| The effects of alloying with small amount of elements of C,P on the microstructure and mechanical behavior of the NiAl and NiAl-34Cr alloys were studied.The alloy ingots of NiAl-C and NiAl-34Cr-P were melted by electric-arc furnace of vaccum non- consumable W-electrode.The microstructure and phases composition were investigated by analysing methods of metallography, SEM,energy spectrometer and X-rays diffractometer.The hardness of alloys with different C,P content were tested by the sclerometer.The compressive properties of NiAl-C were tested by the Gleeble1500 testing machine.The microstructre of the NiAl-C is composed of single-phase NiAl,and the cross direction crystal grain is big enough.The grain size reduces gradually with the C content increasing.The grain size and microstructre are not change greatly after heat treatment. The element of C exists in crystal boundary mostly,a little of C exists in the crystal.A certain level of C can induce softening in polycrystalline NiAl,i.e.,decreased yield stress and hardness and increased room temperature compressive ductlilty. Reduction of Peierls stress was responsible for the softening.The hardness of alloy is reduced with different degree after heat treatment.It is responsible for the C precipitats from the alloy.The microstructre of NiAl-34Cr-P is composed of NiAl,Cr and Ni3P phases,the shape of alloy is regular like typical fir-tree crystal cellular structure.The size of fir-tree crystal cell reduces gradually with the P content increasing.And it is not change greatly after heat treatment. The element of P exists in eutectic cell boundary mostly,a little of P exists in the eutectic cell.The hardness of all the alloys rises earlier and decreases later with the P content increasing,no matter casting or heating treatment,and the hardness maximizing while content 0.02%P.The hardness of alloy is reduced with different degree after heat treatment.It is responsible for the Cr phase accumulative coarsening. |
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