Sui Yuan Chen

Preparation of the Carbon Fiber/Cu Alloy Matrix Self-Lubricating Composite Materials

Using 663-tin bronze, Ni, W, nanoAl2O3, MoS2, graphite, CaF2, and Ni coated graphite as the matrix alloy powder, in which copper-coated carbon fiber of 5%, 7%, 9%, 11% and 13% in volume fraction were added as the reinforcing phase, a novel type carbon fiber/copper-matrix self-lubricating composite materials was prepared by means of powder metallurgy. The results indicate that the mechanical properties of the composite materials are improved after adding copper-coated carbon fibers. The composite materials reach optimal overall mechanical performance under testing when the volume fraction of the added copper-coated carbon fibers is 11%.: with a hardness of 57.8 HV and a compressive strength of 222 MPa. The addition of carbon fiber also improved the friction and wear properties of the composite materials. Increasing the volume fraction of fiber, was found to increase the wear resistance and improve self-lubricating performance. A volume fraction of 11% gave a friction coefficient of 0.09 and abrasion loss of 4mg.

Study on Microstructure of Laser In Situ Formation of TiBX and TiC Titanium Composite Coatings

Two kinds of mixed powders:Ti-6Al-4V/B/C and Ti-6Al-4V/B4C which are pre-pasted or synchronized fed on Ti-6Al-4V substrates separately were scanned by a 500W pulsed YAG laser to induce in situ formation of titanium composite coatings contained TiBx and TiC ceramic reinforced phases. The influences of laser processing parameters including Pulse Frequency (PF), Pulse Width (PW), Laser Power (P) and Scanning Speed (V) together with the powder proportions on the microstructure and properties of the coatings were investigated. Microstructures, phase components of the coating were analyzed by OM, SEM, TEM and XRD respectively. Experimental results show that two and more kinds of ceramic reinforcements were in situ formatted in the matrix of Ti-6Al-4V. TiB and TiC ceramics were formed evenly with the morphology of needle, tiny dendrites and disperse particles in the prepasted single path specimens. For the powder feed laser cladding layers, the ceramic reinforcements were TiB (needlelike), TiB2 (hexagonal prism or rodlike), a small amount of TiC (disperse particles) and non fully reacted B4C. The microhardness increased with the increase of the amount of B4C and B+C additions. When the added B and C contents are the same, the microhardness of the coating with B4C addition is higher than that of the coating with B+C addition. The average micro-hardness of a powder prepasted (with 20 wt.% B4C addition) multi-path laser cladding layer formed under the optimized processing parameters is up to 800HV, which is more than 2 times of that of the substrate (340Hv), and the wear weight loss of the layer decreased nearly 3 times that of the substrate.

Microstructure on Laser In Situ Deposit of TiB x /TiC ReinforcedComposite Coatings

In situ synthesized TiBx/TiC reinforced composite coatings were prepared on Ti-6Al-4V substrate by laser in situ deposition using 10B4C-18TiNi-72Ti-6Al-4V (wt. %) powder blends as the feedstock materials. The microstructural analysis of the composites was performed using scanning electron microscope, and phase analysis was done with X-ray diffraction. The results showed that the composite coatings contained long needle TiB, irregular block TiB2 and disperse particles/dendrites TiC, the thick rod phase which was a inlay structure consisted of TiB2 and TiC. These composite reinforced phases were evenly distribution in the (TiNi+Ti2Ni+α–Ti) substrate.

Synthesis of TiO2@Ag Nano-Composite Particles Using Pulsed Laser Gas Phase Evaporation-Liquid Collection

The targets are micron-sized TiO2 powders and micron-sized Ag powders, TiO2@Ag nanocomposite particles with core-shell structure were synthesized by pulsed laser gas phase evaporation-liquid phase collecting method. The morphology, structure and synthesis mechanism of the samples were studied by means of transmission electron microscopy (TEM), energy dispersive spectrometer (EDS), and X-ray diffraction technique (XRD). The results show that the pure TiO2 nanoparticles sol was firstly prepared as liquid phase collecting system using gas phase evaporation-liquid phase collecting method; then, the target was changed using Ag, and TiO2 @ Ag nanocomposite particles with core-shell structure, which are spherical or ellipsoidal, were successfully synthesized under certain conditions of laser synthesis parameters; the diameters of most TiO2@Ag nanocomposite particles covering synthesized after 2h range from 15nm to 35nm, the diameters of most TiO2 @Ag nanocomposite particles covering synthesized after 4h range from 25nm to 50nm, and the size of nanocomposite particles increases with the increase of covering synthesis time; TiO2 nanoparticles synthesized previously in liquid phase function as crystallized cores, while Ag atoms and their clusters are adsorbed to TiO2 surfaces and surround the surfaces to form TiO2 @ Ag nanocomposite particles.

