XPS analysis of passive film formed on the G3 nickel-base alloy tubing under corrosive conditions

In the present study, the passive film formed on the G3 nickel-base alloy tubing under corrosive conditions including H2S ,CO2 ,and Cl-at 130 ℃ and 205 ℃ is studied with X-ray photoelectron spectroscopy（XPS）. The results reveal that the passive film formed at 205℃ consists of Cr, Ni, Fe, S and O elements and is over 470 nm in thickness. The passive film can be divided into three layers, the outer-layer is composed of NiS2 and Cr2 S3 , the intermediate-layer of Cr（OH） 3, Ni （OH） 2, NiS2, Cr2 $3 and a small quantity of NiO and Cr2 O3, and the inner-layer of NiO, Cr2 O3, and alloy elements. Due to the invasion of S2 - into the passive film and the decrease of the content of chromium oxide in the film, the corrosion resistance of the G3 alloy in the sour environment at 205 ℃ is weakened.

Microstructure evolution and nucleation mechanism of Inconel 601H alloy welds by vibration-assisted GTAW

Nickel-based alloys exhibit excellent high-temperature stxengtfi and oxidation resistance; however, because of coarse grains and severe segregation in daeir welding joints, these alloys exhibit increased susceptibility to hot cracking. In this paper, to improve the hot-cracking resistance and mechaxtical properties ofinckel-based alloy welded joints, sodium daiosulfate was used to simulate crystallization, enabling the nucleation mechanism under mechaxtical vibration to be investigated. On the basis of the results, the grain refinement mechan- ism during the gas tungsten arc welding （GTAW） of Inconel 601H alloy under wxious vibration modes and parameters was investigated. Compared witfi the GTAW process, the low-frequency mechanical vibration processes resulted in substantial grain refinement effects in the welds; thus, a higher haxdness distxibution was also achieved under the vibration conditions. In addition, the 7＇ phase exhibited a dispersed distribution and segregation was improved in the welded joints witfi vibration assistance. The results demonstxated that the generation of free crystals caused by vibration in the nucleation stage was the main mechaxtism of grain refinement. Also, free equiaxed grains and a dispersed 7＇ phase were found to improve the grain-boundary strength and reduce the segregation, contributing to preventing the initiation of welding hot cracking in nickel-based alloys.

Wear Properties of Ni_(3)Al-Ni_(3)V-Zr-Ni_(5)Zr Alloys under Different Atmospheres

The study examines the friction and wear properties of Ni_(3)Al-Ni_(3)V-Zr-Ni_(5)Zr alloys under varying gas conditions.The alloy was tested in the presence of oxygen and carbon dioxide using a controlled atmosphere wear tester.The study revealed that the wear environ‐mental embrittlement resulted from the diffusion of reactive atomic hydrogen into the interior of the Ni_(3)Al-Ni_(3)V alloy.The addition of Zr elements decreased the proportion of Al elements on the surface of the Ni_(3)Al-Ni_(3)V-Zr-Ni_(5)Zr alloy and reduced the proportion of H atoms produced by the chemical reaction between atmospheric water vapour and Al elements.This inhibited the environmental embrittlement and improved the performance of the Ni_(3)Al-Ni_(3)V-Zr-Ni_(5)Zr alloy.The wear performance of Ni_(5)Zr alloy is superior to that of Ni_(3)Al-Ni_(3)V.When exposed to air in an air environment,the surface of Ni_(3)Al-Ni_(3)V-Zr-Ni_(5)Zr alloy forms a protective Al_(2)O_(3) oxide film on the workpiece,result‐ing in a reduction of the friction coefficient and wear rate of the alloy.The wear mechanism of the alloy is mainly oxidation wear and abra‐sive wear.In an oxygen environment,the surface of the alloy generates a significant amount of Al_(2)O_(3) oxide film.The flaking of the oxide film leads to an increase in the friction coefficient and wear rate of the alloy.In a carbon dioxide environment,the surface of the alloy un‐dergoes severe deformation,and plough lines become apparent.This is accompanied by flaking Si_(3)N_(4) abrasive chips adhering to the sur‐face of the alloy,which intensifies the wear of the alloy.The primary wear mechanism is abrasive wear.Therefore,the friction coefficient and wear rate of the Ni_(3)Al-Ni_(3)V-Zr-Ni_(5)Zr alloy in the atmosphere are optimal.