Dong Shiyun

Analysis of Mechanical Properties and Microstructures of Laser Rapid Forming Components with Fe314 Alloy Powders

A component is fabricated with Fe314 alloy powders on the substrate of 45 steels.The interlaminar distributing structures,the microstructure in different regions and mechanical properties of components are investigated.It is indicated that forming layers are stacked up like ladder shapes in aspect of microstructures which are mainly constituted of tiny compact equiaxed grains with distribution of some flat grains and columnar grains on the substrate.Furthermore,the hardness of components is low accompanied with high plasticity and ductility in aspect of mechanical properties because of the composing phases of austenite.There is no appearance of cracks under 690 MPamaximum residual stress,which has shown a high crack resistance is obtained through laser rapid forming (LRF) with Fe314 alloy powders.

Fabrication and hydrophobic characteristics of micro / nanostructures on polydimethylsiloxane surface prepared by picosecond laser

Picosecond laser has ultrashort pulse width and ultrastrong peak power, which makes it widely used in the field of micro-nanoscale fabrication. polydimethylsiloxane (PDMS) is a typical silicone elastomer with good hydrophobicity. In order to further improve the hydrophobicity of PDMS, the picosecond laser was used to fabricate a grid-like microstructure on the surface of PDMS, and the relationship between hydrophobicity of PDMS with surface microstructure and laser processing parameters, such as processing times and cell spacing was studied. The results show that: compared with the unprocessed PDMS, the presence of surface microstructure significantly improved the hydrophobicity of PDMS. When the number of processing is constant, the hydrophobicity of PDMS decreases with the increase of cell spacing. However, when the cell spacing is fixed, the hydrophobicity of PDMS first increases and then decreases with the increase of processing times. In particular, when the times of laser processing is 6 and the cell spacing is 50μm, the contact angle of PDMS increased from 113° to 154°, which reached the level of superhydrophobic.

Effect of process parameters on formability of laser melting deposited 12CrNi2 alloy steel

As a new rapid prototyping technology, the laser melting deposition technology not only has the advantages of fast forming, high efficiency, but also free control in the design and production chain. Therefore, it has drawn extensive attention from community.With the continuous improvement of steel performance requirements, high performance low-carbon alloy steel is gradually integrated into high-tech fields such as aerospace, high-speed train and armored equipment.However, it is necessary to further explore and optimize the difficult process of laser melting deposited alloy steel parts to achieve the performance and shape control.This article took the orthogonal experiment on alloy steel powder by laser melting deposition ,and revealed the influence rule of the laser power, scanning speed, powder gas flow on the quality of the sample than the dilution rate, surface morphology and microstructure analysis were carried out.Finally, under the optimum technological parameters, the Excellent surface quality of the alloy steel forming part with high density, no pore and cracks was obtained.

Novel nondestructive testing applications in old automotive engine

Some new methods and equipments of nondestructive testing used for old automotive engine were presented, including ultrasonic testing, metal magnetic memory testing and eddy current testing. The importance of nondestructive testing in the process of quality control for old engine was pointed out. Technologies and equipments of nondestructive testing for the typical old engine components were introduced, Meanwhile, the demand of special standard for nondestructive testing was raised, which was the difficulty in nondestructive testing for the old engine.

Numerical simulation of ultrasonic propagationand defect testing in laser cladding remanufacturing parts

The laser cladding remanufacturing parts show typical anisotropic behaviors, which is difficult for acoustic detection. Therefore, the propagation behaviors of ultrasonic beam in the laser cladding remanufactured parts should be investigated in-depth, which will provides an important theoretical basis for ultrasonic nondestructive evaluation of this kind of parts. An ultrasonic measurement model for the laser cladding remanufacturing parts was developed. The influence of anisotropic laser cladding coating on the propagation behaviors of ultrasonic beam was analyzed. The propagation behaviors of ultrasonic beam in the laser cladding Fe314 alloy coating were investigated with the help of Rayleigh integral combined with Pencil method. The simulation results show that the influence of anisotropic material on the incident field due to the value of slowness, the direction of beam steering is determined by the normal vector of slowness surface, the beam focusing and defocusing behavior is determined by the curvature of slowness surface. The radiated ultrasonic field maintains a uniform distribution relative to the axis of the incident beam, when the direction of incident beam is consistent with or perpendicular to the grain orientation of laser cladding coating, which the directivity of beam is preferably. The reason lies in the incident direction of ultrasonic wave is perpendicular to the isotropic plane of crystal. In the radiated field of transverse wave angle probe, the transverse wave splits and the beam steers, separates with the change of grain orientation. The fundamental reason that transverse wave splitting due to the anisotropy of the laser cladding coating. The reason that beam steering lies in that the direction of group velocity (the direction of normal vector of slowness surface) is inconsistent with that of phase velocity (the direction of transverse wave vector). The slowness surface of anisotropic laser cladding coating is irregular in shape, the beam will appear in other angles in addition to the main beam, when transverse wave refraction. An ultrasonic measurement model for the laser cladding remanufacturing parts was developed by combining the beam model with the scattering model based on Kirchhoff approximation and Born approximation theory. This model can be used to predict the testing signals from the flaws in laser cladding remanufacturing parts. The accuracy of the provided model was verified by comparisons of the simulation results with the experimental results, both the signal amplitude and phase were in good agreement. Numerical simulation results provide an important theoretical basis for rational design of the process scheme of ultrasonic testing for laser cladding remanufacturing parts.

Compression-Disk Remanufacture Process Research (I)

The reasons for the failure of the compression disk are analyzed in detail. Based on the analysis, composite repair technology is researched and is realized by using the thin-walled parts (compression disk) remanufacturing, comprising laser cladding and restorative machining technology. It also provides reliable evidence for the future research on the cladding bonding strength and cutting surface integrity.