| Titanium alloys are attractive materials for engineering applications such as chemical industry,aerospace,shipbuilding and biomedical,due to their high strength-to-weight ratio,excellent corrosion resistance and good biocompatibility.Despite these excellence properties,the use of titanium is often limited by its poor tribological properties such as low wear resistance,high coefficient of friction and relatively low hardness,especially in the chemical industry,such as pressure vessels,transportation containers,and heat exchangers.In this paper,TA2 commercial pure titanium alloy is chosen as the research object.The new composite modification technology of cold-rolling+450? plasma nitriding and recrystallization was proposed for its poor tribological properties.The microstructure and mechanical properties were characterized by Metallographic Microscope,Scanning Electron Microscope(SEM),EDS energy spectrum analysis,X-Ray Diffraction analysis(XRD),Electron Backscatter Diffraction(EBSD),friction and wear test,microhardness test.The purpose is to study the degree of cold-rolling deformation effect on the microstructure,texture and properties of TA2 alloy under modified technology.Research data shows,with the increase of deformation degree,the refinement phenomenon of the TA2 alloy grain is enhanced gradually and the proportion of low angel grain boundary(LAGB)is increased significantly,the composition of the cylindrical texture{11-20} is decreased,while the basal texture {0001} and the pyramid texture {10-10} is increased.Moreover,the grain orientation changes with the increasing degree of deformation displays the trend of TD?RD?TD.The data of properties shows that comparing the initial TA2 alloy,the wear resistance and microhardness of TA2 alloy after cold-rolling treatment are significantly improved and the 80%deformation alloy sample have the most significant improvement in wear resistance(53.9%)and microhardness(22%).During the recrystallization process,nucleation is preferentially located at the grain boundary,the proportion of LAGBs decrease remarkably with the recrystallization degree increase,and the grain size decrease.The basal texture {0001} has a deflection in the TD?RD direction,the composition of cylindrical texture {10-10} gradually increase,while the cylindrical texture and pyramid texture in the specific orientation are disappears.After recrystallization at 450?for 10h,the hardness of TA2 alloy decreases and the Schmid factor increases with the increase of recrystallization degree,which indicates that the matrix material of TA2 alloy have the good plastic toughness.The result of low temperature plasma nitriding of cold-rolling TA2 alloy shows,the proportion of nitrogen to titanium atoms decrease with the distance from the surface of the alloy increase,and the decreasing trend is slowing down.The reason is that,during nitriding,the interaction force between the atoms of TA2 alloy increase and the density of dislocation decrease,which comprehensive effect hinder the further diffusion of active nitrogen atoms.Compared with the cold-rolling and recrystallization samples,the nitriding treatment further improved the friction coefficient,volume wear rate and microhardness of the deformed alloy.Analysis shows the increase of degree of deformation has a significant promote effect on recrystallization degree of the deformed microstructure,which makes the technology of low temperature nitriding become more feasible.The quality of nitriding modification is determined by the degree of deformation and recrystallization.The increases of deformation degree make the continuity of the microhardness gradient of the composite modified alloy improved,and the wear resistance was improved.which indicates the newly proposed modification technology can effectively achieve the double target that the matrix microstructure regulate+surface modified,and the TA2 alloy with better ratio of strength-plastic is obtained. |
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