Corrosion of Ti-based bulk metallic glasses for small diameter dental implants

Ti-based bulk metallic glasses (BMGs) have been proposed to be an alternative to conventional Ti alloys to be used to manufacture small dental implants. For this application, it is important to determine whether they have suitable corrosion resistance. The corrosion behaviour of BMGs and the alloy, Ti6Al4V was tested in physiological saline (PS), with and without the addition of albumin and hydrogen peroxide. Albumin is the main protein in extracellular fluid, and peroxide (H2O2) is a transient biological species used here to simulate the presence of reactive oxygen species (ROS) that can be formed during infection or inflammation. Electrochemical tests on BMG_Sn2 showed that addition of albumin to PS suppresses the cathodic reaction and enhances the pitting resistance of BMG_Sn2, while H2O2 decreases the pitting resistance of BMG_Sn2. The addition of albumin to H2O2-containing PS suppresses both anodic and cathodic reactions. Most Ti-based BMGs contain a high content of Cu. However, Cu is potentially less biocompatible compared with other elements which can be used to enhance the glass forming potential. In this case, Ga was used to partly replace Cu, up to 10 at.%. Experiments were conducted to check that this partial substitution does not have a detrimental effect on corrosion resistance. It was found that substitution of 10 at.% Ga did not modify the corrosion resistance of Ti-based BMGs in 0.9 wt.% NaCl solution. It was also found that some degree of structural relaxation can slightly improve the corrosion resistance. Mechanically-assisted crevice corrosion (MACC) is a corrosion process associated with abrasive damage to test surfaces. The abrasion causes damage to the passive surface film, leading to a burst of metal dissolution from the bare metal surface. The metal ions hydrolyse and result in local acidity in the crevice. The acid environment delays the repassivation of Ti and can eventually cause severe corrosion. Such wear damage and local acidity have been found for cemented femoral stems and modular orthopaedic Ti implants. There is concern that MACC may also be a risk for dental implants, so it is important to be able to evaluate risk in quantitative way. A new device was developed that can retain the local acidity produced by MACC. A series of parallel tests on BMGs and Ti6Al4V using this device were conducted to compare their MACC resistance. The results have shown that Ti-based BMGs show better MACC resistance than Ti6Al4V evidenced by lower MACC currents, associated with milder local chemistry changes and less wear and corrosion products generated. It has also been shown that MACC gets increasingly worse for Ti6Al4V with time but this was not observed for BMGs in the current test period (16 ks). This can be explained by the fact that Ti-based BMGs possess greater wear resistance than Ti6Al4V, which means the passive film may be better preserved under the abrasive conditions

Erosion-Corrosion of Marine Alloys

Marine alloys such as stainless steels, copper-base alloys and cast iron have a long history of applications over a wide range of industries. They always are exposed to aggressive erosion-corrosion environments to support or transmit forces during the service, where more than millions of pounds are involved to repair the material degradation every year. In order to minimize this cost, lots of money and research have been put into practice, from which more and more erosion-corrosion behaviour and mechanisms of marine alloys were understood, however, downtime of marine systems still happens, moreover it is still a fact that it is quite difficult to choose the optimum material for the specific working environment. In this project, erosion-corrosion performance of eight marine alloys which include three different grade stainless steels, four copper-base alloys and one Niresist cast iron has been assessed under liquid-solid jet impingement over eight sets of test conditions in 3.5% sodium chloride solution. Firstly, the weight loss of different marine alloys ranks the priority of their corrosion, erosion and erosion-corrosion resistance over the range of the test conditions, furthermore the total weight loss test, in conjunction with in-situ electrochemistry measurements, enable the relative contribution of the different mechanisms interacting in the degradation to be quantified, meanwhile the aspects of erosion-corrosion mechanisms of different marine alloys have been detailed. Even erosion-corrosion is a complex process, but microhardness has been found to be the controlling factor in severe erosion-dominated conditions. More importantly, primary concerns have been brought on the factorial contributions of individual environmental parameters and their interactions to the overall material degradations. A full two-level factorial experimental design method combined with following analysis of variance was applied to qualify these factorial contributions, which shows effects of the individual environmental parameters and their interactions on the weight loss during the erosion-corrosion processes, and the prominent factors are velocity, sand loading and their interaction. Fluid temperature has the smallest effect compared with other environmental parameters

