Investigations on temperature-activated coatings for friction reduction during turning of titanium alloys

研究了硬质合金Ti6Al4V车削过程中硬质合金表面含钒物理气相沉积(PVD)硬质涂层的氧化、扩散行为及应用行为。结果表明，在摩擦学模型试验中，以钒为活性元素的CrAlVN在ϑ=80 0°C的工作温度下可形成易剪切的氧化相。另外，在加工Ti6Al4V后，尽管使用了冷却润滑剂，但在刀具涂层的刀具刃口区域仍形成了减摩氧化相。然而，研究表明，在切割过程中形成的氧化物数量太少，不能显著提高刀具寿命。由于强烈的粘着磨损，目前的项目无法实现切屑和主后刀面上的切割温度的确定。因此，有必要对TiAl6V4车削过程中的温度进行测定。对CrAlMoN涂层刀具的初步研究表明，在ϑ≤600°C时已经有了减摩效果。此外，刀具寿命也得到了提高，首次超过了作为最先进技术使用的未涂层基材的刀具寿命。活化温度降低可能是导致这一现象的原因。因此，对切削温度的了解对于将加工引起的扩散和氧化与模型试验的观察结果相关联，从而得出对加工过程中的损伤机制的影响是重要的。这就导致了对CrAlMoN涂层的研究。后续项目的主要目的是了解自润滑CrAlMoN涂层在加工难加工的钛合金Ti6Al4V过程中可以降低刀具载荷的因果关系。为此，制备了不同元素含量的CrAlMoN涂层，并对涂层和复合材料的性能进行了表征。此外，还将在模型试验中研究其氧化和扩散行为以及摩擦行为。此外，利用一种新型的测温装置测量了钛在车削过程中的温度。此外，在车削试验中使用了涂层刀具，并随后进行了详细的损伤分析。

In the research project the oxidation and diffusion behaviour as well as the application behaviour of vanadium-containing physical vapour deposition (PVD) hard coatings on cemented carbide substrates during turning of the difficult-to-machine titanium alloy Ti6Al4V were investigated. The results showed that CrAlVN with vanadium as triboactive element enables the formation of easily shearable oxide phases at operating temperatures of ϑ = 800 °C in tribological model tests. Supplementary, the formation of friction-reducing oxide phases in the area of the cutting edge on the tool coating was proven despite the use of cooling lubricant after the machining of Ti6Al4V. However, the investigations indicate that the number of oxides formed in the cutting process is too small to cause significant tool life increases. The temperature determination of the cutting temperatures on the chip and main flank surface could not be achieved in the current project due to strong adhesive wear. Therefore, a temperature determination during turning TiAl6V4 is necessary. Initial investigations with CrAlMoN coated tools showed a friction-reducing effect already at ϑ ≤ 600 °C. In addition, an improvement in tool life was achieved, which for the first time surpassed the tool life of the uncoated substrate used as state of the art. The reduced activation temperature might be the reason for this. Therefore, the knowledge of the cutting temperature is important to correlate the diffusion and oxidation due to the machining with the observations from the model tests and thus to derive influences on the damage mechanisms during machining. This results in a considerable need for research on CrAlMoN coatings.Main aim of the proposed follow-up project is to gain knowledge on the cause-effect relationships that can lead to a reduction of tool load in the machining processes of the difficult-to-machine titanium alloy Ti6Al4V with self-lubricating CrAlMoN coatings. For this purpose, CrAlMoN coatings with varying element content are deposited, followed by a characterization of coating and composite properties. Furthermore, the oxidation and diffusion behavior as well as the friction behavior will be investigated in model tests. Moreover, the cutting temperature during the turning of titanium is measured by means of a novel temperature measurement setup. Furthermore, coated cutting tools are used in turning tests and subsequently subjected to a detailed damage analysis.