Microstructure And Properties Of Tin Bronze/Steel Bimetal Prepared By Arc Deposition

Tin bronze has good tribological properties and mechanical properties.As a bearing material,it is usually compounded with steel to form tin bronze/steel bimetallic material,which is used for high wear-resistant structural components such as sliding bearing,bearing bush,guide rail,and rocker arm.The advantages of tin bronze/steel bimetallic materials prepared by arc deposition are excellent interfacial bonding and dense tin bronze layer,which improves the fatigue resistance of material.However,the high-temperature during the arc deposition lead to the mutual infiltration and diffusion of dissimilar materials,which damage the properties of both tin bronze and steel.It is of great scientific and engineering significance to prepare tin bronze/steel bimetallic materials with excellent properties by arc deposition and reveal the formation mechanism and suppression method of infiltrated cracks in tin bronze/steel systems.Tin bronze/steel bimetallic materials were prepared by arc deposition process.The linear arc deposition and swing arc deposition were studied.Characteristics,generation mechanism,and suppression methods of infiltrated cracks during the arc deposition were studied by means of metallographic microscope,scanning electron microscope,transmission electron microscope,in-situ tensile,and other testing methods,combined with finite element simulation,molecular dynamics simulation,and first principles calculation.Finally,the microstructure and properties of tin bronze/steel bimetallic materials without infiltrated cracks were analysed.During the linear arc deposition process,the heat was concentrated in the central area of steel substrate,and the peak temperature was high.The prepared tin bronze deposition layer had large thickness and small width.The defects such as pores and flooding iron existed in the deposition layer,and a large penetration was also produced in the central area of the steel substrate.The temperature distribution of swing arc deposition was relatively uniform,and the peak temperature was low.The deposition layer had the characteristics of small thickness and large width.There was no penetration on the steel substrate,and the dilution ratio was almost0.No defect such as pores and flooding iron existed in the deposition layer,and a transition layer with thickness of 1μm was generated between tin bronze and steel.The infiltrated cracks were generated in the tin bronze/steel bimetallic materials during arc deposition process.The infiltrated cracks originated at tin bronze/steel interface and distributed along the grain boundaries of the steel.The copper-rich phase in the infiltrated cracks expanded under low stress and strain,which resulting in the brittle fracture of steel and reducing the mechanical properties of steel.The surface of steel was subjected to three-dimensional tensile stress during arc deposition process.With the increase of heat input,the temperature and thermal stress increased,so that the severity of infiltrated cracks increased and the mechanical properties of steel substrate further decreased.As the tin bronze was deposited on nickel plated steel under low heat input,nickel was enriched at the tin bronze/steel interface,and there was no infiltrated crack in the steel.As the heat input was high,the enrichment of Ni at the tin bronze/steel interface disappeared,and infiltrated cracks also occurred in the steel substrate.The results of molecular dynamics simulation and first principles calculation showed that when liquid Cu contacts solid Fe,Cu atoms were diffused into Fe grain boundaries.The physical structure and electronic structure of the Fe grain boundary were changed,and the strength of the Fe grain boundary decreased due to the diffusion of Cu.While the combined action of Cu and Sn atoms make the drastic decrease of grain boundary.The weakened grain boundary cracked under thermal stress,and further resulting in the formation of infiltrated cracks.Although the combined action of Cu and Ni atoms also reduced the strength of Fe grain boundary,but the reduction was small（compared with the reduction of strength for grain boundary by Cu atoms）.Therefore,infiltrated cracks could be avoided under lower heat input.Arc deposited tin bronze contained fine grain region,columnar dendrite region,and free dendrite region.Microstructures were obviously refined compared with the as-cast tin bronze.The dendritic crystal wasα-Cu（solid solution containing Sn）phase.The(α-Cu+δ-Cu₄₁Sn₁₁+Cu₃P)ternary structure existed in the dendrite gap.The steel substrate was composed of flake pearlite,granular cementite,and ferrite.The bimetallic materials obtained by arc deposition had high mechanical properties.The tensile strength and elongation of the deposition layer were greater than 480MPa and 29%respectively.The tensile strength and elongation of bimetal were greater than 490MPa and 26%respectively.The shear strength of bimetallic was greater than 190MPa.After annealing at 300℃,the tensile strength,shear strength,and hardness of the bimetallic material were decreased,the elongation after fracture was increased.The bimetallic had no crack as it bent 180°.The annealed bimetallic materials were processed into bimetallic standard bearing shells.After the high and low temperature experiment between25℃and 165℃,no cracking and falling off phenomenon occurred,and the sapphire fatigue strength was not less than 202MPa.