RU2411217C1 - Method of producing wear resistant ceramic - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to a method of producing wear resistant ceramic based on zirconium dioxide which is partially stabilised with yttrium oxide, and can be used in making components for tribological application as a draw plate, draw ring, bearings etc. The method employs chemical deposition of zirconium and yttrium hydroxides from a mixture of salts with specific surface area of not less than 200 m²/g, with further thermal treatment of powder at temperature 900-1000°C. Sintering of the workpieces formed from said powder is carried out in the region of existence of a tetragonal phase: sintering to temperature 1300-1350°C is carried out while heating at a rate of 750-1000°C per hour, holding for 2-3 hours and subsequent cooling at a rate of 1000-1100°C per hour. Fast raising and sharp cooling enable to obtain a ceramic with size of structural elements of up to 200 nm and with 100% content of tetragonal crystalline phase.

EFFECT: high wear resistance of the ceramic in conditions of dry friction in a pair with steel.

2 cl, 1 tbl

Description

The invention relates to a method for manufacturing wear-resistant ceramics based on zirconia partially stabilized by yttrium oxide obtained by chemical deposition, and can be used in the manufacture of parts of tribological use as dies, dies, bearings of rotation shafts in pumps for pumping abrasive liquids (oil, etc.) ), friction units operating under conditions of increased thermomechanical loads, ceramic connectors of fiber-optic communication lines.

Zirconia-based ceramics have a low coefficient of friction, high hardness, strength, and wear resistance.

It is known that materials based on partially stabilized zirconia with yttrium oxide under friction under the influence of shear stresses arising from friction can initiate the polymorphic transformation of the tetragonal phase into a monoclinic one. This transformation occurs with an increase in volume, which leads to microcracking and destruction of the ceramic material.

This problem is solved in the invention (RF patent No. 2194028, C04B 35/486, December 10, 2002) by obtaining in the structure of a zirconia-based ceramic partially transformed tetragonal t 'phase partially stabilized (3 mol%) with yttrium oxide, due to which they increase thermomechanical properties. The structure of this material consists of large grains of 70-100 μm in a cubic crystalline phase with nanoscale inclusions of a transformable tetragonal crystalline phase. This method allows to obtain wear-resistant ceramics in conditions of friction with lubricant, but is not suitable for dry friction in contact with metal. In conditions of dry friction, products manufactured by this method, there is a large wear of the surface. The reason for this is the degradation of the material due to the reverse transition of the t 'phase to the tetragonal phase, and that in turn to the monoclinic phase.

There is another way to increase the wear resistance of the surface of ceramic products based on zirconia, RF patent No. 2287503 C1, CB 35/48, 11/20/2006. The technical effect of increasing the wear resistance is achieved by the fact that after sintering ceramics based on zirconia stabilized with yttrium oxide, the surface is irradiated with 1-10 pulses of an electron beam with an energy of 15-30 keV, a pulse duration of 30-100 μs and a density of 40-100 A / cm ² . The yttrium oxide stabilized zirconia powder was prepared by mixing oxides and firing to obtain a solid solution at high temperature (1700 ° C). For this reason, the sintering of ceramics had to be carried out at a high temperature of 1750 ° C in vacuum. The grain size of this material is in the range of 50-100 μm, the level of wear resistance is not sufficient for using ceramics in dry friction in contact with metal for a long time, and materials with such a large grain are subject to degradation due to monoclinic-tetragonal transition.

The closest in technical essence to the claimed method is a method of manufacturing a high-strength ceramic material, RF patent No. 1349199 A1 СВВ 35/48, published September 27, 2000. This method of manufacturing a high-strength ceramic material based on tetragonal zirconium dioxide involves obtaining the initial powder by chemical deposition from salt solutions, molding products firing according to the following regime: heating at a speed of 20-50 ° C / h to 1400-1440 ° C; heating at a speed of 120 ° C / h to 1505-1515 ° C; exposure at the final temperature does not exceed 20 minutes.

The ceramic material obtained by this method has a low density, fracture toughness and a large size of structural elements (> 3 μm), the level of wear resistance is not sufficient for using ceramics in dry friction in contact with metal for a long time.

The aim of the invention is to obtain a material based on zirconium dioxide with high density values, with a nanostructure that provides increased strength properties (K1s) and wear resistance under conditions of dry friction in contact with steel for a long time.

