Materials Science Forum Vols. 654-656

Abstract: The cluster line criterion was used for optimized design of a Cu-Zr-Al alloy used as coating on the AZ91HP magnesium alloy by laser cladding. Results show that the coating mainly consists of an amorphous, Cu8Zr3, and Cu10Zr7 phases, of which the relative content of amorphous phase is estimated to be 61 %. The formation of the amorphous and intermetallics composite structure results in high hardness, good wear resistance and corrosion resistance. The interface between the clad layer and the substrate has good metallurgical bond.

Abstract: Oxide films have been produced on the AM60B magnesium alloy using micro-arc oxidation process in an environmentally friendly alkaline solution with and without addition of titania nanoparticles. The surface morphology and cross-section of anodized samples were analyzed by Scanning Electron Microscopy (SEM) coupled with EDS and the phase composition was investigated by X-ray Diffraction (XRD). Hardness tests were performed by means of a micro-hardness tester and the corrosion resistance was evaluated in 3.5% NaCl solution using potentiodynamic polarization tests. Addition of titania nanoparticles doesn’t affect corrosion resistance significantly, but the oxide films produced in titania-containing solution are denser, thicker and have more uniform morphology. In the oxides produced at 130V-140V in presence of titania (4g dm-3) a spinel (MgAl2O4) was observed. Spinel phase increases the hardness up to 550 HV (10mN, 10 s). The addition of titania nanoparticles in the solution could be an interesting way to synthesize hard coatings on magnesium alloy AM60B by micro-arc oxidation in a short process time (10 minutes).

Abstract: Cold spray coatings are considered promising for surface protection of light metal substrates but the mechanisms of bonding and coating build-up are still poorly understood and are the subject of continuing debate. A variety of coating/substrate combinations have been characterised in detail using electron microscopy to examine the nature of the interparticle and particle/substrate interfaces. Through-thickness residual stress profiles obtained via neutron diffraction show that the internal stress varies significantly depending on the coating materials. The work will present a picture of the cold spray deposition process using different material examples.

Abstract: Aluminizing the surface of a TiAl-based alloy (49.1 at% Al) was carried out by thermally spraying a pure aluminum coating and subsequent diffusion treatment at 1100°C. The influence of the diffusion time for the formation of Ti-Al intermetallic phases in the coating layers and the oxidation resistance of the aluminized TiAl-based alloys were investigated. The layer formed on the outermost surface was comprised of the Al-rich intermetallic T2iAl5 and contained pores. On the other hand, an intermediate layer consisting of TiAl2 and TiAl was formed between the outermost layer and the substrate. The thickness of the outermost layer decreased as the diffusion time increased, while the thickness of the intermediate layer increased. In addition, the coating/substrate interface changed from a wavy to a linear form with the growth of the intermediate layer. The aluminized coating showed good oxidation resistance at 900°C for all diffusion times.

Abstract: Fe-C-Ti-Cr-Ni alloy powder in diameter of 32-53 μm made by argon atomization is low-pressure plasma sprayed to produce stainless cast iron base deposits with finely dispersed titanium carbide particles. The as-sprayed deposit formed on a water-cooled substrate consists of γFe, αFe, TiC and Cr3C2. Heat treatment of the as-sprayed deposit above 873 K results in the formation of Cr7C3. The fine precipitates of approximately 0.2 μm in the as-sprayed deposit formed on a water-cooled substrate are carbide. The as-sprayed deposit produced on a non-cooled substrate and deposits which are obtained by heat treatment of the as-sprayed deposit are composed of γFe, αFe, TiC, Cr3C2 and Cr7C3. As heat treatment temperature increases, carbide precipitates coarsen. The hardness of deposit decreases with increasing heat treatment temperature. The wear resistance of as-sprayed deposit formed on a non-cooled substrate was higher than that of the deposit heat-treated at 1273 K. The as-sprayed deposit and deposit heat-treated at 1273 K have higher wear resistance than a commercial stainless steel.

