Basic Research Of Solid Powder Boronizing On The Surface Of Titanium And Its Alloy

With the development of new technological and industrial revolution,titanium becomes the third metal following iron and aluminum.Titanium and its alloys have good properties of high ratio of strength to weight,low density,non-magnetic,non-toxic,high corrosion resistance and biocompatibility.However low hardness,poor wear resistance limit their application in the friction and wear and other related aspects.In order to overcome the deficiencies in mechanical properties,surface modification to improve the wear resistance of titanium alloy has become a new research focus.Titanium diboride is a kind of material which have high hardness and good thermal conductivity.Boronizing processing on the surface of titanium is a very effective method to improve the wear resistance of titanium.In this paper,TA1(a-Ti)and TC4(?+?-Ti)titanium alloys were boronized using solid powder agent at different temperature holding for different time.The morphology of boride layers and substrates were observed under optical microscopy,scanning electron microscopy.The phase composition of diffusion layer was analyzed using X-ray diffraction.Wear resistance were analyzed by the testing machine of friction and wear.And the experimental results were compared with those which have used common boronizing agent.The ???phase transition temperature of TA1 was decided.The results are shown as the following.TC4 was boronized at the temperature of 800?,900?,800?,1000?,1050?,]100?,1150? for 5 h and cooled in the furnace.The X-ray diffraction results showed that when the boronizing temperature was below 800?,there was no boride layer.TiB appeared when boronized at 800?.When the temperature was up to 900?,TiB2 begun to emerge.TiB and TiB2 grew with the temperature,and TiB2 increased more quickly.When boronizing temperature was near the phase transition temperature(1010?),phase transformation accelerated the diffusion of boron atoms to the substrate,and thus the thickness of boride layer increased.Friction and wear experiments showed that the friction coefficient of boride layer was 0.15?0.2,far below the friction coefficient of the substrate 0.45.It showed that hard titanium boride compounds significantly improved wear resistance property of the surface.The higher the temperature was,the longer the wear time lasted from boride layer to the substrate,which meant the boride layer was thicker.The ???pphase transition temperature of TA1 titanium alloy was measured by the metallographic quenching method.The ? phase transition temperature of TA1 was determined as 915?C.TA1 titanium alloy was boronized in the range of 885? to 930? which near the ?transition temperature.It showed that the boride layer was the thickest when its sample boronized at 900?.However after that,the boride layer became thinner and white strips of ?phase which near the substrate became roughern Friction and wear experimental results showed that the wear resistant performance of samples boronized at 900 ? was optimal.TA1 titnium alloy was boronized at 900? for 5h,8h,10h,12h,15h,18h,20h.Under polarizing microscope,the functional layers(boronizing layer)and hardening area were observed.Friction and wear experimental results showed that the friction coefficient of boronized TA1 ranged from 0.15 to 0.25,while the friction coefficient of the substrate was 0.35?0.45.Compared with the substrate,the friction coefficient of diffusion layer double-fold reduced,indicating the wear resistance property of samples has been significantly enhanced.