Yongxiong Chen

Additive manufacturing of metals by employing continuous wave and short pulse lasers completely changes the way of modern industrial production. But the ultrafast laser has the superiority to short pulse laser and continuous wave laser in additive manufacturing. It has higher peak power, small thermal effect, high machining accuracy and low damage threshold. It can effectively perform additive manufacturing for special materials and improve the mechanical properties of parts. This article reviews the mechanism of the interaction between ultrafast laser and metal materials to rule the manufacturing processes. The current application of ultrafast laser on forming and manufacturing special materials, including refractory metals, transparent materials, composite materials and high thermal conductivity materials are also discussed. Among the review, the shortcomings and challenges of the current experimental methods are discussed as well. Finally, suggestions are provided for the industrial application of ultrashort pulse laser in the field of additive manufacturing in the future.

Shot peening was used synchronously to improve Fe-based amorphous coating performance by delivering ZrO₂ ceramic particles into a low-temperature region of a flame during the high velocity oxygen flame (HVOF) spray process. The coating became denser, and its hardness became higher via the new process. Moreover, the compressive residual stress was induced by shot peening. The results from the dry friction test indicated that the coating’s wear resistance was enhanced obviously. The wear mechanism of coatings with and without shot peening is an abrasive wear combined with an oxidation wear at wear test conditions of a low load and a low frequency. The coating with the best wear resistance did not have the strongest microhardness but had the highest compressive residual stress. The compressive residual stress had a significant positive influence on the wear resistance at a low frequency, while its effect is weakened at a high frequency.

Different-shaped ultrafine MoNbTaW high-entropy alloy powders were firstly prepared by a convenient mechanical alloying method. The phase composition and microstructure of the powders were characterized. The powders are ultrafine with nano-sized grains and a good homogeneous microstructure. All the powders have a single body-centered cubic solid solution phase and form the high-entropy alloy during mechanical alloying. These powders with different shapes are quite attractive for developing high-performance MoNbTaW high-entropy alloy bulk and coatings combined with a following sintering, spraying, or additive manufacturing technique.