The specific cost of the surface grinding of vanadium high-speed steel with superabrasive wheels

The processes of grinding the R6M5F3-grade steel with kubonit and diamond wheels dressed by the electroerosion method have been compared using a criterion for a minimum unitary grinding cost. It has been shown that the unitary grinding costs for wheels being compared are practically equal, which gives the possibility to equally use wheels of the compared superabrasives in grinding the R6M5F3 steel.     

Non-destructive microstructural analysis by electrical conductivity: Comparison with hardness measurements in different materials

The use of non-destructive evaluation (NDE) techniques for assessing microstructural changes in processed materials is of particular importance as it can be used to assess, qualitatively, the integrity of any material/structure. Among the several NDE techniques available, electrical conductivity measurements using eddy currents attract great attention owing to its simplicity and reliability. In this work, the electrical conductivity profiles of friction stir processed Ti6Al4V, Cu, Pb, S355 steel and gas tungsten arc welded AISI 304 stainless steel were determined through eddy currents and four-point probe. In parallel, hardness measurements were also performed. The profiles matched well with the optical macrographs of the materials: while entering in the processed region a variation in both profiles was always observed. One particular advantage of electrical conductivity profiles over hardness was evident: it provides a better resolution of the microstructural alterations in the processed materials. Moreover, when thermomechanical processing induces microstructural changes that modify the magnetic properties of a material, eddy currents testing can be used to qualitatively determine the phase fraction in a given region of the material. A qualitative relation between electrical conductivity measurements and hardness is observed.     

炭/炭刹车副表面硬度对摩擦磨损性能的影响

对等温CVD沉积所得两种不同结构的炭/炭复合材料,不同表面硬度下的摩擦磨损性能进行了研究.其中A材料是光滑层结构,B材料是粗糙层和光滑层的混合结构.摩擦试验在实验室规模的MM-1000摩擦试验机上进行.试验表明:随着热处理温度的提高,不同材料的表面硬度均在下降;但在经历相同热处理温度后,B材料的表面硬度比A材料的低;表面硬度较低的B材料塑性较强,摩擦面上的磨屑易于形成致密、连续的摩擦膜,有利于保持稳定而较高的摩擦系数.     

An investigation on machined surface quality and tool wear during creep feed grinding of powder metallurgy nickel-based superalloy FGH96 with alumina abrasive wheels

In this study, the machined surface quality of powder metallurgy nickel-based superalloy FGH96 (similar to Rene88DT) and the grinding characteristics of brown alumina (BA) and microcrystalline alumina (MA) abrasive wheels were comparatively analyzed during creep feed grinding. The influences of the grinding parameters (abrasive wheel speed, workpiece infeed speed, and depth of cut) on the grinding force, grinding temperature, surface roughness, surface morphology, tool wear, and grinding ratio were analyzed comprehensively. The experimental results showed that there was no significant difference in terms of the machined surface quality and grinding characteristics of FGH96 during grinding with the two types of abrasive wheels. This was mainly because the grinding advantages of the MA wheel were weakened for the difficult-to-cut FGH96 material. Moreover, both the BA and MA abrasive wheels exhibited severe tool wear in the form of wheel clogging and workpiece material adhesion. Finally, an analytical model for prediction of the grinding ratio was established by combining the tool wear volume, grinding force, and grinding length. The acceptable errors between the predicted and experimental grinding ratios (ranging from 0.6 to 1.8) were 7.56% and 6.31% for the BA and MA abrasive wheels, respectively. This model can be used to evaluate quantitatively the grinding performance of an alumina abrasive wheel, and is therefore helpful for optimizing the grinding parameters in the creep feed grinding process.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-020-00305-2     

Preparation of waste glass powder by different grinding methods and its utilization in cement-based materials

Waste glass, as a hard-to-grind material, was often grinded into powder by ball-mill in order to be used as a supplementary cementitious material in concrete. In this study, three different glass powders (GP) referred to as GPd, GPw and GPe were fabricated by different methods (i.e. dry condition, water condition and ethyl alcohol condition), and the effect of GP on the properties of cement-based materials was systematically evaluated. The results showed that the milling efficiency of GP was significantly affected by grinding condition. Ultrafine GP can be obtained as additional water or ethyl alcohol was added during the grinding process. GP showed low pozzolanic reactivity in the early age, even when the particle size was decreased to about 300 nm. GPd with large particle size and non-absorbent feature could increase effective water-to-cement ratio and thus improved the workability and early strength of specimens containing GPd, while the later strength was lower than that of reference ones due to low pozzolanic reactivity of GPd. In contrast, specimens containing GPw and GPe exhibited higher early mechanical strength than reference specimen due to the filling and acceleration effects of GP. An encouraging result indicated that GPe presented high pozzolanic reactivity at 28 d, which was seldom reported in the literature.     

