XXXIV Encuentro del Grupo Español de Fractura: Santander, 29, 30 y 31 de marzo de 2017Durante los últimos años, se han invertido muchos esfuerzos para diseñar nuevos materiales alternativos a los metales
duros (WC-Co), que exhiban respuestas mecánica y tribológica similar a la de estos. El excelente comportamiento de
los compuestos WC-Co se atribuye principalmente a su ensamblaje microestructural, debido a la combinación de dos
fases con propiedades muy diferentes a nivel local. En el presente trabajo se pretende evaluar la relación
microestructura/propiedades micromecánicas de nuevos materiales compuestos cerámico-metal del sistema T i(C,N)-
Fe,Ni. Para ello se ha utilizado un procedimiento sistemático que consta de varias etapas.In recent years, many efforts have been invested to design new alternative materials to substitute hardmetals (WC-Co)
that exhibit similar mechanical and tribological response. The outstanding behaviour of WC-Co composites is mainly
attributed to its microstructural assemblage, due to the combination of two phases with very different properties at the
local level. The present work is aimed to evaluate the microstructurelrnicromechanical properties of new ceramic-metal
Ti(C,N)-Fe,Ni composite systems. A systematic procedure consis ting of several stages has been used for this purpose.The currently study was suppored by the Spanish Ministerio de Economía y Competitividad through Grant MAT2015-70780-C4-3-P (MINECO/FEDER)

Besharatloo, H.

Dios Pérez, Miguel de

Ferrari, Begoña

Gordo Odériz, Elena

Llanes Pitarch, Luis Miguel

Mateo, A.

