R.B. Pérez-Sáez

New experimental device for infrared spectral directional emissivity measurements in a controlled environment

A new experimental device for infrared spectral directional emissivity measurements in a controlled atmosphere is presented. The sample holder, which permits to measure spectral directional emissivity up to 1050K, is placed inside a stainless steel sample chamber that can be evacuated or filled with different gases. The signal detection is carried out by means of a Fourier transform infrared spectrometer. The experimental results focus on the capability of the device to perform emissivity measurements as a function of temperature, emission angle, and in situ surface state evolution. A careful study of the sample temperature homogeneity and the measurement method has been done, including the background radiation, the apparatus response function, and temperature differences between the sample and the blackbody radiator. As a consequence, a compact expression for the sample emissivity that generalizes those previously obtained for the direct radiometric measurement method is found. The error assessment shows...

Radiation thermometry applied to temperature measurement in the cutting process

Temperature measurement of cutting tools used in machining processes has great technological importance, and it is interesting in a large number of industrial applications because wear is directly related to this variable. The influence of emissivity on the temperature measurement using radiation thermometers and the dependence of the measured temperature on the emissivity as a function of the surface roughness and the oxidation state is studied in this paper. Emissivity is measured using the direct radiometric method for uncoated P10 tungsten carbide inserts. Theoretical temperature shifts produced by changes in emissivity are estimated for several types of radiation thermometers, and these shifts are compared to the experimental temperature measurements carried out in the orthogonal turning process of cylindrical samples of 42CrMo4 steel with different machinability grades.

Advanced Shape Memory Alloys Processed by Powder Metallurgy

c) the large orientation dependence of the transformation strain, and d) the grain boundary segregation. In order to suppress the intergranular fracture and to improve the ductility of these alloys, the stress concentration in the grain boundaries must be controlled—either by development of high-textured alloys or development of fine grain alloys. [5] The high texture enables the accommodation of stress among adjacent grains and, as a consequence, the stress concentration in the grain boundaries decreases. Alternatively, the stress concentration decrease is due to the grain-size refinement, which produces smaller stress among adjacent grains. Several techniques are suitable for producing the grain-size refinement: addition of other elements in small quantities, [7] melt spinning, [8‐10] and powder metallurgy. [11,12] Finally, powder metallurgy is a relatively new technique in this area, and no attempts to use it in the development of this kind of alloys had been made, in spite of its promising capabilities. [14,15] Thus, taking into account these facts, a new production process of Cu‐Al‐Ni SMA by powder metallurgy is developed in this work. The first part of the present paper contains a detailed description of each stage of the process, whereas the second one is devoted to the characterization of thermomechanical and fracture properties of the obtained materials. Finally, a comparison of these properties with those of single crystals and polycrystals of the same kind of alloys but obtained by classical methods, is also performed.

Ordering temperatures in Cu-Al-Ni shape memory alloys

The ordering temperatures Tc1 (disordered β to B2 order) and Tc2 (B2 to L21 order) have been obtained in Cu–Al–Ni shape memory alloys with different concentrations by electrical resistivity. The dependence of the ordering temperatures on the concentration has been established. Also, a modification of the theoretical calculations has been proposed to predict the ordering temperatures in Cu–Al–Ni ternary alloys. A good agreement between the theoretical ordering temperatures and the experimental results has been found.

Combined standard uncertainty in direct emissivity measurements

In order to design a device to carry out direct emissivity measurements, a key point is the analysis of all the uncertainty components that give rise to the combined standard uncertainty. This will permit to choose the most appropriate measurement method to minimize the uncertainty, and also to identify the sources of the largest errors. If the experimental device is already in use, the complete uncertainty characterization, in addition to the emissivity uncertainty calculation, will permit the improvement of the device capabilities. Thus, a guideline to the experimentalists working in this subject is provided. In this work, a complete study of the uncertainty components in direct emissivity determination is carried out. First of all, the emissivity measurement method and the uncertainty estimation methodology are introduced. After that, the influence of the uncertainties of each of the magnitudes used to obtain the emissivity is analyzed theoretically. The most important error sources depending on the me...

Analysis of calibration methods for direct emissivity measurements

We analyze two important points related to the experimental emissivity measurements in this paper: the radiometer calibration accuracy and its stability to determine the required frequency of calibration. The usual two-temperature calibration method is compared to a more accurate method, which uses the measurement of blackbody radiation at several temperatures. Additionally, the suitability of the two-temperature method is studied as a function of the gap between both temperatures. Differences higher than 200°C are needed to obtain an acceptable calibration. The temporal stability of the calibration and the influence of the environmental conditions are also analyzed.

Analysis of the internal friction spectra during martensitic transformation by a new temperature rate method

Abstract The internal friction spectra of a martensitic transformation obtained as a function of temperature with T ≠0 , consists of three different contributions: transitory, phase transition, and intrinsic. In order to get a more quantitative information from these internal friction spectra, such as the volume fraction of transformed material, it is necessary to separate the spectra in their different contributions. This paper proposes a new method which allows to analyse the IF spectra. The new procedure is based on the strong dependence of the transitory term on the temperature rate. Thus, the separation of the three different contributions to the IF is completed starting from several IF spectra carried out at different temperature rates. Using this method it is possible to check the validity of the different models proposed in the literature for the explanation of the transitory term. Along with the presentation of the method, its application to a thermoelastic Cu–Al–Ni shape memory alloy is shown.

Ordering kinetics in Cu–Al–Ni shape memory alloys

The atomic order has a strong influence on the martensitic transformation behavior in Cu-based shape memory alloys. In this work we have studied the influence of the quenching and postquench aging treatments on the atomic order of the metastable β phase obtained by quenching in Cu–Al–Ni shape memory alloys by means of thermoelectric power (TEP) measurements. The initial evolution of TEP during aging shows two clear stages where TEP value decreases. These two TEP stages are interpreted as ordering processes at nearest neighbors (B2 order), and ordering processes at next nearest neighbors (L21 order), respectively. The analysis of the isothermal kinetics during aging at different temperatures has allowed us to determine the activation energies for both ordering processes.

Experimental verification of the anomalous skin effect in copper using emissivity measurements

Spectral directional emissivity has been measured in copper between 3 and 24 μm above room temperature. The experimental spectrum shows a weak broad peak between 7 and 14 μm, which is much more acute for higher emission angles. However, the peak width and position are both independent of the emission angle. The experimental results are in very good agreement with the semiclassical theory of the optical properties of metals in the regime of the anomalous skin effect, in particular with the asymptotic approximation. This comparison suggests that this work shows an optical experimental evidence of the anomalous skin effect.

Optical properties of metals: Infrared emissivity in the anomalous skin effect spectral region

When the penetration depth of an electromagnetic wave in a metal is similar to the mean free path of the conduction electrons, the Drude classical theory is no longer satisfied and the skin effect becomes anomalous. Physical parameters of this theory for twelve metals were calculated and analyzed. The theory predicts an emissivity peak epeak at room temperature in the mid-infrared for smooth surface metals that moves towards larger wavelengths as temperature decreases. Furthermore, the theory states that epeak increases with the emission angle but its position, λpeak, is constant. Copper directional emissivity measurements as well as emissivity obtained using optical constants data confirm the predictions of the theory. Considering the relationship between the specularity parameter p and the sample roughness, it is concluded that p is not the simple parameter it is usually assumed to be. Quantitative comparison between experimental data and theoretical predictions shows that the specularity parameter can ...