The mechanism of heavy injection of electric charges to realize linear strain behavior of textured PMN–24%PT ceramics combined with Pt grains

Strain hysteresis is one of the important issues on piezo-ceramic actuators conducting fast and high-precision actuation. In this work, a new regulation mechanism was employed to resolve this issue using 0–3 type metal–ceramic composite. Pb(Mg1/3Nb2/3)_76%Ti_24%O₃ <001> textured ceramics modified by fine Pt grains (Pt@<001>PMN–24%PT) were designed and achieved. Linear strain behavior with zero hysteresis was achieved by 1 vol%Pt@<001>PMN–24%PT composite ceramics. Element maps and TEM images indicated that there was no diffusion between Pt and PMN–24%PT. We explored the correlation between composite structure and strain hysteresis performance. Experimental results and simulation analysis indicated that widely-distributed conjunctions between platinum and PMN–24%PT grains helped to inject a great quantity of charges into PMN–24%PT oxide. The inner high bias field caused by heavy injection of electric charges could pre-tighten the ferroelectric domains of textured PMN–24%PT ceramics. Only when the domain structure has been pre-tightened, linear piezoelectric strain is available.     

Effects of Hf4+ substitute on the enhanced electrostrain properties of 0.7BiFeO3-0.3BaTiO3-based lead-free piezoelectric ceramics

The 0.7Bi_1.05FeO₃-0.3BaHf_xTi_(1?x)O₃ (BF-BHT-x) ceramics are prepared by using conventional method. The mechanism of large electric-induced strain is studied in detail through Rietveld refinement, transmission electron microscopy (TEM), and piezoelectric force microscopy (PFM). The BF-BHT-0.05 ceramics, which possess the coexistence of cubic (Pm-3m) and rhombohedral (R3c) phase proved by Rietveld refinement and TEM measurement, have the maximum electric-induced strain of S_max = 0.58% at 130 kV/cm (1 Hz). The reduced potential barrier is beneficial to the switching and reorientation of domain under an external electric field due to the coexistence of cubic and rhombohedral phase. A mass of nanodomains embedded into the microdomains, which is conducive to domain switching, are observed obviously through PFM. Therefore, the findings show that the large strain is because the external electric field drives the conversion mixed phase into the major rhombohedral phase, the reduced potential barrier, and the nanodomain in macrodomain.     

热处理对5083铝合金晶间腐蚀与力学性能的影响

采用光学显微镜、扫描电镜、硬度试验机和电子万用试验机等研究了合金的显微组织、晶间腐蚀情况和力学性能。结果表明,经过稳定化处理后的试样析出了不连续的第二相,稳定化处理和冷轧后的试样均无晶间腐蚀现象,试样在180℃下退火后,试样内形成了等轴晶粒,晶界上连续分布的β相,出现了晶间腐蚀现象,保温90h比15h晶界上析出β相更多,试样的晶间腐蚀更加明显;合金稳定化处理后硬度最高,冷轧后试样的硬度最低,在180℃下退火保温15和90h的硬度比冷轧后高,但低于稳定化处理后的试样,稳定化处理和退火后的试样的塑性较冷轧态好。     

Preparation and performance of ZrAlN anti-reflective coatings for low-emissivity glasses

Hard and optically selective films are useful for low-emissivity applications and the surface layer of optical elements. In this paper, ZrAlN films were prepared by RF magnetron sputtering on glass substrates at room temperature under different power and gas flow rate. Microstructure, optical properties, chemical compositions and tribological properties of the coatings were investigated and the results indicate that the ZrAlN coatings, prepared with a nitrogen flow rate of 6 sccm, target power of 110 W for both Al and Zr, can give an excellent visible light transmittance that allows 90% of light in the range of 400–600 nm to transfer through the glass and films. Especially, the Transmittance of the ZrAlN is 93.4% at the wavelength of 550 nm which is higher than glass. The emissivity of ZrAlN coating is about 0.74, much lower than bare glass. The coatings maintain the optical properties even under salt spray test for 336 h. the results proved that the ZrAlN films are excellent anti-reflective coatings with superior mechanical property and high corrosion resistance, it can be used in low-emissivity glasses and some other optical components.     

Oxidation and self-healing behaviour of spark plasma sintered Ta2AlC

Self-healing and oxidation of spark plasma sintered Ta₂AlC was investigated using a newly developed wedge loaded compact specimen to determine strength recovery in a single specimen. Previous work had predicted dominant Al oxidation leading to dense and strong reaction products to result in favourable healing properties. However, crack-gap filling and strength recovery of Ta₂AlC were not achieved by oxidation at 600 °C. Oxidation below 900 °C in synthetic and atmospheric air resulted in porous Ta-oxides, with no Al₂O₃ formation. DTA up to 1200 °C revealed a two-step reaction process with the final products Ta₂O₅ and TaAlO₄. The study shows that the kinetics may overrule the self-healing MAX-phase design criteria based on thermodynamics.     

