Formation Of Cr Oxide Research Articles

Chromium partitioning induced evolution of texture, grain boundary constitution, and corrosion behavior of Cu[sbnd]Cr coatings electrodeposited at different temperatures

The corrosion behavior of CuCr coating electrodeposited at three different temperatures (15 °C, 30 °C, 45 °C) was examined. Cr is partitioned in the grain boundaries and as a solute in the Cu matrix. The formation of Cr-oxide at the grain boundaries enhanced the corrosion resistance of the coatings, whereas the presence of Cr as solute significantly altered the matrix micro-texture. The 15 °C deposited coating exhibited the lowest corrosion rate due to higher Cr solute, smaller grain size, (111) surface texture, and a higher fraction of coincidence site lattices. The 45 °C deposited coating exhibited the highest corrosion rate due to lower Cr solute, higher energy (110) surface texture, and higher fraction of high energy grain boundaries.

Microstructural characterization on intergranular stress corrosion cracking of Alloy 600 in PWR primary water environment

• We examine PWSCC cracks of Alloy 600 through microscopic equipment. • Oxygen diffuses into the grain boundaries from the external primary water. • Cr oxides are precipitated on the crack tips and the attacked grain boundaries. • The oxide structure inside a crack consists of double (inner and outer) layers. • The penetrated oxygen strongly affects the PWSCC behaviors of Alloy 600. Stress corrosion cracks in Alloy 600 compact tension specimens tested at 325 °C in a simulated primary water environment of a pressurized water reactor were analyzed using microscopic equipment. Oxygen diffused into the grain boundaries just ahead of the crack tips from the external primary water. As a result of oxygen penetration, Cr oxides were precipitated on the crack tips and the attacked grain boundaries. The oxide layer in the crack interior was revealed to consist of double (inner and outer) layers. Cr oxides were found in the inner layer, with NiO and (Ni,Cr) spinels in the outer layer. Cr depletion (or Ni enrichment) zones were created in the attacked grain boundary, the crack tip, and the interface between the crack and matrix, which means that the formation of Cr oxides was due to the Cr diffusion from the surrounding matrix . The oxygen penetration and resultant metallurgical changes around the crack tip are believed to be significant factors affecting the PWSCC initiation and growth behaviors of Alloy 600.

The Role of Ce Ions in Electrochemical Corrosion of 304 SS in Ce(NO3)3.6H2O

Effects of temperature and potential on the electrochemical corrosion behavior of alloy AISI 304 (UNS S30400) Stainless steel were investigated in 3 wt.% cerium nitrate (Ce[NO3]3.6H2O) solution. With an increase in electrolyte temperature from ambient temperature to 90°C, the corrosion potential of the alloy shifted towards the noble direction, and the resistance to polarization increased due to the formation of Ce-oxide on the electrode surface. The oxide films formed at the open circuit potential (OCP) and a passive potential of 0.4 VSCE were examined by x-ray photoelectron spectroscopy (XPS). The oxide film formed at 50°C and a passive potentialof 0.4 VSCE consists of mixed oxides of Ce and Cr, whereas that at OCP consists of only Cr oxide. The formation of Cr oxides on the electrode surface was primarily due to the nitrate (NO3 −) ions in Ce(NO3)3.6H2O electrolyte.

Chromium enrichment of AISI 304 stainless steel surface after nitrogen ion recoil bombardment of chromium film

When performing nitriding of stainless steels, there is a decrease or even complete depletion of chromium in the nitrogen rich region just beneath the surface, inhibiting the formation of passivated Cr oxide layer, beneficial to withstand corrosive attacks and Cr/Fe nitrides, responsible for hardness enhancement. To overcome this problem, a hybrid technique was used, consisting of depositing a thin chromium film on steel surface and then bombarding it with nitrogen ions. By a complex recoil process, chromium atoms are implanted into the steel matrix. Plasma immersion ion implantation (PIII) was used in this bombardment. The new Cr-rich layer allows the formation of Cr oxides and nitrides. Treated surfaces were characterized by Auger electron spectroscopy (AES) and conversion electron Mössbauer spectroscopy (CEMS), showing formation of a new Cr-rich layer.

Carbon induced metal dusting of iron?nickel?chromium alloy surfaces: a scanning auger microscopy study

In this work, we present an investigation on metal dusting of iron–nickel–chromium (Fe–Ni–Cr) alloy surfaces using scanning auger microscopy. It is shown that the formation of surface Cr-oxide and the surface finish condition can strongly influence and interrupt this catastrophic phenomenon. The accumulation of C within the metal matrix was not always prevented by the Cr-oxide layer. The formation of Cr-oxide was accompanied by a depleted Cr layer (next to the oxide layer) with a depth of several hundreds of nanometers. The depleted Cr layer was significantly broader if the C diffusion within the metal matrix was prevented, while no preferential enrichment of Ni or Fe close to the alloy surface was observed.

Carbon induced metal dusting of iron–nickel–chromium alloy surfaces: a scanning auger microscopy study

In this work, we present an investigation on metal dusting of iron–nickel–chromium (Fe–Ni–Cr) alloy surfaces using scanning auger microscopy. It is shown that the formation of surface Cr-oxide and the surface finish condition can strongly influence and interrupt this catastrophic phenomenon. The accumulation of C within the metal matrix was not always prevented by the Cr-oxide layer. The formation of Cr-oxide was accompanied by a depleted Cr layer (next to the oxide layer) with a depth of several hundreds of nanometers. The depleted Cr layer was significantly broader if the C diffusion within the metal matrix was prevented, while no preferential enrichment of Ni or Fe close to the alloy surface was observed.

Oxidation and protection in copper and copper alloy thin films

The oxidation kinetics of copper thin films have been studied at temperatures below 200 °C in air. The protection of copper from oxidation can be achieved by alloying copper film with Ti, Pd, Cr, or Al. The influence of the composition and microstructure to the oxidation rate has been studied. The compounds Cu3Ti, Cu3Pd, and CuAl2 are stable in the oxidation ambient. The formation of Cr-oxide, which is a passive oxide, explains the inhibition of oxidation on Cu-Cr films. Compared with the crystalline phase, the amorphous Cu65Ti35 alloy film is more oxidation resistant. A TiN layer with oxygen incorporated is more effective in preventing copper oxidation than a TiN layer without oxygen incorporated. A passivating Si3N4 layer on copper thin films can prevent copper oxidation effectively at 350 °C in oxygen ambient.