Effect of alumina impurity on microstructure and properties of alumina based conventionally brazed joints

Mo-Mn metallization of alumina ceramics of different purity has been performed at 1400 degrees C for 10 min in moist hydrogen and nitrogen atmosphere. Nickel coating has been applied onto the metallized alumina ceramics at 1000 degrees C for 1 h in a reducing hydrogen atmosphere. Finally, metallized and nickel coated alumina ceramics has been brazed with another metallized and nickel coated alumina ceramics using CuAg filler alloy at 900 degrees C for 10 min in a vacuum furnace at 1 x 10(-6) Ton pressure. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis has been carried out for phase analysis, microstructural investigation and elemental composition analysis. The adhesive strength of the metallizing layer and brazing strength of the joint have been measured by pull down breaking strength method. SEM study has shown that the width of the interfacial reaction region between the metallizing layer and substrate enhances with increasing the impurity content in the alumina ceramics. It has been observed that the adhesive strength of the metallizing layer depends on the interfacial reaction layer thickness. The adhesive strength of the metallizing layer has been increased with increasing the thickness of interfacial reaction layer. High adhesive strength of the metallizing layer as well as brazing strength has been achieved for alumina ceramics with high impurity content

Effect of alumina impurity on microstructure and properties of alumina based conventionally brazed joints

96-103Mo-Mn metallization of alumina ceramics of different purity has been performed at 1400 °C for 10 min in moist hydrogen and nitrogen atmosphere. Nickel coating has been applied onto the metallized alumina ceramics at 1000 °C for 1 h in a reducing hydrogen atmosphere. Finally, metallized and nickel coated alumina ceramics has been brazed with another metallized and nickel coated alumina ceramics using CuAg filler alloy at 900 °C for 10 min in a vacuum furnace at 1×10-6 Torr pressure. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis has been carried out for phase analysis, microstructural investigation and elemental composition analysis. The adhesive strength of the metallizing layer and brazing strength of the joint have been measured by pull down breaking strength method. SEM study has shown that the width of the interfacial reaction region between the metallizing layer and substrate enhances with increasing the impurity content in the alumina ceramics. It has been observed that the adhesive strength of the metallizing layer depends on the interfacial reaction layer thickness. The adhesive strength of the metallizing layer has been increased with increasing the thickness of interfacial reaction layer. High adhesive strength of the metallizing layer as well as brazing strength has beenachieved for alumina ceramics with high impurity content

Effect of alumina impurity on microstructure and properties of alumina based conventionally brazed joints

Mo-Mn metallization of alumina ceramics of different purity has been performed at 1400 °C for 10 min in moisthydrogen and nitrogen atmosphere. Nickel coating has been applied onto the metallized alumina ceramics at 1000 °C for 1 hin a reducing hydrogen atmosphere. Finally, metallized and nickel coated alumina ceramics has been brazed with anothermetallized and nickel coated alumina ceramics using CuAg filler alloy at 900 °C for 10 min in a vacuum furnace at 1×10-6Torr pressure. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysishas been carried out for phase analysis, microstructural investigation and elemental composition analysis. The adhesivestrength of the metallizing layer and brazing strength of the joint have been measured by pull down breaking strengthmethod. SEM study has shown that the width of the interfacial reaction region between the metallizing layer and substrateenhances with increasing the impurity content in the alumina ceramics. It has been observed that the adhesive strength of themetallizing layer depends on the interfacial reaction layer thickness. The adhesive strength of the metallizing layer has beenincreased with increasing the thickness of interfacial reaction layer. High adhesive strength of the metallizing layer as wellas brazing strength has beenachieved for alumina ceramics with high impurity content

Fabrication of Reliable Joints of Alumina Ceramics by Microwave-Assisted Reactive Brazing Technique

Microwave-assisted reactive brazing technique was utilized for joining of alumina ceramics at 950 degrees C and 1050 degrees C for 20 min in argon atmosphere using TICUSIL (68.8Ag-26.7Cu-4.5Ti in mass%) paste as the braze alloy. Conventional heating technique was also employed for comparison purpose only. The microwave and conventionally brazed joints were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis and Vickers microhardness measurement. X-ray diffraction data showed that the Ti-based compounds were formed at the substrate-filler alloy interfaces of the microwave and conventionally brazed joints. Scanning electron microscopy exhibited the formation of thicker reaction region in the case of joints microwave brazed at higher temperature. Energy dispersive X-ray analysis determined the elemental compositions across the joint cross-section. Vickers microhardness measurements indicated more reliable performance of the joints microwave brazed at lower temperature. Hermiticity of the microwave and conventionally brazed joints was evaluated by Helium leak test and found to be acceptable for actual applications

