document21

141

8 МЕЖДУНАРОДНА КОНФЕРЕНЦИЯ 8 INTERNATIONAL CONFERENCEАВАНГАРДНИ МАШИНОСТРОИТЕЛНИ ОБРАБОТКИ ADVANCED MANUFACTURING OPERATIONS21

Comparative Assessment Of Mechanical Properties Of Thermal Sprayed Coatings

P. Dinkov, Institute of Metal Science, Bulgarian Academy of Sciences, 67, Shipchensky prohod-Str., BG-1574 Sofia; e-mail: [email protected]

Abstract: The article presents investigations of the mechanical properties of thermal sprayed coatings with application as thermal barrier -and wear-resistance shields. The applied 7 different thermal spraying powders were based on: NiCrBSi, NiCr-WC, Al2O3/TiO2 , Cr3C2-NiCr , ZrO2/Y2O3 , WC-Co and NiMoAl. As spraying methods were chosen the flame spraying with subsequent sintering and the atmospheric plasma spraying. The produced composite coatings have been subject to specific tests to get knowledge about the complex loadability and to mark tendencies to their application for thermomechanical protection. The tests included investigations of the adhesion tensile strength, the bending behaviour, the wear resistance and rotating bar bending experiments. To interprete the results received more meaningful, there were performed metallographical investigations and pilot-tests for thermal fatigue resistance. The testing programme was completed by accompanying investigations of the micro-hardness and the surface roughness of the coating layer composites. The experiments have been subsequently assessed and discussed.

Key words: thermal spraying, composite coatings, mechanical properties, ceramic spraying powders

1. Introduction

In wide areas of the mechanical, chemical and metallurgical plant engineering occurs a variety of wear and corrosion problems. Significant financial costs are arising due to repairing measures and plant outages. A great part of these problems can be prevented applying diverse coatings on high loaded construction elements in the way that even longer standing time than new parts do have are to be achieved. Technologies like the flame spraying with thermal post-densification (TS+TN) and the atmospheric plasma spraying (APS) are spraying (or semi-welding) methods, which are used where an economical coating protection of big construction parts is required under high rates of deposition. The so produced coatings (and coating systems) can give new properties to the construction parts [1], [2].

2. Experimental conditions

The materials description is given in the Table 1. The first two spraying powders were deposited on the substrate surface by means of flame spraying with additional thermal post-densification (subsequently sintered) .The rest powders have been processed by APS. The NiMoAl-powder (item Nr.7) was used additionally as bonding intermediate layer in the ceramic grades – items 3, 4 and 5.

The base materials were non alloy quality steels St 37-2 (S235 JR – EN10025) and C 15 (EN10277-2). All of the samples have been dried out and preheated for at least 24 hours in a drying chamber at 100–120ºC. Directly before applying of spraying the surfaces of the substrate samples were sandblasted with corundum of grain size [-500 + 1200 µm]. Thus it was ensured that the samples surfaces became an equal roughness of Rz 64 – 74.

3. Results

3.1 Metallography

On Figure 1 is shown a coating which has a dense and coherent strucuture, typical for the flame spraying

142


with subsequently thermal densification The hard tungsten carbide particles (microhardness HV0,1 = 1761) are distributed in the NiCr – matrix (HV0,1 = 785) in form of clasters. Bigger pores in comparison with that of the system 1 (NiCrBSi) are conspicuous. There can be noticed similar defects like in the transition zone coating-substrate of the system 1.

Figure 1 Flame sprayed Eutalloy RW12112, Castolin (NiCr-WC); without bond coat; x 200

Figure 2 Plasma sprayed (APS-method) Amperit 827.1 (ZrO2/Y2O3-93/7); with bond coat NiMoAl; x 200

The structure on Figure 2 is representative for APS and looks similar to that of the coating system 3. It is fine grained and strong infiltrated by pores. There are no evident pore concentrations directly at the transition zone bond coat – topcoat. The existence however of separate pores in this area can be deemed as a reason (along with the residual stress state – subject of additional investigations) for the fracture initiation during the subsequent adhesion tensile strength tests.

