Grey Clustering Theory to Assess the Effect of Mineral Admixtures on the Cyclic Sulfate Resistance of Concrete

Concrete specimens made with ordinary portland cement or ordinary portland cement incorporating fly ash with the replacement of 10% or 20%, ground blast furnace slag with the replacement of 15% or 30%, or 15% fly ash and 15% ground blast furnace slag were made and exposed to a cyclic sulfate environment. Concrete properties including relative dynamic elastic modulus, chloride ion diffusion coefficient, compressive strength and flexural strength were measured. Effect of mineral admixtures on the cyclic sulfate resistance of concrete was assessed based on the grey clustering theory. The experimental results indicate that the cyclic sulfate resistance of concrete incorporating ground blast furnace slag belongs to the higher grey grade, which exhibits that it possesses excellent cyclic sulfate resistance. With increasing addition of fly ash, the cyclic sulfate resistance of concrete changes from the medium grey grade to the lower grey grade, which shows that incorporation of fly ash is disadvantageous for the cyclic sulfate resistance of concrete.

Cyclic Oxidation Resistance of In718 Superalloy Treated by Laser Peening

The aim of this study was to improve the cyclic oxidation resistance of In718 superalloy by laser peening（LP）. Specimens were treated by LP from one to three times, respectively. The cyclic oxidation tests at 900 ℃ for periods up to 2 h were conducted. Changes of the top surface morphology and microstructure were analyzed by scanning electron microscope （SEM）, energy-dispersive spectra （EDS）, transmission electron microscope （TEM） and X-ray diffraction technique （XRD）, respectively. The weights were measured between the oxidation cycles to assess the oxidation of the specimens. The top surface microstructure after LP was characterized by highly tangled and dense dislocation arrangements and a high amount of twins. Protective oxidation layer was generated more quickly on the surface treated by LP. The average oxidation rate was about 50 % lower. A tiny homogeneous oxidation layer containing （Fe,Cr）2O3, NiCrO3 and Ni（A1,Cr）2O4 spinel was generated on the surface. The experimental results of cyclic oxidation tests show that specimens treated by LP have a better high temperature oxidation resistance, and the antistrip performance of the oxidation layer improves. Moreover, the effects of LP are strengthened with the increase of laser peening.

Si-Al COATING ON PURE MOLYBDENUM SUBSTRATE AND ITS CYCLIC OXIDATION BEHAVIOR

The halide-activated pack cementation method is utilized to codeposit aluminum and silicon on Mo substrate. Emphasis is placed on the microstructure and elevated-temperature oxidation resistance of coatings. The results show that hexagonal Mo(Si, Al)2 as a main phase and a little amount of the lower disilicide Mo5Si3 was formed on Mo substrate through the halide-activated pack cementation method. The resultant Si-Al coating on Mo substrate exhibits excellent cyclic oxidation resistance. The excellent cyclic oxidation resistance of the coatings is attributed to the formation of alumina on the coatings during the oxidation.

Corrosion Behavior of S450EW Low-alloy Weathering Steel in Cyclically Alternate Corrosion Environments

Weathering steel is widely used in various fields due to its excellent mechanical properties and high corrosion resistance. The effect of chromium content on the S450 EW weathering steel in cyclic immersion test was studied. The results indicated that the corrosion resistance of S450 EW weathering steel is closely related to chromium content. The addition of chromium significantly inhibited the weathering steel corrosion. The corrosion rate of experimental steel after 96 h immersion was 1.101 g·m-2·h-1. The rust of S450 EW weathering steel was mainly constituted of Fe OOH and Fe3O4 phase, and the elevation of chromium content promoted the formation of α-Fe OOH. The fine precipitates of the two phases contributed to the formation of dense dust layer of test steel. Furthermore, the increase of chromium is beneficial for the cure of original defects and cracks of the rust layer via the enrichment of chromium. The corrosion potential and the resistance of corrosion process were thus increased, protecting the experimental steel from further corrosion. A S450 EW steel with corrosion resistance more than 1.5 times of Q450NQR1 steel was prepared.

High temperature oxidation and ablation behaviors of HfB_(2)-SiC/SiC coatings for carbon/carbon composites fabricated by dipping-carbonization assisted pack cementation

To improve the uniformity and the content of HfBin Hf B-Si-based ceramic coating and alleviate the damage of substrate,and then enhance the high-temperature(1700°C)oxidation and cyclic ablation resistances of carbon/carbon composites,a close-knit double layer HfB_(2)-SiC/SiC coatings with a mosaic structure and high content of HfBwere prepared by a novel dipping-carbonization assisted pack cementation methods(DPC–HS/S).In contrast,a HfB_(2)-SiC/SiC coatings were also fabricated by pack cementation(PC–HS/S).Results revealed that the oxidation and ablation protective performances of the DPC–HS/S coatings were superior to those of PC–HS/S coatings.After 30 thermal cycles between 1500°C and room temperature,the mass gain of the coated sample was 0.78%,and the mass loss was 1.65%after oxidation at 1700°C for 156 h.Moreover,under an oxyacetylene torch ablation for 180 s(3 cycles),the linear ablation rate of the DPC–HS/S coated specimen was 1.62μm/s,which was much lower than that of PC–HS/S coated specimen(3.08μm/s).