高铌TiAl合金的高温断裂韧性

利用紧凑拉伸试样通过预制疲劳裂纹研究近片层组织Ti-45Al-8Nb-0.2W-0.2B-0.1Y合金和全片层组织Ti-45Al-7Nb-0.2W-0.2Hf-0.3B-0.15C合金在750℃下的断裂韧性,并分析两种组织合金的断口形貌.结果表明,近片层组织和全片层组织高铌TiAl合金750℃时的断裂韧性分别为19.54和31.58 MPa·m1/2,且近片层组织疲劳裂纹开始萌生时的最大疲劳载荷明显低于全片层组织.断口分析表明近片层组织中裂纹主要在等轴γ晶中萌生,裂纹扩展方式包括沿γ晶、穿γ晶及沿片层、穿片层;全片层组织中裂纹主要在垂直于加载方向的片层间萌生,裂纹以沿片层与穿片层的混合方式进行扩展且伴有二次裂纹的萌生. 

High-temperature fracture toughness of high Nb-containing TiAl alloys

The fracture toughness of a nearly lamellar Ti-45Al-8Nb-0.2W-0.2B-0.1Y alloy and a fully lamellar Ti-45Al-7Nb-0.2W-0.2Hf-0.3B-0.15 C alloy at 750℃ was investigated by prefabricating a fatigue crack in the compact tension(CT) specimen,and the corresponding fracture morphologies were observed by optical microscopy and scanning electron microscopy. It is found that the fracture toughness of the nearly lamellar high Nb-containing Ti Al alloy is 19.54 MPa·m1/2 at 750℃,obviously lower than the value of 31.58 MPa·m1/2 for the fully lamellar alloy. The maximum cyclic load at which the fatigue crack initiates in the nearly lamellar alloy is noticeably less than that in the fully lamellar alloy. Fracture images show that for the nearly lamellar alloy,cracks initiate mainly in equiaxed γ grains and propagate in different ways,intergranularly or transgranularly in γ grains or lamellar colonies. But for the fully lamellar alloy,cracks initiate mainly at lamellar interfaces perpendicular to the load direction and propagate in both interlamellar and translamellar ways,in accompanying with secondary crack initiation.