ICMCTF 2022 Session G2-ThM: Surface Modification of Components in Automotive, Aerospace and Manufacturing Applications

To increase the service life of forming tools, coatings by physical vapor deposition (PVD) or chemical vapor deposition (CVD) have been used for decades. However, upscaling to ensure robust processes for large tools is difficult. In this regard, hard chrome electrodeposition has proven to be a common practice. One disadvantage in particular is the limited durability, which in the context of service life, using the example of a car body side tool, is manifested in multiple decoating and recoating involving the use of environmentally critical chemicals. In contrast, plasma nitriding is a thermochemical diffusion process for surface hardening in which the surface layer of a workpiece or component is enriched with nitrogen at low to moderate temperatures. The technology used by Oerlikon allows a loading of up to 40 tons on an area of 3x10m. Thus, an environmentally friendly surface treatment is available even for massive tools, which, compared to hard chrome, requires only a single treatment.

Nevertheless, it should be noted and taken into account that in principle a start-up of these tools have already been done beforehand and therefore process-side interactions with impurities, passivation as well as any pre- and post-treatments are possible. This applies in particular to areas hardened and welded in advance, as well as to subsequent modifications where the already nitrided surface has to be welded. Possible consequences are material-specific and manifest themselves in tempering effects, outgassing and degradation phenomena.

The main topic of the presentation will be the requirements of users and manufacturers of forming tools and the resulting challenges. In addition to various applications and the respective restrictions with large forming tools whose mass can be far more than 10 tons, the measures derived from this to ensure process stability and quality will be discussed.

Titanium alloys are one of the most common materials used in the aerospace industry. The need to machine parts in this industry poses as one of the main problems, since these alloys are well-known to be difficult to machine materials, mainly due to their low Young’s modulus and poor heat conductivity. The consequent restriction in the use of high cutting speeds limits the productivity which lead to the development of self-lubricant coatings as a promising way to improve the lifetime and performance of machining tools. The main focus of this work was to investigate the effect of Ag alloying on the high temperature tribological behaviour and machining performance of TiSiN coatings. The coatings exhibit relatively high hardness (32 to 15 GPa). Tribological behaviour was assessed in pin-on-disc tests at room temperature and at 900ºC, sliding against TiAl6V4 balls. Ag addition show a general decrease in the COF values across all the test temperatures. Increasing the Ag content and the temperature seems to show a beneficial effect in reducing the wear and the amount of adhered ball material. This is a promising result to reduce the built-up edge effect on the machining tests. The machining behaviour during turning of the TiAl6V4 alloy, showed that Ag additions had a beneficial effect on the machining performance of the films, especially for the higher cutting speeds. As observed for tribology, a clear reduce in the BUE was also found in machining when Ag was added to the coatings.