In this work the state of art related to obtaining, properties and application of functionally graded materials is presented. Functionally graded materials (FGM) secure obtaining of cutting tools of wear resistance surface layer and ductile body frame. Diamond - carbide FGMs were prepared using the centrifugal deposition method for material compaction. Phase composition of FGM strongly depends on conditions of centrifugal sedimentation process: duration, rotation speed, solid content, dispersive liquids. The centrifugal deposition process of forming powders guarantees gradient phase composition for materials obtaining in the powder sintering process

Jaworska, Lucyna

Królicka, Bogna

Rozmus, Marcin

Twardowska, Agnieszka

Repozytorium Uniwersytetu Komisji Edukacji Narodowe

Marcin Rozmus, Lucyna Jaworska, Bogna Królicka, Agnieszka TwardowskaFUNCTIONALLY GRADED MATERIALS PREPARED USINGPM METHODSABSTRACTIn this work the state of art related to obtaining, properties and application of functionally graded materials is presented. Functionally graded materials (FGM) secure obtaining of cutting tools of wear resistance surface layer and ductile body frame. Diamond -  carbide FGMs were prepared using the centrifugal deposition method for material compaction. Phase composition of FGM strongly depends on conditions of centrifugal sedimentation process: duration, rotation speed, solid content, dispersive liquids. The centrifugal deposition process of forming powders guarantees gradient phase composition for materials obtaining in the powder sintering process.KEYWORDS: functionally graded materials, diamond -  carbide composite, centrifugal deposition, HPHT sintering, properties1. FUNCTIONALLY GRADED MATERIALS AND THEIR POTENTIAL APPLICATIONFunctionally Graded Material (FGM) is a novel concept for realization of innovative properties and functions that can not be achieved by conventional homogeneous materials. These materials consist of one kind of material on one side and a second material on the other, and intermediate layer whose structure, composition and morphology vary smoothly from one material to the other at the micron level [1], Microstructures of homogeneous and FGM materials were presented in Fig. 1.dispersive structure laminar structure gradient structureFig.l. Scheme of microstructures of homogeneous, layers and graded materials.Functionally Graded Materials are composite materials with a continuous spatial change of properties [1, 2, 3].Mgr inż. Marcin Rozmus, the Institute of Advanced Manufacturing TechnologyProf. AP, dr hab. inż. Lucyna Jaworska, Pedagogical University of Cracow, Institute of Technology; the Institute of Advanced Manufacturing TechnologyMgr inż. Bogna Królicka, the Institute of Advanced Manufacturing TechnologyDr inż. Agnieszka Twardowska, Pedagogical University of Cracow, Institute of TechnologyIt is evident that FGM holds the key for many applications, which include structural materials, that can endure high temperature exposure with wear or corrosion resistance.Also, they have considerable potential to be extended from structural to electrical, chemical, optical, nuclear and biomedical areas, table 1 [2, 4],Materials in nature such as shell, rat incisor, bamboo are traced to inhomogenity of chemical composition, structure and morphology in components of these materials. Both bamboo and shell have high strength near outside surface and softness and toughness inside. In addition, bamboo fulfills other superior characteristics such as lightweight, strength and elasticity owing to its hierarchy, stepwise structure from nodes in hollow. When coconut leaf is blown by wind, 30% of the leaf from the tip is moved freely to every direction as wind blows, but the other 70% is very strong and never be moved, it indicates that is provided with an appropriate structure for the environment. FGMs was first proposed in around 1984-85 years. The body of spaceplanes has to be exposed to very high temperature environment (about 1970 K), therefore, is required to resist a severe condition generated from a temperature difference (about 1000 K difference) between inside and outside of the spaceplane. There was no uniformed material endurable to such condition before. Therefore, the researchers devised a concept of FGM that was to fabricate a material by gradually changing (grading) the composition and to improve both thermal resistance and mechanical properties. They considered of fabricating FGM with ceramic and one with high thermal conductivity; ceramics for a surface to be exposed to high temperature environment and the other one for inner surface. Since then, they have been engaged in this work. In 1987, FGM research was started.. The research resulted in generation of the thermal stress relaxing material. The first international FGM conference was held in Sendai City in 1990 [5, 6],The surface of nitrided steel, the metallic surface modified by ion-implantation are examples of simple, natural “gradient” [1].Table 1. Several types o f FGM and potential applicationType of FGM Properties Methods of obtaining