Microstructure/Property Relations in AIN and Al 2 O 3 Particulate Strengthened NiAl
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MICROSTRUCTURE/PROPERTY RELATIONS INAIN AND A12 0 3 PARTICULATE STRENGTHENED NIAI.
M. G. Hebsur, Sverdrup Technology Inc., Brookpark, OH 44142 J. D.Whittenberger, NASA-Lewis Research Center, Cleveland, OH 44135,
R. M. Dickerson and B. J. M. Aikin, Case Western Reserve University, Cleveland OH 44106 ABSTRACT
The primary objective of this investigation was to confirm previous results on AIN particulate strengthened NiAI (J. Mater. Res_5, 271 (1990)) produced by cryomilling and to determine if cryomilling modified to produce NiAI containing fine AI20 3 particles would also yield a material with equally attractive strength levels. Compression tests conducted on NiAI-AIN at a strain rate of 1.2 x 10-4 s-1 between 300-1300 K and as a function of strain rate at 1300 K indicated that its strength was comparable to previously produced material. While the NiAl-AI20 3 material was stronger than unreinforced NiAI at lower temperatures, at 1300 K itexhibited strength levels commensurate with fine grain sized NiAI. At all test temperatures and strain rates NiAI-AIN exhibited higher strengths compared to either NiAI-AI20 3 or unreinforced NiAI. INTRODUCTION
Recent studies [1-2] have shown that cryomilling of NiAI powder can lead to remarkable improvements inelevated temperature creep strength due to inhomogeneously distributed fine AIN particles surrounding NiAI grains. The results [3] of 1473 Kcyclic oxidation tests have also shown that AIN particulate reinforced NiAI has excellent cyclic oxidation resistance. Thus, this material appears to have excellent potential for development as an elevated temperature structural alloy. The primary objective of this investigation was to validate the previous results on creep properties of NiAI-AIN material and determine ifNiAI containing fine A1 2 0 3 particles also possessed attractive strength levels. EXPERIMENTAL
Two lots of approximately 500 gm of prealloyed NiAI powder were cryomilled under two conditions ina modified Union Process Model 01 -HD Research 1400 cc attritor mill. Inboth cases the attritor outer vessel was cooled by a continuous flow of liquid nitrogen. Inthe first case liquid nitrogen was introduced inthe milling vessel to form AIN and inthe second case the atmosphere was a mixture of nitrogen and air to promote the formation of Al203. At the completion of each milling cycle, the milling vessel was transferred to a glovebox for warming to room temperature under dry argon. The powders were subsequently consolidated by extrusion at 1473 Kand 12:1 reduction ratio after being vacuum canned inmild steel. From the extruded material, cylindrical compression specimens of 3 mm dia x 6 mm long, and bend bars of 1.25 mm thick x 2.0 mm wide x 50 mm long having their longitudinal axis parallel to the extrusion direction were machined by electrodischarge machining followed by grinding. Compression and four point bend tests were conducted on an universal test machine between 300 and 1300 Kinair at a constant crosshead speed of 0.5 mm/s. Compression tests were also conducted inair be
