T.R. Jervis

Structure and mechanical properties of epitaxial TiN/V 0.3 Nb 0.7 N(100) superlattices

Epitaxial TiN/V 0.3 Nb 0.7 N superlattices with a 1.7% lattice mismatch between the layers were grown by reactive magnetron sputtering on MgO(001) substrates. Superlattice structure, crystalline perfection, composition modulation amplitudes, and coherency strains were studied using transmission electron microscopy and x-ray diffraction. Hardness H and elastic modulus were measured by nanoindentation. H increased rapidly with increasing Λ, peaking at H values ≍75% greater than rule-of-mixtures values at Λ ≍ 6 nm, before decreasing slightly with further increases in Λ. A comparison with previously studied lattice-matched TiN/V 0.6 Nb 0.4 N superlattices, which had nearly identical composition modulation amplitudes, showed a similar H variation, but a smaller H enhancement of ≍50%. The results suggest that coherency strains, which were larger for the mismatched TiN/V 0.3 Nb 0.7 N superlattices, were responsible for the larger hardness enhancement. The results are discussed in terms of coherency strain theories developed for spinodally decomposed materials. Nanoindenter elastic modulus results showed no significant anomalies.

NANOINDENTATION OF AG/NI MULTILAYERED THIN FILMS

Nanoindentation was used to study the mechanical properties of Ag/Ni multilayered thin films. Both the hardness and the elastic modulus of the multilayered thin films had values between those for homogeneous Ag and Ni thin films. The trend in the hardness with layer repeat length can be explained by the effects of both the stress and the microstructure. No evidence for interfacial effects on hardness was found. A decrease in modulus at the smallest repeat lengths was compared with literature data on the elastic constants of Ag/Ni multilayers.

Metal film deposition by gas‐phase laser pyrolysis of nickel tetracarbonyl

A new technique for the deposition of nickel metal films by gas‐phase pyrolysis of nickel tetracarbonyl gas is described. A pulsed CO2 laser is used to form a reaction zone adjacent to a cold substrate, resulting in a rapidly quenched film. The technique relies on dielectric breakdown of a mixture of source and carrier gases and therefore lends itself to a variety of source gases and chemistries. Adherence data and compositional and structural analyses are presented.

Effect of nitrogen implantation on the surface hardness of pure aluminum and alloy materials

Abstract Samples of high purity annealed aluminum and 6061-T6 aluminum alloy were implanted with N+ ions at 200 keV at doses of 5, 10, 18, and 28 × 1017 cm−2. Additionally a third sample was implanted with 15 × 1017 cm−2 at 200 keV followed by an implant of 11 × 1017 cm−2 at 100 keV. Implant profiles were analyzed using Rutherford backscattering (RBS). The surface hardness of these samples were measured using a nanoindenter. A substantial increase in surface hardness was observed in all the implanted samples. The thickness and peak hardness of the surface layer were enhanced by dual energy implantation. Beam heating during ion implantation resulted in annealing of the 6061-T6 samples. These effects were confirmed by annealing experiments which produced little change in overall hardness profiles. Large scale cracking of the hard surface layer was observed in low dose pure Al samples. This cracking behavior was altered by annealing.

Effect of excimer laser alloying of Ti on the sliding friction of AISI 304 stainless steel

Dry sliding friction measurements made on titanium layers evaporated on AISI 304 stainless steel in the as-deposited and excimer laser mixed form show a dependence on the film thickness and the amount of mixing. The effect of laser mixing is dependent on the incident fluence with high fluences and/or large numbers of pulses producing surfaces with poor frictional properties. The optimum total fluence depends on the thickness of the surface layer, a result consistent with thorough mixing of the alloyed layer without the surface damage that results from large numbers of pulses.

