Thermal Cycling Treatment Research Articles

Mechanical behavior and fractographic analysis of a TiNi alloy with various thermomechanical treatment

Influence of thermomechanical treatment (deformation, thermal cycling treatment in the temperature range of martensitic transformations B2-B19’) on the TiNi alloys’ mechanical behaviour and fracture was studied. Different states were considered, they are initial coarse-grained (CG), ultrafine-grained (UFG) after ECAP (with a grain size of 200 nm), the state after ECAP and cold upsetting by 30% - UFG state with high dislocation density. It was shown that thermal cycling causes some increase in dislocation density, strength and microhardness in all the states. Thermal cycling of UFG alloys allows forming the states with non-equilibrium grain boundaries, with additional dislocations of “phase hardening”. The nature of the fracture was analysed in the TiNi alloy in various states.

Influence of different thermal cycling treatments on the physical, mechanical and transport properties of granite

Two different types of thermal cycling treatments (slow heating followed by slow cooling or rapid quenching) were carried out on the granite samples in the present research. The responses of physical, mechanical and transport properties of the granite after various thermal cycling treatments were compared and analyzed. Non-destructive tests (mass, volume, longitudinal wave propagation and permeability) and destructive tests (uniaxial compression and Brazilian splitting) were utilized to characterize these properties. Variations of all the properties demonstrate that thermal cycling (heating and cooling) can induce damage in the samples. Mass, density, P-wave velocity, UCS, Young’s modulus and tensile strength decrease, whilst volume and permeability increase with rising temperature. Additionally, the results also demonstrate the importance of cooling method. Rapid quenching has a more significant effect on granite samples, showing lower density, P-wave velocity and strength, but greater permeability, which is due to the generation of thermal gradient cracks. Moreover, the difference between P-wave velocity and UCS of slow cooling and those of rapid quenching increases with temperature up to 500 °C, which can be attributed to the more significant thermal shock cracking induced by higher temperature-gradient stress in the samples during rapid quenching. The microstructural analyses from thin sections show that microcracking in granite subjected to thermal cycling treatments was induced in different severity depending on peak temperature and cooling method.

Effects of space extreme temperature cycling on carbon/carbon-(Zr-Si-B-C-O) composites performances

Microstructures, mechanical properties, and oxidation resistance of ZrC-SiC-ZrB2-ZrO2 modified carbon/carbon composites (C/C-(Zr-Si-B-C-O)) have been investigated in the simulated space environment with different extreme-temperature thermal cycling (ETC) treatment. Cyclic thermal loading was performed in the temperature range between −120 °C and 120 °C for up to 200 cycles. Results showed that the microstructure degradation of the composite after ETC treatment was attributed to the formation of microcracks and the interfacial debonding. ETC treatment resulted in a 16.98% flexural strength decrease after 200 cycles. An oxidation model on the microstructure evolution of ETC treated C/C-(Zr-Si-B-C-O) composites was proposed to explain the oxidation failure mechanism.

