激光熔覆低温相变合金熔覆层的热疲劳性能

Thermal Fatigue Properties of Low Temperature Transformation Alloys Coating by Laser Cladding

采用激光熔覆技术在Q235表面制备低温相变合金熔覆层。采用金属热疲劳的试验方法,对低温相变合金(Low temperature transformation,LTT1,LTT2)熔覆层进行热疲劳实验,热循环次数分别为N=4000、4500、5000和6000,采用单纯的热应力,加热和水淬交替进行,设置上限温度为600℃,下限温度为室温,加热到上限温度并保温55 s,循环水冷却时间10 s。利用3 D激光共聚焦显微镜对低温相变合金(LTT1,LTT2)热疲劳实验后的熔覆层表面裂纹加以观察;利用电子背散射衍射(Electron back scattered diffraction,EBSD)技术研究试样疲劳裂纹附近晶粒形貌及裂纹扩展趋势。结果表明:热疲劳裂纹主要与冷热循环次数有关,随着热循环次数的增加,熔覆层表面裂纹密度也随之增大且相互交错贯通,当循环次数达到6000次时,LTTI熔覆层裂纹深度相对热循环次数为4500次时增大了43.2%,裂纹平均深度达到了210.3μm;裂纹方向沿晶界扩展;合金元素的配比影响合金的热疲劳性能。

The low-temperature transformation alloy cladding layer was prepared on the Q235 substrate by laser cladding technique.The thermal fatigue test of the low temperature transformation alloy(LTT1,LTT2)cladding layer was carried out by the metal thermal fatigue test method.Using simple thermal stress,heating and water were quenching alternately,where in the number of thermal cycles are 4000,4500,5000,6000,respectively.Alternately with water quenching,the upper limit temperature is set to 600°C and the lower limit temperature is at room temperature,heated to the upper limit temperature and kept for 55 s,and the circulating water cooling time was 10 s.The surface crack of the cladding layer after thermal fatigue test of low temperature transformation alloy(LTT1,LTT2)were observed by 3 D laser confocal microscopy.The grain morphology and crack propagation trend of the crystallization near the fatigue crack of the sample were studied by electron backscattered diffraction(EBSD)technique.Results show that the thermal fatigue crack is mainly related to the number of thermal cycles.With the increase of the number of thermal cycles,the surface crack density of the cladding layer also increases and crosses each other.When the number of cycles reaches 6000,the crack depth of the LTTI cladding layer increases by 43.2%compared with the number of thermal cycles of 4500 times,and the average crack depth reaches 210.3μm.The crack direction expands along the grain boundary.The ratio of alloying elements affects the thermal fatigue properties of the alloy.