R.J. Rodríguez

Tribological behaviour of hard coatings deposited by arc-evaporation PVD

Hard coatings deposited by arc-evaporation PVD are adequate solutions for increasing the lifetime of tools and components commonly employed in many different industrial applications. The present paper reports a comparative study of the tribological properties of the most employed hard coatings like TiN, TiCN, TiAlN, CrN and ZrN. In this study, microhardness tests were carried out by using a microindenter. Friction and wear tests were carried out by using a ball-on-disk tribometer and an optical profilometer. AUGER and XPS techniques were employed to measure the stoichiometry and thickness of the different films.

TRIBOLOGICAL PROPERTIES OF ION IMPLANTED ALUMINUM ALLOYS

Abstract Ion implantation of Aluminum is a useful technique to improve hardness and tribological properties. This paper reports on a comparative study of modifications produced by Nitrogen implantations on three different Al commercial alloys. Different Nitrogen doses have been implanted, hardness and wear tests have been carried out to investigate the influence of implantation parameters. Tribological changes are referred to implantation dose and to thermal post-treatments, as well as to testing conditions. Applications are relevant in aeronautical and moulding sectors.

Corrosion behaviour of rare earth ion-implanted hot-dip galvanised steel

Abstract The corrosion and oxidation behaviour of many metallic materials can be modified by ion beam bombardment of their top surface layers. Mechanical and chemical mechanisms co-operate to prevent the progress of corrosion. Rare earth ions have already been employed to avoid high-temperature oxidation of stainless steels and other technological alloys. This paper extends the use of lanthanides to improve the corrosion resistance properties of galvanic layers. By using a mass-analysed ion implanter, different doses of La+ and Ce+ have been implanted at 150 keV in two kinds of galvanic layers: hot-dip galvanised steel samples and galvannealed steel samples. Morphological changes were observed by scanning electron microscopy (SEM), and these are different depending on the substrate, the kind of ion and implanted dose. The study of polarisation curves in NaCl solutions shows that ion implantation clearly improves the corrosion behaviour of ion-implanted layers for the hot-dip galvanised layers, but not as clearly for the galvannealed, La+ implantation being the most effective means.

Nitrogen ion implantation on group IVb metals:: chemical, mechanical and tribological study

This paper reports the study of the effects induced by nitrogen implantation on metals of the IVb group. Different doses of atomic and molecular nitrogen have been implanted on titanium, zirconium and hafnium samples to investigate their reactivity towards nitrides precipitation. Microhardness, friction and wear tests have been carried out. An increase in microhardness was found where, in some cases, was greater than 80%. Moreover, they were observed improvements in the wear resistance and a decrease in the friction coefficient. XPS analysis and AES profiles have been performed on all the implanted samples. The N1s XPS spectra show a binding energy corresponding to the nitride formation which is thought as the main cause of the mechanical and tribological improvement.

Modifications of the stainless steels passive film induced by cerium implantation

In this work X-ray photoelectron spectroscopy studies and cyclic voltammetry are combined to elucidate the effect of Ce implantation on the formation and evolution of passive layers generated on AISI 430 and AISI 304L steels in alkaline medium. The passive films develop in implanted steels result thinner and less defective than in unimplanted. This result is interpreted in terms of a cerium-induced inhibition of the passive film re-oxidation (formation of iron and chromium oxides). The main difference between the behaviour of the two types of steel (ferritic and austenitic) seems to be related to the enrichment in nickel promoted by cerium in the outermost layer of AISI 304L.

Modification of surface mechanical properties of polycarbonate by ion implantation

Abstract Industrial use of polymers ranges across a broad field of structural, mechanical, electrical and optical applications. In many situations, e.g. in biomedical or optical uses, wear resistance is one of the main requirements. Ion bombardment of polymers is thought to have great potential for improving some surface mechanical and tribological properties. In particular, high-energy bombardment of light ions is reported to produce relevant increases in hardness and wear resistance. The reason seems to be cross-linking effects induced by the dominant mechanism of the stopping power: electronic loss of energy (for heavier and slower ions, nuclear loss of energy produces breakage of polymer chains and a decrease in hardness). This paper presents a study on the effects induced by implantation of light ions on polycarbonate used in optical applications. Different doses below 10 16 ions/cm 2 of hydrogen, deuterium, nitrogen and silicon were implanted and microindentation tests were carried out. Although results showed harder surfaces in all cases, except for silicon implantation, the biggest increases in hardness (by a factor three) corresponded to hydrogen and deuterium implantation at high doses. The paper studies the correlation between these results and the estimated electronic energy loss. The optical transmittance was also measured.

