Ti-600合金的热稳定性

研究了Ti-600合金镦制饼材600 ℃热暴露前后室温拉伸性能的变化，并观察合金的拉伸断口、分析其断裂机制。结果表明，600 ℃热暴露100 h后，毛坯热暴露试样的强度较热暴露前固溶时效试样(STA)的提高了3%左右，延伸率降低20%左右；热暴露试样的强度稍有降低，延伸率则降低了45%左右。STA试样室温拉伸断裂起源于试样中心位置，断口形貌呈现韧窝型断裂特征；毛坯热暴露试样断口上可见解理小平面与韧窝并存的特征，为混合型断口；试样热暴露以后，裂纹萌生于试样表面，断口上观察到解理小平面，合金的断裂沿片层α相界面扩展。热暴露试样表层有脆性富氧层存在，富氧层内易诱发细微裂纹并向基体扩展。表面渗氧是Ti-600合金热暴露后塑性下降的重要原因之一

Thermal Stabilities of Ti-600 Alloy

Tensile testes were carried out at ambient temperature on Ti-600 alloy before and after being exposed at 600 °C for 100 h. Fracture morphologies were investigated and the fracture mechanism was also analyzed. The results indicate that the strength of the sample without oxidizing layers increases by 3% or so, the elongation decreases by about 20% for the alloy exposed at 600 °C for 100 h. While for the sample with oxidizing layers, the strength decreases a little bit, and the elongation decreases by 45% or so, which indicates that the plasticity decreases abruptly during the exposure process. For the solutioned plus aged samples, cracks originate from the center of the fracture, and dimple typed fracture can be found in the fractographies. After being exposed at 600 °C for 100 h, for the samples without oxidizing layers, dimples and cleavage facets can both be seen in the fractographies, which displays the feature of hybrid fracture. While for the samples with oxidizing layers, only cleavage facets can be observed in the fractographies, and fractures propagate along the interfaces of lamellar a phases. These results are caused by the precipitation and the existence of the brittle oxidizing layers. The cracks would be formed in the oxidizing layers first and then propagate into the matrix during the tensile tests. Oxygen permeation in the surface layer is one of the important reasons for the decrease of plasticity.