Evolution of the ε and γ phases in biodegradable Fe–Mn alloys produced using laser powder-bed fusion

The key feature of Fe–Mn alloys is gradual degradability and non-magneticity, with laser power bed fusion (LPBF) parameters influencing the microstructure and chemical composition. Our study focuses on biodegradable Fe–Mn alloys produced by mechanically mixing pure metal feedstock powders as part of the LPBF process. The Mn content and, consequently, the γ-ε phase formation in LPBF samples are directly correlated with an adapted energy–density (E) equation by combining the five primary LPBF parameters. We varied laser power (P) in a range of 200–350 W and scanning speed at 400 and 800 mm/s, and a comprehensive study was performed on samples with similar E. The study also showed an almost linear correlation between the LPBF's laser power and the material's hardness and porosity. The corrosion resistance was significantly reduced (from 13 to 400 μm/year) for the LPBF samples compared to a conventionally produced sample due to the dual-phase microstructure, increased porosity and other defects. The static immersion test showed that the process parameters greatly influence the quantity of oxides and the distribution of their diameters in the LPBF samples and, therefore, their corrosion stability. The most challenging part of the study was reducing the amount of ε phase relative to γ phase to increase the non-magnetic properties of the LPBF samples.

Effects of Surface Morphology on Erosion–Corrosion and Corrosion Resistance of Highly Hydrophobic Nickel-Tungsten Electrodeposited Film

Hard nanocrystalline Ni-Co or Ni-W coatings are receiving a growing interest owing to their premium hardness, wear, and corrosion properties for several industrial applications. Furthermore, surface hydrophobicity greatly improves surface corrosion resistance. In this research, the durability of hydrophobic hierarchical NiW electrodeposited film has been evaluated in a high-speed slurry erosion–corrosion (EC) test rig. Two different coatings have been tested: a rough coating obtained in a chloride-based bath (NiWchloride) and a smooth coating obtained in a sulfate-based bath (NiWsulfate). Corrosion behavior over time was evaluated by electrochemical impedance spectroscopy (EIS), while surface hydrophobic performance was determined by the sessile drop method. The morphological features of the coatings were assessed by scanning electron microscopy while roughness modification during the EC tests were identified by means of an atomic force microscopy. During static immersion in the aggressive solution, the impedance modulus of the coatings continuously increased due to an increase in the thickness of corrosion products. During the EC test, the impedance modulus of the smooth NiW coating decreased, losing its barrier property. It was observed that the increase in impedance modulus of the hierarchical structure of the rough NiW coating during EC was far greater than that during static immersion. After 64 min of EC, the NiWchloride was able to resume its hydrophobicity property by storing in air; nevertheless, the NiWsulfate, with a loss of approximately 72% in its initial contact angle, was no longer hydrophobic. The results showed improvements in the lifetime of hydrophobic NiW coatings in erosion–corrosion conditions of the hierarchical nanostructure obtained in a chloride-based electroplating bath.

Corrosion Behavior of Zn, Fe and Fe-Zn Powder Materials Prepared via Uniaxial Compression

Powder metallurgy is one of the most prevalent ways for metallic degradable materials preparation. Knowledge of the properties of initial powders used during this procedure is therefore of great importance. Two different metals, iron and zinc, were selected and studied in this paper due to their promising properties in the field of biodegradable implants. Raw powders were studied using scanning electron microscopy (SEM) coupled with energy dispersive spectrometry (EDX). Powders (Fe, Zn and Fe-Zn in a weight ratio of 1:1) were then compressed at the pressure of 545 MPa to the form of pellets with a diameter of 1.7 cm. Surface morphology and degradation behavior in the Hanks´ solution were studied and evaluated. Electrochemical polarization tests along with the static immersion tests carried out for 21 days were employed for corrosion behavior characterization. The highest corrosion rate was observed for pure Zn powder followed by the Fe-Zn and Fe, respectively. A mixed Fe-Zn sample showed similar properties as pure zinc with no signs of iron degradation after 21 days due to the effect of galvanic protection secured by the zinc acting as a sacrificial anode.

