Key Engineering Materials Vols. 345-346

Abstract: Flow behavior of the surface and center layers of solution-treated, peak-aged, or reversion-treated 2090 Al-Li alloy specimens has been reviewed and discussed in terms of microstructures and textures.

Abstract: The effect of Cr2N precipitation on deformed microstructure in high nitrogen austenitic Fe-18Cr-18Mn-2Mo-0.9N steel was investigated with a particular emphasis on deformation twinning. Based on the crystallographic analysis in the stereographic projection, the orientation relationship between austenite (γ) matrix and Cr2N was determined to be Cr2N [110]γ //[1100] and Cr2N (111) γ //(0001) . The deformation twinning had {111} < 112 > crystallographic component similar to that of cellular Cr2N. The cellular Cr2N precipitates caused a different orientation dependence of deformation twinning: only one twinning system in the <111 > grain was activated almost parallel to the growth direction of Cr2N.

Abstract: This paper is concerned with a manufacturing process and technology to facilitate the economical manufacture of high-quality magnesium alloy sheets. Magnesium alloys AZ31, AZ61, AM60 and AZ91 were used to investigate the appropriate anufacturing conditions for use in twin-roll strip casting. Temperatures of the molten materials and roll speeds were varied to find the appropriate manufacturing conditions. The effects of manufacturing conditions on possible forming were clarified in terms of roll speeds and roll gaps between upper and lower rolls. In addition, microscopic observation of the microstructure of the finished casting was performed. It was clarified that a magnesium sheet of 2.5 to 4.5mm thickness could be produced at a speed of 20 m/min by a horizontal copper roll caster. It was also found that the cast magnesium sheet of AZ31, AZ61, AM60 and AZ91 manufactured by roll strip casting could be used for plastic forming if the appropriate magnesium sheets were produced after the roll casting process. By a warm deep drawing test, it also demonstrated that a limiting drawing ratio of 2.4 was possible in the case of AZ91 sheet that was difficult to be manufactured by conventional extrusion process or DC casting and hot-rolling process for magesium alloy sheets with high aluminium contents.

Abstract: The effect of Mn/S ratio on hot ductility of Bi bearing steels has been investigated at the temperatures ranging from 950
to 1250
. The hot ductility, measured as the reduction ratio of area, was found to depend on the Mn/S ratio and test temperature to provide the largest hot ductility at the ratio of 3.903 at 1200
. The hot workability of Bi bearing free cutting steels seems to depend greatly on the size, volume fraction, and type and distribution of inclusions. In addition, hot deformation behavior of Bi bearing free cutting steel has also been characterized by constructing a processing map developed on the basis of the dynamic material model. A series of hot compression tests has been carried out at the temperatures ranging from 950
to 1250
under the strain rate ranging from 10-3 /s to 102 /s.

Abstract: Manufacturing bulk nanostructured materials with least grain growth from initial powders is challenging because of the bottle neck of bottom-up methods using the conventional powder metallurgy of compaction and sintering. In this study, bottom-up type powder metallurgy processing and top-down type SPD (Severe Plastic Deformation) approaches were combined in order to achieve both full density and grain refinement of metallic powders. ECAP (Equal-Channel Angular Pressing), one of the most promising processes in SPD, was used for the powder consolidation method. For understanding the ECAP process, investigating the powder density as well as internal stress, strain and strain rate distribution is crucial. We investigated the consolidation and plastic deformation of the metallic powders during ECAP using the finite element simulations. Almost independent behavior of powder densification in the entry channel and shear deformation in the main deformation zone was found by the finite element method in conjunction with a pressure dependent material yield model. Effects of processing parameters on densification and density distributions were investigated.

Abstract: The shear plastic deformation behavior of a material during equal channel angular (ECA) extrusion is governed primarily by the die geometry, the material properties, and the processing conditions. Using commercial DEFORMTM 2D rigid-plastic finite element code, this study investigates the plastic deformation behavior of Ti-6Al-4V titanium alloy during 1- and 2-turn ECA extrusion processing in dies containing right-angle turns. The simulations investigate the distributions of the billet mesh, effective stress and effective strain under various processing conditions. The respective influences of the channel curvatures in the inner and outer regions of the channel corner are systematically examined. The numerical results provide valuable insights into the shear plastic deformation behavior of Ti-6Al-4V titanium alloy during ECA extrusion.

Abstract: This paper presents a stochastic method to approximate the thermal deformation of a machine tool, by using the temperature changes of the body. The method examines the relationship between the thermal deformations and temperature changes of plural positions on a machine tool, and determines the appropriate temperature measuring points. In addition, the approximate equation of the thermal deformation is drawn by t-test, which uses those influential temperature changes as parameters. This study shows that the approximation equation of the thermal deformations can be expressed in a simple form with few parameters, and remarkably improve cutting processing.

Abstract: Adhesives are widely used in industrial world. However, it is difficult to characterize their mechanical properties because those strongly depend on environmental and mechanical conditions such as temperature, humidity or strain rate. In this paper, we focus on the strain rate dependence of the interfacial strength and investigate the interfacial strength by peel tests under several peel rates. The results show that, in low rate case (under 10-2 mm/s), the interfacial strength was constant and, in middle rate case (10-2 to 103 mm/s), the interfacial strength increased with the peel rate. Over 103 mm/s case, the interfacial strength became lower than those in middle rate cases. From the observation of peeling front by a high speed video camera, the deformation behavior of adhesives changed with the peel rate.

Abstract: The work hardening behavior by cold rolling was investigated in ultralow carbon and low carbon martensitic steels containing 12%Cr or 18%Ni, and then the effect of carbon on the work hardening behavior was discussed in terms of the change in dislocation density and the microstructure development during deformation. In the ultralow carbon steel, the hardness is almost constant irrespective of the reduction ratio. On the other hand, the low carbon steel exhibits marked work hardening. The dislocation density of these specimens was confirmed to be never increased by cold rolling. It was also found that cold rolling gives no significant influence on the morphology of martensite packet and block structure. TEM images of the cold-rolled steels revealed that the martensite laths in the ultralow carbon steel are partially vanished, while those in the carbon bearing steel are stably remained. These results indicate that the solute carbon retards the movement of dislocations, which results in the high work hardening rate through the formation of fine dislocation substructure within laths.

Abstract: Solution nitriding and aging treatment were applied to Ti-4mass%Cr alloy in order to fabricate a ductile high-nitrogen titanium alloy with fine (α + β) structure. The solution-nitrided specimen with
α’ martensitic structure was significantly hardened by solid solution strengthening by the absorbed nitrogen. During the aging treatment, fine β grains with a size of 1 microns in thickness precipitated along the martensite-plate boundaries. Although the specimen was softened to some extent after the aging treatment, the hardness is kept much higher than that of the aged Ti-4mass%Cr alloy without solution nitriding. This indicates that the nitrogen is still in solid solution of α phase even after the aging treatment, and contributes to strengthening of the fine-structured Ti-4mass%Cr-N alloy.