АЛГОРИТМ УПРАВЛЕНИЯ СИСТЕМОЙ ГЕНЕРАЦИИ СМЕСИ ДЛЯ ПРЕЦИЗИ-ОННОЙ ТЕРМОИМПУЛЬСНОЙ ОБРАБОТКИ

The subjects of the study are methods and devices of generating gas mixtures with a specified accuracy and a high repeatability of the component dosing. The purpose of the article is to develop an algorithm for controlling the fuel mixture generation system for precision thermal pulse treatment. In that behalf, the research tasks are the improvement of the critical hole method with reference to the thermal pulse treatment and the methodology development of parameters assigning for mixture generation system ensuring high accuracy and repeatability of the dosing of its components and heat flows in thermal pulse treatment. The following results are obtained. The method of dynamic mixture formation based on the method of critical holes is proposed. Its special advantage is that during the filling of the chamber, the components of the fuel mixture expire from the pre-filled intermediate pressure vessels with the controlled volume without the application of any regulating devices. The technique for choosing the diameters of critical apertures, the volumes of intermediate tanks and the initial pressure in them, providing accuracy of components dosing at the level 0,01 % is developed. The technical solutions that allow to stabilize the value of heat flow during thermal pulse treatment, considering the operation dynamics of the valves in the mixture generation system and the variable temperature of the chamber walls are proposed. The following conclusions are formulated. The method of generating fuel mixtures for precision thermal pulse treatment based on the method of critical holes is proposed. It is characterized by the fact that during the mixture formation, the free exhaust of gases from pre-filled intermediate tanks is applied. The developed procedure for calculating the parameters of the mixture generator on the basis of the proposed method makes it possible to determine the ratio of the areas of the critical holes, the volumes of the tanks, the initial pressure in them and the time of filling the chamber according to the given composition and pressure of the mixture at normal temperature. The algorithm for controlling the generation of a mixture for precision thermal pulse processing is developed. The necessity of controlling the opening and closing speed of the gas supply valves is shown taking into account the required ratio of the areas of critical holes. To ensure a stable value of heat fluxes during cyclic thermal pulse treatment, it is shown that it is necessary to simultaneously monitor the charge mass and the pressure in the chamber when the fuel mixture is supplied, followed by correcting the treatment time according to the calculated initial temperature of the fuel mixture

Influence of Thermal Aging Parameters on the Characteristics of Aluminum Semi-Solid Alloys

The current study aimed at analyzing the response of semisolid A357 aluminum alloys to unconventional thermal treatment cycles of T4/T6/T7 conditions. The mechanical, electrical, and microstructural characterizations of such semisolid alloys were investigated. The microstructure evolutions of Fe-intermetallic phases and strengthening precipitates were characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. The mechanical failure of such semi solid A357 aluminum alloys, used for suspension automotive parts, is mostly related to cracking issues which start from the surface due to hardness problems and propagate due to severe load variations. For these reasons, the multiple thermal aging cycles, in this study, are applied to enhance the mechanical properties and to have compromised values compared to those obtained by standard thermal treatments. The results obtained in this work indicate that the heat treatment of this alloy can be optimized. The results showed that the optimum characteristics of A357 semisolid alloys were obtained by applying thermal under-aging cycle, interrupted thermal aging cycles and a T7/T6 two steps aging treatment condition. The electrical conductivity and electron microscopy were applied in this study to analyze the characteristics of hardening phases formed due to different aging cycles applied to the alloys investigated.

Phase, microstructure and magnetic properties of 45.5Fe-28Cr-20Co-3Mo-1.5Ti-2Nb permanent magnet

The 47.5-xFe-28Cr-20Co-3Mo-1.5Ti-xM; M = Nb; x = 0.5, 1, 1.5, 2.0, 2.5, 3.0 (wt%) permanent magnets have been investigated after solution annealing, thermomagnetic annealing and step-aging process. Alloys were prepared by vacuum melting and casting technique. Magnets with improved properties were developed through a modified thermal treatment cycle. Solution annealed specimens depict equiaxed α phase grain size of 250 µm while optimally thermomagnetic treated and step aged magnets yield ultra-fine Fe-Co nanorods (10 nm) precipitates in Cr-Ti-Nb matrix. The Nb addition to 47.5Fe-28Cr-20Co-3Mo-1.5Ti alloy expands the α phase structure by suppressing the nonmagnetic phases at annealed state and promotes shape anisotropy for spinodal phases in final treated samples leading to the improvements of magnetic properties. Spinodal phases preferentially aligned and elongated close to applied field direction and retained strong Goss {1 1 0}〈0 0 1〉 orientations. The 45.5Fe-28Cr-20Co-3Mo-1.5Ti-2Nb magnet reveals Hc of 86.9 kA/m, Br of 1.24 T and (BH)max of 57 kJ/m3. High coercivity and remanence in the magnets are attributed to the ideal shape anisotropy of Fe-Co rich nanorods or nanowires.