Abstract: This paper discusses the influence of ultrasonic surface peening on the fatigue property of 7B04 high strength and toughness aluminum alloy. The results showed that a nano-layer of 10-20 μm was formed after ultrasonic surface peening. This nano-layer had a gradient structure with grain size of 10 to 50nm. Further, the ultrasonic surface peening process created residual compressive stress of 200MPa in this nano-layer. This stress caused micro surface cracks to be compressed or closed . Consequently, after ultrasonic surface peening the fatigue life of 7B04 alloy was extended to 5 times.

Abstract: The development of optical mold coatings has become a key technology in precision optical components in recent years. Researchers are still seeking ideal electroforming materials capable of resisting higher temperature and improve the lifespan of optical mold. Examples of these materials include Ni-W, and Ni-Mo-P alloy plating, among others. However, the literature rarely mentions these alloys as protective coatings. This may be because coating stability, flatness, and strength cannot achieve the desired protective effects. This study develops a combination of two wet electrochemical processes to form a multi-layer coating on optical molds. This coating consists of Ni-W, and Ni-Mo-P alloys. The proposed treatment process attempts to enhance the mechanical strength of the mold and extend its lifespan. We first used electro-deposition to form a thick-film Ni-W coating, and then applied the electroless plating by nonisothermal deposition method (NITD) to create a Ni-Mo-P thin-film and form a multi-layer coating. We also measured the composition, hardness, and elastic modulus of the protective coating as a reference basis for the development of optical molds. The results of this study reveal the appropriate process parameters to provide the multilayer films with a high strength and flat surface. This article can serve as a reference for the development of optical mold coatings.

Abstract: A hierarchical roughness surface with micro-and nano-structures was fabricated on mild steel by chemical etching with a mixture acid (2%HNO3 + 6%H2SO4 + 6%H3PO3) solution. The surface was modified by fluoroalkylsilane. The wettability of the modified surfaces was studied by contact angle method and Electrochemical Impedance Spectroscopy (EIS), and their morphology was investigated by Scanning Electron Microscopy (SEM). The roughness of the steel etched consisted of fine micro-steps in grains. The treated surface exhibited super-hydrophobic properties, water contact angle is high to 152° after modification for 6 min at room temperature. The results indicated that with the increase of etching time, the hierarchical structure gradually formed on the surface and the contact angle gradually decreased.

Abstract: Electrochromic properties of transition metal oxides had much attention in recent years. The electrochromic thin films can be assembly as electrochromic devices (ECDs) and then used for applications in devices such as mirrors, panels and smart windows. A kind of complementary ECD is popular in resent years. Therefore, a specific investigation on nickel oxide (NiO) electrochromic properties is completed in this study. The crystalline structure of the NiO films was analyzed using XRD (PANalytical X’Pert PRO) with Cu-Kα radiation. The atmosphere of oxygen concentration increasing has changed the NiO films crystalline from (200) to (111). The thicknesses and surface microstructures of the NiO films were investigated using a scanning electron microscope (SEM, Philips/FEI XL40 FEG). It is observed that films are relatively smooth deposited without oxygen. The characterization of the electrochromic properties was carried out in a two-electrode cell with an electrochemical analyzer (CHI 611B). The NiOx changes the transmittance of NiO films in the wavelength range of 300-1500 nm and the color of the film changes from transparent to brown. The nano-crack exhibits in the NiO film did enhance the electrochromic properties.

Abstract: A novel technique has been successfully developed to grow Fe ion doped diamond-like corbon (DLC) multilayer, with the modified linear ion sources(LIS), on Si(100)substrates. The Fe ions, generated in the specially designed ion source and accompanying the argon ions were implanted into one DLC layer previously grown by pulsed arc ion plating during argon ions sputtering and etching. The Fe-DLC multilayer can be grown by alternating growth of DLC layer and Fe ion implantation. The mechanical properties of Fe-DLC films were characterized. The results show that the Fe ion implanted multilayer significantly improves its mechanical properties. As compared with the conventional DLC films. Its stress drops to 3.9 GPa from 4.5 GPa, its friction coefficient is down to 0.1 from 0.14, and its hardness remains unchanged.