Influence of sample geometry on the effect of pulse plasma nitriding of M2 steel

Abstract

Abstract A comparison of pulse-plasma-nitrided flat coupons and complex shaped substrates such as twist drill test bits show that the incorporation of nitrogen depends strongly on the substrate geometry. Glow discharge optical emission spectroscopy (GDOES) depth profiling and cross-sectional WDX analysis showed that the amount of nitrogen incorporated at the cutting edge of a drill was systematically higher than in flat coupons nitrided under identical plasma conditions. In fact, the observed increase in hardness reaches a value of HV 0.01 =1232 (base hardness HV 0.01 =840), whereas in the corresponding flat coupon, HV 0.01 =980 at a depth typically 10 μm. Bragg–Brentano and glancing angle parallel beam XRD and SEM analysis confirmed that under the optimized process conditions used, the formation of the adhesion reducing compound layer, ϵ , can be completely suppressed. These findings clearly imply that caution must be exercised when extrapolating observations on flat coupons to those of geometrically more complex cutting tools, e.g. on twist drills.