Preparation of complex thin-walled TiAl alloy swirlers by powder injection molding

Abstract

As an important component of aeroengines， the lightweight manufacturing of swirlers is of great significance for improving the service performance of engines. Lightweight， high-strength， and heat-resistant TiAl alloy is a high-temperature structural material with great application potential， but its inherent brittleness and difficulty in preparation and processing seriously limit its application in the fabrication of high-performance swirlers. Therefore， the powder injection molding （PIM） technology was used to prepare the complex thin-walled TiAl alloy swirlers in near-net shape without any machining process by combining the mold design method of water-soluble core and high conformal polyformaldehyde（POM）-based binders. The preparation processes mainly include catalytic debinding， thermal debinding， and two-step sintering. The results show that the binder with a composition of 82%（mass fraction， the same below）POM-5%high density polyethylene（HDPE）-5%ethylene-vinyl acetate copolymer（EVA）-8% stearic acid（SA） has a higher powder loading and better molding filling performance. The powder loading， the flow behavior index n， the viscous flow activation energy E， and the general rheological index αSTV of the feedstock are 62%（volume fraction）， 0.56， 22.95 kJ/mol， and 9.59， respectively. The two-step sintering method under pressureless can achieve synergistic control of high relative density and fine grain. When the sintering process is set to 1430 ℃/1 h+1250 ℃/5 h， the relative density of PIM TiAl alloy reaches 96.3% with a lamellar colony size of about 100 μm. After hot isostatic pressing（HIP） treatment， nearly complete densification of the TiAl alloy is achieved， and the dimensional deviation and surface roughness Ra of the prepared swirlers are ±0.1 mm and 1.046 μm， respectively. The room-temperature tensile strength， yield strength， and elongation of the HIP TiAl alloy are 577， 466 MPa， and 0.96%， respectively.

Keywords

• tial alloy
• swirler
• powder injection molding
• dimensional accuracy
• surface roughness
• mechanical property