SU1749285A1 - Charge on boron carbide-base for preparation of sintered ceramic material - Google Patents

Abstract

The invention relates to powder metallurgy, in particular, to a composition of a boron carbide-based charge for the preparation of a sintered ceramic material. The essence of the invention: the specified mixture containing boron, additionally contains molybdenum carbide in the following ratio, wt.%: Boron 1-20, molybdenum carbide 0.5-10, boron carbide - the rest. The wear resistance of the material increases by 1.5 times. 1 tab.

Description

The invention relates to powder metallurgy, in particular, to ceramic hard and wear-resistant materials, which can be used as sand-jet nozzles, bearings, high-temperature indenters, non-replaceable plates, etc.

A known charge for the preparation of a material based on boron carbide (WDS), containing as the second phase component tungsten carbide (WC). 1 The disadvantage of the material from this mixture is its low wear resistance due to the low level of mechanical properties.

Closest to the invention is a mixture containing boron carbide and boron.

The disadvantage of this mixture is its low wear resistance due to its high brittleness (low fracture toughness).

The aim of the invention is to increase wear resistance by increasing viscosity.

The goal is achieved by the fact that in addition to boron carbide and boron, the mixture additionally contains molybdenum carbide at a ratio of components, wt.%: Bor1-20

Molybdenum carbide 0,5-10 Boron carbide Else

Ceramic material from this mixture is obtained by hot pressing at 2000– 2250 ° C and a pressure of 10–35 MPa in graphite molds.

As a result of the interaction of the components of the mixture under hot pressing conditions, free carbon is boron bound by the reaction

4В + С - B / iC

which leads to an increase in hardness and strength of the material. Reaction

5B “C + 4Mo2C 4Mo2B5 + 9C leads to the appearance of molybdenum boride (Mo2Bs) and free carbon (C) in the structure of the material, which is fully or partially bound by the introduction of boron into the mixture. Boron molybdenum, located at the grain boundaries, increases the viscosity of the destruction of the material and, therefore, wear resistance.

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when the content of molybdenum carbide in the mixture is not less than 0.5%, the mutual influence of EMC and Mo2Bb leads to an increase in fracture toughness, this is explained by the occurrence of stresses around the inclusions of crack propagation around the Mo2Bs inclusions. An increase in the content of B and MoaC in the blend by more than 20 and 10 wt.%, Respectively, adversely affects the hardness and strength of the material and its wear resistance. Due to the addition of boron carbide and molybdenum carbide in addition to boron carbide in the proposed amounts, it is possible to obtain a high complex of mechanical properties, i.e. at the same time, high hardness, strength, fracture toughness and wear resistance.

Example. A mixture of powders of 84 wt.% Boron carbide, 10 wt.% Boron and 6 wt.% Molybdenum carbide with a grain size of less than 45 µm, taken in an amount of 100 g, is granulated by grinding through a sieve with a hole diameter of 500 µm or more, poured into a graphite press -form and pressed at 2200 ° C, a pressure of 3.0 MPa and a holding time of 15 minutes. Of hot-pressed blanks with a porosity of less than 2%, complete cylinders with an internal diameter of 8 mm are made. external 25 mm, length 50 mm, which are then subjected to microhardness tests (Vickers hardness at a load of 5 kgf), bending strength (three-point bending of specimens 3x3x25 with a test base of 20 mm), the fracture toughness is measured by indentation of the Vickers pyramid) and relative wear resistance under aero-abrasive wear (measured on a shot-blasting apparatus 334M using shots, quartz sand with a flow rate of 1500 kg / h, inlet air pressure of 6 MPa, test time 900 h) with respect to the material from the charge, s Hold 90 wt.% boron carbide and 10 wt.% of boron.

Properties of the material obtained1 microhardness 26.5 GPa; flexural strength 440 MPa; fracture toughness 4.8 MPa.m; Relative wear resistance 1.6

Conducted a series of experiments with different content of the components of the claimed mixture.

The results of the experiments are given in the table.

Analysis of the table shows that the wear resistance of the material under abrasive wear is determined by a combination of values

macrohardness, flexural strength and fracture toughness.

. In experiment 6, the amount of boron in the mixture is less than 1%, therefore, a low value of flexural strength was obtained, which negatively affects wear resistance.

In experiment 7, boron and molybdenum carbide in the charge are less than necessary, therefore both the flexural strength and the fracture toughness are low, which entails

decrease in wear resistance. In experiment 8, a lot of boron and molybdenum carbide, therefore, the material has low macrohardness and wear resistance.

The increase in wear resistance of the proposed material (experiments 1-5) with respect to the prototype (experiment 9), as can be seen from the table, is obtained by increasing the fracture toughness due to the introduction of molybdenum carbide,

Claims (1)

Invention Formula Boron carbide-based mixture to obtain a sintered ceramic material containing boron, characterized in that, in order to improve the wear resistance of the material, it additionally contains molybdenum carbide in the following ratio, wt.%: Boron 1-20 Molybdenum carbide 0,5-10 / 0 Carbide boronErest