The fatigue crack growth rate of a novel Ti-6Al-4V-1Mo titanium alloy,which is developed for laser directed energy deposition technique,was investigated before and after cyclic heat treatment(CHT).Changes in microstru...The fatigue crack growth rate of a novel Ti-6Al-4V-1Mo titanium alloy,which is developed for laser directed energy deposition technique,was investigated before and after cyclic heat treatment(CHT).Changes in microstructure,fracture surfaces,and crack growth paths were analyzed before and after CHT.Results indicate that in the stable crack growth region,the growth rates for the as-deposited and cyclic heat-treated specimens follow the relationships da/dN=1.8651×10^(−8)(ΔK)^(3.2271)and da/dN=1.4112×10^(−8)(ΔK)^(3.1125),respectively.Compared with that at the as-deposited state,the microstructure after CHT is transformed from a uniform basket-weave microstructure to a dual-phase microstructure consisting of near-sphericalαandβ-transformed matrix phases.The cyclic process also disrupts the continuity of the grain boundaryα(αGB)at the primaryβ-phase grain boundary.The coarsening of primaryαand the disruption ofαGB continuity are the primary factors to release stress concentration and promote crack deflection,thereby decreasing the fatigue crack growth rate.Additionally,the increased occurrence of crack branching,secondary cracking,and crack bridging in cyclic heat-treated specimens further reduces the crack driving force and slows the fatigue crack growth rate.展开更多
V-N微合金化处理是提高非调质船用钢板力学性能的重要途径。本文通过OM(optical microscope)、SEM(scanning electron microscope)、TEM(transmission electron microscope)、EBSD(electron backscatter diffrac‑tion)等微观分析手段,...V-N微合金化处理是提高非调质船用钢板力学性能的重要途径。本文通过OM(optical microscope)、SEM(scanning electron microscope)、TEM(transmission electron microscope)、EBSD(electron backscatter diffrac‑tion)等微观分析手段,系统表征了不同微合金化试验钢的显微组织,并利用万能拉伸试验机和金属夏比V形缺口摆锤冲击试验仪测试了其力学性能。结果表明,V-N微合金化有效细化了晶粒尺寸,使其平均晶粒直径都为10μm以下,其中V-N试验钢的晶粒为9.1μm,V-N-Ti试验钢的晶粒细化最为显著,为8μm。更重要的是促进了晶内针状铁素体的形成,增加了大角度晶界的比例,V-N试验钢的大角度晶界所占比例最高为77%、V-N-Ti试验钢的大角度晶界所占比例为63.4%。此外,还生成了弥散分布的V(C,N)和(Ti,V)(C,N)。V-N微合金化后试验钢强度与塑性明显提升,V-N-Ti试验钢的强度相较于V-N试验钢进一步提升但塑性却有所降低。在-60℃低温冲击下,V-N微合金化后试验钢的冲击吸收功、裂纹扩展功均明显升高,断裂模式从0V-0Ti试验钢的以准解理断裂为主的脆性断裂转变为V-N试验钢的具有大量等轴韧窝的微孔聚集型韧性断裂,V-N-Ti试验钢由于大角度晶界比例降低及析出物粗化,与V-N试验钢相比,V-N-Ti钢的低温韧性有所下降。V-N微合金化通过“晶粒细化+针状铁素体调控+纳米析出”的多重协同机制,实现了船板钢强韧性的综合提升,而钛的复合添加在带来更强沉淀强化效果的同时,也对韧性构成制约。V-N船板钢实现了强度、塑性与低温韧性的最佳匹配。展开更多
基金National Key Research and Development Program of China(2024YFB4610803)。
文摘The fatigue crack growth rate of a novel Ti-6Al-4V-1Mo titanium alloy,which is developed for laser directed energy deposition technique,was investigated before and after cyclic heat treatment(CHT).Changes in microstructure,fracture surfaces,and crack growth paths were analyzed before and after CHT.Results indicate that in the stable crack growth region,the growth rates for the as-deposited and cyclic heat-treated specimens follow the relationships da/dN=1.8651×10^(−8)(ΔK)^(3.2271)and da/dN=1.4112×10^(−8)(ΔK)^(3.1125),respectively.Compared with that at the as-deposited state,the microstructure after CHT is transformed from a uniform basket-weave microstructure to a dual-phase microstructure consisting of near-sphericalαandβ-transformed matrix phases.The cyclic process also disrupts the continuity of the grain boundaryα(αGB)at the primaryβ-phase grain boundary.The coarsening of primaryαand the disruption ofαGB continuity are the primary factors to release stress concentration and promote crack deflection,thereby decreasing the fatigue crack growth rate.Additionally,the increased occurrence of crack branching,secondary cracking,and crack bridging in cyclic heat-treated specimens further reduces the crack driving force and slows the fatigue crack growth rate.
文摘V-N微合金化处理是提高非调质船用钢板力学性能的重要途径。本文通过OM(optical microscope)、SEM(scanning electron microscope)、TEM(transmission electron microscope)、EBSD(electron backscatter diffrac‑tion)等微观分析手段,系统表征了不同微合金化试验钢的显微组织,并利用万能拉伸试验机和金属夏比V形缺口摆锤冲击试验仪测试了其力学性能。结果表明,V-N微合金化有效细化了晶粒尺寸,使其平均晶粒直径都为10μm以下,其中V-N试验钢的晶粒为9.1μm,V-N-Ti试验钢的晶粒细化最为显著,为8μm。更重要的是促进了晶内针状铁素体的形成,增加了大角度晶界的比例,V-N试验钢的大角度晶界所占比例最高为77%、V-N-Ti试验钢的大角度晶界所占比例为63.4%。此外,还生成了弥散分布的V(C,N)和(Ti,V)(C,N)。V-N微合金化后试验钢强度与塑性明显提升,V-N-Ti试验钢的强度相较于V-N试验钢进一步提升但塑性却有所降低。在-60℃低温冲击下,V-N微合金化后试验钢的冲击吸收功、裂纹扩展功均明显升高,断裂模式从0V-0Ti试验钢的以准解理断裂为主的脆性断裂转变为V-N试验钢的具有大量等轴韧窝的微孔聚集型韧性断裂,V-N-Ti试验钢由于大角度晶界比例降低及析出物粗化,与V-N试验钢相比,V-N-Ti钢的低温韧性有所下降。V-N微合金化通过“晶粒细化+针状铁素体调控+纳米析出”的多重协同机制,实现了船板钢强韧性的综合提升,而钛的复合添加在带来更强沉淀强化效果的同时,也对韧性构成制约。V-N船板钢实现了强度、塑性与低温韧性的最佳匹配。