3.2 Bending tests

The Figures 3 and 4 are examples showing the achieved grade of formability. The bending angle α has been measured after load removal. The results are sumarized in Table 2. It can be observed that the APS sandvich structures (bond coat + top coat) exhibit significantly bigger bending angles till the first cracks initiations occure.

Table 1 Spraying materials

Nr. Description Description by manufacturer

Chemical composition[weight- %]

Grain size[μm]

1 NiCrBSi 11.16.3 GTV C – 0,75; B – 3,5; Si – 4; Cr – 16; Fe – 3; Cu – 2,5; Mo – 2,5; Ni – 67,75

-125 + 45

2 NiCr-WC Eutalloy RW12112, Castolin

C – 0,45; Ni – 47; Cr – 11,5; Fe – 3,5; Synerg. elements ca. 2,5; WC – Rest (34 %)

No reference

3 Al2O3/TiO2-97/3

Amperit 742.069 (HCST – Hermann Starck)

Al2O3 – 96 min.; SiO2 – 0,6 max.; TiO2 – 3,5 max.; FeO – 0,05 max.

- 40 + 10

4 Cr3C2-NiCr-75/20/5

Amperit 584.1 (HCST) Cr: 67 – 71; C: 9,5 – 10,3; Ni: 18 – 22; O: 0,8 max.

- 45 + 22,5

5 ZrO2/Y2O3-93/7 Amperit 827.1 (HCST) Y2O3: 6-8; HfO2: 2,5 max. SiO2 : 1 max.;TiO2: 0,4 max.; Al2O3 : 0,2 max. FeO: 0,2 max.; ZrO2 – Rest

- 45 + 22,5

6 WC-Co – 88/12

Amperit 515.400 (HCST) Co: 11-13; C: 3,6 – 4,2; Fe: 2 max.; W – Rest acc. AMS 7879

7 NiMoAl* – 90/5/5

Amperit 271.2 (HCST) Ni: 85-90; Mo: 4-6; Al: 4-6; Fe: 1 max.; Mn: 1 max.; Si: 1 max.; C: 0,5 max.

- 90 + 45

*) Annotation: The powder Nr.7 (NiMoAl) was used in the coating qualities 3, 4, and 5 as adhesion bonding layer [0.05 – 0.10 mm].

143

There are two reasons for them:

1) The coating compounds of grades 3, 4 and 5 are thinner than the rest. The coating thickness varies between 0.34 and 0.47, while the rest coatings Nr. 1, 2, 6 and 7 were deposited up to 0.7 mm.

2) The sandvich structure (bond coat + top coat) of the APS coatings enables the establishment of a suitable residual stress state in the manner, that the compression preliminary stresses of the coating compounds can receive higher tensile loading during the bending deformation process.

Figure 3 Bent samples (150x20x5mm): coating system 2 (NiCr-WC).

Figure 4 Bent samples (150x20x5mm): Up: coating system 3 (Al2O3/TiO2-97/3); Down: coating system 5 (ZrO2/Y2O3-93/7);

Table 2 Bending tests

Coating Nr Series A Series BBending angle Coating thickness Bending angle Coating thickness

[grade] [ mm ] [grade] [ mm ]1 8 0.55 1.5 0.602 6 0.46 12 0.383 20 0.36 23 0.414 22 0.43 9 0.475 27 0.34 18 0.476 7 0.55 4 0.487 8 0,70 12,5 0,54

3.3 Bonding strength (Adhesion tensile strength)

The measured high adhesion strength values of the flame sprayed specimens of the systems 1 and 2 give no information about the coating adhesion, but about the strength of the adhesive as such, because the fracture occurred always in the adhesive. The bonding strength of similar flame sprayed coatings with subsequent densification is formed predominantly by intensive local metallurgical interchanges and local weld-fusings.

