MICROSTRUCTURE EVOLUTION OF IN SITU COMPOSITE COATINGS FABRICATED BY LASER CLADDING WITH DIFFERENT POWERS

In situ reaction-synthesized TiB-reinforced titanium-matrix composite coatings were fabricated using the rapid, non-equilibrium synthesis technique of laser cladding. The Ti and B mixture was the original powders, while the Ti-matrix composite coatings enhanced with TiB were treated on a Ti-6Al-4V surface with different laser scan powers of 2.5 kW, 3.0 kW and 3.5 kW. The phase composition, microstructure evaluation, and microhardness of the cladding coatings were investigated by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and microhardness. The composite coatings mainly consist of black fishbone-shaped -Ti dendrites and white needle-like TiB phases. The microstructure evolution from the top to the bottom of the coatings was investigated. The TiB reinforcement dispersed homogeneously in the composite coatings and a fine microstructure was obtained in a sample fabricated with a laser power of 3.0 kW. The microhardness of the cladding coatings fabricated by different powders was over 2-fold greater than that of the Ti-6Al-4V titanium alloy substrate and achieved a maximum average of 792.2 HV with the laser power of 3.0 kW. The microstructures and properties of the coatings were changed by adjusting of the laser cladding power. The effects of the laser scan power on the microstructure, hardness and friction and wear properties of the laser cladding coatings were investigated and discussed.

Study on the Friction Characteristics of Plasma Spray Modified Layer on Titanium Alloy in Artificial Sea Water Environment

In order to study the friction characteristics of the plasma spray modified layer on the surface of titanium alloy, the friction sub-combination consisting of three type enhanced Teflon as the pin sample was carried out in the artificial seawater environment. The results show that the friction coefficient and wear degree of the plasma spray surface treatment specimen are also lower than the TC4 titanium alloy substrate, the surface modification sample and the three enhanced Teflon side friction, the side wear is serious, the surface plasma spray modified titanium alloy needs to reduce its surface roughness before it can be used as a friction sub-type material.

Experimental Study on Friction Characteristics of Micro-Arc Oxidation Modified Layer on Titanium Alloy Surface

In order to study the effect of microarc oxidation modification treatment on the friction properties of titanium alloy surface, the surface treatment layer of Ti-6Al-4V ELI specimen modified by Microarc oxidation surface was sampled, the surface layer hardness, roughness and treatment layer thickness were tested, the microscopic morphology was analyzed, The friction tests of TC4 substrate and micro-arc oxidation treatment surface disc with 25% glass fiber, 15% fiberglass +5% graphite and 60% tin bronze reinforced PTFE pin were carried out, and the results showed that the thickness increased slightly and the surface layer hardness increased by about 75% after the micro-arc oxidation surface modification treatment. Compared with the substrate, the surface roughness is obviously improved, and the friction coefficient of the surface treatment specimen is similar to that of the TC4 titanium alloy substrate, but the wear amount is higher than that of the TC4 titanium alloy substrate.

Nanosecond Pulsed Laser Irradiation of Titanium Alloy Substrate: Effects of Periodic Patterned Topography on the Optical Properties of Colorizing Surfaces

Most of the current works based on surface treatments of metals by laser marking technology are focused on the modification of the color tonality of flat surfaces, or the development of specific topography features, but the combination of both processes is not usually evaluated, mainly due to the complexity of controlling the optical properties on rough surfaces. This research presents an analysis of the influence of the micro-geometrical characteristics of periodic patterned laser tracks on the chromaticity and reflectance of Ti6Al4V substrates. The samples were irradiated with an infrared nanosecond pulsed laser in air atmosphere, taking as the control parameter the scan speed of the beam. A roughness evaluation, microscopic inspection, and absorption and chromaticity examination were conducted. Although micro-crack growth was detected in an isolated case (10 mm/s), the possibility of adjusting the result color was demonstrated by controlling the heat-affected zone thickness of the textures. The results of rough/colored combined textures allow new perspectives in industrial design to open, particularly in aesthetic applications with special properties.

MICROSTRUCTURES AND WEAR RESISTANCE OF THE ARGON ARC CLAD NICKEL-BASED COMPOSITES ON TITANIUM ALLOY

The composites were obtained by the argon-arc cladding (AAC) of the Deloro22-Si3N4-Fe pre-placed powders on a TA1 titanium alloy substrate, which improved the wear resistance of the substrate. Such composites were investigated by means of the scanning electron microscope (SEM), the microscope and the high resolution transmission electron microscope (HRTEM). The results indicated that the amorphous phases were produced in such AAC composites, increasing the wear resistance. With addition of Y2O3, lots of the micro/nanoscale particles were formed, which further improved the wear resistance of such AAC composites.

MICROSTRUCTURE PERFORMANCE AND SYNTHESIS OF THE ARGON-ARC CLAD COBALT BASE COMPOSITE COATING

Composite coating was obtained by argon-arc clad (AAC) of the Stellite20-Si3N4 pre-placed mixed powders on a TA7 titanium alloy substrate, which increased the micro-hardness of the substrate surface significantly; then this produced coating was re-melted by an argon arc, forming a hard layer on the coating surface. The AAC and re-melted coatings were investigated using a scanning electron microscope and high-resolution transmission electron microscope, indicating that amorphous and nanocrystalline phases were produced in the coating surface after an argon-arc re-melting process, which increased the wear resistance of such coatings significantly.