VII. Ion-implanted metalsModification of the fatigue behavior of copper and stainless steel by ion implantation
Abstract
A program was undertaken to study the effect of ion implantation on the fatigue lives of copper and austenitic stainless steel. Neon and nitrogen ions of 2 to 4 MeV were implanted into flat plate flexutral type fatigue specimens using the Dynamitron accelerator at SUNY Albany. By using the rotating target method, uniformity of the depth of lattice defects and of the dose of the implanted species was obtained. Control specimens (not implanted) and ion-implanted specimens were fatigue-cycled in flexture under constant and identical displacement and frequency conditions until failure. A substantial improvement was observed in the fatigue life for the Ne-implanted copper when fatigued in air. The stainless steel specimens implanted with N which were fatigued in argon did not show a measurable increase in fatigue life. In order to investigate whether the fatigue life was influenced by the modification of the near-surface deformation characteristics, e.g., by creating barriers against slip activity and the easy formation of persistent slip bands, a study of the most highly stressed fatigue specimen surfaces was undertaken by scanning electron microscopy. The results on both the copper and stainless steel specimens support the concept of slip modification in the implanted layer. While the fatigued control specimens exhibited extensive surface ridges which appear to be extrusions and intrusions from persistent slip bands, the implanted specimens are devoid of such features.
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Cited by (17)
Improvement of the fatigue resistance of materials with thin coatings developed from dynamic ion mixing
1997, Materials Science and Engineering: AA dynamic ion mixing (DIM) technique, which involves a physical vapor deposition (PVD) combined with a simultaneous ion implantation method, has been applied to elaborate adherent NiTi and SiC amorphous thin coatings. Two different metallic materials, a Ti—6Al—4V titanium alloy and a 316L type austenitic stainless steel were used as substrates. The characteristics of such deposits were established by performing scratch-tests and micro hardness measurements, and by measuring their Young's moduli. This process leads to a significant improvement of the fatigue life for both materials, at room temperature, in the low cycle fatigue range. Scanning electron microscopy observations revealed that thin coatings constitute a barrier at the surface which modifies the near surface deformation mode impeding the formation of extrusions—intrusions pairs and strain localization within intense slip bands. Consequently, crack initiation can be considerably delayed or even suppressed. Several factors controlling beneficial effects of DIM treatments on fatigue resistance are pointed out. These factors concern the nature and properties of the coatings and the cyclic deformation processes in the substrates.
Effect of nitrogen implantation on fatigue crack initiation in ferritic Fe-24Cr-4Al alloy
1995, Scripta Metallurgica et MaterialaMultiple ion implantation effects on hardness and fatigue properties of Fe13Cr15Ni alloys
1992, Journal of Nuclear MaterialsEight complex alloys based on the composition Fe13Cr15Ni2Mo2Mn0.2Ti0.8Si0.06C were implanted simultaneously with 400 keV boron and 550 keV nitrogen, and investigated for microhardness changes and bending fatigue life. The dual implantation was found to decrease the fatigue life of all eight alloys although the implantation increased near-surface hardness of all eight alloys. This result was in contrast to the significant improvements found in the fatigue life of four B, N implanted simple Fe13Cr15Ni alloys. It was determined that the implantation suppressed surface slip band formation, the usual crack initiation site, but in the complex alloys, this suppression promoted a shift to grain boundary cracking. A similar phenomenon was also observed when the simple Fe13Cr15Ni alloys were simultaneously implanted with boron, nitrogen and carbon wherein fatigue life decreased, and gain, grain boundary cracks were observed. To test the hypothesis that ion implantation made the overall surface more fatigue resistant but led to a shift to grain boundary cracking, single crystal specimens of the ternary Fe15Cr15Ni were also implanted with boron and nitrogen ions. The fatigue life decreased for the single crystal specimens also, due to concentration of applied stress along fewer slip bands as compared to the control single crystal specimens were applied stress was relieved by slip band formation over the entire gauge region.
Influence of nitrogen ion implantation on tensile behavior of 1018 carbon steel
1992, Thin Solid FilmsIon implantation is shown to be an effective tool for the modification of surface microstructures such that they can have a profound influence on the mechanical properties of metals and alloys. In this paper, the influence of nitrogen ion implantation on tensile behavior of low carbon steel 1018 is reported. The tensile properties of the implanted material are compared with those of the unimplanted counterpart. Implantation was found to decrease the yield strength and marginally improve the ultimate tensile strength. Environmental influence on tensile elongation was less for the implanted material in comparison with the unimplanted counterpart. Fracture was predominantly ductile with evidence of numerous dimples and microvoids. The degradation in yield strength and the improvement in ultimate tensile strength are rationalized on the basis of free dislocations on the surface which promote early yielding and the additional precipitation of nitride particles in the bulk during “aging” that provides increased strengthening.
Ion implantation effects on fatigue properties of Fe-13Cr-15Ni alloys
1992, Surface and Coatings TechnologyBend fatigue tests and microhardness measurements were carried out on eight complex Fe-13Cr-15Ni alloys based on the composition Fe-13Cr-15Ni-2Mo-2Mn-0.2Ti-0.8Si-0.06C, implanted simultaneously with 400 keV boron and 550 keV nitrogen ions to a dose of 2.3 × 1016 ions cm-2 for each ion. For all eight alloys, the dual implantation improved the surface hardness but reduced the fatigue life. Optical microscopy revealed that the implantation suppressed surface slip band formation and slip band crack initiation. Transmission electron microscopy was used to characterize the near-surface microstructures. It is evident that the suppression of slip band formation promoted grain boundary cracking to relieve stresses developed in the grains, thus leading to a reduced fatigue life. A similar study of four simple alloys based on the ternary Fe-13Cr-15Ni indicated that while dual implantation improved fatigue life, up to 250% in one case, triple implantation with boron, nitrogen and carbon ions reduced fatigue life, again owing to a shift to grain boundary cracking. Improvement in fatigue properties of polycrystalline alloys by multiple ion implantation is thus limited by the presence of grain boundaries.
The subject of the present work is the effects of nitrogen ion implantation on mechanical properties of metallic surfaces commonly encountered in machine building, such as electroplated hard chromium, sacrificial phosphate coating on cast iron, and plasmaface-coated hard molybdenum. A unique aspect of the work is that standard production samples, with no special surface preparation prior to the treatment, were investigated. This makes the present results immediately relevant in a production environment.
In the parameter range explored, the treatment resulted in up to 31% wear reduction and 7% friction coefficient reduction for the chromium surface, up to 24% wear reduction and 13% friction coefficient reduction for the phosphate coating, and up to 90% wear reduction (to a tenth of the original value) and 84% surface hardness increase for the molybdenum deposit.
The mechanisms responsible for the observed effects are discussed in detail. Trends in dependences on ion dose and energy permit extrapolation of the obtained data.
These results demonstrate the applicability of ion implantation to unprepared metallic surfaces, and its readiness for immediate practical use.