涡桨发动机涡轮导向器内环失效分析

分析了一起涡轮螺旋桨发动机涡轮导向器内环多处裂纹故障。通过对裂纹断口进行的宏、微观观察,组织和硬度检查,能谱的半定量分析和综合分析,结果显示,导向器内环裂纹性质为热机械疲劳(TMF),疲劳裂纹起源于叶型槽孔角处。叶型槽孔角加工质量不佳,存在应力集中,是造成内环疲劳裂纹的主要原因;大修时叶型槽局部补焊降低了材料的热疲劳抗力,对裂纹的萌生和扩展也有影响。     

飞机APU涡轮导向叶片高温防护涂层失效模式分析

利用扫描电镜(SEM)、能谱分析仪(EDS)等分析了国内某型在役APU涡轮导向叶片的结构特征与热防护机理,研究了叶片失效件中高温防护涂层的厚度变化与失效模式。结果表明:飞机APU导向叶片中存在渗铝涂层+MCrAlY涂层与单一渗铝涂层2种不同的涂层结构;APU导向叶片失效件的MCrAlY涂层厚度从叶片尾缘—叶盆—前缘区域呈先增大后减小的趋势;受叶片构型影响,叶片尾缘区域涂层的氧化程度较严重,而叶盆区域越靠近前缘的位置涂层氧化损伤程度越低,但叶片前缘区域由于受CMAS腐蚀与高温氧化的耦合作用使得该区域涂层损伤最为严重。     

Repair of NiCrAlYSi overlay coating on Ni3Al base alloy IC6

The effect of repair of NiCrAlYSi coating after long time use on the coherence of coating to substrate and mechanical properties of Ni₃Al base alloy IC6 has been studied. The alloy with NiCrAlYSi coating was stressed under the condition of 900 °C/100 MPa for 200 h to simulate the service condition of IC6 turbine vanes. The results showed that the coherence of base alloy/original coating, original coating/first repair coating, first repair coating/second repair coating or base alloy/second repair coating was firm. The interfaces between them had no cracks and porosity, for either partly or entirely repaired coatings. However, there were more Mo rich particles in the affected zone compared with original coating. Compared with IC6 alloy aged at 900 °C for 200 h, the yield strength at ambient temperature of IC6 alloy with first repair coating was almost equivalent, while the elongation decreased slightly; its stress rupture life under 1100 °C/90 MPa condition was about 100 h. For secondary coating repair, the room temperature tensile properties of base alloy had no obvious change, while stress rupture lives decreased, but still were rather long, compared to the alloy with first repair coating. Therefore, NiCrAlYSi coating repair is feasible to prolong the service lives of IC6 turbine vanes.     

Numerical modeling of inconel 738LC deposition welding: Prediction of residual stress induced cracking

A predictive tool has been implemented to determine the suitable conditions for deposition welding of inconel 738LC which is particularly susceptible to hot cracking. Cracking criteria related to liquation phenomenon and reheating rely on comparisons between residual stresses derived from numerical modeling and cracking resistance identified from the confrontation between numerical and experimental results of deposition welding performed on fir tree turbine blades test specimens. A contribution to the validation of the proposed simultaneous thermal, metallurgical and mechanical numerical modeling was based on their application to the repair of upstream guide vanes. In addition, the study has shown the importance of the heating temperature prior to welding.     

K417G合金焊接修复用高温合金粉末设计与工艺

航空发动机涡轮导向叶片在服役过程中形成的裂纹可以采用钎焊粉末冶金修复技术进行修复,针对低压涡轮导向叶片材料和结构特点,设计了K417G合金修复所需的不同成分的粉末填充材料,测试了不同粉末粒度配比的振实密度值,采用金相法、压汞法评估了不同烧结条件下粉末烧结体的孔隙率、平均孔径、中值孔径、最可几孔径等烧结体性能值,优选了粉末填充材料,在此基础上开展了钎焊粉末冶金修复工艺研究,分析测试了钎焊粉末冶金修复接头冶金组织. 结果表明,接头成形良好,焊料润湿铺展充分,接头致密饱满,无明显焊接缺陷.     

