CN101280405A - Lanthanum oxide-alumina composite coating prepared by plasma spraying method and preparation method thereof - Google Patents

Abstract

The invention relates to a lanthanum oxide-alumina composite coating prepared by a plasma spraying method and a preparation method thereof, belonging to the field of wear-resistant ceramic coatings. According to the present invention, the ratio of lanthanum oxide and aluminum oxide is 3/97 to 10/90, and the aluminum oxide and lanthanum oxide powders are weighed and mixed by ball milling; the composite powder is deposited on the cleaned and sandblasted surface by using a plasma spraying process. on metal substrates. Analysis of the microstructure of the lanthanum oxide _- alumina composite coating prepared by the present invention shows that the lanthanum element _is uniformly dispersed in the alumina _matrix phase _. -La ₂ O ₃ coating has a higher deposition efficiency, which can effectively improve the wear resistance of the plasma sprayed coating.

Description

Lanthanum oxide-alumina composite coating prepared by plasma spraying method and preparation method thereof

technical field

The invention relates to a lanthanum oxide-alumina composite coating prepared by a plasma spraying method and a preparation method thereof, belonging to the field of wear-resistant ceramic coatings.

Background technique

As an excellent wear-resistant coating, plasma sprayed alumina coating has been well applied in the fields of machinery, chemical industry, and papermaking. However, on the one hand, the inherent brittleness of ceramic materials and the process characteristics of thermal spraying technology determine the low deposition efficiency and porous structure of alumina coatings, which largely restricts the further application of coatings in the field of wear resistance. ; On the other hand, with the rapid development of science and technology, higher requirements are put forward for the application environment of coating materials. Therefore, how to improve the structure and wear resistance of plasma sprayed alumina coating is a topic worth studying.

Domestic and foreign literature reports that the main ways to improve the structure and mechanical properties of plasma sprayed alumina include: optimization of process parameters, design of powder structure and composition, post-treatment, etc. Since there are more than 50 factors influencing the plasma spraying process and interacting with each other, the experimental workload is large and it is difficult to obtain an optimized process. Although post-treatment means such as dipping sealing and laser remelting can effectively reduce porosity, improve coating density and thermal and mechanical properties (M.Vippola, S.Ahmaniemi, J.Keranen, et al., Mater.Sci. Eng.A, 2002, 32:1-8), but it also complicates the coating preparation process and increases the coating preparation cost. The general process of plasma spray coating is that the molten powder hits the substrate at high speed, spreads, cools, solidifies and accumulates to form a coating. It can be seen that the structure and composition characteristics of the sprayed powder directly affect the flight characteristics of the molten particles and the structure and composition of the deposited coating. performance. Therefore, the composition and structure design of the spray powder has become an important means to improve the wear resistance of the plasma sprayed alumina coating. For example, Al ₂ O ₃ -TiO ₂ , Al ₂ O ₃ -Cr ₂ O ₃ composite powders are prepared by the alloy method, and the coating is prepared by plasma spraying process. Compared with the pure Al ₂ O ₃ coating, its wear resistance has a certain degree Improvement (V. Fervel, B. Normand, C. Coddet, Wear, 1999, 230:70-77). In recent years, researchers are still exploring new composite coating systems.

Contents of the invention

The present invention is based on the prior art, adopts mechanical mixing process to prepare Al ₂ O ₃ -La ₂ O ₃ composite powder, and uses atmospheric plasma spraying technology to deposit Al ₂ O ₃ -La ₂ O ₃ composite coating on the metal substrate. layer.

Concrete technological process of the present invention is as follows:

(1) Take aluminum oxide and lanthanum oxide powder by weighing 3/97～10/90 according to the ratio of lanthanum oxide and aluminum oxide, ball milling and mixing;

(2) Depositing the composite powder obtained in step (1) on the cleaned and sandblasted metal substrate by using a plasma spraying process.

The preferred mass ratio of grinding balls to powder is 1/3-1/2.