The concept of effective hardness in the abrasion of coarse two-phase materials with hard second-phase particles

During the abrasion of a coarse two-phase material which contains hard second-phase particles, a brittleness mechanism can frequently coexist with plastic grooving. By taking R(X) as the abrasion resistance of given material with X as its second-phase volume fraction, the concept of effective hardness, H _eff, gives rise to a modification of the linear rule of mixtures as R(X) ∫ (1-X)H _m + αXH _s, where H _m and H _s are the hardness of pure matrix material and pure second phase, respectively. The parameter α decreases with increasing severity of the brittleness effect. By defining α_c=H _m/H_s, dR/dX<0 provided that α<α_c. The SiC abrasion data of a series of Al-Si alloys (with the volume fractions of pro-eutectic Si particles ranging from 0.023 to 0.219) can be rationalized by the above model since R(X) shows a nice linear fit with X. The α_c value of the test alloys is close to zero. Therefore, as indicated from the wear surface, extensive brittle fracture can occur without deteriorating the abrasion resistance. For those with dR/dX<0, subsurface fracture is also pronounced.     

The important role of titanium microalloying in refining austenite grain of heavy-duty H-beam steel during rough rolling produced by a new technology

A new technology of austenite grain refinement, fine austenite enhanced ferrite transformation, is proposed for heavy-duty hot-rolled H-beam steels in this work. Titanium microalloying is very important and necessary for the new technology. The effect of titanium on the prior austenite grain size of steels during simulated rough rolling was investigated. The results show that the prior austenite grain sizes of specimens with titanium and niobium elements are much finer than those of specimens with niobium but without titanium deformed at the same parameters. For the alloying composition of studied steels, titanium nitride particle maybe precipitated in specimens with titanium at above 1,200 °C, however, niobium carbide particles can't form in specimens without titanium at above 1,150 °C. The thermodynamically stable titanium nitride particles can impede the grain growth at high temperature for example furnace heating before rough rolling and bring the epitaxial growth of niobium carbide on pre-existing themselves which induces a large number of titanium nitride-niobium carbide composite precipitates. These fine precipitates can pin austenite grain boundaries effectively and ensure austenite grain refinement.     

The disturbance produced by an oscillatory pressure distribution in uniform translation on the surface of a liquid

Summary Expressions are derived for the two-dimensional surface elevation resulting from an oscillatory translating surface pressure distribution. The surface elevation is given as the sum of four terms, each of which is associated with an improper integral having a simple pole singularity. Results are presented for the delta function and the uniform spatial pressure distribution.The mean work done on the fluid per unit time by the delta function pressure distribution is given. Numerical results are presented for the surface elevation resulting from the uniform pressure distribution.     

Study of wave propagation in nanowires with surface effects by using a high-order continuum theory

A high-order continuum model is developed to study wave propagation in nanowires. By using the model, heterogeneous nanostructure effects can be captured especially for high wave frequency cases. Surface stress effects are also included by using the incremental deformation approach. The governing equations of motion in the nanowire are derived including both the strain-independent and strain-dependent surface stresses. For simplicity and clarity, specific attention will be paid to the effects of strain-independent surface stress in this study. The accuracy of the proposed model is validated by comparing dispersion curves of longitudinal wave propagation from the current model with those from the exact solution. By conducting a reduced formulation, the results predicted by the current model will be compared with those based on existed high-order models to show capability of the current model. Numerical simulations are then conducted to study both longitudinal and flexural wave propagation in nanowires. The surface stress effects upon both longitudinal and flexural wave propagation in nanowires are demonstrated, from which the size dependent wave information in nanowires can be observed. Some new physical wave phenomena related to the surface stress effects are discussed.     

