DE1621296A1 - Component partly made of boron carbide and process for its manufacture - Google Patents

Description

US serial no. 524.615
Filed: February 1, 1966

National Research Corporation 70 Memorial Drive, Cambridge, Massachusetts, V, St.A,

Component partly made of boron carbide and process for its manufacture

The invention relates to components which partly consist of boron carbide, and to methods for their production.

Boron carbide is a very promising material because of its low density and high mechanical strength. The known methods of processing of boron carbide are so expensive that the use boron carbide has so far only been justified in very few special cases was.

The object of the present invention is based on eliminating this disadvantage and specifying a component consisting at least partially of boron carbide, in particular a layer material, which is relatively inexpensive can be produced and previously unattainable

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BATH ORIGINAL

Has mechanical and chemical properties.

This is achieved according to the invention in that the boron carbide in the form of a black, shiny, brittle layer is present that is at least 2.5. thick, a flexural tensile strength of the order of moderate at least 2 χ 10 kp / cm (500,000 psi) and one

6 2

Modulus of elasticity exceeding 2.8 10 kgf / cm (40,000,000 psi) has and none with CuK - ^ - X-rays Fe crystal structure is detectable.

The boron carbide preferably contains

which corresponds.

borrowed more carbon than the formula B ₂ , G The carbon content is preferably at least ^ O %.

The flexural strength is preferably

4 2
at least 2.8 10 kg / cm (400,000 psi) and the modulus of elasticity is preferably greater than 2.5 10 kp / cm (50,000,000 psi).

In a preferred method of manufacturing

The boron carbide layer is made from a layer of graphite or carbon by vapor deposition of boron Crucible formed at elevated temperature in a vacuum. The borearbide vapors are heated to a comparatively cooler, but to one above the ambient temperature Surface deposited, which is arranged above the crucible.

In a preferred embodiment of the invention, the boron carbide layer is on a

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deposited, whose density is less than 5 g / enr and whose Thickness is at most three times the Borcartoidsehicht, wherein the composite material has a flexural strength of at least

H. ό

1.4- χ 10 kp / cm (200,000 psi) and a modulus of elasticity above 7 χ 10 ^ kp / cm (10 10 psi) and a density below 5 g / cm. In one embodiment, the base is made of aluminum, in another embodiment of a temperature-resistant organic film, for example a polyimide film, such as that made by EI duPont de Nemours & Co., Inc., Wilmington, Delaware under the trade name "Kapton ^11" received- ™ is borrowed.,

The boron carbide layer carried by the base can be processed into a composite body. For areas of application in which the exceptional properties of boron carbide are to be exploited to the greatest possible extent, it can be useful to separate the boron carbide layer from the substrate. This is particularly true for the case where the substrate is relatively thick and the desired composite should have the highest possible strength and stiffness per ä cross-sectional area. In both cases, a substantial part of the total thickness of the composite body should consist of boron carbide layers, so that the physical properties of the composite body are essentially determined by the boron carbide and not by the material of the substrate or matrix. Preferably a number of

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Boron carbide layers with a base to form a layer structure united to form a solid, lightweight component.

The boron carbide layer can be used if desired be separated or partially removed from the base, which in the case of a base made of aluminum by dissolving of aluminum can happen. The boron carbide layer can be broken up into flakes, which then, "e.g. with a Epoxy resin, processed into a composite body. the

^ ~ "Boron carbide layer can, on the other hand, also be applied to a cold, sheet metal made of tungsten, for example, which is then bent to form the boron carbide layer flakes off in the form of flakes.

The invention is based on the drawing

explained in more detail, the single figure of which is a simplified sectional view represents a device for producing boron carbide layers.

The device shown contains a vacuum chamber 10 which can be evacuated by a pump 12. A substrate 14 to be coated is attached to a heating plate 16 which is located above a crucible 18 which contains boron carbide 20. The crucible 18 is surrounded by insulation 22 and an induction coil 24 which is connected to a generator 2.6 . A closure 28 is arranged between the base 14 and the crucible 18, the open position of which is drawn out and the closed position of which is shown in phantom. ^ _v

BATH ORIGINAL

'10 98 19/140 5

In operation, the chamber is after loading evacuated to a relatively low pressure. The crucible is then heated for degassing and finally the shutter is opened in order to vaporize the substrate 14. ·

Example 1 :

The crucible 18 was made of graphite (quality

AP-70 Manufacturer The Carbone Corporation, Boonton, New Jersey), he had one mm inner diameter of about 44, a foreign Λ mm diameter mm of about 63 and a height of about 75 miles. The crucible was mounted on a rod, the diameter of which was 6.3 mm and the length of which was about 150 mm. The lower end of the rod was held in a fireclay brick. The crucible was surrounded with 25 mm fiber charcoal (quality 4C-2, manufacturer Barnebey-Cheney Co., Columbus, Ohio). Outside the carbon fiber insulation there was an induction coil that was fed by an 8.6 kHz generator. The crucible was charged with 100 g of high purity boron carbide (manufactured by The Norton Company, Worcester, Massachusetts). An aluminum support was mounted on a heating plate about 350 mm above the crucible. There was a closure between the base and the crucible. The vacuum chamber was then open

