The degradation of pump components by corrosion and complex, simultaneous damage mechanisms, e.g., erosion–corrosion and cavitation–corrosion leads to high costs through replacement and maintenance of parts. To increase the lifetime of cost-efficient components with superior casting properties, surface welding of duplex stainless steel on gray cast iron parts was performed using inert shielding gas metal arc surface welding (GMA-SW) and plasma transferred arc surface welding (PTA-SW). The thermal conductivity of the used shielding gas and the preheating temperature influenced the dilution of the surface layers, which had a major impact on the corrosion resistance and the microstructure. Lower cooling rates enhanced diffusion and lead to precipitation of carbides. High heat input and prolonged cooling times during surface welding resulted in high dilution and a carbide network. The corrosion resistance in artificial seawater of those surface layers was substantially reduced compared to surface layers with lower heat input and higher cooling rates. The corrosion of the surface layers in the potentiodynamic polarization test was driven by selective corrosion of the phase boundary between Cr–carbides and Cr–depleted austenite. Passive behavior was observed for surface layers with low dilution, which had homogeneous chromium distribution and no carbide networks. In conclusion, the corrosion behavior of gray cast iron was improved by surface welding with duplex stainless steel. The corrosion resistance of the surface layers produced with PTA-SW with no preheating exceeded that of the surface layers produced with GMA-SW and came close to those of a commercially available duplex stainless steel used as reference material.

The good capacity of gray cast iron for the manufacture of complex geometry components is widely recognized, but its low resistance to corrosion and low weldability complicate the use of this material for some industrial applications. The corrosion resistance can be improved by metallic surface layers using welding processes with low percentages of dilution between the filler and base material. However, the welding processes impose very high heat load on the base material, which in the case of cast iron could promote the formation of hard and brittle microstructures, facilitating the formation of cracks. This work deals with weld beads of duplex steel on lamellar gray cast iron made either by plasma-transferred arc powder (PTA-P) or by metal inert gas (MIG) using the cold metal transfer (CMT) technology, with emphasis on achieving low dilution, hardness and imperfections (internal porosities). Preheating was used to reduce the hardness in the heat-affected zone, while different levels of helium were added in the shielding gas to study its effect on the geometry and hardness of the weld beads. The results showed that the PTA-P process resulted in lower values of dilution and hardness because of a low cooling rate compared to that of the MIG-CMT process. In addition, it was observed that preheating the base material reduced the hardness of the heat-affected zone but increased the dilution of the weld bead.

Silicon carbide (SiC) can be tribo-chemically smoothened during a self-mated sliding procedure in the aqueous environment. As well reported in the point-contact tests, this smoothening process works well due to the abundant water as oxidant. After this smoothening process, the tribo-surface is well polished, a closely mated tribo-gap naturally forms, and an ultra-low friction state is built. However, water in the tribo-gap could be insufficient in industrial applications, e.g., the seal gap in mechanical seals. In this study, the tribo-chemical smoothening behavior in such environment was researched. A surface-contact reciprocating test was used to simulate the aqueous environment where water was insufficient. After tests, compared to the published results from the point-contact tests, the same ultra-low friction state was achieved. A part of the tribo-surface was tribo-chemically smoothened. The obtained smoothened surface microstructure was consistent with the published information. Meanwhile, severe abrasive wear occurred. A porous oxygen-rich layer was found existing beneath the abrasion-induced grooves, in which numerous smashed wear debris adhered on the worn surfaces. We concluded that the shortage of water initiated the severe abrasion, meanwhile the generated wear debris aggravated the wear condition. This understanding is instructive for developing new methods to avoid the severe abrasion in the same water insufficient environment.

