3. Materials Science. Advanced SHS Materials

 
 

O-3-01: Nanostructured Materials: Possibilities and Perspectives

R.A.Andrievski

Institute for New Chemical Problems, Russian Academy of Sciences,

Chernogolovka, 142432, Russia Tel/Fax: (7-095)742-0004 E-mail: ara@icp.ac.ru
 
 

 Nanostructured materials (NM) are normally characterized by a grain size below than 100 nm. The great attention to NM, which is fixed in last 15-20 years everywhere, is connected with their unique properties and promising application.

NM can be prepared by different methods of powder technology, by controlled crystallyzation from amorphous state, by various films and coating technology, and by severe plastic deformation. All these methods are characterized and compared. The possibilities of the SHS processes in the nanopowder and nanostructured coating preparation are discussed. The main attention is focused on the size effect in the properties development of NM. The effect of grain size on physical, mechanical, and chemical properties of NM is considered in detail. Different types of the NM deformation and fracture are described.

The main examples of the NM commercial application such as nanostructured hard alloys, magnetic materials and so on are also characterized.


O-3-02: SHS Synthesis of Nanocomposite AlN-SiC Powders

L.Stobierski, Z. Wêgrzyn, J. Lis, M. Buzhko

Department of Advanced Ceramics, Faculty of Materials Science and Ceramics

University of Mining and Metallurgy – AGH, Al. Mickiewicza 30, 30-059 Kraków, Poland
 
 

 A pseudobinary AlN-SiC system posses a potential possibility for creation of nanocomposite materials. The basic compounds, AlN and SiC, have very comparable structures. It brings about, that they show a full solid-state solubility at temperature above 1800oC. At lower temperature, a spinodal decomposition of the solid solutions can create a nanocrystalline microstructure.

The research works have been focused on preparation of AlN-SiC solid solution powders by SHS. The experiments have been realised using a combustion in self-sustaining regime and a thermal explosion method. Structure examinations show, that using the self-propagating combustion, a full range of AlN-SiC solid solutions can be obtained. When the AlN concentration is lower then 30 vol. % , the solid solution has a cubic structure (3C polytype). For 30 vol. % <AlN< 50 vol. %, both 3C and 2H polytypes have been identified in the SHS products. For the highest AlN contents, only 2H polytype have been synthesised. An evolution of solid solution lattice parameters is conformable to the Vegard’s law. The thermal explosion method does not bring to full solubility of AlN in SiC. The mixtures contained of solid solutions, AlN and SiC have been identified by XRD. The synthesised powders have been milled for obtaining powders having a specific surface area of 8-10 m2/g. They have been densified by HP under 25 MPa pressure at 1800oC into near dense polycrystals.


O-3-03: SHS of Ultradispersed Monocrystalline Refractory Compounds

from the Solution in Melt

V.B.Balashov, A.I.Kirdyashkin, Yu.M. Maksimov

Tomsk Branch of the Institute of Structural Macrokinetics and Materials Science Russian Academy of Sciences, Tomsk, 634021, pr. Academicheskii, 10/3, Russia.

E-mail: maks@fisman.tomsk.su
 
 

 The investigations on new method of production of ultradispersed monocrystalline powders of refractory borides are conducted in the work. Monocrystalline, ultradispersed powders (diameter < 0,1 m m) of TiB2, ZrB2 were obtained by SHS. The interaction mechanism of the starting compounds in active solution-melt is presented.

Halogenide compounds of I-II subgroup elements were used as active solution-melt.The interaction of the starting components with active solution-melt in SH synthesis occurs at temperature less then 2000oC.The starting halogenides i.e. "solvents" are chosen by the criterian-melting temperature and chemical activity in relation of main components: Ti, Zr, Hf, B at increased temperature. After passing the synthesis wave, the complexes, being formed at high temperature (Me-Hal-B) favours the extraction and growth of fine monocrystallines.The end product - boride of refractory metal - is easily separated, after SH-synthesis, from the components being introduced by solution in water.

The precipitation of finely dispersed boride powder was conducted through centrifugation, and the halogenides of I-II group metal, being melted were being subjected to recycling. The investigations of fraction composition of the powder with dispersivity of 1-2 m m was conducted with the help of "Analizette-22" and one of the powders with the dispersivity of less then 0,1 ?m was conducted with help of light microscope. In SH synthesis of finely dispersed borides as active solutions-melts following halogenides: MgCl2, NaF, NaCl, CaCl2, CsI, KI, LiF, ZnCl2, ZnI2, MnCl2, MnF2 were investigated, their combustion temperature is form 300 to 1000oC. The investigations conducted allowed to find the following synthesis modes combination of halogenides - "solvents" their concentration, inert gas pressure, etc., which favour the grinding of boride grains.

