Diffusion, convection, and solidification in cw-mode free electron laser nitrided titanium

Daniel Höche,Sven Müller,Peter Schaaf,Michelle Shinn

doi:10.1063/1.3097781

Abstract

Titanium sheets were irradiated by free electron laser radiation in cw mode in pure nitrogen. Due to the interaction, nitrogen diffusion occurs and titanium nitride was synthesized in the tracks. Overlapping tracks have been utilized to create coatings in order to improve the tribological properties of the sheets. Caused by the local heating and the spatial dimension of the melt pool, convection effects were observed and related to the track properties. Stress, hardness, and nitrogen content were investigated with x-ray diffraction, nanoindention, and resonant nuclear reaction analysis. The measured results were correlated with the scan parameters, especially to the lateral track shift. Cross section micrographs were prepared and investigated by means of scanning electron microscopy. They show the solidification behavior, phase formation, and the nitrogen distribution. The experiments give an insight into the possibilities of materials processing using such a unique heat source.

Highlights

Nitriding of metals such as Fe, Al, and Ti is a well known possibility to improve the material properties such as microhardness and wear resistance of strained technical surfaces.1 Established methods for such surface treatments are plasma or gas nitriding known as physical vapor depositionPVD,2 the classical chemical vapor deposition, and salt bath nitriding
It is possible to modify the metallic surface with laser radiation and to synthesize hard coatings directly3 in a reactive ambient
The reduction in the surface quality is a result of strong convectional flow in the melt pool during the synthesis, caused by the high Prandtl number0.11͒ of liquid titanium,25 which makes it sensitive for capillary flow

Summary

Introduction

Nitriding of metals such as Fe, Al, and Ti is a well known possibility to improve the material properties such as microhardness and wear resistance of strained technical surfaces. Established methods for such surface treatments are plasma or gas nitriding known as physical vapor depositionPVD, the classical chemical vapor deposition, and salt bath nitriding. Nitriding of metals such as Fe, Al, and Ti is a well known possibility to improve the material properties such as microhardness and wear resistance of strained technical surfaces.. Nitriding of metals such as Fe, Al, and Ti is a well known possibility to improve the material properties such as microhardness and wear resistance of strained technical surfaces.1 Established methods for such surface treatments are plasma or gas nitriding known as physical vapor depositionPVD, the classical chemical vapor deposition, and salt bath nitriding. The following investigation shows the possibilities of nitriding by means of cw-mode FEL irradiation. This method offers many advantages in relation to the mentioned techniques. First investigations on texture and strain development in relation to the process parameters have been reported in the literature.

Methods

Results

Conclusion