Showing papers on "Salt spray test published in 2001"

Wear and corrosion behaviour of thermally sprayed cermet coatings

Abstract: In order to protect machining parts against wear and corrosion, they are coated by cermet coatings. The coatings consist of WC or Cr3C2 particles in a metal binder, which can be a pure metal or a mixture consisting of Ni, Cr, Co. The examined coatings were produced by high velocity oxy-fuel (HVOF) spraying and were investigated with regard to erosion and corrosion resistance. The combined erosion corrosion tests were carried out at ambient temperature in 0.1 M NaOH and 0.1 M H2SO4 solutions containing sand. Information about the corrosion resistance was gained from electrochemical polarization measurements and salt spray test (NaCl solution). The results of combined wear and corrosion tests showed that the corrosion properties of the sprayed coatings strongly affect the materials loss rate under wear corrosion conditions. Coatings with a less corrosion resistant matrix present enhanced erosion, also. The erosion mechanism of the carbide coatings seams to be controlled by the skeletal network of the carbides. For comparison, flame and plasma sprayed hard Cr2O3 coatings were examined. Due to the low electrical conductivity the corrosion rate of these coatings was very low. Under erosion conditions the hard Cr2O3 coatings exhibited a high erosion rate and the erosion mechanism seems to be that of the brittle erosion due to grain-by-grain removal of oxide grains during impact.

Effects of tungsten carbide thermal spray coating by HP/HVOF and hard chromium electroplating on AISI 4340 high strength steel

Abstract: In cases of decorative and functional applications, chromium results in protection against wear and corrosion combined with chemical resistance and good lubricity. However, pressure to identify alternatives or to improve conventional chromium electroplating mechanical characteristics has increased in recent years, related to the reduction in the fatigue strength of the base material and to environmental requirements. The high efficiency and fluoride-free hard chromium electroplating is an improvement to the conventional process, considering chemical and physical final properties. One of the most interesting, environmentally safer and cleaner alternatives for the replacement of hard chrome plating is tungsten carbide thermal spray coating, applied by the high velocity oxy-fuel (HVOF) process. The aim of this study was to analyse the effects of the tungsten carbide thermal spray coating applied by the HP/HVOF process and of the high efficiency and fluoride-free hard chromium electroplating (in the present paper called ‘accelerated’), in comparison to the conventional hard chromium electroplating on the AISI 4340 high strength steel behaviour in fatigue, corrosion, and abrasive wear tests. The results showed that the coatings were damaging to the AISI 4340 steel behaviour when submitted to fatigue testing, with the tungsten carbide thermal spray coatings showing the better performance. Experimental data from abrasive wear tests were conclusive, indicating better results from the WC coating. Regarding corrosion by salt spray test, both coatings were completely corroded after 72 h exposure. Scanning electron microscopy technique (SEM) and optical microscopy were used to observe crack origin sites, thickness and adhesion in all the coatings and microcrack density in hard chromium electroplatings, to aid in the results analysis.

Chromium (VI)-free conversion layer and method for producing it

Abstract: A chromium(VI)-free, chromium(III)-containing and substantially coherent conversion layer on zinc or zinc alloys presenting, even in the absence of further components such as silicate, cerium, aluminum and borate, a corrosion protection of approx. 100 to 1000 h in the salt spray test according to DIN 50021 SS or ASTM B 117-73 until first attack according to DIN 50961 Chapter 10; being clear, transparent and substantially colorless and presenting multi-colored iridescence; having a layer thickness of approx. 100 nm to 1000 nm; and being hard, adhering well and being resistant to wiping.

Corrosion resistance and Properties of Pump Pistons Coated with Hard Materials

Abstract: In several industrial branches the thermal spray coatings are used to prevent the corrosion of a certain substrate. From the point of view of corrosion resistance, the coating microstructure as well as the chemical, physical and mechanical properties play an important role in the working behaviour of the coated parts. The coating porosity is mainly important because the corrosion media could penetrate towards the substrate through the interconnected pores or other defects located inside the coating. This paper is focussed on the study of wear and corrosion behaviour of Alumina thermal spray coatings for pump piston application. The behaviour of coatings with different percentages of Aluminium Oxide and Titanium Oxide is compared. The whole selected coating materials show high corrosion resistance both in saline and acid environment. The substrate pretreatment, the Ni–Cr bond coat and the spraying procedure ensure to the sprayed layers quite a good adhesion level. The salt spray test and a static immersion test in acid medium have been carried out. Microhardness evaluation, light microscopy and electron microscopy have been used to complete the characterisation programme.

