Primary investigation of corrosion resistance of Ni-P/TiO2 composite film on sintered NdFeB permanent magnet

In this paper, an electroless nickel plating and sol-gel combined technique used to prepare the Ni-P/TiO₂ composite film on sintered NdFeB permanent magnet is described and the composite film was characterized by X-ray diffraction (XRD), environmental scanning electron microscopy (ESEM), and energy dispersive X-ray spectrometer (EDX). The corrosion resistance of Ni-P/TiO₂ film was studied by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The self-corrosion current density (i_corr) of Ni-P/TiO₂ composite film is 2.38μA/cm² in 0.5mol/L H₂SO₄ solution about 33% of that of Ni-P coating and 0.22μA/cm² in 0.5mol/L NaCl solution about 14% of that of Ni-P coating, respectively. In 0.5mol/L H₂SO₄ and 0.5mol/L NaCl solutions, the polarization resistance (Rp) of the composite film is 12.5kΩ cm² and 120kΩ cm², about 1.6 and 2 times that of Ni-P coating, respectively. The results indicate that Ni-P/TiO₂ composite film has a better corrosion resistance than Ni-P coating.     

Indirect determination of martensitic transformation temperature of sintered nickel-free Ti–22Nb–6Zr alloy by low temperature compression test

Nickel-free Ti–22Nb–6Zr alloys were fabricated by conventional powder metallurgy sintering method. X-ray diffractometer (XRD) investigation showed that the as-sintered alloys mainly consisted of β phase, with a few needle-like α phase precipitates. Differential scanning calorimetry (DSC) measurement in the temperature ranging from −70 °C to 400 °C and constant stress thermal cycling test by dynamic mechanical analysis (DMA) were unable to reveal the martensitic start temperature of sintered Ti–22Nb–6Zr alloys. Therefore low temperature compression tests were carried out to evaluate their phase transformation behavior indirectly. There was an obvious drop of both Young’s modulus and recoverable strain at −85 °C ∼ −80 °C in the Young’s modulus-temperature and recoverable strain–temperature curves of sintered Ti–22Nb–6Zr alloys respectively, which was attributed to the occurrence of thermal elastic martensitic transformation at this temperature. At the testing temperature of −85 °C, a superelasticity of as high as 5.9% was achieved in the sintered alloys. The results had revealed that sintered Ti–22Nb–6Zr alloys own a great superelasticity intrinsically and would exhibit a much greater superelasticity at room temperature if their martensitic transformation start temperature (M_s) were closer to room temperature. Along with their noble biocompatibility, sintered nickel free Ti–22Nb–6Zr alloys are thus thought to be potentially competitive biomaterials for biomedical applications.     

Composition and morphology of Fe---N off-equilibrium phases in a nitrided Fe-1.5wt.%Mo sintered alloy

Specimens of an Fe-1.5wt.%Mo sintered at 6.9 and 7.5 g cm⁻³ were subjected to both gas and ion nitriding treatments, under different operating conditions (gas composition, length of treatment and temperature).

The composition, morphology and distribution of the Fe---N phases were investigated by means of optical and scanning electron microscopy, electron probe microanalysis and X-ray diffraction.

The Fe---N reactivity effects were shown and explained on the basis of both the surface chemical potential and the diffusion potential, taking into account the penetration of nitriding media through open porosity, grain boundaries and volume. No effect of Mo---N interactions or Mo segregation could be observed. Significant differences were found between gas and ion nitriding with regard to phase composition and thickness of surface compound layers as well as depth and features of diffusion zones. In particular it was shown that the material density plays an important role in the reaction mechanisms characterizing gas treatments.     

退火处理对烧结Nd-Fe-B永磁体磁性能的影响

本文研究了Nd Fe B材料的低温退火处理,普通商品化生产的N35磁体在3Pa真空度、492℃条件下对普通钕铁硼退火处理1h,其矫顽力Hc和最大磁能积(BH)max值均有较大幅度的提高。     

Solid state sintering of lime in presence of La<Subscript>2</Subscript>O<Subscript>3</Subscript> and CeO<Subscript>2</Subscript>

