Studying of Diffusion of the Titan in Corundum Ceramics

doi:10.4236/msa.2011.27126

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Materials Sciences and Applicatio n, 2011, 2, 946-949

doi:10.4236/msa.2011.27126 Published Online July 2011 (http://www.SciRP.org/journal/msa)

Studying of Diffusion of the Titan in Corundum

Ceramics

Vladimir Gurin1, Lev Derkachenko1, Marcus Schmidt2, Ulrich Burkhardt2, Juri Grin2

1Ioffe Physical-Technical Institute of Russian Academy of Sciences, St Petersburg, Russian Federation; 2Max Planck Institute for

Chemical Physics of Solids, Dresden, Germany.

Email: [email protected]

Received December 30th, 2010; revised March 28th, 2011; accepted May 10th, 2011.

ABSTRACT

For increase in hardness (durability) and fire resistance (stability to melts metals) corundum ceramics on the basis of

Al2O3 authors of the present work have suggested to protect for the first time its surface stronger and fire-resistant cov-

erings, for example, from TiB2. In work results of high-temperature diffu sion TiB2 in a surface of plates from Al2O3 are

shown. For the first time the cathodoluminescen ce (CL) method for identification and a conditio n of atom Ti after diffu-

sion is used, in for an establishment of its quan tity electron probe microa nalysis (EPMA). Durability increa se defin ed a

method microindentification b y means of a pyra mid of Knoop and strength at a bend . Researches have shown perspec-

tivity of ha rdening of a surface corun dum ceramics and use of the above-stated method s for studying of results of diffu-

sion.

Keywords: Corundum Ceramics, Covering from Titanium Diboride, Catodolumin e scence

1. Introduction

Modern the materials technology is characterized by

search new and optimization of known ceramic composi-

tions (in a general sense–compounds of metals with

nonmetals). The basic share thus make oxides materials,

though the quantity oxygen-free (on the basis of oxy-

gen-free refractory compounds-borides, carbides, nitrides

and silicides of metals and nonmetals) ceramics recently

increases. Are used thus and various protective a cover-

ing for ceramics [1-4], including oxides. So, in work [4],

for example, for increase stable properties of a composite

on the basis of corundum coverings from TiB2, ZrС, B4C,

and WC have been used. As it is known, one of the

strongest and cheap ceramic is the ceramics on the basis

of sapphire. One of ways of its further increase durability

and fire-resistant properties is introduction in its surface

of strengthening impurity a method of high-temperature

diffusion.

Thus, as have shown researches, such coverings

co-operate at a heat with a surface of such composite,

partially or completely turning to difficult compounds

and solid solutions—depending on a thickness of a cov-

ering, a way of its drawing and the subsequent thermal

processing. There is a formation of various zones on

depth, in which diffusion covering elements, as a rule,

their components-metals.

2. Materials and Methods

2.1. Materials

In the present work diffusion Ti in ceramics on the basis

of pure sapphire has been investigated. Layer TiB2 has

been put on a surface of ceramic plates (5 × 5 × 1 cm),

and then they have been subjected thermal processing in

argon atmosphere at 1500˚C - 1700˚C during ~ 27 - 48

hours. As a result in sofis a layer some zones on depth to

500 micron and more, containing various quantities Ti

(Figure 1) were formed. Zones consist of sapphire grains

the part from which is covered by a layer containing Ti.

Thus in such layer probably formation of various com-

pounds and the solid solutions [4], which identification

presents considerable difficulties.

2.2. Research Diffusion a Layer in Ceramics

Samples of such ceramics after high-temperature diffu-

sion have been investigated by electron probe micro-

analysis (EPMA), local visible cathodoluminescence (CL)

and microindenting by means of a pyramid of Knoop and

strength at a bend.

Studying of Diffusion of the Titan in Corundum Ceramics 947

(a)

(b)

Figure 1.(a) The general view cross-section corundum ceramic plate with a covering of TiB2 after termoprocess (1700˚C) at

fast heating. 1) a layer of solidified TiB2; 2) a layer like “necklace”; 3) a layer of a little amount of small grains; 4) a layer of a

considerable quantity of small grains, located before pure ceramics; (b)The general view of areas of the basic layers in which

content of Ti was determined by the CL analysis. The four layers show consecutive reduction of the content of Ti in them. Ti

– rosy; Al2O3 – blue; diamond – green (left in hole after polishing).

3. Resalts and Discussion

3.1. Microhardness and Strength

Cross-sections for measurement of microhardness by

means of a pyramid of Knoop prepared by a usual tech-

nique. For surface polishing samples were used by dia-

mond pastes.

Researches strength characteristics have shown that

after diffusion Ti microhardness of ceramics has in-

creased approximately twice (from ~24.5 to ~39 GPa,

that is from 3% to 58% [4]). The greatest values of mi-

crohardness turned out in 1st and 3rd layers, and the least

—in 2nd (see of Figure 1). Such increase is explained

sometimes presence polylayers and orientations nan-

ofragments, perpendicular by planes microindetifikation.

Durability of samples with a covering on a bend (by a

standard technique) has been measured. In comparison

with initial, samples with coverings have shown increase

in strength at a bend on from 11.5 to 45% [4].

3.2. Cathodoluminescence and EPMA

In an optical microscope it is visible that the initial ce-

ramics consists of separate grains-crystals leicosapphir

(Figure 2). Spectra CL in a range from 1.6 - 2.4 eV have

been received with filter JS-17 use. Samples were inves-

tigated at energy electrons 15 KeV.

