Microstructural Evolution of Viscoelastic Properties of Underfills Under Sustained High Temperature Operation

Automotive underhood electronics are subjected to high operating temperatures in the neighborhood of 150 to 200? for prolonged periods in the neighborhood of 10-years. Consumer grade off-the shelf electronics are designed to operate at 55 to 85? with a lower use-life of 3 to 5 years. Underfill materials are used to provide supplemental restraint to fine-pitch area array electronics and meet the reliability requirements. In this paper, a number of different underfill materials are subjected to automotive underhood temperatures to study the effect of long time isothermal exposure on microstructure and dynamic-mechanical properties. It has been shown that isothermal aging oxidizes the underfill, which can change the mechanical properties of the material significantly. The oxidation of underfill was studied experimentally by measuring oxidation layer thickness using polarized optical microscope. The effect on the mechanical properties was studied using the dynamic mechanical properties of underfill with DMA (Dynamic Mechanical Analyzer). Two different underfill materials were subjected to three different isothermal exposure, which are below, near and above the glass transition temperature of the underfills. The dynamic mechanical viscoelastic properties like storage modulus, loss modulus, tan delta and their respective glass transition temperatures were investigated. Three point bending mode was used in the DMA with a frequency of 1 Hz operating at 3?/min.

Study on the Characteristics of a TBC System Containing a PVD-Al Interlayer under Isothermal Loading

In this work, the oxidation behavior of an atmospheric plasma-sprayed thermal barrier coating (TBC) system with a thin Al physical vapor deposition (PVD) film deposited over the bond coat is discussed. The TBC consisted of: (i) CoNiCrAlY bond coat sprayed on the Inconel 600 substrate; (ii) a thin Al interlayer deposited by direct current DC magnetron sputtering; and (iii) yttria-stabilized zirconia (YSZ) sprayed as the top coat. Such thermal barrier coatings (Al-TBC) were isothermally oxidized at 1150 °C with different holding times, and then they were compared with the reference TBC (R-TBC) systems without an Al interlayer (R-TBC). Scanning electron microscopy with energy-dispersive X-ray analysis was used to study the oxide formation along the bond coat (BC) and top coat (TC) interface, as well as crack formation in the yttria-stabilized zirconia top coat. Then, using Image Analysis, the oxide formation and crack formation were characterized in all specimens after a slow heating and cooling cycle, and after 100, 300, and 600 h of isothermal exposure. The results showed that the Al-TBC system proposed here exhibits higher oxidation resistance at the bond coat and top coat interface, less crack formation in the YSZ top coat, and enhanced mechanical stability compared to the conventional TBCs. It was found that enrichment of the bond coat and top coat interface with Al limited the formation of detrimental transition metal oxides during isothermal loading. Finally, the corresponding failure caused by thermally grown oxide (TGO) phenomena is “mixed failure mode” for both studied TBCs.

Investigation of the process of metallized materials production from iron concentrate of hydrometallurgical enrichment of ferromanganese ores of Kuzbass

Study of the processes of solid-phase reduction of iron from oxides using coals as reducing agents and the development of energy-efficient technologies for the production and use of metallized materials from concentrates obtained as a result of hydrometallurgical enrichment is an actual scientific direction in ferrous metallurgy. Theoretical studies of the processes of solidphase reduction of iron from iron-containing concentrate obtained as a result of hydrometallurgical enrichment of ferromanganese and polymetallic manganese-containing ores, by coals grades D (long-flame) and 2B (brown) were carried out by the method of thermodynamic simulation using the “Terra” software complex. The experimental study of the process of solid-phase reduction of iron from experimental mixtures was carried out in a muffle furnace SNOL 4/900 and in a resistance furnace with a graphite tubular heater (Tamman furnace). The influence of the composition and volume of gas phase, formed as a result of volatile components emission in the process of coals of two grades heating at 373–1873 K obtained, optimal temperature and consumption of coals defined, which ensure complete reducing of iron from iron-containing concentrate, compositions as well as volumes of gas phase. The influence of temperature of the isothermal exposure on the rate and degree of solid-phase reduction of iron from iron ore oxides was experimentally determined when using coals of different process grades and coke fines as reducing agents. Empirical equations of reduction degree versus time of isothermal exposure for different metallization temperatures were obtained. It is shown that the change in the degree of recovery on temperature with high accuracy was described by a linear dependence, and the change in the recovery rate on the temperature – by a power dependence. Conditions of effective metallization were determined when using iron concentrate and coals of different process grades for production of spongy metallized materials with content of Femet more than 80%, and 1.5–2.5 % C, 0.1 % S, 0.02 % P. As a result of thermodynamic simulation and experimental study of the process of iron reduction from iron concentrate, optimal consumption of coal of grades D and 2Б at temperature 1473K was determined. It was established that the best reducing agent with a minimum specific consumption is long-flame coal grade D. It was found that with an excess of reducing agent, it is possible to achieve almost complete extraction of iron from the concentrate, at the level of 98–99%.

