Lijuan ZHANG
,
Mike L.JENKINS
,
Glyn TAYLO
,
null
,
null
,
null
材料科学技术（英）
The effects of preparation and crystal growth methods on the microstructure, composition, and oxidation of CoTi(Zr) intermetallics were dealt with . A group of methods has been used to produce CoTi and CoTi(Zr) crystals to prevent the formation of titanium oxide particles during melting and crystal growth. The results show that more oxides formed when using powdered starting materials even though the metals handled were and melted under an inert gas atmosphere; using bulk starting materials produced alloys showed less oxidation than powders, but adding a small amount of Al to getter the oxygen was not sufficient to prevent TiO2 formation. However, using a slightly reducing atmosphere during initial melting was highly effective in reducing the formation of oxide. Crystal growth carried out in Ar did not reduce the amount of oxide but only redistributed the particles. TiO2 particles were found only in the grain boundaries after crystal growing, where they obstructed grain growth. Crystal growth in a vacuum was found to be essential in producing oxide free crystals. A seed selection technique was developed and used in growing CoTi single crystals. The microstructures of the samples were determined using optical microscopy, scanning electron microscopy and transmission electron microscopy, including the morphologies, grain sizes, oxide distributions and crystal structure confirmation.
关键词:
CoTi
,
CoTi(Zr)
,
Intermetallics
,
Crystal
,
gro
S.N. Hosseini
材料科学技术（英）
The nanostructured CoAl intermetallic compound was produced by mechanical alloying (MA) of the Co50Al50 elemental powder mixture in a planetary high energy ball mill. The ordered B2-CoAl structure with the grain size of about 6 nm was formed via a gradual reaction after 10 h of MA. A thermodynamic analysis of the process was also done. The results showed that the intermetallic compound of CoAl had the minimum Gibbs free energy compared to solid solution and amorphous states indicating the initial MA product was the most stable phase in the Co-Al system which was changed to a partially disordered structure with a steady long-range order of 0.82 at further milling. This amount of disordering caused the enthalpy of final product to show an increase of about 5.1 kJ·mol-1. Calculation of enthalpy related to the triple defect formation revealed that the enthalpy required for Al anti-sites formation was about 3 times greater than that for Co anti-sites formation.
关键词:
Intermetallics
Chengwei Liao
,
Jianchun Chen
,
Yang Li
,
Rui Tu
,
Chunxu Pan
材料科学技术（英）
In general, the modification performance of Al−Sr master alloys is primarily dependent upon the morphologies and sizes of the Al4Sr intermetallic phase. In this paper, the crystal structure, morphologies, sizes, hardness and elastic modulus of Al4Sr in Al{Sr master alloys prepared from variant processes were studied by means of optical metallurgical microscope, X-ray diffraction (XRD), scanning electron microscopy (SEM), and nanoindentation system. The results revealed that the microstructures and modi¯cation performance of the Al4Sr phase were related to the preparation processes. That is to say, when a "direct reaction-hot extrusion" process was used, the Al4Sr phase exhibited a homogeneous distribution in the Al matrix with small size and roundish shapes, which ensured the Al−Sr master alloy wire advantages involving high recovery, good reproducibility, no delitescence of modification, no corrosion on equipments, and good workability. However, in the case of the traditional "direct reaction" process, the Al4Sr phase was in large size with shapes of rectangular stripe and plates, which limited the Sr content increasing due to the brittleness of the Al−Sr alloy. It was also found that the morphology and size of the Al4Sr phases changed during heat treatment at high temperature up to 600 °C.
关键词:
Intermetallics
,
null
,
null
,
null
,
null
S.N. Hosseini
材料科学技术（英）
The nanostructured CoAl intermetallic compound was produced by mechanical alloying (MA) of the Co50Al50 elemental powder mixture in a planetary high energy ball mill. The ordered B2-CoAl structure with the grain size of about 6 nm was formed via a gradual reaction after 10 h of MA. A thermodynamic analysis of the process was also done. The results showed that the intermetallic compound of CoAl had the minimum Gibbs free energy compared to solid solution and amorphous states indicating the initial MA product was the most stable phase in the Co-Al system which was changed to a partially disordered structure with a steady long-range order of 0.82 at further milling. This amount of disordering caused the enthalpy of final product to show an increase of about 5.1 kJ·mol-1. Calculation of enthalpy related to the triple defect formation revealed that the enthalpy required for Al anti-sites formation was about 3 times greater than that for Co anti-sites formation.
