ICMCTF2012 Session E4-1/G4-1: Coatings for Machining Advanced Materials and for use in Advanced Manufacturing Methods

The global economic pressures and escalating energy costs create increasing demands on performance of engineered components used in various wear related applications. Surface engineering is an important tool to reach these objectives, especially because of its potential to significantly improve performance without changing structural properties of the substrate. To enable timely and effective development of new products, it is critical to establish smart approaches for leveraging, re-engineering and enhancing the existing technologies to make them suitable for new applications.

This talk discusses the engineering challenges and systematic methodology for developing new thin coating platforms for wear resistant components starting with the current state of the art in metal cutting coating. The methodology is based on understanding fundamental limitations of currently available coatings with respect to the new application area, and developing approaches for modeling, testing and evaluation.

Carbon-based materials have sufficient high temperature strength in inert atmosphere; they are attractive as a substrate material of mold-die for mold-stamping the oxide glasses into optical elements. In recent, most of optical lens system equips diffractive optical elements; e.g. Fresnel pattern is a typical micro-pattern on these elements. Here, new technique is needed to imprint the designed micro-pattern or micro-texture onto glassy carbon substrate or amorphous carbon coatings on the metallic alloy substrate.

In the present paper, diamond-like carbon (DLC) coating via PVD/CVD on the SKD11 substrate is employed to make micro-texturing by using oxygen plasma etching. Original pattern by metal-chromium is first line-drawn on the surface of DLC coating; then, it is subjected to oxygen plasma etching. Even without any hazardous etchants such as CF4, high etching rate is attained only by using oxygen gas; i.e. 2.5 to 3 μm/H. Plasma diagnosis by spectroscopy proves that this etching process is controlled by activated oxygen atom flux of {O, O*}. Direct chemical reaction by C (in DLC) + O* → CO, or, C (in DLC) + O* → C-O, drives this etching. Detection of CO peaks in the wave length range of 200 to 300 nm also proves that this oxygen plasma etching should be advanced by chemical reactions. This etching behavior is insensitive to line width (d) and pitch width (L) for 2 μm < d < 100 μm and 5 μm < L < 100 μm. Scanning electron microscope and laser-profilometer are used to make precise measurement on the etched profiles.

Micro cold forming processes require thin sheets of high strength materials often with a thickness below 30 µm. Due to its good resistance, grain refining and anti-recrystallisation properties, aluminum-scandium is a very promising material for such processes, but cannot be rolled down to such a thickness because of its high strength. A suitable alternative to this issue is to produce aluminum-scandium thin sheets in the form of freestanding thin films using magnetron sputtering. However, a major limitation to the mass production of these sheets is the high cost of scandium. Zirconium, on the other hand, has been reported to act in a similar way as scandium in aluminum alloys, providing precipitation strengthening, grain refining and anti-recrystallisation properties to the material, but features the advantage to be much cheaper than scandium. This study aims to investigate the influence of the deposition process and post treatment parameters on both aluminum-scandium and aluminum-zirconium magnetron sputtered freestanding thin films and to compare their properties regarding to the micro forming process.

The sheets were deposited with a d. c. magnetron sputtering unit using two different targets: aluminum with 1.2 at% scandium and aluminum with 1.2 at% zirconium and argon as process gas. An unalloyed steel sheet of 100 µm was used as substrate. After deposition the steel was chemically removed in a concentrated nitric acid solution which results in a freestanding sputtered film. Several sheets were produced, each time with a different combination of target power and substrate temperature. The samples were then heat treated at 300 °C for 1 hour, and the mechanical properties of both as deposited and heat treated samples were measured with a tensile tester designed for thin samples.

The optimization of moulding surfaces for microinjection of thermoplastics is crucial to attain the manufacturing specifications for high quality of microengineering components or devices.

This paper is aimed on the perspective of evaluate the near frictionless character of thin films based on W-S-Cu system with and without C, to be used to optimize machining surfaces for plastic moulding. The friction characteristics will be evaluated in condition close to the conditions during the polymer injection process. W-S-X coatings were deposited by magnetron sputtering doped with X= Cu and/or C (from 0%at. to 30% at. on stainless steel DIN X42Cr13 surface moulding micromanufactured by laser beam machining (LBM), followed by electron beam machining (EBM) as the finishing process. The selection of the best coatings was based on the conditions for setting to create high density and low roughness of the surface, hardness in the range from 6-8 GPa and an adhesion critical load better than 40N. Low friction characteristics were previous measured when testing against the different surface coated with the polymers (PP, PMMA, PA and POM) balls. These results were compared with those evaluated using a moulding friction equipment (homemade) that is homothetic of the extraction conditions during the injection process.