Effect Of Heating-Assisted Rolling On Friction And Wear Properties Of TC4 Titanium Alloy

TC4(Ti-6Al-4V)is the most popular titanium alloy in advanced manufacturing industry,widely used in medical instruments,aerospace,special processing and other fields.Due to the poor cold hardening ability of titanium alloy,it is difficult to improve its surface mechanical properties by conventional hardening methods.Especially in the aspect of friction and wear resistance,TC4 material surface oxidation layer is very thin,extremely easy to occur damage,cracks and other phenomena in the friction process,resulting in the failure of parts,which has become one of the biggest obstacles to further expand its application field of titanium alloy.Surface rolling can significantly improve the surface smoothness of metal,and the most important is to introduce beneficial residual tensile stress in the surface of the material to produce a plastic reinforced layer structure.However,single surface rolling has limited strengthening effect on TC4 titanium alloy.To solve this problem,the effect of heat-assisted rolling on the surface properties,microstructure and friction and wear properties of TC4 titanium alloy were studied in this paper.The following studies were conducted and certain conclusions were drawn:First,the microstructure of the samples before and after heat-assisted rolling was analyzed by scanning electron microscopy(SEM),and the selected area was analyzed by TEM transmission.The changes of microhardness,surface roughness and residual stress of the samples before and after heat-assisted rolling were measured and the reasons for the changes were analyzed.With the increase of heating temperature during rolling,α phase in microstructure decreases,β phase in slip system increases,and the strengthened layer consists of dense α+βphase.The plastic strengthening layer on the surface of the sample thickened gradually,and the thickness increased by 37μm at 160℃ compared with that at normal temperature.After being rolled at room temperature(25℃),the micro-hardness of the sample surface reaches 426 HV.Under heating conditions,the higher the temperature,the lower the surface roughness of the sample,but the surface roughness is still the lowest under normal temperature.The distribution of residual stress is consistent with that of surface roughness.The thickness of the reinforced layer produced by cold rolling is lower,but the strength is higher.Secondly,ABAQUS finite element analysis was carried out for the heat-assisted rolling strengthening process.The mechanical properties of the samples under different processing conditions were measured from the equivalent stress-strain variation,surface residual stress distribution and energy variation.The finite element results strongly prove the experimental results.The surface residual stress distribution is close to the experimental results,and the influence depth of roll pressure increases gradually with the increase of temperature.By measuring the energy in the whole rolling process,it can be found that the sample rolled at room temperature has the highest total surface energy,and the total surface energy is positively correlated with the surface strengthening quality.Finally,the friction coefficient of the samples were measured,and the morphology and 3D characterization of the fretting marks were systematically analyzed to explore the fretting friction and wear properties.The experimental results prove that,when the friction scene is not serious,the titanium alloy rolled at room temperature has excellent friction and wear resistance due to the high density of the strengthening layer.However,if the material is in the high-frequency friction scene,the surface properties of the rolling sample at 160℃ are close to that of the cold rolling sample,but the strengthening and modification layer is several times thicker than that of the cold rolling sample.It provides a choice for machining titanium alloy under different working conditions.