Study on the Microstructure, Properties and Laser Surface Remelting Behaviors of Fe-based Amorphous Alloy Coatings Deposited by Thermal Spray
|Course||Materials Processing Engineering|
|Keywords||Fe-based amorphous alloy coatings APS HVOF laser surfaceremelting corrosion contributing ratio lead free solder|
In this dissertation, P was replaced by W in Fe-based amorphous alloy powderaccording to the multi-component amorphous alloy design theory, then the powderswere deposited onto Q235substrate through atmospheric plasma spray (APS) andhigh velocity oxgen-fuel spray (HVOF), and the feasibility of replacing P by W inFe-based a morphous a lloy c oatings w as di scussed. A imed a t p orous s tructurecharacteristics of the coating and lower bond strength of the coating and substrate, theFe-based a morphous a lloy c oatings w ere h eat t reated an d l aser su rface r emelted(LSM), and the crystallization and evolution rules of microhardness and propertiesduring processing were studied, and the corrosion resistance of Fe-based amorphousalloy coatings in acid, alkali and salt corrodents was investigated by electrochemicalwork station.First, the feasibility of replacing P by W in Fe-based amorphous alloy coatings(designated as Fe-P and Fe-W, respectively) was demonstrated by investigating theproperties of Fe-based amorphous alloy coatings containing W and P, respectively.Research sh owed t hat t he f racture toughness o f F e-W coatings was s ignificantlyhigher than that of Fe-P coatings, the nano indentor hardness of the two was similar,the in itial crystallization te mperature of F e-W coatings was595.4℃which wa s33.4℃higher t han t hat of F e-P coatings, t he c orrosion current de nsity of Fe-Wcoatings in H2SO4, NaOH and NaCl corrodents were lowered by4.9%,28.6%and21%c omparing w ith t hose of F e-P coatings, respectively. Fe-W coatings couldestablish a stable passivation membrane in NaCl solution and its corrosion potentialwas9times higher than that of Fe-P coatings.Secondly, mechanics of microdefects in L SM al loy ar ea w ere clarified a ndtechnical proposal of alloy height prediction was proposed through research of LSMFe-based amorphous alloy coatings which could provides a theoretical guidance forestablishment of optimized LSM processing scheme. Research showed that when thealloy height was less than the thickness of as s prayed coatings, since the flow ofliquid metal was blocked by t he rough contact surface of bottom LSM bath andunmelted c oatings, internal ga s w as r emained i n t he ba th dur ing r apid c ooling process and circular holes defects were formed, since the stress concentration andtensile stress formed by s olidification of the bath, microcracks were generated inalloy area and unmelted coatings. When alloy height was slightly greater than thethickness of as-sprayed coatings, the LSM coatings had the minimum quantity ofmicrodefects an d p ossessed t he b est co mprehensive p roperties. The alloy he ightcould be p redicted c omparatively exactly through r evising t he one-dimensionalinfinite plate heat conduction formula by self-defined porosity correction factor αand energy efficient utilization rate ξ.Finally, the contributing ratio concept was proposed through affecting factorsinvestigation of corrosion resistance of Fe-based amorphous alloy coatings in NaOHsolution which provided an evaluation method for corrosion resistance of amorphousalloy coatings. Research showed that contributing ratios of amorphous phase content,porosity, alloy e lement a nd surface r oughness to c orrosion pot ential of F e-basedamorphous alloy c oating w ere57.1%,28.7%,14.2%and0%, respectively, a ndcontributing ratios to corrosion current density were85.7%,13.1%,0.6%and0.6%,respectively.