The role of Si on solidification behaviour of the NiAl intermetallic cladding produced by the GTAW process

ABSTRACT

In this research, the role of Si on the solidification behaviour of NiAl cladding produced by the GTAW process was studied. NiAl and Ni₂AlSi compounds were synthesised by mechanical alloying. The produced powders were cladded on the surface of CK45 steel using the GTAW process. Phase evolutions, microstructural changes and fractography of the produced powders as well as the cladded layers were characterised by X-ray diffraction, optical microscopy and scanning electron microscopy methods. After cladding of Ni₂AlSi powder mixture, in the first pass of this coating, only NiAl phase and in the second pass, only (Ni,Si)Al intermetallic compounds were formed. For ternary coating, a narrow area including cellular solidification mode was seen at fusion boundary which transformed to equiaxed dendritic solidification mode. Fractography analysis of the claddings revealed that by the addition of Si into NiAl lattice, brittle fracture changed to more ductile fracture with ‘eggcrate-type’ appearance, indicating solidification cracking.

RÉSUMÉ

Dans cette recherche, on a étudié le rôle du Si dans la solidification du placage intermétallique NiAl produit par soudage tig. Pour ce but, on a synthétisé les composés intermétalliques NiAl et Ni₂AlSi par alliage mécanique. On a plaqué sur la surface de l’acier CK45 les poudres produites en utilisant le soudage tig. Les évolutions de phase, les changements de microstructure et la fractographie des poudres produites ainsi que des couches plaquées, ont été caractérisés par diffraction des rayons X, microscopie optique et méthodes de microscopie électronique à balayage. On a constaté qu’après le placage du mélange de la poudre Ni₂AlSi, dans la première passe de ce revêtement, seule la phase NiAl et dans la seconde passe, seuls les composés intermétalliques (Ni,Si)Al étaient formés. Pour le revêtement ternaire, on a observé une zone étroite incluant un mode de solidification cellulaire à la limite de fusion qui s’est transformée en un mode de solidification dendritique équiaxe. L’analyse fractographique des placages a révélé qu’en ajoutant du Si dans le réseau NiAl, la rupture fragile se changeait en rupture plus ductile à l’apparence de type alvéolé, indiquant une fissuration de solidification.

KEYWORDS:

• Cladding
• NiAl
• Ni₂AlSi
• solidification pathway
• fractography

Disclosure statement

No potential conflict of interest was reported by the author(s).

Notes on contributors

Dr. M. Rafiei is assistant professor at Islamic Azad University, Najafabad Branch (IAUN). He has Ph.D. in materials engineering from Isfahan University of Technology (IUT). His research fields are welding, surface engineering and advanced materials. He has about 50 ISI papers in several scientific journals from 2009 until now.

Mr. M. Javadi is an M.Sc. student of materials engineering (welding) at Islamic Azad University, Najafabad Branch (IAUN), Iran. His research field is welding metallurgy.

Dr. H. Mostaan is assistant professor at Arak University, Iran. He has Ph.D. in materials engineering from Isfahan University of Technology (IUT). His research fields are welding metallurgy, magnetic materials and powder technology. He has about 60 ISI papers in several scientific journals from 2010 until now.

Dr. A. R. Abbasian is assistant professor at Sistan and Baluchestan University, Iran. He has Ph.D. in materials engineering from Materials and Energy Research Center. His research field is advanced ceramic materials. He has about 20 ISI papers in several scientific journals from 2010 until now.