Sintered technical ceramics

Sintered ceramics

Our wide range of sintered technical ceramics will allow you to make a selection of the most suitable material for your application:

Final Advanced Materials manufactures ceramic parts with precision. From the blanks obtained by molding or extrusion, we get these shaped parts by diamond machining for dense ceramics.

We provide the definition and machining of prototypes, as well as the individual production in small and large series. We design and machine the ceramic components adapted to specific customer applications : sensors, medical technology, equipment and mechanical engineering, microsystems technology, chemical and processes engineering.

We only work with calibrated and qualified ceramics of high purity. The ceramic parts that we transform, reproduce without modification, the physical characteristics of the blanks before machining, without any variation or mechanical depreciation.

The intrinsic properties to ceramics, i.e. hardness, abrasion resistance, compressive strength, resistance to high temperatures, to thermal shocks, high dielectric strength, all these qualities are preserved and reproduced on the finished parts.

Classification of sintered ceramics

The sintered ceramics are subdivided into groups according to their mineralogical or chemical composition. We can reference three main groups :

  • Silicate ceramics
  • Non-oxide ceramics
  • Oxide ceramics

Silicate ceramics

As the oldest group amongst all the ceramics, represent the largest proportion of fine ceramic products. The major components of these polyphase materials are clay and kaolin, feldspar and soapstone as silicate sources. Additionally such components as alumina and zirconia are used to achieve special properties such as higher strength. During sintering a large proportion (> 20%) of glass phase material, with silicon dioxide (SiO2) as the major component, is formed in addition to the crystalline phases. Due to the relatively low sintering temperatures, the good understanding of how to control the process, and the ready availability of the natural raw materials, silicate ceramics are much cheaper than the oxide or non-oxide ceramics.

Non-oxide ceramics

Include ceramic materials based on compounds of boron, carbon, nitrogen and silicon. Products made of amorphous graphite do not belong to this category. These ceramics usually contain a high proportion of covalent compounds. This allows their use at very high temperatures, results in a very high elastic modulus, and provides high strength and hardness combined with excellent resistance to corrosion and wear.

Oxide ceramics

Oxide ceralmics are defined as all materials that are principally composed of a single phase and a single component (>90%) metal oxide. These materials have little or no glass phase. The raw materials are synthetic products with a high purity. At very high sintering temperatures a uniform microstructure is created which is responsible for the improved properties.

Implementation of sintered ceramics

A perfect control of the entire process of implementation ensures the microstructure of the material. 3 elements are essential to obtain a sintered ceramic part with optimal characteristics :

  • Powder
  • Pressing
  • Sintering

According to the criteria of your request, we adapt the various stages of implementation:

For the prototypes, we will press 1 block with our standard tooling. There are no tooling costs, nevertheless there is a machining phase before sintering rather long but inexpensive (depending on the geometry of your part). Re-machining with a diamond tool depending on the severity of the required tolerances.

For the series, we will provide an equipment allowing to obtain the part the closest possible to its final geometry to reduce a maximum the cost of materials and the expenses of manufacturing. A re-machining with a diamond tool is always necessary in case of too restrictive dimensional tolerances.

For the validation of a material (chemical composition, particle size, thermal and mechanical characterization, …) we can offer you the realization of diskss samples.

We also have the possibility to produce coloured sintered ceramic parts. During pressing, we mix coloured oxides to the ceramic powder. For example: black Zirconiumoxide ZrO2 for watches and grey, red or blue Aluminiumoxide Al2O3 for jewelery.

Pressing

At first, it is necessary to select a calibrated powder, of high quality, with a controlled and constant shrinkage. The powder particles are compacted to form a coherent shape with sufficient strength for subsequent handling. If necessary, this shaped, unsintered mass of powder (known as a green body) can be machined economically before firing, since corresponding steps are much more expensive after sintering. When applying the various forming processes, care must be taken to avoid significant density gradients and textures in the green body, since these can be amplified during sintering, leading to distortions and internal mechanical stresses. The choice of a suitable forming process is usually determined by economic factors (efficient manufacturing). We can offer you two different pressing types: isostatic or uniaxial.

Firing

As a rule, green bodies made by a forming process like casting, plastic forming and pressing, contain, in addition to the ceramic powder mixture (including the permanent additives), moisture and often organic deflocculants, plasticisers, binders and other additives. All these volatile components at high temperature are removed from the green body at the beginning of sintering.

The goal of ceramic technology is the manufacture of a mechanically strong body able to withstand the widely differing requirements and conditions of the application. There is only a small degree of bonding between the particles of the green body. The ceramic bonding, and the very high strength associated with it, is obtained only by sintering at high temperatures. Firing allows sintering (with or without a liquid phase) to take place, and this is what actually creates the ceramic material. The sintering rate is dependent on purity, grain size, compaction and the sintering atmosphere.

Through reactions that occur during sintering, a strengthening and densification of the ceramic takes place, resulting in a reduction in porosity. This process results in a volume reduction; this is called sintering shrinkage. The amount of shrinkage for the various ceramic materials is widely different. The shrinkage coefficient defined by the quality of powder used allows to calculate the dimensions of the part once sintered.

