International Scientific Colloquium Modelling for Electromagnetic Processing Hannover, March 24-26, 2003

Powder Synthesis for Cermets on the Base of Technology

A. Pechenkov, I. Pozniak, Yu. Udalov, B. Lavrov

Abstract

Carbides, nitrides and borides of of IVB and VIB groups of a periodical law as a sintered production (cermets) are widely used in industry as a test portion of cutting tool and other -working tools. Traditional multi-stages technologies of cermets synthesis do not allow reaching of properties combination. Synthesis process submicron powder mixtures of Al2O3 – TiN, TiN – TiB2, TiC – TiB2, SiC – TiB2 – B4C is based on induction heating technology. Some mathematical approaches to simulate and investigate the process are presented in the paper.

Introduction

Carbides, nitrides and borides of metals of IVB and VIB groups of a periodical law as a sintered production (cermets) are characterizing by of high hardness, chemical passivity and infusibility. These materials are produced by carbothermical or plasma chemical synthesis as submicron powder mixtures [1, 2]. Pure monophase carbides, nitrides and borides are as product of synthesis in both technologies. The powder is exposed by submicron pounding and mixing with other components. Received mixture is fritting at temperature mo then 1500°С. Ceramics, which are produces by this way, are widely used in industry as a test portion of cutting tool and other metal-working tools. Ceramic as a composition of corundum-titanium carbide - titanium nitride is used for cast smoothing at speed rotation more then 150 m/s or it does for cutting of hardened at speed rotation more then 150 m/s, for instance. Worldwide consumption of carbide of titanium, tungsten, zirconium and so on is about 50 t/a (50 millions of cutting tools) were realization value is $ 100 – 150 millions. However, ceramics, which are produced by this way, have low resistance to impact and high cost. Besides, poison gases are generated which have to be neutralized during process. This circumstances requires to find new technologies of synthesis for powders production having well capabilities to sintering and resistance to high temperature oxidation. The technologies have to exclude or decrease costs of submicron pounding and using of cheap and non-hazardous primary raw materials and cheap carbon deoxidizer. Synthesis technology of corundum - titanium nitride mixture from oxides components in the same technological process was an object of investigation. Production of submicron grains of titanium nitride, which are homogeneously distributed between corundum grains, was main goal. Carbothermical deoxidizatoin and nitration of titanium oxide, which was mixed together with corundum, is an idea of technology. Corundum limits of growth of titanium nitride grains and the titanium nitride grains do not allow sintering of corundum grains [3]. Those grains do not allow to growth of each other and prevent of its recrystallization during of product sintering. Crystalline particles of components are homogeneously allocated and its sizes are less then 1 micron. In this case the product has high impact elasticity saving

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high hardness (2450 – 3200 HV), that it is a reason of increasing life time of cutting tools. Cost of the ready-made composition is less then the cost of production of submicron plasma chemical pure powder of carbides, nitrides and borides. Carbonic gas is co-product of suggested technology.

1. Installation and technology

Powdered boron carbide was produced by induction heating method of mixture of boron oxide and coke [4]. It was heated mixture of alunimium oxide, titanium oxide and carbon in graphite in running nitrogen medium to get composit powder Al2O3 – TiN. Common reaction of carbothermic disoxidation and nitration of titanium oxide can be written as: 1 TiO + 2C + N ® TiN + 2CO + q . 2 2 2

Titanium oxide disoxidation can be realized either during direct interaction between atom of oxygen and nitrogen or through gas phase, or by this ways simultaneously. Equation of disoxidation process through the gas phase is the next:

1 TiO + 2CO + N ® TiN + 2CO + q . 2 2 2 2

Sketch of laboratory installation is presented at fig. 1. Power supply is high frequency tube generator. Advantages of suggested way are induction method of heat of graphite crucible (reactor) and possibility of smooth control of voltage at inductor. It is allows to control of heat temperature. Reactor consists of two coaxial hollow graphite with slitted walls, Fig. 2. The slitted crucibles are heated fast by induction method up to required temperature. Internal and external crucibles are heated simultaneously that it is increased the heat efficiency. Moreover, walls slits provide effective deletion of carbon oxide from reaction space during of TiO2 deoxidation and allow to react of nitrogen with titanium. The basic efforts was directed to solve two problems during technology improvement: - production required temperature distribution in powder mixture to start synthesis process; - definition of changing low of power sources in graphite reactor to keep synthesis process. Fulfillment of the first condition provides homogeneous distribution of Al2O3 and TiN phases in the volume of synthesized product. Carbothermical deoxidizatoin titanium oxide is accompanied by heat generation and mixture oxides temperature can be increase. The mixture components can be melted and synthesis of TiN will die. Second condition provides realizability of the solid phase synthesis.

2. Numerical tools and base equations

Investigation of physical-chemical processes on the base of mathematical modeling requires to solve equations which describe electromagnetic and transitional thermal phenomena. It takes to account both electrical and exothermal reaction heat sources. Moreover, currents spread character in the segments of graphite crucible requires solving of 3D equations of electromagnetic field.

