单晶涡轮叶片长期服役组织演化及硬度退化分析

Metallographic Structure Evolution and Hardness Performance Degradation Analysis of Single Crystal Turbine Blades After Long-Term Service

分别选用服役时间为25000和50000 h的燃气轮机用高压涡轮叶片对单晶涡轮叶片长时服役后的显微组织损伤及力学性能退化程度进行评价。截取叶身中部材料进行组织定量表征和显微硬度测试,定量测算了不同服役时间和不同位置的γ'相尺寸、体积分数,二次γ'相尺寸,基体通道宽度,并进行了维氏硬度测试。结果表明,同一服役时间不同位置γ'相尺寸粗化程度不同,前缘、尾缘高温区γ'相尺寸大于叶盆、叶背处,而体积分数稍小于其他两处。服役50000h的叶片γ'相尺寸大于相同位置处服役25000 h叶片,体积分数呈相反规律。部分位置存在二次γ'相析出现象,二次γ'相析出位置基体通道宽度明显增加。经1100℃/2 h空冷/炉冷实验验证,二次γ'相析出与工作高温及冷却方式有关。服役异常高温区出现拓扑密排(TCP)相,该相富含W、Re元素,经分析为μ相。不同服役时长的各个位置显微硬度均有所下降,且显微硬度下降与γ'相尺寸增大呈负相关、与体积分数减少呈正相关关系。因此γ'相尺寸、体积分数可作为本涡轮叶片及材料的损伤评价参量。但当有害相析出或者材料在高应力服役时,需要综合考虑有害相、大应力服役引起的γ′相参量变化以及对材料性能退化的影响。

The high pressure turbine blades of gas turbines at the service time of 25000 and 50000 h were selected to evaluate the damage of microstructure and the deterioration of mechanical properties after long-term service of single crystal turbine blades.The metallographic structure quantitative analysis and microhardness test were conducted at the middle of the blade body.Then,the size ofγ'phase,volume fraction ofγ'phase,size of secondaryγ'phase,width ofγmatrix channel and the Vickers hardness at different service time and positions were measured.The results show that the coarsening degree of the size ofγ'phase is various at different positions in the same leaf.Moreover,theγ'phase size at the leading edge and the trailing edge(at high temperature zone)is larger than that at the pressure side and suction side.While theγ'phase volume fraction is slightly smaller than that of the other two places.It is interesting to notice that theγ'phase size of serviced 50000 h blade is greater than that of the serviced 25000 h blade at the same position.However,the volume fraction displays the opposite law.Furthermore,the secondaryγ'phase precipitates in some positions;meanwhile the width of the base channel significantly increases at the secondaryγ'phase precipitation position.It is verified that the secondaryγ'phase precipitation is related to the high working temperature and the way of cooling by air cooling/furnace cooling experiment of 1100℃/2 h.The TCP phase precipitates in the abnormally high temperature region,which is rich in the elements of W and Re.After analysis,the phase is identified as theμphase.The microhardness at each position decreases at different service time.The decrease of microhardness and the increase of the size ofγ'phase demonstrate that there is a negative correlation between them.On the contrary,the microhardness decreases with the decline of volume fraction,indicating that the microhardness is positively correlated with the volume fraction.Therefore,these results suggest that theγ'phase size and volume fraction can be used as the evaluation parameters for evaluating the damage of the material.However,when the harmful phase is precipitated or the material is in high stress,it is necessary to comprehensively consider the variation of theγ'phase parameter caused by the two factors,and the degradation of the material performance.