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

氧化的锆和钛合金用于摩擦学应用，例如内假体。这类材料的优势在于陶瓷表面，它提供了硬度，耐腐蚀性和耐磨性，以及金属基底，它确保了良好的延展性和韧性。缺点是有时涂层附着力差，这在金属合金的常规氧化过程中会出现。在DFG的前身项目中，对锆合金ZrNb 7的各种热处理工艺进行了更详细的研究，这些工艺显著提高了涂层附着力。这些方法基于氧扩散区，该氧扩散区位于氧化物层下方并改善氧化物与金属基底的化学键合。这在文献中被描述为氧扩散硬化（ODH）。除了锆之外，金属钛和铪在晶格中具有显著的氧溶解度，因此也适用于该热处理工艺。然而，氧化钛合金的一个问题在于氧化层的高缺陷密度，这主要发生在平行于金属表面的地方。本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。这三个系统是1）Ti6 Al 4V，2）涂覆有Zr的Ti6 Al 4V（通过粉末填充）和3）TiZrNbHfTa（20 at.%每个）。Ti6 Al 4V是目前最常用的钛合金。合适的氧扩散硬化可以显著改善该合金在摩擦学应用中的使用。由于热生长的钛氧化物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的氧化物，另一种有前途的方法是使用粉末包装工艺用锆涂覆Ti6 Al 4V合金。然后，氧扩散硬化应类似于当前项目Gl 181/41-1中研究的合金ZrNb 7适用。第三个系统，高度可变形的TiZrNbHfTa高熵合金，包含所有三个元素具有显着的氧溶解度。在氧化过程中形成的近表面层的合金是特别感兴趣的。对于所有三个系统，应制定适当的热处理参数，以提高层的附着力和耐磨性。后者在销/盘和圆柱/平面测试台上进行评估。来自热处理过程的数据将用于开发数学模型，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.