Microstructure and Properties of the Cr–Si–N Coatings Deposited by Combining High-Power Impulse Magnetron Sputtering(HiPIMS) and Pulsed DC Magnetron Sputtering

The Cr–Si–N coatings were prepared by combining system of high-power impulse magnetron sputtering and pulsed DC magnetron sputtering. The Si content in the coating was adjusted by changing the sputtering power of the Si target.By virtue of electron-probe microanalysis, X-ray diffraction analysis and scanning electron microscopy, the influence of the Si content on the coating composition, phase constituents, deposition rate, surface morphology and microstructure was investigated systematically. In addition, the change rules of micro-hardness, internal stress, adhesion, friction coefficient and wear rate with increasing Si content were also obtained. In this work, the precipitation of silicon in the coating was found.With increasing Si content, the coating microstructure gradually evolved from continuous columnar to discontinuous columnar and quasi-equiaxed crystals; accordingly, the coating inner stress first declined sharply and then kept almost constant. Both the coating hardness and the friction coefficient have the same change tendency with the increase of the Si content, namely increasing at first and then decreasing. The Cr–Si–N coating presented the highest hardness and average friction coefficient for an Si content of about 9.7 at.%, but the wear resistance decreased slightly due to the high brittleness.The above phenomenon was attributed to a microstructural evolution of the Cr–Si–N coatings induced by the silicon addition.

Photon energy transfer on titanium targets for laser thrusters

Using two infrared pulsed lasers systems,a picosecond solid-state Nd:YAG laser with tuneable repetition rate(400 kHz-1 MHz)working in the burst mode of a multi-pulse train and a femtosecond Ti:sapphire laser amplifier with tuneable pulse duration in the range of tens of femtoseconds up to tens of picoseconds,working in single-shot mode(TEWALASS facility from CETAL-NILPRP),we have investigated the optimal laser parameters for kinetic energy transfer to a titanium target for laser-thrust applications.In the single-pulse regime,we controlled the power density by changing both the duration and pulse energy.In the multi-pulse regime,the train’s number of pulses(burst length)and the pulse energy variation were investigated.Heat propagation and photon reflection-based models were used to simulate the obtained experimental results.In the single-pulse regime,optimal kinetic energy transfer was obtained for power densities of about 500 times the ablation threshold corresponding to the specific laser pulse duration.In multi-pulse regimes,the optimal number of pulses per train increases with the train frequency and decreases with the pulse power density.An ideal energy transfer efficiency resulting from our experiments and simulations is close to about 0.0015%.