Effect Of Zr Content On Microstructure And Mechanical Properties Of High Temperature Titanium Alloys For Short-term Used At 650?

Short-term high temperature titanium alloys exhibit light weight and high strength,high temperature instantaneous strength and durability,and thus have a wide application prospects in the field of aerospace.At present,the research on short-term high temperature titanium alloys is less focused on Zr element.The ingots of short-time high temperature titanium alloys used at 650? with nominal composition of Ti-6Al-4Sn-x Zr-0.8Mo-1Nb-1W-0.25Si(x=7,9,11)were prepared by vacuum induction melting,then were subjected to hot isostatic pressing to study the effect of Zr content on the microstructure,mechanical properties and tensile fracture mechanism of short-time high temperature titanium alloys at room temperature,650?,700? and 750?.Firstly,the metallographic microstructure was observed by optical microscope.It was found that the microstructure of alloys with Zr content of 7wt.% were straightarranged Widmanstatten microstructure,the microstructure of alloys with Zr content of 9wt.% were straight-arranged mixed-braided Widmanstatten microstructure,the microstructure of alloys with Zr content of 11 wt.% were braided needle-shaped Widmanstatten microstructure.Moreover,with the increase of Zr content,the average grain size,the average thickness of ?GB lamellar,the average width of ? colony and the average length of ? lamellar decreased significantly,but the ? lamellar thickness and its degree of disorder increase gradually.Among them,the average size of the prior ? grains of alloys with Zr content of 7wt.%,9wt.%,11 wt.% was 726?m,478?m,334?m,the average thickness of ?GB lamellar was 8.01?m,5.98?m,4.71?m,the average width of ? colony was 184?m,62?m,and 34?m,and the average length of the ? lamellar was 215?m,145?m,and 74?m,respectively.Thus,the effect of Zr content on the microstructure short-term high temperature titanium alloy used at 650? was revealed,which was that Zr element has the function of refining grain and microstructure.Then the tensile properties of alloys with different Zr content were tested at room temperature and high temperature.With the increase of Zr content the tensile strength and yield strength of the alloys decreased gradually at room temperature,while the plasticity of the alloys decreased first and then increased,and the total decreased slightly.With the increase of Zr content,the tensile strength and yield strength of the alloys increased significantly at 650?,700?,750?,and the plasticity of the alloys showed a trend of first decreasing and then increasing.The effect of Zr content on the tensile properties short-term high temperature titanium alloys used at 650? was revealed,which is that Zr element can obviously improve the strength of the alloys due to effects of Zr elements through solid solution hardening,fine grain hardening and phase content and shape at high temperature.Finally,the tensile fracture morphology of alloys was observed by SEM and the fracture mechanism was described.The tensile fracture mode of alloys was the mixed fracture mode of intergranular fracture and transgranular fracture at 650?;The high temperature tensile fracture mode of the alloys was mainly intergranular fracture at 700?.The tensile fracture mode of alloys with Zr content of 7wt.% and 9wt.% was mainly intergranular fracture at 750?,while the fracture mode of alloys with Zr content of 11 wt.% was mixed mode of intergranular fracture and transgranular fracture at 750?.