Papers by Keyword: Thermal Shock Resistance

Abstract: The rapid development of magnetic materials has witnessed a sustained consumption increase in corundum-mullite kiln furniture application, yet a comparatively short duration of them. In this view, the thermal shock resistance of sagger plate in floppy magnets sintering turns out a factor of critical importance. This paper makes a study concerning the influence of factors including the size of critical electro-melted mullite particles, the electro-melted corundum or mullite as medium particles and the addition of upon the thermal shock resistance. The result shows that, with critical particles of 2 mm, the sheet of about 10mm thickness is characterized by better performance in modulus of rapture and thermal shock resistance. The latter proves to be more outstanding in samples rather than mullite. When zircon powder is added in a two-hour sintering process at the temperature of 1550°C, a remarkable improvement is made by the sample in terms of its thermal shock resistance. SEM analysis shows the existence of micropores in the section of samples with corundum as medium particles, whereas the glasses phase in that of mullite sample, resulting in a dense structure. Finally, zircon powder added makes for the improvement of thermal shock resistance due to the formation of baddeleyite on the particle surface of the corundum.

Abstract: The purpose of the present study is to evaluate thermal shock properties of the ATJ graphite using laser irradiation techniques. Cracks of thermal shock specimens are initiated by maximum tensile stress field. Thermal shock resistance of the ATJ graphite is correlated with thermal parameter and mechanical property. To simulate the thermal stress conditions of rocket nozzle throat for the evaluation of the thermal shock resistance of ATJ graphite, the laser irradiation was applied at the central area of disk specimen. Thermal shock resistance was related to the geometry, the maximum stress, and the thermal and mechanical property. Also the analyses of transient temperature and thermal stress were performed by the finite element method with nonlinear code ABAQUS. Analyses were specially performed for several kinds of shape to determine the minimum power density which could be cracked the specimen. The shape of the thermal shock specimen which was cracked under the lower power density was obtained and the result will be proved to the test.

Abstract: The coating of molten silicate glass on a porous carbon substrate was developed, without the formation of cristobalite at the carbon-glass layer interface, in order to improve the steam oxidation and thermal shock resistance. Initially, suitable conditions for coating were assumed from thermodynamic analysis. Based on these calculations, the wettability of the carbon to molten glass was modified by infiltration and pyrolysis of a Si-N precursor, and the coating with glass was carried out under higher N2 partial pressures. As a result, carbon substrates were completely sealed with glass, without the production of cristobalite at the interface, and the glass was infiltrated into the substrate. In contrast, coating with glass at lower N2 partial pressures, such as in Ar, were followed by the formation of cristobalite along with many pores at the interface. The structural changes occurring as a result of variation of the N2 partial pressure during sealing with glass are in good agreement with the thermodynamic analysis. The glass-coated carbon materials, which were fabricated at higher N2 partial pressure, possessed excellent steam oxidation resistance and thermal shock resistance.

Abstract: Silicon nitride ceramics were prepared by new nitrided pressureless sintering (NPS) process in this study. The microstructures, strengths and thermal properties of the NPS silicon nitride ceramics containing three types of Al2O3 and Y2O3 sintering additives were investigated. Additionally, we have investigated the effect of silicon metal contents changing with 0, 5, 10, 15 and 20 wt% in each composition. The silicon nitride was successfully densified using NPS process, particularly at the starting composition of 5 wt.% Al2O3, 5 wt.% Y2O3, and 5 wt.% Si addition. The maximum flexural strengths and relative densities of these specimens were 500 MPa and 98%, respectively. The flexural strength of sintered specimens after the thermal shock test between 30oC and 1300oC for 20,000 cycles was maintained with the original laboratory strength of 500MPa by low thermal expansion coefficient, 2.9 × 10-6/oC, and high thermal conductivity, 28 W/m⋅oC.

