Topic of the Month January 2009

Test plates with Sol-Gel coatings: Standard Sol-Gel coatings exhibit fissures and cracks at higher layer thicknesses due to their high shrinkage – contrary to Sol-Gel coatings on the basis of Bayresit® VPLS 2331 that hardly show any shrinkage. Source: Bayer MaterialScience AG.

Materials scientists commonly define hardness as the resistance that a material offers against penetration by another material. It is obvious that this material property is of high importance for technical applications. In manufacturing, for example, the hardness of materials is critical for the applicability of specific forming or cutting technologies – also and especially in the production of tubes and wires. And surface hardness is especially critical for the later use of components and semi-finished products in order to control wear and tear processes. This makes hardness a characteristic of materials that determines the safety and function of technical systems and constructions.

Diamond is not only a fascinating material for the jewelry industry: the all-carbon mineral also sets some standards in technical applications. With a Mohs hardness of 10, diamond is the hardest of all known minerals, even surpassing the grinding hardness of corundum by a factor of 140. This makes it an apparently universal hard material for the above applications – especially given the fact that methods have been found some time ago to manufacture diamond synthetically and in commercial quantities in the form of solid material and coatings, e.g. as Diamond like Carbon (DLC).

Diamond is not always the best choice

Some characteristics of diamond, however, prove to be rather a disadvantage and limit the universal use of this material. Its low resistance to oxidation, its propensity to graphitization and its poor suitability for the machining of ferrous materials are only a few examples.

This is why international research efforts in the field of hard materials, with its integral importance within the industrial value chain, are continuously looking to develop custom hard materials. The highest possible hardness is not the measure of all things – it is more important to obtain a defined combination of properties that can meet the complex requirements of a specific application.

Hard finishes as innovation drivers

Finishes and coatings are becoming more important as problem solvers in a wide variety of industries. Completely new material concepts are successfully used, especially for coatings, to implement key optimizations of properties – often with reduced material consumption, with low technical effort and at low process costs.

In this context, scientists of Bayer MaterialScience AG have recently presented a new cross-linking agent that was developed for the production of layers and coatings on the basis of the Sol-Gel process. The cross-linking agent enables a targeted setting of desired surface characteristics if associated with the right reaction reactants or fillers in the coating system. This includes e.g. high elasticity combined with high hardness and improved scratch-resistance – i.e. critical parameters to counteract the impact of wear mechanisms. Moreover, the layer quality may also be modified to obtain a high resistance to solvents and acids or an adequate corrosion resistance.


Better tools through ceramic reinforcement

Laser-beam dispersion of ceramic particles in the basic material improves the cutting edge of tools. Source: Laser Zentrum Hannover e.V.

Lightweight designs and constructions meet a growing demand in all sectors of the industry. This results in an increasing use of high-performance lightweight materials, such as aluminum alloys and high-tensile steel. Conventional tools are subjected to increased wear when machining such materials, which results in significantly lower yields and tool life – which in turn means higher tool costs and disturbing interruptions of production.

Scientists at the Chair or Primary Shaping and Forming Technologies of the Dresden University of Technology are currently working with colleagues at Laser Zentrum Hannover e.V. in a research project that aims at improving the characteristics of shearing tools for such applications. The researchers utilize the so-called laser beam dispersion process in order to integrate extremely hard ceramic particles made of zirconium oxide (ZrO2) into the basic tool material. Subsequent material examinations have shown that the dispersion process using an Nd:YAG laser prevents the disintegration of the hard material and achieves a homogeneous distribution of the ceramic particles within the matrix. Based on current findings, such cutting tools produced with the laser-beam dispersion process provide better wear characteristics and tool life then conventional tools. The wear examinations have also shown that the increase of hardness in the basic material has a positive impact on the life of the cutting tools.

Dr.-Ing. Christoph Konetschny
Material and Nano Expert

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