Effect of Cr3C2 Content on the Microstructure and Wear Resistance of Fe3Al/Cr3C2 Composites

In this paper, an engine piston ring coating comprising composite material of Fe3Al and Cr3C2 mixed powder was prepared by laser cladding onto carbon structural steel. The microstructure and tribological properties of the cladding materials were investigated through X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), and wear tests. The influence mechanism of the Cr3C2 content in cladding powder was studied. During the process of wear, the soft Fe3Al/Fe2AlCr matrix is first ground off, and the hard Cr7C3 phase initially supports the abrasive surface before being worn away into hard particles, resulting in abrasive wear. With the increase in Cr3C2 content, the hardness of the cladding layer increases, the proportion of the Cr7C3 phase increases, and the morphology changes from a sparse network to a dense floccule. Of the cladding layers with different Cr3C2 content, the 15 wt.% Cr3C2 cladding layer had the lowest friction coefficient, and the 25 wt.% Cr3C2 cladding layer had the lowest wear rate. The low wear rate of the 25 wt.% Cr3C2 cladding layer can be attributed to the fact that adhesive wear does not easily occur and the fine microstructure of the strengthening phase, which facilitates better separation in the grinding surfaces

Pathogenicity and molecular characterization of a fowl adenovirus 4 isolated from chicken associated with IBH and HPS in China

Abstract Background Since July in 2015, an emerging infectious disease, Fowl adenovirus (FAdV) species C infection with Hepatitis-Hydropericardium syndrome was prevalent in chicken flocks in China. In our study, one FAdV strain was isolated from commercial broiler chickens and was designated as SDSX1.The phylogenetic information, genetic mutations and pathogenicity of SDSX1 were evaluated. Results The phylogenetic analysis indicated that SDSX1 is a strain of serotype 4, FAdV-C. The amino acid analysis of fiber-2 showed that there were more than 20 mutations compared with the non-virulent FAdV-C strains. The pathogenic evaluation of SDSX1 showed that the mortality of one-day-old chickens inoculated SDSX1 was 100%. The typical histopathological changes of SDSX1 were characterized by the presence of basophilic intranuclear inclusion bodies in hepatocytes. The virus copies in different tissues varied from107 to 1011 per 100 mg tissue and liver had the highest virus genome copies. Conclusion In conclusion, the isolate SDSX1, identified as FAdV-4, could cause one-day-old chicks’ typical inclusion body hepatitis (IBH) and hepatitis-hydropericardium syndrome (HHS) with 100% mortality. The virus genome loads were the highest in the liver. Molecular analysis indicated that substitutions in fiber-2 proteins may contribute to the pathogenicity of SDSX1

A Study on the Influences of Welding Position on the Keyhole and Molten Pool Behavior in Laser Welding of a Titanium Alloy

Various welding positions need be used in laser welding of structures with complex configurations. Therefore, it is necessary to gain knowledge of how the welding positions can influence the keyhole and weld pool behavior in order to better control the laser weld quality. In the present study, a computational fluid mechanics (CFD) model was constructed to simulate the laser-welding process of the titanium alloy Ti6Al4V, with which the keyhole stability and the fluid flow characteristics in weld pool were studied for four welding positions, i.e., flat welding, horizontal welding, vertical-up welding, and vertical-down welding. Results showed that the stability of the keyhole was the best in flat welding, the worst in horizontal welding, and moderate in vertical welding positions. Increasing heat input (the ratio of laser power to welding speed) could increase the keyhole stability. When the small heat input was used, the dimensions and flow patterns of weld pools were similar for different welding positions. When the heat input was increased, the weld pool size was increased, and the fluid flow in the weld pool became turbulent. The influences of gravity became significant when a large heat input was used, especially for laser welding with vertical positions. Too high a heat input in vertical-up laser welding would lead to oscillation and separation of molten metal around the keyhole, and in turn result in burn-through holes in the laser weld. Based on the present study, moderate heat input was suggested in positional laser welding to generate a stable keyhole and, meanwhile, to guarantee good weld quality

Effect of Cr₃C₂ Content on the Microstructure and Wear Resistance of Fe₃Al/Cr₃C₂ Composites

