Weili REN
,
Jianting GUO
,
Gusong LI
,
Jiyang ZHOU
材料科学技术（英）
The influence of strain rate and temperature on the tensile behavior of as-cast and HIPed NiAl-9Mo eutectic alloy was investigated in the temperature range of 700~950℃ and over a strain rate range from 2.08×10-4 s-1 to 2.08×10-2 s-1. The results indicate that HIP process causes an enhancement in ductility and a decrease in ultimate tensile strength (UTS), yield strength (YS), average strain hardening rate as well as a drop in brittle to ductile transition temperature(BDTT) under the same condition. It is noticed that the BDTT of as-cast NiAl-9Mo is more dependent on strain rate than that of HIPed one. The brittle to ductile transition process of the alloy is related to a sharp drop in strain hardening rate. Regardless of strain rate, the fracture morphology changes from cleavage in NiAl phase and debonding along NiAl/Mo interface below the BDTT to microvoid coalescence above BDTT. The apparent activation energy of the BDT of HIPed and as-cast material are calculated to be 327 and 263 kJ/mol, respectively, suggesting that the mechanism is associated with lattice diffusion in NiAl phase.
关键词:
NiAl-9Mo
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null
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null
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null
YANG
,
Jianting GUO
,
Jiyang ZHOU
材料科学技术（英）
A NiAl-based composite with HfB2 dispersed particles has been synthesized by mechanical alloying of Ni, Al, Hf and C powders. The formation mechanism of NiAl-HfC during milling can be attributed to two chemical reactions: Ni+AlNiAl+ΔH; Hf+C→HfC+ΔH, 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 NiAl-10HfC compacts near fully dense. Compressive testing from room temperature to 1000℃ indicated that the yield stress of NiAl-10HfC composite is 3~4 times higher than that of cast NiAl and correspond to the MA NiAl-10TiB2 composite. In the meantime, yield strength at high temperature is dependent on strain rate, and deformation is controlled by diffusion mechanism.
关键词:
NiAl composite
,
null
,
null
,
null
,
null
Rongshi CHEN
,
Jianting GUO
,
Jiyang ZHOU
材料科学技术（英）
The microstructure of multiphase Ni-25Al-15Cr (at. pct) intermetallic alloy consists of dendritic arms (β-NiAl phase) and interdendritic regions (γ/γ´ two phases) under homogenization followed by air cooling condition. Furnace cooling following homogenization does not significantly influence its microstructure. However, the effects of aging treatment on the microstructure strongly depend on cooling rates following homogenization. A single phase g´ layer with a α-Cr `spouse' layer is observed surrounding the dendritic arms, the formation of this ‘couple’ is attributed to a four-phase invariant quasi-peritectoid, i.e: β+γ=γ´+α-Cr .
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