Key Engineering Materials Vol. 813

Abstract: The goal of this work is to evaluate a common final sterilization technique with EtO by measuring its effect on the physicochemical properties of PVD deposited TiN/TiO₂ coatings on Ti-5Al-4V alloy. As the effectiveness of EtO sterilization corresponds to the operation parameters (temperature, duration, humidity, etc.), two different exposure cycles (cool (MS) at 37 °C for 220 min gas expose and warm (SS) at 55 °C for 100 min expose) were examined. SEM analysis revealed that the surface morphology of the coatings was not changed after both MS and SS treatments. In contrast to Ti 2p and O 1s peaks determined by XPS analysis, C 1s peak of TiO₂ layer decreased with increasing sterilization temperature while the percentage contribution of Ti-OH in O 1s increased. This affected the surface hydrophilicity and free energy that increased from 47.37 for the control sample to 50.77 mJ m^-2 in the case of SS specimen. Additionally, EtO sterilized samples demonstrated decreased values of corrosion and passivation current densities in simulated body fluid (pH 7.4) at 37 ± 0.05 °C as opposed to the control sample. The results indicate the suitability of both mild and severe EtO sterilization methods for improvement of the desired physicochemical properties of gradient TiN/TiO₂ coatings.

Abstract: In glass industry, laser cladding is an innovative surfacing technique allowing to deposit a layer of nickel to protect glass mold against corrosion, abrasion and thermal fatigue. This method (powder fusion by projection), well known in additive manufacturing represents a real technological leap for the glass industry. But during laser cladding of Ni-based powder on gray cast iron, cracks can be observed for some process conditions. These cracks are often due to the Heat Affected Zone that creates structural stresses linked to the development of a martensitic structure in the ferritic matrix of the lamellar graphite cast iron. The aim of this work is to observe the impact of laser cladding (without substrate pre-heating usually employed to limit cracking) on the coating behavior but also on the flake-graphite cast iron substrates. The microstructure and the mechanical properties were studied (SEM and microanalysis, microhardness) around the interface cladding/substrate. Also, the impact of the processing parameters (power P (1500-2300 W), scanning speed v (2.5-10 mm/s) and powder feeding rate PFR (24.5-32.5 g/min) was studied by using the ANOVA (ANalysis Of VAriance) technique. It has been observed that laser cladding on graphite cast iron is possible without cracks by limiting the linear energy induced by the process. Also, an optimization of the processing parameters (P, v, PFR) in order to obtain the industrial expected geometry of the coating has been proposed.

Abstract: Laser metal deposition (LMD) is an additive manufacturing process highly adaptable to medium to large sized components with bulky structures as well as thin walls. Low surface quality of as-deposited LMD manufactured components with average roughness values (R_a) around 15-20μm is one of the main drawbacks that prevent the use of the part without the implementation of costly and time-consuming post-processes. In this work laser re-melting is applied right after LMD process with the use of the same equipment used for the deposition to treat AISI 316L thin walled parts. The surface quality improvement is assessed through the measurement of both areal surface roughness S_a(0.8mm) QUOTE and waviness W_a QUOTE (0.8mm) parameters. Moreover, roughness power spectrum is used to point out the presence of principal periodical components both in the as-deposited and in the re-melted surfaces. Then, the transfer function is calculated to better understand the effects of laser re-melting on the topography evolution, measuring the changes of individual components contributing to the surface roughness such as the layering technique and the presence of sintered particles. Experiments showed that while low energy density inputs are not capable to properly modify the additive surface topography, excessive energy inputs impose a strong periodical component with wavelength equal to the laser scan spacing and directionality determined by the used strategy. When a proper amount of energy density input is used, laser re-melting is capable to generate smooth isotropic topographies without visible periodical surface structures.

Abstract: The manufacture of metal parts requires post processing in most cases. These processes include heat treatment for releasing of the residual stresses resulting on the metal surface due to the excessive mechanical forces applies to cut the metal during machining, i.e. milling, turning and drilling. Another example would be the polishing of parts using different techniques. In predominant, polishing is used enhance the part’s roughness to improve the friction coefficient, to give the parts a better view and most important is to adjust the final dimensional accuracy in the microns and sub-microns scale. Traditional polishing methods include the mechanical polishing by using abrasive media or grinding machines, chemical polishing which has the benefit of reaching the inaccessible features although this method requires longer processing time in addition to the impact on environment. Sometimes the thermal deburring method is also applied for the chamfer of sharp edges and corners. In the recent years, the laser polishing technique exhibits interesting efforts and results regarding reproducibility, high control over the processing parameters which allow for the processing of different metals and non-metals materials in addition to the ultrashort processing time. This study is focusing on the laser surface polishing of metal parts, its potentials and limitations. In this study, laser surface polishing using CO₂ laser beam irradiation was implemented on stainless steel Additive Manufactured produced surfaces. Two design of experiment models were implemented for the optimization of the main laser input processing parameters. The processing parameters examined were the laser beam power, the scanning speed, the number of laser scan passes, the percentage overlap of the laser tracks between the consecutive passes and the laser beam focal position. The characterization of the measured surface roughness and the modified layer microstructure were carried out using scanning electron microscopy (SEM) and 3D optical.