Further development should be attained in synthesis of monocrystalline finely dispersed powders of silicides and carbides of Ti, Zr, Hf, W, Mo, Nb, Ta, Cr.
 
 

O-3-04: Nanocrystalline NbAl3 Synthesis by MASHS with in-situ and Post-Mortem Characterizations

V. Gauthier1, C. Josse1, F. Bernard2, E. Gaffet3, J.P. Larpin1

1High Temperature Corrosion Group : L.R.R.S UMR 5613 CNRS

Université de Bourgogne, BP 47870, 21078 Dijon, France

2Fine Grained Materials Group : L.R.R.S UMR 5613 CNRS

Université de Bourgogne, BP 47870, 21078 Dijon, France

3Nanomaterial Group:UPR A0423 CNRSInstitut Polytechnique de Sévenans, 90010 Belfort
 
 

 Niobium aluminides are of considerable interest as candidate materials having high resistance to both high temperature sulfidation and oxidation, since they are expected to form protective scales such as niobium sulfide scale by sulfidation and an alumina scale by oxidation. However, due to the high melting point of niobium and the low boiling point of aluminum, it is difficult to prepare these compounds using conventional methods. At present time, three methods are generally used to produce niobium aluminides : conventional melting/casting, powder metallurgy and combustion synthesis. Recently, an alternative process has been successfully applied to synthesize aluminides intermetallic compounds :the Mechanically Activated Self-propagating High-temperature Synthesis (MASHS). The MASHS process results from the combination of two steps : first, a mechanical activation where powder mixture is milled during a short time with given frequency and energy of shocks ; second, a SHS reaction, for which the exothermic reaction between powder reactants is initiated by an external source of energy, before becoming self-propagating to yield the final product without requiring additional heat. In this work, we have directed our efforts toward NbAl3 which is one of the three intermetallic compound in Nb-Al system. It was elaborated by MASHS both with in-situ and post-mortem characterizations. Based on X-ray diffraction investigations, scanning electron microscopy observations, chemical analysis, various parameters of the MASHS process have been studied : (i) the mechanical activation effect : comparison between Nb/Al powder blended in a Turbula mixer and mechanically activated ; and (ii) the mechanical activation conditions : two milling conditions have been selected. The first corresponds to the friction mode, the other is related to direct shock mode. It has been shown that the mechanical activation induces a decrease of both Nb and Al crystallite size in the nanometer range and significantly reduces the aluminum melting time, the ignition time and the ignition temperature during the SHS process. Moreover, shock mode is more effective that friction one since it leads to complete transformation of Nb+3Al powder mixture into nanocrystalline NbAl3. Moreover, this kind of reaction has been investigated in-situ using the time resolved X-ray diffraction (TRXRD), with an X-ray synchrotron beam (D43 beam line, LURE Orsay) coupled to an infrared thermography to study simultaneously structural transformations and thermal evolutions. With short acquisition times (30 ms per pattern), it has been possible to observe several steps before obtaining compounds. Disilicides elaboration by combustion synthesis: interest of using a mechanical activation step.
 
 

O-3-05: Use of SHS-Powders Increases the Reliability of Advanced Ceramics

R. Pampuch

Department of Advanced Ceramics,AGH, Cracow (Poland), 30-090 al.Mickiewicza 30
 
 

 Ceramic materials are brittle and have a low fracture toughness because their failure involves little dissipation of the applied strain energy. This lowers their reliability as compared with metals and hampers their broader structural applications. It is well recognised that due to the inherent properties of ceramic materials any stress concentrator can originate brittle fracture. As stress concentrators act heterogeneities of the microstructure of the materials. Therefore, in order to increase the reliability methods have to be developed which can ensure an elimination of sources of the heterogeneities. Although the heterogeneities can be introduced at any stage of processing most of them stem from the constitution of the dry flowable powders or their slurries used for production of advanced multiphase ceramics (particulate ceramic matrix composites including nano-composites, composites having a duplex microstructure, fibre reinforced composites a.s.o.) From this point of view the SHS-derived powders, both single phase and multiphase present an advantage because : i. a less heterogeneous distribution of the components can usually be attained in such powders and this in a more simple way than with other powders; ii. the composition ratio between phases in the powders can be adjusted in a relatively wide range enabling a production of composite materials by sintering and/or hot pressing . In order to illustrate these conclusions the fracture toughness is compared of advanced oxide-, carbide- and nitride- based single phase and composite ceramic materials produced from SHS- powders and powders obtained via other main processing routes.


