SU1004806A1 - Method of preparing specimen in determination of brittle material crack resistance - Google Patents

Description

(54) METHOD OF PREPARING THE SAMPLE WHEN DETERMINING THE CRITICAL RESISTANCE OF FRAGILE MATERIALS

The invention relates to the degradation of the mechanical properties of materials, in particular to the determination of the crack resistance of superhard materials. The intensive development of modern technology has led to the development of a new class of tool materials, polycrystalline superhard materials, and this in turn has created the need to study their physicomechanical properties in order to determine their quality. The most suitable for this mechanical characteristic is crack resistance, the definition of which is currently given much attention. Characteristic features of polycrystalline hard materials (PSTM) are small sizes of workpieces ranging from hundreds of microns to several millimeters, which does not allow the traditional loading and shape patterns of these materials to determine the fracture resistance of these materials. High values of mechanical properties and small sizes of samples of superhard materials create considerable difficulties when the initial initiator of fracture is introduced — cracks in the sample under study for correct determination of the crack resistance of the material. A known method of sample preparation in determining the crack resistance Jtpy№. tool materials, zakl1o. This is based on the fact that the test sample has a defect in water in the notch. The notched specimen is then subjected to fatigue loading in order to produce a fatigue crack in the notch vertex. This method is used to determine the crack resistance of brittle materials such as hard alloys and comno3vmHDHHbix materials based on them (hard alloy with diamond inclusions), obtained by sintering and allowing to produce samples of sufficient size, for example, in this case G), G mm gtarmloloish - yes. -one

However, this cannot be applied to the nomiKpiicraJurujeKKiix overthrowing of oikosgga overthrows; gvertsyk; makrpilo received in the devices you? Graphic in the monk of the South African diamond, as a rocket of the workmanship of the high quality of deeply mall n spedovat / yazNo, the size of the gratuity is also small and is w;

In addition to T-jTv. polycristaceous convoluted materl; apy have a flawed xpynKocTTjJO, which makes it possible for a kevosmogshy ps ltcheiie fatigue ratchet.

A known method of preparing a sample when opereg1en - and simulator-brittle brittle materials, iianeeeHKe MP, is formed of a very poorly coupled material from the sample layer — getting trots: with a scrub of application to the sample on

Szdiako dpnshy way IK

bplI: LJ; O size;), and y -; /; t (wa, iTo polt krkstall15eskio sikhterkhterdsh mattershly. small, npipvieiienHe it ™ about the way, v; ii ; is possible.

Izgyustno; that under the thermal action of ia, polycrystalline stertvergo magnetics, such as polycrystalline diamond, occurs: there is a reverse phase-transition of diamond to paphite. Graphite is a low-strength, brittle-1 material compared to agalase and therefore can be used as a brittle layer.

To determine the epergy of a company, it is necessary to get a fragile firmly bonded layer on half-metal-superhard materials, we proceed from a critical technology that has 1Trox; the reverse phase transition goes; h: 1; for example pngbccrystal to graphite.

It is known that the graph temperature is giziza: i, aM; aza tia in the air is - LO) -i-OG; 0 C. If the case is pumped-: ;; ten; , al1L10go source of thermal energy and - ;; luz stic) azier nanj iemie, neob-.O.PR MJ-;: the number of siiepi-ini raschntyva-- l; way

t 9--

The etacium and rpa temperature at the center of the heating spot for a fixed source (G7 /); power density taking into account the goats (| x} 1pie1gga pollyani; diameter of the spotlight; thermal conductivity to ather1-1al.

(2)

%

oooi flow of laser

And the absorption coefficient (for the lycrystallineleh 11X superhard materials AO, 7). And the power of the source of local thermal energy, in this case the laser, is defined. by formula

(3)

,

Giyadi light spot.

