Alumina was joined with graphite by active metal brazing technique at 895,900,905,and 910 ℃ for 10 min in vacuum of0.67 mPa using Ti-Cu-Ag（68.8Ag-26.7Cu-4.5Ti;mass fraction,%） as filler material.The brazed samples ...Alumina was joined with graphite by active metal brazing technique at 895,900,905,and 910 ℃ for 10 min in vacuum of0.67 mPa using Ti-Cu-Ag（68.8Ag-26.7Cu-4.5Ti;mass fraction,%） as filler material.The brazed samples were thermal cycled between 30 and 600 ℃ and characterized.X-ray diffraction results show strong reaction between titanium and carbon as well as titanium and alumina.Scanning electron microscopy and helium leak tests show that the initial and thermal cycled brazed samples are devoid of cracks or anv other defects and hermeticity in nature.Brazing strength of the joints is found to be satisfactory.展开更多
Large-area polycrystalline diamond(PCD)coatings are important for fields such as thermal management,optical windows,tribological moving mechanical assemblies,harsh chemical environments,biological sensors,etc.Microwav...Large-area polycrystalline diamond(PCD)coatings are important for fields such as thermal management,optical windows,tribological moving mechanical assemblies,harsh chemical environments,biological sensors,etc.Microwave plasma chemical vapor deposition(MPCVD)is a standard technique to grow high-quality PCD films over large area due to the absence of contact between the reactive species and the filament or the chamber wall.However,the existence of temperature gradients during growth may compromise the desired uniformity of the final diamond coatings.In the present work,a thick PCD coating was deposited on a 100-mm silicon substrate inside a 915-MHz reactor;the temperature gradient resulted in a non-uniform diamond coating.An attempt was made to relate the local temperature variation during deposition and the different properties of the final coating.It was found that there was large instability inside the system,in terms of substrate temperature(as high asΔT=212℃),that resulted in a large dispersion of the diamond coating’s final properties:residual stress(-15.8 GPa to+6.2 GPa),surface morphology(octahedral pyramids with(111)planes to cubo-octahedrals with(100)flat top surfaces),thickness(190μm to 245μm),columnar growth of diamond(with appearance of variety of nanostructures),nucleation side hardness(17 GPa to 48 GPa),quality(Raman peak FWHM varying from 5.1 cm^(-1) to 12.4 cm^(-1) with occasional splitting).This random variation in properties over large-area PCD coating may hamper reproducible diamond growth for any meaningful technological application.展开更多
文摘Alumina was joined with graphite by active metal brazing technique at 895,900,905,and 910 ℃ for 10 min in vacuum of0.67 mPa using Ti-Cu-Ag（68.8Ag-26.7Cu-4.5Ti;mass fraction,%） as filler material.The brazed samples were thermal cycled between 30 and 600 ℃ and characterized.X-ray diffraction results show strong reaction between titanium and carbon as well as titanium and alumina.Scanning electron microscopy and helium leak tests show that the initial and thermal cycled brazed samples are devoid of cracks or anv other defects and hermeticity in nature.Brazing strength of the joints is found to be satisfactory.
文摘Large-area polycrystalline diamond(PCD)coatings are important for fields such as thermal management,optical windows,tribological moving mechanical assemblies,harsh chemical environments,biological sensors,etc.Microwave plasma chemical vapor deposition(MPCVD)is a standard technique to grow high-quality PCD films over large area due to the absence of contact between the reactive species and the filament or the chamber wall.However,the existence of temperature gradients during growth may compromise the desired uniformity of the final diamond coatings.In the present work,a thick PCD coating was deposited on a 100-mm silicon substrate inside a 915-MHz reactor;the temperature gradient resulted in a non-uniform diamond coating.An attempt was made to relate the local temperature variation during deposition and the different properties of the final coating.It was found that there was large instability inside the system,in terms of substrate temperature(as high asΔT=212℃),that resulted in a large dispersion of the diamond coating’s final properties:residual stress(-15.8 GPa to+6.2 GPa),surface morphology(octahedral pyramids with(111)planes to cubo-octahedrals with(100)flat top surfaces),thickness(190μm to 245μm),columnar growth of diamond(with appearance of variety of nanostructures),nucleation side hardness(17 GPa to 48 GPa),quality(Raman peak FWHM varying from 5.1 cm^(-1) to 12.4 cm^(-1) with occasional splitting).This random variation in properties over large-area PCD coating may hamper reproducible diamond growth for any meaningful technological application.
