SU1413147A1 - Method of treating materials - Google Patents

Abstract

The invention relates to thermal deformation processing of fragile porous materials and can be used in powder metallurgy, radiation materials science, etc. The purpose of the invention is to increase strength. The essence of the invention is that the material is irradiated in a stream of particles, such as neutrons, up to -, 1 fluence 10 -10 N / cm, at a temperature below the brittle-plastic transition temperature, namely at + + 50 ° C, where Tjj - the temperature of the grain-boundary viscosity, while applying a load causing a stress in the material not exceeding 10 MPa, during processing the deformation and its velocity are measured continuously, and at the moment of an abrupt increase in speed the material is deformed by changing the load at a rate not exceeding , and processing terminate upon reaching the deformation of a given value. 3 hp f-ly, 1 tab. with SS (L

Description

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This invention relates to thermal deformation processing of fragile porous materials and can be used in powder metallurgy, radiation materials science, etc.

The purpose of the invention is to increase the strength.

The essence of the invention is that the material is irradiated in a stream of particles, such as neutrons, at a temperature below the brittle-plastic junction temperature, the treatment is carried out at a temperature of grain-boundary viscosity on samples with a grain size of not more than 30 μm under a voltage of i 1 o MPa to fluence

cm

formations 10 s

Do not exceed the speed and interrupt when the sample reaches a given density; the treatment is carried out, not exceeding the deformation of 0.5%, when the stress state is identical to the conditions of the product; compressive stress treatment is interrupted at the time of maximum shrinkage in order to increase strength while simultaneously maintaining the porosity of the specimens, and compressive stress treatment is interrupted after the process of reversible shrinkage is terminated.

The treatment must be carried out at a temperature of grain boundary viscosity. Granular viscosity is the physical state of each polycrystalline material, which manifests itself in a certain temperature range, depending on a number of parameters: the variation in grain sizes and their size, quantity and nature of impurities and phases, the frequency range excited as a result loading and irradiation of material oscillations, etc.

The prerequisites for choosing hardening modes of brittle porous materials are that the processing temperature corresponds to an increase in the level of destructive stresses, the loading rate must correspond to the stress relaxation rate near defects in the material, the final stress should cause some plastic deformation, but its damage will not should lead to a marked accumulation of damage. Significant hardening (see analog) is observed at temperatures above 0.5 Tpl, the value of the final

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the yarn is close to the value of the yield point (100 MPa), and the residual strain does not exceed 0.2%. In the course of the irradiation, conditions are created that prevent the use of the indicated prerequisites. Under given irradiation conditions, an uncompensated flow of vacancies is formed, which, in turn, leads to a significant increase in plasticity in certain temperature ranges, strain rates, stresses and the corresponding structural state of the Material. In this connection, treatment temperatures above 0.5 Tpl, resulting in recrystallization and, as a result, rapid attenuation of increased plasticity, are unacceptable. For the same reason, a level of stresses of the order of 00 MPa, leading to a high strain rate (10 s), is not suitable. Low level (0.2%) of permanent deformation is not suitable for effective strengthening, since it does not allow to compact the sample or change the shape of all defects and

thereby reducing their danger. Therefore, in order to sustainably maintain the increased plasticity of the material without damaging it, radiation momechanical processing (RTMO) is carried out at a temperature of grain-boundary viscosity on samples with a grain size of not more than 30 µm under MPa to a fluence of N / cm, not exceeding the deformation rate. At the indicated fluence, a gas splash is observed, the possibility of sample shrinkage appears. Subsequent reconstitution and additional gas causes the material to swell (i.e., reversible shrinkage), which, combined with a slight external compressive stress in conditions of increased plasticity, gives all the dangerous (in terms of destruction) structure defects round, which, in turn, leads to an increase in strength. Products under operating conditions are characterized by a certain kind of stress state. For more efficient processing of the product, it is necessary to expose it to the action of the same kind as under operating conditions. At the same time, in order to avoid the accumulation of possible damage due to the stretching of the specimen, the deformation does not exceed 0.5%. For kor-;

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the use of treatment modes op comp

In accordance with the internal processes occurring in the material, some property is measured that characterizes the state of the sample, for example, a change in density from a change in geometric dimensions. A dense material without defects in structure always has a higher strength than porous. Therefore, in order to maximize the strength of the sample, it is necessary to bring the processing under compression pressure to maximum shrinkage.

