Salt spray corrosion test of micro-plasma oxidation ceramic coatings on Ti alloy

Ceramic coatings were prepared on Ti-6Al-4V alloy in NaAlO2 solution by micro-plasma oxidation （MPO）. The salt spray tests of the coated samples and the substrates were carded out in a salt spray test machine. The phase composition and surface morphology of the coatings were investigated by XRD and SEAM. Severe corrosion occurred on the substrate surface, while there were no obvious corrosion phenomena on the coated samples. The coatings were composed of Al2TiO5 and a little α-Al2O3 and mille TiO2, and the salt spray test did not change the composition of the coatings. The weight loss rate of the coatings decreased with increasing MPO time because of the increase in density and thickness of the coatings. The surface morphology of the coatings was influenced by salt spray corrosion test. Among the coated samples, the coating prepared for 2 h has the best corrosion resistance under salt spray test.

Effects of laser heat treatment on salt spray corrosion of 1Cr5Mo heat resistant steel welding joints

The surface of 1Cr5 Mo heat-resistant steel welding joint was processed with CO2 laser, and the corrosion behaviors before and after laser heat treatment(LHT) were investigated in the salt spray corrosion environments. The microstructures, phases, residual stresses and retained austenite content of 1Cr5 Mo steel welding joint before and after LHT were analyzed with optical microscope and X-ray diffraction, respectively. The cracking morphologies and chemical compositions of corrosion products after salt spray corrosion were analyzed with field emission scanning electron microscopy(FESEM) and energy disperse spectroscopy(EDS), respectively, the polarization curves were measured on a PS-268 A type electrochemical workstation, and the mechanism of corrosion resistance by LHT was investigated as well. The results show that the passive film of original sample is destroyed owing to the corrosive media penetrating into the subsurface, resulting in the redox reaction. The content of residual austenite in the surface and the self-corrosion potential are increased by LHT, which is contributed to improving the capability of salt spray corrosion resistance.

Effect of Salt Spray Corrosion on Tribological Properties of HVOF Sprayed NiCr-Cr3C2 Coating with Intermediate Layer

The objective of the present work was to determine the influence of the neutral salt spray corrosion on the wear resistance of HVOF sprayed NiCr-Cr3C2 coating with intermediate layer. Ni-Zn-Al2O3 coatings as interlayers were prepared by low pressure cold spray（LPCS） between NiCr-Cr3C2 cermet coatings to form a sandwich structure to enhance the corrosion resistance properties. The tribological properties were examined using the UMT-3 fricition and wear tester by line-contact reciprocating sliding under dry and salt spray one week corrosion. The morphology, element distribution, and phase compositions of the coating and worn sufaces were analyzed by using scanning electron microscopy, energy dispersive spectrometry, and X-ray diffraction respectively. The corrosion behavior of the coating was studied by the open-circuit potential, the electrochemical impedance spectroscopy, potentiodynamic polarization, and salt spray corrosion methods. It is found that the sandwich structured coating has better corrosion resistance than the single layer coating. The results show that under dry wear conditions, the wear mechanism is abrasive and adhesive wear, whereas under salt spray corrosion conditions it becomes corrosion wear. The friction coefficient of the sandwich structured coating after salt spray corrosion is slightly lower than the dry friction coefficient, but the weight of the wear loss is lower than that under dry condition.

Composites Based on GM(1,1)-Markov in the Salt Spray Corrosion Environment

This study was designed to solve the problem of magnesium hazards due to potash extraction in the salt lake region.Using basalt fiber(BF)as the reinforcement material and magnesium oxychloride cement(MOC)as the gelling material,a BF/MOC composite material was prepared.Firstly,the effect of BF addition content on the basic mechanical properties of the composites was investigated.Then,through the salt spray corrosion test,the durability damage deterioration evaluation analysis was carried out from both macroscopic and microscopic aspects using mass change,relative dynamic modulus of elasticity(RDME)change,SEM analysis and FT-IR analysis.Finally,a GM(1,1)-Markov model was established to predict the durability life of composite materials by using durability evaluation indicators.The results show that:when the BF content is 0.10%(by volumetric content),the composites have the best mechanical properties and resistance to salt spray corrosion.However,when the volume of BF content exceeds 0.10%,a large number of magnesium salt crystallization products are observed from the microscopic point of view,and the corrosion of the main strength phase of MOC is more serious.The prediction results of the GM(1,1)-Markov model are highly identical with the raw data.In addition,using the change of RDME as a predictor,RDME is more sensitive to environmental factor compared to the change of mass.Predictions using the change of RDME as a threshold indicate that MOC-BF0.10 has the longest durability life,which is 836 days.The model is important to promote the application of MOC composites in the salt lake region and to promote the healthy development of green building materials.

