BI-METAL: Mechanics of bi-metallic discs

• Research unit: EU RFP
• Project number: 97.0403

Key words (English)

HIgh temperature; bimetallic joint; Udimet 720; single crystal M2C; nondestructive evaluation

Alternative project number (English)

EU project number: $BE 97-4296

Research programs (English)

EU-programme: 4. Frame Research Programme - 2.1 Industrial and materials technologies

Short description (English)

See abstract

Further information (English)

Full name of research-institution/enterprise:
Eidg. Materialprüfungs- und Forschungsanstalt EMPA
Leiter ZfP Sonderverfahren

Partners and International Organizations (English)

Coordinator: CEA/CEREM (F)

Abstract (English)

The main objectives of this project was to develop a methodology to assess the lifetime of a high temperature bimetallic component like a gas turbine disc. The work comprises manufacturing and testing, development of mechanical models to describe both behaviour and damage and finally a validation of the proposed methdology. Two types of bimetallic joints were studied:Coarse grain Unimet 720 (cast and wrought) to fine grain Udimet 720 (powder material) and single crystal MC2 to fine grain Udimet 720. Compared to standard mono material, the bimetallic material shall have better mechanical properties: the coarse grain material or single crystal material being a high creep resistant material is devoted to the rim of the gas turbine disc. The fine grain material (U720 powder material) being a high strength alloy is devoted to the hub.
Nondestructive evaluation methods have been developed by EMPA to inspect the interface zone of the bonded bimetallic joint. Reference bimetallic samples for nondestructive evaluation with intended artificial planar flaws in the joint were manufactured. The artificial flaws were introduced by inserting small aluminia particle in the interface before joining the two materials by HIP (hot isostatic pressure) diffusion bonding process. The reference bimetallic sample underwent X-ray (computer tomography) and ultrasonic inspection to verify the size of the planar interfacial flaws. Some differences were observed between the X-ray measured size and the ultrasonic measured size. But all measured flaw sizes were within the intended diameter range.
Afterwards ultrasonic inspection (using immersion technique and the pulse - echo method) was performed to develop a suitable inspection technique which is able to detect small flaws in the bimetallic joint at increased material distances. The best nondestructive testing results were achieved with spherical focussed ultrasonic transducers with nominal frequency of 5 and 10 Mhz. From the results gained at the reference samples, it can be concluded, that the applied ultrasonic inspection techniques are capable to detect small planar flaws at the bimetallic bonding interface zone.

References in databases (English)

Swiss Database: Euro-DB of the
State Secretariat for Education and Research
Hallwylstrasse 4
CH-3003 Berne, Switzerland
Tel. [phone]
Swiss Project-Number: 97.0403