Under radiation conditions, materials with a certain porosity are used. The shape of the pores can be very diverse. Most dangerous for reducing the strength of the gaps and cracks. These pores are given a round shape during reversible shrinkage (at the swelling stage). Thus, the material in a state with increased ductility is effectively strengthened due to the fact that the processing is carried out, not exceeding the deformation of 0.5% at the appearance of a stress state identical to the conditions of the subsequent work of the product, in combination with the processing under stress compression to round off structural defects after stopping the reversible shrinkage process. Significant hardening is achieved at the time of maximum shrinkage (no defects).

Thus, the known technical solutions do not significantly increase the strength of brittle porous materials. The proposed method makes it possible to increase the hardening efficiency in the brittle area (hardening by 100-250%) due to the optimal combination of external influence with internal processes occurring in the material during irradiation, which allows controlling the structural state of the samples and strength in the brittle area.

Examples of specific implementations of the method.

Radiation thermomechanical processing (RTMO) and testing the strength of the samples from Iso, 5 о, and (U (2 Го,) С (5 N0, mm and beams 3-3-30 mm) were carried out on installations of the type Search with pneumatic (hydraulic) loading system in a medium with a pressure of 80 kPa when irradiated under the conditions of irt-MEPI. Samples of the mouth

between the punches or on the supports (for processing, respectively. compression or bending) of the loading device. Before irradiation, the samples were preloaded (with a force of F 16 kg for cylindrical rods and kg for beams — when processed by compression,

0 when processing according to the three-point bending scheme was applied, 9 kg) to a voltage of L IO MPa, which was regulated during deformation by changing the pressure in the VII loading system. At the same time, the samples were heated to a temperature of about 400 ° C, exceeding the self-heating temperature (200-250 s) of these materials due to irradiation, in order to avoid their destruction due to the low thermal strength at the output of the reactor to power. Then, the samples were irradiated with neutrons with a flux density of 10 N / cm-s, after which the temperature of the samples was increased to Tjg, which was chosen from the known data of annealing of irradiation and hardening defects.

As treatment temperature

0 selected 800 and 900 ° C for UC 5 o.g. 1350 ° C for (Uo, 9 ggo) C N j, g in the range of T j ± 50 ° C, and for comparison - 600,700,1000, 1070 and G 100 C for 2, limits. Temj. melting points VC, and

(Zr) Co, ff are respectively -v. 2900 to, and the temperature of the brittle-plastic transition T, .. fi (0.6-0.7), T 1800-2100 s, which is above the processing temperature of 600-1350 With the proposed method.

The selected materials were held under the indicated conditions (in terms of temperature, voltage and irradiation) until plastic deformation and the resulting jump-like increase in the deformation rate occurred. Plastic deformation was observed with neutron fluence (1.7-2.3) -10, (2.1-2.7). U, (2.2-2.7) -10 sch.

 i Co, 5 Mab and (4.2-5.0) .10 (8.4- 8.2) .IO N / cm for (Zr (,),; which is in the range 10 -10 N / cm, such therefore, the incubation period before deformation is

 with. An attempt to deform (even at Tjg and stresses of 20-30 MPa) outside the specified range did not lead to a positive result.

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During the transition to the state of increased plasticity (PP), the strain rate increased stepwise from 0 to 3.4–10 and 210, respectively, when the fluence reached 2.1 × Ш and 8.4–10 N / cm in 800 and 1350 for Co, 5 N, 5 and (Zr,).

Np. . The defining characteristics of the PP state is the strain rate, as the upper bound

to

The values of which have chosen the value of Yu s Recorded on the potentiometer KSPP-4 under uniaxial compression in the PP state, are strain diagrams N g and. (Ug g Zr о) Cos Np5 in the speed range

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Under these conditions, RTMOs have the following characteristics. In stage I, a compression deformation is observed due to a decrease in the initial porosity p of the sample with 3-4 parts of different strain rates, and in the middle part the speed is 2-4 times higher than the speed in the extreme sections, this stage lasts 30-60 minutes; the maximum deformation fp, achieved at this stage, is equal to (1-2-2T), where (is the transverse deformation coefficient, and turned out to be equal for the specified 8.4-P carbonitrides, 9%. At stage II, there is no deformation (plateau on the curve deformation) for 10–30 min; stage III is characterized in that the compressed sample swells within 20–40 min, restoring its original dimensions to compression, while also observing — 3-4 sections with different strain rates (maximum speeds deformations also in the middle sections), at the end of this stage the velocity n It decreases to O, and the pore structure becomes more equiaxed. Thus, compression results in maximum deformation at the end of stage I, and at the beginning of III, an opposite sign deformation (swelling) is observed, which leads to restoration of the original sample size, i.e. Deformation in the state of PP is reversible. A reversible change in the irradiation of UC and UN in the indicated range of floatation was also found in the study of lattice parameters, electrical resistance, hardness (see, references for Tjg,). Interruption of RTMO at various points of the strain curve under compression

