Study On Fe-based Amorphous Alloy Powder Prepared By Plasma Spraying

Fe-based amorphous alloys are widely used because of a series of excellent properties.But the supercooling is an essential condition to prepare amorphous alloys,leading to a complicate process with a high cost.Plasma spraying has the physical conditions of melting,atomization and rapid cooling spraying materials with high efficiency process.However,the cooling rate is not enough to achieve the conditions for preparing Fe-based amorphous alloys,so the amorphous materials can not be prepared directly by plasma spraying.In view of the above problems,this paper combines the constitutional supercooling of master metal with the rapid cooling of plasma spray,optimizes the process of preparation of amorphous materials by plasma spraying,and reveals the rules of preparation of amorphous materials by plasma spraying.The research takes eutectic point of Fe-based amorphous alloy as the research object.To clarify the influence of several elements on the glass formation ability（GFA）,the first principle molecular dynamics is used to calculate the structural characteristics of master alloy and a few elements can be selected to improve the glass formation ability.The mater alloy is prepared by replacing the iron（Fe）with selected elements in different contents.using plasma spraying method to prepare amorphous materials,further optimize the composition of the alloy.The structure of the alloy at different cooling rates is discussed and analyzed,working out the rules of GFA about undercooling and cooling rate of alloys.Finally the process parameters of plasma spraying equipment and the spraying distance are adjusted and the amorphous powder is prepared by plasma spraying method.The main conclusion are shown as follows:The addition of various elements into Fe₇₅Si₈B₁₇alloy enhanced the solute-solute avoidance in liquid state and amorphous state.The local atomic number of the first nearest neighbor of the amorphous and liquid alloy changed a little,while it mainly affected the chemical composition of the nearest neighbor of the boron（B）atom.Adding chromium（Cr）,cobalt（Co）and manganese（Mn）element into alloy,the nearest neighbor B-B atom pair in amorphous state changed little while the first peak intensity of pair correlation function g（r）_B-Bbecame lower by adding phosphorus（P）and erbium（Er）.The spherical and flatten particles were obtained by plasma spraying master alloy.The structure of spherical particles were crystal which was similar to the mater alloy,while the flatten particles contained partial amorphous structure.For instance,alloy with amorphous content of 15.3at.%could be prepared by plasma spraying Fe₇₅Si₈B₁₇.Replacing the B with the P content of 5at.%,the GFA of alloy was greatly improved,and pure amorphous materials can be prepared by plasma spraying.Upon slow cooling,alloy sample contains several phases,which were mainly metastable phase Fe₃B and stable phaseα-Fe,Fe₂B.And there was onlyα-Fe phase in alloy sample under the condition of sharp cooling.The phase composition of the alloy at lower cooling rate was the same as that ofα-Fe（Co）phase in thermal spraying by adding Co into alloy.The alloy exhibited better GFA with 5at.%addition in Co.The alloy with Er addition presented inhibition the precipitation ofα-Fe（Si）phase,and the thermal stability of the alloy was significantly improved when the Er content was 0.5at.%.The crystallization order of the alloy Fe-Si-B with addition various elements was Fe₂₃B₆--α-Fe--(α-Fe+Fe₂₃B)--（α-Fe+Fe₃B）--（α-Fe+Fe₃B+Fe₂B）--（α-Fe+Fe₂B）.A calculation led to result of the critical thickness of amorphous particles prepared by plasma spraying was 31μm.In order to satisfy the condition of amorphous formation,the cooling rate between the melting point and the crystallization temperature of the alloy must be increased.The cooling rate above the melting point did not affect the formation of amorphous.The thickness of sprayed splats reduces from 80～220μm to 5～21μm with spray parameter as follows.The current of plasma spraying was 700A,the voltage was 50V,argon flow rate was1600L/min,hydrogen flow rate was 300L/min,spraying distance was reduced from 200 to160mm,the master alloy feeding rate was reduced from 50 to 10mm/min,the matrix increased from 100mm×100mm×5mm to 300mm×200mm×5mm,the fixed spray gun was in motion of1m/min.Fe₇₀Si₈B₁₇X₅（X=Fe,Cr,Mn,Co）and Fe₇₄Si₈B₁₇X₁（X=Er）amorphous powder were obtained by plasma spraying.