Qizhou Cai

Formation of Nanocrystalline Tungsten by Selective Laser Melting of Tungsten Powder

Nanocrystalline tungsten was obtained by selective laser melting (SLM) in the present work. The microstructures and compositions revealed that the nanocrystalline tungsten could be fabricated via the SLM method using pure tungsten powder. It was found that the produced nanocrystalline tungsten microstructure could be regarded as a resultant of solid forces by laser, which grow along a special crystal surface. The metallurgical mechanisms for the formation of such a novel structure through SLM process were also addressed.

Preparation and characterization of ZrO2/TiO2 composite photocatalytic film by micro-arc oxidation

Abstract ZrO2/TiO2 composite photocatalytic film was produced on the pure titanium substrate using in-situ Zr(OH)4 colloidal particle by the micro-arc oxidation technique and characterized by scanning electron microscope (SEM), energy dispersive X-ray (EDX), X-ray diffraction (XRD) and ultraviolet-visible (UV-Vis) spectrophotometer. The composite film shows a lamellar and porous structure which consists of anatase, rutile and ZrO2 phases. The optical absorption edge of film is shifted to longer wavelength when ZrO2 is introduced to TiO2. Furthermore, the photocatalytic reaction rate constants of degradation of rhodamine B solution with ZrO2/TiO2 composite film and pure TiO2 film under ultraviolet irradiation are measured as 0.0442 and 0.0186 h−1, respectively.

A Powder Shrinkage Model for Describing Real Layer Thickness during Selective Laser Melting Process

Shrinkage tends to generate when loose metal powder melted in each processing layer along the direction of layer growing during selective laser melting process, resulting in an increased real layer thickness. The shrinkage model for layer shrinkage in SLM process is established. The variation of real layer thickness and the relevant mathematical explanations are discussed in this paper. The results show that the total shrinkage of metal powder layer sharply increases in the initial layers, and then reaches to a plateau value with the increased processing layers. This value is defined by the ratio of sliced layer thickness (h) to relative density (k) during selective laser melting process.

Photocatalytic Ozonation of Oxalic Acid Over Cu(II)-Grafted TiO2 Under Visible Light Irradiation

An efficient photocatalytic ozonation system that is sensitive to visible light was designed and fabricated over Cu(II)-grafted TiO2. The results show that oxalic acid was degraded efficiently in this system under visible light. This high efficiency was attributed to the synergetic effect of photocatalysis and ozonation, which facilitated the generation of holes on TiO2 and hydroxyl radicals. Moreover, Cu(II)-grafted TiO2 proved to be very stable in the reaction without any deactivation and the Cu ions would not leach from TiO2 to aqueous solution. Therefore, this photocatalytic ozonation system is promising to purify wastewater with refractory pollutants under visible light.

Preparation of narrow band gap V2O5/TiO2 composite films by micro-arc oxidation

V2O5/TiO2 composite films were prepared on pure titanium substrates via micro-arc oxidation (MAO) in electrolytes consisting of NaVO3. Their morphology and elements were characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) analysis. Phase composition and valence states of species in the films were characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Ultraviolet-visible diffuse reflectance spectra (UV-Vis DRS) were also employed to evaluate the photophysical property of the films. The V2O5/TiO2 composite films show a sheet-like morphology. Not only V2O5 phase appears in the films when the NaVO3 concentration of the electrolyte is higher than 6.10 g/L and is loaded at the surface of anatase, but also V4+ is incorporated into the crystal lattice of anatase. In comparison with pure TiO2 films the V2O5/TiO2 composite films exhibit significantly narrow band gap energy. The film prepared in an electrolyte consisting of NaVO3 with a concentration of 8.54 g/L exhibits the narrowest band gap energy, which is approximately 1.89 eV. The V2O5/TiO2 composite films also have the significantly enhanced visible light photocatalytic activity. The film prepared in an electrolyte consisting of NaVO3 with a concentration of 8.54 g/L exhibits the best photocatalytic activity and about 93% of rhodamine is degraded after 14 h visible light radiation.