Machining

The green body is machined with a conventional tooling, the fragility of the material requires special attention. Machining cost is rather low. Once sintered, the part can only be machined with a diamond tooling or by ultrasound. This operation is much longer, difficult and expensive.

Our ways of machining: surface, cylindrical grinding, turning, milling, drilling, machining and ultrasonic drilling, plane and cylindrical polishing and tapping, threading or lapping.

We also machine: quartz, ruby, glass, glass-ceramic, porous ceramics of filtration, and composites, glass filled resins, silica, carbon or machinable insulation materials, like calcium silicate, mica, aluminosilicate, etc.

Assembly

Brazing: the ceramic parts are metallised, this metallisation allows brazing up to temperatures of 1200°C in air or under vacuum. Braze alloys suited to materials to be assembled ensure sufficient mechanical strength to ceramic-metal fixtures. The main disadvantage of this type of assembly which is a significant expansion differential between the different materials, is partially controlled with construction principles which permit the consideration of it, or, which allow to reduce the effects of it. Every application is unique and specific, we shall study the appropriate assembly with you.

Adhesion: adhesion on metal ceramic parts implies to know exactly the maximal temperature to stand for, to evaluate the chemical constraints of the environment, the mechanical stress and the electrical capacity expected from this assembly. One of the most important factors is the thermal expansion coefficient of the elements in contact. In the specific case where adhesion between two materials of different nature (i.e. different dilatabilities) must be realised, it is necessary to try to approach these parameters with the glue used, in order to resist better to the contraction or elongation stresses induced. Whatever your problem of ceramic adhesion, do not hesitate to contact us.

Mechanical assembly: we have a long experience of this type of assembly, we can offer you screwing and seaming.

Design of ceramic parts

The use of typical metallic and polymeric materials (steel, cast-iron, aluminium alloys, nickelbased alloys, etc.) for machine and tool construction, automotive construction and process engineering is deeply ingrained in most design engineers: the different characteristics and constraints are known. When a technical problem has to be solved, the designer must create a number of technical elements; if ceramic materials are to be used, he must pay particular attention to the need for the design to be appropriate for the material. Ductile materials react to small area/local overloads, compensating for them through elastic extension in accordance with Kooke’s law, with some plastic deformation in reserve. This does not apply to materials that are hard and therefore brittle - and also not flaw-tolerant. There are therefore considerable differences between the local loading capacity of parts made of ductile (metallic) materials and of brittle/hard (ceramic) materials. This therefore also calls for different design rules.

Characteristics tables

Properties

Units

Alumina

Zirconia

Silicon carbide

Boron nitride

Aluminium nitride

Silicon nitride

Aluminium titanate

Reference N°

 

055-0010

055-0020

055-0021

103-0010

200-0090

055-0030

103-0020

036-0010

Purity

 

Al2O3 99,7%

ZrO2-Y2O3

ZrO2-MgO

SSiC

BN HD

AlN

Si3N4

Al2TiO5

Classification DIN ISO

 

C779

C800

C800

-

-

C910

C935

-

Characteristics table

Density

g/cm3

3.9

6

5.6

> 3.1

2.2

3.3

3.18 to 3.4

3.35

Open Porosity

%

0

0

0

0

0

0

0

12.5

Colour

 

ivory

white

yellow

black

white

grey

grey

ivory

Mechanical characteristics 20°C

Hardness Vickers HV10

N/mm2

> 17 000

> 12 000

> 10 000

> 25 000

-

> 10 500

15 200

< 2000

Compression strength

N/mm2

2 500

> 1800

> 1800

> 2 500

142

> 2000

3 000

-

Flexural strength

N/mm2

> 370

> 600

> 600

> 400

45

> 350

769

25

Elasticity modulus

GPa

> 380

> 200

> 200

400

-

> 320

290

17

Toughness

MPa.m1/2

4

7

8

3.5

 

> 3

7.5

-

Weibull Modulus

 

15

20

16

10

 

-

25

-

Thermal characteristics

Max. operating temperature

°C

1700

1000

1000

1900 (1600 on air)

1400 (850 on air)

1000

1400

1500

Specific heat 20°C

J/kg.K

900

400

400

670

-

-

700

-

Thermal conductivity 100°C

W/mK

30

2.5

3

125

47

180

25

1.4

Thermal expansion 20 to 1000°C

10-6/K-1

8.5

11

11

4.5

5.85

4.6

3.2

< 1

Electrical characteristics

Specific resistivity 20°C

Ω.m

1012

1012

> 10 7

10-3 to 106

1012

> 1010

1012

1012

Specific resistivity 600°C

10 6

> 10 3

> 10 3

-

 

-

-

-

Dielectric strength

kV/mm

17

-

-

-

19.6

15

-

-

Do not hesitate to contact us for more information, for the design and machining of your parts.

Sintered technical ceramics (813.69k)

Data Sheet: Sintered technical ceramics