Effect of Stress-Induced Phase Transformation on the Fracture Toughness of Fe 3 Al Intermetallic Reinforced with Yttria-
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I.
INTRODUCTION
FE3AL intermetallic compound has a high potential to replace some of the expensive stainless steels in many applications due to its low density, high elastic modulus, low cost, and excellent corrosion resistance in sulfidizing and oxidizing environments.[1–4] However, the use of Fe3Al is limited by its low fracture toughness and ductility at ambient temperature as well as low strength at above 873 K (600 C).[5–8] Many attempts have been employed to improve the fracture toughness of Fe3Al and other brittle intermetallics based on different mechanisms such as micro and macro alloying, composite fabrication, grain refinement, and transformation toughening.[4,7–12] The phenomenon of transformation toughening in partially stabilized zirconia (PSZ) and zirconia toughened ceramics has been extensively studied.[13,14] However, there is no systematic study about the improving effects of PSZ particles on the fracture toughness of the brittle intermetallics such as Fe3Al. Zirconia has three different lattice structures: monoclinic at ambient temperature and tetragonal and cubic at higher temperatures.[15] It has been well known that the addition of Y2O3, MgO, CaO to zirconia stabilizes
LIMA AMIRI TALISCHI and AHAD SAMADI are with the Department of Materials Engineering, Sahand University of Technology, P.O. Box: 51335-1996, Tabriz, Iran. Contact e-mail: samadi@ sut.ac.ir Manuscript submitted February 16, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
its tetragonal structure at ambient temperature which can transform to monoclinic structure in the stress field at the crack tip. This stress-induced structural transformation is accompanied by a more than 3 pct volume expansion and 1 to 7 pct shear strain leading to a compressive stress in the matrix phase which can prevent the crack propagation.[15–19] Based on the above mentioned transformation toughening effect of PSZ particles, it seems that by adding PSZ to Fe3Al, the fracture toughness of Fe3Al can be improved. Therefore, in this paper, the effect of yttria-partially stabilized zirconia (Y-PSZ) particles on ambient temperature fractures toughness of Fe3Al intermetallic is evaluated.
II.
EXPERIMENTAL PROCEDURE
Fe3Al and yttria-partially stabilized zirconia (3 mol pct Y2O3) powders were used as starting materials to fabricate bulk samples. The yttria-partially stabilized zirconia powder (98 pct purity) was obtained from Sigma-Aldrich Co. The particle size of the Y-PSZ powder was less than 500 nm. The Fe3Al powder was synthesized by mechanical alloying of pure elemental iron and aluminum powders. The mechanical alloying was carried out in a planetary ball mill laboratory apparatus under argon atmosphere at ambient temperature with a rotational speed of 300 rpm. The ball to powder weight ratio and the milling time of powders were considered to be 10:1 and 70 hours, respectively. The average particle size of the Fe3Al powder was about
500 nm. Other details of the mechanical alloying and characterization of the Fe3Al powder have been previously explained elsew
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