Study of Liquid Impact Erosion in B2‐NiTi and Ti₃Al Based Intermetallic Matrix Composites on Laser Alloyed Ti‐6Al‐4V

Abstract

Ti-6Al-4V is one of the titanium alloys widely used in aerospace, marine and power generation industries due to its high strength-to-weight ratio, excellent corrosion resistance and high temperature properties. A more specific non-aerospace application of this alloy is the use as low-pressure stage (LP) steam turbine blades and which is steadily replacing the use of chromium steels. This replacement is justified by the weight saving of the component and at the same time, the turbine efficiency can also be improved by maximizing the conversion from steam to energy through lengthening the final row of blades. [1,2] However, to cope with the rapidly increasing energy requirement, the turbines need to operate at higher temperatures and speeds which increase the possibility of failure of blades. Liquid impact erosion is one of the major causes of turbine blade failure. As the steam enters from the high pressure or intermediate pressure stage to the last row of LP stage, water droplets condense in the steam flow, become separated and deposited on the concave side of the stator blade. The droplets are then accelerated by the steam flow and strike the convex side of the rotor blades at high speeds close to the rotational speed of the blades. [3] The hydraulic penetration effect of multiple droplet impact and the high pressure shockwaves and lateral jetting associated with the collapse of these droplets will deform the material plastically and initiate material erosion. Protecting the blade surface with erosion resistant coating is one of the feasible solutions to overcome this superficial damage results from liquid impact. Over the years, various processing methods such as high velocity oxy-fuel spraying (HVOF), reactive magnetron sputter ion plating, laser hardening, laser alloying and cladding are effectively adopted to modify the blade surface. [4][5][6][7] Laser alloying and cladding offer the best possibilities to modify the surface with distinct alloy compositions and microstructures without affecting the bulk properties.Nickel titanium (NiTi) shape memory alloys exhibit high resistance to corrosion, wear and cavitation. [8][9][10] Under cyclic loading of austenitic NiTi (B2), the impact stresses are absorbed by the stress-induced martensite phase transformation and the phase reverts to the parent B2-phase when the stress is removed. This super-elastic property is responsible for its superior cavitation resistance. Titanium aluminides of TiAl and Ti 3 Al have found widespread applications as high temperature structural materials due to their low densities, high modulus, good creep and oxidation resistance up to 900°C. [11] In addition, the high work hardening ability of these intermetallics provides excellent cavitation resistance. [12] However, the limited room temperature ductility and poor fracture toughness hinder the practical applications of these intermetallics. Recent advances in the development of IMC with reinforcement can overcome these limitations. [13,14] Although the cavitation erosion resistance char...

FeCrNiMnAl high-entropy alloy coating by spray deposition and thermite reaction

“…The current preparation methods for HEA coatings are laser cladding [8,9], magnetron sputtering [10,11] and thermal spraying [12,13]. Laser cladding technology has fairly good prospects in applications such as surface repair and protection of turbine blades [14], marine propellers [15] and hydraulic turbines [16], owing to a fast cooling rate which leads to high bonding strength and fine crystal grain size. Magnetron sputtering as a method of preparation of ultrathin HEA films provides unique advantages, such as a reduced temperature spike of the substrate and uniform structure of the coating [17,18].…”

Microstructure and tribological properties of in situ synthesized TiN/Ti3Al intermetallic matrix composite coatings on titanium by laser cladding and laser nitriding

“…In the past works, many kinds of hard phases reinforced Ti 3 Al IMCs have been fabricated by various manufacturing technology, such as SiC/Ti 3 Al (by mechanical alloying and hot isostatic pressing) [7], TiB 2 /Ti 3 Al (by explosive shock-compression processing) [8], TiC/Ti 3 AlC/Ti 3 Al (by XD TM technology) [9], TiC/Ti 3 Al (by mechanical milling and hot isostatic pressing) [10], Al 2 O 3 /Ti 3 Al (by reaction sintering) [11], SiC/TiC/Ti 5 (Si,Al) 3 /Ti 3 Al (by laser melting) [12], TiC/Ti 3 Al (by laser alloying) [13,14], etc. However, there have been scarce studies on the tribological properties of these Ti 3 Al IMCs, which may be critical in some applications.…”