The discrepancy in the prediction of surface temperatures by inverse heat conduction models for different quenching processes from very high initial surface temperature

In the current work, an attempt has been made to study the effect of different parameters on the accuracy of the prediction at a very high initial surface temperature by developing two different heat conduction models. The result depicts that MSSE (minimum sum squared error) in the prediction decreases with increasing number of sensors used in the prediction. The accuracy of the prediction enhances with decreasing plate thickness and distance between the thermocouple and quenched surface. Up to a cooling rate of 60?K/s, the selection of model dimension (1-D or 2-D) does not affect, but beyond the previously mentioned cooling rate, 2-D model induces less error than 1-D. Moreover, the inclusion of thermo-physical properties in the model reduces the error in the MSSE. By using Box–Behnken methodology, the optimum conditions (d/D?=?0.81, n/Y?=?0.5 and Y*/Y?=?0.65) for the least MSSE have also been determined.     

Control of morphology and properties by the selective distribution of nano-silica particles with different surface characteristics in PA6/ABS blends

The roles of nano-silica particles in the morphology, rheological, crystallization, and melting properties of polyamide 6/acrylonitrile–butadiene–styrene (PA6/ABS) blends were investigated. With the addition of nano-silica particles possessing different surface characteristics (hydrophilic or hydrophobic), the blends showed a notable difference in the morphology of the dispersed ABS phase in the melt or solid state, which is mainly caused by different distribution states for the two kinds of nano-silica particles. Particularly, it was found that the hydrophilic nano-silica particles tended to distribute in PA6 matrix, whereas the hydrophobic nano-silica particles were almost located at the PA6/ABS interface. Besides, the shear thinning behavior of the composites was significantly changed with the incorporation of hydrophobic nano-silica particles and the contribution from the interface was regarded as the dominated one to influence the rheological properties. Finally, with different surface characteristics and their distribution states, it was found that nano-silica particles can play different roles in crystallization and melting properties.     

Determination of total sulfur at microgram per gram levels in geological materials by oxidation of sulfur into sulfate with in situ generation of bromine using isotope dilution high-resolution ICPMS

We have developed a new, simple, and accurate method for the determination of total sulfur at microgram per gram levels in milligram-sized silicate materials with isotope dilution high-resolution inductively coupled plasma mass spectrometry equipped with a flow injection system. In this method, sulfur can be quantitatively oxidized by bromine into sulfate with achievement of isotope equilibrium between the sample and spike. Detection limits for 32S+ and 34S+ in the ideal solution and silicate samples were 1 and 6 ng mL(-1) and 0.07 and 0.3 microg g(-1), respectively. The total blank was 46 ng, so that a 40-mg silicate sample containing 10 mirog g(-1) sulfur can be measured with a blank correction of < 10%. This total blank can be lowered to 8 ng if a low-blank air system is used for evaporations. To evaluate the applicability of this method, we analyzed not only silicate reference materials with sulfur content of 5.25-489 microg g(-1) and sample sizes of 13-40 mg but also the Allende meteorite with a sulfur content of 2%. The reproducibility for various rock types was < 9%, even though blank corrections in some samples of low sulfur content were up to 24%. This method is suitable for analyzing geological samples as well environmental samples such as soils, sediments, and water samples.     

Evolution of the optical transitions in AlxGa1 − xAs/GaAs quantum well structures grown on GaAs buffers with different surface treatments by molecular beam epitaxy

Al_0.3Ga_0.7As/GaAs Quantum Well structures were grown by molecular beam epitaxy (MBE) on a 500 nm thick GaAs buffer layer subjected to the following surface processes: a) in-situ Cl₂ etching at 70 °C and 200 °C, b) air-exposure for 30 min. The characteristics of these samples were compared to those of a continuously grown sample with no processing (control sample). We obtained the quantum wells energy transitions using photoreflectance spectroscopy as a function of the temperature (8-300 K), in the range of 1.2 to 2.1 eV. The sample etched at 200 °C shows a larger intensity of the quantum well peaks in comparison to the others samples. We studied the temperature dependence of the excitonic energies in the quantum wells (QWs) as well as in GaAs using three different models; the first one proposed by Varshni [4], the second one by Viña et al. [5], and the third one by Pässler and Oelgart [6]. The Pässler model presents the best fitting to the experimental data.