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Microstructures and Mechanical Properties of Two Superalloys and NiAl Eutectic Alloys

Author: XiaoXuan
Tutor: YuHaiPeng;GuoJianTing;YuanXiaoGuang
School: Shenyang University of Technology
Course: Materials Science and Engineering
Keywords: superalloys DZ417G U720LI intermetallics NiAl-Cr(Mo) eutectic alloy microstructures mechanical properties
CLC: TG132.32
Type: PhD thesis
Year: 2007
Downloads: 602
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Abstract


The microstructures and mechanical properties of DZ417G, U720Li superalloys and NiAl-Cr(Mo) alloys have been investigated, aiming to provide using data to develop new high-performance high-temperature structural materials. The research include that: (1) effect of cooling rate from solution treatment and cyclic heat treatment, stability of directionally solidified superalloy DZ417G, (2) thermal stability and creep behavior of U720LI wrought superalloy, (3) Ti alloying of NiAl-31Cr-3Mo (atomic percent) eutectic alloy, (4) as-cast microstructures, compressive property, creep property as well as rupture mechanisms of Ni-32Al-28Cr-3Mo-4Ti alloy, (5) microstructures and compressive property of electromagnetic centrifugal casting (EMCC) NiAl-28Cr -5.5Mo-0.5Hf-0.03P eutectic alloy,The results show that Fast cooling rate from solution heat treatment promotes nucleation of the secondary and tertiaryγ’ in the directionally solidified superalloy DZ417G, while slow cooling rate favors precipitation of the secondary gamma prime other than the tertiaryγ’. With the increasing of cooling rate, the hardness at room temperature increases. After aging at 1220℃for 16 hours, the tertiaryγ’ particles grow markedly with high consumption of small ones. Fast cooling rate followed by age treatment is beneficial to the tensile strength, where as slow cooling rate favors the ductility at room temperature. Good combination of tensile and stress-rupture properties can be achieved by controlling cooling rate from solution heat treatment.With the increasing of cyclic times, the amount of largerγ’ particles in DZ417G superalloy decreases clearly, and the spacing between smallerγ’ particles reduces, leading to the increasing of hardness at room temperature and ultimate tensile strength at 900℃, while tensile ductility drops slightly after 3rd cycle of heat treatments. The rupture life under condition of 980℃and 216 MPa prolongs substantially with the increasing of cyclic times, however, it drops rapidly after 5th cycle of heat treatments.DZ417G alloy maintains good thermal stability without the formation of brittle TCP formation and aggregation of microvoids on eutectic boundaries leads to creep fracture.The fine-lamellar electromagnetic centrifugal casting (EMCC) NiAl-28Cr-5.5Mo-0.5Hf-0.03P eutectic alloy consists of rapid cooling zone dominated by primaryβ-NiAl, eutectic zone ofβ-NiAl andα-Cr(Mo), and hypoeutectic zone of primaryβ-NiAl andβ-NiAl/α-Cr(Mo) eutectic. Deformation behavior of the alloy at 1000℃follows the power law equation, and its strength can be improved by proper heat treatment. The main fracture mechanism at room temperature is cleaving of NiAl matrix and stripping of NiAl/Cr(Mo) interface.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > The alloy learn with a variety of properties of alloys > Special physical properties of alloys > Special thermal properties of alloys > Melting point alloys , refractory alloy , high temperature alloys
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