ABSTRACT
In this dissertation, P was replaced by W in Fe-based amorphous alloy powder according to the multi-component amorphous alloy design theory, then the powders were deposited onto Q235 substrate through atmospheric plasma spray (APS) and high velocity oxgen-fuel spray (HVOF), and the feasibility of replacing P by W in Fe-based a morphous a lloy c oatings w as di scussed. A imed a t p orous s tructure characteristics of the coating and lower bond strength of the coating and substrate, the Fe-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 properties during processing were studied, and the corrosion resistance of Fe-based amorphous alloy coatings in acid, alkali and salt corrodents was investigated by electrochemical work 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 the properties 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 ignificantly higher 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 was 595.4℃ which was 33.4℃ higher t han t hat of F e-P coatings, t he c orrosion current de nsity of Fe-W coatings in H2SO4, NaOH and NaCl corrodents were lowered by 4.9% , 28.6% and 21% c omparing w ith t hose of F e-P coatings, respectively. Fe-W coatings could establish a stable passivation membrane in NaCl solution and its corrosion potential was 9 times higher than that of Fe-P coatings.
Secondly, mechanics of microdefects in L SM al loy ar ea w ere clarified and technical proposal of alloy height prediction was proposed through research of LSM Fe-based amorphous alloy coatings which could provides a theoretical guidance for establishment of optimized LSM processing scheme. Research showed that when the alloy height was less than the thickness of as s prayed coatings, since the flow of liquid metal was blocked by t he rough contact surface of bottom LSM bath and unmelted c oatings, internal ga s w as r emained i n t he ba th dur ing rapid c ooling process and circular holes defects were formed, since the stress concentration and tensile stress formed by s olidification of the bath, microcracks were generated in alloy area and unmelted coatings. When alloy height was slightly greater than the thickness of as-sprayed coatings, the LSM coatings had the minimum quantity of microdefects an d possessed the best comprehensive p roperties. The alloy height could be p redicted c omparatively exactly through r evising t he one -dimensional infinite plate heat conduction formula by self-defined porosity correction factor α and energy efficient utilization rate ξ.
Finally, the contributing ratio concept was proposed through affecting factors investigation of corrosion resistance of Fe-based amorphous alloy coatings in NaOH solution which provided an evaluation method for corrosion resistance of amorphous alloy 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-based amorphous alloy c oating w ere 57.1%, 28.7%, 14.2% and 0%, respectively, a nd contributing ratios to corrosion current density were 85.7%, 13.1%, 0.6% and 0.6%,respectively.
KEY WORDS：Fe-based amorphous alloy coatings, APS, HVOF, laser surface remelting, corrosion, contributing ratio, lead free solder
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