SU1456282A1 - Method and apparatus for compacting powders of refractory compounds - Google Patents

Abstract

The invention relates to the field of powder metallurgy, in particular, to methods for producing high-strength structural structural ceramics from powders of refractory compounds (nitrides, carbides, silicides, borides). The aim of the invention is the expansion of technological capabilities by increasing

Description

The invention relates to the field of powder metallurgy, in particular, to methods for producing high-strength structural-purpose ceramics from powders of refractory compounds (nitrides, carbides, silicides,

borides).

The aim of the invention is the expansion of technological capabilities by increasing the length of the product and increasing strength. The method of hot pressing involves pouring powder into a mold, and hot pressing is carried out in two stages: in the first, pressing is carried out at an initial pressure p of 0.35-0- 85 final pressure P, and at an initial temperature T. is 50-1004 lower than the final temperature T of hot pressing to a density of 80-95%, and in the second stage the hot pressing is carried out at the final temperature and pressure of hot pressing for a given powder.

A device for implementing the proposed method contains a matrix placed in the inductor and counter-punches, in which the press chamber of the dies is made of two cavities with different cross-sectional areas, one of which is 1.1-1.5 times larger than the other, the plug is in the cavity of the press chamber, having a smaller cross-sectional area, is spring-loaded in the axis

direction, and the die is provided with an abutment ensuring its immobility in the second stage of pressing. Hot pressing occurs

in two stages.

In the first stage, under pressure P and temperature TH, the powder is compacted to 80-95% in the cavity of the press chamber with a large cross section area S. In the second stage, the pressure in the cavity with a larger cross section area rises to P value due to loading 5 of the punch installed in this cavity. In this case, the pressure in the cavity of the press chamber having a smaller cross-sectional area S ,, remains equal to Р ,. Due to this, the workpiece, compacted in the first stage, is moved from the first cavity of the press chamber with a larger cross-sectional area to the second under pressure P, -Pi with simultaneous pressing of the compactor in diameter. The temperature in the second pressing stage is raised to a value of Hc + (50-100 ° C).

 The drawing shows a diagram 30 of the device for ocyI ecl of the proposed method for hot pressing a hollow product at the beginning of the pressing process.

The device consists of a mold with powdered powder 1, a refractory compound, a matrix 2, which is installed on the punch 3 and has

314

a stepped pressure chamber with an applied layer of insulating substance 4 and the steps of the pressure chamber are made either with straight transitions 5 or with transitions on curvilinear surfaces. The pressing chamber in the upper part limits the punch 6, and together with the rod 7 on the bottom cooled insulated plate 8, the course of which limits the base plate (stop) 9, on which the induction heater 10 is installed, has heat insulation, water cooling, power supply (not shown), The cooled plate 8 is spring-loaded, for example, by a hydraulic adjustable device consisting of a power hydraulic cylinder 11, a regulating hydraulic cylinder 12 connected to it with a loading device 13, to realize the load of the upper punch 6, there is an upper thermally insulated cooled plate 14 connected to it hydraulically loading (not shown),

Example. The preliminarily prepared mixture of silicon nitride powder with 8 wt.% Yttrium oxide is poured into the pressing chamber of the matrix 2 with the lower punch installed. colloidal solution of boron nitride, ethyl alcohol and glue BF). The cross-sectional areas of the cavities of the press chamber S 36.7 cm (diameter 68 mm), S, 28.3 cm (diameter 60 mm). After installing the upper punch 6, the mold assembly is placed in the inductor 10 of the hot-pressing press. After that, heating to a temperature of 1710 ° C is made and the punch 6 is loaded with a force Hz 24 tf and the powder is pressed bilaterally hot. Due to the different cross sections S S, the lower punch during compaction moves faster and when it reaches the position at which the lower

punch filled all density s /

dies, double-sided hot pressing is completed (first stage). The density of the workpiece after the first pressing stage is

d 5

about

five

five

0

five

0

91% of theoretical. Then, an emphasis 9 is brought under the material P1 2, the temperature is raised to 1760 ° C and the pressure is raised to P 100 MPa (the force of the upper press plate 14 is increased to 36.7 tf). In this case, the force applied to the lower punch 3 remains unchanged and is equal to 24 ts, which is achieved with the help of a hydraulic cylinder 11 mounted on the bottom plate 8. Due to the pressure difference, the workpiece 1 moves into the cavity of the press chamber of a smaller section S in the radial direction. After the whole billet is transferred to a cavity of a smaller section S, hot pressing is completed, the inductor 10 is disconnected and, after cooling to 1400 ° C, the pressure is released and the mold is cooled to a normal temperature. After the final cooling, the mold is pressed out and the compact is removed.

For comparison, experiments were carried out to obtain ceramics based on silicon nitride by a known method.

Claims (2)

1. A method of hot pressing powders of refractory compounds, including pouring powder into a mold, hot pressing with upper and lower punches and removing the product, characterized in that, in order to expand the technological possibilities by increasing the length of the product and increase strength, hot the pressing is carried out in two stages: in the first stage, the initial pressure is 0.35-0.85 of the final pressure and plots it to the upper and lower punches at a temperature of 50-100 ° C lower final temperature of the hot Binding to a density of 80-95%; in the second stage, the temperature is increased to the final hot pressing temperature, and the pressure of the upper punch is increased to the value of the final pressure. 51456282 2. Device for hot pressing; it is equipped with stops, placed powders of refractory joints under the matrix, the internal cavity of the mother is placed in the heaters and is filled with different areas, the matrix and puison. ° - GaGoH tG New from the side of the plot of smaller diameter, made spring-loaded in the axial direction. characterized in that, in order to expand technological capabilities by increasing the length of the product and increasing strength. Silicon nitride Boron carbide Titanium diboride 42.5 50 2100 Table 1 2150 50 0.85 95 1.1 Table 2 Silicon nitride 12 400 17.0 Titanium diboride 0.3