Tribological properties of Fe and Ni base alloys after low energy nitrogen bombardment

Abstract In this paper we investigate the influence of a low energy-high flux nitrogen implantation treatment on the structure and tribological properties of two commercial alloys of interest for industrial applications (AISI 316 and INCONEL600). Nitrogen ion implantations were carried out at 400 °C with a current density of 1 mA/cm2, an accelerating voltage of 1.2 kV and a processing time of 1 h. XRD measurements show clearly the presence of an expanded fcc structure in both alloys AISI316 and INCONEL600. The depth profiles measured by GDOS indicate a high nitrogen content on several microns in all these alloys. It is found that the hardness measured under a 2 mN load increases by a factor of 3,4 for AISI316 and 2 for INCONEL600. Friction and wear tests conducted under a normal load of 1 N with tungsten carbide and 100C6 steel balls show no significant change of the friction coefficient whatever the relative humidity during the test but an important wear resistance improvement is observed for both alloys. The results are discussed in relation with the thickness of the nitrided layer and the microstructural modifications induced by this treatment.

Successive ion implantation of high doses of carbon and nitrogen on steels

Abstract HSS and stainless steel samples were successively implanted with high doses of carbon and nitrogen. Different sequences of implantation (C + , C + +N 2 + , N 2 + +C + and N 2 + +C + +N 2 + ) were carried out in order to achieve C x N y layers of ultra-high hardness. The bonded states of carbon and nitrogen were studied by XPS spectroscopy. The tribological behaviour was measured by means of ball-on-disc and microhardness tests. The microhardness tests showed that increases in hardness are highly influenced by the implantation order. None of the sequences tested led to a hardness increase higher than that for simple carbon implantation. When nitrogen was implanted into carbon-implanted steel, the result was a huge decrease in surface hardness. Ion implantation of high doses of nitrogen and carbon brought about a decrease in the friction and wear coefficients. The samples for which carbon was implanted in the last step showed the lowest friction and wear coefficients.

Modification of corrosion properties of titanium by N-implantation

Abstract Nitrogen implantation in titanium has been carried out at 125 and 100 keV with nominal doses between 4 × 1017 and 8 × 1017 ions cm−2, respectively. Surface characterization by Auger electron spectroscopy has demonstrated the presence of a TiN layer near the surface, which increased the surface hardness from 300 to 1000 HV. From the corrosion viewpoint, N-implantation has little effect in saline solutions, although a slight increase of corrosion resistance could be achieved. In acid solutions, impedance data show that the low frequency impedance of the implanted alloy was higher than that for pure titanium. The capacitance value was similar for all the implanted materials, being somewhat below the value found for unimplanted titanium. These data lead us to conclude that resistance is conferred by the surface formation of titanium nitride, rather than a surface oxide layer. No differences have been found in the corrosion behaviour of samples processed at doses of 4 × 1017 and 8 × 1017 ions cm−2.

The search for new applications of ion implantation treatments

Abstract Recent advances in industrial treatments using ion beams have been made possible by new equipment designs and the development of new techniques (such as ion-beam-assisted deposition (IBAD)). Simultaneously, much effort must be focused on the search for new applications in order to exploit the possibilities of conventional high energy (100–200 keV) ion bombardment. Some case studies are proposed as examples of this task: machining tools for composite materials in the aeronautical industry and coining dies employed in coin and medal manufacture. Tools for machining composite materials are made of HSS steel or Co cemented WC. Nitrogen implantation of the steel tools and titanium implantation of the tungsten carbide tools are demonstrated to be the best techniques for increasing the tool lifetime (by threefold for the particular applications investigated). Coining dies are usually made from tool steels, and hard chromium coatings are regularly employed to achieve wear-resistant surfaces. Nitrogen implantation of chromium layers leads to a fourfold increase in the lifetime. Metal implantation (Cr + , Ti + , Ni + , Mn + ) of dies without hard chromium coatings gives similar results. The food industry is the third field considered in this paper, and some examples of tool implantation (nitrogen in tool steel) are given as a solution to avoid maintenance. This work examines these case studies, with particular attention given to the wear mechanisms and compound formation in the surface layers.