Corrosion and Wear Properties of h-BN Modified TC4 Titanium Alloy Micro-Arc Oxide Coatings

In this study, ceramic coatings were prepared on the surface of TC4 titanium alloy by micro-arc oxidation (MAO). The morphology, element distribution and phase composition of MAO coatings were analyzed by SEM, EDS, XRD and other analytical methods. The effect of hexagonal boron nitride(h-BN) doping on wear resistance and corrosion resistance of micro-arc oxidation layer was studied. The results show that the coating is mainly composed of rutile TiO2, anatase TiO2 and a small amount of h-BN. Furthermore, the composite coating containing h-BN was less porous than particle-free coating. The test results show that h-BN doping slightly affects the hardness of the MAO coating, and it is helpful in improving the thickness, corrosion resistance and wear resistance of the coatings. When the amount of h-BN is 3 g/L, the corrosion current density of the coating is the smallest; When the addition of h-BN is 1.5 g/L, the friction coefficient of the coating is the smallest. The wear mechanism was adhesive wear, accompanied by slight abrasive wear.

Effect of brazing temperatures on microstructure and properties of TC4/Ti57Zr13Cu21Ni9/316L

Titanium alloy is an important metal material with excellent specific strength, which is widely used in aerospace field, nuclear industry, chemical medicine, and military industry. In order to investigate the connection conditions of TC4 titanium alloy and 316L stainless steel at different temperatures, the braze welding measurement with Ti57Zr13Cu21Ni9 filler metal was conducted in vacuum. The microstructure, morphology and phase of the joint were characterized by SEM (scanning electron microscope), EDS (Energy Dispersive Spectrometer) and XRD (X-ray diffraction), respectively. Microhardness and shear strength of the joint at room temperature and the bonding mechanism of TC4 and 316L were also investigated. The obtained results revealed that the main phases in the diffusion layer were Ti-based solid solution and Ti-Fe (TiFe and TiFe2) intermetallic compoundsands (IMCs) the center of the braze was mainly composed of Ti-Fe IMCs, (Ti, Zr)2(Ni, Cu), Ti-based solid solution. Additionally, the increase of brazing temperature firstly increased and then decreased the average shear strength with the maximum value of 133.9 MPa at 960 °C.

Effect of Scanning Mode on Temperature Field and Interface Morphology of Laser Joining between CFRTP and TC4 Titanium Alloy

Hybrid components composed of CFRTP (Carbon Fiber Reinforced Thermoplastic Polymer) and TC4 titanium alloy are increasingly applied in the aerospace field. The scanning mode has a significant influence on the quality of laser joining joint between CFRTP and TC4 titanium alloy. Therefore, the laser joining between TC4 titanium alloy with surface microgrooves and CFRTP has been implemented under oscillating laser joining mode and linear laser joining mode respectively in the present research. The temperature distribution is qualitatively explored based on the established mathematical model of laser joining between CFRTP and TC4 titanium alloy. The interface morphology and the joining strength of CFRTP/TC4 titanium alloy lap joints under oscillating laser joining and linear laser joining are compared. The results indicate that the simulated temperature distribution shows good agreement with the experimental result. Compared with linear laser joining, the oscillating laser joining weakens the heat concentration and creates a heating zone with larger area and more uniform temperature distribution. The interface morphology of laser joining CFRTP/TC4 titanium alloy joints with better resin filling and fewer bubble defects is obtained by oscillating laser joining due to the temperature variation of the form of unequal amplitude oscillations, whereas there are a large number of large-size bubbles in the filling resin and small-sized fusion gaps distributed at the interface with the linear laser scanning mode. By adopting the joining method with oscillating laser scanning mode, higher quality joints can be obtained.