Evaluation of erosive wear resistance of TiN coatings by a slurry jet impact test

In this paper, it is proposed to use a new type of solid particle impact test (slurry jet) to swiftly evaluate wear properties of thin, single layered or multilayered coatings. By the slurry jet, 1.2 μm alumina particles were impacted at high velocity perpendicular to thin PVD coatings of TiN deposited on high speed steel substrate materials under various substrate temperatures. Since the coatings have a much higher wear resistance than the substrate material, the wear rate increases significantly to the higher level of the HSS material when the coatings are penetrated. This is utilized in the quantification of the assessment of coating wear. A ranking of wear resistance and correlations to the coating surface hardness measured by nano-indentation tests, and coating morphology and structures are given and discussed. The TiN deposited under the highest substrate temperature proved to have the highest wear resistance although it had a relatively low hardness. The wear rate of the TiN coatings varies with the orientation of grains, that is, the {1 1 1} orientation that dominates for the high temperature deposition shows a higher wear resistance than the {1 0 0} orientation, which corresponds with the cleavage fracture behavior. Thus, it can be recommended as a screening test when evaluating coatings and coated materials.     

钢的气蚀规律的研究

在旋转圆盘仪上对五种钢的气蚀破坏规律进行了研究。结果表明：钢的气蚀累积失重量与工作时间符合指数关系，且不同性能的钢有不同的气蚀孕育期。     

Relationship between particle erosion and lamellar microstructure for plasma-sprayed alumina coatings

The lamellar structure determines mechanical properties of a thermal spray coating. A model for the erosion of thermally sprayed ceramic coatings resulting from the debonding of flattened ceramic particles is proposed based on the examination of the erosion mechanism. The relationship between erosion rate and microstructural parameters is established both experimentally and theoretically to reveal main lamellar structural parameters controlling erosion of thermally sprayed ceramic coating. The microstructural parameters include the mean bonding ratio between lamellae and thickness of the lamellae. The erosion rate of plasma-sprayed Al₂O₃ coatings was measured at impact angle of 90° under the fixed erosion test conditions. The correlation of theoretical model with the observed structural parameters and erosion data of alumina coatings was examined. It is revealed that the theoretical relationship agreed well with the observed relation. The results clearly revealed that the erosion of plasma-sprayed ceramic coating was inversely proportional to the mean lamellar bonding ratio. The influences of spray parameters on erosion effected mainly through their influences on the lamellar bonding. The erosion resistance of a thermally sprayed ceramic coating was controlled by coating fracture toughness.     

Estimation of Incubation Time of Cavitation Erosion for Various Cavitating Conditions

Estimations have been made, resulting in a general method for the prediction of the incubation time for cavitation erosion using various cavitating conditions and materials. From a single erosion test, the incubation time can be estimated for various conditions and materials by plotting the mass loss as a function of exposure time to cavitation on a log–log scale.     

Evaluation of hydrophilic matrix tablets based on Carbopol® 971P and low-viscosity sodium alginate for pH-independent controlled drug release

Background: The aim of this study was to evaluate matrix tablets containing different ratios of Carbopol^® 971P (CP) to low-viscosity sodium alginate (SA) and assess their suitability for pH-independent controlled drug release. Methods: Two processing methods (physical mixing, PM and spray-drying, SD) were applied before compaction and the release from corresponding matrices was compared. The release from CP-SA PM matrices was also investigated using three model drugs (paracetamol, salicylic acid, and verapamil HCl) and two dissolution media (0.1 N HCl or phosphate buffer, pH?=?6.8), and the release rate, mechanism, and pH-dependence were characterized by fitting of Higuchi and Peppas models, and evaluation of similarity factor. Furthermore, swelling behavior of CP-SA matrix tablets was studied for evaluating its impact on drug release. Results: The processing method (SD or PM) markedly affected the drug release from CP-SA matrices. ANOVA tests showed significant effects of the CP:SA ratio and drug type on the release rate (expressed by the constant, K_H, from Higuchi model) and of the dissolution medium on the release mechanism (expressed by the exponent, n, from Peppas model). Similarity factor (f₂) indicated that the CP:SA ratios ≥?25:75 and ≥?50:50 were suitable for pH-independent release of paracetamol and salicylic acid, respectively, although for verapamil HCl, the matrix with low CP:SA ratio (0:100) showed remarkably reduced pH-dependence of release. Swelling parameters (water uptake and mass loss) were significantly changed with experimental variables (CP:SA ratio, medium, and time) and were in good correlation with drug release. Conclusion: Matrix tablets based on CP and SA form a potentially useful versatile system for pH-independent controlled drug release.     

