Nuclear Instruments and Methods in Physics Research B64 (1992) 452-456 North-Holland zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Nuclear Instruments & Methods in Physics Research Si!ctlon B Quantification of the separate matrix constituents of spheroidal graphite cast iron implanted with ‘“N by nuclear reaction analysis using an ion microprobe A.P. Matthews ‘, C. Jeynes “, K.J. Reeson b, J. Thornton b,’ and N.M. Spyrou b ‘I zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA King’s College, Strand, London W C2R ZLS, UK ” Cnirwssiiy of Surrey, Gctifdfmd, Surrey GLl2 5,yW , UK The retained dose of nitrogen in a spheroidal graphite (SC) cast iron (4% carbon) implanted with 2x IO” “N/cm’ at 200 keV has been determined separately in the iron matrix and in the graphite inclusions of 30 km average diameter randomly dispersed in the matrix, using the “N(p oly)12C resonance at 898 keV and a proton microprobe focussed to less than 20 km spot diameter. In , normalised and tempered SG cast iron the retained doses were 1.09~ lOI and 1.74~ lOi N/cm’ in the pearlitic matrix and graphite nodules, respectively, and in induction hardened SG cast iron the retained doses were 1.18~ 10” and 0.97~ IO” N/cm” in the martensitic matrix and nodules, respectively. The profile shapes are also quite different in both types of samples, and in both matrix and nodule 1. Introduction The use of spheroida graphite (SG). or duct&z cast iron has gradually increased in the engineering indus- try, and now accounts for over 25% of all ferrous castings. Characteristically, these metals contain nodu- lar graphitic inclusions embedded within iron matrices, of structures and compositions equivalent to those of steels. Amongst such alloys, those exhibiting either pearlitic or martensitic matrices, generated by specific heat treatments and variations in alloy composition, are most resistant to wear, and hence are widely used in the automotive industry for components suitable to casting. Considerable improvements in the wear resistance of low carbon steels impIanted with high doses of nitrogen has been repeatedly observed [l-4]. The role of nitrogen is still not completely understood even in simple steels, and the metallurgy of these cast irons is more complex. This is described in detail elsewhere I191. To determine the depth profile of retained nitro- gen, nuclear reaction analysis (NRA) is invariably em- ployed, using the resonant ‘“N(p, ay)“C reaction at 429 keV [S-7], since it has the narrowest resonance width, giving the greatest depth resolution at the sur- face (see table I). However, due to the presence of graphitic inclusions in SG cast iron, determination of the ion impIanted depth profiles in the two phases I Now at: Aeronautical Research Lab., Melbourne, Australia. requires a microbeam. This significantly reduces the proton beam intensity, and favours use of the 898 keV reaction, which has an order of magnitude greater gamma yield per incident proton than that of the 429 keV resonance, as shown in table 1. The loss of resolu- tion is not important in this work since the resolution available is enough for depth profiles on this scale. Depth profiles were normalised together by using the backscattered proton signal collected simultane- ously with the gamma spectrum, and calibrated against implants into pure graphitic carbon and pearlitic steel. The 898 keV reaction has an order of magnitude greater quantum yield than the more frequently used 429 keV one, and near 898 keV the cross-section for elastic proton backscattcring varies only weakly with energy, avoiding the resonance around 450 kcV (shown in fig. 1) 113,141. This normalisation procedure has been described in greater detail previously [15]. tNCtOENT PROTON ENERGY MEV Fig. 1. The measured yield of elastically backscattered protons from carbon, collected at 164”, showing the resonance at 456 keV [13]. 016%S83X/92/$05.00 0 1992 - Elsevier Science Publishers B.V. All rights reserved