Ein differenziertes Thermomanagement bildet in modernen Verbrennungskraftmaschinen eine der Grundlagen zur Erzielung höherer Leistungsdichten. In diesem Zusammenhang wachsen auch die Anforderungen an den Betriebsstoff Kühlmittel. Nur eine auf die Nutzungsdauer hin gewährleistete Mindestqualität des Kühlmittels kann die Funktionsweise des Kühlsystems gewährleisten. Im Folgenden wird auf Basis grundlegender elektrochemischer und analytischer Untersuchungen das Ergebnis einer Sensorentwicklung vorgestellt, die eine rasche und aussagekräftige Bewertung der Korrosionsschutzwirkung von Kühlmitteln ermöglichen soll.

A sophisticated thermal management is one of the main subsystems that enables combustion engines with high power density. In this context the demands on coolants are also increasing. There has to be a certain level of corrosion protection to ensure the functionality of the cooling system. Hereafter the result of an electrochemical sensor development is presented. With the knowledge of analytical and electrochemical results a quick test for characterizing coolants corrosion protection has been developed and validated.

„Downsizing“ is a well‐established practice in a wide range of industrial application. The aim is to reduce energy and raw material consumption through the enhancement of the efficiency of materials in service. In automotive and supply industry this is related to an increasing demand on performance and comfort whilst decreasing fuel consumption and pollutant emission. This is resulting in a higher and more complex material stress. Hence new testing methods have to be developed and implemented in order to meet the upcoming specifications. Aluminium alloys in chassis components are subjected to corrosion fatigue load and therefore have to be qualified for their use. The behavior of the aluminium alloys EN AW‐6082 T6 and EN AW‐7075 T73 are investigated in this study under simultaneous cyclic mechanical and corrosion loading. Load synchronized electrochemical as well as electrochemical noise measurements are performed to investigate the activation‐ and repassivation processes during corrosion fatigue testing. By monitoring the current these effects are assessed. The data monitored is conditioned by Fast‐Fourier‐Transformation in order to investigate the signal of the current density at different frequencies. Electrochemical noise measurements are performed without polarization and therefore a current transient describes local corrosion at very early stages.

This investigation analyses the use of the scanning electrochemical microscopy (SECM) to study the open porosity of PVD-coatings through electrochemical ion detection. CrN und TiN PVD coatings with artificially created permeable areas as well as without any mechanical damage were investigated. Furthermore, the thickness of the interlayers was also modified to increase the diffusion layer thickness. As a result, coatings with different protective effect were obtained and used for comparison purposes. The ion detection was done by means of a microelectrode located over the sample surface. It was used to oxidize ferrous Fe2+ ions coming from the substrate to ferric Fe3+ ions. The measurement of higher currents indicates higher anodic dissolution and consequently higher open porosity of the coating. The validity of the SECM measurements was supported by topographical analysis and optical evaluation of the samples after the measurements.

Translation abstract Adjusting the topography of implant surfaces on a micro-scale allows improvement of osseointegration. Titanium surface modification like sand blasting is one of the known methods to alter the topography of the surface. Polyetheretherketone as a biomaterial is a suitable alternative to titanium but exhibits an inert surface character. The aim of this study was to combine the positive bulk properties of polyetheretherketone with the positive surface properties of sand blasted titanium. For the creation of particle free structured polyetheretherketone surface, four different sand blasted die were pressed on counter die polyetheretherketone to transfer the structure. Furthermore, a titanium layer was applied on the surface using physical vapor deposition. The transfer process of the four different topographies was investigated with roughness measurements and scanning electron microscope. One topography, created with aluminum oxide particles on copper, was found with the required R-a value of 1m and R-z value of 9.2m for improved osseointegration. Ein Schwerpunkt derzeitiger Implantatforschung liegt bei der gezielten Modifikation von Implantatoberflachen zur Unterstutzung der Osseointegration. Raue Oberflachen gelten generell als vorteilhaft. Bei Implantaten aus Titan bietet Sandstrahlen eine gute Moglichkeit, raue Implantatoberflachen zu erstellen. Wird Titan jedoch als Implantatwerkstoff durch ein titanbeschichtetes (6m Titan mittels physikalischer Gasphasenabscheidung) Polyetheretherketon substituiert, mussen Risiken wie Schichtabtrag oder Partikeleinbau in die Oberflache ausgeschlossen werden. Als vielversprechende Alternative wurde ein Verfahren zur Strukturubertragung mittels eines Prageverfahrens entwickelt und patentiert. Hierzu werden gezielt strukturierte Stempel auf Polyetheretherketon gepresst und anschlie ss end beschichtet. Die ubertragene Struktur nach der Strukturierung und nach der Beschichtung wurde mit Hilfe eines Konfokalmikroskops charakterisiert. Au ss erdem wurde das Schichtwachsverhalten rauheitsabhangig mittels Rasterelektronenmikroskop dokumentiert. Es konnte ein R-a Wert von 1m und R-z Wert von 9,2m fur eine der erzeugten Oberflachen zur Verbesserung der Osseointegration erreicht werden.