底吹二氧化碳对炼钢工艺及透气砖影响研究

基于CO_2与钢中元素的反应机理和化学效应,采用中频感应炉研究底吹不同比例CO_2对铁液中元素含量和底吹透气砖的影响,实验结果表明底吹CO_2不会堵塞底吹元件,底吹CO_2降低钢中氮含量,对氧含量无明显影响。     

Corneal erosions in contact lens wear

Contact lens wear continues to be the highest single risk factor for microbial keratitis, particularly when worn in the extended wear modality. For microbial keratitis to occur, the presence of at least a bacterial load as well as a break in the corneal surface is required. One such break occurs in the case of a corneal erosion. These well-circumscribed areas of full thickness epithelial loss can occur both with and without contact lens wear, however the risk of infection is greater in the presence of a lens due to its capacity to provide a vector for the entry of bacterial pathogens. While erosions in non-contact lens wearers are thought to result from defective epithelial basement membrane anchoring, the underlying causes during contact lens wear are yet unknown. This article sets out to review corneal erosions associated with contact lens wear, their associated risk factors such as extended wear, the mechanisms that may be responsible for their formation and the factors that differentiate them from other contact lens related adverse events. Appropriate diagnosis and understanding of the relevant pathophysiology is important to the effective treatment and an understanding of the aetiological factors responsible for erosions is critical to the development of preventative strategies and effective clinical care.     

Cavitation erosion behavior of CLAM steel weld joint in liquid lead-bismuth eutectic alloy

The cavitation erosion of weld joint and base metal of China low activation martensitic(CLAM)steel in liquid lead-bismuth eutectic alloy(LBE)at 550°C was investigated to simulate the cavitation erosion of the first wall and the nuclear main pump impeller in the accelerator driven sub-critical system(ADS).A suit of ultrasonic cavitation facility was self-designed to study the cavitation erosion.By studying the surface micro topography,roughness and mean pit depth of the tested specimens,it was found that some crater clusters and large scale cracks appeared on the tested specimen surface after the formation of numerous single craters,and the base metal exhibited much better cavitation erosion resistance than the weld bead due to the difference in their mechanical properties and microstructures.In addition,by comparing the results of static corrosion and cavitation erosion,it could be concluded that the cavitation erosion and the dissolution and oxidation corrosion in liquid LBE would accelerate mutually.     

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.     

The effect of nanostructure on the oxidation of NiAl

Bulk nanostructured NiAl samples with a grain size of 104 nm have been obtained through cryomilling of NiAl intermetallic feedstock powder and subsequent sintering via SPS. Oxidation testing of these conventional and nanostructured NiAl samples reveals that while the conventional samples have oxidation rates on the order of 10⁻¹¹ g²/cm⁴/s across all tested temperatures, nanostructured samples demonstrate decreasing oxidation rates with temperature, as low as 6.78 × 10⁻¹³ g²/cm⁴/s. This decrease in oxidation rate is attributed to an earlier transition through the metastable aluminum oxide phases, resulting in a stable slow growing α-Al₂O₃ phase earlier in the oxidation tests. In-situ X-ray diffraction (XRD) during high temperature oxidation testing has shown that lattice strain at the surface of the nanostructured samples is substantially higher than conventional, and that the decrease of this lattice strain with temperature is significant. It is believed that the relief of this lattice strain stimulates the earlier θ–α transition seen in the nanostructured samples.