O-3-06: SHS of New Superhard Material Based on Nonstoichiometric b -SiC

by SHS.

M.Gadzyra1, G.Gnesin1, O.Mykhailyk1, O.Shul'zhenko2, O.Bochechka2 1 Institute for Problems of Materials Science,

2 Institute of Superhard Materials, Kiev, Ukraine
 
 

Heating of equiatomic mixture of fine silicon and high-active graphite up to 1300 oC in an inert environment leads to self-propagating high-temperature synthesis (SHS) of submicrometer beta-SiC powder. The measured value of the lattice parameter of beta-SiC prepared by this method, a=4.353 A, is significantly lower than the standard value (a=4.359 A) for ordinary SiC. The Raman spectra of beta-SiC prepared by this method contain the additional peaks of carbon (1332, 1484 and 1580 cm-1). High-temperature annealing of the synthesized powder in vacuum leads to the formation of SiC powder with standard value of the lattice parameter and with decreased level of structural imperfection. It was shown that defect-free beta-SiC, preserving the lower value of its lattice parameter, can be prepared through high pressure and temperature treatment. The calculations of the structural parameters for this structure (parameters of silicon atoms positions occupation, G, isotropic temperature factors, B, and fitting factor, R) were conducted by full-matrix method of least squares. The structural model of the synthesized SiC powder corresponds to a solid solution of carbon in silicon carbide. According to Vegard's law for solid solutions, the decrease of the beta-SiC lattice parameter from 4.359 to 4.353 A corresponds to the solubility of 0.6-0.8 wt.% of carbon in its sublattice. Sintering of ordinary beta-SiC powder (a=4.359 A) under high pressure and temperature results in the formation of an imperfect SiC structure at contact areas of the SiC powder and dense layers of graphite due to partial dissolution of carbon atoms into the SiC lattice. When this takes place, a decrease in lattice parameter (a=4.357 A) and an increase of microhardness of the sintered material occur in the surface areas. Sintering of beta-SiC powder without contact with the carbon container does not lead to this effect. The ordinary beta-SiC and alpha-SiC powders of different sizes were used for sintering. It was shown that the process of the dissolution of carbon atoms into SiC structure is more extensive for submicrometer beta-SiC powder than for alpha-SiC. Sintering of the synthesized beta-SiC powder, which is characterized as a SiC-C solid solution, under high pressure and temperature leads to the formation of ceramics with very high hardness and fracture toughness values (Hv= 40 GPa, K1c=7.7 MPa m1/2 at load 49.0 N). It was shown that variation of sintering parameters can result in decomposition of the solid solution accompanied by an increase in the SiC lattice parameter up to the standard value and a decrease of hardness down to the ordinary value for SiC ceramics (27.5-29.5 GPa). At the same time the growth of SiC grains and the formation of a two phase structure (SiC plus "compressed" graphite or amorphous carbon) was observed. The details of these structural transformations were investigated by TEM, XRD and Raman spectroscopy.


O-3-07: a -Si3N4 Whiskers and Its Growth Mechanism

Chang-Chun Ge, Yong-Ge Cao, Zhang-Jian Zhou

Laboratory of Special Ceramics and Powder Metallurgy

University of Science and Technology Beijing, Beijing 100083, China
 
 

 The excellent high temperature properties of Si3N4 (w) is attractive as a candidate for the advanced materials, but the application of conventional processes to synthesize Si3N4 (w), such as CVD process and nitridation of Si powders, are very expensive. N.S.Makhonin et al. have reported b -Si3N4 fibers by SHS process in 1997. But SHS of a -Si3N4 whiskers or fibers has not ever been reported in previous literatures. In this work, SHS of a - Si3N4 (w) and some aspects of its crystal micromorphology are firstly reported. It is discussed that the growth of a - Si3N4 (w) crystal is dominated by VC (Vapor-Crystal) mechanism. Special additives play determining role in promoting the growth of a -Si3N4 (w) and suppressing the phase transformation of a - Si3N4 to b -Si3N4.


O-3-08: Properties of Composite Ceramics with SiAlON Matrix.

