Mechanical and Corrosion Properties of Laser Surface-Treated Ti13Nb13Zr Alloy with MWCNTs Coatings

Evaluation of adhesion strength, corrosion, and biological properties of the MWCNT/TiO2 coating intended for medical applications

Multi-wall carbon nanotube (MWCNT) coatings are gaining increasing interest because of their special properties used in many science fields. The titania coatings are known for their improvement of osteoblast adhesion, thus changing the surface architecture. Bi-layer coatings comprising 0.25 wt% of the MWCNTs and 0.30 wt% of titania (anatase structure) were synthesized in a two-stage procedure using the electrophoretic deposition method (EPD). The MWCNT and TiO2 coatings were deposited with voltage and time parameters, respectively, of 20 V and 0.5 min, and 50 V and 4 min. EDS, AFM, SEM, Raman spectroscopy, nano-scratch test, potentiodynamic corrosion tests, wettability studies, and cytotoxicity determined with MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) test on human dermal fibroblasts (HDF) and mouse osteoblast precursors (MC3T3), and lactate dehydrogenase (LDH) activity test were carried out on examined surfaces. The prepared MWCNT/TiO2 coating is uniformly distributed by MWCNTs and agglomerated by TiO2 particles of size ranging from 0.1 to 3 μm. Raman spectroscopy confirmed the anatase structure of the TiO2 addition and showed typical peaks of the MWCNTs. The MWCNT/TiO2 coating had higher roughness, higher adhesion strength, and improved corrosion resistance compared to the MWCNT basic coating. The results of biological tests proved that physicochemical properties of the surface, such as high porosity and wettability of MWCNT/TiO2-coated material, would support cell adhesion, but toxic species could be released to the culture medium, thus resulting in a decrease in proliferation.

Laser Welding of UNS S33207 Hyper-Duplex Stainless Steel to 6061 Aluminum Alloy Using High Entropy Alloy as a Filler Material

The high entropy alloy (HEA) filler used during the fabrication method determines the reliability of HEAs for steel-aluminum dissimilar alloy configuration. HEAs have a direct impact on the formation of intermetallic compounds (IMC) formed by the interaction of iron (Fe) and aluminum (Al), and influence the size of the joint’s interaction zone. A novel welding process for Fe-Al alloy joints was developed to prevent the development of a brittle iron-aluminum interface. This research involved investigation of the possibility of using HEA powdered filler. Fe5Co20Ni20Mn35Cu20 HEAs was used as a filler for the laser joining lap configuration joining hyper-duplex stainless steel UNS S33207 to aluminum alloy 6061. This HEA has unique properties, such as high strength, good ductility, and high resistance to corrosion and wear. A tiny portion of the stainless-steel area was melted by varying the welding parameters. The high-entropy alloy (HEA) with slow kinetic diffusion and large entropy was employed to aid in producing solid solution structures, impeding the blending of iron and aluminum particles and hindering the development of Fe-Al IMCs. The weld seam was created without the use of Fe-Al IMCs,. The specimen broke at the HEAs/Al alloy interface with a tensile-shear strength of 237 MPa. The tensile-shear strength achieved was 12.86% higher than for the base metal AA 6061 and 75.57% lower than for the UNS S33207 hyper-duplex stainless steel.

Development of Laser Welding and Surface Treatment of Metals

This Special Issue on Development of Laser Welding and Surface Treatment of Metals contains as many as twenty-two research articles mainly related to the application of lasers, but also on other welding processes that may be competitive to laser technologies under specific conditions. Despite the introduction of lasers for material processing in the 1960s, the continuous development of laser devices also leads to the development and expansion of laser technology applications. This Special Issue is a compendium of knowledge in the field of fusion welding, the manufacturing of surface layers and coatings with increased wear resistance and tribological characteristics, as well as corrosion resistance and the characterization of coatings and surface layers. The topics of the presented research articles include aspects related to laser welding (eight articles), especially technological conditions, the properties of different types of joints, and analytical and numerical aspects of modelling the laser heat sources. The second dominant issue concerns laser cladding and laser surface treatment of different ferrous and nonferrous metallic and composite materials (six articles). In addition, there are interesting results of the study of fusion welding under forced cooling of the deposit or underwater conditions (four articles), results on the characterization of wear resistance coating produced by different technologies that can be competitive for laser cladding (three articles), and an original study on local strengthening of the thin-walled structure by laser treatment (one article). This Special Issue provides very wide and valuable knowledge based on theoretical and empirical study in the field of laser and fusion welding, laser and related coating technologies, characterization of coatings, and wear phenomena.

