Machining behaviour of silicon nitride tools coated with micro-, submicro- and nanometric HFCVD diamond crystallite sizes

2006 ◽  
Vol 15 (11-12) ◽  
pp. 2029-2034 ◽  
Author(s):  
F.A. Almeida ◽  
M. Amaral ◽  
F.J. Oliveira ◽  
R.F. Silva
Keyword(s):  
Silicon Nitride ◽  
Crystallite Sizes ◽  
Diamond Crystallite

CVD of Silicon Nitride Plate from HsiCl3-NH3-H2 Mixtures

1991 ◽  
Vol 250 ◽  
Author(s):  
J. W. Lennartz ◽  
M. B. Dowell
Keyword(s):  
Silicon Nitride ◽  
Line Broadening ◽  
Multiple Correlation ◽  
Deposition Rates ◽  
Reaction Proceeds ◽  
Designed Experiment ◽  
Transport Control ◽  
Crystallite Sizes ◽  
Thickness Variations ◽  
Optimized Conditions

AbstractPreferred conditions for deposition of thick α-Si3 N4 plate from HSiCl3 -NH3-H2 on the vertical surfaces of a lowpressure, hot-wall CVD reactor were identified by means of a designed experiment. The design included the range of temperatures 1300°C-1500°C, pressures 0.5–2.0 Torr, and residence times 0.01–1.0 sec. The vertical deposition surfaces received a viscous, laminar flow of well mixed, thermally equilibrated reactants. Plates 0.05–0.5 mm thick were produced on multiple vertical substrates 350 cm2 in area at deposition rates 5–70 μm/hr. Plates 0.5–4.0 mm thick were produced on horizontal substrates at deposition rates of 60–120 μm/hr. When NH3 flows in stoichiometric excess, deposition rates on vertical surfaces increase approximately linearly with the flow rate of HSiCl3 but depend little on temperature, as would be expected if the reaction proceeds under mass transport control with product depletion. Multiple correlation analyses show that thickness variations in the deposit are reduced by increasing the temperature and decreasing the gas residence time. CVD silicon nitride plate produced under the optimized conditions exhibits theoretical density and is free of pores and cracks. It exhibits a columnar morphology in which the <222> and <101> crystallographic directions are oriented preferentially normal to a surface, which consists of well-defined trigonal facets 10–50 μm across. Crystallite sizes determined by Xray line broadening range from 0.06–1.0 μm. This CVD plate is gray and contains approximately 0.5 w/o C and 0.5 w/o 0 as principal impurities.

Preparation of Diamond Nanocrystallites in Powder by Using a Coaxial Arc Plasma Gun

2012 ◽  
Vol 1395 ◽  
Author(s):  
Aki Tominaga ◽  
Kenji Hanada ◽  
Tomohiro Yoshida ◽  
Tsuyoshi Yoshitake
Keyword(s):  
Diamond Powder ◽  
Hydrogen Atmosphere ◽  
Arc Plasma ◽  
X Ray Diffraction ◽  
Plasma Gun ◽  
X Ray ◽  
Crystallite Sizes ◽  
Diamond Crystallite ◽  
Diffraction Peaks ◽  
Ambient Gas

ABSTRACTWe suggest a new method for fabricating diamond nanoclusters by employing a coaxial arc plasma gun. Diamond powder comprised of diamond nanoclusters and amorphous carbon was fabricated in vacuum and a hydrogen atmosphere, and the diamond crystallite sizes were estimated to be 1.8, 2.3, and 2.3 nm for the powders prepared at hydrogen pressures of 0, 53.3, and 159.6 Pa respectively, from the X-ray diffraction peaks. The hydrogen ambient gas is not necessarily required for the diamond nanoclusters formation. We consider that this method enables us to form diamond nanoclusters in nucleation owing to a supersaturated condition at a facing plate located in front of an arc plasma gun.

