The deformation behavior and microstructure evolution of Ti-6Al-4V alloy under room temperature creep was investigated using mechanical test and scanning electron microscope observation with electron back-scatter diffraction method. The alloys were creep deformed and ruptured under initial stresses of 874MPa, 889MPa and 904MPa at room temperature. The rapid stress change test revealed that creep deformation was controlled by the viscous slip motion of dislocations. The stress exponent was estimated as 59. The strain rate of acceleration creep region calculated by the Nortonʼs law with the high stress exponent was inconsistent with that measured by the experimental creep test. Using the slip trace analysis, it was found that single dislocation slip in basal and prism were mainly activated in the early stage of creep, and multiple slips were often observed as the deformation progresses. Especially, the multiple slip including 1st pyramidal slip believed to be effective for suppressing strain rate acceleration in creep. In addition, the work hardening behavior during creep showed a strain rate dependence, indicating that the lower the strain rate is, the more work hardening occurs.

6000 series aluminum alloys are used in a variety of fields including architectural materials. Many of these products are hollow shapes extruded using a port-hole die. In extrusion processes with complex cross-sectional geometries and extrusion conditions with high productivity, grain-like sloughing defects called pick-up often occur irregularly on the surface of the extruded material, which is a problem that degrades productivity and surface quality of the product. In this research, we focused on the structural change inside the port-hole die and the growth process of pick-up on the die-bearing surface, and investigated the effect of the change of material flow by the port-hole mechanism and the difference of alloying elements on the growth process. The number of pick-up was found to increase with increasing ram stroke during hot extrusion. The addition of more magnesium (Mg) to the billet increased the extrusion load and the number of pick-up. In addition, Mg was preferentially deposited on the die-bearing surface and the deposits of pick-up that occurred were MgO. Oxidation of the die bearing surface and control of the die-aluminum interface are important to control pick-up.

3104 aluminum alloy hard sheet is used for aluminum beverage can body, and it is having high ironing formability. This alloy has large anisotropy of r and n-value, but the effect of such anisotropy on ironing formability is not clear. In this study, cup forming and DI forming were performed using 3104 aluminum alloy cold rolled hard sheets having different anisotropy of r and n-values. Magnitude of the anisotropy changes by drawing and ironing. Ironing fracture tests revealed that fracture occurs at angles between 10 and 20° in the can circumferential direction. From the strain distribution measurement of the can wall, it was found that the axial strain of can wall at fracture angle is larger. Theoretical analysis method of ironing stress considering r and n-value anisotropy, based on Hill's anisotropic plasticity theory (quadratic yield function) was devised. From this analysis, it was found that when the anisotropy of r-value in the can wall are small, (1) the fracture occurs less, (2) margin of stress (calculated from ratio of can axial tensile stress to fracture stress) is larger.

In general, the elastic modulus of a metallic material is proportional to the mechanical strength. A multi-functional beta titanium alloy, Gum Metal has been developed to have both low modulus and high strength after severe cold working. However, both its underlying mechanisms for multi-functional characteristics and its deformation mechanism have not yet been elucidated. In this study, nano-indentation and in-situ compression test in TEM have been performed to investigate the effect of phase stability on local mechanical behavior. We have examined the local mechanical behavior in Ti-18Mo alloy which has a higher bcc phase stability than Gum Metal. Nano-indentation tests revealed that the phase stability does not affect the local dynamic behavior. On the other hand, in situ compression test confirmed the effect of phase stability on the local mechanical behavior. Dislocation motion has been observed in Ti-18Mo alloy by in-situ compression tests in TEM, although such dislocation activity was not observed in Gum Metal in our previous study.

Morphology of blisters generated in a high purity aluminum plate of 99.9997% purity was investigated by using the ion-milling method for preparation of specimen, together with microscopic observation. The set of results revealed that a spherical-shaped void with a diameter of 250μm was formed at 350μm in depth from the top surface of blistering. There was no space inside the protrusion of the blistering.