JOURNAL OF MATERIALS SCIENCE 39 (2 0 0 4 ) 1907 – 1911 Synthesis of TiC 1-x N x and TaC 1-x N x by spark plasma sintering S. URBONAITE, M. JOHNSSON, G. SVENSSON Department of Inorganic and Structural Chemistry, Stockholm University, SE-106 91, Stockholm E-mail: matsj@inorg.su.se Titanium and tantalum carbonitrides are materials with many interesting properties such as high melting point, good wear resistance, high hardness and high electrical- and thermal conductivity. They have found use as the hard phase in sintered hardmetals and ceramic com- posites and also as protective coatings on hardmetal substrates. Due to excellent high-temperature strength and good corrosion resistance, they can also be used as high temperature structural materials. Tantalum car- bide as well as several other transition metal carbides and nitrides have also been reported to be highly active catalytic materials [1–4]. Transition metal carbonitrides can be produced by several methods from solid, liquid and gaseous state. They can be synthesized as thin films, whiskers, and as bulk materials. The most common synthesis methods are self-propagating high-temperature combustion syn- thesis (SHS), ion beam assisted deposition (IBAD), car- bothermal reduction, plasma enhanced chemical vapor deposition (PECVD), plasma vapor deposition (PVD), chemical vapor deposition (CVD), and high pressure sintering (in HIP furnaces) [3, 5–11]. The aim of this work was to prepare titanium and tantalum carbonitrides (TiC 1−x N x and TaC 1−x N x ) us- ing the spark plasma sintering (SPS) technique starting with TiC, TiN, TaC, and TaN with no additional sinter- ing aids. The following starting materials were used: TiC [H. C. Starch GmbH & Co (Germany), grain size <3 μm, purity 99.5%], TaC [ABCR (Germany), grains size <5 μm, purity 99.5%], TiN [Tioxide Chemicals (England), grain size <0.4 μm, purity 99.5%], and TaN [Aldrich Chemical Company, Inc. (U.S.A.), grains size <5 μm, purity 99.5%]. Homogeneous mixtures of the starting powders for preparing TiC 1−x N x and TaC 1−x N x were made in 2-propanol using a planetary mill at a speed of 2000 rev/min for 10 min (Fritsch pulverisette, Germany) with WC milling bodies. TABLE I TiC 1−x N x sintered at 1700 ◦ C for 10 min. The applied pressures were 50 MPa and 80 MPa respectively 50 MPa 80 MPa x -value Density (g/cm 3 ) Relative density (%) a-axis ( ˚ A) Density (g/cm 3 ) Relative density (%) a-axis ( ˚ A) 0 4.91(1) 100.0 4.3260(2) 4.88(1) 99.3 4.3249(5) 0.2 4.90(1) 97.8 4.3094(4) 4.91(1) 98.1 4.3080(4) 0.4 4.92(1) 96.5 4.2911(3) 4.98(1) 97.5 4.2918(3) 0.5 5.02(1) 97.4 4.2855(5) 5.06(1) 98.2 4.2838(12) 0.6 5.02(1) 96.6 4.2782(6) 5.07(1) 97.6 4.2764(4) 0.8 5.18(1) 97.8 4.2595(2) 5.14(1) 97.1 4.2599(3) 1 5.27(1) 97.8 4.2362(6) 5.22(1) 96.9 4.2360(7) A Dr. Sinter 2050 SPS apparatus (Sumitomo Coal Mining Co., Japan) was used for sintering. Samples of 12 mm in diameter and 4 mm in height were pre- pared in vacuum under uniaxial mechanical pressure applied from the start of the experiments. The temper- ature was measured with an optical pyrometer focused on the surface of the graphite die and automatically reg- ulated from 600 ◦ C, once that temperature was reached via a pre-set heating program. The reactions took place at 1700 or 1800 ◦ C for 10 min at 50, 75 or 80 MPa. The heating rate from 600 ◦ C up to the plateau was 100 ◦ C/min. Densities were determined by use of a helium pyc- nometer (Micromeritics, AccuPyc 1330, U.S.A.). The densities of the sintered compacts where compared to tabulated values for the end compositions assuming a linear dependence. Unit cell parameters were determined from X-ray powder diffraction patterns recorded with a Huber Imaging Plate Guinier Camera 670 (Huber Diffraktion- stechnik GmbH, Germany) and a Guinier-H¨ agg focus- ing camera using Cu K α1 radiation (λ = 1.540598 ˚ A). Si (a = 5.430879 ˚ A at 25 ◦ C) was added as an internal standard. The unit cell data was compared with a linear relation from the published data for the end compo- sitions TiC (PDF 32-1383), TiN (PDF 38-1420), TaC (PDF 35-0801), and TaN (PDF 32-1283). Grain size and porosity of sintered compacts were in- vestigated on polished and fractured surfaces in a scan- ning electron microscope (SEM), Jeol 820, operated at 10 kV in backscattered electron (BSE) mode and at 20 kV in secondary electron (SE) mode. Electron diffraction (ED) patterns were obtained in a transmis- sion electron microscope (TEM) Jeol 2000FX operat- ing at 200 kV. Chemical analyses of C, O, and N were made with standard combustion techniques. For sintering the TiC 1−x N x samples one series was prepared at 1700 ◦ C for 10 min with an applied pressure 0022–2461 C  2004 Kluwer Academic Publishers 1907