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I. INTRODUCTION Silicon carbide (SiC) and silicon nitride (Si3 N 4 ) are leading candidate ceramic materials for heat engine applications. They are attractive because of their high strength at high temperatures, good thermal shock resistance, and excellent corrosion and erosion resistance. Some of the surface sensitive properties, such as friction and wear and also surface hardness and toughness, can be further improved by ion implantation and ion-beam mixing. These methods are attractive because they are nonequilibrium processing techniques that can lead to new material properties.1'2 So far, most of the studies3'4 on ion implantation and ion-beam mixing have been performed on Al2 O3 and SiO 2 . A few reports are available on the ion-beam mixing of metal layers with SiC and Si3 N 4 . Narayan et al.5 have studied ion-beam mixing of Ni layers on SiC. Mixing has been observed in this system using 350 keV Xe + ions. The mixed region was found to increase with increasing doses of the implanted ion. The structure of the mixed region was found to be amorphous with occasional presence of crystalline nickel silicide (Ni 2 Si) islands. In the case of the Ni/Si 3 N 4 system, no mixing was observed.3 Chromium has been found to mix with SiC4; however, no studies have been made of the Cr/Si 3 N 4 system. The results of ion mixing of metals with insulators have been found to agree generally with the enthalpy rule, which states that the mixing will take place if the reaction enthalpy is negative and will not mix if it is positive.4 We shall report here the results of high-energy ion-beam mixing of Ti with SiC and Si3 N 4 . II. EXPERIMENT Sohio engineering company's sintered alpha SiC and Norton Company's hot-pressed NC-132 Si 3 N 4 were chosen for these experiments. Substrates were made by cutting 1x1X0.2 cm pieces and polishing them to a mirror finish by using 1 fim diamond paste. The surfaces were cleaned with methanol followed by deionized distilled water prior to mounting them into J. Mater. Res, 2 (2), Mar/Apr 1987

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the evaporation chamber. Films of Ti have been deposited by electron gun evaporation in the presence of lowenergy (550 eV) A r + ions at a current density of 140 //A/cm 2 , which was also used for sputter cleaning the substrates prior to deposition. The pressure in the evaporation chamber was maintained at ~ 10 ~ 6 Torr. Conventional evaporation without the ion-beam results in incorporation of a considerable amount of oxygen ( ~ 50 at. %). Impurity analysis in the films has been made by sputter Auger in a vacuum chamber with a background pressure in the 10~ 9 Torr range. Ion-beam mixing was carried out by using 1 MeV A u + at doses of 1 XlO 16 cm" 2 and 5 XlO 16 cm" 2 . The amount of mixing was evaluated from Rutherford backscattering (RBS) analysis and cross-section transmission electron microscopy (XTEM). The RBS analysis was performed with 3.05 MeV He + ions impinging on the surface at an angle of 75° with the normal. The scattering angle was 168°. The choice of 3.05 MeV H e + wa