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CHARACTERIZATION AND CORROSION BEHAVIOUR OF METALLIC POWDERS COMPACTED UNDER VARIOUS HIP CONDITIONS

Objective


The general outcome of the research was a closer definition of the relationship between hot isostatic pressing (HIP) parameters and the metallurgical variables which affect the corrosion behaviour of materials which have been cast, then powdered by REP and finally compacted by HIP.

For Sancro 28(28 Cr, 32 Ni, 3 Mo) compacted material showed mechanical and corrosion behaviour similar to or better than the wrought one. Field tests using HIP in geothermal environments concluded that PM/REP production followed by HIP is a technology useful for the preparation of near net shape components in the chemical and petrochemical industries.

When processed using HIP, Nimonic 28 (28 Cr, 32 Ni, 3 Mo) showed very bad creep behaviour, as time to rupture, reduction of area and elongation. The corrosion behaviour was similar or slightly better when compared to the wrought material. No improvement was obtained after a solution treatment of compacted material at 1160 C. Compaction of powdersobtained by gas atomization produced no improvement, compared with REP compacted powders. From this it is possible to conclude that PM and HIP are not suitable for Nimonic.

Wear rate and fretting corrosion related to Triballoy 700 are similar to classical wear-resistant materials like Stellite 6. Diffusion bonding on a cylindrical body shows many cracks in the wear-resistant layer and in the carrier material. Triballioy 700 showed insufficient workability when compared to Stellite 6 in bonding tests. The material did yield good results against Stellite 6 in hot wear tests.

For titanium-aluminium alloys heats (TiAl14 and TiAl18) the first results related to HIP materials showedpractically no ductility and fragile fracture. Heat treatment and the addition of small quantities of rare earth metals produced a remarkable improvement in ductility properties and compression strength.

When tested in HIP methods against commercial TiAl6V4, titanium-aluminium alloys showed good corrosion resista nce and oxidation behaviour.
THE PRODUCTION OF METALLIC PARTS BY HOT ISOSTATIC PRESSING (HIP) OF POWDERS IS A GROWING FIELD AND ENCOURAGING RESULTS HAVE BEEN OBTAINED WITH THESE MATERIALS IN WELL DEFINED APPLICATIONS.

RECENTLY THESE TYPES OF METALLIC PARTS HAVE BEEN USED IN ENVIRONMENTS WHERE GOOD CORROSION RESISTANCE IS A SPECIAL FEATURE. HOWEVER, THE CORROSION BEHAVIOUR OF THESE COMPACTED POWDERS IS NOT WELL KNOWN AND IS LIMITED TO A FEW PRELIMINARY STUDIES.

THE OBJECTIVE OF THE PROJECT IS TO DEFINE THE RELATIONSHIPS BETWEEN HIP PARAMETERS AND METALLURGICAL VARIABLES AFFECTING THE CORROSION BEHAVIOUR OF POWDER METALLURGICAL HIP MATERIALS AS WELL AS TO ASSESS THE MICRO-MECHANISMS INVOLVED.

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Coordinator

Ente per le Nuove Tecnologie l'Energia e l'Ambiente (ENEA)
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Address
Via Anguillarese 301
00060 Santa Maria di Galeria Roma
Italy

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Participants (3)