Study On The Influence Of High Temperature Alloy Mechanical Properties And Corrosion Resistance Of The Coating

The thesis is focusing on the influence of the MCrAlY coating on mechanical properties and corrosion behaviors of four different coatings. The microstructure and composition distribution of the coating were also analyzed. MCrAlY coating was prepared by arc ion plating technique in two different directional superalloys with different thickness (40?m and 60?m). The influence of MCrAlY coatings with different thickness on the mechanical properties has been studied. The hot corrosion behaviors as well as the corrosion mechanism in Na2SO4/NaCl (75:25, w/w) mixed salts in the static air at 900? of four different coatings have also been investigated. The analyzing approaches involve mass gain measuring, microstructure observing, phase identification and chemical composition detecting. These approaches were performed with the aid of high-precision optical balance, scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectrum (EDS), and X-ray diffractometer (XRD).The results demonstrate that the MCrAlY coating is dese and adhere tightly to the substrate. The outer layer of the MCrAlY coating is composed of y'/y phase? P-NiAl phase and some a-Cr phase.After the DZ125L superalloy deposited the MCrAlY coating, the yield strength ?0.2 decrease as the coating thickness increased.The creep rupture life increased slightly along with coating thickness at 760?/725MPa and 980?/235MPa.Coating reduced yield strength a0.2?tensile strength ab and percent elongation 8 of DZ38G superalloy, but did not change significantly. The creep rupture of DZ38G at 800?/422MPa increased slightly with thickness, but it decreased by about 7% at 760?/725MPa. So, the effect of coating thickness on creep rupture life is limited on the whole.After hot corrosion, the Ti-Al coating is generally dense and continuous, and the grain size of corrosion product is generally small near the dendritic region. At higher magnificent, hot corrosion product shape rules, thus showing good hot corrosion resistance.For the NiCr-CrAl coating, hot corrosion product were relatively loose except hot corrosion product of DZ38Q and the emergence of spalling phenomenon, even exposed the alloy substrate, so its corrosion resistance was obviously lower than the Ti-Al coating.After hot corrosion, the hot corrosion product of the Co-Al coating on DZ40M surface had serious peeling phenomenon near the dendritic region, the rest of the alloy surface morphology is quite with NiCr-CrAl coating.For the Al-Si coating, the surface morphology of all alloys were similar after hot corrosion, corrosion products are dense and continuous. but near dendritic region, corrosion products are very loose and its shape is very irraguler. The profile of oxide after corrosion is not only compact and discontinuous, but there are different extend of voids, cracks and severe internal oxidation. In four kinds of coating, mass loss rate of the Al-Si coating is the fastest, the corrosion resistance of the worst.