Lattice Imaging of Grain Boundaries in Ceramics

1977 ◽  
Vol 35 ◽  
pp. 114-115
Author(s):  
D. R. Clarke ◽  
G. Thomas
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Silicon Nitride ◽  
Grain Boundaries ◽  
High Temperature Strength ◽  
Current Interest ◽  
Lattice Imaging ◽  
Special Significance ◽  
Structural Applications ◽  
Refractory Ceramics

Grain boundaries have long held a special significance to ceramicists. In part, this has been because it has been impossible until now to actually observe the boundaries themselves. Just as important, however, is the fact that the grain boundaries and their environs have a determing influence on both the mechanisms by which powder compaction occurs during fabrication, and on the overall mechanical properties of the material. One area where the grain boundary plays a particularly important role is in the high temperature strength of hot-pressed ceramics. This is a subject of current interest as extensive efforts are being made to develop ceramics, such as silicon nitride alloys, for high temperature structural applications. In this presentation we describe how the techniques of lattice fringe imaging have made it possible to study the grain boundaries in a number of refractory ceramics, and illustrate some of the findings.

TEM Studies of Grain Boundary Films in Si3N4 Ceramics

1991 ◽  
Vol 49 ◽  
pp. 930-931
Author(s):  
H.-J. Kleebe ◽  
J.S. Vetrano ◽  
J. Bruley ◽  
M. Rühle
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Silicon Nitride ◽  
Hot Isostatic Pressing ◽  
Amorphous Film ◽  
Liquid Phase Sintering ◽  
Second Phase ◽  
High Temperature Mechanical Properties ◽  
Triple Points ◽  
Boundary Films

It is expected that silicon nitride based ceramics will be used as high-temperature structural components. Though much progress has been made in both processing techniques and microstructural control, the mechanical properties required have not yet been achieved. It is thought that the high-temperature mechanical properties of Si3N4 are limited largely by the secondary glassy phases present at triple points. These are due to various oxide additives used to promote liquid-phase sintering. Therefore, many attempts have been performed to crystallize these second phase glassy pockets in order to improve high temperature properties. In addition to the glassy or crystallized second phases at triple points a thin amorphous film exists at two-grain junctions. This thin film is found even in silicon nitride formed by hot isostatic pressing (HIPing) without additives. It has been proposed by Clarke that an amorphous film can exist at two-grain junctions with an equilibrium thickness.

Electron Microscopy of Silicon Nitride-Based Ceramics

1991 ◽  
Vol 49 ◽  
pp. 926-927
Author(s):  
Gareth Thomas
Keyword(s):  
Electron Microscopy ◽  
High Temperature ◽  
Silicon Nitride ◽  
World Wide ◽  
Sintering Temperature ◽  
Liquid Phase Sintering ◽  
High Temperature Strength ◽  
Sintering Additives ◽  
Glass Forming ◽  
Dense Product

Silicon nitride and silicon nitride based-ceramics are now well known for their potential as hightemperature structural materials, e.g. in engines. However, as is the case for many ceramics, in order to produce a dense product, sintering additives are utilized which allow liquid-phase sintering to occur; but upon cooling from the sintering temperature residual intergranular phases are formed which can be deleterious to high-temperature strength and oxidation resistance, especially if these phases are nonviscous glasses. Many oxide sintering additives have been utilized in processing attempts world-wide to produce dense creep resistant components using Si3N4 but the problem of controlling intergranular phases requires an understanding of the glass forming and subsequent glass-crystalline transformations that can occur at the grain boundaries.

Examination of Fracture Interfaces in Silicon Nitride

1975 ◽  
Vol 33 ◽  
pp. 60-61
Author(s):  
Nancy J. Tighe
Keyword(s):  
Silicon Nitride ◽  
Grain Boundary ◽  
Crack Growth ◽  
Subcritical Crack Growth ◽  
Slow Crack Growth ◽  
Ceramic Materials ◽  
Grain Boundary Sliding ◽  
Boundary Phase ◽  
Turbine Engines ◽  
Boundary Sliding

Silicon nitride is one of the ceramic materials being considered for the components in gas turbine engines which will be exposed to temperatures of 1000 to 1400°C. Test specimens from hot-pressed billets exhibit flexural strengths of approximately 50 MN/m2 at 1000°C. However, the strength degrades rapidly to less than 20 MN/m2 at 1400°C. The strength degradition is attributed to subcritical crack growth phenomena evidenced by a stress rate dependence of the flexural strength and the stress intensity factor. This phenomena is termed slow crack growth and is associated with the onset of plastic deformation at the crack tip. Lange attributed the subcritical crack growth tb a glassy silicate grain boundary phase which decreased in viscosity with increased temperature and permitted a form of grain boundary sliding to occur.