K.L.Smirnov, I.P.Borovinskaya

Institute of Structural Macrokinetics and Materials Science, Russian Academy of Sciences, Chernogolovka, 142432, Russia
 
 

 We studied properties of sialon composites obtained by infiltration combustion according to the following reaction scheme:

(6 – 1,5z)Si + zAl + 0,5zSiO2 + diluent (SiC, BN, TiB2) + (4 – 0,5z)N2 ®

â-Si6zAlzOzN8-z

The electrical resistivity was found to vary within wide limits: from 102–103 W × cm for compositions containing transition metals compounds (b -SiAlON–TiB2), to about 1013 W × cm for compositions containing only dielectric phases (b -SiAlON–BN). For materials containing SiC, the resistivity ranges between 105 and 106 W × cm. The flexural strength as a function of ceramic porosity obeys the expression s =s 0exp(–4P), where s 0=240–300 MPa. The greatest value of s f is exhibited by composites containing SiC. Above 1300° C, the values of s f for all of the compositions studied range between 80 and 120 MPa. For the compression strength, this function complicates. For b -Si4.3Al1.7O1.7N6.3-SiC-BN, the maximum value of s c is about 700 MPa (for porosity P~10%). For ceramics of lower porosity but with higher content of free silicon, s c comes down 400 MPa. The initial temperature of decomposition of composite materials in vacuum (104 Pa) is within the range 1650–1700° C, which corresponds to the dissociation temperature for pure silicon nitride under our conditions. The rate of high-temperature decomposition depends on the porosity as well as on sialon content. Synthesized materials exhibit extremely high corrosion resistance to molten metals and slag. In this respect, they are much better than commercially available refractories and their analogs fabricated by conventional methods (Table 1). These materials have also high thermal-shock resistance (more than 30 cycles without destruction at “furnace - water” temperature overfall of about 1300° C). At quenching in running water, SHS sialons withstand temperature overfall of 550–600° C without deterioration of their flexural strength comparable to such high-strength materials as hot-pressed Si3N4.

Table 1: Corrosion resistance to metallurgical melts (T=16000C, t=40 min.)
 
 
 
Ceramics Weight losses in slag, % wt. Weight losses in stainless steel, % wt.
ZrO2–graphite 60 20
Al2O3 – 30
ZrO2 – 50
RBSN (t=15 min.) – 100
HP Si3N4 (t=15 min.) – 17
â-SiAlON (sintered) (t=15 min.) – 5
â-SiAlON–SiC–BN (SHS) 0 0
Si3N4–SiC–TiN (SHS) – 40
BN (SHS) 30 20
BN–SiO2 (SHS) 20 20

 
 
 

O-3-09: Dense in situ Composites via Thermal Explosion

Mode of SHS under Pressure

I.Gotman, E. Gutmanas

Department of Materials Engineering, Technion, Haifa, 32000, Israel

Experimental results obtained for reactive synthesis of in situ composites. Near fully dense particulate reinforced ceramic-ceramic, ceramic-intermetallic and ceramic-metal composites were fabricated from fine Ti-B4C, Ti/Ni-B4C, Ti-BN, Ti/Ni-BN, Ti-Al-BN, Ti-SiC, Ti/Ni-SiC, Ti-B6Si, Ti-Si-C, Ti-W2B5, Ti/Ni-W2B5, Al-TiO2 , Al-AlB2-TiO2 and Al-Mg-TiO2 powder blends with or without the addition of diluents. Two reactive synthesis techniques were employed: thermal explosion/TE (SHS) under pressure, where the compacted reagent blend was placed and rapidly heated in a pressure die preheated slightly above the ignition temperature, and reactive hot pressing/RHP. In both approaches, the processing or preheating temperature (=1250°C) was considerably lower than those typical of the current methods used for the processing of ceramic matrix composites. Partial to full conversion of reagents into products was achieved during TE, and a moderate external pressure of = 150 MPa was sufficient to ensure full density of the final products. Rapid cooling from the combustion temperature due to the 'heat sink' action of the pressure die resulted in the fine/micronsize microstructures of the in situ composites synthesized. RHP processing yielded dense materials with even finer microstructures, however full conversion of reagents into products has not been achieved. For a number of systems results are compared with those obtained without application of external pressure.



 
 

O-3-10: Densification Mechanism of TiB2/TiNi Composites

through Liquid Sintering by SHS under Atmospheric Pressure

M.Shibuya, M.Ohyanagi, M.Koizumi

High-tech Research Center and Dept. of Materials Chemistry, Faculty of Science and Technology, Ryukoku University, Ohtsu 520-2194, Japan
 
 

 In general, SHS products formed under atmospheric pressure are powdery or porous. Simultaneous synthesis and densification by SHS often requires a pressing process during or just after the combustion reaction. However, the composite materials between TiB2 with highly heat of formation and intermetallic compound such as TiNi form dense body even under an atmospheric argon pressure.

