Due to the expansion of the use of powder bed fusion metal additive technologies in the medical field, especially for the realization of dental prostheses, in this paper, the authors propose a comparative experimental study of the mechanical characteristics and the state of their microscale surfaces. The comparison was made from material considerations starting from two dental alloys commonly used to realize dental prostheses: Ni-Cr and Co-Cr, but also technologies for obtaining selective laser melting (SLM) and conventional casting. In addition, to compare the performances with the classical casting technology, for the dental prostheses obtained through SLM, the post-processing stage in which they are in a preliminary finishing and polished state was considered. Therefore, for the determination of important mechanical characteristics and the comparative study of dental prostheses, the indentation test was used, after which the hardness, penetration depths (maximum, permanent, and contact depth), contact stiffness, and contact surface were established, and for the determination of the microtopography of the surfaces, atomic force microscopy (AFM) was used, obtaining the local areal roughness parameters at the miniaturized scale—surface average roughness, root-mean-square roughness (RMS), and peak-to-peak values. Following the research carried out, several interesting conclusions were drawn, and the superiority of the SLM technology over the classic casting method for the production of dental prostheses in terms of some mechanical properties was highlighted. At the same time, the degree of finishing of dental prostheses made by SLM has a significant impact on the mechanical characteristics and especially the local roughness parameters on a miniaturized scale, and if we consider the same degree of finishing, no major differences are observed in the roughness parameters of the surfaces of the prostheses produced by different technologies.

The tribological properties of the friction couple materials have a major influence on the brake system operation and its failure. One of the main phenomena associated as a symptom of failure in the brake system are the noises and vibrations produced during braking. The stick-slip phenomenon is attributed as the cause of these noises and vibrations. The stick-slip phenomenon usually appears at low and very low sliding speeds and is described as intermittences in the friction process caused by the differences between the values of the kinetic and the static friction coefficients. The present paper addresses an investigation about the influence of the static and kinetic friction on the occurrence of above mentioned noises and vibrations in the disc brake system. For this, extensive experimental work was performed on a laboratory tribometer in the form of pin-on-disc tests, where the pin was manufactured out of an automotive brake pad and the disc was manufactured out of an automotive grey cast iron brake disc. The results highlight the effects of the sliding speed and contact pressure on the friction coefficient and its influence on the brake noises and vibrations caused by the stick-slip phenomenon.

Nowadays, due to the carcinogenic effects of chrome, replacing the hard chromium used for hydraulic components like rods and cylinders is becoming increasingly requested. Thermally sprayed coatings are a solution to the problem; however, proper understanding and characterisation of their tribological behaviour are essential for the successful exploitation of surface engineering. Thus, the main aim of this study is to evaluate the abrasive wear characteristics of two metal sprayed layers, tungsten carbide (WC) deposited through the high-velocity oxygen fuel coating (HVOF) method and Fe alloy coating deposited through thermal spraying with an electric arc with a wire-electrode G3Si1, and compare the results with those of an electrochemically deposited hard chromium layer. Their wear resistance is then related to their hardness. The results highlight the tribological performances of the thermally sprayed coatings. The HVOF WC10Co4Cr coating has a wear coefficient and a material wear volume that are hundreds of times lower than those of the other two coatings.

In this work, three hydraulic fluids—a paraffinic mineral hydraulic oil (H46) and two biodegradable oils (HETG46—hydraulic oil based on natural esters and HF-E46—hydraulic oil based on synthetic esters derived from fatty acids extracted from vegetable oils)—were studied in both fresh and thermally degraded states. The study of these oils was performed both from a rheological and spectroscopic point of view using Fourier transform infrared spectroscopy (FTIR). The thermal degradation process consisted of repeated heating and cooling cycles at four different temperatures for 15 min performed eight times. The rheological characterization was initially performed for the fresh oils, and the results obtained were compared with those of the thermally degraded samples. For the rheological characterization, two rheological models (the Newtonian model and the power law model) were used, following which the rheological parameters were determined. At the same time, this work highlights how thermal degradation influences the rheological behavior and chemical structure of hydraulic fluids. The results obtained showed that the Newtonian model best describes the rheological behavior of the analyzed fluids. From a chemical point of view, FTIR analysis did not reveal significant changes between fresh fluids and those subjected to thermal degradation.

An alloy YPbSn10 used for antifriction applications was synthetized in a furnace and the structure was improved by a microalloying technique. The elements chosen for microalloying were Ca 2%wt and Mg 2%wt. The microalloying technique proved to have good results in producing alloys with homogeneous composition, with a good distribution of the hard phase. The alloys were produced in a furnace and samples were collected and investigated. The structural properties were investigated using an SEM technique with EDS analyses and XRD to identify the compounds formed during alloying. The tribological properties were investigated to see the improvement obtained in this area. The results revealed a homogeneous composition for both samples, alloyed with Ca or with Mg, and the friction coefficient was reduced after the microalloying with almost 20%.