Tensile Creep of Y-Si3N4: II. Cavitation

1991 ◽  
Vol 49 ◽  
pp. 972-973 ◽  
Author(s):  
B. J. Hockey ◽  
S. M. Wiederhorn
Keyword(s):  
Silicon Nitride ◽  
Creep Rupture ◽  
Tensile Creep ◽  
Sintering Aids ◽  
Microstructural Changes

ATEM has been used to characterize three different silicon nitride materials after tensile creep in air at 1200 to 1400° C. In Part I, the microstructures and microstructural changes that occur during testing were described, and consistent with that description the designations and sintering aids for these materials were: W/YAS, a SiC whisker reinforced Si3N4 processed with yttria (6w/o) and alumina (1.5w/o); YAS, Si3N4 processed with yttria (6 w/o) and alumina (1.5w/o); and YS, Si3N4 processed with yttria (4.0 w/o). This paper, Part II, addresses the interfacial cavitation processes that occur in these materials and which are ultimately responsible for creep rupture.

A TEM investigation of silicon nitride whiskers

1987 ◽  
Vol 45 ◽  
pp. 160-161
Author(s):  
Tapan Roy
Keyword(s):  
Silicon Nitride ◽  
High Resolution ◽  
Ceramic Matrix Composites ◽  
High Resolution Electron Microscopy ◽  
Molten Silicon ◽  
Matrix Composites ◽  
Ceramic Fibers ◽  
Resolution Electron ◽  
Point To Point ◽  
Technological University

Ceramic fibers are being used to improve the mechanical properties of metal matrix and ceramic matrix composites. This paper reports a study of the structural and other microstructural characteristics of silicon nitride whiskers using both conventional TEM and high resolution electron microscopy.The whiskers were grown by T. E. Scott of Michigan Technological University, by passing nitrogen over molten silicon in the presence of a catalyst. The whiskers were ultrasonically dispersed in chloroform and picked up on holey carbon grids. The diameter of some whiskers (<70nm) was small enough to allow direct observation without thinning. Conventional TEM was performed on a Philips EM400T while high resolution imaging was done on a JEOL 200CX microscope with a point to point resolution of 0.23nm.

The atomic-force microscope and its future in biology

1993 ◽  
Vol 51 ◽  
pp. 704-705
Author(s):  
Jean-Paul Revel
Keyword(s):  
Silicon Nitride ◽  
Laser Beam ◽  
Atomic Force Microscope ◽  
Scanning Tunneling Microscope ◽  
Point Of View ◽  
Scanning Tunneling ◽  
Close Relative ◽  
Tunneling Microscope ◽  
Atomic Force ◽  
Sharp Point

The last few years have been marked by a series of remarkable developments in microscopy. Perhaps the most amazing of these is the growth of microscopies which use devices where the place of the lens has been taken by probes, which record information about the sample and display it in a spatial from the point of view of the context. From the point of view of the biologist one of the most promising of these microscopies without lenses is the scanned force microscope, aka atomic force microscope.This instrument was invented by Binnig, Quate and Gerber and is a close relative of the scanning tunneling microscope. Today's AFMs consist of a cantilever which bears a sharp point at its end. Often this is a silicon nitride pyramid, but there are many variations, the object of which is to make the tip sharper. A laser beam is directed at the back of the cantilever and is reflected into a split, or quadrant photodiode.

Oxidation behaviour and strength degradation of a Yb 2 O 3 -SiO 2 -doped hot-pressed silicon nitride between 1200 and 1500°C

2002 ◽  
Vol 82 (16) ◽  
pp. 3027-3043 ◽  
Author(s):  
Shuqi Guo ◽  
Naoto Hirosaki ◽  
Toshiyuki Nishimura ◽  
Yoshinobu Yammoto ◽  
Mamoru Mitomo
Keyword(s):  
Silicon Nitride ◽  
Strength Degradation ◽  
Oxidation Behaviour
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