Effect of Scribing Modes on Corrosion Test Results

Abstract: A Prohesion salt spray corrosion test was carried out with 32 primer-coated AA2024-T3 (UNS A92024) test panels with four different kinds of scribes (eight test panels each). The scribing width and depth showed little effect on the test results. The extent of damage to the interface between the primer and the substrate alloy produced the greatest influence on the test results. The concurrent electrochemical impedance spectroscopy (EIS) measurement with Prohesion salt spray showed that the sharp drop of the impedance modulus at low frequency (|Z|0.1Hz) for the samples scribed with a spinning cutter tip started much earlier during the Prohesion exposure than for samples scribed without spinning the cutter tip. There was very little difference observed on the impedance modulus values of the samples with different scribe depth and width. The consistent results between the Prohesion test results and EIS data suggest that the concurrent EIS measurement with Prohesion salt spray may provide additional in...

Thermodynamic parameters of electrodeposition of Zn‐Co‐TiO2 composite coatings

Abstract: Zinc‐cobalt alloys have been electrodeposited from a sulphate bath. The effect of process variables, including temperature, time, concentration of cobalt sulfate and current density on the Zn‐Co deposition was investigated from kinetic and mechanistic viewpoints. Activation energies, enthalpies and entropies were determined according to Arrhenius and absolute rate theories. The codeposition mechanism of TiO2 with cobalt‐zinc in the presence of benzyl triethanol ammonium exthoxylate (BTAE) has been studied. The optimum concentration of the additive was reported. The mechanism of incorporation of TiO2 was suggested and confirmed in view of calculated free energy of adsorption of TiO2. Corrosion resistance of Zn‐Co‐TiO2 alloy was determined by a salt spray test under most of the plating conditions studied.

Corrosion behaviour of painted HSLA panels in chloride environment – a comparative study of different paints

Abstract: High strength low alloy steels have attained wide acceptance as structural materials. Research and development have led to different corrosion preventive methods. High strength low alloy (HSLA) of composition C(0.4%), Mn(0.7%), Si(0.25%). Cr(0.8%), Ni(1.7%) was selected for this study. Epoxy iron oxide, epoxy micaceous iron oxide (MIO), zinc‐rich epoxy and zinc ethyl silicate were used for painting the HSLA panels (150mm × 100mm × 3mm). Physical properties such as film thickness, specific gravity, viscosity, drying times of paints were evaluated and salt spray test, AC impedance and metallographic examination were carried out. Performance of zinc ethyl silicate coating over HSLA was found to be the best followed by epoxy micaceous iron oxide system.

The Relativity of the simulated Accelerated Test of Carbon Steel and Low Alloy Steel and Atmospheric Corrosion Test

Abstract: The test throng the contractive analysis about the result of atmospheric corrosion test of WanNing test station and JiangJin test station and the result of litmjusless salt spray test and acidic salt spray test of carbon steel and low alloy steel ,discuss the relativity between simulated accelerated test and atmospheric corrosion test, confirm the acceleration quality and reappeared quality of simulated accelerated test.

A Study on the Corrosion-resisting Properties of Resin Bonded MoS2 Solid Lubrication Films

Abstract: The effects of phosphuration treatment, proportion of adhesive and solid lubricant, and film thinkness on the corrosion resisitance were examined by the salt spray test. The influences of corrosion-resisting additives, and composite film technology on the corrosion-resisting properties of resin bonded MoS2 solid lubrication films were studied. The test results showed that the phosphuration can increase signidicantly the corrosion-resistance, and the proportion of adhesive and solid lubricant shows a great effect on the corrosion-resisting properties of resin bonded MoS2 solid lubrication films. The corrosion-resisting additives and composite film technology can greatly improve their corrosion-resisting properties.

Chromium-free treated galvanized steel sheet excellent in blackening resistance

Abstract: PROBLEM TO BE SOLVED: To provide an organic composite coated steel sheet in which blackening is suppressed while securing needed corrosion resistance by depositing a chromium-free corrosion inhibition film on a galvanized steel sheet subjected to mechanical treatment such as skinpass rolling and roll brush cleaning. SOLUTION: The corrosion inhibition film is the one essentially consisting of a silicic compound and an organic resin, and the area ratio (S) of a new face formed by mechanical treatment and the corrosion resisting capacity (T) evaluated by the area ratio of while rust generated on the surface of the steel sheet after a salt spray test for 72 hr in accordance with JIS Z2371 after the deposition of the film satisfy the following inequality: (1) S 0) or (2) S<=75 (where T=0).