Dynamic Compaction and Hot-Isostatic-Pressing of Nickelaluminides
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DYNAMIC COMPACTION AND HOT-ISOSTATIC-PRESSING OF NICKELALUMINIDES
0. ARKENS*, L. DELAEY*, J.DE TAVERNIER*, B. HUYBRECHTS*,
L. BUEKENHOUT+,
J.C. LIBOUTON", * Department
of Metallurgy and Materials Engineering, Katholieke Universiteit Leuven, de Croylaan 2, 3030 Heverlee (Belgium) * Nobel Explosives Belgium, de Broquevillelaan 12B4, 1150 Sterrebeek (Belgium) + Industrial Materials Technology,National Forge Europe, Industriepark-Noord 7, 2700 Sint-Niklaas (Belgium) ABSTRACT Explosive compaction and HIPping of stoichiometric mixtures of Ni and Al (and B) powder is optimized in order to obtain fine grained NiAl- and NiaAl(+B) intermetallics. Starting from an appropriate mixture of pure fine Ni- and fine Al(and B) powders fine nickel-aluminides are produced due to a selfpropagation high temperature synthesis during processing. HIPping experiments are done also on spherical Ni-coated Al-powders. The specimens are characterized by metallography and the homogeneity of the final product is controlled by microanalytical methods. INTRODUCTION Intermetallic compounds are being recognized as potentially useful structural materials. The nickel-aluminides, Ni3Al and NiAl, possess an excellent oxidation resistance, wear resistance and a high strength at high temperatures. A major problem is their brittleness at ambient temperatures : nickelaluminides are difficult for machining. Progress has been made by adding small amounts of boron (less than 1000 ppm) to Ni3Al which results in a raise of the tensile elongation at room temperature to a percentage as high as 53 % [1]. Grain refinement to below a critical grain size (10 gm) effects also a brittle to ductile transition in NiAl [2],[3]. In our laboratories, a comparing study between different techniques, i.e. reactive sintering (HIPping), dynamic (explosive) compaction, plasma synthesis and combinations of these three techniques, to produce, synthetize and compact intermetallic powders is carried out. This paper reports on powder metallurgical methods in the processing of fine grained nickel-aluminides, starting from an appropriate mixture of pure Ni and pure Al powder (with small addition of B). Dynamic compaction and hot isostatic processing are applied on these mixtures. Hot isostatic compaction is also applied on canned spherical Ni-coated Al-powders. The exothermic reaction, for the formation of NiAl and Ni3AI from a mixture of pure Ni and Al powders, starts around 650"C. The exact temperature of initiation depends on the rate of heating, the grain size of the individual particles and the composition [3]. The reaction enthalpies are : Ni + Al
-- > NiAl
3Ni + Al -- > Ni3AI
H&-9e
= -118.4
kJoule/mol
29aK = -153.2
kJoule/mol
Mat. Res. Soc. Symp. Proc. Vol. 133. @1989Materials Research Society
494
After starting up temperature synthesis.
the
reaction
runs
as
a
self-propagation
high
Powder metallurgical processing techniques are optimized to obtain fine grained NiA1 and Ni3Al products. Samples are metallographically characterized and the homogeneity of the fina
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