EA033973B1 - Method for producing ceramic powder - Google Patents

Abstract

The invention relates to the field of powder metallurgy, and particularly to methods for producing ceramic powders which can be used for obtaining thermal spray heat-protective coatings. The technical task solved by the invention consists in enhanced corrosion resistance to high temperature (at temperatures exceeding 1200°C) salt corrosion and corrosion in fuel combustion products containing sulfur, improved structure stability during long service life under loads, increased plasticity and cheapening of coating process due to the use of hafnium dioxide-zirconium dioxide partially stabilized with yttrium oxide as ceramic material. The set objective is achieved by the fact that in the method of producing ceramic powder comprising mixing of basic oxide and stabilizing oxide that is yttrium oxide, introduction of 8 wt.% of volatile binding agent, granulation at rotation speed of the rotary granulator drum of 30 rpm and inclination angle of 40°, drying at a temperature of 125°C for removal of the binding agent, sintering, fragmenting, screen sizing of powder in plasm, quench hardening of molten powder in 4-11% aqueous hydrochloric acid solution at solution temperature of 70-100°C and baking of the powder with subsequent cooling, where powder spraying in plasm and quench hardening is performed in a chamber filled with argon at the atmospheric pressure, hafnium oxide - zirconium dioxide composition is used as the basic oxide, powder granulation is carried out for 3.0-3.5 h, powder baking is performed at a temperature of 1850-1950°C for 5-7 h with subsequent cooling to 900°C at a rate 150-200°C/min and the power of plasm sprayer is 40 kW.

Description

The invention relates to the field of powder metallurgy, in particular to methods for producing ceramic powders that can be used to obtain thermal thermal coatings.

A known method of producing ceramic powders for heat-protective coatings [1], including mixing the starting components, the introduction of 8 wt.% A volatile binder, granulation at a rotational speed of the rotary granulator drum of 30 rpm and an inclination angle of 40 ° C for 1.1 h, drying at a temperature of 125 ° C until the binder is removed, sintering, crushing, sieving the powder, after sieving, the 20-30 micron fraction powder is sprayed in the plasma and the molten powder is quenched in a 4-11% aqueous solution at 70-100 ° C, then powder annealing at 1 1001300 ° C for 2-4 hours, followed by cooling to 800 ° C at a speed of 150-200 ^ Λ ^ κ

The disadvantage of coatings obtained from partially stabilized with yttrium zirconia produced by this method is the low thermal fatigue of heat-protective coatings at temperatures exceeding 1000 ° C. Moreover, such coatings do not have good resistance in hot corrosion or in the presence of vanadium salts.

A known method of producing ceramic powder [2], including mixing zirconia and a stabilizing oxide, introducing 8 wt.% A volatile binder, granulating at a rotational speed of a rotary granulator drum of 30 rpm and an inclination angle of 40 °, drying at a temperature of 125 ° C to remove a binder, sintering, crushing, sieving the powder, spraying the powder in plasma, quenching the molten powder in a 4-11% aqueous hydrochloric acid solution at a solution temperature of 70-100 ° C and annealing the powder, followed by cooling, as ytterbium oxide is used for the abilizing oxide, the powder is granulated for 2-2.5 hours, the plasma is sprayed and quenched in an argon-filled chamber at atmospheric pressure, and the powder is annealed at a temperature of 1400-1600 ° C for 6-8 hours followed by cooling to 700 ° C at a speed of 200-250 ^ Λ ^ κ

The disadvantage of coatings obtained from partially stabilized by ytterbium oxide zirconia produced by this method is the low thermal fatigue of heat-protective coatings at temperatures exceeding 1150 ° C.

As a prototype, a method for producing ceramic powder [3] was selected, including mixing the basic oxide and stabilizing oxide, introducing 8 wt.% A volatile binder, granulating at a rotational speed of the rotary granulator drum at 30 rpm and an inclination angle of 40 °, drying at a temperature of 125 ° C to remove the binder, sintering, crushing, sieving the powder, spraying the powder in plasma, quenching the molten powder in a 4-11% aqueous hydrochloric acid solution at a solution temperature of 70-100 ° C and annealing the powder, followed by cooling and, moreover, the plasma is sprayed and quenched in an argon-filled chamber at atmospheric pressure, hafnium oxide is used as the main oxide, and yttrium oxide is used as the stabilizing oxide, the powder is granulated for 1-2 hours, the powder is annealed at temperature 2000-2100 ° C for 4-6 hours, followed by cooling to 1000 ° C at a speed of 200-250 ^ / ^ ¾ and the power of the plasma spray is 50 kW.