Table 3 Adhesion tensile strength of the investigated thermal sprayed coatings

Nr Material Adhesion tensile strength, RH, [N/mm2]1 NiCrBSi – 67,5/16/3,5/4 672 NiCr-WC; (47/11,5/34) 643 Al2O3/TiO2-97/3 374 Cr3C2-NiCr-75/20/5 495 ZrO2/Y2O3-93/7 276 WC-Co – 88/12 587 NiMoAl – 90/5/5 60

In Table 3 are shown comparatively the evaluated bonding strengths of the APS-and flame sprayed coating compounds. The WC/Co – 88/12 spraying material belongs to the series Amperit-515 of the company H.C. Starck. It is a molten tungsten carbide – cobalt powder, which particles contain as mean part tungsten carbide, besides cobalt and smaller parts of complex Co-W-C-compositions. This content determines the fine carbide layer morphology,

144


which is characterized by fine pores throughout the entire structure. The high values of WC/Co – 88/12 and NiMoAl – 90/5/5 confirm some results from forerunner works [3] and from other sources [4], [5]. Their wear rates in accompanying tests were also the lowest. A perfect thermal sprayed bonding between substrate and coating was observed.

Figure 5 Cross-view of the surfaces of one coated test specimen and the counter solid after their breaking. Coating: Cr3C2-NiCr-75/20/5 with NiMoAl as intermediate bonding layer – break in the transition zone between bond coat and top coat (koaesive fracture)

The ZrO2-coatings are expressing the tendency to relatively low adhesion strength values (ca. 27 N/mm2) and the fracture appears

up to 90 % at the interface between bond coat (NiMoAl) and top coat (ZrO2/Y2O3).

At the duplex coatings (systems 3, 4 and 5) the fracture appears predominantly in the transition zone top coat – bond coat (Figure 5).

The NiMoAl – bond coat powder (Amperit 271.2) is a spherical, alloyed powder, whose high Ni-content of 85-90 weight % (s. Table 1) secures a strong bond with the NiCr-matrix of the top-coat in the case of system 4 (Cr3C2-NiCr). The coherent morphology of the coating compound explains the different fracture cross sections in the adhesion tensile tests. The so called “cohesive fracture” could be observed especially (Figure 5).

3.4 Rotating bar fatigue tests

The results are given in Figures 6 and 7 using the achieved stress number curves (SN-curves). Fractures and destroying of specimens are visualized by arrow shown in down direction while in case of intact specimen the arrow is in upper direction.

After comparison between the zones of the fatigue endurance strength of the coated specimens and of the uncoated base material S235-JR (Figure 7 – thick line) it gets obvious that the material compounds fitted with coatings ZrO2/Y2O3, Al2O3/TiO2, WC-NiCr and WC-Co exhibit a higher positioned fatigue endurance limit zones.

Interesting results were obtained with the specimens fitted with Cr3C2-NiCr (and NiMoAl as bond coat). Inspite of the fact that the fatigue endurance limit was in much lower position on the diagram than the endurance limit of the base metal, the transition from the fatigue strength for finite life or the creep rupture strength (decreasing curve zone) to the fatigue endurance limit zone (horizontal curve zone) occurs earlier (slightly before 105 cycles).

At the rotating symmetric specimens with coating compounds completely of NiCrBSi or with NiMoAl the horizontal area of the curves begins earlier too, but with values remarkably lower than the “pure” steel substrate S235-JR does (Figure 7). The fatigue strength for finite life or the creep rupture strength areas (decreasing curve zones) of these coated specimens are situated closed to each other. The specimens coated with WC-Co exhibit a decreasing curve zone, which is moved to the highest cycle numbers (to the right direction of the diagram).

Apart from the timely moved transition zones between the fatigue strength for finite life (decreasing curve zone) and the fatigue endurance limit zone (horizontal curve zone), the specimens with ZrO2/Y2O3 (System 5), Al2O3 (System 3) and WC-NiCr (System 2 – Eutalloy) exhibit an increasing of the fatigue strength in comparison to the non coated S235-JR specimens.

