超声滚压Ti-6Al-4V微观组织对应力应变行为的影响

Effect of Ultrasonic Burnished Microstructure on the Stress-strain Behavior of Ti-6Al-4V

目的通过超声滚压提高Ti-6Al-4V的屈服强度。方法将超声振幅作为唯一变量,设置0、5、7、10μm4组试验,分析Ti-6Al-4V被加工表面及表面以下30~50μm处的应力应变行为。通过X射线衍射仪(XRD)测试不同超声振幅下Ti-6Al-4V的两相分布。采用扫描电子显微镜(SEM),分析不同超声振幅下Ti-6Al-4V表面层塑性变形程度。使用能谱仪(EDS)观察不同超声振幅下Ti-6Al-4V表面层元素组成分布。通过万能试验机获得不同超声振幅下Ti-6Al-4V的应力应变曲线。结果Ti-6Al-4V表面层塑性变形程度随着超声振幅的增大而增大。Ti-6Al-4V被加工表面的β相体积分数随着超声振幅的增大呈先减小后增大的趋势。当超声振幅为7μm时,Ti-6Al-4V被加工表面β相的体积分数最大(19.70%)。超声滚压Ti-6Al-4V表面层中β相的体积分数沿深度递减。Ti-6Al-4V表面层α相稳定元素Al和β相稳定元素V未出现明显与两相体积分数相同的变化趋势。Ti-6Al-4V材料的屈服强度随着超声振幅的增大呈先减小后增大的趋势。当超声振幅从5μm增至10μm时,Ti-6Al-4V的屈服强度依次为1.06、1.03、1.16 GPa,相较于在无超声加工下的Ti-6Al-4V屈服强度(0.91 GPa)分别提高了约16.48%、13.19%和27.47%。结论超声振幅的增大,可以增大滚压过程中Ti-Al-4V的塑性变形程度。合适的超声振幅,可以改变Ti-6Al-4V表面层两相分布。经超声滚压后,Ti-6Al-4V的屈服强度受到材料塑性变形和两相分布的共同影响,且Ti-6Al-4V的塑性变形程度对屈服强度的影响更大。

To improve the yield strength of titanium alloy Ti-6Al-4V material by ultrasonic burnishing,ultrasonic amplitude was used as the unique variable in this work.Four groups of experiments were set to analyze the stress-strain behavior of titanium alloy Ti-6Al-4V material on the machined surface and 30-50μm below the surface.Ultrasonic amplitude in four groups was set as 0,5,7 and 10μm,respectively.The burnishing of Ti-6Al-4V material without ultrasonic vibration was adopted as the control group.Two-phase distributions of titanium alloy Ti-6Al-4V material on the machined surface and 30-50μm below the surface were measured by X-ray diffractometer(XRD).Scanning Electron Microscope(SEM)was used to analyze the plastic deformation degree of titanium alloy Ti-6Al-4V grains in the machined surface layer at different ultrasonic amplitudes.Energy Dispersive Spectrometer(EDS)was applied to observe the composition element distribution of the burnished titanium alloy Ti-6Al-4V surface layer under different ultrasonic amplitudes.Universal testing machine was used to obtain the various stress-strain curves of the burnished titanium alloy Ti-6Al-4V samples at different ultrasonic amplitudes.Lastly,the change rules of stress-strain behavior,plastic deformation and two-phase distribution for the burnished titanium alloy Ti-6Al-4V under different ultrasonic amplitudes were comparatively analyzed.The effect of microstructure on the stress-strain behavior for the ultrasonic burnished titanium alloy Ti-6Al-4V was clarified.Results indicated that the plastic deformation degree of titanium alloy Ti-6Al-4V grain increased with ultrasonic amplitude.The volume fraction ofβphase for the ultrasonic burnished titanium alloy Ti-6Al-4V decreased firstly and then increased with the increase of ultrasonic amplitude.When ultrasonic amplitude was 7μm,the volume fraction ofβphase on the burnished titanium alloy Ti-6Al-4V surface reached the maximum value 19.70%.The volume fraction ofβphase in the titanium alloy Ti-6Al-4V surface layer decreased along the depth during ultrasonic burnishing.However,stable element Al forαphase and stable element V forβphase did not show the obvious trend of the same rules with the increase of ultrasonic amplitude.After ultrasonic burnishing,the yield strength of titanium alloy Ti-6Al-4V showed a trend of decrease firstly and then increased with the increase of ultrasonic amplitude.When ultrasonic amplitude increased from 5μm to 10μm,the yield strength value of the ultrasonic burnished Ti-6Al-4V material was 1.06 GPa,1.03 GPa and 1.16 GPa,respectively.Compared to the yield strength value 0.91 GPa of titanium alloy Ti-6Al-4V burnished without ultrasound,the yield strength of the ultrasonic burnished Ti-6Al-4V increased by 16.48%、13.19%and 27.47%,respectively.When ultrasonic amplitude was 10μm,the yield strength of titanium alloy Ti-6Al-4V material reached the maximum.The increase of ultrasonic amplitude can increase the plastic deformation degree of the burnished titanium alloy Ti-6Al-4V material.Appropriate ultrasonic amplitude can change the two-phase distribution of the ultrasonic burnished titanium alloy Ti-6Al-4V.The yield strength of titanium alloy Ti-6Al-4V is commonly affected by the plastic deformation and two-phase distribution of material after ultrasonic burnishing.The plastic deformation degree of titanium alloy Ti-6Al-4V material has a greater impact on the yield strength.