RESUMO
Selective laser melting (SLM) of pure molybdenum encounters all the difficulties of SLM metals due to its intrinsic properties (high melting point, high ductile-to-brittle transition temperature and high surface tension). In this work, we studied the influence of key factors such as powder morphology and processing parameters on SLM fabricated pure molybdenum. Pure molybdenum with a relative density of 99.1% was fabricated by SLM using optimized processing parameters. The formation mechanisms for densification behavior and crack growth behaviors are systematically analyzed. Electron backscattered diffraction analysis indicates that the interlocking grain boundary structure and stretch columnar grains can increase bonding force and inhibit crack growth. The balling and cracking can be reduced by adding support structure and suppressing oxygen content. The hardness of SLM-fabricated molybdenum exceeding 260 HV, which is 30-37% higher than Mo prepared by conventional manufacturing methods, mainly attributed to the fine grains and dislocation strengthening in the SLM process. The bending strength of SLM-ed Mo reached 280 ± 52 Mpa. The fracture mode of SLM Mo was intergranular. This study provides a new route for the fabrication of refractory metals with a complex structure.
RESUMO
In this article, it is demonstrated the generation of high pulse energy, high beam quality and high brightness mode-locked picosecond pulses from a compact Nd:YVO4 master oscillator power amplifier system. This system mainly consisted of a SESAM mode-locked picosecond seed generator and four-stage multi-pass amplifiers. A pulse picker was adopted prior to power amplifiers to efficiently reduce the pulse repetition rate. The maximum average output power of 65.5 W was obtained with a repetition rate of 496.85 kHz and a pulse duration of 16.9 ps, corresponding to a maximum pulse energy of 131.83 µJ and a peak power of 7.8 MW. While simultaneously, the output beam quality factors along the x axis and the y axis were measured to be Mx 2=1.36 and My 2=1.32, respectively, therefore, a brightness as high as 3.22 × 109 W·cm-2·Sr was achieved. As far as we all know, this is the highest brightness for a picosecond pulsed Nd:YVO4 MOPA laser at 1064 nm.
