Papers by Keyword: Differential Scanning Calorimetry

Abstract: The new technique has been developed for measuring the β-transus temperature of (α+β)-titanium alloys with any initial microstructure by means of the DSC method. The technique is based on a linear correlation between extremums of temperature on the DSC time-derivative curve, the Mo-equivalent of an alloy and the equilibrium β-transus temperature. The developed technique enables the determination of the β-transus temperature with the use of a single specimen and it is characterized by high accuracy comparable with that of structural analysis techniques.

Abstract: The effect of different interstitial impurities content (oxygen, carbon) on β - transus temperature and complex of properties in the heat-strengthened condition of the Ti-5Al-5V-5Mo-3Cr-1Zr (VST55531) titanium alloy has been studied. The possibility of determining alloy β - transus temperature by the differential scanning calorimetry method with accuracy comparable with the test quenching method is shown in this paper. It is shown that under identical aging regimes an increase of oxygen content from 0.176 to 0.25 wt.% and carbon content from 0.009 to 0.025 wt.% in VST55531 alloy results in higher strength, plastic characteristics and lower ductility, toughness characteristics, especially those which related to the crack propagation.

Abstract: Hexanediamine adipate, pentanediamine adipate and bio-based pentanediamine adipate were prepared by adipic acid reaction with 1,6-hexanediamine, 1,5-pentanediamine and bio-based 1,5-pentanediamine, respectively. Their structures and thermal properties have been analyzed by infrared spectra, SEM, DSC and TGA. Infrared spectra showed the main differences between 1,6-hexanediamine and 1,5-pentanediamine for the deformation vibration and out of plane bending vibration of N−H. Hexanediamine adipate and pentanediamine adipate had the difference at the asymmetric stretching vibration of −COO^-−. The crystal morphologies of hexanediamine adipate and pentanediamine adipate showed dendritic and acicular, respectively. The melting point of pentanediamine adipate, pentanediamine adipate and bio-based pentanediamine adipate were 208.0 °C, 182.3 °C and 182.9 °C, respectively. The polymerization of hexanediamine adipate, pentanediamine adipate and bio-based pentanediamine adipate happened at 201.0, 190.2 and 194.9 °C, respectively. And the decomposition temperature of PA66, PA56 and bio-based PA56 were 401.8, 403.5 and 405.2 °C, respectively.

Abstract: Traditional description of the rate of the thermoset resin reaction by the Arrhenius relationship multiplied by a reaction function has been used in this study. The Kissinger method and ASTM E 698 procedure have been used for a determination of parameters of the Arrhenius relationship. N-th order, Prout-Tompkins and Kamal-Sourour models have been used and evaluated as the reaction functions to formulate the curing kinetic models of an epoxy resin.An engineering tool based on Microsoft Excel code has been developed by using the developed methodology. This tool has been successfully applied for a building of the curing kinetic model of vinyl ester resin with high microwave absorption properties to be used in the microwave assisted pultrusion processes.

Abstract: The effects of Sn addition on clustering and age-hardening behavior in an Al-0.6Mg-1.0Si (mass %) alloy were investigated. Addition of Sn delayed the age-hardening in single aging at 170 ̊C. On the other hand, Sn promoted the age-hardening response in 3-step aging process which comprises a pre-aging (PA) at 90 ̊C for 18ks followed by natural aging (NA) for 604.8ks and artificial aging (AA) at 170 ̊C. The characteristics of clusters formed during PA and NA were evaluated by differential scanning calorimetry (DSC) analysis and atom probe tomography (APT). The DSC results show that the endothermic peak at around 160 ̊C to 200 ̊C was observed in the Sn-free alloy. On the other hand, in the Sn-added alloy, endothermic peak was not observed. It is suggested that Sn addition suppresses the formation of the clusters formed during NA. The APT results show that the Sn addition decreases the number density of clusters, especially smaller clusters. No Sn precipitates were found in Mg-Si precipitates formed during AA at 170 ̊C for 3.6ks. It is speculated that suppression of smaller cluster formation by addition of Sn promotes the age-hardening response

Abstract: We follow changes in the micro structure at several distances from the weld nugget of friction stir welded AlCuLi-alloy (AA2198) plates occurring due to the tool movement and the created heat by employing different methods: Small Angle X-ray Scattering (SAXS), giving information on type, size and density of precipitates, Differential Scanning Calorimetry (DSC), giving information on formed precipitates by their dissolution signal, and positron annihilation lifetime spectroscopy (PALS), being sensitive to vacancies and dislocations as well as to the formation and growth of precipitates. We start by characterizing the base material as a reference and proceed via the heat-affected zone to the weld nugget. By the use of complementary methods, we obtain information on structure, kind and distribution of precipitates and correlate this with hardness measurements.