Roa, Joan Josep

English

Name not available

Micromechanical properties of a Ti(C,N)-FeNiC composite: statistical method

Universidad Carlos III de Madrid e-Archivo

Este documento es una versión postprint de:Besharatloo, H., Roa, J.J., Dios, M., Mateo, A.; Ferrari, B., Gordo, E., Llanes, L. (2017). Micromechanical properties of a Ti(C,N)-FeNiC composite: statistical method. Anales de Mecánica de la Fractura, 34, pp. 494-497.© ANALES DE MECÁNICA DE LA FRACTURAUniversidad uc3m Carlos Ill de Madrid 0 -Archivo 1MICROMECHANICAL PROPERTIES OF A Ti(C,N)-FeNiC COMPOSITE: STATISTICAL METHOD H. Besharatloo1, J.J.Roa•··, M. Dios2, A. Mateo•, B. Ferrari3, E. Gordo2, L.Llanes1 1CIEFMA-Departament de Ciencia dels Materials i Enginyeria Metal· h1rgica, Universitat Poli tecnica de Catalunya, Campus Diagonal Besos (EEBE), Cl d'Eduard Maristany 10- 14, 0801 9 Barcelona, Espana 2 OTP-Grupo de Tecnologfa de Polvos, Universidad Carlos III Madrid, Escuela Politecnica Superior, Av. De la Universidad 30, 289 11 Leganes, Espana 3 lnstituto de Ceramica y Vidrio (ICV-CSIC), Cl Kelsen 5, Campus de Cantoblando. 28049 Madrid, Espana * Persona de contacto: joan. josep.roa@ upc.edu RESUMEN Durante los ultimos anos, se han invertido muchos esfuerzos para diseiiar nuevos materiales alternativos a los metales duros (WC-Co), que exhiban respuestas mecanica y tribol6gica similar a la de estos. El excelente comportamiento de los compuestos WC-Co se atribuye principalmente a su ensamblaje rnicroestructural , debido a la combinaci6n de dos fases con propiedades muy diferentes a nivel local. En el presente trabajo se pretende evaluar la relaci6n microestructura/propiedades micromecanicas de nuevos materiales compuestos ceramico-metal del sistema T i(C,N)-Fe,Ni. Para elJo se ha utilizado un procedimiento sistematico que consta de varias etapas. PALABRAS CLAVE: Compuestos metal-ceramicos, nanoindentaci6n masiva, amUisis estadfstico ABSTRACT In recent years, many efforts have been invested to design new alternative materials to substitute hardmetals (WC-Co) that exhibit s imilar mechanical and tribological response. The outstanding behaviour of WC-Co composites is mainly attributed to its microstructural assemblage, due to the combination of two phases with very di fferent properties at the local level. The present work is aimed to evaluate the microstructurelrnicromechanical properties of new ceramic-metal Ti(C,N)-Fe,Ni composite systems. A systematic procedure consis ting of several stages has been used for this purpose. KEYWORDS: Metallic-ceramic composites, massive nanoindentation, statistical analysis I. INTRODUCTION The outstanding mechanical properties exhibited by hardmetals (WC-Co system) results from the combination of two phases with quite different properties at the local level. In particular, this is true regarding experimental analysis on the influence of phase nature, crystal orientation and interfacial adhesion strength on hardness for T i(C,N)-FeNiC composites. The present work aims to conduct a systematic micromechanical study of the mechanical integrity of fi ve Ti(C,N)-FeNiC systems. In doing so, it is attempted by combining massive nanoindentation and statistical analysis, using the methodology proposed by Ulm and co-workers to extract the intrinsic hardness for each constitutive phase. 2. EXPERIMENTAL PROCEDURE 2. 1. Sample preparation Titanium carbonitride ([Ti(C,N)] grade C, H. C. Stark, Germany), iron (Fe SM, H.C. Stark, Germany) and nickel (Ni 2 10H, INCO, Canada) subrnicronic powders were used as commercial starting materials. Particle size and specific surface area of the powders were determined with a laser analyzer (Mastersizer S, Malvern instruments Ltd. , UK) and by one point N2 absorption (Monosorb Surface Area, Quantachrome Corporation, USA), respectively. Density of the as-received powders was measured using a Monosrb Multipycnometer (Quantachrome Corporation, USA). T he results are shown in Table I . T bi I Ch a e f h d d aracten zat1on o t e as-receive pow ers. Characteristics Powder Ti(C,N) Fe Ni Size Dvso (µm) 2. 1 3.5 1.7 DsET (µm) 0.4 1.2 0.2 Fag 5.0 3.0 10.0 Density (g·cm·3) 5 .1 7.8 8.9 Surface area (m2/g) 3.0 0 .6 4.0 2From these powders, high solid content suspensions were formulated using water as dispersion media ( I]. The suspensions were prepared in deionized water with HTMA to adj ust the pH up to I 0- 11 , where surfaces are chemically stab le [2,3]. Then 0.4 wt.