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141.
Brazing of Ti3Al alloys with the filler metal NiCrSiB was carried out at 1273–1373 K for 60–1800 s. The relationship of brazing parameters and shear strength of the joints was discussed, and the optimum brazing parameters were obtained. When products are brazed, the optimum brazing parameters are as follows: brazing temperature is 1323–1373 K, brazing time is 250–300 s. The maximum shear strength of the joint is 240–250 MPa. Three kinds of reaction products were observed to have formed during the brazing of Ti3Al alloys with the filler metal NiCrSiB, namely, TiAl3 (TiB2) intermetallic compounds formed close to the Ti3Al alloy. TiAl3+AlNi2Ti (TiB2) intermetallic compounds layer formed between TiAl3 (TiB2) intermetallic compounds and the filler metal and a Ni[s,s] solid solution formed in the middle of the joint. The interfacial structure of brazed Ti3Al alloy joints with the filler metal NiCrSiB is Ti3Al/TiAl3 (TiB2)/TiAl3+AlNi2Ti (TiB2)/Ni[s,s] solid solution/TiAl3+AlNi2Ti (TiB2)/TiAl3 (TiB2)/Ti3Al, and this structure will not change with brazing time once it forms. The formation of over many intermetallic compounds TiAl3+AlNi2Ti (TiB2) results in embrittlement of the joint and poor joint properties. The thickness of TiAl3+AlNi2Ti (TiB2) intermetallic compounds increases with brazing time according to a parabolic law. The activation energy Q and the growth velocity K0 of the reaction layer TiAl3+AlNi2Ti (TiB2) in the brazed joints of Ti3Al alloys with the filler metal NiCrSiB are 349 kJ/mol and 24.02 mm2/s, respectively, and the growth formula was y2=24.04exp(−41977.39/T)t. Careful control of the growth of the reaction layer TiAl3+AlNi2Ti (TiB2) can influence the final joint strength. 相似文献
142.
本文研究了机械合金化制备的纳米晶WC 10Co复合粉末的真空烧结特征 ,分析了孔隙度、显微硬度随绕结时间延长和烧结温度升高的变化规律 ,考察了一种新型抑制剂的作用。结果表明 :在 132 5℃ / 15min的烧结条件下 ,样品的相对密度达到了 98%以上 ;烧结样品的显微硬度随着烧结时间的延长和烧结温度的升高先增加后降低 ,并且在 132 5℃ / 15min的条件下其硬度为 2 2 95MPa ;新型抑制剂A既有利于晶粒长大的控制 ,同时又有利于材料致密化的进行 ,显著地提高了合金的性能。 相似文献
143.
144.
This work aims at determining the constitutive model of four commercial water atomised low alloyed steel powders during cold compaction. Single-action experiments were performed, obtaining cylindrical specimens with different H/D ratios. The distribution of axial and radial stresses was investigated, and the relationships describing both the radial stress transmission coefficient and the flow stress as functions of the relative density were determined. The radial stress transmission coefficient also confirmed the hypothesised value of Poisson’s coefficient. The friction coefficient between the powder column and the die wall was determined, also highlighting the influence of the H/D ratio. Measuring the axial and radial strains due to spring-back, the axial and radial elastic moduli were determined, as functions of the relative density. The results obtained for the four materials were compared, also highlighting both differences and similarities. 相似文献
145.
对于给定的树脂、颜填料体系,采用丹尼尔流动点理论对分散剂进行定性选择和用量试验,并将设计配方推广至生产应用。 相似文献
146.