关键词:
Intermetallics
Chunshan CHE
,
Jintang LU
,
Gang KONG
,
Qiaoyu XU
金属学报(英文版)
doi:DOI: 10.1016/S1006-7191(08)60
In this article, five kinds of silicon-containing steel sheets have been electrodeposited, and then immersed in a pure molten zinc bath at 450℃ for various periods of time. The results by scanning electron microscopy (SEM) show that the coating of the sample (0.09 wt pct Si) with iron-electrodeposited pretreatment eliminates the reactive zones which are found in the coating without iron-electrodeposited pretreatment. The galvanized sample (0.28 wt pct Si) with iron-electrodeposited pretreatment exhibits a compact and coherent coating. The coating of the sample (0.37 wt pct Si) with the iron-electrodeposited pretreatment experiences a transition from a compact and coherent coating to a reactive one. The energy dispersive spectrum (EDS) results reveal that for the galvanized samples with iron-electrodeposited pretreatment, excessive silicon accumulates on the surface of the substrate due to the low solubility of silicon in the τ, after the iron layer is depleted by the increasing growth of the Fe-Zn intermetallics. With the movement of the substrate/τ interface toward the substrate, silicon-enriched α-Fe peels off from the substrate and breaks into the particles. The particles move toward the δ layer through the τ layer because silicon-enriched α-Fe cannot be absorbed in the τ layer. When the particles reach the δ/τ interface, they are dissolved in the δ layer, making the τlayer thin or even vanish.
关键词:
Zn coating
,
null
,
null
,
null
,
null
Yi XIE
材料科学技术（英）
The alloy Ni-Al26.6-Cr13.4-Co8.1-Ti4.3-W1.3-Mo0.9 (at. pct) was fabricated from superalloy K44 and Al element using vacuum induction and casting technique. Investigations to this alloy reveal that a new phase Cr3Ni2 possessing low melting point and poor ductility is formed, which is distributed as a network along NiAl matrix grain boundaries. Subsequent different solution and aging treatments are carried out and lead to microstructural changes to various extents. Rapid cooling after solution at 1250℃ for 20 h gives rise to macrocracks in the specimen while slow cooling after the same treatment results in the formation of spheric α-Cr solid solution and needle-like Ni3Al phase, which are embedded in NiAl matrix. It is comfirmed that aging treatments initiate lath-shaped Ni3Al phase and pearl-shaped α-Cr phase to precipitate from the NiAl matrix, which own orientation relationships with these precipitates.
关键词:
NiAl
,
null
,
null
,
null
Guangye ZHANG
,
Xinghao DU
,
Jianting GUO
,
Hengqiang YE
材料科学技术（英）
Brittle-to-ductile transition (BDT) behavior and creep behavior of extruded NiAl-25Cr alloy at elevated temperatures were investigated. The results reveal that the alloy exhibits obvious BDT behavior with the increase in temperature and BDT temperature (BDTT) is sensitive to initial strain rate. When the initial strain rate increases by two orders of magnitude, BDTT has an increase of approximate 80 K. The creep data in the temperature range of 1073～1123 K reveal two distinct regions of creep behavior in this material. At lower temperature, the creep characteristics are consistent with structural controlled creep process where creep deformation is controlled by dislocation climb. At higher temperature, the creep characteristics are consistent with mobility-controlled deformation where viscous glide of dislocations controls creep. The apparent activation energy determined by creep in both regions exceeds the value for lattice self-diffusion in NiAl by a considerable amount. This can be explained in terms of the simultaneous deformation of second phase particles (γ'-Ni3Al and α-Cr phase) along NiAl matrix during creep.
关键词:
NiAl
,
null
,
null
,
null
,
null
W. Liu
,
C.Q. Wang
,
Y.H. Tian
,
M.Y. Li
,
null
,
null
,
null
,
null
金属学报(英文版)
Formation of AuSn x intermetallic compounds (IMCs) in
laser reflowed solder joints was investigated. The results showed
that few IMCs formed at the solder/0.1um Au interface.
Needlelike AuSn 4 IMCs were observed at the
solder/0.5 um Au interface. In Sn-2.0Ag-0.75Cu-3.0Bi and
Sn-3.5Ag-0.75Cu solder joints, when the laser input energy was
increased, AuSn 4 IMCs changed from a layer to needlelike or
dendritic distribution at the solder/0.9 um Au interface. As for
the solder joints with 4.0 um thickness of Au surface finish on
pads, AuSn 4, AuSn 2, AuSn IMCs, and Au 2Sn
phases formed at the interface. Moreover, the content of AuSn
x IMCs, such as, AuSn 4 and AuSn 2, which
contained high Sn concentration, would become larger as the laser
input energy increased. In the Sn-37Pb solder joints with 0.9 um
or 4.0 um thickness of the Au surface finish on pads, AuSn 4 IMCs were in netlike distribution. The interspaces between them were filled with Pb-rich phases.
关键词:
Laser soldering
,
null
,
null
