Guoqiang Xie

Compound nanostructures formed by metal nanoparticles dispersed on nanodendrites grown on insulator substrates

A composite nanostructure consisting of Pt nanoparticle/W nanodendrite was fabricated on an insulator Al2O3 substrate using an electron-beam-induced deposition process combined with an ion sputtering method. W nanodendrites with the tips of 3nm were grown self-standing at the edge of the Al2O3 substrate. The observed morphology is attributed to a growth mechanism involving an electrical charge-up on the substrate surface, movement of charges, and their accumulation on the convex surface of the substrate as well as at the tips of the deposits. Pt nanoparticles with an equilibrium face-centered-cubic structure were uniformly distributed on the W nanodendrites. These composite nanostructures have potential for application in the fields of catalysis and nanodevices.

Ti-Based Bulk Metallic Glasses for Biomedical Applications

Biomedical materials can improve the life quality of a number of people each year. The range of applications includes such as joint and limb replacements, artificial arteries and skin, contact lenses, and dentures. So far the accepted biomaterials include metals, ceramics and polymers. The metallic biomaterials mainly contain stainless steel, Co-Cr alloys, Titanium and Ti-6Al-4V. Recently, bulk metallic glasses as novel materials have been rapidly developed for the past two decades in Mg-, Ln-, Zr-, Fe-, Ti-, Pd-, Cu-, Ni-based alloy systems because of their unique physical, chemical, magnetic and mechanical properties compared with conventional crystalline alloys. Metallic glass formation is achieved by avoiding nucleation and growth of crystalline phases when cooling the alloy from the molten liquid. Therefore, the different atomic configurations induced significantly different characteristic features such as high strength, good corrosion resistance and excellent electromagnetic properties, which are from their crystalline counterparts. Among different bulk metallic glasses, Ti-based bulk metallic glasses are expected to be applied as biomedical materials due to high strength, high elastic limit, low Young’s modulus, excellent corrosion resistance and good bioactivity of Ti element. Many Ti-based metallic glasses have been developed in Ti-Cu-Ni, Ti-Cu-Ni-Co, Ti-Cu-Ni-Zr, Ti-Cu-Ni-Zr-Sn, Ti-CuNi-Sn-B-Si, Ti-Cu-Ni-Sn-Be, Ti-Cu-Ni-Zr-Be, Ti-Cu-Ni-Zr-Hf-Si and Ti-Cu-Ni-Zr-Nb (Ta) alloys, based on the Inoue’s three empirical rules (Inoue, 1995) i.e., 1) multi-component consisting of more than three elements, 2) significant atomic size mismatches above 12% among the main three elements, and 3) negative heats of mixing among the main elements.

Transmission electron microscopy of martensitic transformation in Xe implanted austenitic 304 stainless steel

Thin film specimens of austenitic 304 stainless steel implanted with 100 keV Xe ions at room temperature were investigated. Microstructural evolution and phase transformation were characterized and analyzed in situ with conventional and high-resolution transmission electron microscopy. The phase transformation in a sequence from austenitic γ face-centered cubic (fcc) to hexagonal close-packed (hcp), and then to a martensitic α body-centered cubic (bcc) structure was observed in the implanted specimens. The fraction of the induced α(bcc) phase increased with increasing Xe ion fluence. Orientation relationships between the induced α(bcc) phase and austenitic γ(fcc) matrix were determined to be (01 1 ) α //(1 1 1) γ and [111] α //[011] γ . The relationship was independent of the induced process of the martensitic phase transformation for austenitic 304 stainless steel specimen, in agreement with the Kurdjumov–Sachs (K-S) rule. It is suggested that the phase transformation is induced mainly by the formation of the highly pressurized Xe precipitates, which generate a large stress level in stainless steels.