A study of the nanostructure and hardness of electron beam evaporated TiAlBN coatings

TiAlBN coatings have been deposited by electron beam (EB) evaporation from a single TiAlBN material source onto AISI 316 stainless steel substrates at a temperature of 450 °C and substrate bias of − 100 V. The stoichiometry and nanostructure have been studied by X-ray photoelectron spectroscopy, X-ray diffraction and transmission electron microscopy. The hardness and elastic modulus were determined by nanoindentation. Five coatings have been deposited, three from hot-pressed TiAlBN material and two from hot isostatically pressed (HIPped) material. The coatings deposited from the hot-pressed material exhibited a nanocomposite nc-(Ti,Al)N/a-BN/a-(Ti,Al)B2 structure, the relative phase fraction being consistent with that predicted by the equilibrium Ti–B–N phase diagram. Nanoindentation hardness values were in the range of 22 to 32 GPa. Using the HIPped material, coating (Ti,Al)B0.29N0.46 was found to have a phase composition of 72–79 mol.% nc-(Ti,Al)(N,B)1 − x+ 21–28 mol.% amorphous titanium boride and a hardness of 32 GPa. The second coating, (Ti,Al)B0.66N0.25, was X-ray amorphous with a nitride+boride multiphase composition and a hardness of 26 GPa. The nanostructure and structure–property relationships of all coatings are discussed in detail. Comparisons are made between the single-EB coatings deposited in this work and previously deposited twin-EB coatings. Twin-EB deposition gives rise to lower adatom mobilities, leading to (111) (Ti,Al)N preferential orientation, smaller grain sizes, less dense coatings and lower hardnesses

Formation and mechanical characterisation of SU8 composite films reinforced with horizontally aligned and high volume fraction CNTs

Carbon nanotube (CNT) reinforced composites have been identified as promising structural materials for the mechanical components of microelectromechanical systems (MEMS), potentially leading to advanced performance. High alignment and volume fraction of CNTs in the composites are the prerequisites to achieve such desirable mechanical characteristics. In particular, horizontal CNT alignment in composite films is necessary to enable high longitudinal moduli of the composites which is crucial for the performance of microactuators. A practical process has been developed to transfer CNT arrays from vertical to horizontal alignment which is followed by in situ wetting, realign and pressurized consolidation processes, which lead to a high CNT volume fraction in the range of 46–63%. As a result, SU8 epoxy composite films reinforced with horizontally aligned CNTs and a high volume fraction of CNTs have been achieved with outstanding mechanical characteristics. The transverse modulus of the composite films has been characterised through nanoindentation and the longitudinal elastic modulus has been investigated. An experimental transverse modulus of 9.6 GPa and an inferred longitudinal modulus in the range of 460–630 GPa have been achieved, which demonstrate effective CNT reinforcement in the SU8 matrix

A Study of the Nanostructure and Hardness of Electron Beam Evaporated TiAlBN Coatings

TiAlBN coatings have been deposited by electron beam (EB) evaporation from a single TiAlBN material source onto AISI 316 stainless steel substrates at a temperature of 450¿C and substrate bias of -100 V. The stoichiometry and nanostructure have been studied by x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD) and transmission electron microscopy (TEM). The hardness and elastic modulus were determined by nanoindentation. Five coatings have been deposited, three from hot-pressed TiAlBN material and two from hot-isostatically pressed (HIPped) material. The coatings deposited from the hot pressed material exhibited a nanocomposite nc-(Ti,Al)N/a-BN/a-(Ti,Al)B2 structure, the relative phase fraction being consistent with that predicted by the equilibrium Ti-B-N phase diagram. Nanoindentation hardness values were in the range of 22 to 32 GPa. Using the hot-isostatically pressed (HIPped) material, coating (Ti,Al)B0.29N0.46 was found to have a phase composition of 72-79 mol.% nc-(Ti,Al)(N,B)1-x + 21-28 mol.% amorphous titanium boride and a hardness of 32 GPa. The second coating, (Ti,Al)B0.66N0.25, was x-ray amorphous with a nitride + boride multiphase composition and a hardness of 26 GPa. The nanostructure and structure-property relationships of all coatings are discussed in detail. Comparisons are made between the single-EB coatings deposited in this work and previously deposited twin-EB coatings. Twin-EB deposition gives rise to lower adatom mobilites, leading to (111) (Ti,Al)N preferential orientation, smaller grain sizes, less dense coatings and lower hardnesses.JRC.I.4-Nanobioscience

