Three-dimensional printing is a dynamically developing field of industry. Its main advantage is the small amount of waste, no need to use specialized tools, and easy control of the mechanical properties of the printed model. One of the most popular techniques of 3D printing is FDM. The main factor influencing the mechanical properties of 3D-printed materials is the filling density. The aim of this study was to determine the mechanical properties of porous structures with a porosity gradient of PLA samples printed using the FDM technique. The accuracy of mapping the structures by computed tomography was assessed, and then a static compression test was performed. It has been shown that the strength properties increased with the increase in the filling density. The highest value of compression strength, amounting to 41.2 MPa, was observed for samples made of PLA with an 80% filling degree, whereas the lowest value of compression strength was found in PLA-T samples with a filling degree of 10%, reaching only 0.6 MPa. It was found that not only the core filling density, but also the outer layers, influences the mechanical properties. The assessment of spatial architecture allowed for a qualitative and quantitative assessment. The obtained images from the computed tomograph showed that the designed sample models were correctly reproduced in the entire volume.

The influence of nanohydroxyapatite on the glass transition region and its activation energy, as well as on the tribological and mechanical properties of polyoxymethylene nanocomposites, was investigated using DMA, TOPEM DSC, nanoindentation, and nondestructive ultrasonic methods. It was found that the glass transition for unmodified POM was in the lower temperature range than in POM/HAp nanocomposites. Moreover,ΔCpand activation energy were larger for POM/HAp nanocomposites. Friction coefficient was higher for POM/HAp nanocomposites in comparison to both POM homopolymer and POM copolymer. Simultaneously, the indentation test results show that microhardness is also higher for POM/HAp nanocomposites than for POM. From ultrasonic investigations it was found that the highest values of both longitudinal and transverse propagation waves and Young’s and shear modulus for POM homopolymer (DH) and POM copolymer T2H and their nanocomposites can be attributed to their higher degree of crystallinity in comparison to UH copolymer. Moreover, for POM/HAp nanocomposites with 5% of HAp, ultrasonic longitudinal wave velocity was almost constant even after 1000000 mechanical loading cycles, evidencing an enhancement of mechanical properties by HAp nanoparticles.

In the present study, a titanium cellular lattice structure with a mathematical designed porosity gradient was successfully fabricated using the selective laser melting method. The samples with smooth gradient transition of porosity of between 60% and 80% were received for different elementary cell geometries. Elementary cells belong to the triply periodic minimal surfaces family (G, D, I2Y, IWP). Each sample was subjected to a comprehensive analysis including: dimensional metrology and assessment of material defects (X-ray micro-tomography), surface morphology tests (scanning electron microscopy) and mechanical properties (universal testing machine). It has been shown that a cellular lattice with high dimensional accuracy (+0.16/–0.08 mm) and full dense struts can be obtained. According to the assumption, the gradient increases the strength of the cellular lattice samples. The highest increase in plateau stress between the samples with and without gradient was found for the I2Y series (about 185%). Furthermore, it was found that the stress-strain response of the samples depends not only on total porosity, but also on the 3D geometry of the cellular lattice. The stress-strain curves for G, IWP and I2Y samples are smooth and exhibit three characteristic regions: linear elasticity, plateau region and densification region. The size of regions depends on the geometric features of the cellular lattice. For series D, in the plateau region, the fluctuations in stress value are clearly visible. The smoothest stress-strain curve can be noted for the G series, which combined with good mechanical properties (the plateau stress and energy absorbed, at respectively 25.5 and 43.2 MPa, and 46.3J and 59.5J for Gyr_80 and Gyr_6080, which corresponds to a strain of almost 65% and 50%) positively affects the applicability of cellular structures with such geometry.

The pitting corrosion of orthodontic apparatus elements in the oral environment is an interest of both clinicians and scientists dealing with the assessment of the biocompatibility of medical materials. This work presents a study on the effect of ready-to-use Listerine^® and Meridol^® mouthwashes and sodium fluoride on the resistance of the commercial Remanium^®-type orthodontic archwire to pitting corrosion in artificial saliva at 37 °C. XRD, SEM, EDS, mechanical properties, and microhardness measurements were used to characterize the archwire. The in vitro corrosion resistance of the archwire was examined using the open-circuit potential method, electrochemical impedance spectroscopy, and anodic polarization curves. The physicochemical characteristics confirmed the presence of a bi-phase alloy with a mixed austenite/ferrite structure containing Fe 74.4(7) at.%, Cr 18.4(4) at.%, and Ni 7.2(4) at.%. The Fe–Cr–Ni alloy was characterized by high tensile strength and Vickers microhardness. EIS revealed the capacitive behavior with high corrosion resistance. It was found that the kinetics of pitting corrosion in the artificial saliva decreased in the presence of NaF and mouthwashes. The potentiodynamic characteristics confirmed the decrease in susceptibility to pitting corrosion after the modification of artificial saliva. The pitting corrosion mechanism of the self-passive oxide layer on the surface of the Fe–Cr–Ni electrode in the biological environment containing chloride ions was discussed in detail. Mechanical properties after corrosion tests were weakened.

The paper presents the results of tests concerning the tribological properties of titanium Grade 2 subjected to thermal oxidation at a temperature of 600°C and 700°C for 72 hours. Morphology of the obtained oxide scale was determined using a scanning electron microscope. After oxidation at 600°C, the resultant oxides concentrated mostly on the roughness elevations formed during the grinding of samples. On raising temperature to 700°C, finer and more agglomerated oxide particles were formed. Tribological tests have shown that titanium Grade 2 in a non-oxidised condition is characterised by very poor resistance to sliding wear. It has been found that the presence of an oxide layer on the surface of titanium significantly improves its poor tribological properties. Oxide layers obtained at temperatures of 600°C and 700°C allowed obtaining as much as a triple reduction of volumetric wear. Analysis of the morphology of the wear trace surface has shown the presence of corrugation wear on a non-oxidised specimen in the form of two alternate regions with different morphologies. It has been demonstrated that oxide layers obtained during thermal oxidation eliminate the phenomenon of corrugation wear.