Effect of microstructure evolution of Ti6Al4V alloy on its cavitation erosion and corrosion resistance in artificial seawater

The investigate about the effect of the microstructure of Ti6Al4V alloy on its cavitation erosion and corrosion properties in marine can provide the key basis for the application.On the basis of as-received Ti6Al4V(TC4)alloy,FC-TC4 and AC-TC4 alloys were prepared by heat treatment with the cooling method of a furnace and atmospheric environment,respectively.Then the microstructure evolutions of three samples were scrutinized and the effect of microstructure on their cavitation erosion and corrosion resistance was explored.The results showed that more recrystallized grains formed as well as its content of α grains and high-angle grain boundaries increased in AC-TC4 alloy.To FC-TC4 alloy,there was obvious grain growth apart from recrystallization.Moreover,many nanotwins of Ti V and Ti Al_(3)were formed separately in FC-TC4 and AC-TC4 alloys due to the dislocation migration during heat treatment.The microstructure evolution led the hardness and elastic modulus of AC-TC4 alloy were the best,followed by FC-TC4 alloy,that of TC4 were the worst.Similarly,passivating ability of AC-TC4 alloy was the best among three samples because of its microstructure.Although cracks extended along the grain boundaries under the action of continual cavitation erosion,the passivation film formed by TiO_(2) and Al_(2)O_(3) would enhance their resistance to further corrosion and cavitation erosion in artificial seawater.

In-situ formation of layer-like Ag_(2)MoO_(4)induced by high-temperature oxidation and its effect on the self-lubricating properties of NiCoCrAlYTa/Ag/Mo coatings

Ag-Mo-O ternary oxide has attracted growing attention because of its potential as a solid lubricant at high temperatures.This work designs and prepares NiCoCrAlYTa/Ag/Mo composite coating,performed using high velocity oxy-fuel(HVOF)spraying technology.The environment temperature plays an important role in the microstructure and phases as well as lubricant properties of NiCoCrAlYTa/Ag/Mo coatings.When the environment temperature is above 600℃,the outer diffusion and oxidation of Ag and Mo lead to the formation of Ag2 MoO4 on the coating surface.Layer-like Ag2 MoO4 could form a continuous lubricant film at 800℃and consequently let the composite coating present the best tribological properties.Meanwhile,a small number of hard particles could play a good bearing role during friction and improve the tribological properties of the composite coating.

Effect of annealing treatment on microstructures,mechanical properties and cavitation erosion performance of high velocity oxy-fuel sprayed NiCoCrAlYTa coating

The mechanical parts serving in the marine environment are up against the dual damage of corrosion and cavitation erosion,so the Ni Co Cr Al YTa coating with excellent corrosion resistance is successfully prepared by high velocity oxy-fuel(HVOF)sprayed technology to protect the equipment from deterioration.The chemical composition and mechanical properties as well as the microstructure evolution of the coating before and after annealing treatment are studied.At the same time,the influence of annealing treatment on the corrosion and cavitation erosion behaviors of the coating is investigated,as well.The NiCoCrAlYTa coating mainly containsγ-Ni,β-Ni Al,andγ’-Ni3Al phases.During the deposition,the microcrystals or incomplete crystals generate in the interior of the coating because of the large temperature difference and impact force.Meanwhile,there is twin crystal structure in the as-spayed coating.After annealing treatment,the growth of grains and the segregation of reactive elements improve interface strength and inhibit the formation of micro-defects in the coating.The annealing temperature is of significance to the microstructure,mechanical properties,anti-corrosion and cavitation erosion resistance of the coating.This study provides a combined approach toward improving the corrosion and cavitation erosion resistance of NiCoCrAlYTa coatings.

High temperature induced“glaze”layer formed in HVOF-sprayed NiCrWMoCuCBFe coating and its wear reduction mechanism

The in-situ formation of oxides on alloy surface induced by high temperature can effectively reduce wear and resist oxidation.In consideration of the solid solution strengthening effect and great oxidation resistance of additional elements at elevated temperature,the NiCrWMoCuCBFe coating was prepared by high velocity oxygen flame(HVOF)spraying technology,and its tribological behavior was scrutinized from 25 to 800°C.By means of high temperature Vickers hardness tester and high temperature X-ray diffractometer,the mechanical properties and microstructures of NiCrWMoCuCBFe coating were measured.And the effect of the mechanical properties and microstructures of the coating on tribological performance was discussed in detail.The results showed both its friction coefficient(0.37)and wear rate(5.067×10^(−6)mm^(3)·N^(−1)·m^(−1))at 800℃ were the lowest,which was mainly related to the formation of“glaze”layer on the coating surface at high temperature.The glaze layer consisted of two parts,which were NiCr_(2)O_(4)oxide film with the ability of interlaminar slip formed in the outer layer and nano-grains existed in the inner layer.Worth mentioning,these nano-grains provided bearing capability while the oxide film was vital to reduce wear rate and friction coefficient.As the ambient temperature increased,many hard oxides were produced on the wear scars,including NiO,Cr_(2)O_(3),MoO_(3),and Mo_(2)C.They can improve tribological and mechanical properties of NiCrWMoCuCBFe coating at a wide temperature range.