32Cr3Mo1V表面激光合金化层热疲劳性能的研究

Thermal fatigue resistance of laser surface alloying layers on the surface of 32Cr3Mo1V substrate

采用万瓦横流CO2激光器在32Cr3Mo1V基体表面合金化Cr粉及Co基粉,获得富含Cr和Co的合金层,并对合金层的成分、组织、硬度及热疲劳性能进行了分析.结果表明:合金层与基体形成完全的冶金结合,组织致密、晶粒细小、无裂纹及孔隙夹杂等缺陷,添加的合金元素Cr与基体形成了富含18.7%Cr的Fe-Cr固溶体,Co合金与基体形成了富含合金元素超过63%的Fe-Cr固溶体和不锈钢相;Co和Cr激光合金化层均能延缓、阻滞疲劳裂纹的产生,并且能降低裂纹扩展的速度,裂纹密度从基体的28.9%分别降为合金化Cr层的12.4%和Co层的9.4%.虽然激光Co层本身具有更小的热疲劳裂纹倾向,但在激光合金化层附近的基体上会发生疲劳裂纹严重聚集,这将大幅度降低整体结构的抗热疲劳性能;热疲劳的机理为氧化-应力开裂,即热疲劳过程中所形成的高硬度脆性氧化物在热应力的作用下断裂.

The pure chromium （Cr） powder and cobalt （Co） base alloy powder were applied on the surface of 32Cr3Mo1V substrate by a ten-thousand-watt CO2 laser to form the layers abundant in elements of Cr and Co, and properties of the layers ineluding microstructure, elements distribution, miero-hardness and anti-thermal fatigue were studies. The result showed that the alloyed layers had full metallurgical bond with the substrate, boasting of advanced properties such as denser structure, smaller grain and free of crack, porosity, and slag inelusion; the laser alloyed Cr layer consisted of Fe-Cr solid solution in which Cr element accounted for 18.7% in wt. , while the laser alloyed Co alloy layer consisted of Fe-Cr solid solution with over 63% of alloyed elements, and stainless steel phase; both of the layers presented significant increase of thermal fatigue resistance and the area of cracks after thermal fatigue test reduced from 28.9% （in the substrate） to 12.4% （in Cr-alloying layer） and 9.4% （in Co-alloying layer）, respectively, therefore, they could prevent and block the generation of eraeks and reduce the expanding rate of eracks. Although the Co-alloying layer had a less crack sensibility than the Cr-alloying layer, there existed a special area with massed crack about 48. 9% in the substrate near the laser alloyed zone, which would cause a sharp decrease in the overall thermal fatigue resistance. The mechanism of the thermal fatigue was oxidation and stress cracking, that is, the brittle oxide formed during thermal fatigue period ruptured under the vast stress of the thermal fatigue.