Evaluation of fire performance of organic fire retardant free acrylic based coatings applied on various building materials by cone calorimetric method

Fire performance of water‐based plaster systems containing acrylic copolymer binder and non‐flammable mineral and ceramic fillers intended for decorative coating application was determined by cone calorimetric method. The coatings were applied on common building substrate materials used in construction sector, namely, Medium Density Fibre (MDF) boards, Gypsum Boards (GIB) and Stainless Steel (SS), and the different plaster finishes attempted on these substrates were Tierrafino, Suave and Bone China respectively. Group numbers of the different test samples were also evaluated following the Kokkala method. Based on various measurements, especially heat release, smoke evolution, mass loss data and the Group number estimates, it is evident that these organic fire retardant free coatings can offer good fire safety if applied on appropriate substrates like GIB or SS. Copyright © 2016 John Wiley & Sons, Ltd.     

(Ti,M)C复式碳化物制备方法的研究进展

对当前(Ti,M)C碳化物的制备方法进行了综述,详细介绍了不同制备方法的制备过程及原理,对不同制备方法的优缺点进行了论述。碳热还原法是目前广泛使用的一种方法,能够制备复杂成分的(Ti,M)C,但该方法耗能大、工艺流程复杂;预合金化法能够制备某些特定成分的碳化物,但其使用范围受限;自蔓延高温合成法可以制备多种成分的(Ti,M)C,但大部分情况下需要预热且存在反应不完全的情况。目前没有一种制备方法同时具有高效、工艺流程简单、适用性强且产物纯度高等优点,对现有制备方法进行改进以满足工业化应用是(Ti,M)C复式碳化物的研究发展方向。     

Structure, corrosion, and hardness properties of Ti/Al multilayers coated on NdFeB by magnetron sputtering

Ti/Al multilayers deposited on sintered NdFeB magnets by direct current magnetron sputtering with ion-beam assistance were studied in this report. Ti layers with a hexagonal close packed structure were obtained in the Ti/Al multilayers. The columnar structure growth of Al layers was successfully interrupted by the intercalated Ti layers. The Ti/Al multilayers showed more compact and uniform surfaces than the Al single layer. The corrosion current densities of the sintered NdFeB magnets coated with Ti/Al multilayers were much lower than that of the Al single layer. The Ti/Al multilayers also presented improved hardness.     

Microstructure and sliding wear behavior of pseudo-alloy PS45/CuAl8 composite coating sprayed by HVAA technique

A pseudo-alloy PS45/CuAl8 composite coating was sprayed on steel substrate by high-velocity activated arc spraying (HVAA) process. Its sliding wear behavior at room temperature was evaluated by M-2000 wear tester. For comparison, a single CuAl8 coating was also prepared and tested under the same conditions. It is found that the pseudo-alloy composite coating consists of α-Cu and γ-Ni metallic matrix phases together with homogenously distributed minor Al 2 O 3 , Cr 2 O 3 oxide phases. Moreover, pseudo-alloy coating possesses much better sliding wear resistance than CuAl8 coating due to the enhanced hardness and microstructural homogenization. Fatigue wear and abrasive wear are responsible for the wear-down mechanism of the pseudo-alloy coating.     

Thermal shock resistance of air plasma sprayed thermal barrier coatings

The spallation resistance of an air plasma sprayed (APS) thermal barrier coating (TBC) to cool-down/reheat is evaluated for a pre-existing delamination crack. The delamination emanates from a vertical crack through the coating and resides at the interface between coating and underlying thermally grown oxide layer (TGO). The coating progressively sinters during engine operation, and this leads to a depth-dependent increase in modulus. Following high temperature exposure, the coating is subjected to a cooling/reheating cycle representative of engine shut-down and start-up. The interfacial stress intensity factors are calculated for the delamination crack over this thermal cycle and are compared with the mode-dependent fracture toughness of the interface between sintered APS and TGO. The study reveals the role played by microstructural evolution during sintering in dictating the spallation life of the thermal barrier coating, and also describes a test method for the measurement of delamination toughness of a thin coating.     

The dual capacity of the NiSn alloy/MWCNT nanocomposite for sodium and hydrogen ions storage using porous Cu foam as a current collector

A nanostructured NiSn alloy/multi-walled carbon nanotube (MWCNT) composite was successfully synthesized for highly reversible sodium and hydrogen ions storage by using an electrochemical deposition process on porous Cu foam. The surface morphology of the resulting NiSn alloy/MWCNT nanocomposite was characterized using a field-emission scanning electron microscope, indicating the formation of sphere-like NiSn alloy nanoparticles with an average size of 190 nm. On the other hand, X-ray diffraction analysis, energy dispersive and Fourier transform infrared spectroscopies were employed to determine the crystalline structure, elemental surface and chemical composition of the nanocomposite electrode. The initial sodium discharge capacity of the electrode was maximized at ∼550 mAh g⁻¹ under the current density of 1000 mA g⁻¹, and a high hydrogen discharge capacity of 5200 mAh g⁻¹ was obtained at 1100 mA g⁻¹ after 20 cycles. A comprehensive comparison between the sodium and hydrogen ions capacities in this study and those of the literature for different materials and structures was also performed. Accordingly, the resulting nanocomposite electrode with dual capacity may offer promising applications in both sodium-ion battery and hydrogen storage.     