Abstract: Thermal shock resistance is one of the important properties for ceramic cutting tool materials in machining operation. Thermal shock resistance of a new SiC/Ti(C,N)/Al2O3 ceramic tool material is investigated in detail by means of the water quenching test. It indicates that the addition of Ti(C,N) and SiC is effective in the improvement of thermal shock resistance of the composite and the tested maximum temperature difference of thermal shock reaches about 330
. Microstructures of the ceramic samples after thermal shock have been observed and analyzed by SEM focusing mainly on the morphologies of cracks and the peeling off of grains as well as the accompanied oxidation phenomenon at elevated temperatures.

Abstract: By adding nano Si3N4 and nano TiC particles into the micro Si3N4 matrix, the Si3N4/TiC nanocomposite ceramics were fabricated via hot pressing technique with Al2O3 and Y2O3 as sintering additives. The thermal shock resistance of Si3N4/TiC nanocomposites were investigated by means of indentation-quenching and quenching-retained strength testing methods. The results revealed that the composite containing 10 wt.% nano Si3N4 particles and 15 wt.% nano TiC nano particles was possessed of the highest thermal shock resistance, with its critical temperature difference being 700~750
. The toughening and strengthening mechanisms by the nano particles addition are deem to be the essential course for the improved thermal shock resistance.

Abstract: Thermal shock resistances of commercially available aluminum nitride and alumina ceramics as used for the circuit substrate were evaluated by infrared radiation heating (IRH) technique. Thermal shock fracture toughness, R2c of these materials was estimated experimentally and theoretically using IRH technique at various ambient temperatures. Temperature dependence of thermal properties of the materials was taken into account for the temperature and the thermal stress analysis. Experimental values of thermal shock fracture toughness were in good agreement with the calculated values. Thermal shock fracture toughness decreased with elevated ambient temperature in both ceramics.

Abstract: Thermal shock resistance of the RE-Si-Mg-O-N glasses (RE = La, Nd, Yb, Lu) with 0 and 20 eq.% of nitrogen was investigated by the indentation-quench method based on propagation of Vickers cracks. Crack growth was measured on the same sample for a test series of different quenching temperatures. Thermal shock resistance of the studied materials was determined as a temperature difference resulting in 10 % growth of the initial cracks (∆T10) and by the thermal shock parameter R calculated from the material properties. Although the comparison of ∆T10 and R values as a function of glass composition revealed some differences between these two approaches, also a common trend was observed. Thermal shock resistance increased with the fractional glass compactness resulting from RE type and N content increase.

Abstract: TiB2-Cu Interpenetrating phase composites (IPCs) were prepared by combustion synthesis of elemental titanium, boron and copper powders. The synthesized product consisted of two spatial continuous phases: TiB2 and copper. Using the experimental data, thermo-physical and mechanical parameters of the materials established the temperature and stress fields made of FEM. Thermal shock behavior of TiB2-Cu IPCs was also investigated using a plasma torch arc heater and the results showed no cracks were found on the thermal shock surface of the TiB2-Cu IPCs. The experimental and numerical modeling results can be used to explain the actual thermal shock resistance and reveal its complex behavior under the severe condition.

Abstract: Anodizing technique was applied to prepare insulated metal substrates (IMS) for BGA packaging. “Ideal” IMS used anodic film of aluminum as the insulating layer instead of epoxy, which led to higher thermal conductivity. But the thermal shock resistance of IMS is poor because of the great difference of thermal expansion coefficient between aluminum and its anodic film. In this study, different anodizing processes of aluminum were analyzed. The parameters, which can affect the thermal shock resistance of IMS, especially the surface temperature of Al substrate, were studied. The anodic film obtained with the optimized parameters of anodizing process had excellent performance, such as the resistivity was over 1013Ω·cm, the breakdown voltage was higher than 600V, and the most important thing was that it could resist thermal shocks between room temperature and 300°C. Then BGA packaging was successfully performed based on this IMS.