In spectra CL characteristic strips connected with dot

Figure 2. Image CL of ceramics after term process on dis-

tance of 200 - 300 micron from a surface –2nd and 3rd lay-

ers (see Figure 1) (in drawing maintenance Ti in weight

percent is specified). On six-sided grain are visible: internal

bluish area-pure sapphire (Ti - 0.0%) and wide diffusive

dark-brown area width to 20 micron) with an internal

crimson edge, where Ti - 0.1%, in other part of this area Ti

- 0.4%.

defects in sapphire crystals are observed some: a strip

with a maximum 3.67 eV connected with a F-centre lu-

minescence in sapphire (vacancy of oxygen with one

electron) [5]; a strip with a maximum of intensity 3.1 eV,

corresponding to a luminescence R—the centers (an-

ion-action vacancies steams) [6]; a strip with a maximum

2.4 eV connected with steams anion the vacancies which

have grasped electrons (the modular centers of F-type)

[7]; and a strip with a maximum 1.8 eV, corresponding to

luminescence Ti3+. The maintenance of impurity Ti in

initial ceramics as has shown method EPМА is less than

0.00 %wt.

Studying of Diffusion of the Titan in Corundum Ceramics

948

After carrying out of high-temperature diffusion in CL

the image it is possible to allocate some the characteristic

areas located on various depths from a surface. In the

area located deep into on 500 micron large grains with

the expressed gradient of maintenance Ti (Figure 2)

were observed. Apparently, in this area Ti got into grains

on depth to 20 micron. In the centre of the majority of

grains there were “single crystal” part of pure sapphire

with zero maintenance Ti.

Luminescent properties of the allocated areas in grains

(Figure 3) have been investigated. In spectra of sapphire

ceramics are allocated a strip with a maximum 3.65 eV

and a strip with a maximum 1.8 eV. For a strip with a

maximum 1.8 eV concentration dependence (Figure 4)

has been constructed.

On depth more than 500 micron from a surface the in-

1,6 1,82,0 2,2

1000

2000 0.4%wt.

energy, eV

1000

2000

0.0%wt

0.1%wt

1000

2000

intensity

Figure 3. Spectra CL of areas in ceramics with various

maintenance Ti.

0,0 0,2 0,4 0,6 0,8 1,0 1,2

200

400

% wt.

CL intensity, a.u.

Figure 4. Dependence of intensity CL of a strip with a

maximum 1.8 eV from maintenance Ti in the investigated

micro volume.

tegrated grains of ceramics also are observed. In this case

Ti diffusion in grains on depth no more than 5 microns

(Figure 5). On depth more than 3 mm from a surface

maintenance Ti corresponded to initial ceramics, i.e.,

0.00% wt.

Comparison (on the area of crimson coloring) CL pic-

tures of the crystal sapphire initially alloyed Ti (with the

maintenance nearby 1% wt., the Figure 6) with the

above-stated pictures of distribution Ti in crystal grains

(Figure 2 see and Figure 5) shows volume alloying Ti

the grains in the crystal sample and superficial alloying

on some depth of grains of ceramics from a covering.

Depth of diffusion Ti in ceramics volume (to 1 - 3 mm

depending on time of heat treatment and a thickness of a

covering from TiB2) on usages exceeds depth of diffu-

sion Ti in single crystal grain of sapphire under the same

conditions. This anomaly is caused by that diffusion Ti

passes in ceramics on intersize to borders. Then from

borders of grains there is diffusion Ti to their centre on

internal dispositions and cracks (area to maintenance Ti

of 0.4% wt.). Ti reachesborder of single crystal grain of

sapphire with the low maintenance of dispositions and-

diffusion on depth of an order of 1 micron (maintenance

Ti in this area of 0.1% wt.). In the grain centre zero-

maintenance Ti remains.

0.0% wt.

0.1% wt.

CL intensity, a.u.

0.4% wt.

Figure 5. Image CL of ceramics after term process on dis-

tance more than 500 microns from a surface (in the end of

3rd layer—see Figure 1). Grains with dark-blue the mid-

dle (Ti - 0.0%) and sites with diffuse Ti - from 0.2 to 0.4%

and no more than 5 micron are visible width.

Energy, eV

Figure 6. General view CL of a picture of single crystal

grains of the sapphire alloyed Ti (~1% wt.). Uniform dis-

tribution Ti is characterized by uniform coloring of grains.

Studying of Diffusion of the Titan in Corundum Ceramics

949

4. Summary

Thus, in the present work results of high-temperature

diffusion Ti from TiB2 in a surface pure corundum ce-

ramics for the first time are shown:

1) depending on a temperature mode it is formed dif-

fusions a layer with various depth (to 500 µm - 3 mm) in

which some zones differ;

2) at transition from a surface deep into the sample,

maintenance Ti in zones decreases with ~0.4 to 0.00% wt.

(It is established with the help visible cathodelumines-

cence);

3) also can be defined and depth of penetration Ti in a

surface of grains of sapphire in the form of ion Ti+3 (it is

maximum to 20 µm, CL);

4) Knoop microhardness after thermodiffusion in-

creases more, than in 1.5 times.

Samples with coverings have shown increase in

strength at a bend on from 11.5% to 45% [4] in compari-

son with initial samples.

In summary it is possible to notice that there are real

prospects of improvement of physicomechanical proper-

ties of a surface of ceramics for the account of ceramic

coverings with the improved properties.

5. Acknowledgements

Authors consider as the pleasant debt to express gratitude

to doctors M. V. Zamoryanskaya, E. V. Ivanova, and V.

M. Krymov for the help in work.

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