145

3.5 Thermal fatigue resistance tests

The test results of the thermal fatigue resistance are presented in Figure 8, Tables 4 and 5. In the cases of the coating qualities 1, 2, 3 and 5 there could be find neither thermal induced cracks, nor some changes of colour. However at the coating system 4 (Cr3C2 – NiCr and NiMoAl as bond coat) the first changes of colour occurred after about 20 cycles. But after optical observation with stereo lens there were not any cracks noticed. The same result came out at the NiMoAl – coatings (quality 7). The cracks however, occured here after about 120 cycles (Table 4).

WC-Co – 88/12 – coatings (coating system Nr.6):

All the tested WC-Co coatings failed after the 40th cyclus. Mostly about 50 % of the coating spalled complete. However the coating as in its intimate structure remained intact and solid.

In order to define the operation zone of this coating system regarding its thermal fatigue resistance, tests were conducted at lower temperature as follows (s. Table 5): coating thickness: 0.6 mm; tact time: 15 seconds; maximum heating temperature Theat = 440 ºC ; cooling temperature Tcool = 235 ºC .

Under the quoted conditions were reached cycle numbers up to 630 without any failure.

Comments to Table 4:

For Nr. 4: After the 20th cycle occured yellow-brown colour changes; After the 40th cycle – total blue-purple colour changes

For Nr. 6: After the 15th cycle – green-blue colour changes; After the 40th cycle – spalling

For Nr.7: First cracks and local yellow colour changes – after the 120th cycle;

For better illustration the results are given compared in Table 6. The thermal fatigue resistance and the wear resistance acc. [6] of the coating compounds are presented with a qualitative assessment.

Figure 6 SN-curves: rotating bar fatigue tests of thermal sprayed specimens

Figure 7 SN-curves: comparison of rotating bar fatigue tests on uncoated and coated steel St37-2 (S235 JR – DIN: EN10025) with NiMoAl – 90/5/5 (Amperit 271.2 (HCST)).

Figure 8 Thermal fatigue resistance tests: T2 = 620 [ºC]; T1 = RT (room temperature); tact time: 5 minutes

146


Table 6 Overview of test results with qualitative assessment

Nr Material Manufacturer`s description

Method Structure (s.tab. 3)

Hardness Raughness [Rz]

Wear resist. *)

Thermal fatigue

resistance [620°C – RT]**)

1 NiCrBSi – 67,5/16/3,5/4(-125 + 45 µm)

11.16.3 (GTV) FS + TN

718 HV0,1 24 ◊ ◊ ◊ ◊ ◊

2 NiCr-WC47/11,5/34

Eutalloy RW12112 (Castolin)

FS + TN

Matrix 785 HV0,1 31 ◊ ◊ ◊ ◊ ◊ ◊Carbide 1761 HV0,1

3 Al2O3/TiO2-97/3(-40 + 10 µm)

Amperit 742.069 (HCST – Hermann Starck)

APS BC 230 HV0,05 33 ◊ ◊ ◊ ◊ ◊

TC 1413 HV0,14 Cr3C2-

NiCr-75/20/5(-45 + 22,5 µm)

Amperit 584.1 (HCST)

APS BC 276 HV0,05 47 ◊ ◊ ◊ ♦ ♦

TC 1192 HV0,1

5 ZrO2/Y2O3-93/7(-45 + 22,5 µm)(PYSZ)


APS BC 280 HV0,05 39 ◊ ◊ ◊ ◊

TC 1192 HV0,1

6 WC-Co – 88/12Grain size according to AMS 7879


APS 1390 HV0,1 32 ◊ ◊ ◊ ◊

7 NiMoAl – 90/5/5(-90 + 45 µm)


APS 262 HV0,05 89 ◊ ◊ ◊ ◊ ♦

Legend:

low medium high Changes of colour*) Wear resistance ◊ ◊ ◊ ◊ ◊ ◊**) Thermal fatigue resistance ◊ ◊ ◊ ◊ ◊ ◊ ♦BC: Bond Coating; TC: Top Coating

Table 4 Testing of the thermal fatigue resistance: T2 = 620 [ºC]; T1 = RT (room temperature); tact time: 5 minutes

