| Titanium alloy has excellent specific strength,good plasticity and toughness,corrosion resistance,processability and excellent biocompatibility,which meets the needs of materials in the industrial field,and is widely used in various fields.TC4 alloy is the most widely used in titanium alloys,and its application accounts for more than 50% of all titanium alloy applications.Due to the high chemical affinity between oxygen and titanium,the formation of oxygen diffusion layer is often accompanied by exposure to high temperature environment,which seriously affects the application of titanium alloy.At present,there are still few studies on the effect of oxygen diffusion layer on the strength and plasticity of titanium alloy,lack of effective quantitative research,and there is no exploration on the wear properties of oxygen diffusion layer.In this paper,TC4 alloy was oxidized by different surface oxygen infiltration process parameters,and the gradient microstructure and microhardness of the oxygen diffusion layer were characterized by means of metallographic observation and microhardness measurement.The suitable process parameters were selected to prepare different concentrations of oxygen diffusion layer samples.The effects of oxygen diffusion layer on the strength,plasticity and wear properties of TC4 alloy were studied quantitatively by tensile test and dry sliding wear test.By means of glow discharge emission spectroscopy,SEM and TEM,the effects of oxygen diffusion layer on strength,plasticity and wear properties were analyzed,and the mechanisms of oxygen diffusion,gradient microstructure formation and oxygen diffusion layer embrittlement were discussed.The main results are as follows:(1)after surface oxygen infiltration,an oxygen diffusion layer with gradient structure is formed on the surface of TC4 alloy,in which the content of α phase decreases gradually and the content of β phase increases gradually.The thickness of the diffusion layer increases with the increase of diffusion temperature and time,and the microhardness increases with the increase of oxygen concentration,and the increase of microhardness is caused by the strengthening of oxygen solution caused by oxygen diffusion,the dispersion strengthening of α 2 phase precipitation and the refinement of β trans.(2)the plasticity of TC4 alloy decreases monotonously with the increase of oxygen diffusion layer concentration.After oxygen infiltration,the tensile crack germinates in the oxygen diffusion layer and extends to the matrix with the increase of tensile deformation.the plasticity of the matrix decreases because the matrix can not exert its plasticity under the condition of triaxial stress.(3)when the oxygen concentration is low,the crack sensitivity of the oxygen diffusion layer is not high and retain a certain plasticity,and the strengthened oxygen diffusion layer also provides a certain contribution to the strength of the alloy,which increases the strength;when the oxygen concentration is high,the complete embrittlement of the oxygen diffusion layer leads to the initiation and propagation of tensile cracks in a small amount of deformation,which reduces the bearing surface of the specimen,leading to the early fracture of the alloy and the decrease of strength and plasticity.(4)with the increase of oxygen concentration,a large number of solid dissolved oxygen atoms in α-Ti inhibit the proliferation of dislocations and change the slip type to plane type,which leads to the embrittlement of oxygen diffusion layer.(5)oxygen diffusion strengthens the surface layer of TC4 alloy and improves the resistance to plastic deformation,so as to restrain the delamination wear in the wear process and achieve the effect of reducing wear.With the increase of the strength of the oxygen diffusion hardening layer,the resistance to plastic deformation is stronger,so the wear reduction effect of the oxygen expanded layer with higher concentration is more obvious. |
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