ApplicationsCeramic/metal bulk FGM:SiC/CC -  thrust chamber;SisN^steel, Cr3C2/steel - turbine blades;Thermal stress relaxation’ high heat resistance and wear resistance, high mechanical strengthSpark plasma sintering processEngine componentsSolid oxide Fuel Cells Electric conductivity, stress relaxation, ionic conductivitySintering ElectrodeBiomaterialsHAp/TiAlVBiocompatibility; high toughnessAdditive layer wise process; direct metal laser sintering of powders (DMLS)implantsFunctionally graded cemented carbides and cermetsWear resistance, thermal crack resistanceSintering Cutting insertsGlass fiber; lens without aberration; perfluorinated optical fiberGraded index, lightguidesOptics and communicationThe first industrial application of the Functionally Graded Materials (FGM) concept has emerged in production of cermet cutting tools in 1996 by Sumitomo Electric Industries, Ltd. In this material, in-situ formation of the graded structure was used. A homogenous mixture of TiCN, 40wt.% WC, 10 wt.% Co and 5wt.% Ni powders was used for the green compact. They were sintered at 1670 K in vacuum and then held for one hour under a controlled nitrogen pressure. During this heat treatment, the WC in the outer layer dissolved in the molten Co-Ni and precipitated at the surface as a solid solution of (Ti,W)(C,N). The molten metal moved from the surface by controlling the atmosphere and the cooling rate. By eliminating the surface metal layer, a high to low gradation in hardness from the surface to the interior was reached [7]. The thin surface layer, which consist of almost 100% (Ti,W)(C,N) ceramics without the metal binder, has high hardness of 22 GPa. The high hardness and high compressive stress at the surface and high toughness in the interior, improve wear resistance about two times and tool life about five times compared with conventional cermet tools. Functionally graded cermets have more amount of hard phase in the surface layer and lower participation of this phase in the body frame. FGMs secure obtaining of cutting tools with hard wear resistance surface layer and the ductile body frame. The coated tools have higher wear resistance and toughness than those of the FGM tools, but sometimes delamination of coating film occur and shorten the tool life. The in-situ formation or one-step formation of FGMs is the nearest route for economical production. Net- shape formation of complex form FGMs is costly, but useful for special applications [4],2. PROCESSING TECHNIQUES FOR FUNCTIONALLY GRADED MATERIALSFGMs are obtained by using a variety of manufacturing processes. The concept of FGM refers to the realization of innovative properties followed by inhomogenity that can not be performed by conventional homogeneous material. Process for the FGM obtaining, must have capability of producing a precisely controlled profile of chemical composition. These processes are roughly classified into three types: gaseous, solid and liquid processes. Gas processes are realized using: CVD, ion plating, plasma spraying, ion mixing methods. Gaseous processes allow to prepare directly thin films or plates while controlling gas flow rates or temperatures [1]. Liquid methods for FGM obtaining are realized using: electrodeposition, plasma spraying, and eutectic reaction methods. Solid state FGM obtaining is realized using SHS (Self Propagating High Temperature Synthesis), powder metallurgy, diffusion methods. The powders metallurgical process is one of the most viable routes for FGM obtaining. The self propagating high temperature synthesis (SHS) is characterized by easy sintering of the bulk material in relatively short time period [1].There is not a FGM material property database and standardized testing methods.It is necessary to develop cost effective processes for FGMs obtaining. The shape and volume of components, devices, and machines could be changed to more effective forms and functions [4],3. P/M FABRICATION PROCESS OF DIAMOND FGMPolycrystalline diamond compacts (PCD) were first introduced in 1972 and the most often consist of a thin layers (0.5 to 1 mm) of sintered polycrystalline diamond bonded to cemented tungsten carbide substrate. The cutter material is made by sintering diamond powders onto WC/Co substrate in the range 1770-2270 K and 5-7 GPa in a High Pressure-High Temperature apparatus. During the material cooling after the HPHT sintering process, the various coefficients of thermal expansion of the materials leave severe residual stresses in the compact. In practice, residual stresses can cause delamination when the PCD cutter is brazed, machined or subjectedto high impact forces, the result of residual stresses could be chipping or cracking of the cutters. Composite PCD was formed from a graded distribution of diamond crystals and particulates of cemented carbide. Composite layers with varying amount of diamond (100% at the surface to 0% at the interior) are bonded to Ti3SiC2 substrate. The concept of conventional PCD inserts and functionally graded diamond inserts are presented in the Fig.2.Fig. 2. Macrostucture of the conventional PCD and