In this paper, an engine piston ring coating comprising composite material of Fe3Al and Cr3C2 mixed powder was prepared by laser cladding onto carbon structural steel. The microstructure and tribological properties of the cladding materials were investigated through X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), and wear tests. The influence mechanism of the Cr3C2 content in cladding powder was studied. During the process of wear, the soft Fe3Al/Fe2AlCr matrix is first ground off, and the hard Cr7C3 phase initially supports the abrasive surface before being worn away into hard particles, resulting in abrasive wear. With the increase in Cr3C2 content, the hardness of the cladding layer increases, the proportion of the Cr7C3 phase increases, and the morphology changes from a sparse network to a dense floccule. Of the cladding layers with different Cr3C2 content, the 15 wt.% Cr3C2 cladding layer had the lowest friction coefficient, and the 25 wt.% Cr3C2 cladding layer had the lowest wear rate. The low wear rate of the 25 wt.% Cr3C2 cladding layer can be attributed to the fact that adhesive wear does not easily occur and the fine microstructure of the strengthening phase, which facilitates better separation in the grinding surfaces

A Comparative Study on the Laser Welding of Ti6Al4V Alloy Sheets in Flat and Horizontal Positions

Laser welding has been increasingly utilized to manufacture a variety of components thanks to its high quality and speed. For components with complex shapes, the welding position needs be continuously adjusted during laser welding, which makes it necessary to know the effects of the welding position on the quality of the laser welds. In this paper, the weld quality under two (flat and horizontal) welding positions were studied comparatively in the laser welding of Ti6Al4V titanium alloy, in terms of weld profiles, process porosity, and static tensile strengths. Results show that the flat welding position led to better weld profiles, less process porosity than that of the horizontal welding position, which resulted from the different actions of gravity on the molten weld metals and the different escape routes for pores under different welding positions. Although undercuts showed no association with the fracture positions and tensile strengths of the welds, too much porosity in horizontal laser welds led to significant decreases in the strengths and specific elongations of welds. Higher laser powers and travel speeds were recommended, for both flat and horizontal welding positions, to reduce weld porosity and improve mechanical properties

Study of Gravity Effects on Titanium Laser Welding in the Vertical Position

To obtain satisfactory welds in positional laser beam welding, it is necessary to know how process parameters will influence the quality of welds in different welding positions. In this study, the titanium alloy Ti6Al4V sheets were laser welded in two vertical welding positions (vertical up and vertical down), and the appearance, porosity, strength, and ductility of the laser joints were evaluated. Results show that undercuts of the vertical up welds were greater than that of vertical down welds, while the porosity contents were much higher in vertical down welds than that in vertical up welds. When welding with a higher heat input, the vertical up welding position resulted in poor weld profiles (undercuts and burn-through holes), whereas the vertical down welding position led to excessive porosity contents in welds. Both severe undercut and excessive porosity were detrimental to the tensile properties of the welds. Weld appearance was improved and porosity contents were reduced by using a lower heat input, achieving better weld quality. Therefore, it is suggested that process parameter settings with relatively high laser powers and welding speeds, which can result in lower heat inputs, are used when laser welding the Ti6Al4V titanium alloys vertically

A Vision-Aided 3D Path Teaching Method before Narrow Butt Joint Welding

For better welding quality, accurate path teaching for actuators must be achieved before welding. Due to machining errors, assembly errors, deformations, etc., the actual groove position may be different from the predetermined path. Therefore, it is significant to recognize the actual groove position using machine vision methods and perform an accurate path teaching process. However, during the teaching process of a narrow butt joint, the existing machine vision methods may fail because of poor adaptability, low resolution, and lack of 3D information. This paper proposes a 3D path teaching method for narrow butt joint welding. This method obtains two kinds of visual information nearly at the same time, namely 2D pixel coordinates of the groove in uniform lighting condition and 3D point cloud data of the workpiece surface in cross-line laser lighting condition. The 3D position and pose between the welding torch and groove can be calculated after information fusion. The image resolution can reach 12.5 μm. Experiments are carried out at an actuator speed of 2300 mm/min and groove width of less than 0.1 mm. The results show that this method is suitable for groove recognition before narrow butt joint welding and can be applied in path teaching fields of 3D complex components