There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Titanium alloys are expected to be much more widely used for implant materials in the medical and dental fields because of their superior biocompatibility, corrosion resistance and specific strength compared with other metallic implant materials. Pure titanium and Ti–6Al–4V, in particular, Ti–6Al–4V ELI have been, however, mainly used for implant materials among various titanium alloys to date. V free alloys like Ti–6Al–7Nb and Ti–5Al–2.5Fe have been recently developed for biomedical use. More recently V and Al free alloys have been developed. Titanium alloys composed of non-toxic elements like Nb, Ta, Zr and so on with lower modulus have been started to be developed mainly in the USA. The β type alloys are now the main target for medical materials. The mechanical properties of the titanium alloys developed for implant materials to date are described in this paper.

Mechanical properties of biomedical titanium alloys

Self-healing polymeric materials: A review of recent developments

The recent development in the field of superhard materials with Vickers hardness of ⩾40 GPa is reviewed. Two basic approaches are outlined including the intrinsic superhard materials, such as diamond, cubic boron nitride, C3N4, carbonitrides, etc. and extrinsic, nanostructured materials for which superhardness is achieved by an appropriate design of their microstructure. The theoretically predicted high hardness of C3N4 has not been experimentally documented so far. Ceramics made of cubic boron nitride prepared at high pressure and temperature find many applications whereas thin films prepared by activated deposition from the gas phase are still in the stage of fundamental development. The greatest progress has been achieved in the field of nanostructured materials including superlattices and nanocomposites where superhardness of ⩾50 GPa was reported for several systems. More recently, nc-TiN/SiNx nanocomposites with hardness of 105 GPa were prepared, reaching the hardness of diamond. The principles of de...

https://mediatum.ub.tum.de/doc/958917/file.pdf

The search for novel, superhard materials

Young's modulus as well as tensile strength, ductility, fatigue life, fretting fatigue life, wear properties, functionalities, etc., should be adjusted to levels that are suitable for structural biomaterials used in implants that replace hard tissue. These factors may be collectively referred to as mechanical biocompatibilities. In this paper, the following are described with regard to biomedical applications of titanium alloys: the Young's modulus, wear properties, notch fatigue strength, fatigue behaviour on relation to ageing treatment, improvement of fatigue strength, fatigue crack propagation resistance and ductility by the deformation-induced martensitic transformation of the unstable beta phase, and multifunctional deformation behaviours of titanium alloys.

Mechanical biocompatibilities of titanium alloys for biomedical applications.

A 3D measurement procedure for internal local crack driving forces via synchrotron X-ray microtomography

In aluminum alloys, it is general that dimple type fracture occurs from inclusions or second phases particles. Intergranular, local shear and delamination type fractures are also sometimes observed. On Al–Li alloy (A2091), effect of inclusion particles on fracture behavior is analyzed using HRR singularity and Eshelby type internal stress analysis. Fracture of inclusions of CuAl2 and Al2CuMg is observed (5–8 μm) and their strength is estimated about 710 MPa and decreased with increasing particle size. Fracture of Al3Zr or Al3Ti particles is not observed. Moreover, it is clarified that delamination occurs when the normal stress against the grain boundary attains 116 and 113 MPa at liquid He and room temperature, respectively. Moreover, newly developed high strength Al–Nb wire with 1 Gpa is introduced. Fracture and fatigue behaviors of aluminum casting alloys are also stated. Increasing the iron content, fracture toughness and fatigue properties (also impact fatigue properties) are degraded. The effect of Ca addition that possesses the modifying effect of the eutectic Si morphology is examined. It has been observed that the harmful effect of iron is largely improved. Increasing the Si content in Al–Si casting alloys, it is generally observed that fatigue strength or ΔKth is increased. Toughness of MMC is generally rather low. Based on the simulation analysis on fracture of Al–SiCW composite, high toughness MMC has been already developed, where some aggregated SiCW granules have been embedded into A6061 matrix. According to FEM analysis, it has been suggested that there is an appropriate aggregation ratio in the granule (i.e. SiCW content in the granule). The above topics have been reviewed.

Strength and fracture of aluminum alloys

Analysis of impact properties of A533 steel for nuclear reactor pressure vessel by instrumented Charpy test

The fabrication of metal matrix composite (MMCp) by vortex process is the general method due to the advantage of its convenience. However in the case of fine particles the surface property of the particle appears dominantly, especially in nano-size particles the agglomeration occurs and the fabrication of MMCp is reduced to be difficult. It is analyzed that the strength of the MMCp is dominated by the ascent of the dislocation density. Further, as the dispersion strengthening mechanism can be anticipated, dispersions of more fine particles into the matrix are required. In this study, the influences on various primary factors for solving an agglomeration problem are examined using SiC particles of 0.3 μm (the minimum diameter in the market) into 6061 Al alloy by the vortex method. From this study, the following results are obtained, (1) It is found that MMCp with no agglomeration can be fabricated by conducting the following procedure; pre-treatment, disagglomeration of powder, Ca addition and stirring in the semi-solid range. (2) It is deduced that the main factors of forming the agglomeration in the matrix of MMCp are the yield of SiO2 on the surface of SiC and the reduction of the void ratio of SiC powder.

Toshiro Kobayashi

Papers

A 3D measurement procedure for internal local crack driving forces via synchrotron X-ray microtomography

Strength and fracture of aluminum alloys

Analysis of impact properties of A533 steel for nuclear reactor pressure vessel by instrumented Charpy test

Fabrication process of metal matrix composite with nano-size SiC particle produced by vortex method

High-density three-dimensional mapping of internal strain by tracking microstructural features