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Nitrogen on

Quartz chamber Slitted graphite crucible

Inductor

Aluminium oxide - titanium oxide mixture

Carbonic oxide

Fig. 1. Sketch of the lab induction furnace Fig. 2. Slitted graphite reactor

Experience of numerical investigations of electromagnetic fields of induction systems with slitted metallic crucibles for oxides melting shown that for suggested process it can be used 2D mathematical model [5, 6]. Electromagnetic model based on combined approach. Interior problem of computation of electromagnetic field in the load is solved by finite element method (FEM) and exterior problem is solved by integral equation method (IEM). Influence of sources (inductor current) is taking into account by means of integral equations. This approach allows to get distributed parameters in the investigating system with a lot of finite elements and short time of calculation. According to the secondary sources method [7] electromagnetic field in conductive region is calculated using conduction currents. Internal problem is solved by 2D differential equation relative vector magnetic potential by FEM [8]. Transient electro-thermal mathematical model in generally accepted terms is described by the next equation system:

. . . . , 2pRi Ei + jw òs j E j M ij dS + jw òs k Ek (M ik - M il )dS =U i S1 S2 . . . . æ 2 2 ö 1 ç ¶ A 1 ¶ A ¶ A A ÷ . + + - = jws A , m ç ¶R 2 R ¶R ¶z 2 R 2 ÷ 0 è ø ¶T ¶ æ ¶T ö 1 ¶ æ ¶T ö Cv = çl ÷ + çlR ÷ + q , ¶t ¶z è ¶z ø R ¶R è ¶R ø

with boundary conditions for thermal problem:

¶T - l = es (T 4 - T 4 )+a(T - T ). ¶R c c

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Solution of the equations system is complicated by nonlinear coefficients and boundary conditions in the equations.

3. Numerical and experimental results

Numerical investigation of electromagnetic and thermal fields in the induction system allowed to define requiring temperature distribution in the graphite reactor and powder and changing voltage low at inductor. The defined changing voltage low provides needed synthesis process conditions. Heat sources and temperature distribution in graphite reactor are shown on Fig. 3 and Fig. 4. Working induction furnace and titanium nitride which was produced by this technology (Fig. 5 and Fig. 6).

z

r

Fig. 3. Heat sources distribution Fig. 4. Temperature distribution

Fig. 5. Working induction furnace Fig. 6. Titanium nitride

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Conclusions

Elaborated technology allows to produce submicron cermets powder from metals oxides of IVB and VIB groups of a periodical law and cheaper carbon deoxidizer. The powders have well capabilities to sintering and resistance to high temperature oxidation. The sintering materials were tested to abrasive ability and single grain strength following Russian standards. Abrasive ability of the material is better then standard specimen in one and half times. Single grain strength is better then standard one in two times.

References [1] Patent of USA № 4.528.119. Patentee Boca Raton, Florida, USA. [2] Patents of USA №№ 4.282.195.979.500, 4.266.999. Patentee PPG Industries Inc., USA. [3] Yudin B. F., Mnatsakanyan E. D., Ordanian S. S. Thermodynamic analysis of interaction in TiN – Al2O3 sistem. J. of Applied Chemistry. 1982. Vol. 55. № 1. P. 103. [4] Tumanov Yu. N. Electrothermal reactions in modern chemical technology and metallurgy. Moscow. Energoizdat, 1981 (in Russian). [5] Pozniak I., Pechenkov A. Special tools for investigation and controlling of induction skull melting processes. Proceedings of the International Colloquium "Modelling for Saving Resources", Latvia, Riga, May 2001, pp. 158 – 163. [6] Pozniak I., Pechenkov A. An Approach of Electrical Conductivity Estimation of Technical Materials Melts. 8th International Conference on Microwave and High Frequency Heating. Bayreuth, Germany, September, 3-7, 2001. [7] Nemkov V., Demidovich V. Theory and calculation of devices of induction heating. Leningrad. Energoatomizdat, 1988 (in Russian). [8] Chari. "Finite Element Solution of the Problem in Magnetic Structures", IEEE Trans. Power App. & Syst., Vol. Pas-93, Jan./Feb. 1974, pp. 62-72.

Authors Dr. Pechenkov, Andrey Dr. Pozniak, Igor Department of Electrotechnology Department of Electrotechnology St. Petersburg's Electrotechnical University St. Petersburg's Electrotechnical University Prof. Popov str., 4 Prof. Popov str., 4 197376, St. Petersburg, Russia 197376, St. Petersburg, Russia E- mail: [email protected] E-mail: [email protected]

Prof. Udalov, Yuri Dr. Lavrov, Boris Department of Electrotechnology and Plasmachemistry Department of Electrotechnology and St. Petersburg's Institute of Technology Plasmachemistry Moskovsky pr., 26 St. Petersburg's Institute of Technology 198013, St. Petersburg, Russia Moskovsky pr., 26 E- mail: [email protected] 198013, St. Petersburg, Russia

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