- Ei，ESCI收录期刊
- 中国科学引文数据库(CSCD)核心期刊
- 中文核心期刊
- 文摘与引文数据库(Scopus)
- 剑桥科学文摘(CSA)
The rotating bar bending fatigue testing specimens made from EA4T high speed axle were grinded. Some of the grinded specimens were surface ultrasonic rolling processed (SURP). The microstructures in surface layer and surface morphologies of the grinded specimens and the SURP specimens were observed. Micro-hardness and residual stress in surface layer and surface roughness of the grinded specimens and the SURP specimens were measured. Fatigue limits of the grinded specimens and the SURP specimens were tested using rotational bending testing method. The results show that fatigue limits of the grinded specimens and the SURP specimens are 352MPa and 401MPa respectively.The increase of fatigue limit of the SURP specimens is mainly due to the decrease of surface roughness and the increase of strength and residual compressive stress in surface layer.
Microstructure, friction and wear properties of Cu30Ni alloy induced by surface punching and stabilizing heat treatment were investigated by using atomic force microscope, micro-hardness tester and abrasion tester. The results show that comparison with original sample, the punched sample has refined microstructure with non-stable grain boundary induced by mechanical punching. This non-stable grain boundary can transform into stable grain boundary or metastable grain boundary under stabilizing heat treatment. As a result, micro-hardness is increased from 93HV to 297HV, wear rate is decreased obviously from 4.2mm3/m to 0.41mm3/m, and friction coefficient μ is slightly decreased from 0.35 to 0.32, and there is no obvious microcracks observed in the morphologies of worn surfaces of the punched samples and after stabilizing heat treatment.
C/SiC composite was fabricated by vacuum infusion method to infiltrate mixing slurry of the SiC powder, phenolic resin and etc into carbon felt. The density, porosity and the mechanical strength of C/SiC composite were determined. The microstructure of C/SiC composite was studied by scanning electron microscope (SEM), meanwhile failure mechanism of C/SiC composite were analyzed. The results show that the compactness and mechanical property of C/SiC composite fabricated by two times vacuum infusion method twice exhibit the changing trend of going up first and falling down later as SiC content increasing in the slurry, the crack propagation process includes several toughening enhancement mechanisms: fiber/matrix debonding, fiber-bridging, fiber friction, crack deflection, fiber pull-out. After comprehensive comparation, when content of SiC is 25%(mass fraction), the compactness and mechanical properties of the C/SiC composite are optimum. Its density reaches 1.31g/cm3, porosity is 15.10%, bending strength and compressive strength are 84.04MPa and 74.22MPa respectively, C/SiC composite has good toughness.
A series of polyimide (PI)-SiO2 nanocomposite aerogels (CPIA-SiO2-0-CPIA-SiO2-7) were successfully prepared via the supercritical carbon dioxide drying process of the nanocomposite PI wet gels derived from 3,3',4,4'-biphenylene tetracarboxylic dianhydride (BPDA) and 2,2'-dimethylbenzidine (DMBZ) with octa(aminophenyl)silsesquioxane (OAPS) as the end-capper, and nano-sized silica particles as the filler. The results indicate that the introduction of nanoscale silica particles have not apparently affected the thermal resistance of the obtained aerogels. However, with the increase of SiO2 loading in the aerogels, the porosity from 89.6% to 79.4% and the Branuaer-Emmet-Teller (BET) surface areas of the composite aerogels decrease from 425.5m2/g to 380.2m2/g, meanwhile, the pore size distribution widens gradually. At last, the atomic-oxygen resistance of the PI-SiO2 aerogels is greatly improved by introduction of nanoscale SiO2 fillers. The atomic-oxygen erosion ratio(2.6%) of CPIA-SiO2-7 with 7% SiO2 loading is only 1/5 that(12.3%) of the pristine CPIA aerogel(CPIA-SiO2-0).
The AerMet100 ultra-high steel was cryogenic treated after quenched and then was tempered under different temperatures, the OM, SEM and TEM techniques were used to observe the microstructure after heat treatment. The effect of different heat treatments on the dynamic mechanical properties was investigated using the split Hopkinson pressure bar. The results indicate that the content of residual austenite is reduced, the dynamic plasticity is enhanced and the comprehensive properties are improved after cryogenic treatment. Under high strain rate (1000-4200s-1), compared with the quasi static, material shows strain rate hardening effect obviously. The dynamic compression strength increases initially and then decreases with increasing tempering temperature, the peak value of about 2800MPa appears when the tempering temperature is 482℃. The material fracture form is the shear fracture when the steel is under the dynamic loading.
