•Wet erosion behavior of WC-based HVOF spray coating was investigated.•The coated specimens exhibited better erosion wear resistance.•The erosion parameters had significant influences on the erosion rates.•The erosion wear models for thermal coated specimens can be identified.In oil and gas industries, erosion wear presents a major problem in the hydraulic fracturing process and severely reduces the erosion life of tools. Tungsten carbide (WC)-based high-velocity oxygen-fuel (HVOF) thermal spray coating is widely applied to improve surface properties. However, the erosion wear mechanism of this coating in liquid–solid two-phase flows is not clearly understood. Therefore, in this study, the HVOF thermal spray WC-based coating was characterized, and the erosion behavior of the coating was studied in a wet erosion test rig. Results showed that the experimental parameters, namely, attack angle, impact speed, particle size, and erosion time, exerted significant effects on the erosion rates of the specimens. The coated specimens exhibited higher hardness and better erosion wear resistance than the uncoated substrate due to the hard phase particles of the coating. The surfaces of the coated specimens showed microcutting, craters, and brittle chipping, as a visible manifestation of material removal. Furthermore, the erosion wear mechanism of the deposited coating was established by analyzing the eroded morphologies. The findings of this study can help enrich the understanding of the erosion wear mechanism of WC coatings in liquid–solid two-phase flows.Download high-res image (208KB)Download full-size image

Silicon carbide (SiC) ceramic has been widely used in modern industry because of its superior mechanical properties, wear, and corrosion resistance even at elevated temperature. However, the manufacture of SiC ceramic is not an efficient process by conventional machining methods. This paper employs a steel-toothed wheel as the tool electrode to machine SiC ceramic using electric discharge milling. The process is able to effectively machine a large surface area on SiC ceramic. To further improve the process performance, three kinds of emulsion are proposed as the dielectric in this paper. The effects of dielectric, tool polarity, pulse duration, pulse interval, peak voltage, and peak current on the process performance such as the material removal rate (MRR) and surface roughness (SR) have been investigated. Furthermore, the microstructure of the machined surface is examined with a scanning electron microscope (SEM), an energy-dispersive spectrometer (EDS), and X-ray diffraction (XRD).

The influence of several operational variables on the electrostatic separation of water-in-oil emulsions is investigated in a Perspex cell equipped with a high-frequency pulsed DC generator using conductivity technique. The ascending and the descending periods of the observed conductivity vs. time curves were fit to the sigmoid and power function, respectively, which revealed the model parameters that were used to quantify dehydration efficiency (DE). Experiment results show that DE increases with decreasing inter-electrode distance, and at a given inter-electrode distance, DE increases with decreasing frequency. Furthermore, at a given pulse interval, DE increases with increasing pulse duration.Graphical abstractResearch highlights▶ We investigate the dehydration efficiency (DE) of high-frequency (in kHz) pulsed DC electrical field on water-in-oil emulsion. ▶ Increasing inter-electrode distance and frequency will decrease DE. ▶ Increasing pulse duration will increase DE if pulse interval is constant. ▶ The results achieved could be related to the optimal design of an efficient electrocoalescer unit.

Silicon carbide (SiC) ceramic has been widely used in modern industry. However, the beneficial properties of SiC ceramic make machining difficult and costly by conventional machining methods. This paper proposes a new process of machining SiC ceramic using end electric discharge (ED) milling. The process is able to effectively machine a large surface area on SiC ceramic at low cost and no environmental pollution. The effects of emulsion concentration, emulsion flux, milling depth, copper electrode number, and copper electrode diameter on the process performance such as the material removal rate, electrode wear ratio, and surface roughness have been investigated. In addition, the microstructure of the machined surface is examined with a scanning electron microscope, and the material removal mechanism of SiC ceramic during end ED milling is obtained.