Oxide Spallation during Post-Isothermal High Temperature Oxidation Cooling of Cr-rich Cast Alloys highly alloyed with Hf
Cobalt, nickel and iron-based alloys containing 25wt.%Cr and strengthened either by chromium carbides or by HfC were oxidized at 1000, 1100 and 1200°C to obtain external oxide scales. The spallation of these oxides during the post-oxidation cooling was studied by exploiting the cooling part of the thermogravimetry curves. The best resistant alloys against scale spallation were the iron-based alloys which did not lose oxide. The nickel-based alloys well behaved too. The worst alloys were the cobalt alloys, principally due to the complex composition of the oxide scales. Beside the base element, the thickness of the oxide was also identified as a major parameter. The presence of Hf with contents much higher than usual was also beneficial for the resistance against spallation.
Superalloys: a technical guide
Superalloys: a technical guide , Superalloys: a technical guide , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی
Mechanical and electrochemical properties of a cast carbon steel. Part 2: Behaviour in corrosion
A ferrito-pearlitic steel, elaborated by foundry with a cylindrical shape has been mechanically studied in compression and hardness in a first part of the present work. In this second part the equivalent samples were tested in corrosion in a sulphuric acid solution by varying both the initial deformation rate and the cutting orientation with respect to the sample axis. Stern-Geary linear polarizations were successively run during half an hour of immersion with recording of open circuit potential and polarization resistance, while cyclic polarizations were performed between the cathodic domain and the anodic solventÂÂs wall. No systematic differences were noted on the cyclic polarization curves between the values, obtained for the different deformation rates and orientations, of the various parameters describing the corrosion state changes (active iÂ® passive and passive iÂ® active), although that some tendencies were seen. In contrast the linear polarization runs showed that the Rp value more clearly depends on both the hardening amount and the surface orientation. It was notably found again that the polarization resistance decreases, and the deduced corrosion rate increases, when the plastic relative deformation is higher, and also, by combining the present results with previous ones, that there is possibly a continuity of evolution of the parallel/perpendicular Rp order from the negative deformations in compression to the positive deformations in traction.