Features of Molding and Structure of Composite Materials Based on TiB/Ti, Obtained by Free SHS Compression Method

The work presents the thermodynamic calculations of the adiabatic combustion temperature and the fraction of the liquid titanium phase during the chemical reaction of the initial titanium and boron powders with the initial titanium content from 5 to 80 wt. % during the synthesis of materials based on TiB-Ti. It is shown that with an increase in the preheating temperature of the initial samples to 500 °C, the combustion temperature of the selected composition increases from 3200 to 3600 K, and the fraction of the liquid phase increases from 40 to 80 %. The peculiarity of molding composite materials based on TiB-Ti under conditions combining self-propagating high-temperature synthesis (SHS) and high-temperature shear deformation is studied. These conditions are realized in the method of free SHS compression, which allows synthesizing, molding and obtaining compact material in tens of seconds without using special molds. It was found that the maximum degree of deformation of the synthesized material corresponds to 20-40 wt. % free titanium. For the selected compositions, compact composite materials were obtained by free SHS compression method, the structural features were studied, and the density and porosity of the central and regional parts of the samples were measured.

Surface Hardening of Machine Parts Using Nitriding and TiN Coating Deposition in Glow Discharge

Surface hardening of machine parts substantially improves their performance. The best results are obtained when combined hardening consists of surface nitriding and subsequent deposition of hard coatings. The nitriding of machine parts immersed in the plasma of glow coatings have been studied, and the study results are presented. Titanium atoms for coating synthesis are obtained via titanium evaporation in a hollow molybdenum anode of the discharge. Stable evaporation of titanium occurs only when the power density of electrons heating the liquid titanium does not exceed ~500 W/cm2. To start evaporation, it is only necessary to reduce the gas pressure to 0.02 Pa. To stop evaporation, it is enough to increase the gas pressure to 0.1 Pa. Fast argon and nitrogen atoms used for cleaning the machine parts, heating them, and bombarding the growing coating are obtained using a grid composed of plane-parallel plates under high negative voltage and immersed in plasma.

Bubble evolution in the titanium alloy melt under vertical centrifugal field

The bubble evolution in the liquid titanium melt under vertical centrifugal field has been studied by the hydraulic experiment simulation. The bubble migration process in the simple and complex cavities, the bubble morphology, bubble dimensional size diversification under different mould rotational speed has been investigated. The results show that the mould wall has a blocking effect on the bubble migration. The bubble migration in the simple cavity deviates from the line between the bubble initial position and the rotation shaft of the casting mould. Also, the bubbles in the complex cavity gather, re-nucleate and form new big ones for the blocking effect of the complex geometry shape on the radial movement of the bubble. The shape of bubbles in both the simple and complex cavity during the migration process is not a perfect sphere, but an elliptical shape. The critical size of bubble released from the bubble generation chamber decreases with the increment of the mould rotational speed. The diameter of the gas bubbles in the simple cavity during the migration process become bigger and bigger for the pressure difference at different positions of the cavity in the vertical centrifugal field.

Deoxygenation of liquid titanium with aluminum addition

To realize radical cost reduction of titanium, a process is needed which can directly make use of low quality material such as scrap, TiO2 or titanium ore. In this work, a highly efficient process has been developed to produce low oxygen titanium alloy using aluminum to rapidly reduce oxygen during melting. In this experiment titanium was prepared including 0.8 mass% oxygen. This titanium and aluminum in the range of 0 – 60 mass% was measured, mixed and melted by PAM (plasma arc melting) or ISM (induction skull melting). After melting, a small piece was taken and the aluminum and oxygen content was analyzed by ICP emission spectrometry and inert gas fusion-infrared absorption method respectively. A sample melted with CaO-CaF2 flux was analyzed as well after flux was mechanically taken off. As aluminum content increased, oxygen content decreased. For example, when 61.9 mass% aluminum was added, the oxygen content decreased to 0.028 mass% and Al2O3 was observed in the cross-section of the sample after melting. This was produced when the aluminum content increased and the oxygen solubility decreased in the metal. Flux addition was also clearly effective for deoxygenation.

Hydraulic Study of Bubble Migration in Liquid Titanium Alloy Melt during Vertical Centrifugal Casting Process

The bubble migration in liquid titanium melt during vertical centrifugal casting process has been investigated by hydraulic experiments. Results show that the gas bubble in the simple cavity ultimately migrates like a line parallel to the wall in the opposite direction to the rotational casting mould. The deviation distance of the bubble in the simple geometry cavity tends to increase with the increment of the mould rotational speed during the migration process. And the gas bubble is much easier to migrate like a line when its initial position is nearer to the casting mould wall which is opposite to the mould rotational direction. The migration trajectories of bubbles located at different position in the complex cavity are more complicated than that in the simple cavity. The casting mould in the complex cavity can hamper both the radial movement and the circular movement of the bubble. And gas bubbles will gather, re-nucleate and form new bigger bubbles beside the casting mould wall. The re-formed gas bubbles in the complex cavity become bigger than which escape from bubble generation chamber.

A Numerical Study of Diffusion of Nanoparticles in a Viscous Medium During Solidification

In the field of additive manufacturing process, laser cladding is widely considered due to its cost effectiveness, small localized heat generation and full fusion to metals. Introducing nanoparticles with cladding metals produces metal matrix nanocomposites which in turn improves the material characteristics of the clad layer. The strength of the laser cladded reinforced metal matrix composite are dependent on the location and concentration of the nanoparticles infused in metals. The governing equations that control the fluid flow are standard incompressible Navier-Stokes and heat diffusion equation whereas the Euler-Lagrange approach has been considered for particle tracking. The mathematical formulation for solidification is adopted based on enthalpy porosity method. Liquid titanium has been considered as the initial condition where particle distribution has been assumed uniform throughout the geometry. During the solidification process of liquid titanium, particle flow and distribution has been observed until the entire geometry solidified. A numerical model implemented in a commercial software based on control volume method has been developed that allows to simulate the fluid flow during solidification as well as tracking nanoparticles during this process. The influence of the free surface of the melt pool has a high importance on the fluid flow as well as the influence of pure natural convection. Thus both buoyancy and Marangoni convection have been considered in terms of fluid flow in the molten region. A detailed parametric study has been conducted by changing the Marangoni number, convection heat transfer coefficient, constant temperature below the melting point of titanium and insulated boundary conditions to analyze the behavior of the nanoparticle movement. With the change in Marangoni number and solidification time, a significant change in particle distribution has been observed. The influence of increase in Marangoni number results in a higher concentration of nanoparticles in some portions of the geometry and lack of nanoparticles in rest of the geometry. The high concentration of nanoparticles decrease with a decrease in Marangoni number. Furthermore, an increase in the rate of solidification time limits the nanoparticle movement from its original position which results in different distribution patterns with respect to the solidification time.