Perspectives on Developing Burn Resistant Titanium Based Coatings-An Opportunity for Cold Spraying

Abstract

Titanium alloys are crucial lightweight materials; however, they are susceptible to spontaneous combustion under high-temperature and high-pressure conditions, limiting their widespread use in aerospace engines. Improving the burn resistance of Ti alloys is essential for the structural safety and lightweight of aerospace equipment. Burn-resistant Ti alloys, such as Ti-V-Cr and Ti-Cu, however, face limitations such as high cost and low specific strength. Surface coatings provide a cost-effective solution while maintaining the high specific strength and good processability of the base material. Conventional surface treatments, such as laser cladding, result in defects and deformation of thin-walled parts. Cold spray technology offers a promising solution, as it uses kinetic energy to deposit coatings at low temperatures, avoiding defects and deformation. In this paper, we review the current research on burn-resistant surface technologies of Ti alloys and propose a new method of bimetallic coating by cold spraying and low-temperature heat treatment, which has the potential to solve the problem of spontaneous combustion of aerospace engine parts. The strategy presented can also guide the development of high-performance intermetallic compound-strengthened metal matrix composite coatings.

Keywords: burn resistant coating; cold spraying; titanium alloy coating.

Figure 1

Principles of various laser and double glow plasma surface technologies. (a) Laser Solid Form-ing (LSF) [22], (b) Laser Cladded (LC) [23], (c) Direct Laser Fabrication (DLF) [24], (d) Double glow plasma surface metallurgy (DG) [25].

Figure 2

Dendrites observed in Ti-25V-15Cr-2Al-0.2C burn-resistant coating produced by direct laser fabrication [19].

Figure 3

Gas porosity in Ti-25V-15Cr coating by laser solid forming. (a) Optical micrograph and (b) SEM micrograph [16].

Figure 4

Cracks in Ti-25V-15Cr-0.2Si coating by laser cladding [14].

Figure 5

SEM image showing 50% porosity of Ti coating by vacuum plasma spray [37].

Figure 6

Schematic diagram of cold spraying mechanism [49]. (a) Adiabatic Shear Instability, first proposed by Assadi et al. [50], and (b) Hydrodynamic Plasticity, proposed by Hassani et al. [51]. TS = thermal softening, SRH = strain rate hardening, Ve = edge velocity, Vs = shock velocity.

Figure 7

(a) cold spray process, (b) SEM images of powder raw materials for cold spray, (c) pictures of 5 cm × 5 cm cold spray samples, (d) SEM of the cross-section of pure Ti coating.

Figure 8

SEM micrographs of cold sprayed Ti6Al4V–CoCr composite coating with pores. The arrows indicate the interface between the coating and substrate [64].

Figure 9

Cold sprayed Ti-Al bimetallic coating by mixture powder, (a) as-sprayed and (b) after 3 h low-temperature annealing at 650 °C. Both intermetallic phases and pores are obtained after annealing [67].

Figure 10

Cold sprayed Ni-Al bimetallic coating by mixture powder, (a) as-sprayed, and (b) annealing at 450 °C. No porosity increase is observed after annealing [71].