Analysis on dynamic control mechanism of naphthenic acid corrosion indicated that the liner relationship between lnv and (-1/T) under high temperature and high flow rate. Analysis on corrosion data of Cr steel in API581 and the simulation experiment results both verify the linear relationship between lnv and (-1/T). The relationship between lnv and (-1/T) can be applied to predict the average naphthenic acid corrosion rate of Cr steel under different temperature. Turbulence distribution on the specimens can be obtained through simulation by the software of Fluent. Correlations between turbulence distribution and local surface 3D corrosion depth on the specimens prove that turbulence intensity can significantly influence the local corrosion depth. The ratio between local max corrosion depth and average corrosion depth in 2% turbulence area was only 1.56, but in 8% turbulence area, the ratio can reach above 3.7 times, the influence of turbulence on local corrosion depth increases with the turbulence intensity.
The base metals of die casting AM60B magnesium alloy were welded by GTAW without filling material after heat treatment at different temperatures and cooling to room temperature. The distribution and morphology of pores in the sections of welds were observed by scanning electron microscopy, the sizes of the pores in the welds were measured by the particle size analysis software of Nano measurer 1.2, and the weld porosity was distinguished and calculated by a secondary developed image analysis program based on Matlab. The results indicate that: the pores are mainly distributed in the fusion zone and near the fusion line. Compared with the weld without heat treatment before welding, both the porosity and the sizes of pores in the welds with heat treatment before welding decrease. With the increase of the heat treatment temperatures before welding, both the porosity and the sizes of pores after welding increase.
An as-cast Al0.3CoCrFeNi high entropy alloy with face-centered cubic (FCC) structure was processed by high-pressure torsion (HPT) to different strain values. This deformation-induced microstructure evolution was investigated by using Vickers hardness, electron backscatter diffraction, X-ray diffraction and transmission electron microscopy. The results show that, during HPT processing,the crystal structure is not changed, remaining FCC structure, while nanocrystallization of grains is induced by HPT to 30nm of average grain size; grain refinement is achieved through twinning (including primary and secondary twinning), de-twinning (including primary and secondary de-twinning) and twin boundary subdivision; competition between twinning and de-twinning processes contributes to the decrease and subsequent increase in twin boundary spacing, while the minimum spacing of primary and secondary twins reach 2.7nm and 0.9nm, respectively.
The zirconium salt as main raw materials, chrome-free chemical conversion treatment was carried out on AA6063 aluminium alloy at room temperature. Through the analysis of SEM, XRD and electrochemical test, the properties of the chrome-free conversion coating were studied. The results show that zirconium coating grows from needle like small cell structure to large round cell, and then develops to uniform black and grey conversion coating; the thickness of zirconium coating is about 8.79μm, which is mainly composed of KZrF3(OH)2·H2O and KZrF3O·2H2O;the corrosion resistance of the zirconium coating is improved by hundreds times than aluminium alloy, and is equivalent to chrome conversion coating; the corrosion resistance of zirconium coating has a certain relationship with post treatment process, the coating structure equivalent circuit is R1+C2/R2+M3.
TiO2 nanowires were synthesized by the ion-exchange and high temperature sintering of sodium titanate nanowires. The effect of ion exchange time and sintering temperature on the formation of TiO2 nanowires by using X-ray diffraction analysis, Uv-visible diffuse reflectance spectroscopy technique, and scanning electron microscopy were studied. The photocatalytic activity of TiO2 nanowires was tested using methyl orange as a target pollutant. The results show that a longer ion exchange time is ideal for the formation of titanic acid nanowires, and the sodium titanate nanowires are completely transformed into titanic acid nanowires when the ion exchange time is 48h. A lower sintering temperature is not beneficial to the formation of TiO2 nanowires, and it is found that the titanic acid nanowires could be converted into TiO2 nanowires at 650℃. Sodium titanate nanowires has almost no photocatalytic activity, while TiO2 nanowires exhibit a much higher photocatalytic activity.
Adhesion force of organic colloidal can improve the interfacial tension of the material surfaces to be connected and thus provide favorable conditions for brazing between dissimilar materials. The epoxy resin was chosen as viscous colloid,TiH2 powder as the source of active elements, and AgCu eutectic alloy foil as filler metal. The mixture of TiH2 and epoxy resin in a certain percentage was coated on the surface of SiO2f/SiO2 composites and heated to evaluate the wetting ability. The results of wetting experiment on the coated surface show that colloid adhesion improves the wetting and spreading of brazing filler materials. The application of this novel method in brazing can realize sound joints between Invar alloy and SiO2f/SiO2 composites, Cf/SiC composites or Al2O3 ceramic.
