Study On The Tissue Friction And Wear Performance Of In Situ （TiC+TiB₂）/Ni Laser Cladding Layer

In this paper,the TiC and TiB₂ reinforcing phases were synthesized in situ by laser cladding process on the surface of 45 steel by pre-coating.And then the（TiC+TiB₂）/Ni laser cladding layer was prepared.The composition and the microstructure of the cladding layer were analyzed and the morphology of the TiC and TiB₂ reinforcing phases were observed.The growth mechanism of TiC and TiB₂ crystals in the cladding layer was investigated.Using a vertical universal friction and wear tester,the Ni-based laser cladding layer with15%,25%and 35%reinforcing phase content and B2 steel are combined in the form of pin-disc.Friction and wear tests were carried out under five load parameters:60N,90N,120N,150N 180N.The friction coefficient and wear rate obtained from the test were compared with the wear conditions of various reinforcing phase contents under different loads.The wear surface,wear section and wear debris morphology were observed.The friction and wear mechanism of the cladding layer was studied and the reinforcement phase was analyzed.The effect of content and load on the friction and wear behavior of the cladding layer was analyzed.The phase composition of the prepared cladding layer is（Fe,Ni）,CrFeB,TiC,TiB₂ and Cr₇C₃.In the morphology of the cladding layer before the etch treatment,the bulk phase is TiB₂,and the granular phase is TiC.After etch treatment,the TiC crystals in the cladding layer mainly have two forms:regular octahedral granules and branches.TiB₂ crystals also have two main forms:lamellar and hexagonal.The cladding layer has three cross-sections from the substrate to the cladding layer,with no enhanced phase formation at the junction and bottom.The growth process of TiC and TiB₂ crystals was systematically analyzed.The growth process of TiC dendrites in the cladding layer was as follows:first,Ti and C atoms formed octahedral growth primitives,and the growth primitives were stacked to form primary octahedral crystals.Under the influence of growth conditions,branches are formed by tip splitting,and finally dendrites are formed;TiB₂ crystals grow in a two-dimensional nucleation manner.According to theory and calculation,the growth rate of each crystal plane is different,and TiB₂ crystals shuold grow to layered form.In the test cladding layer,under certain conditions,Cr element will attach to the crystal surface,which will promote the growth of TiB₂ crystal into a chamfered hexagonal prism.Meanwhile,TiB₂ crystal will form a step structure due to the difference of supersaturation concentration.In the friction and wear test,the average friction coefficient of the cladding layer decreases with the increase of the load;when the content of the reinforcing phase become higher,the average friction coefficient will be lower.The reinforcing phase can improve the wear resistance of the cladding layer.Under low load,the increase of the enhanced phase content is not obvious for the reduction of the wear rate;under high load,the effect of the enhanced phase content on the wear rate reduction is significant.By observing the morphology of the wear surface,it is found that under different loads,the content of TiC and TiB₂ increases in the cladding layer will lead to the increment of tendency of the layer to stripping wear,and the ability to resist adhesive wear is enhanced.The increased load will increase the tendency of the material to adhesive wear.The wear profile of the cladding layer is related to the load and the content of the reinforcing phase.As the load increases,the interface profile gradually becomes rougher from flattening,and the cladding layer with lower enhancement phase content has a higher degree of ruggedness,and at the same time,load and reinforcement also affects the size of the grinding debris.That of the cladding layer of the low reinforcement phase increases with the load,at first,the size of the grinding debris increases and then decreases.It changes from lamellar to fine particles adhered to large pieces of abrasive,and the degree of adhesion will increase;the size of the grinding debris of the cladding layer with high reinforcement phase increases with the increase of load,it always choose sheet as its main shape,its size will increases under high load and large pieces of abrasive debris will be crushed into small pieces of wear debris.