Study On Microstructure And Mechanical Properties Of New Ti-20Zr-xCr Alloy

Due to the high specific strength,good corrosion resistance,lower density,high fatigue resitance,low-temperature toughness and high heat resistance,etc.titaniuam and its alloys have been wildly used in chemistry&chemical industry,ship domain and aerospace filed.Zirconium element and titanium element,which belong to the same main group?IVB?in the periodic table,have the similar physical and chemical properties,such as low density,low expansion coefficient,excellent irradiation resistance,small capture crosssection for thermal neutrons,and good corrosion resistance.All those excellent properties make Zr wildly used in chemistry&chemical and nuclear inductries as the structural materials.With the science and technology development,traditional materials,for example steel,have been incapable of the operating requirement under the extreme condition.Hence,the novel structural materials with the excellent mechanical properties and well physical-chemical properties should be developing at hand.In this paper,a series of Ti alloys with different composition have been developped in laboratory.The phase structure,microstructure,and mechanical properties of the alloys designed are studied,and the influence mechanism of deformation parameters on the pahse,microstructure and mechanical properties of the specimens under the different rolling deformation degree are studied.In this experiment,Ti-20Zr-xCr?x=2,4,6,8,and 10?alloys with the different Cr content are prepared via the non-consumable arc-melting furnace.The results show that the?pahse with the body centered cubic structure appears in specimen after Cr addition.When Cr content is 2 wt.%,the phases of the specimen are mainly composed of?'martensite phase,and a little?pahse and ZrCr₂ intermetallic pahse.With the Cr content increasing,the intensity of?'martensite phase reduces gradually,however,the intensity of?pahse and ZrCr₂ intermetallic pahse increases,which means the relative amount of?pahse and ZrCr₂ intermetallic pahse increase gradually,and the stability of?pahse enhance.Moreover,the diffraction peaks of?pahse are detecked in 4Cr,6Cr,and 8Cr alloys.When Cr content is 2 wt.%,the microstructure of specimen is composed of needle-like?'martensite and partial?grains.With the Cr content increasing,the needle-like?'martensite transform into the coarse?grains.With the Cr addition increasing,the yield strength of the alloys designed present the tendency of first increase and then decrease.The maximum yield strength,i.e.754 MPa,obtained when Cr content is 8 wt.%.Compared with the yield strength of Ti-20Zr alloy?207 MPa?,that of Ti-20Zr-8Cr alloy improves 27%.Ti-20Zr alloy and Ti-20Zr-10Cr alloy possess the good elastic deformability.Furthermore,the elongation of the specimens degreased gradually with the increasing of Cr addition.The Ti-20Zr-2Cr alloy was hold at 1000oC for 30 min and then quenching water.The severe plastic deformation for alloy at 900oC conducted by means of the rolling machine.The result show that the phase of 2Cr are composed of?,?,?'martensite and ZrCr₂ intermetallic phase.With the deformation increasing,the phase transformation of alloy during rolling processing occurs,i.e.?'+???.After the hot rolling processing,the needle-like?'martensite of 2Cr alloy is attached to the corase?grains.With the deformation increasing,the prior?grains are broken,and the the needle-like?'martensite decomposes to the lath?pahse presenting the basket-weave microstructure.When deformation is 60%,the maximum tensile strength and elongation of alloy obtained,i.e.716 MPa and 4%,repectively.With the deformation increasing,the tensile strength and elongation of the specimens decreased gradually.When deformation was 86%,the tensile strength and elongation of specimen reduced to 163 MPa and 1%.The reason of the mechanical properties of specimen reduced might be the bigger deformation,which caused the crack.With the deformation increasing,the micro-hardness of the specimens present the tendency of first increase and then decrease.When deformation was 70%,the micro-hardness reached the maximum,i.e.TD was 610 HV_0.2 and RD was 523 HV_0.2.Ti-20Zr-10Cr alloy was melted by arc-melting furnace,and then all specimens were hot rolled.The results showed that the phase of 10Cr alloy is composed of?phase,?'martensite phase and ZrCr₂ intermetallic.The size of?grains of alloy continuously incrases during the rolling deformation.With the hot rolling deformation increasing,the tensile strength and yield strength of specimens present the tendency of first increasing and then decreasing.When deformation was 65%,the tensile strength got the maximum,i.e.713 MPa.However,when deformation was 70%,the tensile strength and yield strength reduced the minimum,i.e.426MPa and 231 MPa respectively.