% of PEJ was added as dispersant. Ti(C,N) and Fe/Ni (85/1 5 wt.%) slurries were prepared separately and milled in a ball mill for I h, using SiJN4 and nylon balls, respectively. In order to evaluate the e ffect of a small addition o f carbon, a graphite suspension of I O g/L was prepared in ethanol using Black Carbon (ISTA, Germany) with a density of 2.24 g· cm·3 and a mean partic le size of 18 µ111. After milling, Ti(C ,N), Fe/Ni and carbon suspension was mixed to get the desired specimen, see Table 2. Once the suspension was prepared 2 wt.% of polyvinyl alcohol was added as binder [4]. After PVA addition, the suspensio n remained 20 min under mechan.ical stiJTing before it was sprayed. T bi 2 F I . a e ormu at1011 o f h t e suspensions. Samples Vol.% Composition meta l matrix, wt.% T i(C,N) I Fe/Ni Fe I N i le 15FeNiC 85 I 15 85 I 15 I +o.5 Stable aqueous suspensions were submitted to spray-dry to obtain agglomerates able to be pressed (SOP route). For this purpose, an ato mizer LabPlant SD-05 (North Yorkshire, UK) was used with the main controlled operating parameters being the temperature at the inle t ( 190 °C) and at the exhaust ( JOO 0 C), the sluJTy pump rate (2 1/h), and the atomizing nozzle design set to provide spherical agglomerates with high compressibiUty able to be shaped by uniaxial pressing [5]. Subsequently, granules were pressed at 600 MPa in an uniaxial die into cylinders of 16 mm in diameter. Sintering was conducted in high vacuum ( I o-5 bar) at 1450 °C for 2 h, with a step of 30 mi n at 800 °C. Prior the microstructural and micromechanical characterization, the surfaces were polished with di~mond ~aste down to 3 µm, with a fina l polishing step with collo ida l a lumina. 2.2. Microstructural characterization A fie ld e m1ss10 11 scanning e lectron microscopy (FESEM) image of the material investigated is shown in Figure I . Figure micrograph of the I 5FeNiC microstruc ture for the cermet grade studied. Carbide contigui ty was assessed from best-fit equations following empirical relationships proposed by Roebuck and Almond (6-9] , but extending them to include the influence of carbide size [7,8]. Binder mean free path was finally estimated from the contiguity data [6,9]. The corresponding microstructural parameters are: no minal weight fraction of binder, %vol. FeNiC = 15 %; mean grain size of T i(N,C), dTi(N.C) = 2.22 ± 1.14 µm, mean free path in bi.nder, A-FeNiC = 0.76 ± 0. 14 µrn, and contiguity, CTi(N.C) = 0.47. 2.3. Nanoindentation process Mechanical properties of the Ti(C,N)-FeNiC composite included the evaluation of their effective hardness (H) through instrumented indentation. Nanoindentation tests were performed on a Nanoindenter XP (MTS), equipped with a continuous stiffness measurement module. The micromechanical characterization was carried out with a Berkovich indenter tip, and experimental data were analysed using the Oliver and Pharr methodology [ I 0, 11 ]. The diamond indenter shape was carefully ca.librated with a fused silica standard [ I OJ. Two different steps of experiments were done. The composite mechanical response for the Ti(C,N)-FeNiC specimen was assessed as the average behaviour of 16 imprints, organized in an homogeneous array of 4 by 4 , at 2000 nm maximum penetration depth (or until reaching maximum applied load of 650 mN). The distance between imprints was kept constant and equal to 50 µm in order to avoid any overlapping e ffect. After that, in order to statistically determine the intrinsic hardness for each constitutive phase as well as their anisotropy, three different spaced arrays of 625 imprints (25 by 25, and separated 5 µm from each other) were done at 200 11111 of maximum penetration depth, according to the method proposed by Ulm and co-workers [ 12- 15]. 