The disadvantage of coatings obtained from partially stabilized yttrium oxide of hafnium oxide produced by this method is the low corrosion resistance to high-temperature (at temperatures exceeding 1200 ° C) salt corrosion and corrosion in the products of combustion of fuel containing sulfur, insufficient structural stability for long periods service under load, which is associated with a decrease in ductility and the high cost of the source material.

The technical problem solved by the invention is to increase the corrosion resistance to high-temperature (at temperatures exceeding 1200 ° C) salt corrosion and corrosion in the combustion products of fuel containing sulfur, to improve the stability of the structure during long service life under loading, to increase the ductility and the cost of the process of obtaining coatings, - due to the use of hafnium-zirconia oxide partially stabilized with yttrium oxide as a ceramic material.

The problem is achieved in that in a method for producing a ceramic powder, comprising mixing a basic oxide and a stabilizing oxide, which is yttrium oxide, introducing 8 wt.% A volatile binder, granulating at a rotational speed of the rotary granulator 30 rpm and an inclination angle of 40 °, drying at a temperature of 125 ° C to remove the binder, sintering, crushing, sieving the powder, spraying the powder in plasma, quenching the molten powder in a 4-11% aqueous hydrochloric acid solution at a temperature of a thief of 70-100 ° C and annealing the powder, followed by cooling, moreover, the plasma is sprayed and quenched in an argon-filled chamber at atmospheric pressure, the hafnium-zirconia oxide composition is used as the main oxide, and the powder is granulated for 3.0- 3.5 hours, annealing of the powder is carried out at a temperature of 1850-1950 ° C for 5-7 hours, followed by cooling to 900 ° C at a speed of 150-200 ^ / ^ ¾ and the power of the plasma sprayer is 40 kW.

The essence of the invention is as follows: the composition of hafnium oxide-zirconium dioxide yttrium was selected for use as a powder for heat-protective coatings instead

- 1 033973 of the hafnium oxide-yttrium oxide composition because the temperature of the phase transformation upon the transition of the tetragonal phase to the monoclinic phase decreases with increasing concentration of Y2O3, and with increasing concentration of HfO _{2 it} increases, which makes it possible in the HfO ₂ -ZrO ₂ -Y ₂ O _{3 system} to design the production of heat-shielding coatings (TZP) with a given phase transformation temperature. The differences in the crystal lattices of ZrO ₂ and HfO _{2 are} very small, due to the equivalent valence band and the almost equivalent ionic radii Zr ⁺⁴ and Hf ⁴ . For this reason, continuous substitution solutions can form in the ZrO ₂ -HfO ₂ system, and X-ray diffraction patterns of ZrO ₂ , HfO ₂ in solid solutions can be distinguished only using the extremely high resolution X-ray diffraction method. The similarity between ZrO ₂ -Y ₂ O ₃ and HfO ₂ -Y ₂ O ₃ in equilibrium phase diagrams also extends to the formation of nonequilibrium phases. All the considered hafnium dioxide compositions partially stabilized by yttrium oxide upon rapid cooling show one metastable t 'phase, with a microstructure equivalent to the pure t' phase.

Hafnium oxide and zirconia are similar in structural modification, lattice, chemical and physical properties and in their elevated temperature structural transformations. The similarity of Hf ⁺⁴ and Zr ⁺⁴ cations leads to the formation of the same metastable phases during rapid quenching. As a result of the foregoing, an assumption was made that the use of HfO ₂ -ZrO ₂ -Y ₂ O will allow for the preparation of thermal substrates with a resource exceeding the resource of HfO ₂ -Y ₂ O coating.

