Tribological Aspects of Sheet Titanium Forming.

Friction, wear, and lubrication are inherent to all metal-forming processes. Unfortunately, they are particularly troublesome when forming titanium materials, which tend to form titanium buildup on the working surfaces of the forming tools. Lubrication is one of the most effective ways to separate contacting surfaces and eliminate galling, thus reducing tool wear. The paper presents the tribological aspects of titanium sheets forming using environmentally friendly lubricants with the addition of boric acid. The lubricant's effectiveness was assessed on the basis of technological tests, such as the strip drawing test, the Erichsen cupping test, and the formation of spherical drawn parts in industrial conditions. Moreover, the results of the numerical simulation of forming a titanium hat-shaped part are presented. Numerical calculations of forming processes were performed using the PamStamp 2G system based on the finite element method. Both experiments and numerical analyses showed the positive effect of lubricants with boric acid on sheet titanium forming.

Characterization of biomaterials with reference to biocompatibility dedicated for patient-specific finger implants.

PURPOSE: The research was focused on determining basic mechanical properties, surface, and phase structure taking into consideration basic cytotoxicity analysis towards human cells. METHODS: Biological tests were performed on human C-12302 fibroblasts cells using 3D-printed Ti6Al4V alloy (Ti64), produced by laser-based powder bed fusion (LB-PBF) and Alumina Toughened Zirconia 20 (ATZ20), produced by lithography-based ceramic manufacturing (LCM). Surface modifications included electropolishing and hydroxyapatite or hydroxyapatite/zinc coating. Structure analysis was carried out using a variety of techniques such as X-Ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and confocal laser scanning microscopy (CLSM), followed by mechanical properties evaluation using nanoindentation testing. RESULTS: Samples subjected to surface modifications showed diversity among surface and phase structure and mechanical properties. However, the cytotoxicity towards tested cells was not significantly higher than the control. Though, a trend was noted among the materials analysed, indicating that HAp/Zn coating on Ti64 and ATZ20 resulted in the best biological performance increasing cell survivability by more than 10%. CONCLUSIONS: Hydroxyapatite coating on Ti64 and ATZ20 resulted in the best biological properties. Tested materials are suitable for in vivo toxicity testin.

Numerical and Experimental Analysis of Titanium Sheet Forming for Medical Instrument Parts.

The paper analyses the forming of the surgical instrument handles made of Grade 2 titanium sheets. Sheet metal forming is a technology ensuring high strength and light weight of products. Replacing stainless steels with titanium further reduces instrument weight and additionally provides the required resistance to corrosive environments typical for surgeries. The low instrument weight is important to prevent fatigue of surgeons and allow them to maintain high operational accuracy during long term surgeries. The numerical analysis of the technological process was performed in order to adapt it to forming tool handles using titanium sheets instead of steel sheets. The numerical calculations were experimentally verified. It was found that, in the case of titanium handles, it is necessary to use a blank holder in the first forming operation to eliminate sheet wrinkling in the flange area. The shape and dimensional accuracy of the drawn part after trimming were high enough and the 4th forming operation became unnecessary. Moreover, the process modification included lubrication using rapeseed oil with the addition of boric acid, which effectively prevents the galling of titanium on the working surfaces of the steel tools and ensures a more uniform distribution of plastic strains in the drawn part.

A study on the physicochemical properties of surface modified Ti13Nb13Zr alloy for skeletal implants.

As it is widely stated in the literature, biofilms are responsible for most chronic infections, which have grown exponentially over the past three decades. The use of so-called alloys, as a new generation of materials, enables us to find the golden mean in the arena widely known as implantology. The use of the surface layer, using the chosen Atomic Layer Deposition method, is to be the basis for minimizing the risk of an organism reactions. Therefore, the primary objective of this study was to observe the impact of physicochemical properties of the surface layers (bactericidal) on the processes that occur on the implants surface made of titanium biomaterials used in bone structures. The study also attempted to evaluate the physicochemical properties of the ZnO coatings, deposited on the substrate of one of the new generation Ti13Nb13Zr alloys, using the ALD method. Included in the assessment of the physicochemical properties of the surface layers formed in this manner, we perform pitting corrosion resistance tests, scratch tests, tribological tests and surface wettability tests. Based on the obtained data, the differing physicochemical properties of the alloy with ZnO coatings are found to be dependent on the applied surface modification. For the conducted tests, differences are determined for the tests on the corrosion resistance, surface wettability and the abrasion resistance for samples with and without the ZnO coating. In addition, tests show that the coating applied to the alloy, which is previously subjected to the sand-blasted process, is characterized by improved adhesion.

The Analysis of Erosive Wear Resistance of WC-Co Carbides Obtained by Spark Plasma Sintering Method.

