Y Huang
,
H.N Hao
,
Y.L. Chen and B.L.Zhou (1)Department of Materials Science and Engineering
,
Tsinghua University
,
Beijing 100084
,
China 2)Institute of Metal Research
,
Chinese Academy of Sciences
,
Shenyang 110015
,
China Manuscript received 26 August 1996)
金属学报(英文版)
A new way of designing and preparing silicon nitride ceramic composite with high fracture toughness and nacre structure has been proposed. To mimic the laminated structure of nacre, Si_3N_4 matrix ceramic layer can be obtained through compacting rolling method. To mimic the secondary toughening of nacre structure, SiC whisker is added into Si_3N_4 and acts as the secondary toughening phase. Boron nitride (BN)is selected to mimic the organic layer in nacre so as to form the weak interfaces between Si_3N_4 layers. Alumina is added into BN to adjust the bonding strength of the interface.The Si_3N_4 sheets are stacked into the die after coating with BN. After the removal of the organic matter in them, the green body is hot pressed at 1820℃for 1.5 hours under N_2 atmosphere. The fracture toughness of the so-made Si_3N_4 composite at room temperature is 20.36MPa m~(1/2), the three-point bending strength at room temperature is 651.47MPa. The crack spreads and deflects along the interface between BN and Si_3N_4 layer and extends through the BN layer into Si_3N_4 layer. The improvement of the fracture toughness may be due to the staircase-shape-like crack which provides the long crack path, the fracture and deformation of Si_3N_4 layer, and the pullout of SiC whiskers from the Si_3N_4 layer.
关键词:
:secondary toughening
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null
,
null
,
null
Z.S. Zhu
,
N.P.Chen
,
J.L. Gu and M.G. Yan(1)Institute of Aeronautical Materials
,
P.O. Box 8115
,
Beijing 100095
,
China 2)Department of Materials Science and Engineering
,
Tsinghua University
,
Beijing 100084
,
China Manuscript received 26 August 1996)
金属学报(英文版)
By means of crystallite orientation distribution function (ODF) analysis, the influence on orientation variant selection of cold rolling reductions, recrystallization annealing and cooling rates during α→β→α cyclic phase transformation treatments in cold rolled titanium sheet has been investigated. The results show that, cold rolling reduction and annealing treatment both have a great effect on the formation of phase transformation textures.No variant selection occurs in cold rolled and recrystallization annealed titanium sheet which resulte in a more randomly distributed texture.The phase transformation texture formed α→β→α transformation is inherited after 3 cycles of α→β→α phase transformation. The cooling rates during phase transformation have little effect on orientation variant selection.
关键词:
:texture
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null
,
null
,
null
,
null
J.T.Guo
,
S.H. Wang
,
H. Li
,
W.H. Lai and M.H.Tan(Institute of Metal Research
,
Chinese Academy of Sciences
,
Shenyang 110015
,
China Manuscript received 26 August 1996)
金属学报(英文版)
The isothermal oxidation behavior of Ni_3Al containtng 15 at.% Fe and NiAl containing 30 at.% Fe was studied for 100 h at 850, 950, 1050 and 1150℃, respectively. The results show that the oxidation kinetics of the two alloys obey a parabolic law at various temperatures and every parabolic curve possesses two oxidation rate constants. The morphology, microstructure and the chemical composition of the oxide scales were examined using optical metallography, X-ray diffraction analysis, scanning electron microscopy and electron probe microanalysis. The oxide scale of Ni_3Al containing 15 at.% Fe consists mainly of NiO, NiFe_2O_4, and FeAl_2O_4, and that of NiAl containing 30 at.% Fe consists of Fe_2O_3 and (Fe,Ni)Fe_2O_4, contrasting sharply to the oxide scales of pure Ni_3Al and NiAl which consist of Al_2O_3. The oxide scales on the surfaces of Ni_3Al and NiAl containing Fe are not too dense and not too cohesive to the matrix,so their oxidation resistance is not too good.
关键词:
:oxidation
,
null
,
null
,
null
J.T. Guo
,
L.Z. Zhou
,
Z.G. Liu and W.M. Yin(Institnte of Metal Research
,
Chinese Academy of Sciences
,
Shenyang 110015
,
China Manuscript received 26 August 1996)
金属学报(英文版)
Ternary Ni-Al-Fe alloys with different Fe-additions have been synthesized by mechan ical alloying.The results show that 5 and 10 at% Fe-additions prolong the milling time prior to the explosive formation of NiAl(Fe) compound, 15 at.% Fe-addition results in the formation of an "amorphous-like" phase,20 at.% Fe-addition turns the final products to Ni(Al, Fe)supersaturated solid solution with fcc structure,and the increase of Fe-addition can speed up the formation of the solid solution.The addition of Fe improves the plastic deformation ability of the alloys.
关键词:
:mechanical alloying
,
null
,
null
Z.Q. Hu
,
W.R.Sun and S.R. Guo(Institute of Metal Research
,
Chinese Academy of Sciences
,
Shenyang 110015
,
China Manuscript received 26 August 1996)
金属学报(英文版)
The effects of the trace elements, P, S and Si,on the solidification, segregation,microstructure and mechanical properties of GH761 and In718 alloys were studied.It was found that the segregation of the P,S and Si can be greatly aggravated or relieved by the precipitation taking place during the solidification. In the heat treated state,P enhances the intergranular precipitation in the GH761 alloy.The refinement of P in In718 alloy causes the appearance of a film-like δphase.Si increases the intergranular precipitation of the M_6C and the Laves Phase in the In718 alloy.P, S and Si play diverse roles in the tensile and the stress rupture properties of the GH761 and In718 alloys. The most striking effect is that P significantly prolongs the stress rupture lives of the GH761 and In718 alloys in a wide range of 0.00050.015 wt% .The mechanisms by which P,S and Si influence the superalloys are discussed in the text.
关键词:
: superalloy
,
null
,
null
,
null
S. Y Zeng
,
B. Yang and E.L. Zhang(Harbin Institute of Technology
,
Harbin 150001
,
China)M.Z. Ma(Jiamusi University
,
Jiamusi 154002
,
China Manuscript received 26 August 1996)
金属学报(英文版)
Direct reaction synthesis(DRS), based on the principle of self-propagating hightemperature synthesis (SHS), is a new method for preparing particulate metal matrix composites (PMMCs). The effects of the temperature of the aluminum melt and the aluminum content in the preform on the phases and structure of the reacted preform have been investigated by X-ray diffraction and scanning electron microscopy.It has been shown that TiC phase is prone to be synthesized with the increasing of the temperature of the aluminum melt and the decreasing of the aluminum powder content in the preform, and that the size of TiC particle becomes fine with the increasing of the temperature and the decreasing of the aluminum powder content.
关键词:
:direct reaction synthesis
,
null
,
null