Electrochemical corrosion failure mechanism of M152 steel under a salt-spray environment

The corrosion failure mechanism of M152 was studied using the neutral salt-spray test to better understand the corrosion behavior of 1Cr12Ni3Mo2VN（M152）, provide a basis for the optimization of material selection, and prevent the occurrence of failure. Moreover, the mechanism was investigated using the mass loss method, polarization curves, electrochemical impedance spectroscopy（EIS）, stereology microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy（EDS）. The results show that M152 steel suffers severe corrosion, especially pitting corrosion, in a high-salt-spray environment. In the early stage of the experiment, the color of the corrosion products was mainly orange. The products then gradually evolved into a dense, brown substance, which coincided with a decrease of corrosion rate. Correspondingly, the EIS spectrum of M152 in the late test also exhibited three time constants and presented Warburg impedance at low frequencies.

Comparison of corrosion behavior of ZL104 alloy at as-cast and heat treatment states

The corrosion behavior of ZL104 alloy at different states (as-cast and heattreatment) in salt spray corrosion (SSC) was studied. The results show that the sample treated afterrefinement and modification has the least corrosive resistance compared with the sample bearingas-cast structure at the beginning of the corrosion. As the corrosion process continued, however,the trend reversed itself. After 44 h continuous corrosion, the corrosive rates of all samples tendto be stable. After experiments, the sample bearing as-cast structure had the most corrosiveproducts on the surface whereas the sample being refined and modified had the least products. TheFourier transformation infrared spectroscopy (FTIR) analyses of the corrosion products show thatthese products are composed of hydroxyl-containing substances.

Galvanic Corrosion of Magnesium Alloy and Aluminum Alloy by Kelvin Probe

Galvanic corrosion on samples of AZ91D magnesium alloy coupled with 2A12 aluminum alloy during neutral salt spray test was investigated.The variations of the surface potential were measured using scanning kelvin probe（SKP）.The results showed that galvanic effect on the corrosion of AZ91D magnesium alloy is closely related to the potential difference between the anodic and cathodic materials.In the initial period,corrosion only occurred in a narrow area at the coupling interface because of the limited distance galvanic current.Then,the corrosion rate of 2A12 aluminum alloy was accelerated due to its poor stability in strong alkali environment,which was attributed to the strong alkalization caused by the corrosion of AZ91D magnesium alloy.With the increase of the potential of 2A12 aluminum alloy as a result of the continuous covering of corrosion products,the potential difference between the two materials was enlarged,which enhanced the galvanic corrosion.

Corrosion mechanism investigation of TiN/Ti coating and TC4 alloy for aircraft compressor application

It is imperative to develop multifunctional erosion and corrosion resistant coatings for compressor blades of aircraft engines in harsh environment.PVD(Physical Vapor Deposition)technology has the advances in processing erosion-resistant coatings;however,the performance of PVD coatings to combat corrosion depends on various coating defects.Determining and comparing the corrosion performances of PVD TiN/Ti coating and uncoated TC4 alloy was the main objective of present work.The 960 h salt spray corrosion and 116 h hot corrosion tests were conducted to simulate the grounding and working environments of the aircraft compressors.The corrosion mechanisms due to the coating defects such as pinhole,columnar boundary and large grain were analyzed based on the OM,Confocal microscope,electrochemical measurements,SEM,XRD and EDS results.Owing to the disordered state associated with the columnar boundary and the coating defect,nitrogen could be easily replaced by oxygen in the hot corrosion process,these structures were channels for fast diffusion of oxygen.Moreover,the Gibbs energy changes of Ti oxidation and TiN oxidation were thermodynamically calculated according to the working condition of aircraft compressors,and considerable research effort was focused on mapping out the phase diagram of Ti,TiN and high pressure gases.The findings of this research can provide insights into developing multifunctional coatings for future aircraft engines.