-5 - ■

10 torr and the crucible was then gradually heated to about 1500 ° C for 10 minutes. After the arrangement had been completely degassed, the temperature was increased to 2300 ° C. At the same time the temperature of the substrate was raised to 150 ⁰ C by bringing the heating plate to I60 ° C

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became. The closure was now opened and the substrate was vaporized with boron carbide for 20 minutes. After venting the In the vacuum chamber, the pad was removed and examined. The . Thickness of the deposited boron carbide layer was 0.064 mm, what a vapor deposition rate of about j5 yum per minute is equivalent to. During the vapor deposition, the temperature of the substrate was determined by means of an iron-constantan thermocouple and that of the crucible measured by an optical pyrometer. $ To examine the product received

the aluminum base was first removed using an alkaline solution and the flexural strength of the remaining boron carbide layer was removed was measured. The result was a modulus of elasticity of 4.4 χ 10 kp / cm (62 χ 10 psi) and a flexural

4 2

Tensile strength of 2.9 10 kgf / cm (410,000 psi). A chemical analysis of the boron carbide layer showed a carbon content of 40 %. The layer was black, shiny and brittle and looked amorphous, coherent, free of pores and essentially uniform. An X-ray diffraction study with Cu-K ^ radiation did not reveal any crystal structure. Analyzes of microscopic samples showed no discernible fluctuations in the composition along the plane of the layer.

The product obtained was exceptional

rigid and firm and showed an exceptionally good cohesion

it
content, so that / is excellently suited for applications

where extreme strength and rigidity at the same time

low weight are required »" *

BATH

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Example 2;

This example was essentially the same

Example 1 with the exception that instead of the aluminum foil used in Example 1, a 0.014 mm thick polyimide film is used and the heating plate is on 200 ° C was heated, whereby a temperature to be

o steaming surface of the polyamide film of about 150 C resulted.

As in Example 1, a thickness of about 0.03 mm was then formed on the film thick boron carbide layer deposited. The polyimide film coated with boron carbide in this way has flexural strength of about 2.7 10 kp / em (390,000 psi and a Young's modulus of 4.5 kP / cm (64 χ 10 'psi). The downcast Boron carbide sheet was black, shiny, brittle, and looked amorphous. She had properties like that product obtained in example 1. A chemical examination of the deposited layer revealed a carbon content from about 37 # · "

Those prepared according to Examples 1 and 2

Products can be combined into a multi-layer structure using polyimide or epoxy resin as an adhesive that look through extreme flexural rigidity, strength and low weight. Polyimides (e.g. duPont PI4701) are particularly suitable as an adhesive or matrix. However, the usual epoxy resins can also be used, such as those used for plastic components reinforced by inserts

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are known, albeit the adhesive strength and temperature resistance then is not so good.

The carbon content of boron carbide layer

th according to the invention with maximum modulus of elasticity,

between
that is, maximum stiffness, lies between 50 and 50 atomic percent.

If required by the properties of the end product, other layer compositions can be used. If maximum strength is required, a layer with a stoichiometric composition (80 % boron, 20 % carbon) is preferable; Such a layer can easily be produced if one works with electron beam heating instead of the induction heating described. An important trick with electron beam heating is to heat the boron carbide to 150 ° C for one hour in vacuo (10 Torr or less) for degassing prior to vapor deposition; this practically prevents the melt from splashing during electron beam heating. The product can take the form of a ψ together menhängenden layer or a cohesive film of flakes or strands which were cut from a larger layer have. The thickness of the boron carbide layer is preferably on the order of 25 µm if it is to be used in a substantially rigid form; however, the layer thickness may have other values according to the end use. When the layered boron carbide is used to construct complex-shaped layered bodies

1 0 9 8 1 9 / U 0 5

should, it is definitely beneficial to the total thief
of the boron carbide between 2.5 and 25 μm and, in the case of a two-sided coated substrate, in particular between 5.0 and 7.5 μm (0.2 to 0.3 mil). With such a dimensioning, the coated base as a whole is still sufficiently flexible to allow a body to be built up in the most varied of shapes. '

The flexibility of a boron carbide layer becomes

determined by the lower limit of the permissible bending radius of the layer. The following equation applies to this radius R: %

R = t E / S

where t is the thickness, E is the modulus of elasticity and S is the
Strength of the layer.

