Research On Preparation,microstructure And Properties Of CoFeNi-based High Entropy Alloy Coatings By Argon Arc Cladding

In order to satisfy the hardness and wear properties requirements of the alloy cladding layer on the first and second thrust surfaces of the three-cone bit,Mn,Cr,Nb,and Si/SiC were added into the CoFeNi medium entropy alloy which were prepared cladding layer on 20CrMo steel substrate using argon arc method,so that the quality and production efficiency of the thrust surfaces were improved.It was investigated that the each component effect on on the microstructure and properties of the cladding layer.It is expected that CoFeNi-based alloy will be applied in the first and second thrust surfaces of the tri-cone bit replaced Co119 alloy.According to the calculation of high entropy alloy phase formation theory,CoFeNi and CoFeNiMnare both medium-entropy alloys,and others are high entropy alloys,in CoFeNi-based alloys.The cross-sectional microstructure of CoFeNi alloy cladding layer from the fusion line to the top of the cladding layer is as follows:plane crystal,columnar crystal,dendritic crystal and equiaxed crystal.CoFeNi medium-entropy alloys cladding layer is composed of face centered cubic(FCC)single phase solid solution.With the addition of Mn,Crand Nb,the phase composition of the alloys did not change,but the hardness of the alloy increased.The hardness of CoFeNiMnCrNbhigh entropy alloy reaches the highest value?37.2 HRC.For CoFeNiMnCrNbSi_x(x=0.5?1.0?1.5?2.0)high entropy alloy cladding layer,with Si content increasing from x=0.5 to x=2.0,the hardness of the cladding layer increased.t,the high entropy alloy was mainly composed of Fcc phase under x<1.5.In contrast,the alloy was composed of Fcc and Bcc double phases under x?1.5.The formation of Bcc phase caused the sharp rise of the hardness of the alloy.The hardness of CoFeNiMnCrNbSi_2.0 high entropy alloy reached the highest value?68.0 HRC.For CoFeNiMnCrNb(SiC)_x(x=0.5?10?1.5?2.0)high entropy alloy cladding layer,the alloy was mainly composed of Fcc phase under x?0.5.As the fraction of SiC increased to 1.5,the alloy was composed of Fcc and NbC phases.When x?1.5,the alloy was composed of Fcc,Bcc and NbC phases.With SiC fraction increasing,the hardness of cladding layer increased.The hardness of CoFeNiMnCrNb(SiC)_0.5 high entropy alloy cladding layer is 61.3 HRC,which reached the expected hardness range(61?62 HRC),and the hardness of CoFeNiMnCrNb(SiC)_2.0 high entropy alloy is the highest,?1585.5 HV.Using argon arc cladding instead of oxyacetylene surfacing to prepare the cladding layer of the thrust surface could avoid defects such as cracks and pores,and improve production efficiency.Under the same geological conditions,the tri-cone bit using the CoFeNiMnCrNb(SiC)_0.5 high entropy alloy cladding layer caused the drilling depth deeper compared with the tri-cone bit using Co119 alloy cladding layer.The drilling depth of enclosing stratum increased by 16.1%and the drilling depth of ore layer increased by 13.7%,which extended the life of the drill significantly.From an economic perspective,compared with Co119 alloy cladding layer prepared by oxyacetylene surfacing method,CoFeNiMnCrNb(SiC)_0.5 high entropy alloy prepared by argon arc cladding method has lower cost and the bit has higher price.Therefore,the CoFeNiMnCrNb(SiC)_0.5 high entropy alloy cladding layer by argon arc cladding has the potential to become the wear-resistant coating on the first and second thrust surfaces of tooth claws.There are total 31 pictures,22 tables,and 116 references in the thesis.