In the present work, it was confirmed that the products shrunk extremely with an increase in additive Ti-Ni powders in the range of 30-90wt%. Maximum shrinkage volume was approximately –34.3% in addition of 90wt% TiNi. Relative density of the product in case of 90wt%TiNi was approximately 83.2%. The products with the density range of 80 to 90% provided the matrix body for suitable cermet grinder. The product containing TiNi additive lower than 30wt% was identified to consist of hexagonal TiB2 and cubic TiNi by X-ray diffraction and from the each particle shape. The products containing TiNi additive higher than 30wt% shrunk by quick liquid sintering. We, herein, describe densification mechanism of TiB2/TiNi composites through a quick liquid sintering process in the variety range of TiNi.


O-3-11: SHS Composites of Combined Structure

À.N. Tabachenko, S.V. Konovalov, V.A. Kudrjavzev ,S.A. Afanas`eva , A.A. Konjaev

Siberian physicist-technical institute by it. V.D.Kusnezov by Tomsk State University 1, Revolution Sq., 634050, Tomsk, GSP-18, Russia,Fax: (3822) 233034,

E-mail: root@eccspti.tomsk.su

 For getting the komposites of a combined strukture, the method of self propagating high-temperature synthesis (SHS) with simultaneous deforming compaction of an exothermal product of synthesis in layered system (exothermal layer - metallic substrate) is used.

For optimization of the synthesis conditions, the method of final differences is used to calculate the heat exchange in the cell, consisting of layers, one of which presents itself heated by exothermal reaction interlayer, but other is inert (metal). It is shown, that the inert, having a high thermal conductivity and thermal capacity, can greatly reduce a temperature in thin film attached to the exothermal surface and by that to ivfluence on the kinetics and chage completeness of exothermal reactions in a powdered mixture.

On the example of exothermal powdered system TiB2-NiTi and metal interlayer (Al, Fe, Ti) the account of spatially-temporal distribution of temperature under SHS in two-layered system with the different ratio of a thickness of an exothermal layer and substrate, is conducted.

It is shown experimentally, that varying of the ratio of large (d<63 m km) and small-sized (d<1 m km ) fraction of the boron, it is possible to ensure the given combustion wave velocities (from 1.5 to 8.3 sm/s) in an exothermal layer with its following com-paction with a metallic substrate at the optimum conditions. It has been obtained SHS – compacts of TiB2-NiTi system with the various initial ratio of the boron fractions. In synthesized composites, containing in a initial condition polycrystalline a boron, the presence of a large crystals probably Â4Ñ (dìàõ=150 m km ), small particles TiB2 (dmàõ=5 m km) and matrix, based on NiTi is detected. The microhardness of crystals Â4C has made 2000-8600 kg/mm2, composites (TiB2-NiTi) - 770-2600 kg/mm2. Using SHS compaction method it is obtained the composite of a combined structure with hard (up to 85 HRA) cermet layer (TiB2-NiTi) and indissolubly connected with him metallic layer on the basis of Al, Fe and Ti. Theirs mehanical propertis were studied.

This work was supported by the Russian Foundation for Basic Research, Projct no 98-01-00293.
 
 

O-3-12: Optimization method for SHS-FGM Material Design by Genetic Algorithm

  1. Shimojima1, Y. Yamada1, M. Mabuchi, N. Saito1, M. Nakanishi1,
I. Shigematsu1, M.Nakamura1, T. Asahina1, M. Kato2, T. Igarashi2

1National Industrial Research Institute of Nagoya 1-1,Hirate-cho, Kita-ku, Nagoya 462-8510

2Tokyo Tungsten Co. Ltd., Iwasekoshi-machi, Toyama 931-8543, Japan
 
 

 The progress of technologies requires high performance materials. However it is sometimes difficult to achieve the required high performance by a homogeneous material. Therefore composite materials have been studied and developed so far. Functionally Graded Material (FGM), which is a kind of composite materials, can change the material property in each area for its objective such as heat transfer property, stiffness, and so on, by controlling a compositional distribution profile of materials. Therefore we can make a product which has two or more different material properties in one body. However it is difficult to design a compositional distribution profile of an FGM as a desired one, because material properties of one part relates to the other part, and its shapes and surroundings also affect the properties. In this paper, we propose the compositional distribution profile design system for FGM made by SHS processing. The proposed system optimizes the compositional distribution profile to satisfy requirements automatically. The design system consists of two parts: Analyzer and Optimizer. We employ the Finite Element Method as Analyzer for analysis of the state of the product in SHS fabrication process and in use. We also use Genetic Algorithms as Optimizer for optimization of the compositional distribution profile. To show the effectiveness of the proposed design system, we apply the proposed system to thermal stress relaxation problem.
 
