Sonic metamaterials have a wide range of applications in wave control and super-resolution imaging, and are favored for their several unique and advantageous properties. However, current double-negative sonic metamaterials have complex structures composed of various materials, which limits their design and application. Thus, we must produce double-negative features using a simple structure of one material. Because of their unique concave configurations and various resonances, star-shaped structures readily form band gaps and show superior material properties. In this study, we designed and simulated star-shaped single-phase metamaterials, considered ideal structures. Our numerical results suggest that these metamaterials have two band gaps as well as double-negative properties over specific frequency ranges. Moreover, we investigated how their band gap and double-negative properties depended on the concave angle.

Marine noise pollution generated by propellers is of wide concern. Traditional propeller materials (nickel–aluminum bronze (NAB) alloys) can no longer meet the requirements for reducing shaft vibration. However, the Mn–Cu alloy developed to solve the problem of propeller vibration is affected by seawater corrosion, which greatly limits the application of the alloy in the field of marine materials. In this study, the M2052–NAB gradient alloy was developed for the first time using LENS technology to improve the corrosion resistance while retaining the damping properties of the M2052 alloy. We hope this alloy can provide a material research basis for the development of low-noise propellers. This study shows that, after solution-aging of M2052 alloy as the matrix, the martensitic transformation temperature increased to approach the antiferromagnetic transformation temperature, which promoted twinning and martensitic transformation. The aging process also eliminated dendrite segregation, promoted the equiaxed γ-MnCu phase, and increased the crystal size to reduce the number of dislocations, resulting in obvious modulus softening of the alloy. NAB after deposition had higher hardness and good corrosion resistance than the as-cast alloy, which offers good corrosion protection for the M2052 alloy. This research provides new material options for the field of shipbuilding.

Here, we report a skeletal nickel catalyst prepared by cumulative processing. The Ni, Al, and CoCrMo multi-component alloys were printed by a dual-powder laser-engineered net-shaping system, and alloy samples with different components were obtained through high-throughput design. After leaching in 5 mol/L NaOH at 40 °C for 2 h, the specific surface area of the catalyst increased with increasing Al content. Increasing the leaching temperature and prolonging the leaching time also effectively increased the specific surface area of the catalyst. After leaching at 80 °C for 12 h, the specific surface area was 42.36 m2/g. After cleaning and hydrogen-reduction treatment at 400 °C, the catalyst showed high catalytic activity. The highest conversion rate of CO reached 89.56%, and the selectivity of CH4 remained above 98% for a long time.