A NiAI-based composite with HfB2 dispersed particles has been synthesized by mechanical alloying of Ni, Al, Hf and C powders. The formation mechanism of NiAI-HfC during milling can be attributed to two chemical reacti...A NiAI-based composite with HfB2 dispersed particles has been synthesized by mechanical alloying of Ni, Al, Hf and C powders. The formation mechanism of NiAI-HfC during milling can be attributed to two chemical reactions: Ni+AI→NiAI+△H; Hf+C→HfC+△H, induced by mechanical collision in a certain period of time, which results in an abrupt exothemic reaction. Hot pressing (HP) and hot isostatic pressing (HIP) have been used to make the NiAI-10HfC compacts near fully dense. Compressive testing from room temperature to 1000℃ indicated that the yield stress of NiAI-10HfC composite is 3-4 times higher than that of cast NiAl and correspond to the MA NiAI-10TiB2 composite. In the meantime, yield strength at high temperature is dependent on strain rate, and deformation is controlled by diffusion mechanism.展开更多
Microstructure of the deepest zone of high speed steel W6Mo5Cr4V2(M2)melt after laser fu-sion was found to be so fine as the ehill zone of a solidified ingot.When narrower chill zoneformed,the long columnar dendrites ...Microstructure of the deepest zone of high speed steel W6Mo5Cr4V2(M2)melt after laser fu-sion was found to be so fine as the ehill zone of a solidified ingot.When narrower chill zoneformed,the long columnar dendrites grow into the melt and then the fine equiaxed cellularstructure appears in upper melt region nearly surface.The substructure of cellular grains anddendrites was observed to consist of martensite and retained austenile,while the carbides asM_6C_■ Cr_7C_3 and MC distributed at their boundaries.It is believed that the highermicrohardness up to HV_(0.1)=865-960 of the laser fused structure of the alloy is due to the oc-currence of martensite.展开更多
基金This research was supported by the National Natural Science Foundation of China(59895152)the National High Technology Committee of China(863-715-005-0030).
文摘A NiAI-based composite with HfB2 dispersed particles has been synthesized by mechanical alloying of Ni, Al, Hf and C powders. The formation mechanism of NiAI-HfC during milling can be attributed to two chemical reactions: Ni+AI→NiAI+△H; Hf+C→HfC+△H, induced by mechanical collision in a certain period of time, which results in an abrupt exothemic reaction. Hot pressing (HP) and hot isostatic pressing (HIP) have been used to make the NiAI-10HfC compacts near fully dense. Compressive testing from room temperature to 1000℃ indicated that the yield stress of NiAI-10HfC composite is 3-4 times higher than that of cast NiAl and correspond to the MA NiAI-10TiB2 composite. In the meantime, yield strength at high temperature is dependent on strain rate, and deformation is controlled by diffusion mechanism.
文摘Microstructure of the deepest zone of high speed steel W6Mo5Cr4V2(M2)melt after laser fu-sion was found to be so fine as the ehill zone of a solidified ingot.When narrower chill zoneformed,the long columnar dendrites grow into the melt and then the fine equiaxed cellularstructure appears in upper melt region nearly surface.The substructure of cellular grains anddendrites was observed to consist of martensite and retained austenile,while the carbides asM_6C_■ Cr_7C_3 and MC distributed at their boundaries.It is believed that the highermicrohardness up to HV_(0.1)=865-960 of the laser fused structure of the alloy is due to the oc-currence of martensite.