 

O-3-13: Micropyretic Synthesis of Nb - Al - Ti Composites

G. K. Dey, S. Adhikari, S. Banerjee

Materials Science Division, Bhabha Atomic Research Center, Trombay,

Mumbai 400 085, India
 
 

 Recent studies have shown that Nb-Al-Ti alloys have application potential at high temperatures. Micropyretic synthesis is a very elegant method of synthesizing intermetaillic compounds.

In this study, an attempt has been made to develop composites containing mixed aluminides of Nb and Ti as the main ingredient. The problem of poor combustibilty has been circumvented by incorporating additional reactants, which generate heat, by secondary combustion reactions. Two approaches have been used –

  1. Adding a mixture of Nb2O5 and Al, which leads to the secondary reaction resulting in Nb and Al2O3.
  2. 2. Adding a combustible mixture comprising MoO3, Si and Al, which results in the formation of MoSi2 and Al2O3.
X-ray diffraction of the alloys indicated the presence of a bcc phase as the matrix phase for a majority of the compositions studied. The other phases that could be detected were the MoSi2 and the Al2O3 phases. In the compositions containing a higher amount of the combustible mixture, a very fine-grained microstructure could be seen. A detailed microstructural examination of the synthesized alloys has been carried out. The combustion characteristics of the alloys were found to depend on the composition of the alloys and a clear transition from stable to unstable combustion could be noted in some compositions. The mechanism of synthesis of the alloys from the elemental powders has been examined in the case of the alloys containing Nb oxide in the presynthesized state.



 
 

O-3-14: Graded and Layered Structures Prepared by SHS Metallurgy

V.I.Yukhvid

Institute of Structural Macrokinetics and Materials science of RAS

Chernogolovka, 142432 RUSSIA., E-mail: yukh@ism.ac.ru
 
 

 The basic variant of creation of graded and layered materials by methods of SHS-metallulrgy are considered in the work. One part from them is based on forming of structure during SHS, another- on using of SHS-metallurgy products in tradditional technique.

The large attention is given to an experimental research of burning of one and multilayer thermite and elemental mixes, phase separation of multiphase burning products melt , mass and heat exchange high-temperature melt with a “cold" base, the filtrating of melt in a porouse layer of a burning products. The strong influence of gravitational and electromagnetic fields on formation of final structure is shown. The analytical and numerical models of forming of layered structures are proposed.

The examples of using of SHS metallurgy products for creationof graded and layered structures by plasma methods, elektro-arc and inducting surfacing methods are shown.


O-3-15: Structure of the Ceramic Layer and Quality of the Ceramic-Steel

Composite Pipes

Zhang Shuge, Zhou Xiaoxin, Qian Donghao

Research Institute of Electric Light Source Materials Nanjing KeYuan Combustion Synthesis Co. Ltd, Nanjing 210015, China

Tel:(025)8805313(O), Fax:(025)8805313 E-Mail:sgzhang@public1.ptt.js.cn
 
 

 Ceramic-steel composite pipes have been produced with industrial scale in China by combustion synthesis or thermit-centrifugal process. The themit reaction Fe2O3+2Al=2Fe+Al2O3+836KJ/mol in the steel pipe products molten metal (Fe) and ceramics(Al2O3) which separate under the influence of the centrifugal force and a ceramic-lining layer on the inner surface of pipe is formed. The key to the production technology is the settlement of the unmatched thermal expansion coefficients between the steel tube and ceramic layer. Lowering the reaction temperature is not correct approach even though it can moderate the contradiction of the expansion coefficients, but it decreases the quality of the products. The network structure of the ceramic layer enhances the layer strength, and eliminates the crack of the layer. Improving the macrostructure of the ceramic layer seems to be an efficient approach to a stable and high quality of the composite pipes.


O-3-16: The Cermet-Lined Composite Pipes Made by a SHS

Centrifugal Process

Liu Mu, Yin Sheng, Lin Tao, Wei Yanping

P/M Department, University of Science and Technology Beijing, 30# Xueyuan

Road, Beijing, The People’s Republic of China 100083
 
 

 The ceramet-lined composite pipes were produced by a SHS-centrifugal process. The ceramet layer with low porosity was made from the systems of Fe2O3:CrO3:Al:Ti:C and Fe2O3:Al:Ti:C respectively. The properties and microstructure of the ceramet were investigated.

Investigation was also expanded to the effects of composition, preheating and centrifugal force etc. on ceramet. It was found that there was higher content of carbon compounds and higher hardness in the ceramet made from Fe2O3:CrO3:Al:Ti:C system.
 
