The Characterization of Nitrogen Implanted WC/Co
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THE CHARACTERIZATION OF NITROGEN IMPLANTED WC/Co DANIEL W. OBLAS GTE Laboratories Incorporated, Waltham Massachusetts,
02254, USA
ABSTRACT Although the mechanical properties of nitrogen implanted cemented carbides show significant improvements in performance over unimplanted specimen, the chemical or physical mechanisms giving rise to these improvements are not well understood. Furthermore, the mechanical properties of the implanted samples under thermal stress may not be stable. This study presents analytical results obtained for a series of nitrogen implanted cemented carbides that were subsequently characterized by Auger Electron Spectrometry (AES) and Thermal Desorption Mass Spectrometry (TDMS). Results show that, in the fluence range of 0.5 to 2.5x10 1 7 N2/cm2 , peak nitrogen concentration is linear and reaches a maximum concentration of 25 a/o for the highest fluence and 180 keY energy. During vacuum heating, the implanted nitrogen is evolved rapidly between 600-700 0 C, which corresponds to an activation energy of approximately 7 kcal/mole (.30 ev). A small quantity of nitrogen is still present after heating to 1000 0 C, at an estimated average concentration of 3 a/o with little diffusional broadening as a result of post-implant heating. INTRODUCTION The improved performance of cemented carbide tools such as punches, drills and wire drawing dies after nitrogen implantation has been widely reported (1-3). Unimplanted cemented carbides have excellent mechanical properties that are sustained to temperatures as high as 800 0 C. However, the improvements induced by ion implantation may not be retained at high operating temperatures. In general, the physical or chemical mechanisms giving rise to these improvements are not well understood (4,5) and the temperature range over which these changes are stable has not been clearly established. In a recent study (6), N+, Ar+ and other species were implanted into WC/Co at 50 keV. Improvements in microhardness were observed for all species, and nitrogen showed the best results. Post heating the implanted specimen 0 up to 600 C produced small improvements in hardness and heating to higher temperatures caused the hardness to decrease rapidly. The delineation of the effects of radiation damage and chemistry on microhardness is still not clear. The purpose of this study is to present some initial data on nitrogen implanted WC/Co using Thermal Desorption Mass Spectrometry (TDMS) and Auger Electron Spectrometry (AES) to characterize the implanted specimen. The nitrogen concentration, distribution, and thermal stability were determined 17 N2/cm2. as a function of fluence in the range of 0.5 to 2.5x10 EXPERIMENTAL The samples for this study were WC/Co tool inserts (0.5"x0.5"x0.25") 94%/6% by weight, respectively. The WCgrain size was between .5 and 2.5 microns with an average size of 1.25 microns. The specimen was polished to a 3 micron finish with diamond paste and cleaned. Subsequently, it was heated in hydrogen for one half hour at 8001C prior to implantation to remove surfa
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