Development of Energy-Efficient Modes of Installations for Heat Treatment of Concrete Products Using Numerical Calculation Methods

Production of concrete and reinforced concrete products in the conditions of the Republic of Belarus and in the countries with similar climatic conditions requires heat treatment in heat-technological installations in order to achieve the desired strength of the products at the appointed time, which consumes a great amount of thermal energy. In this case, the purpose of equipment operating modes is associated with a number of difficulties when it comes to new products of complex spatial configuration and structure. The optimality criteria of such modes are, as a rule, the duration and temperature limits of processing, providing the required strength with minimal energy consumption. In the conditions of serial production in the case of structurally simple objects, the assignment of heat treatment modes is carried out empirically. As the analysis shows, the modes obtained in this way do not meet the above criteria, especially from the standpoint of energy saving. The paper, using a mathematical model previously developed by the authors, proposes dependencies for calculating the optimal modes of heat treatment of concrete products that are distinguished by a complex spatial shape and multi-component structure. The method is based on three-dimensional transfer equations, taking into account internal sources of heat release due to the ongoing hydration reaction of the active components of the cement clinker, and the boundary conditions corresponding to the structure of the processed product, as well as the type of heat technology device for accelerated hydration. Equations are proposed for calculating the amount of heat energy supplied to the processed product providing a given strength at a specified time. On the example of a manufactured industrial concrete product and for the conditions of an actually used device for accelerated hydration, a comparison has been made between two limiting modes of heat treatment: with isothermal exposure and in its absence. As a result of the performed calculations, the dependences of energy consumption, temperature fields and the degree of hydration in the product for both modes have been obtained and an energy-saving mode of heat treatment corresponding to the case under consideration has been developed. It is shown that the used numerical method allows to solve problems of this type and to achieve thermal energy savings.

OPTIMIZATION OF THE PROCESS OF MULTILAYER CENTRIFUGAL INDUCTION SURFACING OF COATINGS BASED ON ALUMINUM ALLOYS

As a result of the conducted research, using the methods of mathematical planning of the experiment, the optimization of the process of multilayer centrifugal induction surfacing of antifriction coatings based on aluminum alloys was performed, which made it possible to develop a mathematical model and determine the optimal range of values of technological modes. The dependences of the minimum wear rate of the coating material Iq (mg/m) on the parameters of multilayer induction centrifugal surfacing of aluminum alloy coatings are established. The main factors affecting the wear rate of the coating were the heating temperature of the part T (°C), the time of the isothermal exposure t (min) and the speed of rotation of the part n (rpm). Based on the results of computational and experimental modeling, it is shown that in order to obtain the optimal wear intensity of the aluminum alloy coating material, the parameters of the multilayer centrifugal induction surfacing process should be as follows: the rotation speed of the part n = 1,750–1,875 rpm, the heating temperature of the part T = 775–800 °C, the isothermal exposure time t = 7–8 min.

Optimization of the Choice of Technological Methods for Nanomodification of Natural Aluminosilicates through the Parameters of the Element-Oxygen Chemical Bond

The paper shows the possibility of using such quantitative characteristics of the element-oxygen chemical bond as the covalent character, metallic character and ionic character in substances to select a set of technological methods and develop a technology for nanomodification of natural bentonite aluminosilicates. The research results showed that thermal activation of bentonite at 200, 300, 380 and 400 °C with different modes of isothermal exposure (15, 30, 60, 120 minutes) does not significantly affect the efficiency of its modification with silicon (SS) and aluminum (AS) oxide nanoparticles, estimated by the increment of the compressive strength and the adsorption index for methylene blue. Obtaining a 46 % aqueous suspension of bentonite and modifying it with silicon and aluminum oxide nanoparticles followed by ultrasonic treatment after standing decreases the particle size by more than 4 times, which is a promising technological solution for improving the performance properties of ceramics, molding mixtures, adsorbents and other materials based on bentonite from various deposits.