1) Granulation of hafnium oxide-zirconia powder is granulated for 3.0-3.5 hours for a maximum yield of a powder fraction of 50-63 microns.

Based on literature data, it is known that the best quality of TZP based on partially stabilized zirconia is achieved using fine fractions of powders (5063 μm).

2) The powders obtained after granulation, drying, sintering and crushing are characterized by a complex geometric shape and a developed surface relief of the particles. The particle sizes during free filling and dispersion by ultrasound, respectively, are in the range: (50% HfO ₂ -50% ZrO ₂ ) -8% Y ₂ O ₃ -10-220 microns, 0-63 microns.

A noticeable difference in the sizes of composite particles with free sprinkling and dispersion by ultrasound indicates the tendency of the powders to form lumps. This is due to the hygroscopicity of the powders, their complex shape and topography. The tendency to lump formation reduces the fluidity of powder materials and their manufacturability during plasma spraying of coatings. Therefore, to improve the technological parameters of the powders, they were sprayed with a plasma atomizer in an argon medium to spheroidize the powder particles.

3) Annealing of the powder is carried out at a temperature of 1850-1950 ° C for 5-7 hours, followed by cooling to 900 ° C at a speed of 150-200 ° C / min.

Annealing at a temperature of 1850-1950 ° C for 5-7 hours is carried out to remove intergranular moisture, transform the monoclinic phase into a tetragonal phase and stabilize the tetragonal phase. When annealing for less than 5 hours and at a temperature below 1850 ° C, the monoclinic phase does not completely transition to the tetragonal phase, and when annealing for more than 7 hours at temperatures above 1950 ° C, crystals of the tetragonal phase of hafnium oxide grow and coarsen, which reduces their stability also leads to decomposition into the monoclinic and cubic phases upon cooling of the coatings. This leads to a decrease in thermal fatigue of the coatings. Powder cooling after annealing to a temperature of 900 ° C at a rate of 150-200 ° ^ min is carried out in order to preserve the structure and phase composition of hafnium-zirconia oxide powders obtained during annealing, which is achieved by a quick passage of 1-1.5 min temperature range in which a reverse transition from the tetragonal to monoclinic phase is possible.

When cooling at a rate higher than 200 ° € 7min, the amount of monoclinic phase formed does not decrease, and when cooling at a rate lower than 150 ° ^ min, the amount of monoclinic phase increases, which reduces the thermal fatigue of coatings based on hafnium-zirconia.

Example

Received powders of hafnium-zirconia, partially stabilized with yttrium oxide of the following compositions:

Starting materials less than 5 microns in size were loaded into a porcelain drum and mixed for two hours at a rotation speed of 40 rpm. Then weighed samples of the charge, in an amount of 200 g with the addition of 8% of a binder component - ethyl alcohol brand A (GOST 17299-78) were placed in the drums of a granulator brand 03-03-01. Granulation was carried out for 1.5-4 hours with a drum rotation speed of 30 rpm, with a drum angle of 40 °. In the table. 1 and in FIG. 1 shows the fractional composition of the powder - (50% HfO ₂ -50% ZrO ₂ ) -8% Y ₂ O ₃ after granulation.

- 2 033973

Table 1. The fractional composition of the powder - (50% HfQ ₂ -50% ZrQ) -8% YQ after granulation

A method of granulating powder at a rotational speed of a rotary drum granulator 30 rpm and angle of inclination 40 ° The percentage of the fractional composition of the powder is (50% NU ₂ - 50% ZrO ₂ ) -8% Y ₂ O ₃ after granulation., Microns 0-20 20-50 50-63 63-80 80-100 for 1.5 hours 37 32 25 6 - within 2 hours 40 24 thirty 5 1 within 2.5 hours 23 26 36 10 5 within 3 hours 8 22 53 eleven 6 within 3.5 hours 5 26 60 4 5 within 4 hours 3 19 43 21 14

In FIG. 1 shows the effect of the time of the granulation process on the content of various fractions in the powder treatment products (50% HfQ ₂ -50% ZrQ ₂ ) -8% Y ₂ Q ₃ -: 1 - fraction 0-20 μm; 2 - fraction of 20-50 microns; 3 - fraction of 50-63 microns; 4 - fraction 63-80 microns; 5 - fraction 80-100 microns.

