Ruidi Li

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.

Effects of sintering processes on second-phase grain morphology of ITO ceramics and grain growth

Due to the importance of grain morphology and grain size of ITO ceramics on the properties of ITO films, 12 ITO ceramics were sintered at different sintering process parameters in order to investigate the effects of heating rate, singtering temperature, holding time, cooling rate and oxygen flow velocity on the second-phase grain morphology and grain growth of ITO ceramics by SEM, XRD, BSE and EPMA et al.. The results show that the high quality ITO ceramics can be achieved with the heating rate of 120u2009°C/h, the sintering temperature of 1580u2009°C, the holding time of 5xa0h, the cooling rate of 240u2009°C/h and oxygen flow velocity of 10xa0L/min. It can also conclude that the change of the second-phase grain morphology is only relevant to the sintering temperature. Meanwhile, the grain growth kinetics was first introduced to analyze the grain growth mechanism and calculate the corresponding diffusion datas (nu2009=u20097, ku2009=u20099.282u2009×u20091022xa0nm3/min, Qu2009=u2009405.588xa0KJ/mol). In addition, the mass transport mechanism leading to the considerable grain coarsening and the change of second-phase grain morphology is evaporation–condensation followed by the increased solubility of SnO2 in In2O3.

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.

Effect of laser parameters on microstructure, metallurgical defects and property of AlSi10Mg printed by selective laser melting

AlSi10Mg alloy has been widely used in selective laser melting (SLM). However, the formation of metallurgical defects in this material during SLM process has not been studied sufficiently. In this work, different laser parameters were adopted to fabricate the specimens. The effects of volumetric energy density (VED) on the metallurgical defect, densification, phase composition and mechanical property were also comprehensively analyzed. At low VED of 37.39J/mm3, a nearly full dense sample with density of 2.602g/cm3 can be printed. The sample with maximal tensile strength of 475MPa can be printed. While with the increase of VED, the ultimate tensile strength decreases due to the formation of micro-pores. The formation mechanisms of micro-pores including gas pores and keyhole-induced pores were disclosed from the angle of alloy smelting. Better understanding of the influence mechanisms of the laser parameters on the formation of metallurgical defects is beneficial for the production of high performance SLM p...

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.

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.