The range of process parameters for optimal control is:

Current 600～700 amperes

Plasma gas H ₂ 7～20 standard liters/minute

Plasma gas Ar 40～55 standard liters/minute

Powder carrier gas Ar 3.5～4.2 standard liters/minute

Spray distance 80～120mm

A preferred metal substrate is a stainless steel substrate.

Analysis of the microstructure of the lanthanum oxide-alumina composite coating prepared by the present invention shows that the lanthanum element is uniformly dispersed in the alumina matrix phase (Fig. 3), and the XRD pattern shows that the crystal phase composition of the coating is: γ-Al ₂ O ₃ , α-Al ₂ O ₃ , La ₂ O ₃ , La(OH) ₃ ( FIG. 4 ).

Compared with spraying pure Al ₂ O ₃ coating, plasma spraying Al ₂ O ₃ -La ₂ O ₃ coating has higher deposition efficiency (Fig. 5), and effectively improves the wear resistance of plasma spraying coating (Fig. 6 ).

Description of drawings

Figure 1 is the surface morphology of the Al ₂ O ₃ -5wt.% La ₂ O ₃ composite powder: it can be seen that the La ₂ O ₃ powder is well dispersed.

Figure 2 is the X-ray diffraction pattern of Al ₂ O ₃ -La ₂ O ₃ composite powder doped with different contents of lanthanum oxide: because Al ₂ O ₃ -La ₂ O ₃ is easy to absorb water in the air, there is La(OH) in the XRD pattern ₃ peaks.

Figure 3 shows the cross-sectional morphology and component analysis of the Al ₂ O ₃ -5wt.% La ₂ O ₃ composite coating: the component analysis shows that the rare earth La element is more uniformly dispersed inside the coating.

Figure 4 is the X-ray diffraction patterns of Al ₂ O ₃ -La ₂ O ₃ composite coatings doped with different contents of lanthanum oxide: the main crystal phase of the coating is γ-Al ₂ O ₃ , accompanied by a certain amount of α-Al ₂ O ₃ , La ₂ O ₃ , La(OH) ₃ phases.

Figure 5 shows the effect of lanthanum oxide doping on the deposition efficiency of the plasma sprayed Al ₂ O ₃ coating: it can be seen that the addition of La ₂ O ₃ improves the deposition efficiency of the Al ₂ O ₃ coating.

Figure 6 and Figure 7 Effect of lanthanum oxide doping on wear resistance of plasma sprayed Al ₂ O ₃ coatings: It can be seen that the addition of La ₂ O ₃ reduces the wear rate and effectively improves the wear resistance of Al ₂ O ₃ coatings wear resistance.

Detailed ways

The present invention is further illustrated below through examples, but not limited thereto.

Example 1

Weigh aluminum oxide and lanthanum oxide powders according to the mass percentage of lanthanum oxide at 3%, and then weigh zirconia balls with a diameter of 3mm according to the ball powder ratio of 1/3, put them into a ball mill bottle together, and dry mix them on a ball mill After 2 hours, Al ₂ O ₃ -La ₂ O ₃ composite powders with lanthanum oxide mass percentages of 3%, 5% and 10% were prepared. Atmospheric plasma spraying technology was used to control the process parameters according to Table 1, and the composite coating and pure alumina coating were sprayed on the surface of the cleaned and sandblasted stainless steel friction disc with a size of Φ50×Φ6.5×8mm. It can be seen from Figure 5 that under the same process conditions, the thickness of the composite coating doped with rare earth lanthanum oxide is 20-35% higher than that of the pure alumina coating, and the increase in the thickness of the deposited coating reflects that the rare earth lanthanum oxide The addition of AlO greatly improves the deposition efficiency of the alumina coating.

