Enhanced microhardness of four modern steels following nitrogen ion implantation

Samples of two kinds of hot-work steels (Orvar Supreme, QRO 90 Supreme), on e cold-work steel (Sverker 21) and one ultra-high-strength aircraft steel ( AerMet 100) were implanted with 120 keV N-2(+) ions (60 keV/N+) at doses ra nging from 5 x 10(15) to 1.2 x 10(17) ions/cm(2) at room temperature. Also implanted into the four steels were 60 keV C+ ions using the same doses. Th e Knoop microhardnesses on the sample surfaces increased by 31-72% at load of 25 gf after nitrogen ion implantation. There was no obvious effect on mi crohardness after carbon ion implantation. Tribological properties of the n itrogen ion implanted samples were evaluated. A heat-treatment study of nit rogen ion implanted (8 x 10(16) ions/cm(2)) AerMet 100 and Sverker 21 showe d that the hardness reduction arising from heat treatment was clearly lower for the implanted samples heat-treated at 400 degreesC. The microhardness of the implanted layers alone was calculated by the Jonsson-Hogmark model. The layer thickness used for the calculation of implanted-layer hardness wa s obtained from a molecular dynamic simulation code (TRIM). The residual st ress of the surface after nitrogen ion implantation was measured by X-ray d iffraction. Friction and wear properties of the implanted samples were also measured. Nanohardness and Young's modulus were measured for the nitrogen ion implanted layers. Grazing angle X-ray diffraction (GXRD) analysis shows the possible formation of nitride phases after nitrogen ion implantation. After nitrogen implantation, samples were depth profiled by AES (Auger Elec tron Spectrometry) to confirm the depth distribution of the implanted nitro gen ions. Implanted samples showed increased hardness, wear resistance and surface compressive stress. By using X-ray photoelectron spectroscopy (XPS) , Cr2N phases were found in Orvar Supreme and Sverker 21 samples implanted with nitrogen ions. These two steels have higher content of Cr (5.2% and 12 %), and thus their hardness increase is greater than in the steels with low er Cr content. (C) 2001 Elsevier Science B.V. All rights reserved.