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led to values of strength, differing from the initial compressive strength and bending of UC o, and Uj, 3 Zr,) C in the bruise area. In addition, the bending treatment of specimens from UC NQ in the PP condition was used to increase the brittle flexural strength. As is known, the defining characteristic for maintaining the PP condition is the strain rate, PTC UC g, j (porosity 5.9%, average grain diameter 22 µm, T 800 ° C, fluence (2.1–2.7) x 2 X10 N / cm, a voltage of 8 MPa) led to a strain rate at the beginning of stage I equal to 2.5. . By decreasing the pressure of the gas in the pneumatic loading system, the voltage applied to the sample was reduced to 4 MPa (i.e., the load was reduced from 12.8 kg to 6.4 kg), as a result of which the speed in the middle section of stage I started at 6.10 and in the third segment was (2-4). As a result, at the I stage, the maximum deformation of compression was 8.4%. After 11 minutes no deformation, the sample began to swell, i.e. the deformation of the opposite sign was measured (Stage III). At the first section of this stage, the speed was 5-10 s, the compressive stress was again increased to 8 MPa, the speed at the second section became, and at the third (W – 3), a gradual decrease in the strain rate to 0 was observed. The deformation at the stage swelling proved to be equal to 8.2%, B. case of exceeding the strain rate

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PP state abruptly stopped5

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Moose. At the swelling stage, a similar one, the sample from UCj, J Npj at 6 4 MPa showed a speed of 5 9 I in the middle section, after which the PP disappeared, and the speed dropped abruptly to O after 3 minutes, with the result that the reversible deformation reached only 5, 4%. A high voltage application (20–30 MPa) at the beginning of the PP development resulted in a rate of 10 ° C, as a result of which in the first 3–5 min the deformation reached 20–30% with an accumulation of considerable damage to the samples. This led to a decrease in even the initial strength; by a factor of 2–3, Deforming at 0 1Sha in the middle segment of stage I resulted in a speed of 3 10 s-1

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and a sharp cessation of the PP after 3 min, the reduction of the same stress in the first section to 3 MPa resulted in a speed of (7–9) 10 and the realization of the entire deformation curve with a smooth transition. to O at the end of stage III. In this connection, the value of

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As lower bound

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accepted strain rate of 10 s

since lower values lead to low productivity and processing efficiency over a limited time of PP development (1.5-2 hours). To exclude the damage of the material before deformation and in accordance with the o.th. optimal rate of deformation, the upper limit of the applied stresses was limited to 10 MPa. At 20, the voltage was adjusted by changing the pressure in the loading system in the first sections of stages I and III so as to avoid exceeding the optimum speed in the middle 2 areas of these stages.

Tests for strength (in compression and bending) after P GMO showed (see table) a significant change in the initial strength. Its maximum Q increase (2.5–3 times) was found in specimens treated to maximum compressive strain, and a significant increase (1.5–2 times) in strength in the presence of porosity was shown by specimens after the natural cessation of reversible strain. Interrupting treatment at intermediate points leads to lower strengths, i.e. to reduce the positive effect. The PTM was interrupted by decreasing the temperature by 150–200 ° C below T, or the radiation device with the samples was removed from the irradiation zone and the heater. Since the strength of brittle porous materials is determined by the state of defects, the risk of internal defects of ground samples is reduced due to plastic deformation. Did it in PP state? In this connection, the termination of RTMO 2 hours before the appearance of PP (U Zr) N 5 (grain size 1-5 µm, porosity 10%, voltage 10 MPa, T х 350 ° С) or the same treatment 55 above fluence 10 N / cm (and in the range up to Yu N / cm, the voltage was within 1-2 MPa) led to an increase in

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initial compressive strength by 20-40%. The processing of the same material B in the PP condition (at stresses of 5-10 MPa, strain rates (5-9) iiJCr c-, fluence (8.4-9.2) x 0 N / cm) led to a similar deformation . 11.9%, which it interrupted and tested at room temperature for compressive strength. The initial strength was 350–30 MPa, after processing 770 + 50 MPa. With the strain rate I, 9 1 in the middle part of the swelling Up, and the speed in the middle part I of the stage I, the PP state stopped after 3 min. As a result, the compressive strength in the first case was equal to 560 + 30 MPa, in the second - 900 + 90 MPa with a maximum compressive strain of 6.4%. The obtained strength is 1.3–1.5 times lower than the tabulated values of specimen strength after the pre-RTMT procedure at the end of stages III and I. Processing outside the limits (+50 C) of grain-boundary viscosity also leads to a decrease in the positive effect. Fragile compressive strength UC N ,. at room temperature (interruption of RTMO at the beginning of stage II led to compression deformations at 700,600,1000 and 1070 C, respectively 4.5; 3.0; 2.7 and 1.2%) was equal to 500 + 30, 630 + 40 , 580 + 35 MPa, i.e. strength decreased by 2-2.5 times compared with that with similar treatment at Tj j, (see table). When the PP effect did not manifest itself, the interruption of RTMO with a fluence of N / cm led to an increase in the brittle strength of only 15-30%.

