Kinetics And Wear Resistance Of VC_p/Fe Surface Gradient Composite Produced By In Situ

The usability of material can be improved by realizing compoment and microstructure gradient distribution on the surface of a homogeneous material,which due to better bonding strength between enhancement layer and matrix.The controllability of the surface gradient composite make it widely used in aviation aerospace,cutting tools,metallurgy,mine and other fields.The VCp/Fe surface gradient composite was prepared by using vanadium plate(99.90%)and grey cast iron as raw materials,which make use of the better carbide formation characteristics of metal vanadium.And the in situ reaction process,microstructure evolution,growth dynamics of the reaction layers and wear resistance of the composite were sutdied.The main research results include:(1)The VCp/Fe surface gradient composite can be prepared by solid phase reaction method.With the increase of heat preservation temperature(950?,1000? and 1050?)and the holding time(0.5h,1h,2h,4h),the original phase(V2C and V8C7)increased gradually,and no new phase was formed.The thickness of the layer is 55 ?m when the holding temperature and time are 950? and 0.5h,respectively,while 168 ?m for 4h.With the increase of the holding time,the thickness of the reaction layer increased gradually,while the density of the dense layer of VSC7 decreased.(2)The relationship among the thickness of reinforcement layer,the temperature and holding time of the VCp/Fe gradient composites was studied.The results showed that with the increase of temperature,the thickness of V2C and V8C7 dense layer exponentially increase gradually;at the same time,with the prolonging of holding time,the thickness of V2C and V8C7 dense layer is parabola growth.Calculation shows that the V2C and V8C7 dense layer growth activation energy were 53.92kJ/mol and 42.39kJ/mol,respectively.It is deduced that the relationship between the thickness of V2C or V8C7 dense layer(d)and reaction temperature(T)and time(t):For V2C dense layer,d=d0+kt1/n=3.52×10-4+2.10×10-8 exp(6063.94/T)t 1/2 For V8C7 dense layer,d=d0+kt1/n=8.10 × 10-4+1.810-6 exp(8114.28/T)t1/2(3)The microhardness of the VCp/Fe surface gradient composites showed a gradient distribution from the surface to the matrix.The microhardness of the V2C dense layer is the highest and the average hardness is 1963 HV0.1,which is six times higher than that of the matrix(235 HV0.1).The average hardness of V8C7 dense reaction layer reach to 1707 HV0.1.The elastic modulus of V8C7 dense layer is 431.98 GPa by nanoindentation.The fracture toughness of the V8C7 dense layer is 3.73 MPa·m1/2.Under abrasive wear conditions,the relative wear resistance of V2C and V8C7 dense layer is 23.41.V2C layer on the worn surface of only a small amount of scratching and shallow furrows,and V8C7 in dense tissue also exist in the carbide grain crushing and spalling.Under friction wear conditions,V8C7 dense layer on the wear resistance were 4 times(room temperature),9 times(400?)and 3 times(800?)of the matrix.At room temperature,the wear mechanism of V8C7 dense layer is mainly abrasive wear and slight adhesive wear,and the wear mechanism is mainly adhesive wear and oxidation wear at high temperature(400? and 800?).