一种镍基高温合金蠕变过程中碳、硼化物的演变行为及结构表征

Evolution and Structure Characterization of the Carbide and Boride during Creep in A Ni-based Superalloy

通过对一种镍基铸造K417G高温合金进行760℃/645 MPa、900℃/315 MPa和950℃/235 MPa 3种条件下的蠕变性能测试,并采用扫描电镜、透射电镜等实验方法对蠕变后高温合金微观组织进行表征,分析不同条件下的蠕变机理,并对比分析蠕变前后合金中碳、硼化物的形态、分布、晶体结构,研究不同蠕变温度和应力条件对碳、硼化物析出和演变行为的影响,并揭示碳、硼化物对镍基高温合金不同条件下蠕变性能的影响。结果显示,K417G高温合金的蠕变寿命随着蠕变条件由760℃/645 MPa向900℃/315 MPa和950℃/235 MPa转变先升高后降低。760℃/645MPa下,蠕变裂纹产生于MC型碳化物的碎裂;900℃/315 MPa下,蠕变裂纹一部分产生于晶界,另一部分产生于MC型碳化物碎裂;950℃/235 MPa下,蠕变裂纹全部产生于晶界。在760℃/645 MPa下,MC型碳化物不分解,晶界没有析出细小碳、硼化物;900℃/315 MPa下,MC型碳化物分解产生M23C6型碳化物,晶界析出细小均匀分布的M23C6型碳化物和M3B2型硼化物;950℃/235 MPa下,晶界M23C6型碳化物和M3B2型硼化物长大,呈条状分布。

The creep property of a Ni-based K417 G superalloy was tested at 760 ℃645 MPa, 900 ℃/315 MPa and 950 ℃/235 MPa, and then the microstructure after creep was characterized through scanning electron microscope（SEM） and transmission electron microscope（TEM）. The creep mechanism under different conditions was analyzed. Moreover, by comparing the morphology, distribution and crystal structure of carbides and borides before and after creep tests, the influences of creep condition on the precipitation and evolution of carbides and borides were investigated, and the effects of carbides and borides on the creep properties of Ni-based superalloy were revealed. Results show that as the creep condition varies from 760 ℃/645 MPa to 900 ℃/315 MPa and 950 ℃/235 MPa, the creep life of K417 G superalloy increases firstly and then decreases. At 760 ℃/645 MPa, the creep crack initiates at the broken MC carbide; At 900 ℃/315 MPa, the creep crack initiates at both the broken MC carbide and grain boundary; At 950 ℃/235 MPa, the creep crack initiates at grain boundary. In addition, at 760 ℃/645 MPa, the MC carbide does not decompose, and there is no carbide or boride precipitate at the grain boundary; At 900 ℃/315 MPa, the MC carbide decomposes and M（23）C6 carbide forms. M（23）C6 carbide and M3B2 boride precipitate uniformly at the grain boundary; At 950 ℃/235 MPa, the M（23）C6 carbide and M3B2 boride at the grain boundary grow up and distribute as strip.