For E ^ 2.8 χ 10 ⁶ kp / cm ² (.40 χ 10 ⁶ psi) and

4 2
S = 2.1 x 10 kgf / cm (300,000 psi) is obtained

for a thickness t of: a radius R of:

0.33 mm 0.0133 inches 0.67 mm 0.0266 inches 1.01 mm 0.0399 inches d 1.35 mm 0.0532 inches 1.69 mm 0.0665 inches

So if, for example, a body is to be formed in the form of an ⁿ W ^M , the layer thickness and the bending radius must be applied
the corners of the "w" are matched to each other. The smaller
the allowable radius of curvature at the corners of the "w", the greater the design latitude. For the production

0AD QFUGtNAL 10 9 8 19/1405

2.5 /around 0.1 mil 5.0 /around 0.2 mil 7.5 AXOl 0.3 mil 10.0 around 0.4 mil 12.5 /around 0.5 mil

a body of such a shape is, for example, a Plastic film coated with boron carbide and several such layered films form a layer structure combined and brought into the desired shape, as long as the glue is still soft between the layers. After hardening of the adhesive, the W-shaped body is then very rigid and dimensionally stable. On the other hand, bodies of such a shape can be very difficult to manufacture by hot pressing boron carbide. The described use of a layer structure on the other hand, simplifies production considerably and provides composite bodies whose properties are those of homogeneous boron carbide to an extent approximately equal to the volume percent of the composite on boron carbide.

ORIGINAL 109819/1405

Claims (10)

Patent claims 1. Component that is at least partially made of Boron carbide, characterized in that that the boron carbide is in the form of a black, shiny, brittle layer which has a thickness of at least 2.5 yum, a flexural strength of the order of magnitude it ρ 6 at least 2 χ 10 kp / cm (300,000 psi) and one i2.8 χ 10 kp / The elastic modulus in excess of cm (40,000,000 psi) has ^ and in the case of an X-ray diffraction analysis with CuKv radiation no crystal structure is detectable. 2. Component according to claim!, Characterized by a coherent boron carbide layer, which is supported by a coherent film, whose density is less than 5 g / enr and whose thickness is at most three times the thickness of the boron carbide layer and that the thickness of the layer is between 2.5 and 25 µm is and is dimensioned so that the coated film as the whole is flexible and can be processed into layered molded bodies. 3. Component according to claim 2, characterized marked reject that it is made up of a number of Layers of films coated with boron carbide and bonded with adhesive. 10981 9 / UO 5 4, component according to claim 2 or j5, characterized in that the coated Foil has a flexural strength of at least 1.4 χ kp / cm (200,000 psi), a density below 5 g / cnr and one 5 2 6 Modulus of elasticity exceeding 7 10 kp / cm (10 10 psi) has ο 5 «component according to claim 2, j5 or 4, characterized in that the film is made of aluminum. 6 »Component according to claim 2, 3 or 4, characterized in that the film made of polyimide. 7. Component according to claim 2, 3 or 4, characterized in that the film consists of a polymer material. 8. Component according to one of claims 2 to 7, characterized in that the composite arrangement © ine flexural strength of over π ρ 2 χ 10 ^ kp / cm (JOO,000 psi) and a modulus of elasticity greater than 2.8 χ 10 kp / cm ² (40 10 psi). BAD ORIQ3NAU 1 Π 9 8 1 9/1 A Π 5 296 9. Component according to one of claims 2 to 8, characterized in that the Foil is provided on both sides with a boron carbide layer, the thickness of which is 5 to 7.6 μm per side. 10. Component according to one of the preceding claims, characterized in that that the boron carbide layer has the stoehiometric composition corresponding to the formula B ^ C ". 11. Component according to one of claims 1 to 9, characterized in that the boron carbide layer is at least JO to 50 atomic percent carbon contains. 12. A method for producing a component according to any one of the preceding claims, characterized in that marked, _ that boron carbide (20) consists of a ζ « consisting of carbon ^ Cegel (l8) at a temperature of about 2J5OO ⁰ C in a chamber evacuated to a pressure below 1 χ lo "* ^ Torr is evaporated on a base (14), the density of which is below 5 g / cm, to the thickness of the vapor-deposited boron carbide is at least one third of the thickness of the base. BATH 1 f) 9 8 1 9/1 k fi p Γ3. Method according to claim 12, characterized marked that the document is substantially removed and that the remaining self-supporting boron carbide layer is incorporated into a composite structure will. 14. The method according to claim Γ5, characterized marked that the substrate is bent after the coating and that that flakes off when bent Boron carbide flakes are incorporated into a composite body. 15. The method according to claim 14, characterized characterized that as a base a tungsten foil is used. 16. The method according to claim 12, characterized G eke nnz e rejects that the coated substrate ■ with other similarly coated substrates to form a layer structure is united. 10 9 8 19/1 4 0