Qingwei Liu

TA15 titanium alloy holds great significance as a crucial material in the aerospace industry. In order to gain deeper insights into the influence of hot isostatic pressing (HIP) temperature on the tensile characteristics of materials formed through laser powder bed fusion (L-PBF), a comparative heat treatment experiment was crafted, aligning with the HIP treatment temperature settings. Specifically, the temperatures selected for this investigation were 900 °C, 940 °C, 980 °C, and 1020 °C, while the duration of the holding time was set at 2 h. Notably, the microstructure within the β phase region demonstrated distinct disparities between the HIP-treated specimens and those subjected to heat treatment. The heat-treated specimens exhibited the formation of Widmanstatten structure at 980 °C, while the metallographic structure of the HIP-treated specimens consisted of the lath α phase. In heat-treated specimens, an upward trend in temperature from 900 °C to 1020 °C led to a gradual decrease in UTS (995 MPa, 947 MPa, 886 MPa, and 892 MPa), YS (921 MPa, 865 MPa, 799 MPa, and 784 MPa). The elongation (15.7%,14.6%, and 13.3%) diminished as the temperature increased from 900 °C to 980 °C. At 1020 °C, the elongation slightly increased to 13.9%. The HIP-treated specimens showcased a declining trend in UTS (1008.5 MPa, 947 MPa, 886 MPa, and 892 MPa) and YS (939 MPa, 897.5 MPa, 839.5 MPa, and 844.5 MPa) with an increase in HIP treatment temperature from 900 °C to 980 °C, after which they experienced a slight increment upon further elevation to 1020 °C. The elongation (16%,18.3%, and 20.5%) demonstrated a remarkable improvement from 900 °C to 980 °C. At 1020 °C, the elongation decreased to 17.5%.

In this study, pure Al and Al-Al₂O₃ composite coatings with a low porosity and high density were prepared on magnesium alloys by cold spraying. The surface morphology, component, hardness, interfacial bonding, wear and corrosion properties were investigated. Additionally, the relationship between the interface structure and the protective coatings’ quality was preliminarily established. Pure Al powder was used to create a coating with a homogeneous and dense microstructure. The hard-phase Al₂O₃ in the composite coatings was non-oxidized and would reduce the porosity of the coatings to improve their density and interfacial bonding by up to 55.82 MPa. The bonding mode of the pure Al coatings is primarily mechanical, whereas the bonding mode of the Al-Al₂O₃ mixed coatings is mechanical and metallurgical. The tough Al₂O₃ particles combined to form a layer of work-hardening reinforcement that resisted wear and effectively prevented it from spreading. The three Al-based coatings had excellent corrosion properties, as evidenced by their corrosion current being several orders of magnitude lower than that of the magnesium alloy substrates. The thick coating was significantly more corrosion-resistant than the thin coating and provided greater protection to the substrate. This study offers theoretical and technological assistance for the surface protection of magnesium alloy equipment in demanding conditions.

Split-ring resonators are excellent left-handed metamaterials for significant electromagnetic coupling behavior. In this work, a split-ring resonator prepared with Ni-doped zeolitic imidazolate framework-67/epoxy resin (ZIF-67/ER) was embedded in the top layer to optimize microwave absorption efficiency in the 2–4 GHz frequency band. The Ni-doped ZIF-67/epoxy resin served as the bottom layer to improve microwave absorption efficiency in the 4–8 GHz frequency band. Honeycomb with a conductive carbon black coating served as the middle layer to generate electromagnetic loss for the overall frequency band. Based on the composite structure integration technology, RL < −10 dB was realized under the oblique incidence of 0–70 degrees. Both simulation and experiments indicate that a split-ring resonator made of lossy material can be an effective strategy to broaden the effective absorption bandwidth and increase the corresponding structure’s insensitivity to polarization and the incidence angle of microwave.

The development of broadband and high-efficiency broadband microwave-absorbing materials is one of the keys to resisting electromagnetic radiation and electromagnetic interference. In this paper, we used zeolitic imidazolate framework-67 (ZIF-67) as the template to obtain Ni-doped ZIF-67 via Ni(NO₃)₂ etching followed by pyrolysis to prepare Co-Ni/C composites successfully. The morphology and microstructure of Co-Ni/C composites can be well-tuned by altering the Ni doping content. ZIF-67-derived Co-Ni/C porous materials exhibit extremely strong microwave absorption performance thanks to dielectric loss, magnetic loss, and the synergistic effect between different components. When the dosage of Ni(NO₃)₂ used reaches 0.32 g, the obtained composite possesses the optimal absorbing properties with a maximum reflection loss (RL) of −72.88 dB and an effective bandwidth (f_e, representing RL ≤ −10 dB) of 7.04 GHz (9.76–16.8 GHz) corresponding to a thickness of 2.53 mm. The results of this work indicate that Co-Ni/C composites have potential application value in the field of microwave absorption.