L Journal of Alloys and Compounds 285 (1999) 242–245 Thermal expansion and compressibility of Co W C 6 6 a, a a b b * N.A. Dubrovinskaia , L.S. Dubrovinsky , S.K. Saxena , M. Selleby , B. Sundman a Theoretical Geochemistry, Institute of Earth Sciences, Uppsala University, Villavagen 16, 75236 Uppsala, Sweden b Department of Materials Science and Engineering, Royal Institute of Technology, SE-100 44, Stockholm, Sweden Received 14 October 1998 Abstract Using powder X-ray diffraction, the pressure-volume (PV) data on Co W C were determined at ambient temperature and pressures up 6 6 to 32 GPa with the following results: isothermal bulk modulus K (GPa): 462(11); pressure derivative K9 (fixed): 4; molar volume 300,1 300,1 3 21 21 V (cm mol ): 97.43(2). Isobaric thermal expansion determined by in-situ X-ray diffraction study at 1 atm is given by (K ): 300,1 25 28 2 a 58.64(2)310 17.48(9)310 T22.19(6)/ T  1999 Elsevier Science S.A. All rights reserved. T Keywords: Co W C; Compressibility; Thermal expansion; In situ X-ray diffraction 6 6 1. Introduction measuring the positions and intensities of Bragg reflec- tions, it allows us to register all changes in crystal The Co–W–C ternary alloys are widely used in modern structures under changing P–T conditions. Microsamples industry and technology. The Co–W–C coatings, for (100–200 mm in diameter) used for analysis in modern example, exhibit a good resistance against formation of X-ray diffraction facilities, have high homogeneity due to failure [1], and extend the lifetime of graphite fibers at their small sizes, and at the same time they give a complete elevated temperatures [2]. Most cemented carbides are diffraction pattern (compare, for example, with the trans- based on the Co–W–C system [3]. mission electron microscopy (TEM) of a very thin trans- Despite the importance of the Co–W–C system for mission specimen; therefore the electron beam, in travers- industrial applications, basic knowledge of the individual ing the specimen, sees a lattice that is nearly two-dimen- phases, phase relationships, and their thermodynamic sional [8]). properties is still incomplete. Modern metallurgical indus- try utilises computer programs and thermodynamic models for the calculation of phase equilibria ( THERMO-CALC- [4], 2. Experimental technique F*A*C*T- [5], PANDA- [6], MTDATA- [7]). The new com- puterised tools now allow a better understanding of how We have obtained powder X-ray diffraction data with a different compositions, heat and pressure treatments in- Siemens X-ray system consisting of a Smart CCD Area fluence the structure of the alloys. The more reliable Detector and a direct-drive rotating anode as X-ray genera- experimental data are input in the calculations, the more tor (18 kW). Mo Ka radiation (tube voltage 50 kV, tube reliable predictions can be made. current 24 mA, cathode gun 0.131 mm) monochromatized Traditional metallographic examinations give informa- by using an incident beam graphite monochromator was tion only about macro- and microstructure of samples and passed to the sample through a collimator with a diameter require large specimens [8]. They do not give an oppor- of 50 mm. The diffracted X-rays were collected on a tunity to observe processes in situ. 5123512 pixels area detector. Data were acquired in Among a number of modern analytical methods (TEM, different experiments at different fixed 2 u settings of 0, 10, SEM, MA etc.), high pressure and high temperature in-situ 15 and 208 (corresponding to fixed positions of the X-ray diffractometry is one of the most powerful methods detector) and by varying the sample-to-detector distance to study behaviour of materials. Due to a high accuracy in (120–260 mm). Settings of the detector were carefully calibrated using three independent standards (Pt, NaCl, * Corresponding author. Al O ) at each position of the detector. Since a large 2 3 0925-8388 / 99 / $ – see front matter  1999 Elsevier Science S.A. All rights reserved. PII: S0925-8388(98)00932-3