The goal is achieved by ball grinding a mixture of zirconium and yttrium salts to a specific surface of at least 200 m ² / g, with further heat treatment of the powders at a temperature of 900-1000 ° C, followed by molding and final sintering, with a heating rate of 750-1000 ° C / h to a maximum temperature of 1300-1350 ° C, with exposure at this temperature for 2-3 hours, followed by cooling at a speed of 1000-1100 ° C / h, with an apparent density of at least 5.95 g / cm ³ , 100 % of the tetragonal phase and the size of the structural elements of the ceramic material up to 200 nm.

The method is as follows.

To obtain a ceramic material based on partially stabilized zirconia composition: (ZrO ₂ + 3 mol.% Y ₂ O ₃ ) 94 wt.% ZrO ₂ + 6 wt.% Y ₂ O ₃ prepare a mixture of salts in an amount of 2500 g of zirconium chloride, 160 g of yttrium chloride. The mixture and grinding balls of zirconia in an amount equal to 1: 3 are placed in a ball mill with a lining of zirconia for grinding to a specific surface area of at least 200 m ² / g, measured by the BET method. The resulting mixture of salts is placed in a chemical reactor and, with a constant speed, 10 l of a 3% aqueous ammonia solution are fed into the precipitator with constant stirring. The resulting suspension is washed with distilled water to a pH of 7 from chloride salts. A suspension with a concentration of 15-20% solids is placed in a spray dryer with an outlet temperature of 100-120 ° C and dried. The resulting mixture of hydroxides is calcined at a temperature of 900-1000 ° C with holding at these temperatures for 2 hours and ground in a ball mill with a lining and grinding balls of ZrO ₂ . Then formed by thermoplastic injection molding of the blanks of the plates 10 × 10 × 4 mm and samples with a size of 7 × 7 × 70 mm Sintering is carried out in an air atmosphere at a temperature of 1300-1350 ° C for 2-3 hours with a heating rate of 750-1000 ° C / h and cooling at a speed of 1000-1100 ° C / h. The phase composition was measured on sintered samples by X-ray phase analysis, and the density and porosity of the workpieces were measured by hydrostatic weighing, and mechanical properties were measured on the samples.

Tests on the wear resistance of the samples are carried out on a serial friction machine UMT-1, according to the "finger-disk" scheme, in which a stationary test ceramic sample is pressed against a rotating disk with a diameter of 12 mm and rubs the end surface along the plane of a disk made of hardened tool steel U10A (GOST 5950-73) with a hardness of HRC 49-52. Pressure 5 MPa, sliding speed 2 m / s.

Comparison of ceramic manufacturing methods, physical and mechanical properties of products are presented in the table.

When precipitated from solutions of chloride salts, an agglomerated powder is obtained (experiment No. 1), which prevents the ceramic material from sintering to a dense state of 5.95 g / cm ³ . If salt mixtures have a specific surface area of less than 200 m ² / g, then precipitation produces a powder more agglomerated and it is impossible to obtain dense ceramics (experiment 2). When tested for wear resistance, these materials wear out more than materials (experiment 3) obtained by precipitation from a mixture of salts with a specific surface area of more than 200 m ² / g. If the sintering temperature of ceramic from a powder obtained by precipitation from a mixture with a specific surface area of more than 200 m ² / g is greater than 1350 ° C, the grain grows to 2 μm, which leads to greater wear under dry friction. An increase in the powder firing temperature of more than 1000 ° C leads to the fact that the ceramics do not sinter to a dense state (experiment 4) and a monoclinic phase appears, which causes friction polymorphic transformation with a change in volume and cracking, and as a result, increased wear of the material is observed.

The inventive method for producing wear-resistant ceramics based on zirconia and stabilizing yttrium oxides in comparison with the prototype has several advantages:

- allows at lower sintering temperatures 1300-1350 ° C to obtain ceramics in the tetragonal phase with a density of more than 5.95 g / cm ³ ;

- fast rise and rapid cooling make it possible to obtain ceramics with a nanostructure up to 200 nm, which increases the wear resistance of ceramics under conditions of dry friction paired with steel tens of times.

Claims (2)

1. A method of manufacturing a wear-resistant ceramic based on tetragonal zirconia, comprising mixing zirconia with stabilizing yttrium oxide by co-precipitation from salts, heat treatment, grinding, molding and sintering, characterized in that the mixing is carried out by co-precipitation from a mixture of solid zirconium and yttrium salts with a specific surface area of at least 200 m ² / g, heat treatment is performed at a temperature of 900-1000 ° C, sintering at a temperature 1300-1350 ° C is carried out with a heating rate of 750- 1000 ° C / hr, followed by cooling with rate of 1000-1100 ° C / h. 2. The method according to claim 1, characterized in that the sintering is carried out with exposure for 2-3 hours