PSI - Issue 23

Ivo Černý et al. / Procedia Structural Integrity 23 (2019) 493 – 498 Ivo Černy / Structural Integrity Procedia 00 (2019) 000 – 000

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It can be seen from Fig. 2 that despite of the constant laser parameters during the welding process – power, focus and surface speed, the character of the cross section at different positions of the single track is obviously different. Unlike the surface width affected by the laser beam diameter, which is more or less constant, approximately 5 mm, the laser track height and depth of penetration into the base material is distinctly different. Another interesting physical phenomenon can be seen in Fig. 2a, namely a kind of exsolution bends like a “beach marking”, giving evidence of an important high-speed dynamical, wave motion factor during the very fast melting process. Such waves of exsolution in Fig. 2b are negligible at all.

a) b) Fig. 3. Macrostructure of a) the single additive layer and b) double layer in cross sections.

Macrostructure of the single additive layer of five overlapping tracks and the similar double layer is documented in Fig. 3. The scale of both photographs is the same, determined by the abscissa in the bottom of Fig. 3b, which is 5000  m. The vertical distance of the additive welds from the original surface of the base plate in case of the single and double layer is approximately 1.05 mm and 2.2 mm, respectively, as expected. Note that the mutual metallurgical connection between the first and second layer is excellent, as well as the penetration to the base material in both cases. In general, the macrostructure including the overlapping of the layers was quite similar to that published in Telesang et al. (2015). 3.2. Microstructure Microstructure of the base material was, as expected, of ferritic – pearlitic type with a uniform size of ferritic grains – Fig. 4s. The width of heat affected zone (HAZ) was 0.9 mm. Towards the additive weld, the microstructure became finer up to fusion zone with martensitic microstructure – Fig. 4b. Microstructure of the additive welds was of martensitic type with a dendritic character – Fig. 4c.

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b) c) Fig. 4. Microstructure of a) base material b) heat affected and fusion zones and c) additive weld.