Композиты Alnano/h–Bnnano, изготовленные методом шарового размола и искрового плазменного спекания

В работе изучено получение высокопрочных композитов на основе Al/h–BN, изготовленных путем сочетания шарового размола и искрового плазменного спекания с использованием порошков Alnano и h–BNnano.Al/h–BN composites with high strength were fabricated by a combination of ball milling and spark plasma sintering using nano Al and nano BN powders.Работа выполнена при финансовой поддержке CzechNanoLab, MEYS CR (LM2018110) и проекта OPVVV «Новые нанострук туры для инженерных приложений» № CZ.02.1.01/0.0/0.0/16_026/0008396.The work was carried out with the financial support of CzechNanoLab, MEYS CR (LM2018110) and the OPVVV project “New nanostructures for engi neering applications” No. CZ.02.1.01/0.0/0.0/16_026/0008396

Композиты на основе Ni, содержащие наночастицы h-BN

В работе впервые показана возможность армирования композитов на основе Ni наночастицами h-BN комбинацией шарового размола и спекания.For the first time, Ni metal matrix composites were reinforced by h-BN nanoparticles and fabricated by a combination of ball milling and sintering.С. Кортей благодарит Российский фонд фундаментальных исследований (номер проекта № 20-33-90110).S. Corthay thanks the Russian Foundation for Basic Research (project number No. 20-33-90110)

Magnetization performance of hard/soft Nd9.6Fe80.3Zr3.7B6.4/α-Fe magnetic nanocomposites produced by surfactant-assisted high-energy ball milling

Neodymium iron boron (NdFeB) magnets are sintered anisotropic materials. They were commercially introduced in the early 1980s, and since have been used in different applications owing to their superior properties. Herein, we investigated the influence of 0.5 to 8 h of milling time on the morphological, structural, and magnetic performance of Nd _9.6 Fe _80.3 Zr _3.7 B _6.4 powders produced using surfactant-assisted high-energy ball milling (SA-HEBM). The results revealed that the relationship between coercivity ( H _ci ) and milling time had a non-monotonous character reaching a maximum value of H _ci = 8.92 kOe after 1 h of milling. The effect of the volume ratio of various magnetic phases (Nd _2 Fe _14 B and α -Fe) on microstructure and magnetic properties was also reported. The highest specific saturation magnetization ( σ _s = 120 emu g ^−1 ) was attained after 8 h of milling for powders with volume fraction: Nd _2 Fe _14 B–81 ± 2% and α -Fe–12 ± 2%. The expected value of Nd _2 Fe _14 B specific saturation magnetization was estimated ( σ _N = 108 ± 2.5 emu g ^−1 ) using the experimental value of σ _s and magnetic phase volume fractions. The ratio of remanence to saturation magnetization of the Nd _2 Fe _14 B with milling time was also determined and analyzed

Elevated-temperature high-strength h-BN-doped Al2014 and Al7075 composites: experimental and theoretical insights

High-strength Al2014 (Al2) and Al7075 (Al7) series composites with and without addition of hexagonal BN (h-BN) flakes (1, 3, and 5 wt%) were fabricated from the powder mixtures of individual elements using a combination of high-energy ball milling (HEBM) and spark plasma sintering (SPS). Phase compositions of Al2 and Al7 composites were different from standard alloys obtained via casting and subsequent heat treatment. Thorough structural study revealed the presence of the following phases: Al(Mg,Si,Mn,Fe,Cu), AlCux, MgOx, and Al5Cu6Mg2 [Al2], Al(Mg,Si,Mn,Fe,Cu), AlCux, Al5Cu6Mg2, Al6CuMg4, MgO2, AlB2, and SiNx [Al2-BN], Al(Cu,Zn,Mg), Fe(Al,Cu), AlCu3, Al2Cu/Fe3Al, Al5Cu6Mg2, Al4Cu9, MgO2 [Al7], and Al(Cu,Zn,Mg), AlCux, MgOx, MgNxOy, MgB2, Mg3(BO3)2, BN, and BNO [Al7-BN]. The important role of h-BN additives in the microstructure formation during HEBM and SPS was demonstrated. Classical molecular dynamics simulations were carried out to estimate critical shear stress between Al nanoparticles with and without intermediate h-BN layers. The obtained results indicated that the h-BN nanosheets had provided solid lubrication, prevented nanoparticle agglomeration during HEBM, led to a reduced porosity and more homogeneous reinforcing phase distributions in the powder mixtures and resultant composites. Structural analysis showed, that during SPS, one part of BN additives had reacted with Al, Si, and Mg to form AlB2, SiNx, and MgB2/Mg3(BO3)2 inclusions, while the other part remained unreacted and contributed to the material strength. Doping with 3 wt% of BN led to an increase in hardness from 76 HV10 to 123 HV10 (Al2 series), and from 97 HV10 to 130 HV10 (Al7 series). The maximum room-temperature tensile strength of 310 MPa (Al7-BN) and 235 MPa (Al2-BN) was observed for the samples with 3 wt% of BN, which corresponds to an increase in strength by approximately 74% and 16%, respectively. At elevated temperatures, the tensile strength values were 227 MPa (350 °C) and 221 MPa (500 °C) for Al2–3%BN, and 276 MPa (350 °C) and 187 MPa (500 °C) for Al7–3%BN. The superior mechanical properties were attributed to the combination of high thermal stability of the reinforcing phases, solid solution hardening, and Orowan (precipitation) strengthening.</p

Multicaloric Effect in 0–3-Type MnAs/PMN–PT Composites

The new xMnAs/(1 − x)PMN–PT (x = 0.2, 0.3) multicaloric composites, consisting of the modified PMN–PT-based relaxor-type ferroelectric ceramics and ferromagnetic compound of MnAs were fabricated, and their structure, magnetic, dielectric properties, and caloric effects were studied. Both components of the multicaloric composite have phase transition temperatures around 315 K, and large electrocaloric (~0.27 K at 20 kV/cm) and magnetocaloric (~13 K at 5 T) effects around this temperature were observed. As expected, composite samples exhibit a decrease in magnetocaloric effect (<1.4 K at 4 T) in comparison with an initial MnAs magnetic component (6.7 K at 4 T), but some interesting phenomena associated with magnetoelectric interaction between ferromagnetic and ferroelectric components were observed. Thus, a composite with x = 0.2 exhibits a double maximum in isothermal magnetic entropy changes, while a composite with x = 0.3 demonstrates behavior more similar to MnAs. Based on the results of experiments, the model of the multicaloric effect in an MnAs/PMN–PT composite was developed and different scenario observations of multicaloric response were modeled. In the framework of the proposed model, it was shown that boosting of caloric effect could be achieved by (1) compilation of ferromagnetic and ferroelectric components with large caloric effects in selected mass ratio and phase transition temperature; and (2) choosing of magnetic and electric field coapplying protocol. The 0.3MnAs/0.7PMN–PT composite was concluded to be the optimal multicaloric composite and a phase shift ∆φ = −π/4 between applied manetic fields can provide a synergetic caloric effect at a working point of 316 K