Crystallization and oxidation behavior of Mo-Si-N coatings

Abstract Mo-Si-N coatings with different nitrogen concentrations were produced by nitrogen alloying simultaneously during sputter deposition from a planar magnetron MoSi 2 target with nitrogen plasma onto steel substrates. The ratio of molybdenum and silicon concentrations was 0.5. The nitrogen concentrations of the samples were 20, 35, and 50 at.% and the concentration profile was uniform througout the film thickness. The initial microstructure at all nitrogen concentrations involved was amorphous and the crystallization temperature was strongly dependent on nitrogen concentration. The sample with 50 at.% N was still amorphous after annealing at 1000°C whereas the sample with 35 at.% N was crystallized at 740-760°C and the sample with 20 at.% N at 660-680°C. Even this was higher than the crystallization temperature of a pure MoSi 2 coating, about 500°C. The oxidation behavior of the Mo-Si-N coatings with 50 at.% N was determined in wet oxidation conditions from 400 to 1000°C by measuring oxygen concentration on the surface using a nuclear reaction 16 O(d,p) 17 O or non-Rutherford scattering of He + . The excellent oxidation resistance of this coating on low carbon steel was confirmed up to 800°C, above which diffusion of nitrogen occurred, resulting in crystallization and degrading of the beneficial properties. The oxidation behavior of the Mo-Si-N coating can be explained in terms of amorphous microstructure and silicon-nitrogen interaction.

Non-Rutherford backscattering analysis of nitrogen content in titanium substrates

Abstract The cross section for 167° backscattering of 4He from 14N in the energy range from 4.5 to 9.0 MeV was measured. The targets were made by evaporating 500 A of zirconium on a carbon substrate and implanting with 1.3 × 1017 N2/cm2 at 33 keV. A large scattering resonance, approximately 80 times Rutherford and FWHM > 200 keV, was found at 8.81 MeV. Titanium samples were irradiated using pulsed excimer laser radiation at 248 nm in nitrogen gas at 1 atm. The nitrogen content was measured using the 14N alpha scattering resonance at 8.81 MeV. For fluences greater than 500 J/cm2, concentrations of nitrogen approaching that of TiN were observed. The thickness of the nitride layer is on the order of 0.35 μm.

Mechanical properties of epitaxial TiN/(V0.6Nb0.4)N superlattices measured by nanoindentation

We have used nanoindentation to measure the mechanical properties of epitaxial TiN/(V0.6Nb0.4)N superlattices, grown on MgO(100), as a function of the wavelength λ. The V/Nb ratio within the VNbN layers was chosen to provide a lattice match with TiN, minimizing effects resulting from coherency strains. For λ≥4 nm, the hardness was found to be significantly enhanced relative to a homogeneous reference film of the same average composition. For λ<4 nm, the hardness decreased to a value close to that of the reference film. The elastic modulus was found to be constant for λ≥4nm, at a value close to that predicted by the law of mixtures. For samples with λ=2.3 and 2.8 nm, there was a 15% decrease in modulus. The observed variations appear not to be an effect of interfacial strain. Possible mechanisms are discussed.

Characterization of the surface oxide formed by excimer laser surface processing of AISI 304 stainless steel

Abstract We have used excimer laser processing in air to grow thick oxide layers on AISI 304 stainless steel and have characterized the resulting oxide layer using a variety of techniques including Mossbauer, Auger, and Rutherford backscattering spectroscopy, X-ray and electron diffraction, transmission electron microscopy, and nuclear reaction analysis. The resulting oxide, which is grown under rapid quenching conditions, has a spinel structure and a complex composition. In particular, a Cr to Fe ratio of approximately one was observed to persist throughout the oxide. Carbon incorporation at approximately 13 at%, presumably from surface contamination, and N at approximately 5 at% were also found.

Excimer Laser Surface Modification: Process and Properties

Surface modification can improve materials for structural, tribological, and corrosion applications. Excimer laser light has been shown to provide a rapid means of modifying surfaces through heat treating, surface zone refining, and mixing. Laser pulses at modest power levels can easily melt the surfaces of many materials. Mixing within the molten layer or with the gas ambient may occur, if thermodynamically allowed, followed by rapid solidification. The high temperatures allow the system to overcome kinetic barriers found in some ion mixing experiments. Alternatively, surface zone refinement may result from repeated melting-solidification cycles. Ultraviolet laser light couples energy efficiently to the surface of metallic and ceramic materials. The nature of the modification that follows depends on the properties of the surface and substrate materials. Alloying from both gas and pre-deposited layer sources has been observed in metals, semiconductors, and ceramics. Surface enrichment of Cr by zone refinement of stainless steel has also been seen. Rapid solidification after melting often results in the formation of non-equilibrium phases, including amorphous materials. Improved surface properties, including tribology and corrosion resistance, are observed in these materials.