IC6合金铸造裂纹补焊工艺研究

采用大间隙钎焊法对Ｎｉ３Ａｌ基合金ＩＣ６的铸造裂纹进行了补焊，补焊的ＩＣ６合金大间隙钎焊接头持久强度达母材的８０％以上，补焊的ＩＣ６合金导向叶片已通过地面和空中试车。     

Hot cracking in laser braze joint of high strength stainless steel using gold brazing filler metal – prevention of hot cracking by controlling thermal cycle

Abstract

The hot cracking behaviour in the diode laser braze joint of 13Cr–4Ni stainless steel using Au–18Ni, Ag–10Pd and Ag–21Cu–25Pd filler metals has been investigated. The types of joint investigated were the T fillet joint and the L fillet joint which simulated the second braze bead in the T fillet joint. Tandem beam brazing was also carried out in order to prevent the hot cracking by post-heating treatment with a trailing beam. A centreline crack, characterised as a ductility dip crack, occurred in the second braze bead of the T fillet joint using Au–Ni filler metal. On the other hand, no cracks occurred in either the first or the second braze bead in T fillet braze joints using Ag–Pd and Ag–Cu–Pd filler metals. The hot cracking susceptibility of the Au–Ni braze metal was evaluated by the spot Varestraint test. Most of the cracks observed in the spot Varestraint test specimen were also characterised as ductility dip cracks, and the susceptibility to such cracking increased with increasing the augmented strain. The ductility dip temperature range (DTR) was estimated from the crack position and length to be 1000–1250 K at strains over 0·4%. Numerical analyses of the thermal stress and strain revealed that the plastic strain–temperature curve intersected the DTR in the single beam brazing, but did not intersect the DTR with post-heating during the laser brazing. The effect of post-heating on the crack prevention was verified by tandem beam brazing of L fillet joint with a trailing beam. No cracks occurred in the braze bead made with a trailing beam at laser powers of 200–300 W. The authors concluded that hot cracking in the Au–Ni braze metal could be successfully prevented by controlling the thermal cycle during the laser brazing process.     

发动机低压涡轮导向叶片裂纹分析

低压涡轮导向叶片是发动机中重要热端部件之一,叶片在高温燃气环境下工作,服役条件十分恶劣。发动机工作结束后,发现低压涡轮导向叶片表面存有裂纹和基体缺失现象。通过外观检查、断口宏微观分析、材质分析、气膜孔检查及热模拟试验等手段,对低压涡轮导向叶片的裂纹性质及萌生原因进行分析研究。结果表明:故障低压涡轮导向叶片的裂纹性质为疲劳裂纹,叶片在工作过程中热障涂层脱落,导致叶片组织超温,使其抗疲劳性能下降并萌生疲劳裂纹。     

导叶叶片数对多相混输泵内能量损失的影响北大核心

为了提高混输泵的做功性能,降低能量损失,在不同导叶叶片数下,对多相混输泵的外特性及其内部能量损失进行分析。结果表明:当导叶叶片数为10时混输泵的外特性明显比导叶叶片数为7和8时更差,且最高效率偏向小流量工况;不同流量下,导叶叶片数为8时混输泵叶轮内的收缩损失和湍流耗散损失最小,而导叶叶片数对导叶进口的冲击损失影响很小,可不考虑其影响;在所选3组导叶叶片数下,当导叶叶片数等于8时混输泵的性能最优且流道内能量损失最小。     

线能量对电子束焊缝成形影响的研究

本文提供了航空工业中四种常用材料薄板电子束焊的下限线能量、上限线能量和线能量段的试验值;并提出了成形良好、穿透焊缝的下限线能量的近似计算方法。阐述了下限线能量和上限线能量对焊缝成形的影响,并介绍了利用线能量段曲线选择规范、优选焊缝的方法。本文提供了利用线能量段曲线,经一次试焊就成功地焊接了一台份喷气发动机涡轮导向器叶片(75片,100条焊缝)的实例。