Navařování drátu z materiálu Inconel 718 pomocí elektronového paprsku a následné boridování – vytváření nových duplexních vrstev na povrchu vysoce zatížených součástí

Buchwalder Anja - TU Bergakademie Freiberg (Germany)

Inconel 718 has a number of advantageous properties, especially at elevated temperatures and in aggressive corrosion media. Disadvantages are the high price, the difficult formability and machinability and the partly limited wear resistance.
For overcoming the given limitations, the aim of our research activities was to develop a technology for the wire-based (Inconel 718) cladding using electron beam on a cheaper but corrosion-resistant austenitic steel (AISI 347) and subsequent boriding for wear protection. The aim is to demonstrate a low-cost alternative to the current use of components made of Inconel mono material.
The paper focuses on the influence of the different successive thermal cycles, including heating and cooling rates, on the development of the microstructure and properties of the surface composite. In case of Inconel 718, the solidification morphologies of the Ni austenite and the proportions of the various phases have a particular influence on the property level. Special attention is paid to the Laves phase.
In electron beam cladding, relatively high heating and cooling rates are generated, which in principle has a positive effect on the suppression of the Laves phase. Another influencing factor, however, is the Fe/Ni ratio, which changed continuously from single-layer to multi-layer deposition. The associated microstructural changes are discussed on the basis of light optical and scanning electron microscopy images, element depth profiles and hardness measurements. The temperature cycle of the subsequent boriding influences the formation of the boride layer in terms of layer thickness, phase fractions and hardness as well as the age hardening behaviour of the Inconel 718 layer.
On the basis of the knowledge gained, statements are to be made on the general necessity and the parameters of a volume heat treatment in order to set an optimum hardening level for both the layer as well as the base material.

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