By carrying out the in situ deformation experiments in an HVEM, the velocities of edge and screw components of expanding dislocation loops in high purity molybdenum single crystals were measured directly as a function of the applied stress. And then, a new method is proposed to obtain from the analysis of expanding processes of a these dislocation loops the mobilities of dislocations as a function of the effective stress. As an application, the results obtained on the mobilities of edge and screw dislocations in high purity molybdenum at 150K are presented.

The shot peening process is known to produce a hard layer, known as the white layer” on the surface of coil springs. However, little is known about the fatigue properties of this white-layer. In this study, coil springs with a white-layer were manufactured. The surface of these springs was then examined using micro Vickers hardness, FE-SEM etc. to test fatigue strength of the springs. From the results obtained, a microstructure of the white-layer with grain size of 50–100 nm was observed, with a Vickers hardness rating of 8–10 GPa. Tow category springs were manufactured utilizing a double-peening process. These springs had the same residual stress destruction and surface roughness. Only one difference was observed: one spring had a nanocrystalline layer on the surface, while the other did not. The results of the fatigue test realized an increase in the fatigue life of the nanocrystalline surface layer by 9%.

4,328,296 5/1982 Tanaka et al. ...................... 501/103 4,360,598 11/1982 Otagiri et al......... ... 501/103 4,500,412 2/1985 Takahashi et al. ... ... 204/425 4,510,036 4/1985 Takeuchi et al. ... ... 204/425 4,522,633 6/1985 Dyer .................... ... 428/698 X 4,544,607 10/1985 Kaneno et al. ...................... 428/472 4,598,028 7/1986 Rossing et al. ....................... 429/30 4,601,809 7/1986 Kitahara ........... ... 204/425 4,642,174 2/1987 Shibata ......... ... 204/425 4,776,943 10/1988 Kitahara .............................. 204/426

The shot peening process produces a nanocrystalline layer on the surface of carbon steel. This nanocrystalline surface layer is harder than the matrix phase. Therefore, there are expectations that this nanocrystalline layer could become a new solution for surface hardening. However, little information exists on the effect this nanocrystalline surface layer has on fatigue properties. In this study, coil springs prepared with this nanocrystalline surface layer were investigated and were compared with springs of the same physical properties without this nanocrystalline surface layer. Coil springs were made from oil-tempered steel wire with chemical composition of 0.6C, 1.4Si, 0.7Mn and 0.7Cr(mass%) and were formed into compressive coil springs. Two types of springs were manufactured using different shot peening conditions. These springs had the same surface hardness and residual stress destruction, one with a nanocrystalline surface layer, and the other without. Fatigue testing was carried out on a spring fatigue test machine operated over 5×107 cycles. This test method has the merit of reproducing almost exactly the actual working condition of the valve springs. The results of the fatigue test showed that the spring with a nanocrystalline layer had a fatigue limit of τm±τa=600±531 MPa at 107 cycles, whereas the other spring had a limit of τm±τa=600±489 MPa. Thus, it was evident that this nanocrystalline surface layer could increase the fatigue life by 8%.

The fractal pattern formation on the free surface of annealed Al/amorphous-Ge bilayer film deposited on a SiO2 substrate (Al/Ge/SiO2) was investigated with scanning electron microscopy (SEM). When the Al/Ge/SiO2 bilayer film is annealed at lower temperatures than the crystallization temperature of amorphous Ge itself (e.g. 383-418 K), amorphous Ge crystallizes, i.e. the so-called metal-mediated-crystallization (MMC) takes place. In the course of MMC, crystalline Ge aggregates appear on the free surface, which results in the formation of fractal patterns with branching. The morphology of fractal patterns and hence the fractal dimensions are different depending on the relative difference in thickness between a-Ge and Al layers. In-situ SEM observations indicate that the aggregation of Ge atoms takes place at the points of protruding branches, then the protruded branches run out further and further but the morphological changes can scarcely be observed at the portions other than the growing points.

Pt 60 Ni 15 P 25 metallic glass ribbons prepared by a single-roll melt-spinning method were deformed in tension at a strain rate of 2 × 10 -2 s -1 in the supercooled liquid region. In-situ observations of the deformation behavior of the metallic glass ribbons were carried out using an optical microscope. It was found that a homogeneous deformation of more than 200% elongation took place by a viscous flow of the supercooled liquid of Pt 60 Ni 15 P 25 metallic glass at 523 K, an intermediate temperature in the supercooled liquid region. In the case of the tensile tests after partial crystallization at 543 K, it was found that the residual supercooled liquid deformed preferentially without deformation of the crystalline solid, and therefore inhomogeneous deformation occurred.