 
 
 

O-3-17: Improvement in Properties of Stainless Steel Lined Steel

Pipe made by centrifugal-SHS process

Yin Sheng, Xi Wenjun, Lai Hoyi

School of Materials Science and Engineering, University of Science and

Technology Beijing, Beijing 100083, People’s Republic of China
 
 

 In this paper the tension properties, microstructure and the causes of crack formation of stainless steel layer in the composite pipe made by centrifugal-SHS process were investigated. It was shown that the tensile strength and elongation was 316Mpa and 5~8%, respectively. The nonmetal inclusions make the stainless steel brittle. In the brittle stainless layer the crack is caused by the thermal stress. The plastic deformation of the stainless steel can relax the thermal stress. The plasticity of steel can be improved by accelerating the process of phase separation and reducing the nonmetal inclusions in the stainless steel. Increasing the fluidity of the molten products by introducing CaF2 into thermit was helpful for reducing the nonmetal inclusions.
 
 

O-3-18: SHS Refractory Ceramic Materials for Metallurgical Application

M.R.Filonov1, E.A.Levashov1, A.N.Shulzhenko1, I.P.Borovinskaya2

1Center of SHS, Moscow Steel and Alloys Institute

(Technological University),Leninsky prospect, 4, Moscow 117936

2Institute of Structural Macrokinetics Russian Academy of Science, Russia
 
 

 The use of SHS ceramic compositions as refractory materials in the metallurgical industry is one possible application. A series of investigations was carried out to measure refractoriness, thermoresistance, and resistance to metallurgical melt influence at the temperatures 1500-1700oC. Compositions based on BN, TiB2, SiAlON, AlN, and Si3N4 produced by the method of nitration combustion were studied. Refractoriness degree was determined according to the following method. A sample of investigated substance was weighed preliminarily, the geometric dimensions were measured, and its phase composition was determined in an X-ray diffractometer. Then the sample was placed in a furnace, where it was heated at a rate of 10^o/min, to the necessary temperature (1600, 1800, 2000 oC), at which it was held during 20 min. The method of thermoresistance determination is based on the requirements of GOST-7875-83. It conists in the determination of the rmochanges; an article can stand up to 20% loss of the initial mass by heating its end part at 1300^oC, with subsequent cooling in running water. A low wetting degree and small interaction with ceramics are characteristic for metal solutions based on Fe, Ni and Co. Investigations of SHS compositions' interaction with metallurgical slag were carried out to estimate their resistance in ion solutions. Thermogravimetric and dilatometric researching ceramic samples are carried out. It is established, that the properties of SHS-ceramic materials define largely unreacted initial components, and collateral substances, which arise during the high-temperature synthesis. Refractory SHS-ceramic materials for various purposes were tested in the metallurgical plants of Russia. Laboratory and industrial crucibles for melting metals and alloys, refractory products for pouring, conduits for liquid metal, sliding shutters, thermocouple covers, etc. were made. Tests have shown that these materials uch more exceed oxide compositions, which used at the present time. For example, durability of sliding shutters made of composition BN-TiB2 as 5-10 times as more than the same ones made of traditional products. BN-TiB2, BN-Si02 and SiAlON-SiC-BN compositions can be distinguished as the most promising refractory materials for the metallurgical industry.
 
 
 
 

O-3-19: Some Regularities of a -Si3N4 Synthesis in a Commercial Reactor

V.V. Zakorzhevsky , I.P. Borovinskaya

Institute of Structural Macrokinetics and Materials Science,

Russian Academy of Sciences, Chernogolovka, 142432, Russia
 
 

 Method for producing a -modification of silicon nitride with SHS has been developed. The synthesis is performed in a commercial reactor with working capacity of 30 liters. Temperature dependence of Si3N4 phase composition is determined. It is shown that conversion degree of Si® a -Si3N4 in nitrogen depends on temperature in synthesis zone. To regulate a -phase content in a combustion product, parameters like nitrogen pressure and introduction of a diluent and salt additives into the green mixture were used. Silicon nitride produced by that method exhibits high chemical purity, contains above 95% a -phase and has a fine-fibrous microstructure that provides large specific surface. The prevailing particle size is the following: 0.4–1m m in diameter and 4–10m m in length.
 
 

O-3-20: Utilization in a Flow Reaction of the Heat Released during SHS

V. D. Zhigarev

Central Institute of Chemistry and Mechanics (State Research Center),

Nagatinskaya 16a, 115487, Moscow M-487,Phone:111-51-29, 117-16-77/Fax: 116 278218
 
 

 Self-Propagating High-Temperature Synthesis (SHS) is one of the most promising directions of the modern R&D due to its wide application in developing new production methods. However, high heat release during SHS has been poorly taken into account and utilized in practice. This situation can be explained by the following feature of SHS technological process: during cooling SHS products, the heat released dissipates through the walls of a reactor to the atmosphere and cooling time can attain several hours ( there is little point in automation of SHS).