Where

Fig. 1 shows a diagram of a iiarpy-image ia irpK definition of a crack cTrjh; ocivi: 1a pkrieta, lyl supertvershchzz to the mattress

(H5razep 1 in fort-le disk with central W:) 1M nldrezom 2, along the contour of which a fragile tightly bound layer 3 is formed, nprv / ajifipHTemnio unload radial usi: I eat 0.2-0.3 Pj., As a result which at the tips of the incision are cracks 4, which pass through the layer and stop in a shaped material. After measuring the fracture surface, the specimen is destroyed with the critical load. The appearance of cracks at the tops of the notch is due to the fact that the maximum stress concentration caused by the diametral compression of a disk with a crack located along the load line occurs precisely at the crack tips. When using another figurative, for example, such as a beam, there is no need to make a preliminary cut. In this case, the surface of the sample is affected by a local source of thermal energy and a strip of brittle, firmly bonded layer is obtained on its surface and by means of preloading a crack. Example. A sample of polycrystalline TeKcaHvrr-P polycrystalline material in a disk with a diameter of 4.5 mm and a thickness of 1.2 mm is exposed to 10 o laser radiation on a continuous-action laser system with a 150W quintet. The laser radiation is focused on the sample using a lens taken from the CS with a focal length F 100 mm in a spot with a diameter equal to 0.2 mm. At the same time, the laser radiation power is required to obtain a brittle strength.

The proposed method of sample preparation in comparison with the prototype makes it possible to determine the correct values of crack resistance (K.) on samples of polycrystalline superhard materials, for example, polycrystalline diamonds and polycrystals based on boron nitride.

The method of sample preparation in determining the crack resistance of polycrystalline materials allows ultimately to determine the quality of the material.

Taking into account that at present the quality of polycrystalline superhard materials is determined by the results of tests during the cutting process (this method for evaluating the quality of PSTM is taken as the basic object), the proposed method allows to determine the specific quality characteristic of PSTM - fracture toughness; reduce the cost of on-line testing of polycrystalline superhard materials. For example, replacing tests of only one polycrystalline superhard material Teksanit-R for durability in the process of cutting hardened steels for testing the cutting element blanks in order to determine treshine resistance — this material gives an economic effect of about lOdb rub. on the party (1000 tt.) Reep. The sample layer bound to the sample material is 90 W. It is calculated by the formula (3). based on the fact that the onset temperature of the reverse phase transition for this material based on boron nitride is 12 ° C. To determine the amount of energy to obtain a brittle layer on other superhard materials, it is necessary to know the temperature of their reverse phase transition. After obtaining a brittle layer by applying a load of about 22O + 250 N to the sample, cracks are obtained with a length of at least 0.05 + 0.1 mm. The loading was carried out on an upgraded test device IMASH 20-75 with the registration of the crack length using a microscope MBT-71, which allowed to follow the behavior of the sample during the loading process. After measuring the length of the crack, the sample is loaded until failure with registration of the critical load. The results of the determination of crack resistance (K (-) for Texanitare specimens with a crack resulting from the destruction of a brittle layer tightly bound to the sample material at the apex of the notch) are given in the table.

I and pmu l invention

The method of sample preparation for determining the crack resistance of brittle materials, including applying a layer firmly bound to the sample material to the jcpjTTKoro, and producing a crack by applying a load to the sample, characterized in that, to determine the crack resistance of superhard materials, the application of a brittle tightly bound The sample material is layer produced by

local influence of thermal energy in an amount that ensures the reverse phase transition of the material is shaped into a brittle layer created.

Sources of information, with these to be taken into account during the examination

1, Ko Ovalenko, I., K., et al. The method for determining the crack resistance of superhard materials at high temperatures. Superhard materials, 1980, N9 5, p. 29-34.

2. USSR author's certificate number 892266, cl. GOLM 1/28, 1978.

Claims (1)

Claim A method for preparing a sample in determining the crack resistance of brittle materials, including applying a brittle layer firmly bound to the sample material to the sample and producing a crack by applying a load to the sample, characterized in that, in order to determine the crack resistance of superhard materials, the brittle layer is firmly bonded to the sample material by local exposure to thermal energy in an amount that ensures the reverse phase transition of the material is figurative in the created brittle layer.