Surface welding of duplex stainless steel on lamellar grey cast iron was performed to produce thick (several millimetres) protective surface layers with a regulated gas metal arc welding process. As dominant parameters, the influence of the composition of the shielding gas (argon‐helium mixture) as well as preheating temperature on the corrosion resistance were investigated. Both the addition of helium to shielding gas and preheating of the base material increase the heat input and reduce the cooling rates and result in higher dilution. This leads to reduced hardness in the heat affected zone and prevents cracking. However, the formation and portion of carbides in the surface layers increase. The influence of these parameters on the microstructure in the surface layers as well as in the heat affected zone and the influence on the corrosion behaviour in artificial seawater were investigated with immersion tests and potentiodynamic polarization measurements. The corrosion properties of the parent lamellar grey cast iron were greatly enhanced by the surface layers, but inferior to duplex stainless steel. With additional metallographic investigations the corrosion mechanisms were investigated. The corrosion mechanisms are extensively influenced by the phase distribution in the surface layers and by the formation of carbides.

The degradation of pump components by corrosion and complex damage mechanisms, e.g. erosion and cavitation leads to high costs through replacement and maintenance of parts. To increase the lifetime of cost-efficient components with superior casting properties, gray cast iron parts are surfaced with duplex stainless steel using an inert shielding gas metal arc welding process. The dilution of the surfacing increases with both increasing heat input and increasing thermal conductivity of the shielding gas. The microstructure is highly affected by the cooling conditions that may enhance diffusion processes and eventually lead to precipitation of deleterious carbides. Higher heat input and prolonged cooling duration during surfacing lead to high dilution and a pronounced carbide network and thus, substantially reduced corrosion resistance in artificial seawater. The corrosion of the surfacings in the potentiodynamic polarization test is driven by selective corrosion of the phase boundary between carbides and chromium-depleted austenite. Passive behavior is observed for coatings with low dilution and higher cooling rates, which showed homogeneous chromium distribution and no interconnected carbide networks. In conclusion, the corrosion behavior of gray cast iron was improved by surfacing with duplex stainless steel.

Especially for industrial applications like pumps, mining or off shore industries, where high demands on the abrasive properties of the materials are required, thermal sprayed Fe-based coatings become increasingly important. Novel FeCrMnBC alloys, which have economic and ecological advantages compared to Ni-based or Co-based coatings, are in the focus of this work. In order to produce adequate coatings with a three-cathode plasma torch, different powder fractions (-45+20 mu m, -25+10 mu m) and varying chemical composition of FeCrMnBC coatings have been investigated and compared with respect to corrosion, abrasion, and erosion properties. In case of wear reduction, selected coatings were additionally subsequent plasma nitrided to study the effect of this treatment on coating morphology and microstructure. The corrosion and tribological behavior were investigated by means of current/density potential curve measurements and ball-on-disc experiments in view of wear morphologies. Erosion-corrosion behavior has been investigated in a pump test rig with 10 wt.-% solid content of corundum in artificial sea water. In general, samples with small powder fractions exhibit accelerated corrosion and decreased erosion behavior, based on their microstructural characteristics. Plasma nitrided coatings show a decrease in corrosion and erosion resistance, which is presumably due to partial formation of chromium carbide in the coatings. Based on the results, the advantages and disadvantages of FeCrMnBC coatings for the application as wear and corrosion protection of complex pump parts are discussed with respect to varied parameters.

