Solidification Effect on the Microstructure and Mechanism of Laser‐Solid‐Forming‐Produced Flame‐Resistant Ti–35V–15Cr Alloy

Abstract

Ti–35V–15Cr alloy has become an indispensable material in aerospace industry due to its excellent flame‐resistance properties. Herein, the block and thin‐wall Ti–35V–15Cr samples are built by laser solid forming (LSF) under the same processing parameters, and the evolution of solidification microstructure is investigated. This work focused on the effect of molten pool solidification parameters and complex thermal cycling conditions on the morphology of β grains and the substructure in the grains. The microstructure of LSF‐produced Ti–35V–15Cr block sample mainly consists of epitaxial columnar dendritic grains, whereas that of the deposited thin‐wall sample is mainly composed of near‐equiaxed grains together with subgrains formed in the near‐equiaxed grains. Such different microstructure results from extremely sensitive thermal behavior condition in LSF process. The simulated thermal behavior characteristics using finite element method illustrate that the thermal cycles during block deposition are very complex and the temperature gradient at the last solidification in block deposition is much higher than that in the deposition of thin‐wall samples, resulting in significantly different solidification microstructure between thin‐wall and block samples.

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

“…Other techniques include electroplating, high-energy mechanical alloying, friction stir machining, and similar methods. Laser cladding [13,14], laser solid forming [15,16], and direct laser fabrication [17][18][19][20][21] were used to prepare burn-resistant coating on the surface of Ti alloys. The related deposition principle is similar (Figure 1), which implies that the surface of the base material is irradiated using different fillers in order to make the deposit and the thin layer of the base material melt simultaneously.…”

“…Further, after rapid solidification, a deposited layer that is metallurgically combined with the base material is formed. The Ti-based burnresistant coating prepared using the laser technology is mostly burn resistant β-Ti-V-Cr alloys, which include Ti-25V-15Cr [16,17], Ti-25V-15Cr-0.2Si [14], Ti-35V-15Cr [15], and Ti-25V-15Cr-2Al-0.2C coatings [18][19][20][21]. that combustion always originates from the surface, various surface technologies have been proposed to improve the burn-resistance of Ti alloys.…”

“…Further, after rapid solidification, a deposited layer that is metallurgically combined with the base material is formed. The Ti-based burn-resistant coating prepared using the laser technology is mostly burn resistant β-Ti-V-Cr alloys, which include Ti-25V-15Cr [16,17], Ti-25V-15Cr-0.2Si [14], Ti-35V-15Cr [15], and Ti-25V-15Cr-2Al-0.2C coatings [18][19][20][21]. Form-ing (LSF) [22], (b) Laser Cladded (LC) [23], (c) Direct Laser Fabrication (DLF) [24], (d) Double glow plasma surface metallurgy (DG) [25].…”

“…Therefore, the deposition coating on the surface of Ti alloys using laser technology or using Ti alloys as the deposition raw material should be carried out under a protective atmosphere. In each of the above studies, the vacuum process chamber was filled with high-purity Ar during coating deposition in order to ensure low oxygen content (<5 ppm [18][19][20], <100 ppm [13][14][15][16]). [22], (b) Laser Cladded (LC) [23], (c) Direct Laser Fabrication (DLF) [24], (d) Double glow plasma surface metallurgy (DG) [25].…”

“…The thermal stress caused due to the rapid cooling rate is unavoidable, and post-treatment is required to eliminate the stress [18]. Moreover, the non-equilibrium solidification process also leads to dendrite (Figure 2) [13,16,19] and defects such as pores (Figure 3) [18] and cracks (Figure 4) [14,15]. Hot isostatic pressing technology is used to improve the coating density [18].…”