Coating system Coating thickness [mm] Temperature difference: ΔT [ºC]NiCrBSi 0.6 55NiCr-WC 0.7 65Al2O3/TiO2-97/3 0.1 + 0.5 50Cr3C2-NiCr-75/20/5 0.1 + 0.2 55ZrO2/Y2O3-93/7 0.1 + 0.2 90WC-Co – 88/12 0.6 60NiMoAl* – 90/5/5 0.6 -

Table 5 Testing of the thermal fatigue resistance (Maximum heating temperature Theat = 440ºC; Cooling temperature Tcool = 235ºC)

Nr Coating System BCBond coat

[mm]

TCTop coat

[mm]

Tact time[s]

Cycles number

TDS[°C]

TS[°C]

4 Cr3C2-NiCr 0,1 0,2 15 630 230 2106 WC-Co - 0,6 15 630 440 235

147

3.6. Wear resisting behaviour

Variations of the running time and of the contact force had been undertaken during the test performing. The volumetric wear rate was used as a criteria for the wear rate because in this way the various specific weight of the coating materials might not be considered. The following dependancies for the volumetric wear rate V were examinated:

As function of the contact force at constant running time and quality of the abrasive counter solid (SiC – grade 120);As function of the various running time at constant contact force and quality of the counter solid (SiC – grade 120).

The results are given graphically in Figure 9(a-d). The volumetric wear rate as a function of the contact force is illustrated in Figure 9(a). It gets clear that 3 groups of coating qualities in relation to their wear rates can be extracted:

1st group: NiCr-WC and WC-Co :

The wear rates are the lowest. A slight increasing of the wear volume as function of the contact force Fn can be noticed. The perfect thermal sprayed bonding between substrate and coating was evident.

2nd group: NiCrBSi, NiMoAl, Al2O3/TiO2 and Cr3C2-NiCr :

Here is remarkable the abrupt decreasing of the wear rates of the coating quality 4 (Cr3C2-NiCr) with the initial increasing of the contact force from 60 N to 80 N. This can be brought in relation with the surface roughness of the coating (s. Figure 9d) and so concluded that the Cr3C2-NiCr-coatings (Amperit 827.1) are very susceptible in the initial test-phase. Similar behaviour in the initial test phase have the Al2O3/TiO2 – 97/3 –coatings.

However the relatively high roughness values measured of NiMoAl (Figure 9(d) are not leading to high wear rates. In contrary – the NiMoAl-coatings have the same lamellar structure as the usually used in the maintenance selffluxing NiCrBSi-based alloys. Still during the layers consolidation in the thermal spraying process occurs an optimal mechanical clamping and wetting of the solidifying coating layers.

3rd group: – ZrO2/Y2O3-93/7 with NoMoAl-bond coat:

These specimens show the lowest wear resistance. In Figure 9b are given the rates of the volumetric wear as a function of the time. The WC-containing coatings (system 2 and system 6) have the lowest wear rates. In the second group is an other tendency obvious – the systems 3 and 4 (Al2O3-based and Cr3C2-based) wear identically. The same is valid for the systems 7 und 1 (NiMoAl and NiCrBSi) in the same group. The following interpretations can be made basing on Figure 9d:

The system 5 (ZrO2/Y2O3) has the highest wear rate (about 230 μm) under an average raughness value of Rz = 39 μm.

The system 7 (NiCrMoAl) occupies the second place with a wear rate of about 160 μm. The volumetric wear rate [mm3] is comparable with those of the coating qualities 3 and 4 (Figure 9d). The obtained high wear rates of system 7 during the initial test phase (30 seconds) are to be related with the higher surface roughness value of (Rz 89 μm).

The noticed fluctuations in the residual coating thickness of the NiCrBSi-wear specimens were caused by the unequal plane parallelity of the coating surface. The reason was the quasi-molten-liquified state of the coating surface during the flame spraying process (becoming visible as the so called “wet appearance”).

In [5] was reported from adhesive wear resistance (Taber Abraser Tests) of similar materials. Different thermal sprayed coatings had been examinated in respect of their behaviour under the “Stud – Disc” – wear test conditions according another source – [4]. The APS – Al2O3/TiO2-97/3 showed the highest wear resistance and let to be categorized along with the flame sprayed selffluxing NiCrBSi – alloys.