Example 2

Weigh alumina and lanthanum oxide powders according to the mass percentage of lanthanum oxide at 5%, and then weigh zirconia balls with a diameter of 3mm according to the ball powder ratio of 1/3, put them into a ball mill bottle together, and dry mix them on a ball mill After 2 hours, Al ₂ O ₃ -La ₂ O ₃ composite powders with lanthanum oxide mass percentages of 3%, 5% and 10% were prepared. Atmospheric plasma spraying technology was used to control the process parameters according to Table 1, and the composite coating and pure alumina coating were sprayed on the surface of the cleaned and sandblasted stainless steel friction disc with a size of Φ50×Φ6.5×8mm. It can be seen from Figure 5 that under the same process conditions, the thickness of the composite coating doped with rare earth lanthanum oxide is 20-35% higher than that of the pure alumina coating, and the increase in the thickness of the deposited coating reflects the rare earth lanthanum oxide. The addition of AlO greatly improves the deposition efficiency of the alumina coating.

Example 3

According to the mass percentage of lanthanum oxide is 10%

Weigh alumina and lanthanum oxide powders, and then weigh zirconia balls with a diameter of 3 mm according to the ball-to-powder ratio of 1/3, put them together into a ball mill bottle, and dry mix them on the ball mill for 2 hours to make lanthanum oxide with a mass of 100%. Al ₂ O ₃ -La ₂ O ₃ composite powder with a content of 3%, 5% and 10%. Atmospheric plasma spraying technology was used to control the process parameters according to Table 1, and the composite coating and pure alumina coating were sprayed on the surface of the cleaned and sandblasted stainless steel friction disc with a size of Φ50×Φ6.5×8mm. It can be seen from Figure 5 that under the same process conditions, the thickness of the composite coating doped with rare earth lanthanum oxide is 20-35% higher than that of the pure alumina coating, and the increase in the thickness of the deposited coating reflects that the rare earth lanthanum oxide The addition of AlO greatly improves the deposition efficiency of the alumina coating.

The coated friction discs prepared in Examples 1, 2, and 3 are subjected to a certain grinding and polishing process (surface roughness is about 0.5 μm), and Φ9.5mm stainless steel balls are used as ball-on-disc (ball-on-disc) discs. ) contact mode to grind. The friction equipment is the UMT-3 multifunctional friction and wear tester of American CETR. The friction test conditions are: load 15N, rotational speed and friction radius 1000rpm and 15mm respectively (line speed about 1.7m/s), friction time 10min. The friction and wear results are shown in Figure 5. From the comparison of friction coefficient and wear rate, it can be seen that rare earth doping effectively improves the wear resistance of the coating.

Table 1

Current 660 amps Plasma gas H ₂ 12 standard liters/minute Plasma gas Ar 49 standard liters/minute Powder carrier gas Ar 4.0 NL/min Spray distance 110mm

Claims (5)

1, the method for preparing lanthanum oxide-aluminum oxide composite coating by plasma spraying method, is characterized in that comprising the following steps: (1) Take aluminum oxide and lanthanum oxide powder by weighing 3/97～10/90 according to the ratio of lanthanum oxide and aluminum oxide, ball milling and mixing; (2) Depositing the composite powder obtained in step (1) on the cleaned and sandblasted metal substrate by using a plasma spraying process. 2, prepare the method for lanthanum oxide-aluminum oxide composite coating by the plasma spraying method described in claim 1, it is characterized in that the parameter of selected plasma spraying process is: Current 600～700 amperes Plasma gas H ₂ 7～20 standard liters/minute Plasma gas Ar 40～55 standard liters/minute Powder carrier gas Ar 3.5～4.2 standard liters/minute Spray distance 80～120mm 3. The method for preparing a lanthanum oxide-alumina composite coating according to claim 1, wherein the metal substrate is a stainless steel substrate. 4. The method for preparing a lanthanum oxide-alumina composite coating according to claim 1, wherein the mass ratio of the grinding ball to the powder is 1/3-1/2. 5. The lanthanum oxide-alumina composite coating prepared by the method for preparing a lanthanum oxide-alumina composite coating according to claim 1 or 2 or 3 or 4.

Images