X.M. Wang

Bulk amorphous FC20 (Fe-C-Si) alloys with small amounts of B and their crystallized structure and mechanical properties

The addition of a small amount (0.4 mass%) of B to a commercial FC20 cast iron was found to cause the formation of an amorphous phase in melt-spun ribbon and cast cylinders with a diameter of up to 0.5 mm. The structure of a melt-spun B-free FC20 alloy consisted of {alpha}-Fe, {gamma}-Fe and Fe{sub 3}C. The effectiveness of additional B is presumably due to the generation of attractive bonding nature among the constituent elements. The amorphous alloy ribbon exhibits a high tensile strength of 3,480 MPa and good bending ductility. The annealing causes the formation of an amorphous phase containing {alpha}-Fe particles with a size of about 30 nm. The mixed phase alloy exhibits an improved tensile strength of 3,800 MPa without detriment to good ductility. With further increasing temperature, the mixed amorphous and {alpha}-Fe structure changes to {alpha}-Fe + Fe{sub 3}C + graphite through the metastable structure of {alpha}-Fe + Fe{sub 3}C. The structure after annealing for 900s at 1,200 K has fine grain sizes of about 0.5 {micro}m for {alpha}-Fe, 0.3 {micro}m for Fe{sub 3}C and 1 {micro}m for graphite. The graphite-containing alloy exhibits high tensile strength of 1,200--2,000 MPa and large elongation of 5--13%. The high tensilemorexa0» strength and good ductility were also obtained for the 0.5 mm cylinder annealed at 1,200 K. The good mechanical properties are due to the combination of fine subdivision of crack initiation sites by the homogeneous dispersion of small graphite particles and the dispersion strengthening of Fe{sub 3}C particles against the deformation of the {alpha}-Fe phase. The synthesis of the finely mixed {alpha}-Fe + Fe{sub 3}C + graphite alloys having good mechanical properties by crystallization of the new amorphous alloy in the melt-spun ribbon and cast cylinder forms is encouraging for the future development of a new Fe-based high-strength and high-ductility material.«xa0less

Distribution of Nb and Co in an α-Fe/Nd2Fe14B-type nanocomposite

Atom probe field ion microscopy was employed to investigate the distribution of the alloying elements in a nanocrystalline Fe76.5Nd8Co8B6Nb1.5 (at.u200a%) alloy consisting of soft magnetic α-Fe and hard magnetic Nd2Fe14B. It was found that Co atoms prefer to partition into Nd2Fe14B phase. The partitioning factor of Co in the hard magnetic phase is approximately 2 with respect to the soft magnetic phase, α-Fe. Atom probe concentration and integrated depth profiles showed that the Nb atoms segregate at the interfaces between the soft and the hard magnetic phases. Based on the atom probe results, the beneficial effects of Nb and Co on the microstructure and the hard magnetic properties of the nanocomposite are discussed.

Possibility of bulk glassy and nanogranular alloys as biomedical materials

This paper reviews our recent results on the formation, fundamental properties and application examples of nanogranular body-centered cubic (bcc) Ti-based alloys, bulk glassy Ti-based alloys and porous Pd- and Zr-based glassy alloys with the aim of clarifying the possibility of practical uses as biomedical materials. The bcc Ti-based alloys with low Young’s modulus, large elastic elongation and high mechanical strength have already been used as eyeglass frame materials. New Ti-based bulk glassy alloys with a critical diameter of 7 mm in Ti-Zr-Cu-Pd system have been developed and tested as artificial dental root materials in various environmental conditions. The Pd- and Zr-based bulk glassy alloys can include spherical or polyhedral pores in a wide porosity range. The porous bulk glassy alloys have unique mechanical properties which are comparable to bones of human beings. These results indicate the possibility that the present nanogranular bcc Ti-based alloys as well as the bulk glassy alloys in Ti-, Pd- and Zr-based systems are used as biomedical materials in the near future.

Apatite Forming Ability of Bulk Metallic Glass Surface via Hydrothermal Treatment

Apatite forming and bonding ability of Ti based bulk metallic glass ((Ti0.40Zr0.10Cu0.36Pd0.14)99Ca1: BMG) were investigated as a new type of biomaterials. Powder mixture of CaHPO4･2H2O and Ca(OH)2 and the BMG disks were treated with autoclave for hydrothermal hot-pressing simultaneously (150°C, 40MPa). And then the BMG disks were soaked in simulated body fluid (SBF, Kokubo solution). Apatite were deposited and covered on the surface of the BMG. It was firstly demonstrated that surface of Ti based bulk metallic glass could be revealed apatite forming ability.

Melting Liquid Joint Method of Ti(Cu)-Base Bulk Metallic Glassy Alloy

Techniques for joint of materials are developed over 2000 years. The metallic liquid jointing technique which enables the joint of Ti41.5Cu42.5Ni7.5Hf5Zr2.5Si1 bulk glassy alloy without any crystallization is very useful to produce large bulk metallic glass. High velocity molten alloy streams are generated by ejection of alloy liquid through two nozzles at different sites. The jointed region has nearly the same structure, thermal stability and mechanical properties as those for the original glassy Ti41.5Cu42.5Ni7.5Hf5Zr2.5Si1 alloy.