We investigate the effects of Yb₂O₃ and calcium aluminosilicate (CAS) glass as sintering additives on the sintering behavior of AlN. The AlN specimens are sintered at temperatures between 1700°C and 1900°C for 2 h in a nitrogen atmosphere. When the Yb₂O₃ content is low (within 3 wt.%), an isolated shape of secondary phase is observed at the AlN grain boundary. In contrast, when 3 wt.% Yb₂O₃ and 1 wt.% CAS glass are added, a continuous secondary phase is formed at the AlN grain boundary. The thermal conductivity decreases when the CAS glass is added, but the sintering density does not decrease. In particular, when 10 wt.% Yb₂O₃ and 1 wt.% CAS glass are added to AlN, the flexural strength is the highest, at 463 MPa. These results are considered to be influenced by changes in the microstructure of the secondary phase of AlN.

Ti_0.5Al_0.5N/CrN nano-multilayers, which are known to exhibit excellent wear resistances, were prepared using the unbalanced magnetron sputter for various periods of 2–7 nm. Ti_0.5Al_0.5N and CrN comprised a cubic structure in a single layer with different lattice parameters; however, Ti_0.5Al_0.5N/CrN exhibited a cubic structure with the same lattice parameters that formed the superlattice in the nano-multilayers. The Ti_0.5Al_0.5/CrN multilayer with a period of 5.0 nm exceeded the hardness of the Ti_0.5Al_0.5N/CrN single layer, attaining a value of 36 GPa. According to the low-angle X-ray diffraction, the Ti_0.5Al_0.5N/CrN multilayer maintained its as-coated structure up to 700°C and exhibited a hardness of 32 GPa. The thickness of the oxidation layer of the Ti_0.5Al_0.5N/CrN multilayered coating was less than 25% of that of the single layers. Thus, the Ti_0.5Al_0.5N/CrN multilayered coating was superior in terms of hardness and oxidation resistance as compared to its constituent single layers.

In this study, the effect of the content of MgO-CaO-Al₂O₃-SiO₂ (MCAS) glass additives on the properties of AlN ceramics is investigated. Dilatometric analysis and isothermal sintering for AlN compacts with MCAS contents varying between 5 and 20 wt% are carried out at temperatures ranging up to 1600°C. The results showed that the shrinkage of the AlN specimens increases with increasing MCAS content, and that full densification can be obtained irrespective of the MCAS content. Moreover, properties of the AlN-MCAS specimens such as microhardness, thermal conductivity, dielectric constant, and dielectric loss are analyzed. Microhardness and thermal conductivity decrease with increasing MCAS content. An acceptable candidate for AlN application is obtained: an AlN-MCAS composite with a thermal conductivity over 70 W/m·K and a dielectric loss tangent (tan δ) below 0.6 × 10⁻³, with up to 10 wt% MCAS content.

In this study, MgO–CaO–Al₂O₃–SiO₂ (MCAS) nanocomposite glass powder having a mean particle size of 50 nm and a specific surface area of 40 m²/g is used as a sintering additive for AlN ceramics. Densification behaviors and thermal properties of AlN with 5 wt% MCAS nano-glass additive are investigated. Dilatometric analysis and isothermal sintering of AlN-5wt% MCAS compact demonstrates that the shrinkage of the AlN specimen increases significantly above 1,300°C via liquid phase sintering of MCAS additive, and complete densification could be achieved after sintering at 1,600°C, which is a reduction in sintering temperature by 200°C compared to conventional AlN-Y₂O₃ systems. The MCAS glass phase is satisfactorily distributed between AlN particles after sintering at 1,600°C, existing as an amorphous secondary phase. The AlN specimen attained a thermal conductivity of 82.6 W/m·K at 1,600°C.

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• Effect of MgO-CaO-Al₂O₃-SiO₂ Glass Additive Content on Properties of Aluminum Nitride Ceramics
  Kyung Min Kim, Su-Hyun Baik, Sung-Soo Ryu
  Journal of Korean Powder Metallurgy Institute.2018; 25(6): 494.     CrossRef

Aluminum nitride (AlN) powder specimens are treated by high-energy bead milling and then sintered at various temperatures. Depending on the solvent and milling time, the oxygen content in the AlN powder varies significantly. When isopropyl alcohol is used, the oxygen content increases with the milling time. In contrast, hexane is very effective at suppressing the oxygen content increase in the AlN powder, although severe particle sedimentation after the milling process is observed in the AlN slurry. With an increase in the milling time, the primary particle size remains nearly constant, but the particle agglomeration is reduced. After spark plasma sintering at 1400°C, the second crystalline phase changes to compounds containing more Al₂O₃ when the AlN raw material with an increased milling time is used. When the sintering temperature is decreased from 1750°C to 1400°C, the DC resistivity increases by approximately two orders of magnitude, which implies that controlling the sintering temperature is a very effective way to improve the DC resistivity of AlN ceramics.

Ti alloys are extensively used in high-technology application because of their strength, oxidation resistance at high temperature. However, Ti alloys tend to be classified very difficult to cut material. In this paper, The powder synthesis, spark plasma sintering (SPS), bulk material properties such as electrical conductivity and thermal conductivity are systematically examined on Ti₂AlN and Ti₂AlC materials having most light-weight and oxidation resistance among the MAX phases. The bulk samples mainly consisted of Ti₂AlN and Ti₂AlC materials with density close to theoretical value were synthesized by a SPS method. Machining characteristics such as machining time, surface quality are analyzed with measurement of voltage and current waveform according to machining condition of micro-electrical discharge machining with micro-channel shape.

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• Comparative Study on Ablation Characteristics of Ti-6Al-4V Alloy and Ti₂AlN Bulks Irradiated by Femto-second Laser
  Ki Ha Hwang, Hua Feng Wu, Won Suk Choi, Sung Hak Cho, Myungchang Kang
  Journal of the Korean Society of Manufacturing Process Engineers.2019; 18(7): 90.     CrossRef