WC-Co (tungsten carbide-cobalt) composites are widely used in industry, wear-resistant parts, and cutting tools. As successful tool materials, WC-Co carbides are widely applied in metal cutting, wear applications, chipless forming, stoneworking, wood, and plastic working. These materials are exposed to severe solid particle erosion by sand particles, such as in the wood industry. During the production of furniture with HDF (High Density Fibreboard), MDF (Medium Density Fibreboard), or OSB (Oriented Strand Board), there are observed problems with tool erosion. Contamination, mainly of the HDF by sand, is quite often, which is why all tools used for the machining of such materials are exposed to erosion by sand particles. Although many studies have been performed on the erosion of various metals, and erosion models exist to predict their erosion behavior, the issue is still relevant. The aim of the study was to determine the effect of grain size (submicron, ultrafine) and the manufacturing technology (SPS-Spark Plasma Sintering, conventional) used on the erosive properties of WC-Co sintered carbides. Sinters produced by the SPS method with different sizes of WC grains and commercial samples were used for the tests. Ten two-hour cycles were carried out under medium conditions of quartz sand and quartz sand with 10% SiC added. Used samples were characterised using scanning electron microscopy (SEM) and roughness was determined. Furthermore, erosion studies allowed individuating a wear mechanism as well as the possibility to foresee cutting performance in prospective application.

Biocompatibility testing of composite biomaterial designed for a new petal valve construction for pulsatile ventricular assist device.

This paper presents the results of biocompatibility testing performed on several biomaterial variants for manufacturing a newly designed petal valve intended for use in a pulsatile ventricular assist device or blood pump. Both physical vapor deposition (PVD) and plasma-enhanced chemical vapor deposition (PECVD) were used to coat titanium-based substrates with hydrogenated tetrahedral amorphous carbon (ta-C:H) or amorphous hydrogenated carbon (a-C:H and a-C:H, N). Experiments were carried out using whole human blood under arterial shear stress conditions in a cone-plate analyzer (ap. 1800 1/s). In most cases, tested coatings showed good or very good haemocompatibility. Type a-C:H, N coating proved to be superior in terms of activation, risk of aggregation, and the effects of generating microparticles of apoptotic origin, and also demonstrated excellent mechanical properties. Therefore, a-C:H, N coatings were selected for further in vivo studies. In vivo animal studies were carried out according to the ISO 10993 standard. Intradermal reactivity was assessed in three rabbits and sub-acute toxicity and local effects after implantation were examined in 12 rabbits. Based on postmortem examination, no organ failure or wound tissue damage occurred during the required period of observation. In summary, our investigations demonstrated high biocompatibility of the biomaterials in relation to thrombogenicity, toxicity, and wound healing. Prototypes of the petal valves were manufactured and mounted on the pulsatile ventricular assist device. Hydrodynamic features and impact on red blood cells (hemolysis) as well as coagulation (systemic thrombogenicity) were assessed in whole blood.

Antibacterial Optimization of Highly Deformed Titanium Alloys for Spinal Implants.

The goal of the work was to develop materials dedicated to spine surgery that minimized the potential for infection originating from the transfer of bacteria during long surgeries. The bacteria form biofilms, causing implant loosening, pain and finally, a risk of paralysis for patients. Our strategy focused both on improvement of antibacterial properties against bacteria adhesion and on wear and corrosion resistance of tools for spine surgery. Further, a ~35% decrease in implant and tool dimensions was expected by introducing ultrahigh-strength titanium alloys for less-invasive surgeries. The tested materials, in the form of thin, multi-layered coatings, showed nanocrystalline microstructures. Performed direct-cytotoxicity studies (including lactate dehydrogenase activity measurement) showed that there was a low probability of adverse effects on surrounding SAOS-2 (Homo sapiens bone osteosarcoma) cells. The microbiological studies (e.g., ISO 22196 contact tests) showed that implanting Ag nanoparticles into Ti/TixN coatings inhibited the growth of E. coli and S. aureus cells and reduced their adhesion to the material surface. These findings suggest that Ag-nanoparticles present in implant coatings may potentially minimize infection risk and lower inherent stress.

Properties of WCCo Composites Produced by the SPS Method Intended for Cutting Tools for Machining of Wood-Based Materials.

This paper presents the possibility of using the Spark Plasma Sintering (SPS) method to obtain WCCo composite materials. Such materials are used as cutting blades for machining wood-based materials. Two series of composites, different in grain size and cobalt content, were analyzed in the paper. The produced materials were characterized using Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), and tribological properties were determined. In addition, preliminary tests were carried out on the durability of the blades made of sintered WCCo composites while machining three-layer chipboard. The results of the microstructure analysis proved that the SPS method makes it possible to obtain solid composites. Phase analysis showed the occurrence of the following phases: WC, Co, and Co3W9C4. The lowest friction coefficient value was found in samples sintered using powder with an average primary particle size of 400 nm (ultrafine).