Interruption of RTMO at the beginning of stage II (maximum deformation of compression) leads to the greatest positive effect (see table). Processing up to a maximum compressive strain of 8.4-8.6% UC ,, Ng led (on average) to an increase in compressive strength from 365t +35 Sha to 1300 + 100 MPa, and during bending from 120 + 30 to 495+ 75 MPa. At the same time, the interruption of processing outside the form of change (i.e., without plastic deformation) or treatment according to the RTMO-P scheme results in a strength gain of 30% in the first case and the absence of hardening in the second.

In some cases it is necessary to use porous materials. Dyako source porosity, especially

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brittle materials, significantly reduces their strength. In order to reduce the stress concentration in the zone of structural defects (i.e., in order to improve the strength while maintaining the porosity of the material), the ESA under compressive stress was interrupted after the reversal of deformation (at the end of stage III) was stopped. This treatment led to an increase in average strength from 365 ± 35 to 705 + 35 MPa in compression: and “from 120 + 30 to 285 + 55 MPa in bending. As can be seen from the table, the greatest | increase in strength due to the treatment | compression is accompanied by significant deformations (8.4–8.6%). In the absence of such a possibility, the hardening of materials characterized by the action of tensile stresses under the working conditions was performed by the RTMO with stresses of identical nature. This is also due to the fact that the compression treatment is not very effective for increasing strength (in the presence of porosity) under stretching. RTMO Ico, 5 (porosity 6.3%, grain diameter 15-25 µm, T "800 C,

strain rate 4 -10 s

fluen

; 2.2–10 N / cm) in the range of deformations of 0.1–1% and subsequent strength tests were carried out under bending. The calculation of stresses, strains and their velocities was carried out using the known formulas.

The treatment with three-point bending was interrupted with deformations of 0.1; 0.2; 0.35; 0.6 and 1%, then tested for flexural strength. Received the following values of strength (respectively, deformation): 250 + 25 (gain 60-70%), 235 + 25 (90-100%), 245 + 25 (100%), 210 + 10 (70-80%)., 160 + 10 (30-40%). As can be seen, to the greater positive effect of graft, it ate in the range of bending deformations of 0.2-0.5%. This makes it possible to recommend the use of RTMO under stresses that are identical during processing and strength testing, containing a stretching band.

ponentu and causing deformation in the range of 0.2-0.5%.

Thus, as a result of brittle porous materials RTM, the strength increases (as compared with the prototype) by 50–200%, which can be widely used in powder metallurgy and radiation materials science.

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Claims (4)

1. A method for processing materials, predominantly brittle, porous and fine-grained, including heating to a temperature not higher than the brittle-plastic transition temperature with irradiation in a neutron flux to a fluence of 10 -10 N / cm, which differs from that, in order to increase strength, in the interval (Tjj-50 c) - (Tjj + 50 C), where TJ is the temperature of the grain-boundary viscosity, with the simultaneous application of a static load causing a voltage not higher than 10 MPa and deformation in the material, the magnitude of the deformation is measured continuously and speed, and at the moment of a jump-like increase in the strain rate by changing the magnitude of the applied load, the strain rate is maintained at no more than 10 1 / s, and when the strain reaches a given value, the processing is stopped. 2. The method according to claim 1, differing from that with the fact that a load is applied that causes a tensile stress, and the treatment is completed on reaching a strain of 0.2-0.5%. 3. A method according to claim I, characterized in that a load is applied that causes a compressive stress, and the treatment is completed when the deformation is reached as large as possible. 4. The method according to claim 3, which is also distinguished by the fact that the treatment is terminated after the reversible deformation is stopped. Bend Gain in relation to the initial strength, Z 90-150 420-570 230-340 130-190 90-150 Porosity -6, 3T d grain 15-25 microns Tj, -900 С 310 IUO 33 ОЕ, .с-8,6t . - (1-7) -IQ- c- f juens (1.7-2.3) MO N / cm