Discontinuities in Oxidation Kinetics: A New Model and its Application to Cr–Si-Base Alloys

Some alloys such as many Cr-based systems show mass gain discontinuities during thermogravimetric measurements which strongly affect the oxidation kinetics. The behaviour cannot be described by the current models available in the literature. Thus, a novel $$k_\mathrm{para}$$ k para –$$k_\mathrm{lin}$$ k lin -P-model was developed to describe oxidation kinetics during the isothermal exposure of materials which show such behaviour. Beside the parabolic rate constant $$k_\mathrm{para}$$ k para and the linear mass loss constant $$k_\mathrm{lin}$$ k lin , the P-value and $$f_P$$ f P are introduced to take into account spontaneous rapid mass gains due to local oxide scale failure. The parameter P serves as a measure for the mass gain due to discontinuous events and $$f_P$$ f P is the frequency of such events. The both parameters can be related to oxide scale detachment and growth stresses. The application of the model is demonstrated for the oxidation of Cr–Si-based alloys in synthetic air at $$1200^{\circ }\hbox {C}$$ 1200 ∘ C for 100 h. For these alloys, the origin of the mass gain discontinuities is discussed and the meaning of P and $$f_P$$ f P is explained in more detail. Using this newly developed model, an insight into growth and nitridation resistance of oxide scales as well as scale adhesion is gained.

A Short Review on the Phase Structures, Oxidation Kinetics, and Mechanical Properties of Complex Ti-Al Alloys

This paper reviews the phase structures and oxidation kinetics of complex Ti-Al alloys at oxidation temperatures in the range of 600–1000 °C. The mass gain and parabolic rate constants of the alloys under isothermal exposure at 100 h (or equivalent to cyclic exposure for 300 cycles) is compared. Of the alloying elements investigated, Si appeared to be the most effective in improving the oxidation resistance of Ti-Al alloys at high temperatures. The effect of alloying elements on the mechanical properties of Ti-Al alloys is also discussed. Significant improvement of the mechanical properties of Ti-Al alloys by element additions has been observed through the formation of new phases, grain refinement, and solid solution strengthening.

Microscopic kinetics of isothermal sintering of Fe-20 % (mаs.) Mo alloy

Purpose of work. To investigate the features of microscopic kinetics of peritectoid transformation in Fe-Mo system alloys in an isothermal mode. Experimental part. Microscopic analysis of samples on light (Jenaphot 2000, K. Zeiss) and scanning electron (REM 106I, Selmi) microscopes, X-ray spectral microanalysis of the component’s concentrations distribution between the phases, X-ray phase analysis (Rigaku Ultima IV diffractometer). Results. Microstructure changes, phase composition and crystal lattices parameters of the phase constituents of the powder alloy during sintering at 920 °C were investigated. Variation in the phase constituents mass fraction during 7 hours of the isothermal exposure is analyzed. The formation of anomalous diffusion porosity at the beginning of the process, the nonmonotonic change in the phase constituents fraction and formation of intermediate phases with an unstable component’s concentration are the main features of the microscopic kinetics. The sintering mechanism is proposed. Scientific novelty. A local peritectoid transformation existence at the Fe/Mo interface was established by analyzing the local diffusion flows of components atoms. This transformation occurs upon isothermal supply of Mo atoms with the formation of a cooperative peritectoid structural constituents according to the α- Fe + Mo → α + μ scheme with residual Mo crystals. Formulation of the problem. This work aims to clarify the phenomenological theory of peritectoid transformation during isothermal α-Fe grains enrichment with molybdenum by studying the features of microscopic kinetics in the Fe-Mo system alloys. Practical value. Peritectoid (α + μ) with branched phase соnstituents of cooperative genesis forms a developed system of local diffusion flows of Mo atoms in α -Fe. This increases the molybdenum peritectoid transformation rate at a relatively low sintering temperature for these alloys and reduces the energy consumption in the technological process.