Influence of cyclic thermal treatments on the oxidation behavior of Ti-6Al-2Sn-4Zr-2Mo alloy

Ti-6Al-2Sn-4Zr-2Mo is one of the most common titanium alloys for aerospace industry. This alloy experiences oxidation phenomenon at elevated temperatures. In the present study, cyclic thermal treatments were performed in air at 500, 593 and 700 °C, up to 500 cycles, in order to determine the oxidation kinetics and to analyze the oxide scale and alpha-case formation. Moreover, results were compared to those achieved under isothermal conditions to elucidate differences between both thermal conditions. In this sense, metallographic techniques and X-ray diffraction, together with a detailed advanced characterization of the microstructure by Field Emission Scanning Electron Microscopy and Focus Ions Beam, were used to analyze surface oxidation evolution. Results pointed out that cyclic treatments induced a strong increase of the weight gain compared to isothermal treatments. The analysis of the oxide scale revealed the formation of not only rutile, as isothermal treatments, but also anatase. Thickness of the oxide scale was higher for cyclic conditions, while alpha case did not exceed values reached by isothermal treatments and even became lower at 500 °C.

Effect of thermal cycles on the laser beam welded joint of AA2060 alloys

Abstract

Improving plasticity of the Zr46Cu46Al8 bulk metallic glass via thermal rejuvenation

In this paper, effects of cryogenic thermal cycling on deformation behavior and thermal stability of the Zr46Cu46Al8 bulk metallic glass (BMG) were studied. The results show that with the increase of the number of cryogenic thermal cycles (CTC), thermal stability remains almost unchanged, while the plasticity is increased, indicating that the cryogenic thermal cyclic treatment is an effective way to improve plasticity of metallic glasses without distinctly deteriorating thermal stability. Our analysis suggests that the increase in the defect density resulted from the cryogenic thermal treatments are responsible for the plasticity increment. Variation of yield strength can be well interpreted from microstructural percolation which affected by both density and characteristic volume of the defect sites.

On the technical properties of the Carovigno stone from Apulia (Italy): physical characterization and decay effects by means of experimental ageing tests

Apulia (southern Italy) is typified by widespread outcrops of rocks exploited in the last centuries in historical architectures and religious constructions, as building and decorative stone. Today, as in the past, these stones represent an important source for region economy and prestige, due to their uses for modern works, restoration of local medieval churches and also exporting abroad. Among these, a noteworthy and still poorly known material is the Carovigno stone. In this paper, firstly an overall view on the, mineralogical and petrophysical features of the stone was reached through a multianalytical approach based on several investigation procedures and techniques, including ultrasonic test, X-ray diffractometry, scanning electron microscopy, optical microscopy, mercury intrusion porosimetry. In order to simulate decay phenomena, the Carovigno stone samples were processed to three different ageing tests: cycles of thermal treatments at different high temperatures, cycles of heating–cooling and cycles of exposure to decahydrate sodium sulphate and sodium chloride saline solutions. During and after each ageing processes, mineralogical transformations and petrophysical changes were evaluated. Results suggested that the Carovigno stone is a fine-grained calcarenite, pure or nearly pure, characterized by high porosity and, consequently, very notable thermal stress resistance. Conversely, the type and amount of porosity causes stone predisposition to salt crystallization decay.

Regeneration of organovermiculite with thermal treatment after sorption processes

Vermiculite is a well-known natural material which can be used as sorption material. It is very efficient sorbent of non-polar organic compounds in its organically modified form. Many research works are aimed to organically modified vermiculites and their properties. However, only few studies are focused on their treatment after utilization. One of the options is thermal treatment. This work is aimed to study: 1) an influence of different temperatures on regeneration of organovermiculite used as a sorbent and 2) structural changes after thermal treatment. The prepared and tested samples were investigated using X-ray diffraction method, FT-infrared spectrometry and phase carbon analysis. Both series of the organovermiculites treated at 100 and 200 °C in the repeated cycle of thermal treatment showed over 90% sorption efficiency of original HDP-vermiculite.

Cyclic cryogelation: a novel approach to control the distribution of carbonized cellulose fibres within polymer hydrogels

The fabrication of conductive composite hydrogels is still challenging mainly because of the heterogeneous distribution of conductivity across the structure. Carbon substrates are mostly used to induce conductivity in the polymer hydrogels. The first step towards an effective induction of conductivity is to reach a uniform dispersion of carbon within the hosting matrix. This paper describes a new cyclic cryogelation method for the fabrication of conductive hydrogels using chitosan as the polymer matrix and conductive cellulose based fibres as the filler. This is achieved by the cyclic thermal treatment of gelatinized chitosan solution, and orderly control of the hydrogen bonding network formation before the solvent evaporation. These networks regularly limit the chain mobility of polymer across the hydrogel and restrict the agglomeration of fibres within the matrix. As a result, a significant improvement in the homogeneity of conductivity across the treated hydrogel was achieved, shown by thermal camera mapping. In addition, the thermally treated chitosan/20 wt% fibres demonstrated a tensile strength improvement of about 50% compared to that of the untreated composite. The proposed method offers a good control of fibre dispersion within the polymer matrix, and can serve as a practical design concept for 3D conductive hydrogels in biotechnological applications.