Abstract: Additive Manufacturing (AM) is one of the Key Enabling Technologies (KET’s) in Industry 4.0. One of the most worldwide used technologies is Fussed Deposition Modelling (FDM), a technology commonly used for domestic purposes. However, it could become a profitable option for industrial applications such as protections parts, flexible clamping systems or large volume parts. One of the issues that keeps this technology away from the mainstream industry is the lack of dimensional accuracy and the appearance of layer deposition defects that are produced as a consequence of the nature of the process. Those defects are usually reduced using chemicals post treatments. However, this option considerably increases the cost of the part as well as it environmental impact for big size parts. This work studied machining procedures as sustainable post-operation in order to reduce FDM dimensional and superficial defects. For this purpose, Acrylonitrile-Butadiene-Styrene (ABS) parts produced by FDM were machined using different machining strategies. Parts were perimetral milled using up milling and down milling strategies and finally a face milling operation was performed. The relationship between the layer height and the directionality of the layers in machining results was analyzed, in terms of surface quality (Ra, Rz, Rsm) and dimensional accuracy. Rz and Rsm results had been analyzed to verify that the grooves produced in FDM process disappeared. Ra values were reduced by up to ten times after milling process. Dimensional accuracy is increased by up to 50% while the removed rate was kept in a maximum of 7%. Additionally, removed material can be reused by means of proper chip extraction system, favoring the performance of the resources.

Abstract: Damage due to atmospheric corrosion on metal structures is a significant aspect for both the design of new constructions and the maintenance of existing buildings. The paper discusses the corrosion depth trends for steel structures comparing an experimental campaign of measurements, given by Fratesi in 2002, with literature 2^nd level models calibrated from experiments on immersed elements, literature models based on testing in atmosphere and standard codes (i.e. EN ISO 9224 and EN 12500). Results show a significant variability of values using different models and codes. In addition, the paper underlines that literature studies and codes neglect specific models for nineteenth-century “wrought iron” constructions, that are very sensitive to corrosion phenomena. Based on this, the paper discusses results obtained by a new interpretative model developed by authors for the prediction of corrosion depth on wrought iron structures.

Abstract: The influence of nitriding temperature (900 and 850°C) and partial pressure of nitrogen (10⁵ and 1 Pa) on morphology and phase structural state of modified surface layers of commercially pure titanium (cp-Ti) was determined. It was shown that nitrided titanium provided much better anti-corrosion protection than nitrided Ti-6Al-4V alloy, and its corrosion resistance increased with decreasing nitriding temperature and partial pressure of nitrogen.

Abstract: In the present study, sintered austenitic stainless steel type 316L was laser surface alloyed with Inconel 625 powder by the fibre optic laser. The Inconel 625 spheroidal powder of grain size 60-150 μm was introduced by the coaxial feeding head directly to the liquid metal, during laser surface alloying. The process parameters were selected to melt and fully dissolve alloying powder into the alloyed surface. As a result of laser alloying, the porosity of sintered stainless steel was eliminated, a uniform distribution of nickel and molybdenum in the entire alloyed zone was obtained. The alloyed surface shows fully austenitic microstructure of 17%Cr, 18%Ni, 3%Mo. The superficial hardness, microhardness and surface wear resistance were significantly improved in respect to an untreated substrate material. The presented technique of laser surface alloying can be easily applied for sintered austenitic stainless steel components where selected component surfaces require an improved surface performance.

Abstract: Bioactive coatings have predominately been explored through plasma spray; but this technique has associated heat and melting of the feedstock materials thereby degrading the novel bioactive properties of hydroxyapatite (HA), as well as deteriorating the adhesion of the coating to the implant. The current study discusses a novel approach to producing biocompatible coatings that have been deposited at temperatures well below their melting point. The cold spray process was used to deposit 100 wt.% titanium (Ti) and composite powders with 80 wt% titanium (Ti) and 20 wt% hydroxyapatite (HA) onto Al6061, 316SS and Ti-6Al-4V substrates with the aim of achieving well-bonded homogeneous coatings; the effect of process parameters and substrate material was investigated. Preliminary results indicate the phase composition of the HA remained the same before and after synthesis of coating. Dense composite coatings were obtained with thicker coatings yielding the least amount of total porosity.

Abstract: The main purpose of this publication was to describe in details the correlation between microhardness and scratch test results of the tested coatings deposited by PVD (Physical Vapour Deposition) method on the cavitation generators working in cavitation environment. First coating in the form of composite layer CrN+WC/C and second WC/C plate coating were deposited on two selected steels which already are used or can be use on constructional elements working in a cavitation wear environment. Steel P265GH is commonly used for pressure devices working at elevated temperatures, with a ferritic – pearlitic structure, and the other tested steel from a group of stainless steels, i.e. chromium – nickel X2CrNi18-9 (304L) steel with an austenitic structure due to its corrosion resistance, it can also be used in these conditions. The tests results obtained allow to conclude composite CrN+WC/C coating exhibit better adhesion than WC/C plate coatings deposited on the both tested constructional steels. A critical load value for the CrN+WC/C coating spans between 29 and 34N and is 35-40% higher than for the plate WC/C coating.