3. STATISTICAL METHOD The statistica l analysis proposed by Ulm and Constantinides [ 12-15] is based on the consideration of a sample as composed by several distinct constituent and phases, i.e. ceramic partic les, Ti(C,N), and metallic binder, FeNiC, with different mechanical properties. This methodology considers that distribution, p;, of the micromechanical properties, in terms of hardness, H, for 3each constituent and phase following a Gaussian distribution: ( I ) where a; is the standard deviation and H; the arithmetic mean hardness for each of the number of indentations on the material phases (i). The different results are represented by cumulative distribution function, considering that density functions are correctly fined by Gaussian distribution. In this sense, the experimentally measured intrinsic hardness values may be fitted by using the following expression: " II [H-H.] CDF = I. }2 · J;- e,f - ' ; 2 Ji ·<7, (2) where f; is defined as the relative fraction occupied by each constituti ve phase. During the deconvolution process, several restrictions were programmed in order to obtain a re liable value. In this regard, the sum of the fraction for each constitutive phase was set at I , and the fitting process was programmed to be completed when the chi-square was less than I 0·15. 4. RESULTS AND DISCUSSION 4. 1. Microstructural parameters Figure 2 shows the grain size histogram for the Ti(C,N) particles, with a constant bin size of I 00 nm, determined from 675 different grains. It mainly presents a bimodal distribution. Peak values at about 3. 1 µm and 1.3 µm, are attributed to coarse and fine Ti(C,N) particles, respectively. 40+---'-----'---'--~-----i-Fine grams = .!!,. 20 " ,: 8 0 6 Grain siLc. di.c. ,, (µm) Figure 2. Grain size histogram with 100 MPa of bin size. T he simulated fine and coarse distribution are overlapped to the experimental values. 4.2. Micromechanical properties Hardness obtained from Nanoindentation as a function of the displacement into surface is shown in Figure 3. Surface roughness and indenter tip effects on the mechanical response are discerned at very low penetration depths. Hardness for the Ti(C,N)-FeNiC specimen studied is found to be 18.0 ± 0.2 GPa. Furthermore, FESEM micrograph depicted in Figure 3 (inset) presents the possible damage mechanisms activated during the indentation process around the Berkovich imprint at maximum displacement into surface. As it is evidenced, around the residual imprint several damage events li ke cracks may be identified (see white arrow). l0..---~-----1.i ,, ... - ,, ~ .. = !!I R 20 ! 1l 10 ! Hn.c \·,-i,\,c::: 18 GP.:I Dasrlacanent imo wrfxc. h 1nm) Figure 3. (a) Hardness evolution of Ti(C,N)-FeNiC as a function of the displacement into surface, and (b) residual imprint observed by FESEM. The hardness histogram, with a constant bin size of 500 MPa, is shown in Figure 4. Three different peaks may be discerned. Two extreme high peak values of around 33 and 24 GPa are attributed to the ceramic phase, while the lowest value peak, centred at 13.9 GPa, is associated with the metallic FeNiC binder phase. The latter is presented here as one of the main outcomes of this research. W ithin this observation, it is evident that the Ti(C,N) is strongly anisotropic in terms of hardness. Further research may be carried out in order to correlate their intrinsic hardness as a function of their crystallographic orientation. ioo~--------------, D E.,p,nmm..i c1a .. -Ti(C'.i'l)~ • un,\Olrop,cf*Ju• Ti(CN) ph:uc 1.50 - ,~,.c. l-0 °o 10 :?O 'O l-0 11:in!ncss. II (Gl'a) Figure 4. Hardness histogram with 500 MPa of bin size. The simulated hardness using the statistical fitting parameters (summarised in Table 3) are overlap through the statistical method fitting. As it was mentioned above, in order to obtain a representative distribution of the hardness properties in the heterogeneous composite Ti(C,N)-FeNiC system, a grid of 1875 imprints was performed in the specimen of 4interest. Figure 5 corresponds to a FESEM image of a small region of the indentation array. ., - , : .-·· .,.,_, ' }; •; -t;:. 1. • . "' , . ·. l .., . ·~'. 'r ·. ' .-·. .'~ • ~· l£ , ,.J• -~ • , l.'L.1 ;._ ..... '' ,., ,·. '~ .. · . ··\.~.~-. ··L~' ..... _··~. --~;.; .. ,~~.( .~Z':.· > ~ ~ . . . '}. .. ,. . . . ·. . • .. , . .,.,. . r • ·,'-~ ., .. , ·. ', .·' / /,'4_ ..... .. - ,..~.· ,. ';,IF•,• • . . • . I , ·, .. ··A I" 1 ~-. • .• ' ,... '. ': -# .... ' • ,, ', •• ·-., • b. -4·. , . ' I y . , ,\,· ' ... •, •• ' ' . ... a. .; [. •, . : ~ ... . 1. ,. ... '.'.• ' . . '"': .J . -- '<jo ' . ·". ... • -( • .. :. ~ ,.t \i· '.L', •-:-.• ·~ , •• . r .... .-.