In FIG. 2 shows the morphology of the powder particles (50% HfQ ₂ -50% ZrQ ₂ ) -8% Y ₂ Q ₃ after granulation (* 300).

Then, the conglomerates obtained were placed in alundum boats, which were installed in the SNOL 3.5 / 300 oven. The binder was dried at a temperature of 125 ° C for 1.1 hours. The sintering operation was carried out at 1300 ° C for 6 hours. The morphology of the powder after the annealing operation is shown in FIG. 3

In FIG. 3 shows the morphology of the powder particles (50% HfQ ₂ -50% ZrQ ₂ ) -8% Y ₂ Q ₃ after the sintering operation (* 300).

After the sintering operation, crushing of the material was carried out. Crushing of the material was carried out on a ball mill MBL -1 using steel balls as grinding bodies. The sieving operation was carried out using an air classifier to isolate fractions of 50-63 microns. After sieving, a powder with a fraction of 50 to 63 μm was introduced into the plasma spray jet (F4 plasma torch from Plasma-Technic, Switzerland) and sprayed into a steel cylinder 1 m long, filled with argon in a VPS (vacuum spraying) chamber. The powder was quenched from the molten state in a 5-10% aqueous hydrochloric acid solution at a solution temperature of 80-100 ° C. The power of the plasma jet was varied from 20 to 60 kW (Fig. 4). The degree of spheroidization was determined by the particle form factor (degree of non-sphericity, a value of 1 corresponds to the sphere) by optical metallography. The maximum degree of spheroidization corresponds to a power of a plasma jet of 40 kW (Fig. 4).

In FIG. Figure 4 shows the dependence of the change in the powder form factor - (50% HfQ2-50% ZrQ2) -8% Y2Q3 depending on the power of the plasmatron.

In FIG. 5 shows the morphology of the powder particles of the powder (50% HfQ ₂ -50% ZrQ ₂ ) -8% Y ₂ Q ₃ after passing through plasma (* 500).

Then, the powder was placed in PD-KVPT brand alundum crucibles and annealed in an Naber furnace (Germany) for 5-7 hours at a temperature of 1850-1950 ° C. After the end of the annealing operation, the heating elements of the furnace were turned off and room temperature grade argon A was introduced into the furnace working space in an amount that ensured a decrease in temperature to 900 ° C at a rate of 150 to 200 ° ^ min. When the temperature reached 900 ° C, the gas supply was stopped and the powder was cooled further to room temperature with the furnace. The phase composition of the powders after the annealing operation is given in table. 2. Of the powders of each composition, coatings were applied to 5 groups of 5 samples in each. To obtain comparative data, parallel coating was carried out of the powder obtained by the method described in the prototype. The phase composition of the powders and coatings was determined by X-ray diffraction analysis using a DRON-3 X-ray diffractometer. The quantitative content of the phases was determined using a Nanolab-7 scanning electron microscope.

Table 2. Phase composition of partially stabilized hafnium oxide powders and plasma coatings thereof

Material Composition The content of the phases, May. % monoclinic tetragonal cubic NU ₂ -25 wt.% U ₂ About ₃ 3.6 / - 93.3 / 90.4 3.1 / 9.6 (50% NU ₂ - 50% ZrO ₂ ) -8% Y ₂ O 2,3 / 1,2 96.5 / 97.9 1.2 / 0.9 (25% HfO ₂ - 75% ZrO ₂ ) -8% Y ₂ O. 1.9 / - 98.1 / 99.3 - / 0.7

* - Phase composition of powders / plasma coatings from them.

- 3 033973

Coating was carried out on a plasma spray coating equipment company Plasma-Technician, which includes a computer control panel for coating conditions, a robot to move the plasma torch, and a table for attaching the sprayed samples.

Coatings were applied to the end surface of ZhS-32 alloy disk samples with a diameter of 30 mm and a thickness of 10 mm. Before applying a layer of ceramic coating with a thickness of 0.40 mm, a 0.10 mm thick NiCrAlY sublayer was applied by plasma spraying in dynamic vacuum.