148


4 Discussion

Due to the big majority of combinations of spraying parameters and the limited literature data regarding test conditions as well, it is very difficult to make ultimate comparative analysis or if so – only with compromises. Usually the materials related aspects of coating morphology are thoroughly discussed without assessment of spraying conditions and parameters or vice versa. Here arises the need of using FEM-methods and electronic-optical determination of the opened and closed porosity for modeling the morphology of the coating compounds. At the same time thermal and mechanical generated strain-stress states can be simulated and further compared with the test results ([1], [7], [8]).

Metallography:

The accompanying metallographic investigations helped to give the evidence that the coating adhesion strength was local impaired by impurities (rests of steel and grit particles). A coherent porosity in the lower areas of the coating structures (however not a continuous porosity reaching to the coating surface) was ascertained additionally. Therefore a longer “pure” blasting stage by compressed air without grit supply is highly recommended during the substrate preparation in the grit blasting chamber.

a) b)

c) d)Figure 9 (a-d). Volumetric wear rates V30 [mm

3] as a function of the contact force Fn [N], time, coating systems. Countersolid surface with SiC-grain size 120 μm

149

Bending behaviour:

The coatings 3, 4 and 5 have an optimal thickness and are generally thinner than the coatings of the rest samples (to be compared with the coating thickness of series A and B in Table 2). The thicknesses vary between 0.34 and 0.47 mm, while the rest coatings (1, 2, 6 and 7) had not any bond coat and the thicknesses were up to 0.7 mm. Because of the sandvich structure of the APS-sprayed coatings a suitable inherent residual stress state has been established, so that the compression preloaded coating compounds could receive higher tensile stress loadings during the deformation process.

Adhesion tensile strength:

The ZrO2-based coatings showed the tendency to relatively low adhesion strength values (ca. 27 N/mm2). At the

duplex coatings (systems 3, 4 and 5) the fracture appears predominantly in the transition zone top coat – bond coat. At the system 4 (Cr3C2-NiCr) were observed different fracture cross sections because of the strong bond between the Ni-containing bond coat and the Ni-containing matrix of the top coat (coherent morphologies).The so called “cohesive fracture” could been observed especially.

Rotating fatigue strength:

The compound with WC-Co exhibits a decreasing curve zone, which is moved to the highest cycle numbers (to the right direction of the diagram).

Apart from the timely moved transition zones between the creep rupture area / fatigue strength for finite life (decreasing curve zone) and the fatigue endurance limit zone (horizontal curve zone), the specimens with ZrO2/Y2O3 (System 5), Al2O3 (System 3) and WC-NiCr (System 2 – Eutalloy) exhibit an increasing of the fatigue strength in comparison to the non coated S235-JR specimens. The explaination of such behaviour can be searched (like preliminary results of the 3-point bending tests have already shown – [9]), in a convenient compression residual stress state, which is established in the periphery of the rotation symmetric specimens.

Thermal fatigue behaviour:

In the cases of the coating qualities 1, 2, 3 and 5 there could be find neither thermal induced cracks, nor some changes of colour. However at the coating system 4 (Cr3C2 – NiCr and NiMoAl as bond coat) the first changes of colour occurred after 20 cycles but without cracks. A limited thermal fatigue behaviour showed the NiMoAl – coatings (quality 7). It was stated also that the WC-Co-88/12-coatings have a low resistance against thermal induced loading. This susceptibility begins above 440°C. The latter is true without limitations only under the conservative test conditions.

By means of dilatometer measurements there were determined linear expansion coefficients – α –of the thermal sprayed WC-Co-coating with values of 6,58 (in the range: RT to 300 ºC) und 7,17 (RT – 600 ºC). The difference between the measured value of α –of the WC-Co coating obtained and the α – value for St37-2 (14.10-6K-1) as well the lack of interface bond layer between the steel substrate and the WC-Co thermally sprayed coatings are the reasons, which can be regarded for the failing of this coating compound.