Zr55Al10Ni5Cu30 bulk metallic glass composite containing 10 vol% crystalline ZrC particles was prepared by an in-situ reaction between Zr-based melt and graphite powder being followed by an injection casting into a copper mould. The crystallization process of the composites during annealing at 723 K has been investigated by using DSC, TEM and microhardness test. It is found that an unknown crystalline phase appears first along the interface between ZrC particle and the matrix of the composite, and then a homogeneous nanocrystallization occurs in the matrix. The nanocrystalline phase precipitated in the matrix is determined to have orthorhombic structure by using TEM diffraction. It has a higher hardness than the hardness of the amorphous phase which remained in the matrix. Hardness of the matrix increases with increasing the volume fraction of the nanocrystalline phases. After annealed at 723 K for 40 min, most of the matrix has been transformed into crystalline phases with a final average grain size of about 120 nm.

Pt60Ni15P25 metallic glass ribbons prepared by a single-roll melt-spinning method were deformed intension at a strain rate of 2 x 10(-2) s(-1) in the supercooled liquid region. In-situ observations of the deformation behavior of the metallic glass ribbons were carried out using an optical microscope. It was found that a homogeneous deformation of more than 200% elongation took place by a viscous flow of the supercooled liquid of Pt60Ni15P25 metallic glass at 523 K, an intermediate temperature in the supercooled liquid region. In the case of the tensile tests after partial crystallization at 543 K, it was found that the residual supercooled liquid deformed preferentially without deformation of the crystalline solid, and therefore inhomogeneous deformation occurred.

The fundamental mechanism underlying the hydrogen exfoliation phenomenon at the damaged layer in Si was investigated. We studied the distribution of the defects as a function of implanted hydrogen dose and clarified the key role of defects in the action of exfoliation. A damaged layer formed by high dose hydrogen implantation in a silicon wafer was observed by cross sectional transmission electron microscopy (XTEM). In the damaged layer caused by hydrogen implantation, (100) defects and (111) defects were observed. The density and size of defects were analyzed and compared with the hydrogen profile obtained by second ion mass spectroscopy (SIMS). The defect distribution was in agreement with the hydrogen concentration obtained by SIMS. The density of (111) defects became higher as the area from the surface deepened, and the sizes of (100) defects and (111) defects grew larger. These results indicate that hydrogen in (111) defects moves toward (100) defects at projection range, and the pressure of hydrogen gas caused by annealing leads to the exfoliation.

The fundamental mechanism of the hydrogen exfoliation phenomenon that occurs at the damaged layer in H ion-implanted silicon was investigated. A damaged layer formed by high-dose hydrogen implantation in a silicon wafer was observed by cross-sectional transmission electron microscopy (XTEM), and (100) platelets and (111) platelets were visible. Density and size of the platelets in the damaged layer were analyzed quantitatively. Although the density and size of (100) platelets are almost twice those of (111) platelets, the density of (111) platelets in the deeper area is greater than the density of (100) platelets. Neither the densities nor size of either (100) or (111) platelets have any relation with implantation dose in the dose range from 5.0×1016 to 8.0×1016 (Hcm−2). The sizes of (111) platelets in the deeper area approach a certain size (about 10nm), because of their partial combination with (100) platelets.

Ti-37.5 at%Si powder mixtures were mechanically alloyed in a planetary ball mill under an argon atmosphere. The powder milled for 180 ks consisted of amorphous and nano-sized titanium and/or silicon grains. Crystallization temperature of the powder was about 780 K. It was consolidated using a cubic-type anvil apparatus under a high hydrostatic pressure of 5.4 GPa (HHPC method). The obtained compact consolidated at below 663 K was fully densified with the retention of amorphous phase, while the compact prepared at above 723 K almost crystallized. The compressive strength of the compact prepared by HHPC method at 623 K was measured to be 2.52 GPa at room temperature. The value was about 0.5 GPa higher than that of the compact prepared by HHPC method at 723 K. It suggests amorphous phase is attributed to toughening of the compact.

Ti-37.5 at%Si powder mixtures were mechanically alloyed in a planetary ball mill under an argon atmosphere, The powder milled for 180ks consisted of amorphous and nano-sized titanium and/or silicon grains. Crystallization temperature of the powder was about 780 K. It was consolidated using a cubic-type anvil apparatus under a high hydrostatic pressure of 5.4 GPa (HHPC method). The obtained compact consolidated at below 663 K was fully densified with the retention of amorphous phase, while the compact prepared at above 723 K almost crystallized. The compressive strength of the compact prepared by HHPC method at 623 K was measured to be 2.52 GPa at room temperature. The value was about 0.5 GPa higher than that of the compact prepared by HHPC method at 723 K. It suggests amorphous phase is attributed to toughening of the compact.

Gradient distribution alumina short fibre reinforced 6061 aluminium alloy have been fabricated by taking advantage of preform compressive deformation during squeeze casting. Pressure was applied mechanically by a punch. Velocity of the punch, pre-heat temperature of the preforms and pouring temperature were controlled during the infiltration of molten 6061 alloy into alumina short fibre preforms. The distribution of hardness along the infiltration direction in the composites was measured and the distribution of volume fraction along the infiltration direction was calculated by the hardness. Velocity of the inflow, pre-heat temperature of the preform, pouring temperature of the molten metal, binder content of the preform and volume fraction of fibres, all have a very great effect on the gradient distribution of alumina short fibres in the aluminium alloy composites.