《Ceramics International》2021,47(18):25425-25439
An optimal performance of bone implants with bioceramic coatings is closely related to the surface modification technology. For the first time, we have evaluated a gas detonation deposition (GDD) approach to obtain biocompatible ceramic coatings based on bioglass (BG) and calcium phosphates on Ti-based alloys as prospective materials towards their application for the development of bone implants. For the production of the coatings, hydroxyapatite (HA), HA metal-substituted (containing Ag+, Cu2+, or Zn2+) and tricalcium phosphate (TCP) were synthesized and characterized. Pure powders and their combination with BG were used to obtain coatings on a Ti–6Al–4V alloy using the developed automatized GDD setup. The microstructure, phase and chemical composition of the produced coatings were studied using XRD, SEM-EDS and Raman spectroscopy. The produced coated materials were evaluated in vivo in Wistar rats to analyze a reparative osteogenesis over a period of 12 weeks. The results regarding the optimization of the GDD method indicate its high productivity, as confirmed by high deposition rates. The highest deposition rate was observed for the coatings obtained from the HA metal-substituted powders. The results revealed a partial transformation of a HA phase to an α-TCP phase during the deposition, with a prevalence of the HA-phase in the coatings. According to the histological evaluation, the reparative osteogenesis occurs through the perimeter of the titanium implants, whereas the regeneration level increases from the 4th to the 12th week. The highest osteointegration level was detected for the implants coated with a biocomposite consisting of BG, HA and TCP. The results of the current study demonstrate an effectiveness of the GDD method to produce biocompatible coatings on Ti-based alloys. This provides excellent prerequisites towards the application and standardization of the GDD technology to manufacture bone implants for bone fixation and defect replacement, as well as the development of dental implants. 相似文献
147.
This Special Issue “Biodegradable Materials” features research and review papers concerning recent advances on the development, synthesis, testing and characterisation of biomaterials. These biomaterials, derived from natural and renewable sources, offer a potential alternative to existing non-biodegradable materials with application to the food and biomedical industries amongst many others. In this Special Issue, the work is expanded to include the combined use of fillers that can enhance the properties of biomaterials prepared as films. The future application of these biomaterials could have an impact not only at the economic level, but also for the improvement of the environment. 相似文献
148.
A new kind of anhydrous, transparent, and flexible potassium dihydrogen phosphate (KH2PO4 or KDP)/polyvinyl alcohol (PVA) composite in the form of film (0.10 mm) has been prepared by solution casting technique. KDP is well dispersed in the polymer matrix as observed from the microstructural studies. Frequency and temperature dependent dielectric properties of the composites have been studied with varying KDP concentrations. The PVA/KDP composite films exhibited extraordinarily high relative permittivity ε′ ∼ 430 (80 times higher compared with pure PVA and even higher than KDP) near the percolation threshold (ϕC = 2.5 wt % KDP) with low dielectric losses (∼ 0.15) at 1 kHz and room temperature. Such flexible, low loss and high dielectric permittivity material has enormous importance for application in devices. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 相似文献
149.
Linseed cake (LC), a byproduct of linseed oil extraction, is used as a functional filler for production of biodegradable composites. To determine the influence of residual linseed crude oil contained in lignocellulosic filler on the properties of the poly(lactic acid) (PLA)-based composites with 5–30% filler content, two types of LC were analyzed: a defatted and an unmodified one. Complex analysis of the composites' properties change was conducted in relation to their structure modification caused by the addition of a waste filler. It was found that the addition of LC resulted in simultaneous plasticization and improved crystallization of PLA. Lignocellulosic particles and crude linseed oil contained in the LC powder provided a modifying effect, influencing the level of crystallinity and mechanical and thermomechanical properties. Using LC may thus overcome one of the main drawbacks of PLA, which is brittleness and low crystallinity. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47152. 相似文献
150.
《Particulate Science and Technology》2012,30(8):927-931
ABSTRACTMaterials based on bismuth(III) oxide are candidate to be used in optical and electronic devices because of their properties such as a variable band gap, photoconductivity, photoluminescence, high refractive index, and dielectric permittivity. These properties are dependent of several factors, e.g., present phases and crystal morphology. The microwave-assisted hydrothermal method (MAH) is a fast and efficient approach of synthesis to obtain semiconductor powders. However, the synthesis of monoclinic bismuth oxide (α-Bi2O3) with acicular morphology by MAH was not found in literature. In this paper, microcrystals of acicular α-Bi2O3 (monophasic) were successfully obtained by MAH using a synthesis temperature of 80°C for 0.5?h. X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron, and transmission electron microscopies showed the formation of a monoclinic structure (space group P21/c) with acicular morphology that grew along the [001] direction. The temperature and time necessary to synthetize acicular microcrystals were significantly lower than those found for acicular microcrystals obtained by conventional hydrothermal method. 相似文献