Corrosion and Corrosion Fatigue of Steels in Downhole CCS Environment—A Summary

Static immersion tests of potential injection pipe steels 42CrMo4, X20Cr13, X46Cr13, X35CrMo4, and X5CrNiCuNb16-4 at T = 60 °C and ambient pressure, as well as p = 100 bar were performed for 700–8000 h in a CO2-saturated synthetic aquifer environment similar to CCS sites in the Northern German Basin (NGB). Corrosion rates at 100 bar are generally lower than at ambient pressure. The main corrosion products are FeCO3 and FeOOH with surface and local corrosion phenomena directly related to the alloy composition and microstructure. The appropriate heat treatment enhances corrosion resistance. The lifetime reduction of X46Cr13, X5CrNiCuNb16-4, and duplex stainless steel X2CrNiMoN22-5-3 in a CCS environment is demonstrated in the in situ corrosion fatigue CF experiments (axial push-pull and rotation bending load, 60 °C, brine: Stuttgart Aquifer and NGB, flowing CO2: 30 L/h, +/− applied potential). Insulating the test setup is necessary to gain reliable data. S-N plots, micrographic-, phase-, fractographic-, and surface analysis prove that the life expectancy of X2CrNiMoN22-5-3 in the axial cyclic load to failure is clearly related to the surface finish, applied stress amplitude, and stress mode. The horizontal grain attack within corrosion pit cavities, multiple fatigue cracks, and preferable deterioration of austenitic phase mainly cause fatigue failure. The CF life range increases significantly when a protective potential is applied.

The examination, evaluation and comparison of corrosion effect on different metal surface by various crops based biodiesel

Biodiesel is relatively higher corrosive compared to Diesel; consequently, the concern of viability is now a foremost issue. The biodiesel is self-oxidative in the environment; thus, its characteristics might be changed as fuel. The current work investigates the behavior of numerous biodiesel corresponding to corrosion when exposed to the surface of metal coupons. A gas chromatography mass spectrometry (GC-MS) was performed on eight biodiesel and a hypothesis was proposed to corroborate the hypothesis; static immersion tests, scanning electron microscopic (SEM) and surface roughness analysis were conducted. The immersion test was conducted for 150 days at ambient temperature conditions; later on, the corrosion rate of metals was examined. Results indicate that the Bronze has a maximum corrosion rate of 0.0674 mpy with Karanja biodiesel, followed by palm biodiesel. The Karanja biodiesel has the highest susceptibility to corrosion with all metals, while the Diesel is found to be the lowest with intermediate values for Rapeseed and Castor.

Static corrosion tests of iron-based biomaterials in the environment of simulated body fluids

Biodegradable metallic implants are materials that serve as a temporary implants and scaffolds. They degrade directly in vivo and therefore eliminate need for secondary surgical intervention. They are often made of metals such as magnesium, iron, zinc and can be modified by coating with the inorganic or polymeric layer. In this work iron-based biomaterial was prepared and modified with polymeric (polyethyleneimine, PEI) layer. Its degradation behavior was studied under conditions of simulated body fluids at 37 ± 0.2 °C in the form of static immersion tests. It has been shown that the surface modification caused an acceleration of degradation of the material and also had an influence on the corrosion mechanism.

Corrosion of the metal parts of diesel engines in biodiesel-based fuels

Biodiesel, an environmentally-friendly bio-fuel, has been regarded as one of the most promising alternatives to fossil fuels whose use is rampant in the transportation sector. However, it is important that the corrosive effects of this fuel on engines are studied. This work reviews the corrosiveness that biodiesel exerts on various engine components, especially those made out of metals. First, an analysis of the corrosion mechanisms of metals exposed to biodiesel is provided. The conventional and advanced analysis methods will be applied to measure the level of corrosiveness in static immersion test, and to assess the formation of secondary products, if any, in biodiesel and any metal strips in contact with biodiesel-based fuel. The use of inhibitions to guard against corrosion will be mentioned. Lastly, several significant causes of metal corrosion, namely, the presence of dissolved oxygen and oxidation products, TAN change, a rise in dissolved water, the presence of metals, and the changes in biodiesel properties will also be presented. ©2019. CBIORE-IJRED. All rights reserved