Three compositions, (Ni75Si25)-5Cr, (Ni75Si25)-10Cr and (Ni75Si25)-15Cr, have been
cladded onto Ni-based suaperalloy substrate by pre-placing laser cladding process with a 5 kW
continuous wave CO2 laser. Ni75Si25 was also cladded with the same method for comparison. The
process parameters have been optimized to obtain defect free claddings. The microstructure and the
hardness of the cladded layers were characterized by optical microscopy, scanning electron microscopy,
X-ray diffraction and microhardness measurement. The corrosion resistance of the cladded layers was
measured in a sulfuric acid solution.
Surface modification is a promising technique to improve wear properties of titanium and titanium alloys by modifying either the surface composition or microstructure. Laser remelting and laser nitriding of commercial purity titanium were carried out under pure argon and pure nitrogen ambient, respectively. Characterization of the laser treated surface was done by optical microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), microhardness tester. During laser irradiation heating, Ti exhibits a height activity and combines with N in the atmosphere of pure nitrogen forming TiN and TiN0.3, whereas Ti only transform into martensitic Ti in pure argon. The Vickers microhardnesses are greatly improved by laser remelting and laser nitriding.
Laser cladding experiment was carried out with a 5 kW continuous wave CO2 laser by preplacing Ni75Si25 and Ni78Si13Ti9 powders onto Ni-based superalloy substrate. The microstructure of the specimens was monitored by using optical and scanning electron microscopy. The chemical compositions of the alloys and their phases were obtained using X-ray diffraction and energy dispersive x-ray spectroscopy. The phase transformation temperatures were determined by non-isothermal differential scanning calorimetry tests. The microhardness of the laser cladded sample was measured.
Based on a high power CO2 laser beam passing by an integral mirror, the bioceramic coatings of gradient composition were designed and fabricated on titanium alloy substrate (Ti-6Al-4V). The relations among laser processing parameters, microstructure and thermal behavior of the gradient bioceramic coatings were investigated. The morphology of the composites was observed by scanning electron microscope (SEM). Phase composition of the coatings was analyzed by X-ray diffraction (XRD). And the thermal behavior of raw powders was evaluated through thermal gravimetry and differential scanning calorimetry (TG-DSC) test. The results demonstrated that the bioceramic coatings were metallurgically bonded to the titanium alloy substrate. The bioceramic coatings contained such bioactive phases as HA and β-TCP, which offered an advantageous condition for osseo-connection. The DSC thermograms showed the endothermic peaks at different temperature, which resulted from the different transitions process, respectively. Furthermore, the DSC results were in accordance with TG data of the powders and showed that with the increasing temperature the weight of sample accordingly decreased.
According to the arrangement of atoms, the solid materials can be divided into the crystals and the non-crystals. Short for quasi-periodicity crystal, quasicrystal, also known as the "quasi crystal" or "mimetic crystal", is an intermediate between crystals and non-crystals. Three mathematical laws hidden in the quasicrystal are Penrose puzzles, Fibonacci sequence and golden section, and the uniqueness of quasicrystals is five rotational symmetry nonexistent in common crystals. A few quasicrystals (such as Al65Cu20Fe10Mn5, Al75Fe10Pd15) are stable phases, while most of the quasicrystals belong to the metastable products, both of which are formed largely by the method of rapid cooling. Quasicrystal materials have a very high hardness, low coefficient of friction and non-stick characteristic, of which the unique performance is successfully applied in the frying pans, razor blades and surgical tools.
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