The effect of soaking time after ultrafast heating on the microstructure and mechanical behavior of a low carbon steel

The main objective of this study is to understand the effect of the soaking time during the ultrafast heat treatment of a low carbon steel on its complex multi-phase microstructure, tensile mechanical behavior and properties of individual microconstituents. Tensile tests were performed to determine the macro-mechanical properties. Nanoindentation testing was carried out on individual microconstituents (martensite, recrystallized ferrite and non-recrystallized ferrite) identified a priori via EBSD analysis to measure their properties. It is shown that ultrafast heating combined with short soaking times results in improved macro-mechanical properties due to finer grain size and higher fraction of non-recrystallized ferrite, that has a higher nanohardness than recrystallized ferrite. Prolonged soaking times eliminate the advantages of the ultrafast heat treatment. This occurs because, even though a long soaking time promotes a higher volume fraction of martensite than a short one, it also induces substantial grain growth and complete recrystallization of the ferritic matrix. On the micro-scale, the ferritic grains show two different types of mechanical response. The recrystallized ferritic grains are prone to show pop-in events on the nanoindentation curves that are associated to dislocation nucleation events as a consequence of their low dislocation density, while non-recrystallized ferritic grains demonstrate a continuous response. The relationship between microstructure and mechanical properties on the macro- and micro-scales is discussed with respect to the microstructure, which in turn strongly depends on the applied heating rate and soaking time. A general recipe for microstructural design to improve the tensile mechanical behavior of low carbon steels implementing controlled heating and soaking conditions is outlined

Hard and Superhard TiAlBN Coatings Deposited by Twin Electron-Beam Evaporation

Superhard nanostructured coatings, prepared by plasma-assisted chemical vapour deposition (CVD) and physical vapour deposition (PVD) techniques, such as vacuum arc evaporation and magnetron sputtering, are receiving increasing attention due to their potential applications for wear protection. In this study we report the synthesis and characterisation of PVD nanocomposite Ti-Al-B-N coatings deposited by electron-beam (EB) evaporation. Coatings were deposited onto Si (100), AISI316 and M2 substrates by co-evaporating Ti and hot isostatically pressed Ti-Al-B-N material, consisting of a mixture of 50 wt.% TiB2, 30 wt.% BN and 20 wt.% AlN, from a thermionically enhanced twin crucible EB evaporation source in an Ar plasma at 450°C. A combination of optical emission spectroscopy and partial pressure control was utilised to control the evaporation rates and hence the composition in the coating. The coating stoichiometry, relative phase composition, nanostructure and mechanical properties were determined using X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), in combination with transmission electron spectroscopy (TEM) and nanoindentation measurements. Al (app. 10 at.% in coatings) was found to substitute for Ti in the cubic TiN structure. The formation of nanocrystalline (Ti,Al)N grains separated by an intergranular amorphous BN phase was observed. (Ti,Al)B0.14N1.12 coatings, consisting of app. 90 mol% (Ti,Al)N and app. 10 mol% BN with an average (Ti,Al)N grain size of 26 nm, showed hardness and elastic modulus values of 40 and 360 GPa, respectively. These coatings retained their mechanical properties for more than 90 months at room temperature in air, comparing results gathered from eight different nanoindentation systems and one laser acoustic surface wave method. Vacuum annealing experiments revealed a moderate, but significant, increase in hardness to 45 GPa for (Ti,Al)B0.14N1.12 coatings. Independent of the composition, all coatings examined exhibited structural stability in vacuum to temperatures in excess of 900°C.JRC.I.4-Nanotechnology and Molecular Imagin

Nanostructural Studies of PVD TiA/B Coatings

TiAlB coatings with different compositions were deposited by co sputtering from TiAl and TiB2 targets onto AISI316 stainless steel substrates at a temperature of 170 C. The stoichiometry and nanostructure have been studied by xray photoelectron spectroscopy (XPS), xray diffraction (XRD) and transmission electron microscopy (TEM). Analysis of the XPS spectra suggests the presence of phases in agreement with the equilibrium TiAlB phase diagram. Diffraction studies (XRD and TEM) indicate that coatings with B/Al ratios 6 are amorphous, while coatings with B/Al ratios 6 exhibit a nanocomposite structure with average TiB2 grain sizes of 2-3 nm for the highest B/Al ratio of 16. Nanocomposite coatings show significantly improved H/E ratios which is beneficial when protecting soft steels and light alloys. .JRC.I.4-Nanotechnology and Molecular Imagin

