LOW-TEMPERATURE NITRIDING BEHAVIOR OF COMPRESSIVE DEFORMED AISI 316Ti AUSTENITIC STAINLESS STEELS

The effects of compressive cold deformation under the quasi-static loads on the nitride formation, nitride layer growth and surface hardness properties were researched in this study. Martensite structure did not form in AISI 316Ti stainless steel as a result of quasi-static deformation. Diffusion layer did not form in all nitrided samples. Both the deformed and undeformed samples have only compound layer on the surfaces at the low-temperature nitriding conditions (400∘C, 7[Formula: see text]h). According to the X-ray diffraction (XRD), energy-dispersive spectroscopy (EDS) and electron probe microanalysis (EPMA) results, S-phase and chromium nitride (CrN) were formed in the compound layers of the deformed samples. However, CrN did not form in the compound layer of the undeformed sample. The optical microscope (OM) results showed that the compressive cold deformation increased the nitrogen diffusion rate and led to thicker nitrided layer than the undeformed sample under the same plasma-nitriding conditions. All nitrided layers presented higher microhardness values ([Formula: see text][Formula: see text]HV) when compared with the untreated sample hardness. It was also verified that the deformation amount did not affect significantly the nitrided layer hardness.

The IF Spectrum of Fe-C-N and Fe-17%Cr-C-N Alloys Measured by the Impulse Excitation Technique

The temperature dependence of the dynamic Young’s modulus, E, and the damping, Q-1, of Fe-C-N and Fe-17%Cr-C-N alloys with different C, N contents were studied in the temperature range of 25°C to 600°C by the impulse excitation internal friction technique at 1KHz. Hot rolled samples were cold rolled to a thickness of 1.2mm and recrystallization annealed at 820°C for 30sec then gas jet cooled (-50°C/sec). Samples were subsequently tensile strained 6% and 16%. A Snoek peak was observed at 120°C in the undeformed sample and a Snoek-Koster peak was observed at 400°C after deformation. In the case of the Fe-Cr-C-N alloy, a high damping background due to magneto-mechanical damping was observed in the temperature range of 25°C to 400°C. A broaden Snoek peak in FeCr was observed at 300°C. The internal friction peaks observed in this study showed the strong dependence of the amount of interstitial contents and deformation and were well correlated to previous internal friction studies measured mainly by torsion pendulum and inverted torsion pendulum.

Evaluation of matrix strength in ultra-fine grained pure Al by nanoindentation

Nanoindentation measurements of the grain interiors of an ultra-fine grained (UFG) pure Al produced by equal channel angular pressing were taken to evaluate the contribution of the matrix strength. Specimens were subjected to 0, 1, 2, 4, and 8 passes at ambient temperature. The nanohardness of the deformed samples was always higher than that of the undeformed sample 0P in the range of the indentation depth that was investigated, suggesting a strengthening of the matrix in the UFG Al. The increase in hardness that was contributed by the matrix to the macroscopic scale hardness was significantly large in about 40% of the deformed samples. The microstructural characterization and the deformation response analysis with the pop-in event during indentation suggested that the strengthening of the matrix originated from dislocation strengthening and some other presumable factors in the grain interiors.

Superplastic Extrusion of Ultra Fine-Grained 3Y-TZP/Al2O3 Ceramic for Turbine Disk

Superplastic extrusion of axial forcing and radial flowing under different conditions was adopted to form a turbo-rotor, using hot-press sintered compact of zirconia (3Y)-toughened alumina composite that was prepared at 1450 °C for 1 hour with relative density of higher than 96%. Subsequent superplastic extrusion was attempted at temperature of 1500 °C-1650 °C. The results indicate that 3Y-ZrO2 plays an important role as a second-phase pinning agent and inhibits grain growth. The material shows good deformability and potential of near-net-shape forming. Comparing with undeformed sample, extruded sample was observed apparent coarsening in grain size and the remaining mechanical properties after deformation are not improved, irrespective of improved density. The dominating deformation mechanism is grain sliding and rotation accommodated with zirconia coordinated deformation.