Abstract: Precipitation hardening aluminium alloys are widely used for automotive applications. To enhance the application of aluminium profiles, improved formability is needed. Tailor Heat Treated Profiles (THTP) with locally different material properties attempt to increase formability e.g. in bending processes. Tailoring of local properties is obtained by a local short-term heat treatment, dissolving the initial precipitate state (retrogression) and still allowing subsequent ageing. In the present study, the dissolution and precipitation behaviour of the aluminium alloy EN AW-6060 T4 was investigated during heating with differential scanning calorimetry (DSC). Heating curves from 20 to 600 °C with heating rates of 0.01 up to 5 K/s were recorded. Interrupted heat treatments with different maximum temperatures were performed in a deformation dilatometer. Immediately afterwards, tensile tests were carried out at room temperature. The course of the recorded mechanical properties as a function of the maximum temperature is discussed with regard to the dissolution and precipitation behaviour during heating. Finally, the aging behaviour of the investigated alloy was recorded after different typical short-term heat treatments and is discussed with reference to the DSC‐curves. The correlation of the microstructure and the mechanical properties enables the derivation of optimal parameters for the development of THTP through a local softening.

Abstract: Quenching is an important step during age hardening of aluminium alloys. It significantly influences on microstructures, properties, residual stresses and component distortion. Due to high heat transfer, thermal stresses occur in quenched components. I.e., all premature precipitates during undercritical quenching form on condition of mechanical stresses. Opposite, quench sensitivity investigations, e.g. recording of continuous cooling precipitation diagrams, are usually performed in stress-free conditions and may therefore be incomplete. We have developed a new method of thermomechanical analysis and calorimetric reheating to investigate stress induced precipitation during quenching of aluminium alloys. For aluminium alloy 2024, it has been shown for the very first time that mechanical stresses during quenching also influence on quench-induced precipitation reactions.

Abstract: Despite the benefits associated with the use of natural fibers instead of synthetic ones as composite reinforcement, there are still some limitations to their application. Among the disadvantages associated with natural fibers stands the low thermal resistance. This imposes restrictions to the composite utilization when it is exposed to temperatures above 100 oC. For one point, the hydrophilic nature of lignocellulosic fibers causes absorption of water, but at high temperatures this water is lost, what produce pores and flaws in the composite polymer matrix. Moreover, the fiber cellulose, hemicellulose and lignin are degraded at higher temperatures. The objective of the present work was to conduct a comparative differential scanning calorimetric investigation between polyester and epoxy matrixes composites incorporated with different volume fractions of giant bamboo fibers. A substantial loss of mass was found up to 120 oC. The DSC curves revealed a variation in the enthalpy as a function of the giant bamboo fiber fractions and the corresponding polymeric matrix.

Abstract: Epoxy adhesive used in electronic packaging could normally be cured by ultraviolet light, heat at high temperature or dual cured by both processes. Differential scanning calorimetry (DSC) has been used to identify and analyze the occurred reaction during the curing process. The structural modification of epoxy during curing could be examined by measuring its thermal properties, and the change in molecular structure of epoxy could be observed by a relative small area of DSC peak. This provided the heat amount required for complete cure. It is found that the DSC peak area after heat cure at 90 °C increased linearly as a function of heating time while that at 120 °C decreased exponentially. For UV cure, it indicated that the curing mechanism was strongly depend on the energy from UV light. For dual cure at 90 °C, the heat curing time could be reduced from single curing process of 50 minutes to 6 minutes, while the heating time for dual cure at 120 °C could be reduced from 4 minutes to 2 minutes.