High temperature nanoindentation response of RTM6 epoxy resin at different strain rates

This paper explores the feasibility of characterizing the mechanical response of the commercial aerospace grade epoxy resin RTM6 by nanoindentation tests at varying temperatures and strain rates. Since glassy polymers exhibit time-dependent mechanical properties, a dynamic nanoindentation technique was used. This method consists on superimposing a small sinusoidal force oscillation on the applied force. Viscoelastic properties are then characterized by their storage and loss moduli, whereas the visco-plastic response of the material can be associated to its hardness. In such experiments, thermal stability of the measuring technique is critical to achieve a low thermal drift and it becomes increasingly important as the measuring temperature increases. Our results show that conventional methods applied for drift correction in nanoindentation of inorganic materials are not applicable to glassy polymers leading to physically inconsistent results. We propose a method for drift correction based on the hypothesis that viscoelastic modulus should be a function of the applied load and frequency but independent of the global strain rate. Using this method, it was possible to determine the viscoplastic properties of RTM6 between RT and 200 °C.Fil: Frontini, Patricia Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); Argentina. Universidad Nacional de Mar del Plata. Facultad de Ingeniería; ArgentinaFil: Lotfian, S.. IMDEA Materials; EspañaFil: Monclus, M.A.. IMDEA Materials; EspañaFil: Molina Aldareguia, J.M.. IMDEA Materials; Españ

The effect of temperature and strain rate on the grain boundary sliding in a CM247 LC Ni-based superalloy processed with laser based powder bed fusion

The current work explores the meso-scale deformation behaviour of an additively manufactured CM247 LC at room and high temperatures. In particular, the study focuses on assessing grain boundary sliding (GBS), which can play a crucial role in the high-temperature deformation of superalloys. Specific samples were produced using the Laser Based Powder Bed Fusion technique (PBF-LB), heat treated and tested under monotonic compression in a Gleeble® system. Compression tests were carried out in a wide temperature range at two strain rates and the effect of testing parameters on GBS activity was studied. A thorough microstructural characterization of the PBF-LB material using EBSD and TEM revealed a γ/γ’ microstructure consisting of columnar grains decorated with Hf-rich MC carbides without any segregations of alloying elements. Qualitative and quantitative analysis of GBS was performed using FEG-SEM and AFM, and contribution of GBS into plastic deformation was estimated. It was demonstrated that GBS is activated at 760 °C. A direct correlation between the contribution of GBS into plastic deformation and testing temperature was found, while strain rate has the opposite effect. The highest GBS contribution (∼32%) was recorded at 1093 °C/10−3 s−1. Finally, intergranular microcracking at triple junctions and along grain boundaries was observed when the material was tested at the highest temperatures (871 °C and 1093 °C). The effect of the temperature and the strain rate on the GBS activity in the PBF-LB material is discussed

Effect of layer thickness on the mechanical behavior of oxidation-strengthened Zr/Nb nanoscale multilayers

The effect of bilayer thickness (L) reduction on the oxidation-induced strengthening of Zr/Nb nanoscale metallic multilayers (NMM) is investigated. Zr/Nb NMMs with L = 10 and 75 nm were annealed at 350 °C for a time ranging between 2 and 336 h, and the changes in structure and deformation behaviour were studied by nanoscale mechanical testing and analytical electron microscopy. Annealing led to the transformation of the Zr layers into ZrO2 after a few hours, while the Nb layers oxidised progressively at a much slower rate. The sequential oxidation of Zr and Nb layers was found to be key for the oxidation to take place without rupture of the multilayered structure and without coating spallation in all cases. However, the multilayers with the smallest bilayer thickness (L = 10 nm) presented superior damage tolerance and therefore structural integrity during the oxidation process, while for L = 75 nm the volumetric expansion associated with oxidation led to the formation of cracks at the interfaces and within the ZrO2 layers. As a result, the nanoindentation hardness increase after annealing was significantly higher for the nanolaminate with L = 10 nm. Comparison between nanoindentation and micropillar compression behaviour of the oxidised NMMs demonstrates that the hardness increase upon oxidation arises from the contribution of the residual stresses associated with the volume increase due to oxidation and to the higher strength of the oxides