Advanced Materials Research Vols. 189-193

Abstract: In this paper, the process of direct laser fabricating (DLF) thin-walled parts with Inconel 625 alloy was studied. The interrelationship between deposition quality and process parameters has been analyzed in the aspects of laser power. Scanning velocity, powder feed velocity, z-increment. The further investigations of study lie on the influence of process parameters on geometrical characterization of single cladding layer, the Axis-Z increments on height of thin-walled part, as well as the microstructure of fabricated sample of Inconel 625. The results based on above experiments show that the Inconel 625 alloy parts can be fabricated by direct laser fabrication method and the samples were fully dense, homogenous and free of defects with the parameters under a certain range.

Abstract: Adopted the compounding Ni-base alloy powder and properly mixed a few functional powders, the study on surface strengthening for slab crystallizer base material by substrate pre-heated and laser coaxial feeding cladding was investigated. The results indicate that the laser coaxial feeding cladding can effectively decrease cladding layer’s pores and crackers compared with laser pre-laid cladding, the cladding layer structure is compact, uniform with typical rapid freezing character and the structure can be controlled by compounding alloy powders. The elements of substrate and cladding layer infiltrate and dilute to each other, the bonding interface is good with metallurgic and tight combination and the rate of dilution is very low. The erosion resistance and thermal fatigue of substrate are improved evidently by this treatment.

Abstract: Performance of recoating system is a key factor influencing building accuracy and fabricating resolution of stereolithography (SL) system. In order to obtain thinner resin layer, a piston recoating system was adopted in high-resolution SL system. To improve the recoating performance of piston recoating system, studies were carried out to investigate the influences of recoating parameters on thickness of recoating layer, and a mathematic model of resin layer thickness has been established. Experiments results show that thickness of resin layer increases with the gap between blade and object, and thickness of resin layer increases with the resin volume added into the vat during recoating. Experiments results also indicate that thickness of resin layer decreases with blade speed and blade thickness. The research provides a basis for optimizing the recoating parameters for the piston recoating system.

Abstract: Laser cutting of thin metal parts involves packing 2-D arbitrary objects into rectangle work space. The problem is shown to be NP-complete. This paper presents a novel approach to solve the problem, by dividing the problem into 2 parts. The first part finishes packing minimum envelop rectangles of the objects by applying Particle Swarm Optimization (PSO) with the lowest line packing as its fitness function. The second part moves the objects to a most suitable place by detecting interference with neighbor objects. A complete interference detection method between two polygons, either convex or concave has been suggested. In addition, two approaches, both the scanning approach and the circumcirlcle approach, have been developed to find the neighbor objects of the current moving object. And the order to move the objects has also been found in a scanning manner. Computational experiments have been carried out both for the first and the second part and the results are inspiring.

Abstract: In order to improve the fatigue strength of TC4, Nd:Glass pulse laser was used to impact the surface of cylindrical specimens, X-ray stress analyzer was used to test the residual stress distribution of treated area, the laser shock processing on different ratio (η) between the diameter of specimens and laser spot were simulated with ANSYS at the same time. The numerical simulation results were well agreement with experimental data. The results indicate that the different η mainly affect residual stress distribution along the circumferential direction. Contrarily, it has few effects on longitudinal direction and in-depth direction.

Abstract: Optical films have been prepared on K9 glass by electronic beam evaporation. Parameters of S-polarized Nd: YAG laser used for pretreatment and damage tests are: wavelength is 355nm, pulse width is 8ns, and incidence angle is 33.75 degree. The results reflect that: the influence of laser pretreatment on laser induced damage threshold of films is uncertain. Laser pretreatment not always improve the laser induced damage threshold of films, and sometimes it will cause negative influence. As for damage probability, for a certain testing energy density, there is an energy density scope, pretreatment pulse with energy density in which can reduce the laser induced damage probability of films. The energy density of laser pretreatment pulse should be selected according to the serving conditions of films.

Abstract: Laser melting was carryed out by HL-1500 CO₂ lase rmachine on 40 Cr steel. The phase composition, microstructure, microhardness and corrosion resistance of the melting coating were investigated by means of scanning electron microscope, X-ray diffractometer, electrochemical test system, salt spray tester etc. The result showed that, melt zone、transformation hardened zone and the heat affected zone as mainly region in melting coating. Laser melting coating constitute by Fe₃O₄, Fe₃C and martensite etc. The microstructure are mixed martensite and undissolved carbides, acicular martensite and retained austenite. The microhardness increased nearly twice as that of the 40Cr when scanning speed is 2.0 m/min. With the increase of the scanning speed, the corrosion resistance increased first and then decreased.

Abstract: To reduced the defect of the layer cladding reinforced by WC/WC-Ni Particles, and to attained the effective handicraft to strengthen the properties of the mold surface, using laser cladding technique , nano TiC reinforced WC/WC-Ni composite cladding were fabricated on the surface of H13 steel substrates. The cladding microhardness was measured with Victoria-hardness tester, the cross-section microstructure of the claddings was observed with optical microscope. The fabrication of the composite claddings was investigated. The friction and properties were examined under dry sliding conditions with a WTM—1E type ball-on-disc tester. The wear tracks were observed with a JSM-5610 type scanning microscope. The wear mechanisms were discussed as well. The results showed that, owing to the NanoTiC fine-crystalline strengthening and dispersive strengthening, the Nano TiC/WC/WC–Ni composite cladding was very compact and good blinding with the substrate after laser remelting, and then sub-micro-fracture and adhesion wear of WC cladding were reduced. During the friction process, Nano TiC particles had a significant influence on the Friction and wear behavior of laser cladding: The friction coefficient reduced and wear-resistance strengthened of composites with increasing proportion of TiC. The wear mass loss of the 20% TiC composite cladding reduced to about 1/3 of those with 5% TiC cladding.

Abstract: In the process of metal powder laser rapid forming, various defects may be caused in forming parts on account of technical parameters, equipment performance, material characteristics and other factors. While dimensional accuracy error and surface sticky powder caused by powder factor are the two major defects of forming parts. The experimental analysis finds that less or over accumulation resulting from powder feed delay is the main reason for affecting the dimensional accuracy of cladding and the main reason which affects the appearance of surface sticky powder is specific energy.

Abstract: TiC reinforced titanium matrix functionally graded materials （FGM） has been produced by processes of laser metal deposition through changing the powder feed rate of Ti and Cr3C2 powder. The OM, SEM, EDS methods were used to analyze the components and microstructure of the coatings. Microhardness and wearing resistance at 500°Ctemperature of the FGM coating were examined by microhardness tester and wear tester respectively. The results show that FGM coating reinforced by in-situ TiC apparently improved hardness of Ti alloy; the microhardness can reach HV1100, and present gradient distribution along deposition direction. Dry sliding wear properties of these FGM coatings have been compared with substrate materials wearing. The observed wearing mechanisms are summarized and related to detailed microstructural observations. The results show the wear resistance of the coating can be improved by 2.8 times.