Cracking induced tribological behavior changes for the HVOF WC-12Co cermet coatings

HVOF sprayed WC based cermet coatings have been widely used in industries as barriers against wear and hydrodynamic cavitation due to their high hardness and relatively high toughness. However, cracking of the coatings can occur during coating production or in service, which can reduce operational performances. It can be difficult to assess the performance impact due to cracks within the coating and as to whether the cracked coatings should be resprayed or removed from service. In this work, artificial cracks of different widths were introduced to liquid fuel HVOF sprayed WC-12Co coating through uniaxial tension of the coated steel substrate to assess the implications of such cracking. Tribological performances of the cracked coatings were examined using rubber wheel dry abrasion, ‘ball on disc’ sliding wear, and ultrasonic cavitation erosion. The results show that the crack deteriorates the abrasive wear resistance of the coating at the initial stage due to preferable mass loss at the cracks. However, after 30?min of abrasion, all the cracked coatings showed the same wear rate as compared to the non-cracked coating, with the abrasive wear resistance acting independent to the crack characteristics. Because the cracks could store wear debris and thus minimize the debris induced abrasion to the coating surface during sliding wear test, both improvement in wear resistance and reduction in coefficient of friction (COF) were detected in the cracked coatings. During the cavitation test, it was found that the mass loss of the specimen increased significantly (up to 75%)with crack width and density suggesting that the crack presence greatly deteriorated the cavitation resistance of the cermet coatings.     

Friction and wear properties of high-velocity oxygen fuel sprayed WC-17Co coating under rotational fretting conditions

Rotational fretting which exist in many engineering applications has incurred enormous economic loss. Thus, accessible methods are urgently needed to alleviate or eliminate damage by rotational fretting. Surface engineering is an effective approach that is successfully adopted to enhance the ability of components to resist the fretting damage. In this paper, using a high-velocity oxygen fuel sprayed(HVOF) technique WC-17 Co coating is deposited on an LZ50 steel surface to study its properties through Vickers hardness testing, scanning electric microscope(SEM), energy dispersive X-ray spectroscopy(EDX), and X-ray diffractrometry(XRD). Rotational fretting wear tests are conducted under normal load varied from 10 N to 50 N, and angular displacement amplitudes vary from 0.125° to 1°. Wear scars are examined using SEM, EDX, optical microscopy(OM), and surface topography. The experimental results reveal that the WC-17 Co coating adjusted the boundary between the partial slip regime(PSR) and the slip regime(SR) to the direction of smaller amplitude displacement. As a result, the coefficients of friction are consistently lower than the substrate's coefficients of friction both in the PSR and SR. The damage to the coating in the PSR is very slight. In the SR, the coating exhibits higher debris removal efficiency and load-carrying capacity. The bulge is not found for the coating due to the coating's higher hardness to restrain plastic flow. This research could provide experimental bases for promoting industrial application of WC-17 Co coating in prevention of rotational fretting wear.     

Faceted crack initiation characteristics for high-cycle and very-high-cycle fatigue of a titanium alloy under different stress ratios

Ultrasonic fatigue tests were conducted at the stress ratios of −1, −0.5, −0.1, 0.1 and 0.5 for a Ti–6Al–4V alloy in high-cycle and very-high-cycle fatigue regimes. Experimental results showed that faceted crack initiation was the main failure mode for specimens at the stress ratios of −0.1, 0.1 and 0.5, and multi-site faceted crack initiation was observed at the stress ratios of 0.1 and 0.5. The measurements indicated that the number of facets increased with the increase of stress ratio. Based on the observations, the mechanism of faceted crack initiation was proposed, i.e., (i) cleavage of isolated primary α grains in cluster; (ii) gradual growth of originated cracks (facets), and the coalescence of adjacent facets; and (iii) coalesced facets forming a main crack in the cluster. Moreover, a model based on Poisson defect distribution is proposed to describe the effects of stress ratio on faceted crack initiation, which is in agreement with the experimental results.     

工程机械用丙烯酸中涂树脂的制备及应用

以苯乙烯、丙烯酸、丙烯酸羟丙酯、丙烯酸乙酯为原料，通过溶液聚合法合成了丙烯酸中涂树脂，用该树脂、填料和助剂制备了工程机械用丙烯酸中涂漆，并讨论了各组分对涂料性能的影响。