Irreversible tunability of through-thickness electrical conductivity of polyaniline-based CFRP by de-doping

Carbon fiber reinforced plastics (CFRPs) are known for their tunable mechanical properties but not for having tunable electrical properties. In this work, a composite CFRP based on conductive polyaniline (CF/PANI) was prepared, which demonstrates electrical conductivity that is controllable post-fabrication. A thermosetting matrix of PANI doped with dodecylbenzenesulfonic acid (DBSA) and dispersed in cross-linking divinylbenzene (DVB) polymer was used to impregnate carbon-fiber fabric. The electrical and mechanical properties of the CF/PANI composite were measured. For the first time, it was shown that thermal de-doping in PANI can be used to control the electrical conductivity of a CFRP made with PANI-based thermosetting matrix. An average electrical conductivity of 1.35 S/cm in the through-thickness direction of the CF/PANI is reported, which can be irreversibly reduced to a desired value by thermal annealing. UV-Vis and FT-IR spectroscopy were used to evaluate the doping quantitatively. Images obtained from an optical microscope fitted with a heating plate system demonstrate the de-doping of PANI. The mechanical properties of the composites were measured after each thermal treatment cycle to determine any deterioration; the irreversible modification of the CF/PANI's electrical conductivity occurs without any degradation of the mechanical properties.

Increase in Ductility of High Carbon Steel Due to Accelerated Precipitation of Cementite

Eutectoid steel AISI 1080 is studied after annealing at 850°C and thermal cycling treatment (TCT) that involves heating at a rate of 10 K/min to 775°C, holding for 10 min, and cooling at a rate of 95 K/min. An increase is established in the content of cementite precipitating over austenite grain boundaries, and relative elongation with retention of yield and ultimate strengths with an increase in number of TCT cycles. After five cycles relative elongation reaches 29% with ultimate strength of 670 MPa.

Smart tuning of 3D ordered electrocatalysts for enhanced oxygen reduction reaction

Extensive research has been devoted to the development of advanced oxygen reduction reaction (ORR) catalysts with functionally diverse active sites. Herein, we show a smart approach to advancing the ORR catalytic activity of a 3D porous perovskite. The facile oxidative-reductive-oxidative (O-R-O) thermal treatment cycle executed on Ag doped LaFeO3 could stepwise switch on three different reaction sites (exsolved Ag-NPs, oxygen deficiency and Fe4+ with optimal electron configuration) for ORR. Detailed characterizations illustrate that the ORR activity is basically derived from the hierarchically porous scaffold which provides a large surface area and enough pore volumes for mass and ion diffusion. More importantly, the unique synergistic effects among three separate kinds of reaction sites endow the speed-up of oxygen adsorption, activation and O2− transportation. The exemplified results set out new design principles for the optimization of alternative catalysts.

Cycle rapid cooling treatment effect on the magnetic properties and giant magnetoimpedance properties of Co-based amorphous alloy ribbons

The influence of cycle rapid cooling treatment on the giant magnetoimpedance (GMI) properties in Co-based amorphous alloys was investigated. Hysteresis loops show that the saturation magnetization of ribbons has been improved by cycle treatment. It can be found that the GMI ratio was increased from 89% to 130% at 1MHz by the thermal cycle (TC) treatment. Moreover, GMI ratio of TC treatment sample increased up to 321% at 5MHz. It is considered that internal thermoelastic stress leads to surface roughness, magnetic domain structures and saturation magnetization changes of the ribbons during different cycle processes. It was also found that the asymmetric GMI (AGMI) phenomenon occurred in the Co-based alloys with TC treatment after annealing, which can be regarded as a new method to get GMI-valve to improve GMI sensitivity.