The sintering of lime by double calcination process from natural limestone has been conducted with La₂O₃ and CeO₂ additive up to 4 wt.% in the temperature range 1500–1650° C. The results show that the additives enhanced the densification and hydration resistance of sintered lime. Densification is achieved up to 98.5% of the theoretical value with La₂O₃ and CeO₂ addition in lime. Grain growth is substantial when additives are incorporated in lime. The grain size of sintered CaO (1600°C) with 4 wt.% La₂O₃ addition is 82 μm and that for CeO₂ addition is 50 μm. The grains of sintered CaO in presence of additive are angular with pores distributed throughout the matrix. EDX analysis shows that the solid solubility of La₂O₃ and CeO₂ in CaO grain is 2.9 and 1.7 weight %, respectively. The cell dimension of CaO lattice is 4.803 %C. This value decreases with incorporation of La₂O₃ and CeO₂. The better hydration resistance of La₂O₃ added sintered lime compared to that of CeO₂ added one, is related to the bigger grain size of the lime in former case.     

Spontaneous reactive infiltration of porous ceramic preforms with Al-Mg and Mg in the presence of both magnesium and nitrogen—new experimental evidence

Conditions for the initiation of spontaneous reactive infiltration were studied on quartz sand, boron-carbide, and silicon-nitride powder beds, as well as sintered amorphous silica preforms, infiltrated with Al-5Mg and Mg in a nitrogen atmosphere.

The experimental conditions (presence of both magnesium and nitrogen) were selected to favor the formation of Mg₃N₂ and AlN phases. However, these products were not detected in energy dispersive spectroscopy (EDS) spectra, particularly not as the main product phase at the infiltration interface.

Apart from significant microstructural differences mostly caused by the different extent of chemical reactivity between the ceramic skeleton and the molten metal, the similar EDS spectra observed at the matrix-reinforcement interfaces suggest that spontaneous infiltration in all the applied preforms is most probably induced by the same (or similar) spontaneous infiltration mechanism.

The mechanism proposed in this work is based on the formation of Al₂O₃-MgO-SiO₂ containing phases, which completely or partly coat the ceramic particles and enhance wetting.     

粉煤灰和赤泥的综合利用

讨论了用粉煤灰、赤泥生产烧结砖的可行性 ,介绍了原料主要性质、主要工艺参数、工艺流程。针对不同性质的赤泥 ,采用了不同配方。试验结果表明 :用粉煤灰、赤泥生产的烧结砖达到了MU10级砖的标准     

远红外辐射及负离子释放功能微晶玻璃研究

以粉煤灰为主要原料,将电气石直接掺入,采用烧结法制备微晶玻璃,分析了电气石掺入量对微晶玻璃样品的密度、显微强度、弯曲强度、吸水率、耐酸耐碱性、远红外辐射率和负离子释放量的影响,采用XRD对该种微晶玻璃的微观结构进行了研究。结果表明,随着电气石掺入量的增加,微晶玻璃的密度、显微硬度、弯曲强度和耐碱酸性稍微下降,吸水率略增大,远红外辐射率和负离子释放量都随着电气石掺量增加而增大。     

La，Co离子取代法生产高性能烧结铁氧体的工艺研究

介绍了提高烧结铁氧体磁性能的原理、生产工艺。论述并分析了制备高性能烧结铁氧体应该具备的几个条件,原材料选择、配方、预烧、初级粉碎、二次掺杂、球磨、成型、烧结、磨加工和清洗;对生产工艺过程的关键工序,一次配方、球磨、成型和烧结进行了详细的分析、探究。     

Wear-resistant iron-based Mn–Cu–Sn matrix for sintered diamond tools

The objective of the present work was to determine the suitability of a new iron-based Mn–Cu–Sn matrix alloy for the manufacture of diamond-impregnated tool components. A number of specimens were consolidated by the hot press route from ball-milled powders. Density, microstructural features, phase composition, bending properties and hardness were evaluated. The results revealed excellent mechanical properties, including σ_0.2?>?850?MPa in 3-point bending and HK0.5?>?300. A commercial Co-WC reference matrix alloy was also produced for comparison purposes. Diamond-impregnated specimens with different matrices were tested for wear rate on abrasive sandstone using a test rig specially designed to simulate tool application conditions. The tests that involved 3- and 2-body abrasion ranked the alloys in different orders. Statistical analysis showed that the wear rate of diamond-impregnated composites was mainly affected by diamond concentration, but statistically significant contribution of the matrix resistance to 3-body abrasion was also found.