The heat released during SHS can be utilized only at intensive heat removal e.g. the SHS reactor should work in the mode of heat generator. Such a mode can be realized by using a flow reactor in which gaseous cooling agent is blown through holes in the SHS charge. In this case, the cooling time is some seconds (that is rather close to the reaction time).

The reliability and efficiency of this project were proved by results of a number of experimental studies of gas permeability of SHS charge (measuring strength characteristics before, during, and after combustion) and combustion modes and by estimation of thermal characteristics of the flow reactor.

Our results may be used for developing high-efficiency production line with utilization of the heat released during SHS. Application of the SHS heat is exemplified by a method of utilizing SHS heat for drying green mixture in drying-boxes.
 
 

O-3-21: Production of TiC-Based Cermet and TiC-Al2o3 Thermal Spray

Powders by Shs

P. Lintula1, J. Maunu1, M. Heinonen2, P. Vuoristo2, T. Mä ntylä 2

1 vtt Manufacturing Technology, P.O. Box 17031, Fin-33101 Tampere, Finland

2 tampere University of Technology, Institute of Materials Science, P.O. Box 589,

Fin-33101 Tampere, Finland
 
 

 Titanium carbide cermet and titanium carbide-alumina ceramic powders for thermal spraying were produced by self propagating high temperature synthesis. Starting materials were elemental Ti, C and NiCrMo powders for TiC-cermets and TiO2, Al and C for titanium carbide-alumina powders. The powders were crushed by ball mill and classified to desired particle size ranges by sieving or air classifying. The properties of powders were charactericed by laser scattering (particle size distribution), XRD analysis, scanning electron microscopy (SEM) and energy-dispersive spectrometer (EDS). Internal structure of each cermet particle was dense and consisted of fine distribution of carbides embedded in a metallic matrix.

Cermet coatings on the base of titanium carbide as a hard phase and nickel chromium molybdenum alloy as a metal binder were prepared by detonation gun spray (DGS) and high-velocity oxygen-fuel (HVOF) spray processes. TiC-Al2O3 coatings were prepared by atmospheric plasma spraying (APS). The coatings were analysed by optical microscopy and SEM, microhardness measurements and XRD analysis. The abrasion wear resistance of the coatings was evaluated by the rubber wheel abrasion wear test. Coatings from commercial thermal spray powders, WC-Co, WC-CoCr, WC-(W,Cr)2C-Ni and Cr3C2-NiCr, were also prepared and used as a reference samples. The results showed that the sprayability of the powders prepared by SHS with optimum conditions and with optimal post-processing is good. The microstructure of coatings obtained is dense having good properties in the wear test. According to the XRD analysis the amount of retained carbides in the coatings is high. The carbide phase has a spherical shape also in the coatings.
 
 

O-3-22: Industrial Application of New Composite SHS Produced Electrode

Materials and Technologies for Electrospark Surfacing

A.E. Kudryashov, E.A. Levashov, A.N. Sheveiko

Center of SHS of Moscow Steel and Alloys Institute (Technological University)

and Institute of Structural Macrokinetics and Materials Science of RAS,

Leninsky prospect, 4, Moscow 117936, Russia, Fax/Phone: 007- 095-236-5298
 
 

 The industrial application of SHS- materials as electrodes for electrospark alloying (ESA) is most effective. The technologies of strengthening by ESA method with SHS electrode materials of cutting tools (cutters, drills, broaches), dies (hammer, cutting, bending, for cold, hot and isothermal stamping) and rollers for copper wire production were developed at the Research Training Center of SHS of the Moscow Steel and Alloys Institute. The developed technologies were adopted at the Russian factories such as Ufa Motors Building Factory, Podolsk Machine Building Plant, Aircraft Constructing Factory (Nizhny Novgorod City), Russian- Finnish Factory "ELCAT" (Moscow), "ZIL" Company, etc. The carried out industrial tests demonstrated a growth of the strengthened tool wear resistance: of drill (D= 24,5 mm) in 7-8 times; cutters in 2-5 times; markers in 2-2.5 times; bending dies in 3-3.5; hammer dies (in particular large scale, weighting more than 1 t) in 1.8-2.5 times; isothermal dies in 2.3-2.4 times; cutting dies in 3.5-5 times; dies for cold stamping in 10-12 times; rollers in 2-4 times. The application of SHS hard alloy electrodes based on TiC, NiAl, TiB shaped as discs allowed to mechanize ESA process and to raise considerably its' efficiency when treating axisymmetric articles such as rollers. The strengthening under high-power regimes allowed reducing the initial dimensions of the wearied out rollers.