Mechanical behavior of the in situ composite alloys in the al-ni-ti system near the l1 2 phase field
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I.
INTRODUCTION
IN the companion article,Eli microstructural evolution of multiphase intermetallic alloys in the ternary A1-Ti-Ni system near the L12 A13(Ti,Ni) phase field is reported. The ingots of particularly good quality were obtained for threephase alloys containing the mixture of the L12 A13(Ti,Ni), face-centered cubic (fcc) AI2TiNi, and A12Ti phases. The specimens cut from these ingots were used for Vickers microhardness (VHN) at room temperature and compressive testing at ambient and elevated temperatures up to 1000 ~ Microhardness testing was used to compare the microhardness of the various phases and their resistance to cracking at room temperature. Compressive testing was carried out with the focus on the composite behavior of the investigated alloys.
II.
imen were 3 • 3 • 6 mm, making the uniaxial compressive strength independent of the ratio of the specimen length (/) to the diameter (d) (l/d > 2.0)531 Specimens were tested in air at room temperature, 600 ~ 800 ~ 900 ~ 950 ~ and 1000 ~ on an Instron machine, with the compression platens fitted with the inserts of A1203/SiC ceramic matrix composite. The initial strain rate was 5.5 • 10 -4 S-1, calculated from the crosshead speed (0.02 crn/min) and the height of the specimen (6 mm). A three heating zone furnace with thermocouples (accuracy __.10 ~ at different zones was used for the tests at elevated temperatures. A load-displacement curve was registered on the Instron chart. In order to reduce the frictional effect at the specimen/compression platen interface, samples for tests at room temperature were lubricated with silicone grease, in addition to a piece of silver foil placed in between the sample and compression platen, whereas DELTAGLAZE 19" was used for elevated temperature tests.
EXPERIMENTAL PROCEDURES
Vickers microhardness testing at room temperature was performed on polished and etched specimens using different loads compatible with the size of the phase under investigation. A minimum of five indentations were made at each load. Both diagonals were measured with an optical microscope using the Java Image Analysis package.[2] The compression testing was done using specimens cut from the homogenized (at 1000 ~ for 48 hours) alloy 5 (for composition, see Reference 1) by electrodischarge machining with a wire. The nominal dimensions of the spec-
S. BISWAS, formerly Graduate Student, Department of Mechanical Engineering, University of Waterloo, is Process Engineer, Greening Donald Co. Ltd., Erin, ON, Canada NOB 1T0. R.A. VARIN, Professor of Materials Science and Engineering, is with the Department of Mechanical Engineering, University of Waterloo, Waterloo, ON, Canada N2L 3G1. Manuscript submitted October 13, 1994. METALLURGICALAND MATERIALSTRANSACTIONS A
*DELTAGLAZE 19 is a trademark of Acheson Industries Inc.
Because of the initial porosity content and microcrack formation during compressive deformation, the so-called "plastic strain" also contains a deformation content due to the preceding two factors. Therefore, the term "permanent de
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