Effects of Y on microstructure and property of heat treated AZ91D magnesium alloy prepared by lost foam casting process

Abstract As cast AZ91D and AZ91D+1·0 wt-%Y magnesium alloy were prepared by the lost foam casting process and then treated by solution and aging treatment. The effects of Y on the microstructure and mechanical properties of heat treated AZ91D magnesium alloy were investigated. The results show that the addition of Y to AZ91D alloy formed the Al2Y phase, which still existed after solution treatment. During the aging treatment process, the rate of β-Mg17Al12 phase precipitating in AZ91D+1·0 wt-%Y alloy was much slower than in AZ91D alloy because the formation of Al2Y phase led to the depletion of Al atoms. The addition of Y was thus claimed to play a key role in delaying the age hardening peak on AZ91D alloy.

Characterisation and photocatalytic activity of SnO2 films via plasma electrolytic oxidation

Abstract SnO2 films were prepared by plasma electrolytic oxidation technology in solution containing different concentrations. The structure and photocatalytic activity of the films were characterised by X-ray diffraction, SEM, EDX, Brunauer–Emmett–Teller (BET) and UV-vis spectrophotometer. The result shows that films consisted of pure SnO2, but the grain size increased with the increase of concentration. Porous and rough SnO2 films were formed on the substrate. The BET surface area increased with the increase of concentration and reached its maximum when the concentration of was 0·05M. The absorption edge of the films shifted from 370 to 408 nm when the concentration of increased from 0·01 to 0·03M. Degradation of rhodamine indicated that photocatalytic activity of film formed in 0·03M was highest due to its smaller grain, larger BET surface area and greater photon absorption.

Effects of Na2WO4 Additive on Properties of Plasma Electrolytic Oxidation Coatings on 6061 Al Alloy

Plasma electrolytic oxidation (PEO) ceramic coatings were prepared on 6061 aluminum alloy substrate in silicate based electrolyte with and without Na2WO4 additive with different pulse frequency. The composition, surface morphology and corrosion resistance of PEO coatings were investigated by means of SEM, XRD, potentiodynamic polarization and EIS measurement in a 3.5% NaCl solution. These results show that Na2WO4 can contributing to the transition from the metastable γ-Al2O3 to a better thermal stability α-Al2O3, while has certain inhibitory effect on the deposition of SiO32- anion on the surface during the plasma discharge process. After adding Na2WO4 in the electrolyte, the surface layer of PEO coatings are more smoother and less distinctly discharge holes appear which leads to the PEO coatings have better corrosion resistance than those of samples coated in the electrolyte without Na2WO4 additive.

Development on Microalloyed High Carbon Steel Used for Fracture Splitting Connecting Rods

The fracture splitting method is being increasingly used for manufacturing connecting rods that are made of the powder forging material, high-carbon steel, etc., which are comparatively easy to fracture, in order to improve the accuracy and productivity. In this paper, a microalloyed high carbon steel used for fracture splitting connecting rod is developed by the process “EAF-EBT-LF-CC-CR”. The steel microstructure, nonmetallic inclusions, precipitated phases, mechanical property and fracture surfaces are investigated by microscope, SEM and TEM. The results show that the steel is constituted of pearlite and a small mount of ferrite, the nonmetallic inclusions in the steel include MnS, Al-rich (taken to be Al2O3) and Al-Ca-rich (taken to be CaO-Al2O3) particles. The precipitations mainly are VC, VN, (Mn, Cu)S, etc. these precipitations are beneficial to fine the pearlite group, short lamellar spacing of pearlite and improve the strengthening of the microalloyed high carbon steel. The tensile tests indicate that the microalloyed high carbon steel has high yield strength, ultimate tensile strength (UTS), but low elongation and contraction of area. It is required for heavier loads, higher performance of automobile engine and less distortion on fracture splitting. The fracture surface of connecting rod shows distinct brittle fracture character and it is beneficial to improve fracture splitting performance.

Microstructural Evaluations of Oxide Films during Spark Anodizing of Mg-Al Alloy in Alkaline Fluoride Electrolytes

Spark anodizing (SA) used on magnesium and its alloys can be backtracking to W.F. Higgins’s fluoride anodizing treatment [1]. In the subsequent applications about sparking anodizing on magnesium, the electrolyte recipes which contained fluoride became more and more popular. Later SA process began to exhibit some new characters, such as more diluted and environmental friendly electrolyte solution, higher application voltage and modified waveform, changeable electric polarity and pulse frequency, which significantly decreased the defects (pore, sealed cavity, micro-crack etc.) in the anodized film and greatly increased the process efficiency. Recently a lot of patented commercial spark processes for Mg and its alloys are emerging, such as Tagnite, Magoxid, Keronite etc.