Ultra-short pulse laser-based additive manufacturing of high hardness tungsten

Refractory metal tungsten (W) has a very high melting point (3420℃) and excellent high temperature mechanical properties, and has great prospects for application in aerospace, nuclear industry and other defense fields. Due to the high melting point and high thermal conductivity of pure tungsten, high power is required to melt it, while tungsten has a high ductile-brittle transition temperature (DBTT) and a low room temperature brittleness. These two aspects make it impossible to avoid porosity or cracking during machining, limiting its further application. So more effective tools are needed. The ultrafast laser can reach high peak power due to its extremely short pulse width. Adjusting the frequency can achieve heat accumulation in the heated region. These two effects make it possible to process materials with high melting points without having to increase the power all the time. The ultra-fast laser excessively high peak power can lead to cold processing of the material for removal, so figuring out the right process parameters is especially important. Femtosecond laser additive manufacturing of pure tungsten has been previously documented and compared with parts made using different pulse widths and CW lasers, showing that fully dense tungsten parts with finer grain size and increased hardness were obtained. By further reducing the pulse width at 200 fs, we achieved printing of pure tungsten at higher densities. Hardness tests demonstrated the superior performance of the printed samples compared to those made by conventional casting, continuous wave laser and 800 fs laser-selective melting, and this study is expected to promote the wide application of narrow pulse width lasers in laser additive manufacturing.