Enhanced stretch formability and mechanical properties of a magnesium alloy processed by cold forging and subsequent annealing

A magnesium alloy AZ21 was multi-directionally forged at room temperature to cumulative strains of ΣΔɛ = 1.5 and then subjected to various annealing treatments. The results showed that the initial grains were gradually subdivided into ultrafine ones by mechanical twins. The annealing temperature had a pronounced effect on the microstructural evolution. At 523 K, a homogeneous structure with a mean grain size of 3.8 μm was obtained, which exhibited remarkable texture weakening compared with the as-annealed specimen, resulting in significantly increase of ductility and stretch formability. Increased and decreased annealing temperature can both lead to a coarsening of grain size. Moreover, the analysis on the recrystallization kinetics during annealing indicated that it could be well described by Johnson–Mehl–Avrami–Kolmogorov model and the activation energy for recrystallization was calculated to be about 63.4 kJ/mol.     

微波烧结制备碳酸化多孔羟基磷灰石纳米陶瓷

采用活性炭辅助微波烧结的方法制备多孔碳酸化磷酸钙纳米陶瓷。通过考察多孔陶瓷坯体在不同烧结温度的线收缩率和抗压强度得到合适的烧结温度。1000℃微波烧结得到多孔碳酸化磷酸钙纳米陶瓷：抗压强度约为2.5MPa,平均晶粒尺寸约为132nm,孔隙率约为75%。与常规陶瓷相比,该种陶瓷抗压强度相当、晶粒尺寸更小并且微观结构更均匀...     

基于DEFORM的U型截面铝合金锻件淬火入水方式对残余应力的影响

采用DEFORM软件对U型截面铝合金锻件固溶后淬火入水方式进行了数值模拟分析,研究了4种入水姿态和自由落体、5 m/s及2 m/s的入水速度对锻件温度场和残余应力的影响规律。结果表明,锻件入水姿态和入水速度对残余应力的影响显著,该锻件以U型面旋转90°姿态和自由落体入水时,残余应力值最小且分布最均匀。     

Studies on magnetic,dielectric and magnetoelectric behavior of (x) NiFe1.9Mn0.1O4 and (1 − x) BaZr0.08Ti0.92O3 magnetoelectric composites

In the present research work, the magnetoelectric (ME) composites of ferrite and ferroelectric phases with (x) NiFe_1.9Mn_0.1O₄ and (1 ? x) BaZr_0.08Ti_0.92O₃ (where x = 0.10, 0.20 and 0.30) respectively were synthesized by the conventional ceramic method. The X-ray diffraction pattern of the composite reveals a spinel phase formation for the ferrite and perovskite phase formation for the ferroelectric phase without any other phase. The SEM micrographs of composites were taken to determine the average grain size and also to study the surface morphology. The effect of constituent phase variation on the B–H hysteresis behavior and the dielectric properties was examined. The dielectric constant shows usual dielectric dispersion behavior with increasing frequency which is due to the Maxwell–Wagner type surface interfacial polarization. From the ac conductivity study, it is confirmed that the conduction in the present composites is of small polaron type. The static magnetoelectric (ME) voltage coefficient developed on the surface of magnetoelectric material was measured as a function of applied dc magnetic field. The maximum ME conversion factor of 1.18 mV/cm Oe was observed for x = 0.10 composite. Such composites may be useful to fabricate the magnetic field sensors and applicable in many linear ME devices.     

Dynamic recrystallization and texture evolution of Mg–Y–Zn alloy during hot extrusion process

The microstructure and texture evolution of Mg_98.5Y₁Zn_0.5 and Mg_92.5Y₅Zn_2.5 (atomic percent) alloys during hot extrusion were systematically investigated. The coarse LPSO phases with higher volume fraction (~ 57%) suppressed the twinning generation in the initial stage of extrusion, and accelerated the dynamic recrystallization through the particle deformation zones. Therefore, the volume fraction of DRXed grains in as-extruded Mg_92.5Y₅Zn_2.5 alloy was much higher than that of Mg_98.5Y₁Zn_0.5 alloy. The intensive recrystallization process resulted in the conventional basal texture weakening, although the texture evolution was mainly dominated by flow behavior. The dynamic recrystallization behavior in Mg_92.5Y₅Zn_2.5 alloy restricted the formation of deformation texture, and thus the more random texture was observed during the whole extrusion process.