Rapid production of Iron Disilicide thermoelectric material by Hot Press Sintering Route

In present research work, a method has been established through powder metallurgical route to produce β-FeSi2 thermoelectric material without giving long time mechanical alloying treatment to the elemental powders and long duration heat treatment cycle. The elemental powders of iron (98.9% purity, 200 mesh) and silicon (98.5% purity, 400 mesh) have been mechanically alloyed for 6h using high-energy Attritor ball-mill and was subjected to Hot Press Sintering (HPS). Effect of HPS parameters on density of compacts was studied. The compacts with higher densities (82–92% relative density) were later on subjected to the thermal cycling treatment. The density as well as the amount of β-FeSi2 phase formation got enhanced due to thermal cycling treatment.

Effect of thermal cycling treatment on local structure, thermal stability and magnetic properties of Fe80Si8.75B10Cu1.25 metallic glass

In this study, we have investigated variations in the local structure and thermal stability of Fe80Si8.75B10Cu1.25 amorphous ribbons after thermal cycling treatment between room temperature and 77K. All samples are characterized by X-ray diffraction, transmission electron microscopy, differential scanning calorimetry, magnetometry and Transmission Mössbauer spectroscopy. It confirms that the structure of melt spun ribbons is much compacted after thermal cycling treatment. In addition, the nucleation and growth activation energies of α-Fe significantly increase after thermal cycling. Moreover, an increase of the saturation flux density from 1.46T to 1.55T and a decrease of coercivity from 9.21A/m to 8.54A/m can be achieved by the thermal cycling treatment.

Modeling the heat inactivation of foodborne pathogens in milk powder: High relevance of the substrate water activity

Due to the ability of foodborne pathogens to survive in low moisture foods, the decontamination of these products is an important issue in food hygiene. Up to now, such decontamination has mostly been achieved through empirical methods. The intention of this work is to establish a more rational use of heat treatment cycles. The effects of thermal treatment cycles on the inactivation of dried Salmonella Typhimurium, Salmonella Senftenberg, Cronobacter sakazakii and Escherichia coli were assessed. Bacteria were mixed with whole milk powder and dried down to different water activity levels (0.11, 0.25, 0.44 and 0.58). The rate of inactivated bacteria was determined after thermal treatment at 85°C, 90°C, 95°C and 100°C, from 0s to 180s in closed vessels, in order to maintain aw during treatment. In a first step, logarithmic bacterial inactivation was fitted by means of a classical loglinear model in which temperature and aw have a significant effect (p<0.05). DT,aw values were estimated for each T, aw condition and the results clearly showed that aw is a major parameter in the thermal decontamination of dried foods, a lower aw involving greater thermal resistance. In a second step, Bigelow's law was used to determine zT, a classical parameter relative to temperature, and yaw values, a new parameter relative to aw resistance. The values obtained for zT and yaw showed that the bacterium most resistant to temperature variations is Salmonella Typhimurium, while the one most resistant to aw variations is Escherichia coli. These data will help design decontamination protocols or processes in closed batches for low moisture foods.

Effects of low-temperature thermal cycling treatment on the microstructures, mechanical properties and oxidation resistance of C/C-ZrC-SiC composites

Carbon/Carbon (C/C) composites modified with ZrC and SiC particles were prepared by precursor infiltration and pyrolysis (PIP) process. Effects of the simulated low earth orbit environment including the vacuum environment (under the high-vacuum state of 1.3 × 10−3 Pa) and low-temperature thermal cycling (the temperature is ranged from 153 K to 393 K for 200 times) on C/C-ZrC-SiC composites were investigated. These results show that the significantly generated microcracks, interspaces and interface debondings contributed to the increase of open porosity. The interfacial damages of C/C-ZrC-SiC composites caused by low-temperature thermal cycling in short-cut webs and non-woven webs were generated at fiber/matrix interface and fiber bundle/matrix interface, respectively. The flexural strength of C/C-ZrC-SiC composites increased by 9.35% after 100-time thermal cycles and then decreased dramatically to 83.99% of pristine strength after 200-time thermal cycles, accompanied by the transformation of fracture behavior from the brittle fracture mode into the pseudo-plastic fracture mode. In addition, the defects induced by the low-temperature thermal cycling accelerated the oxidative damage of C/C-ZrC-SiC composites during thermal shock between 1773 K and room temperature.