A ceramic coating layer of partially stabilized by yttrium oxide of hafnium oxide was applied in the mode: arc voltage of 70 V, arc current of 750 A, sputtering distance of 110 mm, argon consumption

- 40 l / min, flow rate of hydrogen - 9 l / min, flow rate of powder -2.5 kg / h, flow rate of transporting gas (argon)

- 8 l / min.

A ceramic coating layer of partially stabilized by yttrium oxide of hafnium zirconia was applied in the mode: arc voltage of 60 V, arc current of 700 A, sputtering distance of 100 mm, argon flow rate of 50 l / min, hydrogen flow rate of 8 l / min, powder flow rate - 2.0 kg / h, flow rate of transporting gas (argon) - 8 l / min. After coating, tests were carried out for resistance to thermal cycling and for strength characteristics. Comparative test data for coatings obtained by the prototype and the proposed method are given in table. 3.

Table 3. The effect of the chemical composition of HfO ₂ - ZrO ₂ - 8% Y ₂ O on the resistance to thermal cycling and on the strength characteristics

The chemical composition of the material Powder method The number of terocycles Adhesion Strength, MPa NU ₂ -15 wt.% U ₂ About ₃ prototype - 910 34.1 (50% NU ₂ - 50% ZrO ₂ ) - 8% Y ₂ O ₃ 1216 40.5 (25% HfO ₂ - 75% ZrO ₂ ) - 8% Y ₂ O ₃ - 1271 42.6

Adhesion was determined using an Instron tear-off machine. Quantitative estimates of the parameters were determined as averaged over five measurements. The coatings were subjected to cyclic testing in an oven at a temperature of 1300 ° C. The temperature in the furnace was measured with a platinum thermocouple and maintained at 1300 ± 10 ° C. The cycle consisted of heating for 10 min, holding at 1300 ° C for 60 min, and 60 minutes cooling to 300 ° C. For every 10 cycles, samples were removed from the furnace to check when the temperature dropped to 300 ° C. The tests continued until the destruction of the ceramic coating, for which the formation of a crack visible with the naked eye was taken. The furnace was equipped with a medium simulating conditions in a combustion chamber of a gas turbine, a medium containing products of combustion of diesel fuel containing 1% sulfur and additives 8 · 10 ^-4 %, synthetic sea salt ASTM 665-135 (Na ₂ SO ₄ -3,6 salt % PbSO ₄ 5 mg-cm ^-2 ).

Data on heat resistance and adhesion of coatings obtained by the prototype and the invention are shown in table. 3.

As can be seen and table. 3 coatings sprayed from powders (25% HfO ₂ -75% ZrO ₂ ) obtained by the technology developed by the authors withstand 1.4 times more heating-cooling cycles (cyclic testing in an oven at a temperature of 1300 ° C) than the coating obtained from a powder of HfO ₂ 25% Y ₂ O ₃ made according to the technology of the prototype, while the adhesion strength of the coatings increases by 1.25 times.

Thus, the proposed method allows to increase the heat resistance of heat-protective coatings and provides increased adhesion, which leads to longer protection of the substrate from high temperatures.

Claims (1)

CLAIM A method of obtaining a ceramic powder, including mixing the base oxide and a stabilizing oxide, which is yttrium oxide, introducing 8 wt.% A volatile binder, granulating at a rotational speed of the rotary granulator drum at 30 rpm and a tilt angle of 40 °, drying at a temperature of 125 ° C for removing the binder, sintering, crushing, sieving the powder, spraying the powder in plasma, quenching the molten powder in a 4-11% aqueous hydrochloric acid solution at a solution temperature of 70-100 ° C and annealing the powder, followed by cooling by spraying, and the plasma is sprayed and quenched in an argon-filled chamber at atmospheric pressure, characterized in that the composition of the main oxide is hafnium oxide zirconium dioxide, the granulation of the powder is carried out for 3.0-3.5 hours, the powder is annealed at at a temperature of 1850-1950 ° C for 5-7 hours, followed by cooling to 900 ° C at a speed of 150200 ° C7min, and the power of the plasma sprayer is 40 kW.