··' r sµm ·-Figure 5. FESEM micrograph image showing one array of indents performed at 200 nm of maximum penetration depth. The distance between imprints has been kept constant to 5 µm in order to avoid any overlapping effect. Attempting to evaluate whether the penetration depth employed to conduct the massive indentation process is suitable to extract the intrinsic prope rties for each constitutive phase, magnified FESEM micrograph o f a random region (square white region presented in Figure 5) were directly observed, see Figure 6. On the basis of the FESEM observation presented in Figure 6, indentation maximum penetration depth of 200 nm guarantees each indentation test could be treated as an independent statistical event, see * in Figure 6. Figure 6. Magnified FESEM image. 5. CONCLUSIONS In this study, experimental and statistical Nanoindentation technique has been implemented for assessment and analysis of the mechanical response of the constitutive phases of Ti(C,N)-FeNiC composite. The main conclusions are as follows: Intrinsic hardness values are analysed and determined for the constitutive phases for Ti(C,N)-FeNiC systems, by either different chemical nature or distinct Ti(C,N) orientation. Maximum penetration depth of 200 nm, is found to be suitable nanoindentation testing parameters for successful implementation of statistical me thod in Ti(C,N)-FeNiC systems. A clear hardness anisotropy is evidenced for Ti(C,N) crystals. In this regard, hardness for the Ti(C,N) phase is higher than for the me tallic FeNiC binder. ACKNOWLEDGEMENTS The currently study was suppo1ted by the Spanish Ministerio de Econo mfa y Competitividad through Grant M AT20 I 5-70780-C4-3-P (MINECO/FEDER). REFERENCES [I] J . A. Escribano, J. I. Garcfa, P. alvaredo, B . Ferrari, E. gordo, A. J . Sanchez-Herencia, Colloidal processing of Fe-based metal ceramic composites with high content of ceramic reinforcement, Bo/. Soc. Esp. Ceramica Vidr. 52, 247-250, 2013. [2] J . A. Escribano, J. L. Garcfa, P. AJvaredo, B . Ferrari, E. Gordo, A. J . Sanchez-Herencia, FGM stainless steel-Ti(C,N) cermets through colloidal processing, lnt. J. Refract. Met. Hard Mater. 49, 143-152, 2015. [3] P. Parente, A. J . Sanchez-Herencia, M. J. Mesa-Galan, B . Ferrari , Funcionalizing Ti-surfaces through the EPD of hydroxyapatite/Nano Y 20 3, J. Phys. Chem. B, 117, 1600- 1607, 2013. [4] R. G. Neves, J . A. Escribano, B. Ferari, A. J . Sanchez-Herencia, E. Gordo, Improvement of Ti Processing through Colloida l Techniques, Key Eng. Mater. 520, 335-340, 2012. [5] R. G. Neves, B . Fe rrari, A. J . Sanchez-Herenc ia, E. Gordo, Colloidal approach for the design of T i powders sinterable at low temperature, Mat. Lett. 107, 75-78, 201 3. [6] B. Roebuck, E. A. Almond, Deformation and fracture processes and the phys-ical metallurgy of WC-Co hard metals, lnt. Mater. Rev. 33, 90- 1 I 0, 1988. [7] Y. Torres [Ph.D. thesis], Comportamiento a fractura y fatiga de carburos cementados WC- Co, Universitat Politecnica de Cata/unya , 2002. [8] D. Coureaux [Ph.D. thesis], Comportamiento mecanico de carburos cemen-tados WC- Co: influencia de la microestructura en la resistencia a la fractura, la sensibilidad a la fatiga y la tolerancia al dafio inducido bajo so licitaciones de contacto, Universitat Politecnica de Catalunya, 2012. [9] H . E. Exner, Physical and chemica l nature of cemented carbides, lnt. Met. Rev. 4, LL49- 11 73, 1979. [10] W. C. Oliver, G. M. Pharr, An improvement technique for determining hardness and e lastic modulus using load and displacement sensing indentation experiments, J. Mater. Res. 7, 1564-1 580, 1992. [I I] W. C. O liver, G. M. Pharr, Measurement of hardness and elastic modulus by instrumented indentation: Advances in understanding and refinements to methodology, J. Mater. Res. 19, 3-20, 2004. [12] Constantinides G, Ulm F-J, Van Vliet K. On the use of nanoindentation for cementitious materials. Mater Struct 2003;36: 191- 6. [1 3] Constantinides G, Chandran KSR, Ulm F-J , Van Vliet K. Grid indenta-tion analysis of composite 5microstructure and mechanics: principles and validation. Mater Sci Eng A 2006;A430: 189-202. [14] Constantinides G, Ulm F-J. The nanogranular nature of CS H. J Mech Phys Solids 2006;55:64- 90. [15] Ulm F-J, Vandamme M, Bobko C, Ortega JA, Tai K, Ortiz CJ. Statistical indentation techniques for hydrated nanocomposites: concrete, bone, and shale. J Am Ceram Soc 2007;90:2677- 92. 

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Micromechanical properties of a Ti(C,N)-FeNiC composite: statistical method

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