A. Lanzutti

Atomic layer deposition: state-of-the-art and research/industrial perspectives

Abstract Interest on nanometric conformal coatings is currently growing across a wide range of applications, from electronic components to corrosion protection, chemical barriers or even wear decrease. Currently, atomic layer deposition (ALD) is one of the most promising nanometric deposition technologies: it offers the possibility to obtain conformal coatings even on very complex tridimensional substrates, with a strict thickness tolerance. During an ALD cycle, only one molecular layer is deposited on the substrate surface, enabling the theoretical possibility to tailor the composition of the deposit up to molecular resolution. In the first part of this review, a brief history of ALD is presented to better understand the evolution of the technique during the past five decades; in the second part, a short description of the main ALD techniques is given, considering their main advantages and drawbacks. In the third part, a short review about ALD applications is presented, and in the fourth part the most useful and used instruments for the analysis and characterization of ALD are listed; some results are discussed and particular emphasis on the corrosion protection of different metallic alloys of common industrial interest is given.

Resistance to localized corrosion of pure Ni, micro- and nano-SiC composite electrodeposits

The aim of this work was the production and characterization of composite Ni matrix electrodeposits. Pure Ni, micro- and nano-SiC Ni matrix composite deposits have been produced from a Watts’s-type electroplating bath under both direct (DC) and pulse current (PC) conditions. The obtained deposits have been characterized regarding their microstructure by scanning electron microscopy (SEM) observations on both top surface and cross-section and their SiC content by energy-dispersive X-ray spectrometry (EDXS) and glow discharge optical emission spectrometry (GDOES) analyses. The resistance to localized corrosion has been evaluated by exposing the samples in a salt spray cabinet and performing visual observation as well as electrochemical impedance spectroscopy (EIS) measurements every five days. Both the use of PC and the codeposition of the nanoparticles lead to a grain refinement of the Ni matrix. The use of the PC did not influence in a significant way the resistance of the pure Ni deposits to the localized corrosion. The incorporation of micro-SiC led to a decrease of the corrosion resistance for the deposits produced under DC, while the microcomposites produced under PC presented a corrosion resistance comparable to the pure Ni deposits. The nanocomposites presented the highest corrosion resistance due to the more compact and fine-grained microstructure. EIS revealed the presence of a localized corrosion attack earlier than the visual observation, giving useful information about the failure mechanism.

Chemical and Mechanical Characterization of Thermal-Multilayered Al2O3 Atomic Layer Depositions on AISI 316L Stainless Steel

In this work, three different nanometric, multilayered Al2O3 coatings, obtained by alternating two different deposition temperatures, have been applied on AISI 316L stainless steel by atomic layer depositions. The coating morphology has been investigated using atomic force microscopy (AFM) and scanning electron microscopy. Thickness analysis has been performed using AFM and glow discharge optical emission spectrometry (GDOES). In-depth compositional profiles have been performed using GDOES. The corrosion protection has been investigated using polarization curves in aggressive NaCl electrolyte. All variations of the coatings appeared to be adherent to the substrate with thickness in the range of the nominal values. Compositional analysis confirmed the presence of the Al2O3 layers. Vickers indentations used to evaluate coating adhesion showed that all coatings have a good adhesion to the substrate and in particular the amorphous/crystalline 20-nm-thick coating showed almost no sign of coating delamination. All samples show a higher corrosion resistance when compared with bare AISI 316L.

Steel Contamination of Biomedical Titanium Alloys during Hot Isostatic Pressing Treatments

Hot isostatic pressing (HIP) is an industrial treatment for the consolidation of metallic components. In the biomedical field, HIP processes are applied to titanium alloys fabricated by other sintering techniques to reduce residual porosity and improve the mechanical characteristics. Stainless steel sheet encased HIP processes are used when surface open porosities are present, in particular for powder metallurgy products or when nitrogen absorption is a major concern. In these circumstances, localized steel contamination may occur on the titanium surface. Contamination could be easily avoided using titanium encasing sheets, but these are rarely applied in industrial practice. In this work, Grade 2 and Grade 5 titanium have been treated with a standard HIP process. During treatment both alloys have been kept in contact with stainless steel casement, causing diffusion of elements inside the titanium. Samples have been investigated using two-dimensional profilometry and scanning electron microscopy. Qualitative and semi-quantitative compositional analyses have been performed using energy-dispersive x-ray spectroscopy and glow discharge optical emission spectrometry (GDOES). Microstructural analyses have been obtained after GDOES plasma etching in order to avoid any further surface preparation and easily obtain comparable results from the two different alloys. Localized potentiodynamic polarization curves were obtained on the different regions of the samples using microcell equipment. Both alloys were contaminated by stainless steel elements in the stained regions. A reduction in the corrosion resistance of the alloys has been observed due to the contamination. The experimental setting demonstrated the corrosion susceptibility of stainless steel contaminated biomedical titanium alloys after HIP, even if the passive behavior of titanium was not completely compromised.