or V-rich condition can highly affect the electrochemical dissolution behaviors due to thermodynamical instability caused by element segregation.The dissolution rate in the metastable passivation process is controlled by the stability of the produced film that is affected by phases distribution,especially the difficult-to-dissolve phase.And then,the dissolution rate of the phases in the transpassivation region is consistent with the rank in the activation process because the dense film is not capable of being produced.Compared to the annealed sample,the higher dissolution rate of the STA sample is beneficial to the electrochemical machining(ECM)of Ti6Al4V.

采用Tafel极化、恒电位极化和交流阻抗测试研究激光增材制造Ti6Al4V合金的电化学溶解和钝化。结果表明,与退火处理相比,固溶时效(STA)加剧元素的微观偏析,导致不同样品中相的Al和V含量不同。由元素偏析导致的热力学不稳定性决定富Al或富V条件对相的电化学溶解行为有显著影响。亚稳钝化过程中的溶解速率是由生成膜的稳定性控制,该稳定性受相分布的影响显著,尤其是难溶解相。在过钝化区中合金表面不能产生致密的钝化膜,因此,相的溶解速率与活化过程排序一致。与退火试样相比,STA试样具有较高的溶解速率,有利于Ti6Al4V的电解加工。