A method to characterize the grain size of the material by the spectrum energy of ultrasonic signals was proposed. In order to study the new method, firstly, some austenitic stainless steel materials with different grain sizes were prepared by different heat treatment regimes. Then the grain sizes of those prepared materials were characterized by using the attenuation coefficient, velocity and spectrum energy, respectively. The results show that attenuation coefficient calculated by the proposed method and the average grain size exhibit nonlinear relationship. The predicted error of the grain sizes is within 4%-15%, which is superior to the conventional methods, and verifies the effectiveness of the proposed method
The effect of Al-5Ti-1B and Al-5Ti-0.2C grain refiners on the microstructure evolution rule of 7050 aluminum alloy with Zr at as-cast, as-homogenization and as-ageing states, precipitation behaviour of the second phases and mechanical properties was studied by optical microscope (OM),scanning electron microscope (SEM) and energy dispersive spectrometer (EDS), combined with mechanical tensile properties and Vickers hardness test. The results show that the existence of Zr element in 7050 aluminum alloy causes Al-5Ti-1B and Al-5Ti-0.2C refining occurring the phenomenon "poisoning",which reduces the refining effect of grain refiner; comparing with Al-5Ti-1B, increasing the amount of Al-5Ti-0.2C grain refiner is more effective to ease the "Zr poisoning" phenomenon, to refine grains, and can improve the strength and hardness, while keeping good elongation rate; Meanwhile, comparing with the 7050 alloy using the Al-5Ti-1B grain refiner, the distribution of the second phases present in 7050 aluminum alloy is more dispersed and uniform than the alloy using Al-5Ti-0.2C refiner.
The numerical model of evaluating ceramics' fracture toughness by traditional indentation method was calculated with the application of virtual crack closure technique, based on which, the measurement errors and application scope of several typical formulas employed in traditional indentation method to evaluate the fracture toughness of ceramic materials were analyzed. The results show that, compared with Evans formula, Lawn formula, JISR formula and Niihara formula of traditional indentation method, the value of fracture toughness measured by using Anstis formula is closer to the theoretical value, enjoying relatively accurate testing results with a maximum error of 12.9%, when the material's ratio of unloading work to total loading work fell 0.3≤We/Wt≤0.45. When the material's ratio of unloading work to total loading work ranged 0.45<We/Wt≤0.7, the measurement error of traditional indentation method for evaluating the fracture toughness of ceramic materials increased rapidly with We/Wt increasing, especially when We/Wt equals 0.7, the measurement errors of fracture toughness of ceramic materials, using Anstis formula, Evans formula, Lawn formula, JISR formula and Niihara formula are 70%, 148.5%, 48.8%, 98.7% and 166.6% respectively, indicating that, in this range of We/Wt, the measurement error of traditional indentation method for evaluating fracture toughness of ceramic materials is excessively large.
The evolution of oxide layer and its influence on nitriding after different decarburization time and holding time in grain-oriented silicon steel was investigated by field emission scanning electron microscopy and energy dispersive spectrometer. The results indicate that oxide layer gets thicker with the decarburization time prolonging and is beneficial to nitriding, accompanying with the process of lamellar silica transform into spherical silica. The three-layer structure of oxide layer is beneficial to nitriding, the main contribution to nitriding comes from lamellar silica, while thicker spherical silica plays certain suppression role in nitriding, the nitriding content of oxide layer with solely spherical silica structure is much less than that of three-layer structure. There are some influences on the morphology of nitride after nitriding process.
Effect of temperature and stress on velocity of ultrasonic longitudinal wave, polarized shear wave, longitudinal critically refracted (LCR) wave in pre-stretched 7050 aluminum alloy plate was investigated. Regularity of LCR wave with different frequency propagating in gradient stress field was analyzed. The results show that effect of temperature on velocity of ultrasound is more than that of acousto-elastic effect. When specimen is axially tensioned, velocity of LCR wave propagating along axial and shear wave polarizing parallel to axial decreases, velocity of shear wave polarizing perpendicular to axial increases, and velocity of longitudinal wave propagating perpendicular to axial hardly changes. LCR wave with higher frequency indicates stress nearer to surface. Tested stress by acoustic elasticity represents mean stress components in direction of particle vibration induced by ultrasonic.
As the advanced processing technology developed in recent years, electron beam technology has the advantages in superalloy has been paid extensive attention. The research and application of electron beam technology in the field of preparation and processing of superalloy were reviewed, including the electron beam forming and fabrication of superalloy, electron beam smelting of superalloy, electron beam welding, surface modification and electron beam physical vapor deposition of superalloy, the challenge for electron beam technology at present was pointed out, and the development of electron beam technology in the field of superalloy was discussed.
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