functionally graded diamond -  Ti3SiC2 insert.The bonding of diamond particles was the second and very important role of Ti3SiC2. Since these transition, layers create a slowly changing gradient in elastic modulus and coefficients of thermal expansion, residual stress and spalling should be greatly reduced In these studies FGMs were prepared by a powder metallurgical processes using the layers pressing method for the powders consolidation and the centrifugal deposition method.Method of powders consolidation has a significant influence on microstructure and materials properties. For the processing of advanced ceramics and other hard particles, a variety of compacting methods are used, but many dry processes are not optimum in respect to the homogeneity of the green bodies. Wet (or colloidal) processing are rather effective for such purpose since the presence of media reduces frictions between particles during compaction [15, 16]. Better compaction are achieved for centrifugal compaction of slips of fine powders (High- Speed Centrifugal Compaction Process, HCP). The particles in slips sediment on the metallic dies under high centrifugal force. For homogeneous materials (not FGMs) selection of starting powders and the strong classification.The homogenous mixture of 70 wt.% diamond powder (3-6 pm, MDA Element 6) and 30 wt.% Ti3SiC2 (below 2 pm, SHS method AGH) powders was prepared.The mixture of powders was dispersed by the ultrasonic method in solution of water with organic additives. This suspension with 0.3 wt.% of solid content was introduced into special dismountable centrifugal tubes. Deposition process was carried out in ultra centrifuge UP 65M (prod.Germany) with rotational speed of 15000 to 25000 rpm/min, for 20 minutes. The deposited materials were removed from the centrifugal tubes and directly put into graphite heaters (O =15mm, h =5 mm). After that, materials were dried and put into the special assembly for the HT- -HP sintering. Samples were HPHT sintered using an special assembly. Compacts were obtained at pressure of 8.0.0±0.2 GPa and temperature of 2070±50 K in the high pressure Bridgman type apparatus.4. RESUTS AND DISCUSSIONDeposition process was carried out using the ultra centrifuge UP 65M with rotational speed of 15000 to 25000 rpm/min for 20 minutes. Parameters of powder mixtures deposition (duration of deposition, rotational speed) have significant influence on the gradient of phases distribution in materials. FGM macrostructure is shown in the Figure 3.Poly crystalline diamond layerWC-CoHigh diamond content (>80%)Diamond and the T i3 SiC2 bonding phaseLow diamond content (<5%)Fig. 3. Macrostructure of the FGM diamond -  Ti3SiC2 composite. Table 2. Elements concentration in three zones o f the FGM diamondElement contents Surface layer Atomic %Concentration in intermediate zone, wt.%Bottom layer wt.%C 99.360 54.475 24.670Si 0.364 20.201 33.940Ti 0.256 25.324 41.391* elements from waters organic liquid.In Table 2 element concentration differences in FGM diamond is shown. In the Figure 4 microstructure and elements distribution of the diamond FGM with the phases composition gradient, obtained by the centrifugal deposition method were presented too.Fig. 4. Elements: C, Ti, Si distributions in diamond composites with the gradient of phases content distributionThe gradient of hardness measurements results from the top surface to the bottom surface of samples obtained by 20 minutes centrifugal deposition processes is presented in the Figure 5.102,1587 .1572 .1557 .1542 .1527 .1512.15hardness [GPa]0,10 0 ,30 0 ,60 1,00 2 ,00 3 ,00 4 ,00 5 ,00distance [mm]Fig. 5. The hardness HV0.5 distribution in the diamond FGM with graded microstructure; material prepared by the 20 minutes of powder centrifugal depositionCONCLUSIONS• The centrifugal deposition process guarantees graded structures of phase compositions.• Phase composition of functionally graded materials strongly depends on conditions of the centrifugal sedimentation process (duration, rotational speed, solid content, water organics liquid)• Diamond concentration in the surface layer is about 100%, in the substrates layer there is not diamond• The transition layers characterized a slowly changing concentration of diamond LITERATURE1. Kawasaki A., Watanabe R.: Ceramics International (1997) Nr 23, s.73-83.2. Koizumi M.: Journal of the FGM-Forum, National Aerospace Laboratory, Nippon Oil Company (1994) Nr 24, 3-6.3. Borchert R., Willert-Porada M.: Mat. 9th - World Ceramic Congress and Forum on New Materials CIMTEC, Florence 1999, PartC, s.313-320.4. Miyamoto Y.: Mat. 9th - World Ceramic Congress and Forum on New Materials CIMTEC, Florencja 1999, Part C, s. 287-298.5. http://fgm.nal.go.ip: FGMs database, 2002.6. Sasaki M., Hitari T.: Journal of Ceram. Soc. Jpn (1991) Nr 99, s. 970-980.7. Tsuda K, i inni: Technical Report ,,Sumitomodenki“ (1995) Nr 147.

Functionally graded materials prepared using pm methods

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Functionally graded materials prepared using pm methods

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