The effect of Ti interlayers on the corrosion resistance of TiN PVD coatings is investigated. The coatings were deposited using direct current magnetron sputtering (DCMS) and high power impulse magnetron sputtering (HIPIMS). Ti interlayers with different thicknesses but same composition and deposition parameters were studied. The barrier effect was investigated using potentiodynamic polarization tests, electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscopy (SECM) together with a chemical porosity test. Remarkable improvement of the corrosion resistance with increased thickness of the Ti interlayers was found. The results showed a good agreement between potentiodynamic polarization tests, EIS, SECM and the microscopic inspection.

Low-alloyed, high-strength steels with yield strength above 1200 MPa are frequently used in the automotive industry, in order to reduce the weight of the components. However, hydrogen embrittlement susceptibility is often a concern for this group of materials. Hydrogen can be produced on the metal surface, as a result of electrochemical corrosion reaction during service. The aim of this study is to evaluate the impact of the various loading procedures according to the existing technical specifications for environmental hydrogen embrittlement (EHE) testing. The hydrogen embrittlement susceptibility of high strength fasteners (strength class 14.8) was tested according to the well-established testing specifications: DIN 50969-2, DIN EN ISO 7539, ASTM F1624-12 in 5 wt.-% sodium chloride solution acidified to pH 3 with hydrochloric acid. Open circuit potential measurements were carried out during the testing procedure to gain understanding of the damage process in each of the testing approaches. Under the chosen testing conditions, rising step load (RSL) testing approach, specified in ASTM F1624-12, appeared as the most sensitive method for the evaluation of the material's hydrogen embrittlement susceptibility.

This paper presents an approach to assessing the cumulative fatigue under spectrum loading and simultaneous salt corrosion for aluminium alloys. Fatigue tests, in air and in 5 % sodium chloride solution, were performed with two different structural aluminium alloys (EN AW-6082 T6 and EN AW-7075 T73) using unnotched and notched specimens. The alloy EN AW-7075 T73 proved to be unsuitable for automotive applications due to its high susceptibility to corrosion. For fatigue lifing, a modified cumulative damage calculation based on the material susceptibility, which comprises the influence of salt corrosion on fatigue lifetime, has been proposed. On this basis, potential structural aluminium alloys for chassis applications can be evaluated and selected, prior to validation tests.

Additional silica (silicon dioxide) nanoparticles were added in the tribo-gap to prevent the severe abrasive wear. The method was a flat surface-contact reciprocating sliding test between the sintered silicon carbide surfaces with water lubrication. Before testing, the silica nanoparticles were added in the tribo-gap. These silica nanoparticles acted as a buffer layer during the initial running-in, thus the abrasion risk was decreased. After running-in, the silicon carbide surface was tribo-chemically smoothened without severe abrasion. Comparing to the same tests without silica nanoparticles, the same ultra-low friction state (friction coefficient was approx. 0.01) was built, and the running-in period was shortened by 80 %. As has been well reported, the tribo-chemical smoothening process for silicon carbide needs abundant water, e. g., in the point-contact tests. However, in the surface-contact case, water is locally insufficient, which induces severe wear. The preset silica nanoparticles can solve this wear problem. Therefore, it is not necessary to polish the silicon carbide surfaces as the seal faces in mechanical seals. Instead, a pair of rough silicon carbide surfaces can be pressed onto each other and then proceed to a running-in with preset silica nanoparticles. After running-in, a pair of precisely mated tribo-chemically smoothened surfaces can be naturally obtained.