| Fe-based amorphous alloys are considered as potential engineering materials due to their relatively low cost and many unique properties,including high hardness and strength as well as excellent wear and corrosion resistance.However,the limited cooling rate limits Fe-based amorphous alloys to powder,strip,and bulk of finite shape and size.In addition,the highly-localized shear bands and inhomogeneous shear deformation behavior at room temperature lead to the catastrophic brittle fracture in a shear mode,which seriously limited the engineering application of the Fe-based amorphous alloys.The preparation of Fe-based amorphous coating by thermal spraying can not only realize the application of Fe-based amorphous alloys on large-scale workpieces,but also can effectively exert its wear-resisting protective effect.Given the excellent wear resistance of Fe-based amorphous coatings,this dissertation therefore takes Fe-based amorphous coatings prepared by detonation spraying as research targets.The tribological properties and wear mechanism of as-sprayed coatings,cryogenic thermal cycling treated coatings and powder-treated coatings have been investigated by using differential scanning calorimetry?DSC?,X-ray diffraction?XRD?,scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,Vickers microhardness tester,nanoindentation and friction/wear testing system as well as the process of cryogenic thermal cycling.The details are as follows:The Fe-based amorphous coating has been successfully deposited on a 9Ni steel substrate by D-gun spray method.The wear behaviors of the Fe-based alloy coating were studied in detail under dry sliding condition in a ball-on-disc mode by using Si3N4 ball as the counterpart.The results showed that the Fe-based amorphous coating prepared by the D-gun spray method had a substantially complete amorphous structure,and its coating thickness,porosity,and surface hardness were 200±30?m,and 822±10 Hv0.1,respectively.The coatings therefore presented pretty good wear-resistant properties under dry sliding wear conditions with wear rates of?2.7416.30?×10-6 mm3N-1m-1.Moreover,it was found that the wear rate of the present Fe-based amorphous coatings was more sensitive to the applied sliding speed than the normal load.As the sliding speed changed from low(0.1 m s-1)to high(1.0 m s-1)speed,the wear rate changed very significantly.This is mainly because the wear mechanism of the present Fe-based amorphous coating changed from oxidative wear to delamination wear as the slip speed increases.Using the process of cryogenic thermal cycling,Fe-based amorphous coatings spraying with different process parameters were treated from 060 cycles with the interval10 cycles.Effects of cryogenic thermal cycling on microstructure,mechanical and tribological properties were investigated.It was found that,after 60 cycles,high-porosity?2.1%and 1.0%?coatings prepared at low acetylene flow did not or few cracks,while low-porosity?0.4%?coatings prepared at high acetylene flow showed cracking networks.The uniformity of hardness distribution had a trend of increasing first and then keeping steady with the increase of cycles,and the turning point is 30 cycles.The plastic work Wp continued to increase slighty with the increase of cycling.Elasticity index H/E and plasticity index H3/E2 also showed an increasing trend before 50 cycles,but both decreased significantly after the cycling reaches 60 cycles.The COF and wear rate of coatings increased initially,then followed by a decrease,but then again increased with the increase of cryogenic thermal cycling cycles.The 50-cycles coatings exhibited the lowest COF?0.60?and wear rate(0.56×10-5 mm3N-1m-1).The results indecated that,by controlling the porosity of the coatings and utilizing the cryogenic thermal cycling process,the friction and wear properties of the Fe-based amorphous coating can be optimized.Powder-original and powder-treated Fe-based amorphous coatings have been deposited by detonation spraying successfully to study the effect of cryogenic thermal cycling treatment?-196?-25??of Fe-based amorphous powder on tribological properties of D-gun sprayed coatings.The results showed that the powder was still amorphous structure after cryogenic thermal cycling treatment,and no cracking and breakage occurred.Compared with the powder-original coating,the porosity of the powder-treated coating decreased from 1.0%to 0.4%.The unmelted particles decreased obviously,and the powder spreading was more sufficient.The microhardness decreased slightly from 845.4 Hv0.1 to 813.5 Hv0.1,but the test error significantly reduced.And the slope of Weibull distribution fitting line increased obviously from 7.1196 to 9.6414.The friction coefficient decreased from 0.76 to 0.73 and become more stable.The wear rate is similar,both on the order of 10-6 power.The wear mechanism transformed from fatigue delamination wear of the powder-original coating to dominated by oxidative wear and plastic deformation. |
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