As another reason for the failure of the WC/Co – 88/12 can additionally be approached the allotrope transformation of the Cobalt-matrix at 417 – 420ºC from the hexagonal (ε) in to the cubic plane centered (α) lattice structure. This transformation can cause a distortion of the matrix assisted with cracks initiation. The partially coherent porosity stated in the transition zone of the interface coating – substrate can also be deemed as a failure factor ([6], [9], [10]).

Wear resistance:

The coatings with NiCr-WC and with WC-Co (or those containing tungsten carbide) exhibited the highest wear resistance against SiC (with 120 grain size). The changing of the wear rates is degressive. According to the expectations the ZrO2/Y2O3 – specimens wear out rapidly. A progressive change of the wear rates is observed. The rest of the coatings (Cr3C2-NiCr, Al2O3/TiO2, NiCrBSi and NiMoAl) has nearly a linear wear behaviour. The results of the wear tests can be brought into relation with the adhesion tensile strength (Table 3) of the same coatings.

150


Acknowledgements

This work was performed with the technical support of Bayer AG Leverkusen, IN-ATU Werkstofftechnik. This valuable support is gratefully acknowledged.

References

Gudenau, H.W., Dahl, W., Dinkov, P. & Scheiwe, M., 1991. Rechner-Simulation eines thermoschock-1. beanspruchten metall-keramischen Schichtverbundes. Werkstoffe und Konstruktion, 5 (2), p.105-117. Dinkov, P., 1991. 2. Beitrag zum Schutz von thermisch und mechanisch hoch belasteten Bauteiloberflaechen durch Verbundwerkstoffe, VDI-Fortschritt-Berichte, Reihe 5: Grund- und Werkstoffe, 216, VDI-Verlag, Duesseldorf. Protogerakis, E. & Kreisel, K. 1989. 3. Metallische und oxidische thermische Spritzschichten, Bayer-Bericht, IN-ATU Werkstofftechnik, IN-ZWS-W, Metallischer Oberflaechenschutz, Leverkusen, Sept. 1989. Elsing, R., Heintz, H.-R., Knotek, O. & Strompen, N., 1989? probable decade. 4. Eigenschaften thermisch gespritz-ter Metalloxid- und Oxidschichten; DVS 98, p. 99 – 102. Zografou, C., Dhupia, G. S., Kroenert, W. & Protogerakis, E., 1986. Microstructural aspects related to the quality 5. of thermally sprayed ceramic coatings; Journal des physique, suppl. 2, Tome 47, fevr. 1986, p. 171-175. Dinkov, P., 2004b. Wear resistance of coatings with application in the chemical plant engineering.6. In IV Inter-national Congress Mechanical Engineering Technologies’04 in Varna, Scientific Proceedings of the Scientific-Technical Union of Mechanical Engineering, Year XI, Vol. 5/73, Sec.3, September 2004, p. 225 – 228. Balting, U., 1990. 7. Untersuchung plasmagespritzter Al2O3-Schicht-Substrat-Verbundsysteme mit Hilfe der Simu-lation, DVS-Verl., Schweisstechnische Forschungsberichte, Bd. 37, Duesseldorf, 1990. Koerfer, M., Gudenau, H.W., Dinkov, P. & Scheiwe, M., 1990. Energie- und CO-Gasrückgewinnung beim LD-8. Prozeß – Korrosionsprobleme und Spannungsbetrachtungen im Abhitzekessel. In 6. Aachener Stahlkolloquium (ASK), 12.-13.6. 1990, Tagungsband, p. 4.3-1/7. Dinkov, P., 2003. Mechanical properties of thermal sprayed coatings with application in the plant engineering. 9. In RaDMI 2003, 3rd International Conference “Research and Development in Mechanical Industry”, 19-23 September 2003, Herceg Novi, Serbia and Montenegro, A 19, p.182-187.Dinkov, P., 2004a. Investigation of the adhesion tensile strength of thermal sprayed coatings with application in 10. the chemical plant engineering. In Scientific Conference with International Participation “Manufacturing and Management in the 21st Century, Ohrid, Rep. Macedonia, Sept. 16-17, 2004, p. 110 – 114.