Interfacial and Cross-sectional Studies of Thermally Cycled Alumina-Monel Brazed Joint

Alumina and monel superalloy was successfully joined by active metal brazing technique using Ticusil (68.8Ag-26.7Cu-4.5Ti in wt%) filler alloy in a vacuum furnace at 910oC for 10 min under a vacuum of 5x10(-6)Torr. Phase analysis of the monel-filler alloy and alumina-filler alloy interfaces was conducted by X-ray diffraction analysis. Interfacial and cross-sectional microstructural investigation and determination of elemental composition were performed by scanning electron microscopy and energy dispersive X-ray analysis. No crack was found at the joint interfaces after thermal cycling test for 100 cycles between 50 degrees and 600 degrees C. Microhardness was estimated by Vickers hardness tester at the cross-section of the joint after thermal cycling test. Typical brazing strength of the thermally cycled joint was above 23 MPa. Helium leak tests indicated good hermiticity of the thermally cycled brazed joints

In vitro evaluation of bioactive glass ceramic coating for application on Ti6Al4V based biomedical implants

The present study showed the suitability of bioactive glass-ceramics for application as bioactive coating on Ti based biomedical implants. The desired properties of bioactive glass-ceramic coating were obtained through controlled crystallization. XRD, optical microscopy, SEM in association with EDX data showed the phase composition and morphology of the glass-ceramic coatings. Microhardness distribution across the coated substrates and the scratch resistance property of the coatings were varied for the differently heat treated coated substrates. The bioactivity of the fluroapatite based glass-ceramic coating on Ti6Al4V substrate was investigated in vitro in simulated body fluid (SBF) solution. After immersion in SBF solution the glass-ceramic coating surface was characterized by SEM, EDX analysis and the elemental compositional change of the SBF solution was determined by chemical analysis technique. SEM, EDX analysis and chemical analysis indicated that the glass-ceramic coatings reacted with the SBF solution and formed fluroapatite layer on their surfaces

Interfacial properties of metallized alumina ceramics

An alumina ceramic material (purity-96%) was metallized by the conventional molybdenum-manganese (Mo-Mn) process in which an alumina substrate was coated with Mo-Mn paste and subsequently heat treated at 1400 A degrees C for 10 min. During the entire process a moist H-2 and N-2 gas mixture (dew point-20 A degrees C) with 3:1 ratio was passed continuously through the furnace. X-ray diffraction analysis of the metallized alumina substrate identified only molybdenum phase at the surface of the metallizing layer. The microstructural observations of the metallized alumina substrate were made by scanning electron microscopy. Energy dispersive X-ray analysis showed the elemental compositions along the cross-sectional region of the metallized alumina substrate. The adhesion of the metallic coatings on the alumina substrates was evaluated qualitatively by a scratch testing technique and quantitatively by an adhesion tester. Nanohardness measurements showed gradual change in the nanohardness values across the metallized alumina substrate

Effect of Processing Parameters on Thermal Cycling Behavior of Al2O3-Al2O3 Brazed Joints

In the present study, alumina ceramics were active metal brazed at different temperatures ranging from 1163 K to 1183 K (890 A degrees C to 910 A degrees C) using TICUSIL (68.8Ag-26.7Cu-4.5Ti in wt pct) foil as filler alloy of different thicknesses. The brazed joints were subjected to thermal cycling for 100 cycles between 323 K and 873 K (50 A degrees C and 600 A degrees C). The microstructural and elemental composition analysis of the brazed joints were performed by scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) before and after thermal cycling. Helium (He) leak test and brazing strength measurement were also conducted after thermal cycling for 100 cycles. The joint could withstand up to 1 x 10(-9) Torr pressure and brazing strength was higher than 20 MPa. The experimental results demonstrated that joints brazed at the higher temperature with thinner filler alloy produced strong Al2O3-Al2O3 joints

Microwave-assisted brazing of alumina ceramics for electron tube applications

Alumina was joined with alumina using microwave-assisted and conventional brazing methods at 960 (a similar to) C for 15 min using TiCuSil (68.8Ag-26.7Cu-4.5Ti in wt.%) as the brazing alloy. The brazed joints were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, Vickers microhardness evaluation, brazing strength measurement and helium leak test. X-ray diffraction analysis confirmed the formation of Ti-based compounds at the substrate-filler alloy interfaces of the microwave and conventionally brazed joints. The elemental compositions at the joint cross-section were determined by energy dispersive X-ray analysis. Vickers microhardness measurement indicated reliable joint performance for the microwave-assisted brazed joints during actual application in an electron tube. Brazing strength measurement and helium leak test provided the evidence for good alumina-alumina joint formation