Kinetic aspects of aluminium titanate layer formation on titanium alloys by plasma electrolytic oxidation
Kinetic aspects of aluminium titanate layer formation on titanium alloys by plasma electrolytic oxidation
复制标题
DOI：
10.1016/s0169-4332(02)00848-6
复制
发表时间：
2002-11
影响因子：
6.7
通讯作者：
A. Yerokhin;A. Leyland;A. Matthews
中科院分区：
文献类型：
--
作者：
A. Yerokhin;A. Leyland;A. Matthews
本文系统研究了工艺参数对Ti-6Al-4V合金在0.05-0.2moll− 1铝酸钠溶液中等离子体电解氧化（PEO）表面层生长动力学的影响，以及表面层结构、相组成和力学性能的相关变化。采用重量分析、SEM和XRD分析以及显微硬度和划痕测试等方法研究了表面层的传质和相结构变化。层形成的可能机制进行了讨论，其中包括钛电极的电化学氧化的OH−阴离子，辅以化学沉淀的Al（OH）3和等离子体诱导的表面放电中的转换。在总收率为20- 30%的条件下，这些工艺导致主要形成Al_2TiO_5相，并具有Al_2TiO_5·TiO_2和3Al_2TiO_5·Al_2O_3共晶的非均相沉淀。该组织中富Al和富Ti组元的硬度分别为1050-1480和300- 845 HK，0.02。膜层生长速率随电解液浓度的增加而增加，膜层最大厚度超过60μm，表面粗糙度（Ra）为3-4μm。将电解液pH从12.0增加到12.8导致表面层的平滑和增厚，但样品增重较低，这与Ti电氧化过程的增强有关。PEO形成的表面层的过程中的形态变化包括逐渐转变的原始细粒度的，但多孔的结构到一个致密的，融合的形态，这是由放电引起的热应力的不利影响，导致层的粘附强度的退化。
The paper reports on a systematic investigation into the effects of process parameters on the growth kinetics and associated changes in the structure, phase composition and mechanical properties of surface layers formed on Ti–6Al–4V alloy by plasma electrolytic oxidation (PEO) treatment in 0.05–0.2moll−1solutions of sodium aluminate. Methods of gravimetric, SEM and XRD analysis, as well as microhardness and scratch testing, are employed to investigate mass transfer and phase-structure transformations in the surface layer. The probable mechanisms of layer formation are discussed, which comprise electrochemical oxidation of the Ti-electrode by OH−anions, complimented by chemical precipitation of Al(OH)3and plasma-induced transformations in the surface discharges. Running with a total yield efficiency of 20–30%, these processes lead to the formation of predominantly the Al2TiO5phase with heterogeneous precipitation of Al2TiO5·TiO2and 3Al2TiO5·Al2O3eutectics. Al- and Ti-enriched constituents of this structure show hardnesses of 1050–1480 and 300–845HK,0.02, respectively. The layer growth rate increases with increasing electrolyte concentration, providing a maximum thickness of over 60μm and a surface roughness (Ra) of 3–4μm. Increasing the electrolyte pH from 12.0 to 12.8 results in smoothing and thickening of the surface layer but a lower sample weight gain, associated with an enhancement of the Ti electro-oxidation process. Morphological changes during PEO formation of the surface layer include gradual transformation of the original fine grained but porous structure into a dense, fused morphology which is adversely affected by discharge-induced thermal stresses, causing a degradation of the layer adhesion strength.