On the Aged Structure of Heat-Resisting Alloy A286 and Its Fracture Process at Elevated Temperature

Abstract

Relations of aged structures to the fracture process in the heat-resisting alloy A286 were studied by means of microscopic observation on the ruptured specimens at 650°C. The effect of melting procedures and natures of rupture tests on the fracture process also was investigated. The results obtained in the present experiment were summarized as follows:
Contributions of the surface between G phase and grain boundary to crack nucleation were significant. Although the contributions were also recognized with η phase, the contributions. from η phase were less important than those from G phase. Intergranular precipitates such as TiC and Laves phase had no essential effect on the propagation of crack so long as these precipitates had no continuous arrangement.
Difference between creep rupture and tensile rupture was notable, that is, nucleation and. propagation of crack was less structure-sensitive in the case of tensile rupture, while crack was much correlated with G phase, η phase, grain boundary and so on in the case of creep rupture.
Effect of melting procedure on the fracture process was remarkable, that is, the resistance to crack nucleation and propagation was more increased with the vacuum-melted alloy than with the air melted one. It was supposed that the phenomena as abovementioned might be due to an existence of boron atoms which had come into the solution from the crucible during the melting process.