Study on Macroscopic Morphology and Microstructure of Single Ni60 Laser Clad Tracks Prepared Using a Variable Laser Beam Shaper

The objective of the present study was to find the influence of laser beam shape on macroscopic morphology and microstructure of single Ni60 laser clad tracks. Laser cladding of Ni60 alloy powder can be used to manufacture and remanufacture backup rollers for the steel industry. Controlling temperature distribution can assist with achieving favorable macroscopic morphology and microstructure. Five different beam profiles were used in our experiment to prepare clad tracks. The beam profiles varied in terms of the ratio of energy densities between the internal and external parts. The macroscopic morphology and microstructure was tested using SEM. The study founds decreasing the ratio is possible to achieve wider clad tracks with a larger cross section area. It was found that microstructure in upper region tended to form net-like dendrite microstructure at low energy density ratios.

Temperature Field Simulation of Laser Heated 1045 Steel Using with Shaped Laser Beam Profiles

In this paper, a three-dimensional dynamic simulation model is established for a laser heating process taking into account heat flow by conduction and a temperature dependent specific heat capacity in the material. An unorthodox laser beam profile is characterized by two simple beam shape parameters in the model; the difference in energy distributions between the centre and outer edge of the beam and between the leading and trailing edges of the beam is varied by an adjustment of these parameters. In this way, laser surface heating with unorthodox beam profiles is simulated and studied using COMSOL Multiphysics finite element modeling software.

Microstructure and Wear Properties of Laser Synthesized Composite Coatings on Ti-6Al-4V

Ti-6Al-4V, C and TiB2 powders (71.5%Ti-6Al-4V+ 26.2%TiB2+2.3%C in wt. %) were prepasted and then laser clad on Ti-6Al-4V substrates. Laser cladding was carried out with a Nd:YAG pulse laser with the parameters of defocus length 15mm, pulse frequency 15Hz, scanning speed 2-4mm/s, electric current 200-240A. Microstructure and phases were analyzed with the Optical Microscopy(OM), Scanning Electron Microscopy(SEM) and X-Ray Diffraction(XRD). Laser cladding layers with smooth surfaces, good metallurgical bonding with no cracks and pores were formed. The average thickness of the coatings is approximately 80μm. Reactions among Ti, C and TiB2 in the laser molten pool cause in-situ synthesis of TiB, TiB2 and TiC reinforcements. The average microhardness is 836HV, which is more than twice that of the Ti-6Al-4V substrate (320HV). Friction coefficients of the cladding coatings fluctuate between 0.26-0.3. Laser cladding specimen with powder mixture of 71.5%Ti-6Al-4V+ 26.2%TiB2+2.3%C (weight loss 0.0007g after sliding 245m) possesses better wear property than that of the specimen with powder mixture of 90%Ti-6Al-4V+ 10%B4C (weight loss 0.0068g).

The Structure and Frictional Properties of Aluminum Alloy Anodic Oxide Film

Anodic oxide films were prepared firstly on the surface of a 2024 aluminum alloy. Then the effect of different heat-treatment temperatures on the structure and properties of the films was studied. The results indicate that the construction units of Al2O3 oxide film were composed of tubules less than 100nm in external diameter, and the film became more compact and uniform as a result of the increased temperature after the heat treatments of 100, 150, 200, 250, 300, 350, and 400°C under the protection of a H2 atmosphere. The hardness of the films increased linearly with the increase of heat treatment temperature; whereas the wear loss tended to decrease first and then increase. After being treated at the temperature of 250°C, the hardness reaches 606HV, the wear loss is a minimum of 11mg. The structure of the film heat-treated at 250°C has a compact structure, higher hardness, and the best wear resistance.

Microstructure and Wear Behaviour of Laser Induced In-Situ Formation of TiBx and TiC Titanium Composite Coatings

Two kinds of mixed powders:Ti-6Al-4V/B/C and Ti-6Al-4V/B4C which are pre-pasted on Ti-6Al-4V substrates separately were scanned by a 500W pulsed YAG laser to induce in situ formation of titanium composite coatings contained TiBx and TiC ceramic reinforced phases. The influences of laser processing parameters including Pulse Frequency (PF), Pulse Width (PW), Laser Power (P) and Scanning Speed (V) together with the powder proportions on the microstructure and properties of the coatings were investigated. Microstructure, phase components and micro-hardness of the coating were analyzed by OM, SEM, TEM, XRD and micro-hardness tester respectively. The optimized processing parameters of a single path laser scanned specimen in this case are as follows: PF: 15Hz, PW: 3ms, for the Ti-6Al-4V/B4C specimens the laser line energy ~12.5J/mm, for the Ti-6Al-4V/B/C specimens the laser line energy ~11J/mm. TiB and TiC ceramic were formed evenly reinforced in the matrix of Ti-6Al-4V with the morphology of needle, tiny dendrites and disperse spherical particles. The maximum micro-hardness of single-path layers is up to 750 Hv, which is over twice of that of the substrate (367Hv).The wear weight loss decreased nearly 3 times that of the substrate.