Tiechui Yuan

Microstructural Modification of Laser-Deposited High-Entropy CrFeCoNiMoWC Alloy by Friction Stir Processing: Nanograin Formation and Deformation Mechanism

Nanostructured CrFeCoNiMoWC high-entropy alloy layer was developed through laser-melting deposition and severe plastic deformation (SPD). The laser-deposited CrFeCoNiMoWC alloy consists of dendritic and subeutectic with a continuous network structure. After SPD, the laser-deposited microstructure with grain size 3 to 4xa0μm was transformed into nanostructure with grain size 5 to 100xa0nm and the continuous networks were crushed into dispersed nanoparticles. The new phases of WC and Co3W were presented in the plastic zone after SPD due to the worn debris of the SPD tool. More interestingly, amorphous phase was found in the plastic zone, owing to the high temperature, high hydrostatic pressure, and large shear stress. The refined microstructure resulted in the enhancement of microhardness and electrochemical corrosion property. Many nanotwins were detected in the plastic zone; thus, strengthening mechanisms were reasonably inferred as twinning strengthening, work hardening, dispersion strengthening, refinement strengthening, and dislocation strengthening. The Lomer–Cottrell lock, full dislocation interacting with a partial dislocation at the twinning boundary, and high density of dislocation at the twinning boundary, stacking fault, and grain boundary were observed, which account for the property enhancement of the nanocrystalline.

Investigation to impurity content and micromorphology of high purity titanium powder prepared by molten salt electrolysis

Abstract In this work, the high purity Ti powder was prepared by molten salt electrolysis. The impurity content and micromorphology of Ti powder were systematically studied. The results showed that the main impurities in electrolytic Ti were Mn, Al, Cr, Fe, Ti, N, C and O, and the impurity originations and distributions were disclosed. Increase in the initial soluble Ti ion concentration can reduce the impurity content effectively. The electrolysis devices should be made by Ti alloy, which enables the impurity contents in Ti powder to be much lower than electrolysis devices made by other materials. After the electrolysis, the electrolytic Ti at the upside of cathode was platy bulk and dense, while the downside was loose powder. High current density and low soluble Ti concentration could produce dendritic and fine electrolytic Ti powder, and conversely, the electrolytic Ti powder was coarse polygon.

Effects of sintering processes on the element chemical states of In, Sn and O in ITO targets

The element chemical states of In, Sn and O could affect the resistivity of ITO targets so as to affect the electrical property of ITO films. In the work, nine kinds of ITO targets were prepared in order to investigate the effects of sintering processes on the element chemical states of In, Sn and O in ITO targets by XPS. The results show that the heating rate of 60xa0°C/h, the sintering temperature of 1580xa0°C, the holding time of 5xa0h and the cooling rate of 240xa0°C/h are favorable for the preparation of ITO targets with the optimum conductivity. The change rule of the element chemical states of In, Sn and O in ITO targets sintered with different sintering process parameters has been proved by the theoretical analysis of thermal decomposition kinetics of In2O3 and SnO2.

Microstructure evolution and grain orientation in ITO targets and their effects on the film characteristics

ITO targets sintered at 1560–1600xa0°C were selected to deposit ITO films at 25 and 150xa0°C with a purpose of investigating the relationship between microstructure evolution and grain orientation in ITO targets and the film characteristics. It is found that, with increasing the sintering temperature, the triangle grains of In4Sn3O12 (secondary phase) transform into the dendritic grains of In2SnO5 (secondary phase), following by the increase of the solid solubility of tin oxide in In2O3 phase (main phase). Besides, the sintering temperature has a great influence only on the texture of secondary phase. More solid solubility of tin oxide in In2O3 phase, stronger texture intensity of secondary phase and higher sputtering temperature were found to promote the crystallinity of ITO films resulting in the lower sheet resistance and obtain the films with lower compression stress and strong adhesion. The transmittance of ITO films deposited at 25xa0°C is closely related to the film surface roughness, while it is mainly associated with the crystal structure for ITO films deposited at 150xa0°C.

Microstructural evolution and sintering kinetics during spark plasma sintering of Fe and Al blended powder

Abstract The reaction diffusion between Fe and Al during spark plasma sintering (SPS) was studied. Microstructural evolution was investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) and the sintering kinetics was disclosed. The main interphase of the SPS sample was Fe 2 Al 5 at 773–873 K. Ball-milling enabled a large number of lattice defects and grain boundaries thus the reaction kinetics was accelerated, although the direct current can also promote those defects. After milling, the phase transformation kinetics was improved from 0.207 before mill to 4.56×10 −3 . Besides, this work provided more details for the generation of Joule heating. The resistance offered to the electric path was considered to be the source of Joule heating, and particularly the resistance offered by the different contact interfaces of die, punch, graphite foil and the sample played a leading role for the generation of Joule heating during spark plasma sintering.

Effect of spark plasma sintering on microstructure and friction characteristics of boron carbide

Spark plasma sintering (SPS) of pure commercially sub-micron B4C powder at 1700–1900∘C for 20min has been conducted and their wear properties have been investigated by reciprocating friction and wear test. It was found that the relative density increased with the increase and the grain size increased a little at 1700–1900∘C. Wear mechanisms in the temperature range of 1700–1900∘C have been proposed such that at 1700∘C the wear mechanism was dominated by plastic deformation and intergranular fracture, while at 1800–1900∘C there was transition to the surface fracture or grain pull-out. A model for the spherical abrasive wear was proposed to describe the friction and wear of the B4C ceramics which is well-fitting with the experimental results.

Preparation of Co3O4 from a leaching solution of cobalt-rich slag by ozonation

Abstract Cobalt-rich slag from blister refining is leached with an oxidising acid, and Co3O4 powder is prepared by an ozonation–precipitation–calcination method after iron has been removed from the solution by the goethite process at different pH values. The effects of stirring speed, gas flow rate, ozone concentration, pH and solution temperature on the precipitation rate of cobalt are investigated. The solution pH has an obvious effect on the precipitation rate, as do the stirring speed, gas flow rate and ozone concentration, but the temperature has little effect. With almost all the cobalt precipitated from the solution, the losses of copper and zinc are about 10% and 1·5%, respectively. The cobalt is precipitated in the form of amorphous CoOOH, identified by X-ray diffraction and with some physicochemical properties similar to those of cobalt hydroxide. The amorphous CoOOH is transformed into spherical Co3O4 powder by the calcination treatment.