Characterisation of biomedical titanium layers deposited by a vacuum plasma spray process

In this paper we will describe the process of the deposition of thick layers of VPS-Ti coating, which is used as a bonding layer for the upper porous Ti coatings on implant substrates. In order to deposit the powder, we used HoGANaS Ti powder labelled as AMPERIT 154.086-63 mu m. In order to test the mechanical properties and microstructure of the VPS-Ti coating, the powder was deposited on C 4171 (X15Cr13 EN10027) steel substrates. Mechanical tests of the microhardness of the coating were per-formed by the Vickers hardness test method (HV0.3) and tensile strength by measuring the force per unit area (MPa). The micro-hardness of the coating is 159 HV0.3, which is consistent with the microstructure. The coating was found to have a good bond strength of 68 MPa. The morphology of the powder particles was examined on a scanning electron microscope. The microstructure of the coating, both when deposited and etched, was examined with an optical microscope and a scanning elec-tron microscope. By etching the coating layers, it was found that the structure is homogeneous and that it consists of a mixture of low-temperature and high-temperature titanium phases (alpha-Ti + beta-Ti). Our tests have shown that the deposited layers of Ti coating can be used as a bonding layer for porous Ti coatings in the production of implants

A coupled thermo-mechanical model of friction stir welding

A coupled thermo-mechanical model was developed to study the temperature fields, the plunge force and the plastic deformations of Al alloy 2024-T351 under different rotating speed: 350, 400, and 450 rpm, during the friction stir welding process. 3-D FE model has been developed in ABAQUS/Explicit using the arbitrary Lagrangian-Eulerian formulation, the Johnson-Cook material law, and the Coulomb’s Law of friction. Numerical results indicate that the maximum temperature in the friction stir welding process is lower than the melting point of the welding material. The temperature filed is approximately symmetrical along the welding line. A lower plastic strain region can be found near the welding tool in the trailing side on the bottom surface. With increasing rotation speed, the low plastic strain region is reduced. When the rotational speed is increased, the plunge force can be reduced. Regions with high equivalent plastic strains are observed which correspond to the nugget and the flow arm

Mechanical and structural characteristics of atmospheric plasma-sprayed multifunctional tio2 coatings

Titanium dioxide (TiO2) is a multifunctional oxide that is an interesting material for many technological applications. This paper presents the mechanical properties and microstructure of TiO2 coatings resistant to dry sliding friction, corrosion, grain abrasion and erosion of particles at operating temperatures up to 540 degrees C. Layers of TiO2 coatings have been successfully deposited on test samples of steel C.4171 (X15Cr13 EN10027) using the atmospheric plasma spray (APS) process with plasma gun distances of 100 mm and 110 mm from the substrate. The APS procedure is used to produce relatively thick coatings of biocompatible and antibacterial TiO2 ceramic coatings for orthopedic applications. The coatings were deposited using the Plasmadyne company plasma spray system and Metco TiO2 powder, whose particles have an angular morphology produced by the melting and grinding cast blocks. The evaluation of the mechanical properties of the layers was made using the microhardness testing method HV0.3 and the tensile bond strength by tension testing. The analysis of the microstructure of the sprayed TiO2 coating layers was made in accordance with the Pratt & Whitney standard, using optical microscopy (OM). The morphology of the powder particles, the surface of the deposited coating and the coating fractures were examined by scanning electron microscopy. Tests have shown that the layers of TiO2 coatings deposited with a plasma spray distance of 110 mm have good mechanical properties and microstructure, which allow its use in the development of biomedical implants

Relationship of Problematic Internet Use and Positive Orientation Indicators in Adolescents

© 2020 by authors This paper investigates a model connecting problematic Internet use (PIU) and positive orientation (i.e., life satisfaction, self-esteem, and optimism as its indicators) in an adolescent population. The sample included 1263 adolescents (59.5% girls; Mage = 16.85 [SD = 1.01] years), attending four grammar schools and six vocational schools in Vojvodina, Serbia. The following scales were used: the Problematic Internet use, Satisfaction with life, Optimism and Pessimism, and Rosenberg Self Esteem scale. The tested model indicates that the extracted variables are good predictors of PIU, with 20% of the total variance explained. Pessimism was the main individual variable to explain the PIU variance. Future research should investigate the effects of situational contexts on the connection between mental health factors and PIU

Effect of liquid glass type on hygienic characteristics of coated electrodes for arc welding of tin bronzes

The results of investigations of chemical composition and emission rates of the welding fume, generated during welding using electrodes for copper alloys, are presented with the aim of improvement of their sanitary and hygienic characteristics. It is shown that in order to create new grades of welding electrodes with improved hygienic characteristics, it is necessary to have the data of the initial sanitary and hygienic evaluation in accordance with international standards. It was established that the use of binder based on pure lithium liquid glass in the coating of electrodes for welding copper alloys, increases the rate of welding fume emission into the air, as well as the content of manganese and copper oxides in it. The minimum rates of harmful emissions were recorded during the use of sodium-potassium binder, which is recommended for mass production of this type of electrodes

Fracture toughness of base and weld metal of aluminum alloy EN AW 7049A T652 FSW joint

The paper analyses the impact of the tool geometry on the friction stir welding (FSW) method on fracture toughness values of the base metal (BM) and weld metal (WM) of a butt welded joints of a high strength aluminium alloy. Values of fracture toughness were obtained using single-edge notched bend (SENB) specimens with fatigue pre-crack sampled from the BM and TMAZ (thermo-mechanically affected zone). Single specimen method was used according to ASTM E 1820 and parameters of elastic-plastic fracture mechanics were determined (CTOD crack tip opening displacement and the J integral). Although the welding tools had different values of cone angle (α = 2.5° - 10°) and the variable length of the pin (h = 5.1 mm - 5.4 mm) at a constant ratio of the number of tool revolutions and the speed of welding, the largest value of fracture toughness has the retreating side of the weld, then the advancing side of the WM, while the BM has the lowest value. This is the effect of recrystallization process in the retreating side of the WM due to combined rotating-straight forward motion of the tool during which the softened material is repeatedly transformed from one side to the other side around the centre of the tool