Combined Effects Of Ag/Cu And Y On Microstructure And Properties Of NIAL Intermetallic Compound

In this paper, NiAl alloys with different YAg/YCu contents were prepared by non-consumable electro-arc furnace, and some of these samples were treated by high-temperature solid solution way. The combined effects of Ag/Cu and Y on microstructure and properties of NiAl intermetallic compound were investigated by SEM, energy spectrometer, X-rays diffractometer, and testing machine. Meanwhile, the probing on the effects of combined addition of Ag/Cu and Y on the mechanical properties of brittle B2-type NiAl intermetallic compound originates from a well-estabished physical concept.Based on the observations, with the increase of YAg content, the grain size of NiAl reduces gradually. When the content of YAg is less than 1.0 wt. %, the microstructure characteristic of columnar shape has found in the resultant alloy. However, for the alloys with 5.0 wt. % YAg and 10.0 wt. %YAg, the solidification mode has changed from directional mode into bulk mode. After solid solution and aging treatment, compared with the as-casted alloys, microstructure has become coarser with more elements have segregated at the phase interface. Corresponding to this, compressive yield strength also gradually enhanced. For the ones with the content of YAg up to 10.0 wt. %, the compression strength rearched its maximum value of 633.4 MPa, and the compressive strain were 13.4 wt.%, both are much higher than that of NiAl intermetallic compound. However, after heat treatment, the compressve strength and strain reduced. The reason is mainly in that, after heat treatment, many segregatedY and Ag elements returned to more modest state.The combined effects of Cu and Y on microstructure of NiAl intermetallic compound were also investigated. With the content of YAg increasing, the average cells size have gradually decreased. Microstructure has changed from columnar morphlogy into equiaxial morphlogy. After solid solution and aging treatment, the crystal grains became larger, and bluk second phases emerged. Compressive strength of as-cast NiAl alloys were found to be affected remarkablely by the content of YCu with the highest compressive strength up to 671.6 MPa for 10.0 wt. % YCu. And the maximum compressive strain was 13.2% for the ones with 1.0 wt. % YCu. After heat treatment, compressive strength of 1.0% wt. YCu alloy raised, but its ductility reduced. On the contrary, compressive strength of the NiAl-5.0 wt. %YCu reduced, however the ductility raised from 8.7% to 10.1%. The combined functions of solid solution strengthening, elements segerated strengthening and fine-grain strengthening are regared as the responsible mechanism.