National Educators' Workshop: Update 1989 Standard Experiments in Engineering Materials Science and Technology

Presented here is a collection of experiments presented and demonstrated at the National Educators' Workshop: Update 89, held October 17 to 19, 1989 at the National Aeronautics and Space Administration, Hampton, Virginia. The experiments related to the nature and properties of engineering materials and provided information to assist in teaching about materials in the education community

Synthesis, CFD simulation and characterization of direct laser metal deposition (LMD) of Al-Cu-Ti coatings on Ti-6Al-4V alloy for aerospace application

Abstract: This research study was aimed at researching the synthesis, simulation and characterization of Direct Laser Metal Deposition (DLMD) of Al-Cu-Ti Coatings on Ti-6Al- 4V Alloy for aerospace application. This investigation was accomplished by numerical analysis and experimental techniques. In the category of manufacturing techniques (Additive Manufacturing), the Direct Laser Metal Deposition (DLMD) technique is quite a new field in the industry. This manufacturing technique is flexible, in the sense that it can be used to manufacture working parts or components for bigger assemblies, freeform shapes according to the designer specifications, advanced coatings on the surfaces of working components, and fully solid structures. This research also enquires into the enhanced properties (mechanical, hardness and corrosion) of the modified coating powders (Al-Cu-Ti) on the Titanium alloy (Ti-6Al-4V) and its applications for components and parts enhancements in aerospace industries...M.Ing. (Mechanical Engineering Science

Direct Writing Of Polymeric Coatings For Corrosion Control And Tunable Release Of Bioactive Materials

The interface between a medical device and its surrounding tissue can be critical to biocompatibility, performance and therapeutic effectiveness. Careful choice and application of materials at this interface is therefore a key to the success of any medical device. This research employed a novel direct-write inkjet printing technique for polymeric surface modification of bioresorbable AZ31 Mg alloy towards corrosion control and tunable release of bioactive agents. In the first phase of this research, the direct-write inkjet printing technique was successfully used to fabricate thin films of different blends of poly (ester-urethane) urea embedded with taxol coatings on mechanically polished AZ31 Mg coupons. A corrosion study was performed using the electrochemical impedance spectroscopy (EIS) technique. The polarization resistance values obtained using the equivalent circuit model were analyzed using the ECHEM analyst commercial software developed by Gamry®. The polarization resistances obtained indicated that the corrosion resistance of the polymeric materials increases in this order: uncoated AZ31 \u3c PEUU-SB \u3c PEUU-PC \u3c PEUU-V

National Educators' Workshop: Update 95. Standard Experiments in Engineering Materials Science and Technology

This document contains a collection of experiments presented and demonstrated at the National Educators' Workshop: Update 95. The experiments related to the nature and properties of engineering materials and provided information to assist in teaching about materials in the education community

Closure development for high-level nuclear waste containers for the tuff repository; Phase 1, Final report

This report summarizes Phase 1 activities for closure development of the high-level nuclear waste package task for the tuff repository. Work was conducted under U.S. Department of Energy (DOE) Contract 9172105, administered through the Lawrence Livermore National Laboratory (LLNL), as part of the Yucca Mountain Project (YMP), funded through the DOE Office of Civilian Radioactive Waste Management (OCRWM). The goal of this phase was to select five closure processes for further evaluation in later phases of the program. A decision tree methodology was utilized to perform an objective evaluation of 15 potential closure processes. Information was gathered via a literature survey, industrial contacts, and discussions with project team members, other experts in the field, and the LLNL waste package task staff. The five processes selected were friction welding, electron beam welding, laser beam welding, gas tungsten arc welding, and plasma arc welding. These are felt to represent the best combination of weldment material properties and process performance in a remote, radioactive environment. Conceptual designs have been generated for these processes to illustrate how they would be implemented in practice. Homopolar resistance welding was included in the Phase 1 analysis, and developments in this process will be monitored via literature in Phases 2 and 3. Work was conducted in accordance with the YMP Quality Assurance Program. 223 refs., 20 figs., 9 tabs

