Quo vadis gamma titanium aluminide

doi:10.1016/S0966-9795(01)00064-4

Intermetallics

Volume 9, Issue 12, December 2001, Pages 997-1001

https://doi.org/10.1016/S0966-9795(01)00064-4 Get rights and content

Abstract

A perspective is offered on the implementation of γ-TiAl for various components in aircraft engines, aerospace vehicles and automotive engines. The key to acceptance within the next 5 years is a manufacturing route that balances cost and benefit. The two basic routes are (1) near net-shape casting, which is an economical way to produce a component for evaluation, and (2) a wrought route for specific components utilizing ingot extrusion. Cast LP (low-pressure) turbine blades and static structural components for aircraft engines are reviewed with attention directed to automotive cast turbocharger wheels and exhaust valves as promising market possibilities. Wrought processing via ingot extrusion, which provides shape and structure for isothermal forging of compressor blades and LP turbine blades has emerged as the preferred manufacturing route, and shown to be successful for higher alloyed versions of TiAl. Finally, the total implementation costs and concerns are summarized along with the factors governing the selection of a rotating component in an aircraft engine.

Introduction

It is now 18 years since structural intermetallic alloys have been studied for possible industrial applications. Advances made in the last decade have generally been concerned with improvements in mechanical properties through the development of processes leading to improved microstructures, with emphasis placed on the two γ-Ti Al alloys: Ti–48Al–2Nb–2Cr perfected by GE Aircraft Engines and Ti–45Al–2Nb–2Mn plus 0.8 vol. % TiB₂(45XD) by Howmet-Pratt & Whitney.

Despite the large potential benefits, no alloy has been selected for use in a production aircraft engine. However, following a risk-phased approach to technical feasibility and cost, specific components have been in the critical evaluation stage for implementation. This assessment will summarize their current status and will emphasize the importance of the manufacturing route for a particular component. This also applies to aerospace sheet and automotive castings, which are considered less critical than the application of a component in an aircraft engine.

Section snippets

Near net shape casting

Based on the available property data, and the incremental low-risk approach, the aircraft engine builders focused their attention on evaluating γ-TiAl for cast low-pressure turbine blades and static structural components. Casting is the most economical way to produce a component for study and the investment casting industry has perfected the requested near net-shapes. Low-risk applications that have been evaluated by GE Aircraft Engines include transition duct beams, a radial diffuser and a

Wrought processing route

Concerns have been in maintaining ingot integrity and chemistry aims in large ingots. Attention in Europe has focused on an appropriate ingot size for wrought processing of a particular end product [11], [12]. This would be by either forging to billet and subsequent forging to near net-shape or hot extrusion to a billet or bar product for forging or rolling. The effort in Europe has confirmed the homogeneity problem in higher alloyed TiAl (of specific interest) that has been improved by

In-progress developments

Whether the component is derived from casting or wrought processing, tensile ductility that is consistent and at a level, which is acceptable to design engineers (⩾ 1% elongation), is necessary. There is a persistent need to improve the tensile ductility or fracture toughness of TiAl without compromising the desired properties of the material at high temperatures. As applications start to emphasize damage-tolerant design, fracture toughness and fatigue crack growth become increasingly important

Status

The major pay-off possibilities in aircraft engines are cast or forged turbine blading and forged compressor blading, and the paramount issues are resolution of the cost and benefit trade off. At present, the US effort is on hold because a high volume application for which TiAl offers attractive cost reduction has not been identified. In regard to LP turbine blades for commercial engines, the cost versus the benefit problem was not resolved when it was considered [3]. A cost-effective

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Limited strength and ductile joints for bonding γ-TiAl intermetallics are one of the main concerns on γ-TiAl applications in the aerospace industry. In this study, a new ductile brazing filler with TiZrCuNi system was developed by an established model for calculating the electrons distribution of the unit cell for the filler. Three kinds of fillers with fixed amount of Cu and Ni as 25 wt.%, but different Zr level (25, 18, 10 wt.%) were designed. It was found that the filler diffusion was affected by the filler composition, which was insufficient with high Zr content up to 37.5 wt.%. And the defects such as the voids and the cracks were observed with medium Zr level as 25 wt.% and brazing temperature as 1000 °C. The sound joints by Zr as 18 wt.% and 10 wt.% filler at 950 °C and 980 °C respectively were achieved with tensile strength as 520 MPa–570 MPa at room temperature. This tensile strength was remained as 495 MPa in average at 600 °C. The strong joints were attributed to the fine, randomly oriented Ti₃Al grains and evenly distributed elements at the interfaces.
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ReviewQuo vadis gamma titanium aluminide

Abstract

Introduction

Section snippets

Near net shape casting

Wrought processing route

In-progress developments

Status

Intermetallics

Intermetallics

A perspective on intermetallic commercialization for aero-turbine applications

Titanium aluminides—great potential but not yet flying

The future use of gamma titanium aluminides by Rolls Royce

Use of gamma titanium aluminide for automotive engine valves

Metallurgical Science and Technology, Teksid

Cast gamma TiAl alloys: are we there yet?

Review
Quo vadis gamma titanium aluminide