Procedia Materials Science最新文献

In this paper we present importance of depolarization effects modeling to fit spectroscopic Mueller matrix ellipsometry data. The relevant theoretical background based on Mueller matrix formalism is presented. The sample of SiO₂ layer (approx. 1 μm thick) on silicon substrate is used to demonstrate depolarization effects in obtained experimental data. In the first step the presence of interferences in the layer is used for modeling of depolarization effects caused by finite spectral resolution of the Mueller matrix ellipsometer. In the next step the depolarization caused by focusing of the probe light is analyzed and modeled. Both finite spectral resolution and beam focusing is a common issue in the optical characterization of samples with lateral dimensions smaller than (commonly used) collimated beam. Therefore to fit experimental data with model it is important to assume those depolarization effect into model.

This paper deals with investigation of surface damage induced by grinding operation on the rings made of 100Cr6 bearing steel of hardness 62HRC. Progressively developed grinding wheel wear is caused by using the series of identical rings while the surface properties of machined rings like a hardness, residual stresses, microstructure alterations and magnetic Barkhausen noise (BN) emissions are monitored as manifestations of increased thermal damage. The noninvasive observations based on the BN emissions are performed on each ring while more laborious experimental techniques are used on selected rings. The presented results also indicate that properly suggested monitoring system based on BN emissions can reliably detect surface burn induced by thermal damage of ground surface.

This paper deals with nondestructive magnetic evaluation of ground surfaces of chosen material hardness. The properties of prepared surfaces are studied with respect to the progressively worn grinding wheel. The nondestructive testing is based on the Barkhausen noise (BN) technique and obtained BN signals are supplemented by metallographic observations. The results show that the nature of thermal injury of the surfaces prepared by strongly worn grinding wheel significantly depends on the hardness of material. The typical thermal softening induced by grinding cycle is found on the surfaces of hardness 62 HRC whereas samples of lower hardness exhibit rehardening effect associated with the formation of white layer. These material changes are strongly correlated with the BN properties.

In this paper the Mueller matrix ellipsometry in the spectral range from 0.73 to 6.4 eV measured using dual rotating compensator ellipsometer RC2 (Woollam company) is applied to study anisotropic crystals. First we summarize the effects of optical anisotropy to Mueller matrix spectra. As an example of an uniaxial sample we have characterized a Rutile (TiO₂) tetragonal crystal. The optical axis of the sample is parallel to its surface. The sample is characterized at variable angle of incidence and variable azimuthal rotation angle. The Mueller matrix spectra are fitted to the model based on Kramers-Kronig consistent Basis spline and obtained optical functions are compared with tabulated data and ab-initio models based on first-principle calculated electronic structure.

The paper presents the estimation of the fatigue life under multiaxial cyclic loading of selected construction materials: two aluminum alloys PA4 (6068) and PA6 (2017A), alloy steel S355JOWP (in past called 10HNAP) and cast iron GGG 40. Calculations were based on three criteria of multiaxial fatigue, which is based on the concept of critical plane and the coefficients present in the expressions for the equivalent stresses are calculated on the basis of classical fatigue limits.

The fatigue crack growth modeling that based on linear fracture mechanics under the Mode I condition provided a good estimate of the stress intensity range for subsurface crack growth in α or near α-type titanium alloys. Based on the relationship between crack growth rate and stress intensity factor range, the fatigue crack propagating life was evaluated by the Paris rule. The subsurface crack initiation process consumed a large number of cycles to failure. Microstructure may strongly affect on not only subsurface crack initiation but also crack growth. The microstructural modification to prevent microcrack growth should be taken into account.

Tensile test methodology for ceramic foams has been elaborated and test specimens of different dimensions and those containing central sharp notch (simulating a crack) were tested. Tested material was commercially available alumina based ceramic foam commonly used as filters of light metals melts. The foam cell size used within this study was 60 PPI. The main aim of the investigation has been to prove experimentally whether there is any stress concentration effect in the open cell structures. The fracture load (tensile strength) values were analysed and, in particular, the samples containing central sharp notch and comparable unbroken cross-section were compared with the unflawed samples. Specimens with central through thickness sharp notch have shown demonstrably the strength values comparably lower than the strength level of samples having the same cross-sectional area without stress concentrator. The explanation has been seen in stress concentration effect beneath the internal sharp notch root.

The crevice corrosion repassivation potential was determined by the Potentiodynamic–Galvanostatic-Potentiodynamic (PD–GS–PD) method. Alloys 625, C–22, C–22HS and HYBRID–BC1 were used. Specimens contained 24 artificially creviced spots formed by a ceramic washer (crevice former) wrapped with a PTFE tape. Crevice corrosion tests were performed in 0.1 mol/L and 1 mol/L NaCl solutions at temperatures between 20 and 90 °C, and CaCl₂ 5 mol/L solution at temperatures between 20 and 117 °C. The crevice corrosion resistance of the alloys increased in the following order: 625 < C–22 < C–22HS < HYBRID–BC1. The repassivation potential (E_CO) showed the following relationship with temperature (T) and chloride concentration ([Cl⁻]) E_CO = (a + b T) log [Cl⁻] + c T + d; where a, b, c and d are constants. At temperatures above 90 °C, E_CO for alloy 625 stabilized at a minimum value of –0.26 V_SCE.

In this paper, microstructure and mechanical properties of Nano/ultra-fine structured 7075 Aluminum alloy were investigated by accumulative roll bonding process at room temperature. After the accumulative roll bonding, the tensile yield strength, ultimate strength and microhardness of the Nano/ultra-fine structured 7075 Aluminum alloy were 216%, 114%, and 122% higher than those of the coarse-grained samples, respectively, while elongation to failure was lower than the primary sample. The elongation to failure decrease value is high after the first pass while after subsequent passes, it remains almost constant. Evolution of microstructure of the samples was investigated by transmission electron microscopy (TEM) and field emission scanning electron microscope (FESEM). In addition, phase analysis after ARB were performed using X-ray diffraction analysis. The micro scale tensile fracture morphology of the Al 7075 alloy at different ARB strains were investigated by using FESEM. According to TEM micrographs, the ARB processed materials after six passes were homogeneously filled with the ultra-fine grains, meaning that grain sizes were about 130 nm. XRD, FESEM and TEM results show that MgZn2 precipitates were broken, and small spherical particles were formed during ARB, which is distributed uniformly throughout the material. Uniform distribution of these fine particles restricted grain growth, resulting in the formation of ultra-fine grains. Fracture morphologies of samples after ARB show that the average dimple size gradually decreases with increasing number of ARB passes, which lead to fracture type changes from ductile to brittle.