A study on the low-cycle fatigue(LCF)behavior of K 416 B alloy was conducted at 650℃.According to the results,the LCF behavior of K 416 B alloy at 650℃ is mainly manifested as elastic deformation and the fatigue lif...A study on the low-cycle fatigue(LCF)behavior of K 416 B alloy was conducted at 650℃.According to the results,the LCF behavior of K 416 B alloy at 650℃ is mainly manifested as elastic deformation and the fatigue life of the alloy is determined by the level of material strength.When tension-compression fatigue occurs,the deformation mechanism of the alloy is reflected in the form of dislocation slip,and the deformation dislocations are bowed out in the matrix by Orowan mechanism,which leads to a dislocation configuration similar to the Frawk-Reed source.At the late stage of low-cycle fatigue,the fatigue-induced cracks develop from the alloy surface.As fatigue test proceeds,it is possible for the cracks to continue development along the regions of eutectic and the bulk M 6 C carbide due to stress concentration,thus causing the alloy to show cleavage fracture.展开更多
The prediction of fatigue life of metallic alloys is justly accepted as one of the most important phenomena in the field of metallurgical and mechanical engineering.At elevated temperatures,oxidation of the surfaces h...The prediction of fatigue life of metallic alloys is justly accepted as one of the most important phenomena in the field of metallurgical and mechanical engineering.At elevated temperatures,oxidation of the surfaces has an effective role in the fatigue strength and ductility of the alloys.In the present work,the effect of prior cyclic oxidation on the high temperature low cycle fatigue(HTLCF)properties of nickel-based superalloy Rene®80 has been assessed in the uncoated state and in the Pt-aluminide(Pt-Al)coated condition at 930℃.To apply cyclic oxidation,simulation of engine thermal exposure was carried out by exposing coated and uncoated fatigue specimens in the burner rig(120 cycles at 1100℃).The cyclic oxidation procedure led to a changing in the coating microstructure from the dual-phase(ξ-PtAl_(2)+β-(Ni,Pt)Al)to single phase(β-(Ni,Pt)Al).Results of HTLCF tests showed an improvement in the HTLCF life around 11.5%in the unexposed coated specimen(pre-cyclic oxidation)as compared to unexposed bare specimen,while this rise for exposed coated specimen(post-cyclic oxidation)was only 5%.Although a mixed mode fracture morphology(ductile and brittle)was observed on the fracture surfaces of failed specimens,the wider regions of brittle fracture belonged to exposed coated/uncoated ones.展开更多
系统探讨了温度对第四代粉末高温合金FGH4108低周疲劳变形机制的影响。通过在400~850℃温度下开展应变控制低周疲劳(Low-cycle fatigue,LCF)试验,结合扫描电镜(Scanning electron microscopy,SEM)、电子背散射衍射(Electron backscatter...系统探讨了温度对第四代粉末高温合金FGH4108低周疲劳变形机制的影响。通过在400~850℃温度下开展应变控制低周疲劳(Low-cycle fatigue,LCF)试验,结合扫描电镜(Scanning electron microscopy,SEM)、电子背散射衍射(Electron backscatter diffraction,EBSD)和透射电镜(Transmission electron microscopy,TEM)等表征手段,揭示了温度主导下合金从循环硬化向循环软化主导机制的演化过程。结果表明,600℃及以下FGH4108合金表现出显著的循环硬化趋势,700℃以上则发生软化,尤以850℃最为显著。断裂模式由穿晶逐步过渡至沿晶,变形机制亦由基体内位错累积转向位错剪切γ'相及层错、孪晶协同机制。TEM观察显示,高温下γ'相稳定性下降,局部区域出现明显的层错结构及局域γ'剪切行为。EBSD分析表明,600~850℃范围内晶内局部畸变整体分布稳定,表明温度对位错密度影响相对有限。研究结果有助于深入理解FGH4108合金高温疲劳行为的演化机制,为新一代粉末高温合金的服役性能评估与优化设计提供理论支撑。展开更多
基金Projects(51701212,51771191,51971214)supported by the National Natural Science Foundation of ChinaProject(2019-MS-336)supported by the Liaoning Provincial Natural Science Foundation,China。
文摘A study on the low-cycle fatigue(LCF)behavior of K 416 B alloy was conducted at 650℃.According to the results,the LCF behavior of K 416 B alloy at 650℃ is mainly manifested as elastic deformation and the fatigue life of the alloy is determined by the level of material strength.When tension-compression fatigue occurs,the deformation mechanism of the alloy is reflected in the form of dislocation slip,and the deformation dislocations are bowed out in the matrix by Orowan mechanism,which leads to a dislocation configuration similar to the Frawk-Reed source.At the late stage of low-cycle fatigue,the fatigue-induced cracks develop from the alloy surface.As fatigue test proceeds,it is possible for the cracks to continue development along the regions of eutectic and the bulk M 6 C carbide due to stress concentration,thus causing the alloy to show cleavage fracture.
文摘The prediction of fatigue life of metallic alloys is justly accepted as one of the most important phenomena in the field of metallurgical and mechanical engineering.At elevated temperatures,oxidation of the surfaces has an effective role in the fatigue strength and ductility of the alloys.In the present work,the effect of prior cyclic oxidation on the high temperature low cycle fatigue(HTLCF)properties of nickel-based superalloy Rene®80 has been assessed in the uncoated state and in the Pt-aluminide(Pt-Al)coated condition at 930℃.To apply cyclic oxidation,simulation of engine thermal exposure was carried out by exposing coated and uncoated fatigue specimens in the burner rig(120 cycles at 1100℃).The cyclic oxidation procedure led to a changing in the coating microstructure from the dual-phase(ξ-PtAl_(2)+β-(Ni,Pt)Al)to single phase(β-(Ni,Pt)Al).Results of HTLCF tests showed an improvement in the HTLCF life around 11.5%in the unexposed coated specimen(pre-cyclic oxidation)as compared to unexposed bare specimen,while this rise for exposed coated specimen(post-cyclic oxidation)was only 5%.Although a mixed mode fracture morphology(ductile and brittle)was observed on the fracture surfaces of failed specimens,the wider regions of brittle fracture belonged to exposed coated/uncoated ones.
文摘系统探讨了温度对第四代粉末高温合金FGH4108低周疲劳变形机制的影响。通过在400~850℃温度下开展应变控制低周疲劳(Low-cycle fatigue,LCF)试验,结合扫描电镜(Scanning electron microscopy,SEM)、电子背散射衍射(Electron backscatter diffraction,EBSD)和透射电镜(Transmission electron microscopy,TEM)等表征手段,揭示了温度主导下合金从循环硬化向循环软化主导机制的演化过程。结果表明,600℃及以下FGH4108合金表现出显著的循环硬化趋势,700℃以上则发生软化,尤以850℃最为显著。断裂模式由穿晶逐步过渡至沿晶,变形机制亦由基体内位错累积转向位错剪切γ'相及层错、孪晶协同机制。TEM观察显示,高温下γ'相稳定性下降,局部区域出现明显的层错结构及局域γ'剪切行为。EBSD分析表明,600~850℃范围内晶内局部畸变整体分布稳定,表明温度对位错密度影响相对有限。研究结果有助于深入理解FGH4108合金高温疲劳行为的演化机制,为新一代粉末高温合金的服役性能评估与优化设计提供理论支撑。