Corrosion Resistance

The book has covered the state-of-the-art technologies, development, and research progress of corrosion studies in a wide range of research and application fields. The authors have contributed their chapters on corrosion characterization and corrosion resistance. The applications of corrosion resistance materials will also bring great values to reader's work at different fields. In addition to traditional corrosion study, the book also contains chapters dealing with energy, fuel cell, daily life materials, corrosion study in green materials, and in semiconductor industry

Abrasion-corrosion of cast CoCrMo in simulated hip joint environments

Metal-on-metal (MoM) hip joint replacements have been increasingly used for younger and more active patients in recent years due to their improved wear performance compared to conventional metal-on-polymer bearings. MoM bearings operate at body temperature within a corrosive joint environment and therefore are inevitably being subjected to wear and corrosion as well as the combined action of tribo-corrosion. Issues such as metal sensitivity/metallosis associated with high levels of metal ion release triggered by the wear and corrosion products remain critical concerns. During the past few decades, significant research has been conducted into understanding the wear/lubrication mechanisms within the MoM hip joints in order to improve their performance and thereby prolonging their life. However, not much attention has been given to the combined effect of wear and corrosion of such devices in the hip joint environment, in addition, the role of third body particles and the effects of proteins have not been well understood.In this work, a systemic approach is presented for the first time for the mapping of abrasion and tribo-corrosion performance of a cast CoCrMo (F75) in simulated hip joint environments. The effects of third body particles have been studied in the MoM context using 4 ?m SiC, 1 ?m and 300 nm Al2O3, as well as sub-micron BaSO4. Modified tribo-testers (micro-abrasion, nanoindenter/scratching) incorporating a novel electrochemical cell have been used to monitor the abrasion-corrosion behaviour of the alloy in situ. The effects of solution chemistry, abrasives size / concentration and presence of proteins on the wear / corrosion level, wear-corrosion mechanisms, and the depassivation/repassivation kinetics of the CoCrMo have been explored. A variety of surface and sub-surface characterization techniques have been employed to identify the microstructual wear mechanism interactions. Results show that the change of protein concentration (0, 25% and 50% bovine serum) and pH (pH 7.4 and pH 4.0) of the test solutions can significantly influence the protein adsorption behaviour, which subsequently influence the wear rates (synergy), wear mechanisms as well as the wear-induced corrosion currents of the CoCrMo. For abrasion-corrosion tests, reducing abrasive size from 4 ?m to 300 nm and/or abrasive volume concentration from 0.238 vol% to 0.006 vol% results in different abrasion-corrosion wear mechanisms (rolling or grooving abrasion) and the average wear-induced corrosion currents show a linear correlation with wear rates for 4 ?m and 1 ?m abrasives. For low volume concentration (< 0.03 vol%) slurries containing bovine serum, organo-metallic conglomerates have been found within the wear scars. These conglomerates help separate the surfaces, impose less damage to the surface passive film and polish the wear scars through a chemical mechanical polishing mechanism. In addition, tribo-corrosion tests at micro-/nano- scales reveal the effects of single abrasive particle on the surface/sub-surface microstructual change. This investigation has revealed the nanoscale wear mechanisms that generate nanoscale wear debris, the mechanical mixing of the surface nanostructure with adsorbed denatured protein and also the slip/dislocation systems that are present near and on abraded surfaces that are likely to disrupt the surface passive films. The findings give a better understanding of the evolution of the sub-surface nanocrystalline structures and tribo-layers formation seen for the retrieved implants. This near surface nanostructure layer and phase transformation might offer better wear resistance through these inherent self-protecting mechanisms (i.e. increased hardness); conversely, it may become the precursors to debris ejection and enhanced ion-release into the CoCrMo joints.This work established an experimental technique that gives greater understanding of the tribocorrosion behaviour of cast CoCrMo in simulated hip joint environments. In particular, the roles of third body abrasive particles and proteins have been addressed, which are relevant to clinical applications. The material multi-scale wear mechanisms as well as the evolution of the surface / subsurface microstructures and tribo-layers have been elucidated, which provide new insights into the in vivo wear mechanisms of CoCrMo. The findings of this study may provide some important indications for improved MoM joint materials, design, manufacture and evaluation