"Oxygen Diffusion Hardening" (ODH) of titanium group elements and their tribological properties

氧化锆和钛合金用于摩擦学应用，如内窥镜修复术。这类材料的优点在于陶瓷表面提供了硬度、耐腐蚀和耐磨性，金属衬底保证了良好的延展性和韧性。缺点是有时涂层附着力差，这是在金属合金的常规氧化过程中出现的。在DFG的前身项目中，对ZrNb7锆合金的各种热处理工艺进行了更详细的研究，这些热处理工艺显著提高了镀层的附着力。这些方法基于位于氧化物层下方的氧扩散区，并改善氧化物与金属衬底的化学键合。这在文献中被称为氧扩散硬化（ODH）。除锆外，金属钛和铪在晶格中具有明显的氧溶解度，因此也适用于这种热处理工艺。然而，氧化钛合金的一个问题在于氧化层的缺陷密度很高，这些缺陷主要平行于金属表面。该项目的目的是研究三种系统对氧扩散硬化的适用性，并为此目的改善氧化层的机械性能。三种体系分别是：1)Ti6Al4V, 2) Ti6Al4V包覆Zr（通过粉末填料）和3)TiZrNbHfTa （20 at）。%)。Ti6Al4V是迄今为止最常用的钛合金。适当的氧扩散硬化可以显著改善该合金的摩擦学应用。由于热生长的氧化钛通常具有比二氧化锆更复杂的结构，并形成许多亚化学计量氧化物，另一种有前途的方法是使用粉末包装工艺在Ti6Al4V合金上涂覆锆。然后，氧扩散硬化应类似于当前项目Gl 181/41-1中所研究的合金ZrNb7。第三种体系是高度可变形的TiZrNbHfTa高熵合金，包含所有三种元素，具有明显的氧溶解度。这种合金在氧化过程中形成的近表层是特别有趣的。对于这三种体系，应制定合适的热处理参数，以提高层的附着力和耐磨性。后者在销/盘和圆柱/平试验台进行评估。热处理过程的数据将用于开发一个数学模型，该模型可以预测在给定温度和热处理时间下的层结构和各个层的厚度。

Oxidized zirconium and titanium alloys are used in tribological applications such as endoprosthetics. The advantage of this material class lies in the ceramic surface, which provides hardness, corrosion and abrasion resistance, and the metallic substrate, which ensures good ductility and toughness. A disadvantage is the sometimes poor coating adhesion, which arises during the conventional oxidation of the metallic alloys.In the DFG predecessor project, various heat treatment processes for the zirconium alloy ZrNb7 were examined in more detail, which significantly improve the layer adhesion. These methods are based on an oxygen diffusion zone which lies below the oxide layer and improves the chemical bonding of the oxide to the metallic substrate. This is described in the literature as Oxygen Diffusion Hardening (ODH). In addition to zirconium, the metals titanium and hafnium have a pronounced oxygen solubility in the lattice and are therefore also suitable for this heat treatment process. A problem with oxidized titanium alloys, however, lies in the high defect density of the oxide layers, which occur mainly parallel to the metal surface.The aim of this project is to investigate three systems for their suitability for oxygen diffusion hardening and to improve the mechanical properties of the oxide layers to this end. The three systems are 1) Ti6Al4V, 2) Ti6Al4V coated with Zr (via powder packing) and 3) TiZrNbHfTa (20 at.% each). Ti6Al4V is by far the most commonly used Ti alloy. A suitable oxygen diffusion hardening could significantly improve this alloy for use in tribological applications. Since thermally grown titanium oxides generally have a more complex structure than zirconium dioxide and form many substoichiometric oxides, another promising approach is to coat Ti6Al4V alloy with zirconium using a powder packing process. Oxygen diffusion hardening should then be applicable analogous to the investigated alloy ZrNb7 from the current project Gl 181/41-1. The third system, the highly deformable TiZrNbHfTa high entropy alloy, contains all three elements with pronounced oxygen solubility. The near-surface layers that form during the oxidation of this alloy are of particular interest.For all three systems suitable heat treatment parameters should be developed to improve both the layer adhesion and the wear resistance. The latter is evaluated in pin/disc and cylinder/flat test benches. The data from the heat treatment processes will be used to develop a mathematical model that can predict the layer structure and the thicknesses of the individual layers at a given temperature and heat treatment time.