Investigation On The Mechanical Properties And Wear Resistance Of Si Monel Alloy

Monel is a nickel-copper alloy based on nickel,with a typical composition of 70%nickel and 30%copper.It is an important type of nickel-based corrosion-resistant alloy.The alloy with silicon element added to the traditional Monel alloy is called Si Monel alloy.The addition of silicon element can improve the comprehensive mechanical properties and wear resistance of alloy.This study aims to systematically reveal the influence of the second-phase particles on the comprehensive mechanical and wear resistance of Si Monel alloy,and explore the wear mechanism of Si Monel alloy.In the present work,Monel alloys with different silicon contents were prepared by two different methods:non-vacuum intermediate frequency induction melting and vacuum intermediate frequency induction melting.The microstructure morphology,mechanical properties and dry sliding behavior of Si Monel alloys were investigated systematically.The microstructure of alloy was observed using optical microscope,scanning electron microscope and electron probe microscope analysis.The experimental results indicated that Si Monel alloy contains solid solution matrix and a dual-scale second-phase in the matrix,i.e.microscale second-phase(MSP)particles and nanoscale precipitates(NP).When the silicon contents are2.5wt.%,3.5wt.%,4.5wt.%and 5.5wt.%respectively,with the content increasing,the volume fraction of MSP particles and NP both increase and the aspect ratio of MSP particles increases.The morphology of MSP particles gradually transforms from small granular to long strip shape,and finally connects with one another to form a complete network structure.In the hardness test and tensile test,as the volume fraction of MSP particles and NP increases,the resultant hardness,yield strength and ultimate tensile strength of Monel alloy increase significantly while the elongation is reduced.When the Si content increases from 3.5wt.%to 4.5wt.%,it is demonstrated that the main fracture mode of alloy transforms from ductile failure to quasi-cleavage failure.The changes in the mechanical properties of alloy are also particularly significant here.After the friction experiments,the worn surfaces of samples are observed by confocal laser scanning microscope(CLSM)and atomic force microscope(AFM).It is demonstrated that the main wear mechanism converts from the mixture of abrasive and adhesive wear to single abrasive wear,and the thickness of plastic deformation layer gradually decreases.With the Si content increasing from 2.5wt.%to 4.5wt.%,the wear rate descends from 115.3×10^-13m³/m to the minimum of 56.8×10^-13m³/m,at the same time the friction coefficient decreases from 0.53to 0.47.Due to the existence of completely netlike MSP particles which are likely to split the matrix,the Ni-30Cu-5.5Si alloy exhibits an abnormal higher wear rate even with the highest hardness.The cracks form and propagate easily along the interface between the matrix and netlike MSP during friction,which results in the continuous spalling of MSP particles and the decrease in friction performance.In this case,the decreasing deformation rate is overweighed by the increasing crack nucleation and propagation rate with the increase of surface hardness.It is believed that the netlike second-phase particles can split the matrix and deteriorate the friction performance of alloy,which should be avoided in wear-resistant materials.This present work provides a significant guidance for the design of wear-resistant materials.