Mechanical Properties and Residual Stress Measurements of Grade IV Titanium and Ti-6Al-4V and Ti-13Nb-13Zr Titanium Alloys after Laser Treatment

Nowadays, surface engineering focuses on research into materials for medical applications. Titanium and its alloys are prominent, especially Ti-6Al-4V and Ti-13Nb-13Zr. Samples made of pure grade IV titanium and the titanium alloys Ti-6Al-4V and Ti-13Nb-13Zr were modified via laser treatment with laser beam frequency f = 25 Hz and laser beam power P = 1000 W during a laser pulse with duration t = 1 ms. Subsequently, to analyze the properties of the obtained surface layers, the following tests were performed: scanning electron microscopy, chemical and phase composition analysis, wetting angle tests and roughness tests. The assessment of the impact of the laser modification on the internal stresses of the investigated materials was carried out by comparing the values of the stresses of the laser-modified samples to those of the reference samples. The obtained results showed increased values of tensile stresses after laser modification: the highest value was found for the Ti-6Al-4V alloy at 6.7434 GPa and the lowest for pure grade IV titanium at 3.742 GPa. After laser and heat treatment, a reduction in the stress was observed, together with a significant increase in the hardness of the tested materials, with the highest value for Ti-6Al-4V alloy at 27.723 GPa. This can provide better abrasion resistance and lower long-term toxicity, both of which are desirable when using Ti-6Al-4V and Ti-13Nb-13Zr alloys for implant materials.

Titanium Functionalized with Polylysine Homopolymers: In Vitro Enhancement of Cells Growth

In oral implantology, the success and persistence of dental implants over time are guaranteed by the bone formation around the implant fixture and by the integrity of the peri-implant mucosa seal, which adheres to the abutment and becomes a barrier that hinders bacterial penetration and colonization close to the outer parts of the implant. Research is constantly engaged in looking for substances to coat the titanium surface that guarantees the formation and persistence of the peri-implant bone, as well as the integrity of the mucous perimeter surrounding the implant crown. The present study aimed to evaluate in vitro the effects of a titanium surface coated with polylysine homopolymers on the cell growth of dental pulp stem cells and keratinocytes to establish the potential clinical application. The results reported an increase in cell growth for both cellular types cultured with polylysine-coated titanium compared to cultures without titanium and those without coating. These preliminary data suggest the usefulness of polylysine coating not only for enhancing osteoinduction but also to speed the post-surgery mucosal healings, guarantee appropriate peri-implant epithelial seals, and protect the fixture against bacterial penetration, which is responsible for compromising the implant survival.

Nanotubular Oxide Layer Formed on Helix Surfaces of Dental Screw Implants

Surface modification is used to extend the life of implants. To increase the corrosion resistance and improve the biocompatibility of metal implant materials, oxidation of the Ti-13Nb-13Zr titanium alloy was used. The samples used for the research had the shape of a helix with a metric thread, with their geometry imitating a dental implant. The oxide layer was produced by a standard electrochemical method in an environment of 1M H3PO4 + 0.3% HF for 20 min, at a constant voltage of 30 V. The oxidized samples were analyzed with a scanning electron microscope. Nanotubular oxide layers with internal diameters of 30–80 nm were found. An analysis of the surface topography was performed using an optical microscope, and the Sa parameter was determined for the top of the helix and for the bottom, where a significant difference in value was observed. The presence of the modification layer, visible at the bottom of the helix, was confirmed by analyzing the sample cross-sections using computed tomography. Corrosion tests performed in the artificial saliva solution demonstrated higher corrosion current and less noble corrosion potential due to incomplete surface coverage and pitting. Necessary improved oxidation parameters will be applied in future work.

Laser Dissimilar Welding of AISI 430F and AISI 304 Stainless Steels

A dissimilar autogenous laser welded joint of AISI 430F (X12CrMoS17) martensitic stainless steel and AISI 304 (X5CrNi18-10) austenitic stainless steel was manufactured. The welded joint was examined by non-destructive visual testing and destructive testing by macro- and microscopic examination and hardness measurements. With reference to the ISO 13919-1 standard the welded joint was characterized by C level, due to the gas pores detected. Microscopic observations of AISI 430F steel revealed a mixture of ferrite and carbides with many type II sulfide inclusions. Detailed analysis showed that they were Cr-rich manganese sulfides. AISI 304 steel was characterized by the expected austenitic microstructure with banded δ-ferrite. Martensitic microstructure with fine, globular sulfide inclusions was observed in the weld metal. The hardness in the heat-affected zone was increased in the martensitic steel in relation to the base metal and decreased in the austenitic steel. The hardness range in the weld metal, caused by chemical inhomogeneity, was 184–416 HV0.3.